Original ArticleThe HSP90 inhibitor, NVP-AUY922, attenuates intrinsic PI3K inhibitor resistance in KRAS-mutant non-small cell lung cancer

•RSK activation bypasses PI3K inhibition in KRAS mutant NSCLC cells with intrinsic resistance to PI3K inhibition.•AUY922 effectively suppresses both PI3K-AKT-mTOR and RAF-MEK-ERK-RSK activation.•AUY922 sensitizes NSCLC cells with intrinsic resistance to PI3K inhibitor, omipalisib.

More than 25% of non-small cell lung cancers (NSCLCs) carry mutations in KRAS, one of the most common oncogenic drivers in this disease. KRAS-mutant NSCLC responds poorly to currently available therapies; therefore, novel treatment strategies are needed. Here, we describe a particularly promising targeted therapeutic strategy against KRAS mutation-harboring NSCLC intrinsically resistant to treatment by PI3K inhibition. We found that intrinsic resistance to PI3K inhibition derived from RAF/MEK/ERK and RSK activation, bypassing blockage of the PI3K/AKT/mTOR pathway. The HSP90 inhibitor AUY922 suppressed both PI3K/AKT/mTOR and RAF/MEK/ERK signaling, rendering cells sensitive to a PI3K inhibitor (omipalisib, GSK458). Combining these two drugs achieved a synergistic effect, even using only sub-therapeutic concentrations. Dual inhibition of the HSP90 and PI3K signaling pathways with sub-therapeutic doses of these combined anticancer drugs may represent a potent treatment strategy for KRAS-mutant NSCLC with intrinsic resistance to PI3K inhibition.