RAS Pathway Inhibitors Combined with Targeted Agents Are Active in Patient-Derived Spheroids with Oncogenic KRAS Variants from Multiple Cancer Types.

The Kirsten rat sarcoma viral oncogene homolog (KRAS) gene is among the most frequently altered genes in cancer, and the KRAS protein was long deemed undruggable. Recent strategies to target oncogenic KRAS have included both direct inhibition of the KRAS protein and indirect inhibition of its activity by targeting upstream and downstream signaling pathway mediators. A high-throughput screen of multicell-type tumor spheroids was designed to identify active combinations of targeted small molecules and KRAS pathway inhibitors. Inhibitors of the nonreceptor protein tyrosine phosphatase Src homology 2 domain-containing protein tyrosine phosphatase (SHP2) and the guanine nucleotide exchange factor Son of Sevenless homolog 1 (SOS1) were tested to evaluate indirect upstream pathway inhibition, whereas sotorasib directly inhibited the KRAS G12C variant. As single agents, sotorasib and the SHP2 inhibitor batoprotafib (TNO155) exhibited selectivity toward spheroids with KRAS G12C, whereas the SOS1 inhibitor BI-3406 showed varying activity across KRAS variants. Vertical inhibition of the rat sarcoma virus (RAS)/MEK/ERK pathway by targeting SHP2 or SOS1 and the downstream kinases MEK (trametinib) or ERK (temuterkib) was highly effective. Inhibition of upstream tyrosine receptor kinases with nintedanib in combination with batoprotafib or BI-3406 was also effective and, in combination with sotorasib, demonstrated synergy in spheroids harboring KRAS G12C. Dual inhibition of the RAS/MEK/ERK and PI3K/Ak strain transforming (AKT)/mTOR pathways by batoprotafib or sotorasib with either the mTORC1/2 inhibitor sapanisertib or the AKT inhibitor ipatasertib demonstrated combination activity, primarily in spheroids harboring KRAS G12C. The BCL-2 inhibitor venetoclax, in combination with sotorasib, batoprotafib, or BI-3406, resulted in additive and synergistic cytotoxicity. Lastly, concurrent inhibition of the KRAS pathway with sotorasib and batoprotafib demonstrated combination activity in spheroids containing KRAS G12C.

Significance: KRAS variants are oncogenic drivers for a range of human cancers. Multiple combinations of small-molecule agents that target RAS signaling were screened and reduced the viability of multicell-type tumor spheroids from a variety of human solid tumors. Combinations warranting further testing were identified.