Blocking p85β nuclear translocation by importazole enhances Alpelisib efficacy against PIK3CA-helical-domain-mutant tumors.

PIK3CA, which encodes protein p110α, is one of the most frequently mutated oncogenes and a promising drug-target for human cancer. Previously, we demonstrate that p85β is released from PI3K complex which contain PIK3CA helical domain mutations and translocates into nucleus to regulate tri-methylation of H3K27, thereby promoting tumorigenicity. Here, we identify DIRAS2 and SOWAHB as target genes of nuclear p85β in PIK3CA-helical-domain-mutant tumors. DIRAS2 and SOWAHB are tumor suppressive genes, whose expression are repressed by nuclear p85β through histone methyltransferase EZH2. More importantly, combination of PI3K inhibitor and importin-β inhibitor effectively inhibits the growth of PIK3CA-helical-domain-mutant tumors by synchronously blocking both AKT signaling and nuclear p85β/DIRAS2 and SOWAHB axis. In this study, we evaluate the combination effect of Alpelisib and Importazole for PIK3CA helical domain mutant tumors and demonstrate its underlying mechanism.