MET-Independent Lung Cancer Cells Evading EGFR Kinase Inhibitors Are Therapeutically Susceptible to BH3 Mimetic Agents

Abstract

Targeted therapies for cancer are inherently limited by the inevitable recurrence of resistant disease after initial responses. To define early molecular changes within residual tumor cells that persist after treatment, we analyzed drug sensitive lung adenocarcinoma cell lines exposed to reversible or irreversible EGFR inhibitors, alone or in combination with MET kinase inhibitors, to characterize the adaptive response that engenders drug resistance. Tumor cells displaying early resistance exhibited dependence on MET-independent activation of BCL-2/BCL-XL survival signaling. Further, such cells displayed a quiescence-like state associated with greatly retarded cell proliferation and cytoskeletal functions that were readily reversed after withdrawal of targeted inhibitors. Findings were validated in a xenograft model, demonstrating BCL-2 induction and p-STAT3[Y705] activation within the residual tumor cells surviving the initial anti-tumor response to targeted therapies. Disrupting the mitochondrial BCL-2/BCL-XL antiapoptotic machinery in early survivor cells using BH3 mimetic agents such as ABT-737, or by dual RNAi-mediated knockdown of BCL-2/BCL-XL, was sufficient to eradicate the early resistant lung tumor cells evading targeted inhibitors. Similarly, in a xenograft model the preemptive co-treatment of lung tumor cells with an EGFR inhibitor and a BH3 mimetic eradicated early TKI-resistant evaders and ultimately achieved a more durable response with prolonged remission. Our findings prompt prospective clinical investigations using BH3-mimetics combined with targeted receptor kinase inhibitors to optimize and improve clinical outcomes in lung cancer treatment.

Elimination of quiescent/slow-proliferating cancer stem cells by Bcl-XL inhibition in non-small cell lung cancer

“…13,14 NSCLC commercial cell lines have been reported to be moderately sensitive to ABT-737 as a single agent. 26,27 However, lung tumor cells that survive treatment with EGFR kinase inhibitors show decreased proliferation and increased sensitivity to ABT-737, 28 suggesting the existence of a link between quiescence, Bcl-2 family members and drug resistance in lung cancer cells. In patient-derived LCSC spheroids we found a constant expression of Bcl-X L , but not Bcl-2, confirming the observations reported by Fan et al 28 in lung cancer cell lines.…”

“…26,27 However, lung tumor cells that survive treatment with EGFR kinase inhibitors show decreased proliferation and increased sensitivity to ABT-737, 28 suggesting the existence of a link between quiescence, Bcl-2 family members and drug resistance in lung cancer cells. In patient-derived LCSC spheroids we found a constant expression of Bcl-X L , but not Bcl-2, confirming the observations reported by Fan et al 28 in lung cancer cell lines. Importantly, Bcl-X L inhibition was more effective than Bcl-2 inhibition in decreasing LCSC viability and clonogenic capacity in LCSC lines expressing both factors.…”

WZ4002, a third-generation EGFR inhibitor, can overcome anoikis resistance in EGFR-mutant lung adenocarcinomas more efficiently than Src inhibitors

“…27 Recent articles have demonstrated that even established cancer cell lines are not homogeneous, and identified rare, slowly cycling subpopulations in lung, melanoma, breast, and colon cancer cell lines. 22,[28][29][30] During our manuscript preparation, subpopulations of HCC827 cells with a quiescence-like state that resist EGFR TKIs have been reported to be highly susceptible to ABT-737, the predecessor of ABT-263. 29 Moreover, a report showed that HDAC inhibitors synergistically enhanced the levels of EGFR TKI-induced apoptosis in EGFR-mutant lung adenocarcinoma cell lines.…”

“…22,[28][29][30] During our manuscript preparation, subpopulations of HCC827 cells with a quiescence-like state that resist EGFR TKIs have been reported to be highly susceptible to ABT-737, the predecessor of ABT-263. 29 Moreover, a report showed that HDAC inhibitors synergistically enhanced the levels of EGFR TKI-induced apoptosis in EGFR-mutant lung adenocarcinoma cell lines. 31 Therefore, it seems reasonable that suspended HCC827 cells were highly vulnerable to the combined treatment with WZ4002, ABT-263 with or without TSA, and consequently resulted in almost complete cell death by the long-term combination therapy (Figure 6d).…”

Understanding the Biology Behind the EGFR to Improve NSCLC Patients’ Treatment

“…Level of signal transducer and activator of transcription 3 (STAT3) are increased almost immediately after starting erlotinib treatment in EGFR-mutant NSCLC cells [18]. Furthermore, STAT3 activation through IL-6R and FGFR, in response to inhibition of an oncogenic kinase might significantly contributes to resistance of the cell population to drug treatment and consequently limits the efficacy of such agents [19].…”