Reference Detail

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Abstract

PMID

Authors

Gabi Tarcic; Limor Cohen; Stacie Peacock Shepherd; Natalie Filippov Levy; Hana Billauer; Lea Birnbaum; Sara Gasasa; Roey Maor; Reham Abu-Liel; Eden Goldfarb

Title

Abstract 4609: Plixorafenib (plixo) synergizes with MEK inhibitors (MEKi) in MAPK pathway inhibition in BRAF V600 and non V600 alterations, with higher potency compared to early generation BRAFi and pan-RAFi

Journal	Vol	Issue	Date	Pages	Journal Short Title
Cancer Research	84	6_supplement	March 22 2024	4609	Cancer Res

URL

https://aacrjournals.org/cancerres/article/84/6_Supplement/4609/736221

Abstract Text

The efficacy of BRAFi in V600 mutated tumors is established and requires effective inhibition of the MAPK pathway. However, the use approved BRAFi leads to paradoxical MAPK pathway activation associated with toxicities and to acquired resistance. Therefore, these inhibitors were combined with MEKi to mitigate toxicities, which has been shown to be more effective than monotherapy in some settings. Although effective, these combinations result in bothersome side effects, a high discontinuation rate, and risk of secondary malignancies, indicating a continued unmet need. Also, ~35% of all BRAF mutations occur outside the V600 codon, composed of a wide array of missense mutations, fusions, and in-frame deletions, which are not targeted by the earlier generation BRAFi. By design, plixo (FORE8394; PLX8394), a clinical stage BRAFi, binds the monomeric form of BRAF and inhibits its dimerization, while sparing the WT form, avoiding paradoxical MAPK pathway activation. We hypothesized that the combination of plixo with a MEKi will improve its efficacy and potency through maximal suppression of the MAPK pathway. Using ForeSight assay, a unique platform for testing MAPK signaling, we tested the efficacy of plixo and 4 MEKi (trametinib, cobimetinib, binimetinib and mirdametinib) across a cohort 18 BRAF alterations (V600E, 2 class II and 15 fusions) as single agents and in combinations. The combinations of plixo with the different MEKi were synergistic across all BRAF alterations tested. Furthermore, we compared the potency of a combination of plixo with binimetinib (bini) to that of another BRAFi (vemurafenib) or pan-RAFi’s (tovorafenib and lifirafenib) with bini in 2 class I, 3 class II and 7 BRAF fusions using the foresight assay. The IC:50 of BRAF V600E expressing cells treated with plixo + bini was 6nM compared with 57nM, 103nM and 190nM for the tovorafenib, vemurafenib, and lifirafenib combinations with bini respectively. A similar trend was shown in 9 of 11 additional alterations tested, indicating the potency of the combination of plixo + bini. Results were validated using western blot analysis and cell viability assays of both melanoma and CRC V600E mutated cell lines. Western blot correlated with ForeSight results both in single agents and combination treatment. Cells treated with plixo + bini showed complete growth inhibition while the same drug concentrations of vemurafenib + bini and tovorafenib + binimetinib showed no growth inhibition beyond the effect of bini single agent. These results indicate the improved efficacy of plixo + bini combination in inhibiting MAPK signaling and cancer cell proliferation. Overall results support that maximal suppression of the MAPK pathway with plixo is more potent in combination with a MEK inhibitor in BRAF V600 and non-V600 nonclinical models compared to BRAF or pan-RAF combinations.

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Molecular Profile	Treatment Approach

Gene Name	Source	Synonyms	Protein Domains	Gene Description	Gene Role

Therapy Name	Drugs	Efficacy Evidence	Clinical Trials

Drug Name	Trade Name	Synonyms	Drug Classes	Drug Description

Gene	Variant	Impact	Protein Effect	Variant Description	Associated with drug Resistance

Molecular Profile	Indication/Tumor Type	Response Type	Therapy Name	Approval Status	Evidence Type	Efficacy Evidence	References
BRAF V600E	melanoma	predicted - sensitive	Binimetinib + PLX8394	Preclinical - Cell culture	Actionable	In a preclinical study, treatment with the combination of Mektovi (binimetinib) and PLX8394 inhibited viability of melanoma cells harboring BRAF V600E in culture (Cancer Res (2024) 84 (6_Supplement): 4609).	detail...
BRAF V600E	colorectal cancer	predicted - sensitive	Binimetinib + PLX8394	Preclinical - Cell culture	Actionable	In a preclinical study, treatment with the combination of Mektovi (binimetinib) and PLX8394 inhibited viability of colorectal cancer cells harboring BRAF V600E in culture (Cancer Res (2024) 84 (6_Supplement): 4609).	detail...