Camptothecin Sensitizes Refractory Lung Cancer Cells to Receptor Kinase Inhibitor

Background Receptor tyrosine kinases (RTKs) represent a large class of receptors that are upregulated in many cancers. The Ephrin‐A type‐2 precursor (EphA2) is an important RTK whose overexpression in lung cancer promotes growth, metastasis and acquisition of resistance phenotypes to therapies. Further, EphA2 is a downstream target of the epidermal growth factor receptor (EGFR) which is transcriptionally regulated by the oncogenic SOX2 transcription. This study investigates the effect of combination treatment with camptothecin (CPT) and the RTK inhibitor (RTKI) drug Erlotinib (Erl) in inhibiting survival mechanism in lung cancer cells. Methods Cell viability of H1299 and H1975 was determined using the Resazurin dye assay following single and combination treatments with CPT and Erl for 72 hours. The effect of 48‐hour single and combination CPT (1.0 μM) and Erl (10 μM and 20 μM) treatments on H1299 cell migration, apoptosis, and protein expression were investigated by wound healing assay, acridine orange‐ethidium bromide (AO‐EB) staining, and western blot respectively. Results H1299 and H1975 were resistant to Erl treatment (concentrations that killed 50% of cells, IC 50 = 291.14±15.84 μM and 92.06±10.06 μM respectively). CPT was relatively more potent in inhibiting H1299 cell proliferation (IC 50 = 7.01±0.35 μM). CPT co‐treatment at concentrations of 0.1 μM and 0.5 μM with different concentrations of Erl inhibited H1299 cell proliferation by 2‐(IC 50 = 137.12±13.53 μM) and 10‐fold (IC 50 = 27.88±2.88 μM) respectively. Combination treatment with CPT and Erl induced apoptotic events and inhibited H1299 cell migration compared to control and single treatment 48 hours after treatment. Additionally, SOX2 and c‐Myc expression as well as EphA2‐mediated cell migration signaling (phospho‐EphA2 Tyr588 and Tyr594 expression) were abrogated. Conclusion CPT is a potent, but highly toxic anticancer agent whose clinical utility is hindered by adverse dose‐dependent hematopoetic and other adverse effects. In this study, however, sub‐toxic doses of CPT was effective in sensitizing highly resistant H1299 cells to Erl through inhibition of cell migration and induction of apoptosis. Combination treatment with low‐dose CPT may be a viable means of sensitizing refractory cancer cells to therapy. Support or Funding Information Dr. Terrick Andey MCPHS UniversityE‐mail address: Terrick.andey@mcphs.edu