Chemical formula: C₂₃H₁₈ClF₂N₃O₃S Molecular mass: 489.922 g/mol PubChem compound: 42611257
Vemurafenib is an inhibitor of BRAF serine-threonine kinase. Mutations in the BRAF gene result in constitutive activation of BRAF proteins, which can cause cell proliferation without associated growth factors.
Preclinical data generated in biochemical assays demonstrated that vemurafenib can potently inhibit BRAF kinases with activating codon 600 mutations (table).
Kinase inhibitory activity of vemurafenib against different BRAF kinases:
| Kinase | Anticipated frequency in V600 mutation-positive melanomat | Inhibitory Concentration 50 (nM) |
|---|---|---|
| BRAFV600E | 87.3% | 10 |
| BRAFV600K | 7.9% | 7 |
| BRAFV600R | 1% | 9 |
| BRAFV600D | <0.2% | 7 |
| BRAFV600G | <0.1% | 8 |
| BRAFV600M | <0.1% | 7 |
| BRAFV600A | <0.1% | 14 |
| BRAFWT | N/A | 39 |
t Estimated from 16,403 melanomas with annotated BRAF codon 600 mutations in the public COSMIC database, release 71 (November 2014).
This inhibitory effect was confirmed in the ERK phosphorylation and cellular anti-proliferation assays in available melanoma cell lines expressing V600-mutant BRAF. In cellular anti-proliferation assays the inhibitory concentration 50 (IC50) against V600 mutated cell lines (V600E, V600R, V600D and V600K mutated cell lines) ranged from 0.016 to 1.131 μM whereas the IC50 against BRAF wild type cell lines were 12.06 and 14.32 μM, respectively.
Before taking vemurafenib, patients must have BRAF V600 mutation-positive tumour status confirmed by a validated test. In the phase II and phase III clinical trials, eligible patients were identified using a real-time polymerase chain reaction assay (the cobas 4800 BRAF V600 Mutation Test). This test has CE marking and is used to assess the BRAF mutation status of DNA isolated from formalin-fixed, paraffin-embedded (FFPE) tumour tissue. It was designed to detect the predominant BRAF V600E mutation with high sensitivity (down to 5% V600E sequence in a background of wild type sequence from FFPE-derived DNA). Non-clinical and clinical studies with retrospective sequencing analyses have shown that the test also detects the less common BRAF V600D mutations and V600K mutations with lower sensitivity. Of the specimens available from the non-clinical and clinical studies (n=920), that were mutation-positive by the cobas test and additionally analyzed by sequencing, no specimen was identified as being wild type by both Sanger and 454 sequencing.
Vemurafenib is a Class IV substance (low solubility and permeability), using the criteria described in the Biopharmaceutics Classification System. The pharmacokinetic parameters for vemurafenib were determined using non-compartmental analysis in a phase I and phase III studies (20 patients after 15 days of dosing at 960 mg twice daily, and 204 patients in steady state day 22) as well as by population PK analysis using pooled data from 458 patients. Among these patients, 457 were Caucasians.
The bioavailability at steady state ranged between 32 and 115% (mean 64%) relative to an intravenous microdose, in a phase I study with uncontrolled food conditions in 4 patients with BRAF V600 positive malignancies.
Vemurafenib is absorbed with a median Tmax of approximately 4 hours following a single 960 mg dose (four 240 mg tablets). Vemurafenib exhibits high inter-patient variability. In the phase II study, AUC0-8h and Cmax at day 1 were 22.1 ± 12.7 μg⋅h/mL and 4.1 ± 2.3 μg/mL. Accumulation occurs upon multiple twice daily dosing of vemurafenib. In the non-compartmental analysis, after dosing with 960 mg vemurafenib twice daily the Day 15/Day 1 ratio ranged from 15- to 17-fold for AUC, and 13- to 14-fold for Cmax, yielding AUC0-8h and Cmax of 380.2 ± 143.6 μg⋅h/mL and 56.7 ± 21.8 μg/mL, respectively, under steady-state conditions.
Food (high fat meal) increases the relative bioavailability of a single 960 mg dose of vemurafenib. The geometric mean ratios between the fed and fasted states for Cmax and AUC were 2.5 and 4.6 to 5.1 fold, respectively. The median Tmax was increased from 4 to 7.5 hours when a single vemurafenib dose was taken with food.
The effect of food on steady state vemurafenib exposure is currently unknown. Consistent intake of vemurafenib on an empty stomach may lead to significantly lower steady state exposure than consistent intake of vemurafenib with or a short time after a meal. Occasional intake of vemurafenib on an empty stomach is expected to have limited influence on steady state exposure due to the high accumulation of vemurafenib at steady state. Safety and efficacy data from pivotal studies were collected from patients taking vemurafenib with or without food.
Variability in exposure may also occur due to differences in gastro-intestinal fluid content, volumes, pH, motility and transition time and bile composition.
At steady state, the mean vemurafenib exposure in plasma is stable during the 24-hour interval as indicated by the mean ratio of 1.13 between the plasma concentrations before and 2-4 hours after the morning dose. Following oral dosing, the absorption rate constant for the population of metastatic melanoma patients is estimated to be 0.19 hr-1 (with 101% between patient variability).
The population apparent volume of distribution for vemurafenib in metastatic melanoma patients is estimated to be 91 L (with 64.8% between patient variability). It is highly bound to human plasma proteins in vitro (>99%).
The relative proportions of vemurafenib and its metabolites were characterised in a human mass balance study with a single dose of 14C-labeled vemurafenib administered orally. CYP3A4 is the primary enzyme responsible for the metabolism of vemurafenib in vitro. Conjugation metabolites (glucuronidation and glycosylation) were also identified in humans. However, the parent compound was the predominant component (95%) in plasma. Although metabolism does not appear to result in a relevant amount of metabolites in plasma, the importance of metabolism for excretion cannot be excluded.
The population apparent clearance of vemurafenib in patients with metastatic melanoma is estimated to be 29.3 L/day (with 31.9% between patient variability). The population elimination half-life estimated by the population PK analysis for vemurafenib is 51.6 hours (the 5th and 95th percentile range of the individual half-life estimates is 29.8-119.5 hours).
In the human mass balance study with vemurafenib administered orally, on average 95% of the dose was recovered within 18 days. The majority of vemurafenib-related material (94%) was recovered in faeces, and <1% in urine. Renal elimination does not appear to be of importance for vemurafenib elimiation, whereas biliary excretion of unchanged compound may be an important route of elimination. Vemurafenib is a substrate and inhibitor of P-gp in vitro.
Based on the population PK analysis, age has no statistically significant effect on vemurafenib pharmacokinetics.
The population pharmacokinetic analysis indicated a 17% greater apparent clearance (CL/F) and a 48% greater apparent volume of distribution (V/F) in males than in females. It is unclear whether this is a gender or a body size effect. However, the differences in exposure are not large enough to warrant dose adjustment based on body size or gender.
In the population pharmacokinetic analysis using data from clinical trials in patients with metastatic melanoma, mild and moderate renal impairment did not influence the apparent clearance of vemurafenib (creatinine clearance >40 ml/min). There are no data in patients with severe renal impairment.
Based on preclinical data and the human mass balance study, major part of vemurafenib is eliminated via the liver. In the population pharmacokinetic analysis using data from clinical trials in patients with metastatic melanoma, increases in AST and ALT up to three times the upper limit of normal did not influence the apparent clearance of vemurafenib. Data are insufficient to determine the effect of metabolic or excretory hepatic impairment on vemurafenib pharmacokinetics.
Limited pharmacokinetic data from six adolescent patients aged between 15 and 17 years with stage IIIC or IV BRAF V600 mutation positive melanoma suggest that vemurafenib pharmacokinetic characteristics in adolescents are generally similar to those in adults.
The preclinical safety profile of vemurafenib was assessed in rats, dogs, and rabbits.
Repeat-dose toxicology studies identified the liver and bone marrow as target organs in the dog. Reversible toxic effects (hepatocellular necrosis and degeneration) in the liver at exposures below the anticipated clinical exposure (based on AUC comparisons) were noted in the 13-week dog study. Focal bone marrow necrosis was noted in one dog in a prematurely terminated 39-week BID dog study at exposures similar to the anticipated clinical exposure (based on AUC comparisons). In an in vitro bone marrow cytotoxicity study, slight cytotoxicity was observed in some lympho-haematopoietic cell populations of rat, dog and human at clinically relevant concentrations.
Vemurafenib was shown to be phototoxic, in vitro, on cultured murine fibroblasts after UVA irradiation, but not in vivo in a rat study at doses up to 450 mg/kg/day (at exposures below the anticipated clinical exposure (based on AUC comparison). No specific studies with vemurafenib have been conducted in animals to evaluate the effect on fertility. However, in repeat-dose toxicity studies, no histopathological findings were noted on reproductive organs in males and females in rats and dogs at doses up to 450 mg/kg/day (at exposures below the anticipated clinical exposure based on AUC comparison). No teratogenicity was observed in embryofoetal development studies in rats and rabbits at doses up to respectively 250 mg/kg/day and 450 mg/kg/day leading to exposures below the anticipated clinical exposure (based on AUC comparison). However, exposures in the embryofoetal development studies were below the clinical exposure based on AUC comparison, it is therefore difficult to define to what extent these results can be extrapolated to humans. Therefore an effect of vemurafenib on the foetus cannot be excluded. No studies were performed regarding pre- and postnatal development.
No signs of genotoxicity were identified in in vitro assays (bacterial mutation [AMES Assay], human lymphocyte chromosome aberration) nor in the in vivo rat bone marrow micronucleus test conducted with vemurafenib.
Carcinogenicity studies have not been conducted with vemurafenib.
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