Abstract A42: Antiangiogenic-induced increase in tumor hypoxia in RCC and NSCLC human tumor xenografts and its selective targeting by the hypoxia-activated prodrug TH-302: A model for clinical exploration?
Authors: Hart Charles P. , Ahluwalia Dharmendra , Liu Qian , Meng Fanying , Bhupathi Deepthi , Curd John G. , Matteucci Mark D. 
Published: June 2012

Abstract
Several published studies have demonstrated an increase in tumor hypoxia after administration of anti-angiogenesis agents that target VEGF signaling (e.g., sunitinib, sorafenib, bevacizumab). We tested the hypothesis that the hypoxia-activated prodrug (HAP) TH- 302, currently in phase 1/2 trials for the treatment of cancer, would exhibit enhanced efficacy in the context of an antiangiogenic- mediated increase in tumor hypoxia and potentiate the antitumor efficacy of the antiangiogenic. To characterize sunitinib-induced effects on tumor vasculature and tumor hypoxia, 786-O (RCC) and H460 (NSCLC) human ectopic tumor xenografts were treated with sunitinib (20 or 40 mg/kg) daily for 5 days and then 72 hours later animals were injected with pimonidazole to label hypoxic cells and Hoechst 33342 to label vascular perfusion. The NSCLC model (H460) exhibits a baseline hypoxic fraction of 7%. Sunitinib induced a dose-dependent increase in tumor hypoxia volume (24 ± 3.2% with 40 mg/kg vs. 7.3 ± 3.8% with Vehicle, p&lt;0.05) and a corresponding decrease in tumor microvasculature. The 786-O RCC model is a well- vascularized tumor as characterized by CD31 and Hoechst staining with a relatively small baseline hypoxic compartment (&lt;5% volume) in the xenograft tumors. Sunitinib also induced a dose-dependent increase in tumor hypoxia volume (17.2 ± 7.1 % with 40 mg/kg vs. 1.4 ± 0.9% with Vehicle, p&lt;0.05) and a corresponding decrease in functional vasculature in the RCC model. We then tested whether TH-302, a 2-nitroimidazole triggered bromo-isophoramide mustard (Br-IPM) DNA crosslinker, could selectively target the antiangiogenic induced increase in tumor hypoxic fraction. H460 NSCLC tumor- bearing animals (~150 mm3 at start of dosing) were randomized into groups of 10 and treated with sunitinib at 20,40, or 80 mg/kg p.o. daily for 3 weeks (QDx21). After one week of sunitinib monotherapy animals began combination therapy with the addition of TH-302 at 50 mg/kg i.p. daily for 5 days on and 2 days off (QDx5) for 2 weeks. Sunitinib was administered 4 hours before TH-302 on days when both agents were given. Control arms included all 3 doses of sunitinib monotherapy, TH-302 monotherapy, and vehicles-only groups. Sunitinib exhibited dose-dependent antitumor efficacy (by TGI, TGD, and conditional survival), as did TH-302 monotherapy. All three combination therapy treatment groups exhibited superior efficacy compared to the corresponding monotherapy groups. A similarly designed experiment was performed in the RCC (786-O) model. in vitro monolayer cell-based profiling of the two cell lines (H460 and 786-O) with sunitinib and TH-302 in combination, under hypoxic or normoxic conditions, did not show any synergism. Taken together, the combination therapy efficacy observed in the xenograft models are consistent with complementary pharmacological effects at the tumor microenvironmental level, rather than cell autonomous effects. Morphometric analysis of TH-302 effects on hypoxic compartment volume in six different xenograft models (H460 intrapleural and H82 SCLC, H460 and Calu-6 NSCLC, and SU.86.86 and Hs766t CaPanc ectopic models) showed selective targeting of the hypoxic compartment resulting in a decrease in relative hypoxic volumes. Analogous experiments testing TH-302 effects on sunitinib-induced increases in tumor hypoxia volume are underway. The results support the hypothesis that the hypoxia-activated prodrug TH-302 may be an effective addition to antiangiogenic-containing chemotherapy regimens.
Citation Information: Clin Cancer Res 2010;16(14 Suppl):A42.