FDG-PET is a good biomarker of both early response and acquired resistance in BRAFV600 mutant melanomas treated with vemurafenib and the MEK inhibitor GDC-0973

Abstract

BackgroundThe BRAF inhibitor, vemurafenib, has recently been approved for the treatment of metastatic melanoma in patients harboring BRAFV600 mutations. Currently, dual BRAF and MEK inhibition are ongoing in clinical trials with the goal of overcoming the acquired resistance that has unfortunately developed in some vemurafenib patients. FDG-PET measures of metabolic activity are increasingly employed as a pharmacodynamic biomarker for guiding single-agent or combination therapies by gauging initial drug response and monitoring disease progression. However, since tumors are inherently heterogeneous, investigating the effects of BRAF and MEK inhibition on FDG uptake in a panel of different melanomas could help interpret imaging outcomes.Methods18 F-FDG uptake was measured in vitro in cells with wild-type and mutant (V600) BRAF, and in melanoma cells with an acquired resistance to vemurafenib. We treated the cells with vemurafenib alone or in combination with MEK inhibitor GDC-0973. PET imaging was used in mice to measure FDG uptake in A375 melanoma xenografts and in A375 R1, a vemurafenib-resistant derivative. Histological and biochemical studies of glucose transporters, the MAPK and glycolytic pathways were also undertaken.ResultsWe demonstrate that vemurafenib is equally effective at reducing FDG uptake in cell lines harboring either heterozygous or homozygous BRAFV600 but ineffective in cells with acquired resistance or having WT BRAF status. However, combination with GDC-0973 results in a highly significant increase of efficacy and inhibition of FDG uptake across all twenty lines. Drug-induced changes in FDG uptake were associated with altered levels of membrane GLUT-1, and cell lines harboring RAS mutations displayed enhanced FDG uptake upon exposure to vemurafenib. Interestingly, we found that vemurafenib treatment in mice bearing drug-resistant A375 xenografts also induced increased FDG tumor uptake, accompanied by increases in Hif-1α, Sp1 and Ksr protein levels. Vemurafenib and GDC-0973 combination efficacy was associated with decreased levels of hexokinase II, c-RAF, Ksr and p-MEK protein.ConclusionsWe have demonstrated that 18 F-FDG-PET imaging reflects vemurafenib and GDC-0973 action across a wide range of metastatic melanomas. A delayed post-treatment increase in tumor FDG uptake should be considered carefully as it may well be an indication of acquired drug resistance.Trial registrationClinicalTrials.gov NCT01271803

It takes two to tango – signalling by dimeric Raf kinases

“…This possibility has not been directly tested yet, but vemurafenib treatment of drug 20 resistant A375 melanoma cells (which express B-RafV600E) elevated the concentrations of KSR1 and Raf-1 proteins, and enhanced ERK activation. 63 Unfortunately, the dimerization status of KSR1, B-Raf and Raf-1 was not determined in this study, but based on the KSR studies described above 25, 62 25 expression changes should influence which dimers are formed, suggesting that KSR may play a role in the resistance to Raf inhibitors.…”

Cobimetinib: First Global Approval

“…Cobimetinib in combination with vemurafenib was associated with a greater inhibition of signaling, increased tumor cell apoptosis and better tumor response than vemurafenib alone in preclinical cancer models [5,12]. Moreover, tumor samples from patients with BRAF V600 mutation-positive locally advanced or metastatic melanoma participating in the BRIM7 study and receiving combination treatment with cobimetinib and vemurafenib showed robust modulation of tumor cell signaling and transcription [13].…”

Comparação entre a associação de cobimetinibe e vemurafenibe e outras opções terapêuticas para o tratamento de melanoma metastático com mutação BRAFV600: número necessário para tratar (NNT)

“…A inibição direta e específica da quinase mutada mostrou uma redução significativa no crescimento do tumor e aumento na sobrevida do paciente (Blue Cross and Blue Shield Association, 2015). O vemurafenibe (GDC-0941) é um inibidor competitivo do domínio quinase do oncogene BRAF, disponível para administração oral (Baudy et al, 2012). Esse medicamento suprime o fluxo de sinalização por meio da inibição da quinase serina-treonina BRAF, inibindo a proliferação celular em células tumorais que possuem gene BRAF com mutações V600 (Produtos Roche Químicos e Farmacêuticos S.A., 2014).…”

“…Esse medicamento suprime o fluxo de sinalização por meio da inibição da quinase serina-treonina BRAF, inibindo a proliferação celular em células tumorais que possuem gene BRAF com mutações V600 (Produtos Roche Químicos e Farmacêuticos S.A., 2014). Além disso, o vemurafenibe demonstrou resultados positivos em pacientes portadores da mutação BRAF V600E , resultando em regressão quase total do tumor e sobrevida livre de progressão (SLP) de sete meses (Baudy et al, 2012).…”

“…Além disso, os queratinócitos predispostos com HRAS mutado podem se tornar altamente proliferativos devido à ativação paradoxal da via MAP-quinase, resultando no desenvolvimento de carcinoma de células escamosas em alguns pacientes (Baudy et al, 2012). Essa resistência adquirida se deve na maioria dos casos à reativação da via MAP-quinase pela proteína MEK.…”