Abstract 857: Preclinical evaluation: efficacy of DI17E6, a therapeutic antibody against alpha v integrins, compared to cilengitide in sensitizing human cancers to radiation therapy

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Purpose: Integrins are implicated in resistance of solid tumors to radiation therapy, suggesting that their inhibition would enhance therapeutic efficacy. We investigated the efficacy of DI17E6, a therapeutic antibody targeting alpha v (αv) integrins, in enhancing the radiosensitivity of non-small cell lung carcinoma (NSCLC) and head & neck cancer (HNSCC) cells using in vitro and in vivo models, and compared to the previously reported effects of the cyclic peptide cilengitide (inhibits αvβ3 and αvβ5 integrins). Methods: NSCLC lines (A549 and H460) and HNSCC lines (FaDu and HN-5) were examined. Basal level of αv integrin was assessed by viable cell flow-cytometry and by Western blot. The effects of DI17E6 on cell viability were determined by MTS assay, and on cellular radiosensitivity by clonogenic cell survival assay after exposing the cells to γ-radiation with or without DI17E6. In vivo effect of DI17E6 on radioresponse of xenografts was evaluated by tumor growth delay assay. DI17E6 was given i.p.; as a single loading dose of 180 mg/kg followed by weekly doses of 10, 30 or 100 mg/kg given for 6 weeks; fractionated doses of local tumor irradiation was delivered using 137Cs γ-ray source (2 Gy daily for 7 days). When combined, the loading dose of DI17E6 was given either 4 h before or after the first radiation dose. Results: DI17E6 (0.01-10 µg/ml, 24 h) had a minimal effect on the cell viability. However, DI17E6 reduced the plating efficiency of A549, H460 and FaDu with no effect on HN-5 cells. When combined with radiation, DI17E6 enhanced the radiosensitivity of NSCLC cells but not the HNSCC cells. These data are consistent with previously observed effects of cilengitide in vitro. In vivo experiments with A549 xenografts showed that DI17E6 as a single agent had no antitumor activity, but in combination with radiation it suppressed the tumor growth in a schedule- and dose-dependent manner. These data were compared to the previously reported effect of cilengitide, which did not enhance the response of A549 xenografts to radiation therapy. DI17E6 has an extended pharmacokinetics (with a half-life of >7 days) and blocks more αv integrins than cilengitide. The results imply that when αvβ3 and αvβ5 integrins were inhibited by cilengitide either the duration of blockade was insufficient, or that other αv integrins may have provided tumor growth advantage. In vivo studies on other tumor types are underway. Conclusions: Inhibition of αv integrins by DI17E6 in combination with radiation enhanced radiosensitivity of NSCLC cell lines in vitro and in vivo enhanced A549 tumor xenograft response to radiation in mice. These results suggest that DI17E6 may improve the treatment outcome of patients with NSCLC when combined with radiotherapy in a clinical setting. Supported by EMD Serono Merck KGaA, Germany Citation Format: Amit A. Deorukhkar, David P. Molkentine, David R. Valdecanas, Kathryn A. Mason, Uma Raju. Preclinical evaluation: efficacy of DI17E6, a therapeutic antibody against alpha v integrins, compared to cilengitide in sensitizing human cancers to radiation therapy. [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 857. doi:10.1158/1538-7445.AM2014-857