Abstract 571: Osteopontin (OPN) inhibition as a novel therapeutic strategy in targeting non-small cell lung cancer (NSCLC)

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL OPN is a secreted glyco-phosphoprotein that is involved in many pathological processes. Several studies have shown that OPN plays a major role in driving tumor cell proliferation, migration, invasion, adhesion, angiogenesis and apoptosis evasion. In NSCLC, elevated plasma OPN level has been associated with worse treatment outcomes and surgical tumor resection resulted in normalization of secreted OPN level. Therefore, OPN may serve as both a biomarker and a therapeutic target in NSCLC. Since the use of blocking antibodies has become a successful therapeutic strategy in the clinics for several molecular targets, utilization of an OPN-neutralizing antibody may be an effective novel therapy for NSCLC. We have previously found that the RGD domain of OPN is critical for mediating tumor growth and metastasis by protecting tumor cells from stress-induced apoptosis. We therefore generated a rabbit polyclonal OPN antibody against a large peptide spanning this domain and verified that the purified antibody recognized both intracellular and secreted human and mouse OPN specifically. Functionally, treatment of LKR10 and LKR13 (two murine K-ras activated NSCLC cell lines of adenocarcinoma subtype) with OPN antibody attenuated their migration, observed in trans-well and scratch migration assays. We also observed decreased cell proliferation, through BrdU incorporation, in anti-OPN pre-treated LKR10 cells. Additionally, treatment of these cells with OPN antibody prior to radiation enhanced radiation cell kill 2.4 and 1.6 fold (in LKR10 and LKR 13, respectively) under hypoxia, but not normoxia, as measured by clonogenic survival. The same radiosensitivity effect was also observed in XTT and MTT cell viability assays. This hypoxia-specific radiation sensitization effect appears to involve OPN interaction with the CD44 cell surface receptor since pre-treatment with CD44-specific antibody also resulted in enhanced radiation cell kill under hypoxia but not normoxia. However, pre-treatment with Integrin avb3 antibody did not elicit the same increase in radiation sensitivity under either normoxia or hypoxia. Finally, OPN-antibody pre-treatment did not affect cell cycle distribution 24 hours after cell irradiation under normoxia or hypoxia, determined by flow cytometric analysis of PI staining. In conclusion, potentially through CD44 receptor signaling, antibody inhibition of OPN attenuated migration, proliferation and clonogenic capacity after radiation under hypoxia in LKR cells. Our findings support the therapeutic potential of utilizing antibodies to inhibit OPN in NSCLC, however future studies will be conducted to determine the mechanism by which our OPN antibody sensitizes cells to radiation under hypoxia and to evaluate the therapeutic effect of OPN antibody when used in conjunction with radiotherapy in NSCLC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 571. doi:10.1158/1538-7445.AM2011-571