Synthetic Lethal Screening with Small-Molecule Inhibitors Provides a Pathway to Rational Combination Therapies for Melanoma

Abstract

Recent data demonstrate that extracellular signals are transmitted through a network of proteins rather than hierarchical signaling pathways suggesting why inhibition of a single component of a canonical pathway is insufficient for the treatment of cancer. The biological outcome of signaling through a network is inherently more robust and resistant to inhibition of a single network component. In this study, we performed a functional chemical genetic screen to identify novel interactions between signaling inhibitors that would not be predicted based on our current understanding of signaling networks. We screened over 300 drug combinations in nine melanoma cell lines and have identified pairs of compounds that show synergistic cytotoxicity. The synergistic cytotoxicities identified did not correlate with the known RAS and BRAF mutational status of the melanoma cell lines. Among the most robust results was synergy between sorafenib, a multi-kinase inhibitor with activity against RAF, and diclofenac, a non-steroidal anti-inflammatory drug (NSAID). Drug substitution experiments using the NSAIDs celecoxib and ibuprofen or the MEK inhibitor PD325901 and the RAF inhibitor RAF265 suggest that inhibition of cyclooxygenase (COX) and MAP kinase signaling are targets for the synergistic cytotoxicity of sorafenib and diclofenac. Co-treatment with sorafenib and diclofenac interrupts a positive feedback signaling loop involving ERK, cPLA2, and COX. Genome-wide expression profiling demonstrates synergy-specific down-regulation of survival-related genes. This study has uncovered novel functional drug combinations and suggests that the underlying signaling networks that control responses to targeted agents can vary substantially depending on unexplored components of the cell genotype.

BRAF V600E Is a Determinant of Sensitivity to Proteasome Inhibitors

“…The next challenge of personalized medicine will be tailoring the right combinatorial therapy to the right complex tumor genotype. Indeed, approaches to perform high-throughput screenings of combinations of compounds have been published and showed remarkable results also in the analysis of BRAFmutant melanoma cells (48,49). Therefore, we envision that the screening of drug combinations on specific components of the matrix, such as genotypes harboring BRAF mutation, will represent a valuable strategy to unveil more effective therapy-genotype correlations.…”

An Unbiased Oncology Compound Screen to Identify Novel Combination Strategies

“…In these studies, known biomarkers of response were validated and biomarker hypotheses were generated demonstrating the power of this approach to aid in drug development. More recently, combination screens have been undertaken to identify novel drug combinations for specific cancer indications, such as melanoma and leukemia, in which resistance to targeted agents has frequently been observed (7)(8)(9).…”

Applications of Systems Biology to Identify Mechanisms of Adaptive Response to Targeted Single and Combinatorial Drug Treatment in Cancer

“…The problem with this approach is that expected MAPK and other known resistance pathways (PI3K, mTOR, apoptosis, cell cycle, etc.) (Martz et al, 2014) may not be the critical drivers of resistance, as we observed in our previous study in melanoma (Roller et al, 2012). Additionally, these candidate approaches tend to yield relatively little insight into the full response of the cell to primary treatment.…”

“…Resistance to BRAFV600E inhibition can involve activation of alternative growth pathways that can diminish dependence on the MAPK pathway Held et al, 2013;Kugel et al, 2014;Roller et al, 2012). Generally, BRAF V600E melanomas strongly depend on signaling through the mutated BRAF V600E…”

“…A complementary option for identifying combinations is drug screening based on a strategy that we (Roller et al, 2012) and other groups (Held et al, 2013) have used. Having found that a combination of sorafenib and diclofenac yields a synergistic cytotoxic response (Roller et al, 2012), we determined that the BRAF kinase and COX2, respectively, were being specifically targeted by these two drugs (Roller et al, 2012).…”