Pharmaceutical Reactivation of Attenuated Apoptotic Pathways Leads to Elimination of Osimertinib Drug-Tolerant Cells

Osimertinib is an EGFR tyrosine kinase inhibitor (TKI) with proven clin-ical efficacy; however, acquired resistance presents an obstacle to curing EGFR-driven disease. Recent studies have shown that drug-tolerant per-sister cells (DTP) have a distinct transcriptional profile that may confer specific vulnerabilities. By definition these cells avoid apoptosis, yet little is known about how their survival is regulated. We found that paradox-ically, the proapoptotic gene BIM was upregulated in osimertinib DTPs, and cotreatment with BH3 mimetics could trigger DTP cell death. Fur-thermore, cIAP proteins, antiapoptotic members of the extrinsic pathway, were significantly elevated in DTPs. cIAP antagonists could block DTP for-mation as an up-front combination, and could eliminate preformed DTPs. Critically, when treated at the time of maximal osimertinib response, cIAP or MCL1 inhibitor treatment could significantly attenuate the regrowth of EGFRm cell line mouse xenografts. Finally, we show that apoptosis can be maximized in cell lines with acquired osimertinib resistance by combin-ing BH3 or SMAC mimetics with agents that target the resistance driver in these models. Taken together, these data suggest novel therapeutic strate-gies at the point of minimal residual disease or full osimertinib resistance for patients in this critical area of unmet need.