Abstract 3461: C-kit inhibitors and radiation: A promising combination in NSCLC

Background: NSCLC comprises 80% of lung cancer cases, and of these, about 40% are unresectable. Ionizing radiation (IR) and chemotherapy are used for patients with unresectable tumors, but radiotherapy remains largely palliative due to radioresistance. The failure of NSCLC therapy is associated with the tremendous heterogeneity in terms of cell of origin, pathology, etiology, and molecular/genetic pathogenesis. The existence of CSCs, undifferentiated cells with the capacity to self-renew and restore the tumor cell population, reflects the cellular heterogeneity within NSCLC. Evidence suggests that resistance to IR treatment is associated with CSCs within human tumors. Thus, targeting CSCs represents a new strategy for cancer treatment. We reported on our ability to isolate, culture and assay human lung CSCs from cultured cell lines. We found the stem cell factor (SCF) and its receptor c-kit functions, in a crucial pathway, for the self-renewal and proliferation of human lung CSCs. Hypothesis: CSCs survived after IR treatment of NSCLC cells. SCF/c-kit signaling is a central component of the self renewal and the survival of CSCs in lung tumors. The combination of IR treatment and c-kit pathway inhibition will eliminate bulk NSCLC cells and CSCs. Methods: CD133-positive and c-kit positive lung CSCs were isolated from H460 and A549 cultured NSCLC cell lines and from tumor samples from patients with NSCLC. The expression of cell surface markers, stemness of the cells and their resistance to IR were evaluated. Lung CSCs were treated with c-kit inhibitors and neutralizing SCF antibody and the growth of tumor spheres were assessed. Bulk NSCLC cells were irradiated and then were grown in the media with c-kit inhibitors and neutralizing SCF antibody for 3-12 days. The growing clones will then be counted and analyzed for expression of CSC markers. Cells from clones were re-plated and grown in stem cell-selective media and the CSC nature of the cells were analyzed. Results: We found that human lung CSC radioresistance is mediated by preferential activation of the DNA damage checkpoint response and an increase in DNA repair capacity. Tyrosine kinase inhibitors, with anti c-kit activity (eg.imatinib, dovitinib, sunitinib, and axitinib), were compared for their ability to abrogate lung CSC proliferation and potentiate the effect of IR on NSCLC. We found that lung CSCs proliferation was abrogated by all of the four c-kit inhibitors; however, axitinib showed the most profound anti- CSC effect. Conclusions: Targeting c-kit signaling, in c-kit and CD133-positive NSCLC cells with neutralizing SCF antibody or RTK inhibitors, suppressed CSC self renew and enhanced radiation response. The combination of IR treatment with SCF/c-kit pathway inhibition eliminated bulk NSCLC cells and radiation resistant CSCs. Work is supported by the grants: P50 CA090440 and The Pittsburgh Foundation (M2010-0021). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3461. doi:1538-7445.AM2012-3461