Risk factors for severe rash with use of vemurafenib alone or in combination with cobimetinib for advanced melanoma: pooled analysis of clinical trials

Off-targets of BRAF inhibitors disrupt endothelial signaling and vascular barrier function

Targeted therapies against mutant BRAF are effectively used in combination with MEK inhibitors (MEKi) to treat advanced melanoma. However, treatment success is affected by resistance and adverse events (AEs). Approved BRAF inhibitors (BRAFi) show high levels of target promiscuity, which can contribute to these effects. The blood vessel lining is in direct contact with high plasma concentrations of BRAFi, but effects of the inhibitors in this cell type are unknown. Hence, we aimed to characterize responses to approved BRAFi for melanoma in the vascular endothelium. We showed that clinically approved BRAFi induced a paradoxical activation of endothelial MAPK signaling. Moreover, phosphoproteomics revealed distinct sets of off-targets per inhibitor. Endothelial barrier function and junction integrity were impaired upon treatment with vemurafenib and the next-generation dimerization inhibitor PLX8394, but not with dabrafenib or encorafenib. Together, these findings provide insights into the surprisingly distinct side effects of BRAFi on endothelial signaling and functionality. Better understanding of off-target effects could help to identify molecular mechanisms behind AEs and guide the continued development of therapies for BRAF-mutant melanoma.

Relationship Between Apparent Systemic Clearance of Vemurafenib and Toxicity in Patients With Melanoma

Vemurafenib, a B rapidly accelerated fibrosarcoma inhibitor, is commonly used in combination of cobimetinib for the treatment of melanoma. In the current study, we evaluated the relationship between vemurafenib exposure, as measured by the estimated apparent clearance (CL_B ) at steady state and any grade ≥3 toxicity, grade ≥3 skin rash, or toxicity requiring dose modification using pooled data from 3 prospective clinical trials involving 898 patients. A total of 69% had any grade ≥3 toxicity; grade ≥3 skin rash in 15% and 47% had a dose reduction/interruption or cessation. The median vemurafenib CL_B was 1.35 L/h (interquartile range, 1.15-1.65 L/h). Lower vemurafenib CL_B was significantly associated with an increased risk of grade ≥3 toxicity (hazard ratio [HR], 0.62; P < .001), grade ≥3 rash (HR, 0.29; P < .001), and adverse events requiring vemurafenib dose reduction/interruption or cessation (HR, 0.5; P < .001). When the patients were divided into 3 groups based on the vemurafenib CL_B thresholds, those with low CL_B (<1.22 L/h) had significantly increased incidence of any grade ≥3 toxicity or skin rash or dose adjustment, interruption, or cessation at 12 months and at day 28 when compared to those with medium (≥1.22 and <1.55 L/h) or high (>1.55 L/h) vemurafenib CL_B . In conclusion, the estimated CL_B of vemurafenib is associated with severe toxicities and dose adjustment or cessation, suggesting that an early estimation of vemurafenib exposure may be useful in identifying patients at risk of experiencing toxicity.

Early Exanthema Upon Vemurafenib Plus Cobimetinib Is Associated With a Favorable Treatment Outcome in Metastatic Melanoma: A Retrospective Multicenter DeCOG Study

Background

The combination of BRAF and MEK inhibitors has become standard of care in the treatment of metastatic BRAF V600-mutated melanoma. Clinical factors for an early prediction of tumor response are rare. The present study investigated the association between the development of an early exanthema induced by vemurafenib or vemurafenib plus cobimetinib and therapy outcome.

Methods

This multicenter retrospective study included patients with BRAF V600-mutated irresectable AJCC-v8 stage IIIC/D to IV metastatic melanoma who received treatment with vemurafenib (VEM) or vemurafenib plus cobimetinib (COBIVEM). The development of an early exanthema within six weeks after therapy start and its grading according to CTCAEv4.0 criteria was correlated to therapy outcome in terms of best overall response, progression-free (PFS), and overall survival (OS).

Results

A total of 422 patients from 16 centers were included (VEM, n=299; COBIVEM, n=123). 20.4% of VEM and 43.1% of COBIVEM patients developed an early exanthema. In the VEM cohort, objective responders (CR/PR) more frequently presented with an early exanthema than non-responders (SD/PD); 59.0% versus 38.7%; p=0.0027. However, median PFS and OS did not differ between VEM patients with or without an early exanthema (PFS, 6.9 versus 6.0 months, p=0.65; OS, 11.0 versus 12.4 months, p=0.69). In the COBIVEM cohort, 66.0% of objective responders had an early exanthema compared to 54.3% of non-responders (p=0.031). Median survival times were significantly longer for patients who developed an early exanthema compared to patients who did not (PFS, 9.7 versus 5.6 months, p=0.013; OS, not reached versus 11.6 months, p=0.0061). COBIVEM patients with a mild early exanthema (CTCAEv4.0 grade 1-2) had a superior survival outcome as compared to COBIVEM patients with a severe (CTCAEv4.0 grade 3-4) or non early exanthema, respectively (p=0.047). This might be caused by the fact that 23.6% of patients with severe exanthema underwent a dose reduction or discontinuation of COBIVEM compared to only 8.9% of patients with mild exanthema.

Conclusions

The development of an early exanthema within 6 weeks after treatment start indicates a favorable therapy outcome upon vemurafenib plus cobimetinib. Patients presenting with an early exanthema should therefore be treated with adequate supportive measures to provide that patients can stay on treatment.