Inhibiting Carbonic Anhydrase Ix Targets Hypoxic Small Cell Lung Cancer Cells

Abstract Small-cell lung cancer (SCLC) is an extremely aggressive disease, exhibiting acquired resistance to therapy and poor patient prognosis. Therapy resistance can in part be attributed to tumor hypoxia. Hypoxic SCLC cells up-regulate carbonic anhydrase IX (CA IX) in order to survive. CA IX is involved in pH maintenance of cells and presents a novel therapeutic target for SCLC. This study aimed to investigate the potential of inhibiting CA IX in SCLC as a novel therapeutic target. Hypoxic conditions (0.1% O2) increased CA IX expression over 24 hours in both COR-L24 and DMS 79 SCLC cells in culture. S4 belongs to a sulfamate class of carbonic anhydrase inhibitors and has shown anti-metastatic properties in breast cancer xenografts. Treatment with 30μM and 100μM S4 significantly decreased CA IX protein levels in hypoxic COR-L24 and DMS 79 SCLC cells, respectively (p<0.05 for both treatments). Exposure to S4 for 24 hours resulted in predominantly hypoxic cell death in both cell lines (p<0.05). Combining S4 with etoposide (0.3µM) and cisplatin (0.5µM) chemotherapeutic agents resulted in additional cell death, which was also seen under normoxic conditions (20% O2). Sub-cutaneous xenograft tumors were grown in nude mice using either COR-L24 or DMS 79 SCLC cells. Resultant tumors (1000mm3) expressed CA IX largely adjacent to regions of necrosis. Treating mice with 50mg/kg S4 on two consecutive days each week resulted in greater necrosis than saline controls, coupled with up-regulation of CA IX. Analyzing tumors for characteristic neuroendocrine (pro-opiomelanocortin) and epithelial (cytokeratin) markers revealed heterogeneous expression; however, this did not correlate with CA IX expression and is not altered in response to treatment. In summary, CA IX is upregulated in hypoxic SCLC cells and tumors. Inhibition of CA IX resulted in hypoxic cell death and had an additive effect to the response observed with chemotherapy treatment alone. This suggests that directly targeting hypoxic SCLC cells via CA IX inhibition holds promise in improving treatment outcome for this aggressive disease. Citation Format: Jennifer L. Bryant, Suzanne L. Meredith, Roben G. Gieling, Brian A. Telfer, Muhammad Babur, Claudiu T. Supuran, Kaye J. Williams, Anne White. Inhibiting carbonic anhydrase IX targets hypoxic small cell lung cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4980. doi:10.1158/1538-7445.AM2014-4980