BOSULIF Film-coated tablet / Hard capsule Ref.[6578] Active ingredients: Bosutinib
Source: European Medicines Agency (EU) Revision Year: 2025 Publisher: Pfizer Europe MA EEIG, Boulevard de la Plaine 17, 1050 Bruxelles, Belgium
Pharmacodynamic properties
Pharmacotherapeutic group: Antineoplastic agents, protein kinase inhibitors
ATC code: L01EA04
Mechanism of action
Bosutinib belongs to a pharmacological class of medicinal products known as kinase inhibitors. Bosutinib inhibits the abnormal BCR-ABL kinase that promotes CML. Modelling studies indicate that bosutinib binds the kinase domain of BCR-ABL. Bosutinib is also an inhibitor of Src family kinases including Src, Lyn and Hck. Bosutinib minimally inhibits platelet-derived growth factor (PDGF) receptor and c-Kit.
In in vitro studies, bosutinib inhibits proliferation and survival of established CML cell lines, Ph+ ALL cell lines, and patient-derived primary primitive CML cells. Bosutinib inhibited 16 of 18 imatinib-resistant forms of BCR-ABL expressed in murine myeloid cell lines. Bosutinib treatment reduced the size of CML tumours growing in nude mice and inhibited growth of murine myeloid tumours expressing imatinib-resistant forms of BCR-ABL. Bosutinib also inhibits receptor tyrosine kinases c-Fms, EphA and B receptors, Trk family kinases, Axl family kinases, Tec family kinases, some members of the ErbB family, the non-receptor tyrosine kinase Csk, serine/threonine kinases of the Ste20 family, and 2 calmodulin-dependent protein kinases.
Pharmacodynamic effects
The effect of bosutinib 500 mg administration on corrected QTc was evaluated in a randomised, single-dose, double-blind (with respect to bosutinib), crossover, placebo- and open-label moxifloxacin-controlled study in healthy subjects.
The data from this study indicate that bosutinib does not prolong the QTc in healthy subjects at the dose of 500 mg daily with food, and under conditions that give rise to supratherapeutic plasma concentrations. Following administration of a single oral dose of bosutinib 500 mg (therapeutic dose) and bosutinib 500 mg with ketoconazole 400 mg (to achieve supratherapeutic concentrations of bosutinib) in healthy subjects, the upper bound of the 1-sided 95% confidence interval (CI) around the mean change in QTc was less than 10 ms at all post-dose time points, and no adverse events suggestive of QTc prolongation were observed.
In a study in liver impaired subjects, an increasing frequency of QTc prolongation >450 ms with declining hepatic function was observed. In the Phase ½ clinical study in patients with previously treated Ph+ leukaemias treated with bosutinib 500 mg, QTcF increase >60 ms from baseline was observed in 9 (1.6%) of 570 patients. In the Phase 3 clinical study in patients with newly-diagnosed CP CML treated with bosutinib 400 mg, there were no patients in the bosutinib treatment group (N=268) with a QTcF increase of >60 ms from baseline. In the Phase 3 clinical study in patients with newly-diagnosed Ph+ CP CML treated with bosutinib 500 mg, QTcF increase >60 ms from baseline was observed in 2 (0.8%) of 248 patients receiving bosutinib. In the Phase 4 clinical study in patients with Ph+ CML previously treated with 1 or more TKI(s) treated with bosutinib 500 mg (N=163), there were no patients with a QTcF increase >60 ms from baseline. A proarrhythmic potential of bosutinib cannot be ruled out.
Clinical efficacy
Clinical study in CP previously untreated CML in adult patients
Bosutinib 400 mg study
A 2-arm, Phase 3, open-label, multicentre superiority trial was conducted to investigate the efficacy and safety of bosutinib 400 mg once daily alone compared with imatinib 400 mg once daily alone in adult patients with newly-diagnosed Ph+ CP CML. The trial randomised 536 patients (268 in each treatment group) with Ph+ or Ph- newly-diagnosed CP CML (intent-to-treat population [ITT]) including 487 patients with Ph+ CML harbouring b2a2 and/or b3a2 transcripts and baseline BCR-ABL copies >0 (modified intent-to-treat [mITT] population).
The primary efficacy endpoint was the proportion demonstrating a major molecular response (MMR) at 12 months (48 weeks) in the bosutinib treatment group compared with that in the imatinib treatment group in the mITT population. MMR was defined as ≤0.1% BCR-ABL/ABL ratio by international scale (corresponding to ≥3 log reduction from standardised baseline) with a minimum of 3 000 ABL transcripts as assessed by the central laboratory.
Key secondary endpoints included complete cytogenetic response (CCyR) by 12 months, duration of CCyR, duration of MMR, event-free survival (EFS), and overall survival (OS). CCyR by Month 12, was defined as the absence of Ph+ metaphases in chromosome banding analysis of ≥20 metaphases derived from bone marrow aspirate or MMR if an adequate cytogenetic assessment was unavailable. The p-values for endpoints other than MMR at 12 months and CCyR by 12 months have not been adjusted for multiple comparisons.
Baseline characteristics for the mITT population were well balanced between the 2 treatment groups with respect to age (median age was 52 years for the bosutinib group and 53 years for the imatinib group with 19.5% and 17.4% of patients 65 years of age or older, respectively); gender (women 42.3% and 44.0%, respectively); race (Caucasian 78.0% and 77.6%, Asian 12.2% and 12.4%, Black or African American 4.1% and 4.1%, and Other 5.7% and 5.4%, respectively, and 1 unknown in the imatinib group); and Sokal risk score (low risk 35.0% and 39.4%, intermediate risk 43.5% and 38.2%, high risk 21.5% and 22.4%, respectively).
After 60 months of follow-up in the mITT population, 60.2% of patients treated with bosutinib (N=246) and 59.8% of patients treated with imatinib (N=239) were still receiving first-line treatment.
After 60 months of follow-up in the mITT population, discontinuations due to disease progression to AP or BP CML for bosutinib-treated patients were 0.8% compared to 1.7% for imatinib-treated patients. Six (2.4%) bosutinib patients and 7 (2.9%) imatinib patients transformed to AP CML or BP CML. Discontinuations due to suboptimal response or treatment failure as assessed by the investigator occurred for 5.3% of patients in the bosutinib-treated group compared to 15.5% of patients in the imatinib-treated group. Twelve (4.9%) patients on bosutinib and 14 (5.8%) patients on imatinib died while on study. No additional transformations occurred in the ITT population, there were 2 additional deaths in the bosutinib arm in the ITT population.
The efficacy results of MMR and CCyR are summarised in Table 5.
Table 5. Summary of MMR at Months 12 and 18 and CCyR by Month 12, by treatment group in the mITT population:
| Response | Bosutinib (N=246) | Imatinib (N=241) | Odds ratio (95% CI)a |
|---|---|---|---|
| Major molecular response | |||
| MMR at Month 12, n (%) (95% CI) | 116 (47.2)b (40.9,53.4) | 89 (36.9) (30.8,43.0) | 1.55 (1.07,2.23) |
| 1-sided p-value | 0.0100b | ||
| MMR at Month 18, n (%) (95% CI) | 140 (56.9) (50.7,63.1) | 115 (47.7) (41.4,54.0) | 1.45 (1.02,2.07) |
| 1-sided p-value | 0.0208c | ||
| Complete cytogenetic response | |||
| CCyR by Month 12, n (%) (95% CI) | 190 (77.2)b (72.0,82.5) | 160 (66.4) (60.4,72.4) | 1.74 (1.16,2.61) |
| 1-sided p-value | 0.0037b | ||
Note: MMR was defined as ≤0.1% BCR-ABL/ABL ratio by international scale (corresponding to ≥3 log reduction from standardised baseline) with a minimum of 3 000 ABL transcripts assessed by the central laboratory. Complete cytogenetic response was defined as the absence of Ph+ metaphases in chromosome banding analysis of ≥20 metaphases derived from bone marrow aspirate or MMR if an adequate cytogenetic assessment was unavailable.
Abbreviations: BCR-ABL=breakpoint cluster region-Abelson; CI=confidence interval; CMH=Cochran-Mantel-Haenszel; CCyR=complete cytogenetic response; mITT=modified intent-to-treat; MMR=major molecular response; N/n=number of patients; Ph+=Philadelphia chromosome-positive.
a Adjusted for geographical region and Sokal score at randomisation.
b Statistically significant comparison at the pre-specified significance level; based on CMH test stratified by geographical region and Sokal score at randomisation.
c Based on CMH test stratified by geographical region and Sokal score at randomisation.
At Month 12, the MR4 rate (defined as ≤0.01% BCR-ABL [corresponding to ≥4 log reduction from standardised baseline] with a minimum of 9,800 ABL transcripts) was higher in the bosutinib treatment group compared to the imatinib treatment group in the mITT population (20.7% [95% CI: 15.7%, 25.8%] versus 12.0% [95% CI: 7.9%, 16.1%], respectively, odds ratio (OR) 1.88 [95% CI: 1.15, 3.08], 1-sided p-value=0.0052).
At Months 3, 6, and 9, the proportion of patients with MMR was higher in the bosutinib treatment group compared to the imatinib treatment group (Table 6).
Table 6. Comparison of MMR at Months 3, 6, and 9 by treatment in the mITT population:
| Time | Number (%) of subjects with MMR | Odds ratio (95% CI)a | |
|---|---|---|---|
| Bosutinib (N=246) | Imatinib (N=241) | ||
| Month 3 (95% CI) | 10 (4.1) (1.6,6.5) | 4 (1.7) (0.0,3.3) | 2.48 (0.77,7.98) |
| 1-sided p-valueb | 0.0578 | ||
| Month 6 (95% CI) | 86 (35.0) (29.0,40.9) | 44 (18.3) (13.4,23.1) | 2.42 (1.59,3.69) |
| 1-sided p-valueb | <0.0001 | ||
| Month 9 (95% CI) | 104 (42.3) (36.1,48.4) | 71 (29.5) (23.7,35.2) | 1.78 (1.22,2.60) |
| 1-sided p-valueb | 0.0015 | ||
Note: Percentages were based on number of patients in each treatment group. MMR was defined as ≤0.1% BCR-ABL/ABL ratio on international scale (corresponding to ≥3 log reduction from standardised baseline) with a minimum of 3 000 ABL transcripts assessed by the central laboratory.
Abbreviations: BCR-ABL=breakpoint cluster region-Abelson; CI=confidence interval; CMH=Cochran-Mantel-Haenszel; mITT=modified intent-to-treat; MMR=major molecular response; N=number of patients.
a Adjusted for geographical region and Sokal score at randomisation.
b Based on CMH test stratified by geographical region and Sokal score at randomisation.
By Month 60 in the mITT population, the proportion of patients with MMR, MR4 and MR4.5 was higher in the bosutinib group compared to the imatinib group (Table 7). MMR rates by Month 60 across Sokal risk subgroups are summarised in Table 8.
Table 7. Summary of molecular response by Month 60 in the mITT population:
| Response | Bosutinib (N=246) | Imatinib (N=241) | Odds ratio (95% CI)a |
|---|---|---|---|
| Molecular response by Month 60, n (%) (95% CI) | |||
| MMR | 182 (74.0) (68.5,79.5) | 158 (65.6) (59.6,71.6) | 1.52 (1.02,2.25) |
| MR4 | 145 (58.9) (52.8,65.1) | 120 (49.8) (43.5,56.1) | 1.46 (1.02,2.09) |
| MR4.5 | 119 (48.4) (42.1,54.6) | 93 (38.6) (32.4,44.7) | 1.50 (1.05,2.16) |
Note: MMR/MR4/MR4.5 were defined as ≤0.1/0.01/0.0032% BCR-ABL/ABL ratio on international scale (corresponding to ≥3/4/4.5 log reduction from standardised baseline) with a minimum of 3 000/9 800/30 990 ABL transcripts assessed by the central laboratory.
Abbreviations: BCR-ABL=breakpoint cluster region-Abelson; CI=confidence interval; mITT=modified intent-to-treat; MMR=major molecular response; MR=molecular response; N/n=number of patients.
a Adjusted for geographical region and Sokal score at randomisation.
Table 8. Summary of MMR by Month 60 by Sokal risk score in the mITT population:
| Response | Bosutinib | Imatinib | Odds ratio (95% CI) |
|---|---|---|---|
| Low Sokal risk MMR, n (%) (95% CI) | N=86 67 (77.9) (69.1,86.7) | N=95 68 (71.6) (62.5,80.6) | 1.40 (0.71,2.76) |
| Intermediate Sokal risk MMR, n (%) (95% CI) | N=107 79 (73.8) (65.5,82.2) | N=92 62 (67.4) (57.8,77.0) | 1.37 (0.74,2.52) |
| High Sokal risk MMR, n (%) (95% CI) | N=53 36 (67.9) (55.4,80.5) | N=54 28 (51.9) (38.5,65.2) | 1.97 (0.90,4.32) |
Note: Percentages were based on number of patients in each treatment group. MMR was defined as ≤0.1% BCR-ABL/ABL ratio on international scale (corresponding to ≥3 log reduction from standardised baseline) with a minimum of 3 000 ABL transcripts assessed by the central laboratory.
Abbreviations: BCR-ABL=breakpoint cluster region-Abelson; CI=confidence interval; mITT=modified intent-to-treat; MMR=major molecular response; N/n=number of patient
The cumulative incidence of CCyR adjusted for the competing risk of treatment discontinuation without CCyR was higher in the bosutinib treatment group compared to the imatinib treatment group in the mITT population (83.3% [95% CI: 78.1%, 87.4%] versus 76.8% [95% CI: 70.9%, 81.6%] at Month 60; hazard ratio [HR] from a stratified proportional sub distributional hazards model: 1.35, [95% CI: 1.11, 1.64]). The median time to CCyR (responders only) was 24.0 weeks (range: 11.4 to 120.7) in the bosutinib group compared to the 24.3 weeks (range: 11.4 to 96.6) in the imatinib group.
The median time to MMR, MR4 and MR4.5 (responders only) was 36.1 weeks (range: 11.9 to 241.9), 83.7 weeks (range: 12.4 to 244.3), and 108.0 weeks (range: 24.1 to 242.1), respectively, for the bosutinib treatment group versus 47.7 weeks (range: 12.1 to 216.1), 84.4 weeks (range: 23.6 to 241.9), and 120.4 weeks (range: 24.6 to 240.7), respectively, for the imatinib treatment group in the mITT population.
The cumulative incidence of MMR, MR4 and MR4.5 adjusted for the competing risk of treatment discontinuation without the event was higher with bosutinib compared to imatinib as shown in Figures 1 to 3.
Figure 1. Cumulative incidence of MMR (mITT population):
Figure 2. Cumulative incidence of MR4 (mITT population):
Figure 3. Cumulative incidence of MR4.5 (mITT population):
In the mITT population, among patients who achieved CCyR, the Kaplan-Meier estimate of maintaining a response at Year 4 was 97.4% (95% CI: 93.9%, 98.9%) and 93.7% (95% CI: 88.9%, 96.5%) in the bosutinib and imatinib groups (HR 0.39 [95% CI: 0.14, 1.13]), respectively. Among patients who achieved MMR, the Kaplan-Meier estimate of maintaining a response at Year 4 was 92.2% (95% CI: 86.8%, 95.4%) and 92.0% (95% CI: 85.9%, 95.5%) in the bosutinib and imatinib groups (HR 1.09 [95% CI: 0.49, 2.44]), respectively.
By Month 60, 43.9% (95% CI: 37.7%, 50.1%) and 38.6% (95% CI: 32.4%, 44.7%) of bosutinib- and imatinib-treated patients (OR 1.24 [95% CI: 0.87, 1.78]) in the mITT population, respectively, had sustained MR4 defined by the following criteria: treatment for at least 3 years with at least MR4 at all assessments during a 1-year period.
The cumulative incidence of on-treatment EFS events at Month 60 in the mITT population was 6.9% (95% CI: 4.2%, 10.5%) in the bosutinib arm and 10.4% (95% CI: 6.9%, 14.6%) in the imatinib arm (HR 0.64, 95% CI: 0.35, 1.17).
The Kaplan-Meier estimates of OS at Month 60 for bosutinib and imatinib patients in the mITT population were 94.9% (95% CI: 91.1%, 97.0%) and 94.0% (95% CI: 90.1%, 96.4%), respectively (HR 0.80, 95% CI: 0.37, 1.73).
In a retrospective analysis, among evaluable patients in the ITT population, more patients in the bosutinib arm 200/248 (80.6%) achieved early molecular response (BCR-ABL transcripts ≤10% at 3 months) compared to patients in the imatinib arm 153/253 (60.5%), OR 2.72 (95% CI: 1.82, 4.08). MMR and EFS at Month 60 in bosutinib patients with and without early molecular response are summarised in Table 9.
Table 9. Outcomes at Month 60 in bosutinib patients with BCR-ABL ≤10% vs >10% at Month 3 in the ITT population:
| Bosutinib (N=248) | Patients with BCR-ABL ≤10% at 3 Months (N=200) | Patients with BCR-ABL >10% at 3 Months (N=48) | Hazard Ratio (95% CI)a |
|---|---|---|---|
| Cumulative incidence of MMR, % (95% CI) | 84.0 (78.1,88.4) | 56.5 (41.1,69.4) | 2.67 (1.90,3.75) |
| Cumulative incidence of EFS events, % (95% CI) | 5.5 (2.9,9.3) | 12.5 (5.1,23.4) | 0.40 (0.14,1.17) |
Abbreviations: BCR-ABL=breakpoint cluster region-Abelson; CI=confidence interval; ITT=intent-to-treat; MMR=major molecular response; EFS=event free survival; N=number of patients with ≥3 000 ABL copies at Month 3.
a Adjusted for geographical region and Sokal score at randomisatio
Fewer patients in the bosutinib arm [6 (2.4%) bosutinib and 12 (5.0%) imatinib] had newly detectable mutations at 60 months in the mITT population.
Phase ½ Clinical study in imatinib-resistant or intolerant CML in CP, AP, and BP
A single-arm, Phase ½ open-label, multicentre trial was conducted to evaluate the efficacy and safety of bosutinib 500 mg once daily in patients with imatinib-resistant or -intolerant CML with separate cohorts for chronic, accelerated, and blast phase disease previously treated with 1 prior TKI (imatinib) or more than 1 TKI (imatinib followed by dasatinib and/or nilotinib).
There were 570 patients treated with bosutinib in this trial including CP CML patients previously treated with only 1 prior TKI (imatinib), CP CML patients previously treated with imatinib and at least 1 additional TKI (dasatinib and/or nilotinib), CML patients in accelerated or blast phase previously treated with at least 1 TKI (imatinib) and patients with Ph+ ALL previously treated with at least 1 TKI (imatinib).
The primary efficacy endpoint of the study was the major cytogenetic response (MCyR) rate at Week 24 in patients with imatinib-resistant CP CML previously treated with only 1 prior TKI (imatinib). Other efficacy endpoints include the cumulative cytogenetic and molecular response rates, time to and duration of cytogenetic and molecular responses, response in baseline mutations, transformation to AP/BP, progression free survival and OS for all cohorts.
Patients who were still receiving bosutinib at the end of the Phase ½ study and were benefiting from bosutinib treatment as judged by the investigator, as well as those patients who had already discontinued bosutinib as part of the Phase ½ study and were in long-term follow-up for survival or had completed the Phase ½ study, were eligible for enrollment into the extension study. Each patient remained in the extension study, either on bosutinib treatment or in long-term survival follow-up, until the last patient reached 10 years of follow-up, as calculated from the date of his/her first dose of bosutinib administered in the Phase ½ study.
Extension study efficacy endpoints included duration of cytogenetic and molecular responses, transformation to AP/BP, progression free survival, and OS.
The efficacy analyses included data from this completed extension study.
CP CML patients
The efficacy results for Ph+ CP CML patients previously treated with imatinib and at least 1 additional TKI (minimum follow-up 120 months, median treatment duration of 9 months (range: 0.23 to 164.28 months) and 20.2% and 7.6% still on-treatment at 60 and 120 months, respectively) and the results for Ph+ CP CML patients previously treated with only imatinib (minimum follow-up 120 months, median treatment duration of 26 months (range: 0.16 to 170.49 months) and 40.5% and 19.4% still on-treatment at 60 and 120 months, respectively) are presented in Table 9.
AP and BP CML patients
The efficacy results for AP (minimum follow-up 120 months, median treatment duration of 10 months (range: 0.10 to 156.15 months) and 12.7% and 7.6% still on-treatment at 60 and 120 months, respectively) and BP (minimum follow-up 120 months, median treatment duration of 2.8 months (range: 0.03 to 71.38 months) and 3.1% and 0% still on-treatment at 60 and 120 months, respectively) Ph+ CML patients are present in Table 10.
Table 10. Efficacy results in previously treated patients with chronic and advanced phase CML*:
| Ph+ CP CML with prior imatinib treatment only | Ph+ CP CML with prior treatment with imatinib and dasatinib or nilotinib | Accelerated phase with prior treatment of at least imatinib | Blast phase with prior treatment of at least imatinib | |
|---|---|---|---|---|
| Cumulative cytogenetic responsea MCyR, % (95% CI) CCyR, % (95% CI) | N=262 59.9 (53.7,65.9) 49.6 (43.4,55.8) | N=112 42.0 (32.7,51.7) 32.1 (23.6,41.6) | N=72 40.3 (28.9,52.5) 30.6 (20.2,42.5) | N=54 37.0 (24.3,51.3) 27.8 (16.5,41.6) |
| Cumulative molecular responsea MMR, % (95% CI) MR4, % (95% CI) | N=197 42.1 (35.1,49.4) 37.1 (30.3,44.2) | N=107 17.8 (11.0,26.3) 15.0 (8.8,23.1) | N=54 16.7 (7.9,29.3) 13.0 (5.4,24.9) | N=48 10.4 (3.5,22.7) 10.4 (3.5,22.7) |
| Time to MCyR for responders onlyb, median (range), weeks | 12.3 (4.0,346.0) | 12.3 (3.9,550.6) | 12.0 (3.9,144.7) | 8.2 (3.9,25.1) |
| Duration of MCyRb K-M at year 5, % (95% CI) K-M at year 10, % (95% CI) Median, weeks (95% CI) | N=157 70.7 (63.1,78.3) 65.3 (56.6,74.0) N/R | N=47 66.6 (51.5,81.7) 55.3 (36.3,74.4) N/R | N=29 40.8 (20.9,60.7) 40.8 (20.9,60.7) 84.0 (24.0,N/E) | N=20 21.2 (0.1,42.3) N/E 29.1 (11.9,38.3) |
| Time to CCyR for responders onlyb, median (range), weeks | 24.0 (7.7,240.6) | 24.0 (11.6,216.0) | 23.8 (4.1,120.0) | 8.4 (3.9,25.1) |
| Duration of CCyRb K-M at year 5, % (95% CI) K-M at year 10, % (95% CI) Median, weeks (95% CI) | N=130 69.7 (61.3,78.2) 63.4 (54.0,72.8) N/R | N=36 54.4 (36.7,72.1) 40.8 (22.0,59.6) 252.0 (24.0,N/E) | N=22 40.0 (18.5,61.5) 40.0 (18.5,61.5) 72.0 (36.1,N/E) | N=15 24.9 (0.9,48.9) N/E 20.0 (9.1,29.6) |
| Time to MMR for responders onlyb, median (range), weeks | 35.6 (3.1,367.1) | 12.4 (4.0,171.7) | 36.1 (12.1,144.1) | 4.7 (3.9,168.9) |
| Duration of MMRb K-M at year 5, % (95% CI) K-M at year 10, % (95% CI) Median, weeks (95% CI) | N=83 74.1 (64.2,83.9)63.4 (50.2,76.6) N/R | N=19 70.0 (47.5,92.5) 70.0 (47.5,92.5) N/R | N=9 66.7 (35.9,97.5) 66.7 (35.9,97.5) N/R | N=5 60.0 (17.1,100.0) N/E N/R |
| Time to MR4 for responders onlyb, median (range), weeks | 28.0 (3.1,583.1) | 23.8 (4.0,240.1) | 24.1 (22.9,96.0) | 4.7 (3.9,284.9) |
| Duration of MR4b,e K-M at year 5, % (95% CI) K-M at year 10, % (95% CI) Median, weeks (95% CI) | N=73 74.7 (64.2,85.2) 60.8 (46.1,75.4) N/R | N/A | N/A | N/A |
| Transformation to AP/BPc On-treatment transformation, n | N=284 15 | N=119 5 | N=79 3 | N/A |
| Progression-free survivalc CumInc at year 5, % (95% CI)d CumInc at year 10, % (95% CI)d | N=284 19.7 (15.6,24.9) 23.9 (19.5,29.5) | N=119 24.4 (17.8,33.4) 26.9 (20.0,36.2) | N=79 41.8 (32.2,54.2) 41.8 (32.2,54.2) | N=64 67.2 (56.6,79.7) N/E |
| Overall survivalc K-M at year 5, % (95% CI) K-M at year 10, % (95% CI) Median, months (95% CI) | N=284 83.5 (78.7,88.3) 71.5 (64.4,78.7) N/R | N=119 74.1 (64.8,83.4) 60.4 (47.2,73.7) N/R | N=79 58.5 (46.9,70.2) 50.7 (36.5,65.0) N/R | N=64 22.5 (7.1,37.9) 22.5 (7.1,37.9) 10.9 (8.7,19.7) |
Snapshot date: Phase ½ Study 02Oct2015, Extension Study 02Sep2020.
Cytogenetic Response criteria: MCyR included Complete [0% Ph+ metaphases from bone marrow or <1% positive cells from fluorescent in situ hybridisation (FISH)] or partial (1%-35%) cytogenetic responses.
Cytogenetic responses were based on the percentage of Ph+ metaphases among ≥20 metaphase cells in each bone marrow sample. FISH analysis (≥200 cells) could be used for post-baseline cytogenetic assessments if ≥20 metaphases were not available. In the extension study, CCyR was imputed from MMR if a valid cytogenetic assessment was not available on a specific date.
Molecular response criteria: In the Phase ½ Study, MMR/MR4 was defined as ≤ 0.1/0.01% BCR-ABL transcripts as assessed by a central laboratory (not on the international scale). In the extension study, responders had MMR/MR4 denoted on the case report form as assessed by a local laboratory.
Abbreviations: AP=accelerated phase; BP=blast phase; Ph+=Philadelphia chromosome-positive; CP=chronic phase; CML=chronic myelogenous leukaemia; K-M=Kaplan-Meier; N/n=number of patients; N/A=not applicable; N/R=not reached as of minimum follow-up; N/E=not estimable; CI=confidence interval; MCyR=major cytogenetic response; CCyR=complete cytogenetic response; CumInc=cumulative incidence; MMR=major molecular response; BCR-ABL=breakpoint cluster region-Abelson.
a Includes patients (N) with a valid baseline assessment for cytogenetic and patients not from China, South Africa, India, or Russia for molecular as samples could not be exported for molecular assessment in those countries. The analyses allow baseline responders who maintained response post-baseline to be responders. Minimum follow-up time (time from last patient first dose to data snapshot date) of 120 months.
b Includes patients (N) who attained or maintained response.
c Including patients (N) who received at least 1 dose of bosutinib.
d Cumulative incidence analysis adjusting for the competing risk of treatment discontinuation without the event.
e Not analysed for groups with limited numbers.
The Overall Survival in the CP, AP and BP cohorts is displayed graphically in Figure 4.
Figure 4. Kaplan-Meier Estimate of Overall Survival (OS) in CP2L, CP3L, AP, and BP:
Based on the limited clinical information from the Phase ½ study, some evidence of clinical activity was observed in patients with BCR-ABL mutations (see Table 11).
Table 11. Response by baseline BCR-ABL mutation status in CP CML evaluable population: prior imatinib and dasatinib and/or nilotinib (third-line):
| BCR-ABL mutation status at baseline | Incidence at baseline n (%)a | MCyR attained or maintained Resp/Evalb (%) N=112 |
|---|---|---|
| Mutation assessed | 98 (100.0) | 36/92 (39.1) |
| No mutation | 59 (60.2) | 23/55 (41.8) |
| At least 1 mutation | 39 (39.8) | 13/37 (35.1) |
| Dasatinib resistant mutations | 10 (10.2) | 1/9 (11.1) |
| E255K/V | 2 (2.0) | 0/2 |
| F317L | 8 (8.2) | 1/7 (14.3) |
| Nilotinib resistant mutationsc | 13 (13.3) | 8/13 (61.5) |
| Y253H | 6 (6.1) | 5/6 (83.3) |
| E255K/V | 2 (2.0) | 0/2 |
| F359C/I/V | 7 (7.1) | 5/7 (71.4) |
Snapshot date: Phase ½ Study 02Oct2015, Extension Study 02Sep2020
Note: Baseline mutations were identified before the patient's first dose of study drug.
Abbreviations: BCR-ABL=breakpoint cluster region-Abelson; CP=chronic phase; CML=chronic myelogenous leukaemia; MCyR=major cytogenetic response; N/n=number of patients; Resp=responders; Eval=evaluable.
a The percentage is based on number of patients with baseline mutation assessment.
b The evaluable population includes patients who had a valid baseline disease assessment.
c 2 patients had more than 1 mutation in this category.
One patient with the E255V mutation previously treated with nilotinib achieved CHR as best response.
In vitro testing indicated that bosutinib had limited activity against the T315I or the V299L mutation. Therefore, clinical activity in patients with these mutations is not expected.
Phase 4 Clinical study in Ph+ CML previously treated with 1 or more TKI(s)
A single-arm, Phase 4 open-label, non-randomised, multi-centre study was conducted to evaluate the efficacy and safety of bosutinib 500 mg once daily in patients with TKI-resistant or TKI-intolerant CML with separate cohorts for CP, AP or BP disease previously treated with 1 or more prior TKIs.
There were 163 patients treated with bosutinib in this trial including 46 patients with CP Ph+ CML and treated previously with 1 prior TKI (imatinib or dasatinib or nilotinib), 61 CP Ph+ CML patients previously treated with 2 prior TKIs (imatinib and/or dasatinib and/or nilotinib), 49 CP Ph+ CML patients treated with 3 prior TKIs (imatinib and dasatinib and nilotinib), 4 patients with AP Ph+ CML previously treated with at least 1 TKI (2 patients treated with 2 prior TKIs and 2 patients treated with 3 prior TKIs) and 3 patients with Ph- CML treated with at least 1 prior TKI.
The primary efficacy endpoint was cumulative confirmed MCyR by 1 year (Week 52) in patients with CP Ph+ CML previously treated with 1 or 2 prior TKIs and patients with CP Ph+ CML previously treated with 3 prior TKIs. For patients with AP and BP Ph+ CML with any prior TKI therapy, the primary efficacy endpoint was cumulative confirmed overall haematological response (OHR) by 1 year (Week 52). Other efficacy endpoints in Ph+ CP CML patients include cumulative cytogenetic and molecular response, the duration of cytogenetic and molecular responses, response in baseline mutations, transformation to AP/BP, PFS, and OS. Additional endpoints in the Ph+ AP/BP cohort include cumulative cytogenetic and molecular responses rates, PFS and OS.
CP CML patients
The primary endpoint of cumulative confirmed MCyR (95% CI) rate by 1 year (52 weeks) was 76.5% (66.9, 84.5) in patients treated with 1 or 2 prior TKIs and 62.2% (46.5, 76.2) in patients treated with 3 prior TKIs.
Additional efficacy results at study closure, after a minimum follow-up of 3 years, in Ph+ CP CML patients treated with 1 (median treatment duration 47.5 months (range: 0.9 to 50.1 months) and 60.9% still on-treatment), 2 (median treatment duration 41.9 months (range: 0.4 to 48.9 months) and 45.9% still on-treatment) and 3 (median treatment duration 20.0 months (range: 0.2 to 48.9 months) and 38.8% still on-treatment) prior TKIs are presented in Table 12.
Table 12. Efficacy results in previously treated patients with chronic phase Ph+ CML:
| Ph+ CP CML treated with 1 prior TKI | Ph+ CP CML treated with 2 prior TKIs | Ph+ CP CML treated with 3 prior TKIs | Total Ph+ CP CML cohort | |
|---|---|---|---|---|
| Cumulative confirmed | N=43 | N=55 | N=45 | N=143 |
| MCyRa by 1 year, % (95% CI) | 83.7 (69.3,93.2) | 70.9 (57.1,82.4) | 62.2 (46.5,76.2) | 72.0 (63.9,79.2) |
| Cumulative cytogenetic responsea,b | N=43 | N=55 | N=45 | N=143 |
| MCyR, % (95% CI) | 88.4 (74.9,96.1) | 85.5 (73.3,93.5) | 77.8 (62.9,88.8) | 83.9 (76.9,89.5) |
| CCyR, % (95% CI) | 86.0 (72.1,94.7) | 83.6 (71.2,92.2) | 73.3 (58.1,85.4) | 81.1 (73.7,87.2) |
| Cumulative molecular responsea,b | N=46 | N=55 | N=48 | N=149 |
| MMR, % (95% CI) | 82.6 (68.6,92.2) | 76.4 (63.0,86.8) | 56.3 (41.2,70.5) | 71.8 (63.9,78.9) |
| MR4, % (95% CI) | 73.9 (58.9,85.7) | 63.6 (49.6,76.2) | 41.7 (27.6,56.8) | 59.7 (51.4,67.7) |
| MR4.5, % (95% CI) | 58.7 (43.2,73.0) | 50.9 (37.1,64.6) | 35.4 (22.2,50.5) | 48.3 (40.1,56.6) |
| Time to cytogenetic response for responders onlyb, median (range), months | ||||
| MCyR | 3.0 (1.0,11.8) | 2.9 (0.3,6.4) | 3.0 (1.8,8.8) | 3.0 (0.3,11.8) |
| CCyR | 3.0 (1.0,17.6) | 2.9 (0.3,6.4) | 3.0 (1.8,8.8) | 3.0 (0.3,17.6) |
| Duration of cytogenetic responseb | ||||
| MCyR, K-M at year 3, % (95% CI) | 96.6 (77.9,99.5) | 94.4 (79.2,98.6) | 96.9 (79.8,99.6) | 95.6 (88.7,98.4) |
| CCyR, K-M at year 3, % (95% CI) | 96.4 (77.2,99.5) | 94.4 (79.2,98.6) | 100.0 (100.0,100.0) | 96.5 (89.5,98.9) |
| Time to molecular response for responders only, median (range), months | ||||
| MMR | 3.0 (2.8,23.3) | 3.0 (1.0,35.9) | 3.1 (1.8,9.3) | 3.0 (1.0,35.9) |
| MR4 | 6.0 (2.8,47.4) | 3.1 (1.0,36.1) | 3.2 (1.8,47.9) | 5.5 (1.0,47.9) |
| MR4.5 | 9.2 (2.8,47.6) | 6.0 (2.8,36.2) | 5.8 (1.8,18.0) | 6.0 (1.8,47.6) |
| Duration of molecular responseb | ||||
| MMR, K-M at year 3, % (95% CI) | 90.7 (73.9,96.9) | 81.5 (63.2,91.3) | 90.2 (65.9,97.5) | 87.2 (78.0,92.7) |
| MR4, K-M at year 3, % (95% CI) | 89.5 (70.9,96.5) | 68.7 (48.0,82.5) | 85.2 (51.9,96.2) | 80.7 (69.4,88.1) |
Snapshot date: 23Nov2020.
Abbreviations: Ph+=Philadelphia chromosome-positive; CP=chronic phase; CML=chronic myelogenous leukaemia; K-M=Kaplan-Meier; N=number of patients; CI=confidence interval; MCyR=major cytogenetic response; CCyR=complete cytogenetic response; MMR=major molecular response; MR4=≥ 4 log-reduction in BCR-ABL transcripts from standardised baseline; MR4.5=≥ 4.5 log-reduction in BCR-ABL transcripts from standardised baseline.
Cumulative Confirmed MCyR criteria: Response is confirmed with 2 consecutive evaluations at least 28 days apart. To be considered a responder, the patient must have maintained a baseline response for at least 52 weeks or improved from baseline. Patients with partial cytogenetic response (PCyR) at baseline must attain CCyR on-treatment to be counted as a cytogenetic responder. Patients with at least MMR and a deeper molecular response than baseline are counted as confirmed CCyR.
Cumulative Cytogenetic Response criteria: Major Cytogenetic Response included Complete [0% Ph+ metaphases from bone marrow or <1% positive cells from fluorescent in situ hybridisation (FISH)] or partial (1%-35%) cytogenetic responses. Cytogenetic responses were based on the percentage of Ph+ metaphases among ≥20 metaphase cells in each bone marrow sample. FISH analysis (≥200 cells) could be used to assess CCyR if ≥20 metaphases were not available. Patients without a valid bone marrow or FISH assessment and with at least MMR are counted as CCyR.
Cumulative Molecular Response criteria: MMR, MR4, and MR4.5 were defined as ≤0.1%, ≤0.01%, and ≤0.0032% BCR-ABL/ABL ratio on international scale, respectively (corresponding to ≥3, ≥4, and ≥4.5 log-reduction from standardised baseline) with a minimum of 10 000, 10 000, and 32 000 ABL transcripts assessed by the central laboratory, respectively.
a Includes patients (N) with a valid baseline assessment. Minimum follow-up time (time from last patient first dose to data snapshot date) of 36 months.
b Includes patients (N) who attained or maintained response.
The cumulative incidence of MMR, MR4 and MR4.5 adjusted for the competing risk of treatment discontinuation without the event are shown in Figure 5.
Figure 5. Cumulative Incidence of Molecular Response (CP Evaluable Population):
Achieved molecular responses by line of treatment are shown in Table 13.
Table 13. Achieved molecular responses:
| Ph+ CP CML treated with 1 prior TKI | Ph+ CP CML treated with 2 prior TKIs | Ph+ CP CML treated with 3 prior TKIs | Total Ph+ CP CML cohort | |
|---|---|---|---|---|
| Patients without MMR at baselinea | N=25 | N=28 | N=26 | N=79 |
| MMR, % (95% CI) | 76.0 (54.9,90.6) | 64.3 (44.1,81.4) | 38.5 (20.2,59.4) | 59.5 (47.9,70.4) |
| Patients without MR4 at baselinea | N=37 | N=38 | N=37 | N=112 |
| MR4, % (95% CI) | 70.3 (53.0,84.1) | 55.3 (38.3,71.4) | 32.4 (18.0,49.8) | 52.7 (43.0,62.2) |
| Patients without MR4.5 at baselinea | N=42 | N=46 | N=43 | N=131 |
| MR4.5, % (95% CI) | 54.8 (38.7,70.2) | 43.5 (28.9,58.9) | 30.2 (17.2,46.1) | 42.7 (34.1,51.7) |
| Patients with MMR at baselinea | N=21 | N=27 | N=22 | N=70 |
| Deeper MR, % (95% CI) | 85.7 (63.7,97.0) | 66.7 (46.0,83.5) | 63.6 (40.7,82.8) | 71.4 (59.4,81.6) |
Snapshot date: 23Nov2020.
Abbreviations: Ph+=Philadelphia chromosome-positive; CP=chronic phase; CML=chronic myelogenous leukaemia; N=number of patients; CI=confidence interval; MMR=major molecular response; MR=molecular response; MR4=≥ 4 log-reduction in BCR-ABL transcripts from standardised baseline; MR4.5=≥ 4.5 log-reduction in BCR-ABL transcripts from standardised baseline.
a Includes patients (N) with a valid baseline assessment. To be considered a responder, patients must have achieved an improved response from baseline. Molecular Response criteria: MMR, MR4, and MR4.5 were defined as ≤0.1%, ≤0.01%, and ≤0.0032% BCR-ABL/ABL ratio on international scale, respectively (corresponding to ≥3, ≥4, and ≥4.5 log-reduction from standardised baseline) with a minimum of 10 000, 10 000, and 32 000 ABL transcripts assessed by the central laboratory, respectively.
In CP patients, there were no on-treatment progressions to AP or BP CML.
AP CML patients
In patients with Ph+ AP CML, the median duration of treatment was 22.1 months (range: 1.6 to 50.1 months), the cumulative confirmed OHR by 1 year (52 weeks) was 75.0% (95% CI: 19.4, 99.4), as was the cumulative CCyR rate, all 3 patients maintained their CCyR on-treatment.
Response by BCR-ABL Mutations at baseline
Ten patients in the CP cohort had mutations at baseline (A365V, E453K, E255K, E255V, Q252H, L298V [n=1 each], Y253F and G250E [n=2 each]). One patient in the CP cohort had a F359I mutation identified on study day 8. One patient in the AP cohort had 2 mutations (F311L and L387F) at baseline. In the CP cohort, among patients with mutations, molecular responses were observed in 4/11 (36.4%) patients, 1 patient with a E255V mutation achieved MMR and 3 patients with F359I, Y253F and A365V respectively achieved MR4.5. The patient with mutations in the AP cohort did not achieve any response.
Paediatric population
The efficacy of Bosulif in paediatric patients was evaluated in the BCHILD trial "A Phase I/II study of bosutinib in paediatric patients with newly-diagnosed chronic phase or resistant/intolerant Ph+ CML".
The BCHILD trial is a Phase I/II, multicentre, international, single-arm, open-label study conducted to identify a recommended dose of bosutinib administered orally once daily in paediatric patients (aged 1 to <18 years) with newly-diagnosed chronic phase Ph+ CML (ND CML) or Ph+ CML who have received at least one prior TKI therapy (R/I CML) and to assess preliminary estimate the safety tolerability and efficacy, and to evaluate the Pharmacokinetics of bosutinib in this patient population.Paediatric patients with newly-diagnosed CP Ph+ CML
The efficacy of Bosulif in paediatric patients with newly-diagnosed CP Ph+ CML (CP1L) was evaluated as part of the BCHILD trial. In the Phase II dose expansion portion 30 patients with ND CML received bosutinib at a dose of 300 mg/m² once daily. The median duration of follow-up for overall survival in the total cohort (N=30) was 21.91 (1.08, 45.11) months in ND CML patients, and the median treatment duration was 13.68 (0.20, 43,70). A summary of cumulative cytogenetic and molecular responses at any time in patients with ND CML is shown in Table 15. Among responders, one patient lost CCyR and MCyR.
Among evaluable ND patients (ABL copies ≥10 000), 81.08% (95% CI: 64.2, 97.7) had a BCR-ABL ratio ≤10% at 3 months, and 62.5% (95% CI: 38.8, 86.2) had a BCR-ABL ratio ≤1% at 6 months. There were no deaths in the ND cohort and no progressions to AP or BP.
Paediatric patients with imatinib-resistant or intolerant Ph+ CP, CML
The efficacy of Bosulif in paediatric patients with resistant or intolerant Ph+ CML was evaluated as part of the BCHILD trial.
In the Phase I dose escalation portion, 28 patients with R/I CML received bosutinib at doses ranging from 300 to 400 mg/m² once daily. 6 patients were enrolled in the Phase II portion (400 mg/m²).
Table 14. Demographic characteristics of CML patients:
| Phase 1 (300 mg/m²) (N=6) | Phase 1 (350 mg/m²) (N=11) | Phase 1 (400 mg/m²) (N=11) | Phase 2 CP1L (300 mg/m²) (N=30) | Phase 2 R/I (400 mg/m²) (N=6) | |
|---|---|---|---|---|---|
| Age (Years), n (%) | |||||
| ≥1-<6 | 2 (33.3) | 2 (18.2) | 0 | 2 (6.7) | 0 |
| ≥6-<12 | 3 (50.0) | 4 (36.4) | 3 (27.3) | 10 (33.3) | 1 (16.7) |
| ≥12-<18 | 1 (16.7) | 5 (45.5) | 8 (72.7) | 18 (60.0) | 5 (83.3) |
| Median (range) | 8.50 (1, 17) | 11.00 (4, 17) | 15.00 (6, 17) | 12.50 (5,17) | 14.50 (11, 16) |
| Gender, n (%) | |||||
| Male | 5 (83.3) | 4 (36.4) | 7 (63.6) | 18 (60.0) | 4 (66.7) |
| Female | 1 (16.7) | 7 (63.6) | 4 (36.4) | 12 (40.0) | 2 (33.3) |
| Race, n (%) | |||||
| White | 0 | 5 (45.5) | 7 (63.6) | 22 (73.3) | 4 (66.7) |
| Black or African American | 0 | 1 (9.1) | 1 (9.1) | 5 (16.7) | 1 (16.7) |
| Asian | 0 | 1 (9.1) | 3 (27.3) | 1 (3.3) | 1 (16.7) |
| American Indian or Alaska Native | 0 | 0 | 0 | 0 | 0 |
| Native Hawaiian or Other Pacific Islander | 0 | 0 | 0 | 2 (6.7) | 0 |
| Unknown | 6 (100.0) | 4 (36.4) | 0 | 0 | 0 |
| Ethnicity, n (%) | |||||
| Hispanic or Latino | 0 | 0 | 2 (18.2) | 7 (23.3) | 0 |
| Not Hispanic or Latino | 0 | 8 (72.7) | 9 (81.8) | 23 (76.7) | 6 (100.0) |
| Unknown | 6 (100.0) | 3 (27.3) | 0 | 0 | 0 |
The median duration of follow-up for overall survival in the total phase 1 portion (N=28) was 29.27 months (15.21, 85.88) and in the phase 2 portion (N=6) was 9.66 (2.00, 15.54). The median treatment duration in the phase 1 portion was 17.26 months (range 0.30 to 60.85) and 9.64 months (1.97, 15.54) in the phase 2 portion.
A summary of cumulative cytogenetic and molecular responses at any time in patients with CML is shown in Table 15. In Phase I, among responders, three patients lost CCyR and 2 patients lost MCyR. In the phase 1 portion, the probability of maintaining MMR at 18 months was 92.3% (95% CI: 56.6, 98.8).
There were no progressions to AP or BP.
Table 15. Efficacy results in paediatric patients with resistant or intolerant Ph+ CML:
| Phase 1 Total (R/I) (N=28) | Phase 2 CP1L (300mg/m²) (N=30) | Phase 2 R/I (400mg/m²) (N=6) | |
|---|---|---|---|
| Cumulative MCyR, n% (95% CI) | 24 (85.7) (67.3, 96.0) | 26 (86.7) (69.3, 96.2) | 6 (100.0) (54.1, 100.0) |
| Cumulative CCyR, n% (95% CI) | 23 (82.1) (63.1, 93.9) | 25 (83.3) (65.3, 94.4) | 6 (100.0) (54.1, 100.0) |
| Patients without MCyR at baseline, N | 4 | N/A | 1 |
| MCyR, n% (95% CI) | 3 (75.0) (19.4, 99.4) | N/A | 1 (100.0) (2.5, 100.0) |
| Patients without CCyR at baseline, N | 9 | N/A | 2 |
| CCyR n% (95% CI) | 7 (77.8) (40.0, 97.2) | N/A | 2 (100.0) (15.8, 100.0) |
| Cumulative MMR, n% (95% CI) | 16 (57.1) (37.2, 75.5) | 13 (43.3) (25.5, 62.6) | 4 (66.7) (22.3, 95.7) |
| Cumulative MR4, n% (95% CI) | 6 (21.4) (8.3, 41.0) | 5 (16.7) (5.6, 34.7) | 1 (16.7) (0.4, 64.1) |
| Cumulative MR4.5, n% (95% CI) | 5 (17.9) (6.1, 36.9) | 0 (0.0) (0.0, 11.6) | 0 (0.0) (0.0, 45.9) |
Abbreviations: CCyR=complete cytogenetic response; CI=confidence interval; CML=chronic myelogenous leukaemia; CP=chronic phase; MCyR=major cytogenetic response; MMR=major molecular response; MR=molecular response; N=number of patients; n=number of events; Ph=Philadelphia chromosome-positive; R/I=resistant or intolerant.
Pharmacokinetic properties
Bosutinib pharmacokinetics were assessed following oral dosing with food in adult patients with CML and were presented as geometric mean (CV%), unless otherwise specified.
Absorption
Following administration of a single dose of bosutinib (500 mg) with food in healthy subjects, the absolute bioavailability was 34%. Absorption was relatively slow, with a median time-to-peak concentration (Tmax) reached after 6 hours. Bosutinib exhibits dose-proportional increases of AUC over the dose range of 100 to 600 mg. The bosutinib PK parameters for adults were derived from a population PK analysis using pooled data across studies. Bosutinib steady state Cmax was 127 ng/mL (31%), Ctrough was 68 ng/mL (39%) and AUC was 2 370 ng•h/mL (34%) following multiple oral doses of Bosulif 400 mg; Bosutinib steady state Cmax was 171 ng/mL (38%), Ctrough was 91 ng/mL (42%) and AUC was 3 150 ng•h/mL (38%) following multiple oral doses of Bosulif 500 mg.
No clinically significant differences in the pharmacokinetics of bosutinib were observed following administration of either the tablet or intact hard capsule dosage forms of bosutinib at the same dose, under fed conditions. Bosutinib hard capsule contents mixed with applesauce or yogurt exhibited comparable PK to the bosutinib intact hard capsule under fed condition in healthy adult participants.
The solubility of bosutinib is pH-dependent and absorption is reduced when gastric pH is increased (see section 4.5).
Effect of food
Bosutinib Cmax increased 1.8-fold and AUC increased 1.7-fold when bosutinib tablets were given with a high-fat meal to healthy subjects compared to administration under fasted condition. In a separate study, bosutinib hard capsule administration under the fed condition resulted in exposures approximately 1.5 – 1.6-fold higher than administration under fasted conditions.
Distribution
Following administration of a single intravenous dose of 120 mg bosutinib to healthy subjects, bosutinib had a mean (% coefficient of variation [CV]) volume of distribution of 2,331 (32) L, suggesting that bosutinib is extensively distributed to extra vascular tissue.
Bosutinib was highly bound to human plasma proteins in vitro (94%) and ex vivo in healthy subjects (96%), and binding was not concentration-dependent.
Biotransformation
In vitro and in vivo studies indicated that bosutinib (parent compound) undergoes predominantly hepatic metabolism in humans. Following administration of single or multiple doses of bosutinib (400 or 500 mg) to humans, the major circulating metabolites appeared to be oxydechlorinated (M2) and N-desmethylated (M5) bosutinib, with bosutinib N-oxide (M6) as a minor circulating metabolite. The systemic exposure of N-desmethylated metabolite was 25% of the parent compound, while the oxydechlorinated metabolite was 19% of the parent compound. All 3 metabolites exhibited activity that was ≤5% that of bosutinib in a Src-transformed fibroblast anchorage-independent proliferation assay. In faeces, bosutinib and N-desmethyl bosutinib were the major drug-related components. In vitro studies with human liver microsomes indicated that the major cytochrome P450 isozyme involved in the metabolism of bosutinib is CYP3A4 and drug interaction studies have shown that ketoconazole and rifampicin had marked effect on the pharmacokinetics of bosutinib (see section 4.5). No metabolism of bosutinib was observed with CYPs 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, or 3A5.
Elimination
In healthy subjects given a single intravenous dose of 120 mg bosutinib, the mean (%CV) terminal elimination half-life was 35.5 (24) hours, and the mean (%CV) clearance was 61.9 (26) L/h. In a mass-balance study with oral bosutinib, an average of 94.6% of the total dose was recovered in 9 days; faeces (91.3%) was the major route of excretion, with 3.29% of the dose recovered in urine. Seventy-five percent of the dose was recovered within 96 hours. Excretion of unchanged bosutinib in urine was low with approximately 1% of the dose in both healthy subjects and those with advanced malignant solid tumours.
Special populations
Hepatic impairment
A 200 mg dose of bosutinib administered with food was evaluated in a cohort of 18 hepatically impaired subjects (Child-Pugh classes A, B, and C) and 9 matched healthy subjects. Cmax of bosutinib in plasma increased 2.4-fold, 2-fold, and 1.5-fold, respectively, in Child-Pugh classes A, B, and C; and bosutinib AUC in plasma increased 2.3-fold, 2-fold, and 1.9-fold, respectively. The t½ of bosutinib increased in hepatic impaired patients as compared to the healthy subjects.
Renal impairment
In a renal impairment study, a single dose of 200 mg bosutinib was administered with food to 26 subjects with mild, moderate, or severe renal impairment and to 8 matching healthy volunteers. Renal impairment was based on CLCr (calculated by the Cockcroft-Gault formula) of < 30 mL/min (severe renal impairment), 30 ≤ CLCr ≤ 50 mL/min (moderate renal impairment), or 50 < CLCr ≤ 80 mL/min (mild renal impairment). Subjects with moderate and severe renal impairment had an increase in AUC over healthy volunteers of 35% and 60%, respectively. Maximal exposure Cmax increased by 28% and 34% in the moderate and severe groups, respectively. Bosutinib exposure was not increased in subjects with mild renal impairment. The elimination half-life of bosutinib in subjects with renal impairment was similar to that in healthy subjects.
Dose adjustments for renal impairment were based on the results of this study, and the known linear pharmacokinetics of bosutinib in the dose range of 200 to 600 mg.
Age, gender and race
No formal studies have been performed to assess the effects of these demographic factors. Population pharmacokinetic analyses in patients with Ph+ leukaemia or malignant solid tumour and in healthy subjects indicate that there are no clinically relevant effects of age, gender or body weight. Population pharmacokinetic analyses revealed that Asians had a 18% lower clearance corresponding to an approximately 25% increase in bosutinib exposure (AUC).
Paediatric population
The pharmacokinetics of bosutinib in 41 newly-diagnosed or resistant/intolerant paediatric patients 1 to <18 years of age were evaluated over the dose range of 300 mg/m² to 400 mg/m² administered orally once daily with food. In paediatric patients, median Tmax occurred at approximately 3 hours post-dose (range 1 to 8 hours post-dose). Exposures increased in a dose proportional manner between 100–600 mg. The geometric mean AUCtau in the 300 mg/m² to 400 mg/m² cohorts was within the range (+ / - 20%) of geometric mean AUCtau for the adult dose level in the respective newly-diagnosed and resistant or intolerant Ph+ CML indications, however Cmax and clearance were higher and Cmin was lower in paediatric patients than in adults.
Preclinical safety data
Bosutinib has been evaluated in safety pharmacology, repeated dose toxicity, genotoxicity, reproductive toxicity, and phototoxicity studies.
Safety pharmacology
Bosutinib did not have effects on respiratory functions. In a study of the central nervous system (CNS), bosutinib treated rats displayed decreased pupil size and impaired gait. A no observed effect level (NOEL) for pupil size was not established, but the NOEL for impaired gait occurred at exposures approximately 11-times the human exposure resulting from the clinical dose of 400 mg and 8-times the human exposure resulting from the clinical dose of 500 mg (based on unbound Cmax in the respective species). Bosutinib activity in vitro in hERG assays suggested a potential for prolongation of cardiac ventricular repolarisation (QTc). In an oral study of bosutinib in dogs, bosutinib did not produce changes in blood pressure, abnormal atrial or ventricular arrhythmias, or prolongation of the PR, QRS, or QTc of the ECG at exposures up to 3-times the human exposure resulting from the clinical dose of 400 mg and 2-times the human exposure resulting from the clinical dose of 500 mg (based on unbound Cmax in the respective species). A delayed increase in heart rate was observed. In an intravenous study in dogs, transient increases in heart rate and decreases in blood pressure and minimal prolongation of the QTc (<10 msec) were observed at exposures ranging from approximately 6-times to 20-times the human exposure resulting from the clinical dose of 400 mg and 4-times to 15-times the human exposure resulting from the clinical dose of 500 mg (based on unbound Cmax in the respective species). The relationship between the observed effects and medicinal product treatment were inconclusive.
Repeated-dose toxicity
Repeated-dose toxicity studies in rats of up to 6 months in duration and in dogs up to 9 months in duration revealed the gastrointestinal system to be the primary target organ of toxicity of bosutinib. Clinical signs of toxicity included foecal changes and were associated with decreased food consumption and body weight loss which occasionally led to death or elective euthanasia.
Histopathologically, luminal dilation, goblet cell hyperplasia, haemorrhage, erosion, and oedema of the intestinal tract, and sinus erythrocytosis and haemorrhage in the mesenteric lymph nodes, were observed. The liver was also identified as a target organ in rats. Toxicities were characterised by an increase in liver weights in correlation with hepatocellular hypertrophy which occurred in the absence of elevated liver enzymes or microscopic signs of hepatocellular cytotoxicity, and is of unknown relevance to humans. The exposure comparison across species indicates that exposures that did not elicit adverse events in the 6- and 9-month toxicity studies in rats and dogs, respectively, were similar to the human exposure resulting from a clinical dose of 400 mg or 500 mg (based on unbound AUC in the respective species).
Genotoxicity
Genotoxicity studies in bacterial in vitro systems and in mammalian in vitro and in vivo systems with and without metabolic activation did not reveal any evidence for a mutagenic potential of bosutinib.
Reproductive toxicity and development toxicity
In a rat fertility study, fertility was slightly decreased in males. Females were observed with increased embryonic resorptions, and decreases in implantations and viable embryos. The dose at which no 38 adverse reproductive effects were observed in males (30 mg/kg/day) and females (3 mg/kg/day) resulted in exposures equal to 0.6-times and 0.3-times, respectively, the human exposure resulting from the clinical dose of 400 mg, and 0.5-times and 0.2-times, respectively, the human exposure resulting from the clinical dose of 500 mg (based on unbound AUC in the respective species). An effect on male fertility cannot be excluded (see section 4.6).
Foetal exposure to bosutinib-derived radioactivity during pregnancy was demonstrated in a placental transfer study in gravid Sprague-Dawley rats. In a rat pre- and postnatal development study, there were reduced number of pups born at ≥30 mg/kg/day, and increased incidence of total litter loss and decreased growth of offspring after birth occurred at 70 mg/kg/day. The dose at which no adverse development effects were observed (10 mg/kg/day) resulted in exposures equal to 1.3-times and 1.0-times human exposure resulting from the clinical dose of 400 mg and 500 mg, respectively (based on unbound AUC in the respective species). In a rabbit developmental toxicity study at the maternally toxic dose, there were foetal anomalies observed (fused sternebrae, and 2 foetuses had various visceral observations), and a slight decrease in foetal body weight. The exposure at the highest dose tested in rabbits (10 mg/kg/day) that did not result in adverse foetal effects was 0.9-times and 0.7-times the human exposure resulting from the clinical dose of 400 mg or 500 mg, respectively (based on unbound AUC in the respective species).
Following a single oral (10 mg/kg) administration of [14C] radiolabelled bosutinib to lactating Sprague-Dawley rats, radioactivity was readily excreted into breast milk as early as 0.5 hr after dosing. Concentration of radioactivity in milk was up to 8-fold higher than in plasma. This allowed measurable concentrations of radioactivity to appear in the plasma of nursing pups.
Carcinogenicity
Bosutinib was not carcinogenic in the 2-year rat and 6-month rasH2 mouse carcinogenicity studies.
Phototoxicity
Bosutinib has demonstrated the ability to absorb light in the UV-B and UV-A range and is distributed into the skin and uveal tract of pigmented rats. However, bosutinib did not demonstrate a potential for phototoxicity of the skin or eyes in pigmented rats exposed to bosutinib in the presence of UV radiation at bosutinib exposures up to 3-times and 2-times the human exposure resulting from the clinical dose of 400 or 500 mg, respectively (based on unbound Cmax in the respective species).
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