Antihypoxic Potentiation of Standard Therapy for Experimental Colorectal Liver Metastasis Through Myo-Inositol Trispyrophosphate

   Purpose: Tumor hypoxia activates hypoxia-inducible factors (Hifs), which induce a range of malignant changes including vascular abnormalities. Here, we determine whether inhibition of the hypoxic tumor response through myo-inositol trispyrophosphate (ITPP), a compound with antihypoxic properties, is able to cause prolonged vascular normalization that can be exploited to improve standard-of-care treatment.
   Experimental Design: We tested ITPP on two syngeneic orthotopic mouse models of lethal colorectal cancer liver metastasis. Tumors were monitored by MRI and analyzed for the hypoxic response and their malignant potential. A Hif activator and in vitro assays were used to define the working mode of ITPP. Hypoxic response and vasculature were re-evaluated 4 weeks after treatment. Finally, we determined survival following ITPP monotherapy, FOLFOX monotherapy, FOLFOX plus Vegf antibody, and FOLFOX plus ITPP, both overlapping and sequential.
   Results: ITPP reduced tumor load, efficiently inhibited the hypoxic response, and improved survival. These effects were lost when mice were pretreated with a Hif activator. Its immediate effects on the hypoxic response, including an apparent normalization of tumor vasculature, persisted for at least 4 weeks after treatment cessation. Compared with FOLFOX alone, Vegf antibody combined with FOLFOX prolonged survival by 〈30%, whereas ITPP combined with FOLFOX extended survival by 〉140%, regardless of whether FOLFOX was given in overlap or after ITPP exposure.
   Conclusions: Our findings reveal a truly antihypoxic mechanism for ITPP and demonstrate the capacity of this nontoxic compound to potentiate the efficacy of existing anticancer treatment in a way amenable to clinical translation.