Horizontal Combination of MEK and PI3K/mTOR Inhibition in BRAF Mutant Tumor Cells with or without Concomitant PI3K Pathway Mutations

Dominika Rittler,Tamás Garay,József Tímár,Eszter Molnár,Marcell Baranyi,Balázs Hegedűs,József Tóvári,Clemens Aigner,Luca Hegedűs

doi:10.3390/ijms21207649

Abstract

The RAS/RAF and PI3K/Akt pathways play a key regulatory role in cancer and are often hit by oncogenic mutations. Despite molecular targeting, the long-term success of monotherapy is often hampered by de novo or acquired resistance. In the case of concurrent mutations in both pathways, horizontal combination could be a reasonable approach. In our study, we investigated the MEK inhibitor selumetinib and PI3K/mTOR dual inhibitor BEZ235 alone and in combination in BRAF-only mutant and BRAF + PI3K/PTEN double mutant cancer cells using short- and long-term 2D viability assays, spheroid assays, and immunoblots. In the 2D assays, selumetinib was more effective on BRAF-only mutant lines when compared to BRAF + PI3K/PTEN double mutants. Furthermore, combination therapy had an additive effect in most of the lines while synergism was observed in two of the double mutants. Importantly, in the SW1417 BRAF + PI3K double mutant cells, synergism was also confirmed in the spheroid and in the in vivo model. Mechanistically, p-Akt level decreased only in the SW1417 cell line after combination treatment. In conclusion, the presence of concurrent mutations alone did not predict a stronger response to combination treatment. Therefore, additional investigations are warranted to identify predictive factors that can select patients who can benefit from the horizontal combinational inhibition of these two pathways.

Highlights

The RAS/RAF/MEK/ERK and PI3K/Akt/mTOR pathways have a crucial regulatory role in mammalian cells by controlling the cell growth, proliferation, differentiation, protein synthesis, motility, metabolism, and survival [1,2]
The inhibition of both mTORC1 and mTORC2 is critical for effective blocking of PI3K/Akt pathway which cannot be achieved by rapamycin but with BEZ235 [44,54]
We presented the effectiveness of the MEK inhibitor selumetinib and the PI3K/mTOR inhibitor BEZ235 alone and in combination on BRAF and BRAF + PI3K/PTEN mutant human cancer cell lines from different types of cancer, in line with the current basket-type clinical trial design for BRAF mutant tumors [55]

Summary

Introduction

The RAS/RAF/MEK/ERK and PI3K/Akt/mTOR pathways have a crucial regulatory role in mammalian cells by controlling the cell growth, proliferation, differentiation, protein synthesis, motility, metabolism, and survival [1,2]. One of the most frequently mutated gene is BRAF, a member of a family with three specific isoforms (ARAF, BRAF, and CRAF). It has oncogenic mutations in 50–60% of melanomas, 5–15% of colon cancers, and 3–5% of lung adenocarcinomas. The V600E alteration is the most prevalent present in 80–90% of BRAF mutant melanomas, in 50% of BRAF mutant lung adenocarcinomas, and in 90% of BRAF mutant colorectal cancers [6,7,8]. Further downstream mutations in RAF/MEK/ERK cascade (MEK1/2, Erk1/2) are rarely detected in melanoma (4–8%), colorectal cancer (3–4%), or lung adenocarcinoma (0.5–1.5%) [11]. MEK1/2 are the exclusive kinase of Erk1/2, the inhibition of MEK1/2 could be an efficient approach to inhibit the constitutively activated pathway [12]

Methods

Results

Conclusion