Modulation of Therapeutic Response

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In the interest of improving cancer treatment, considerable attention has been placed on the modification of radiation damage. The interaction of a variety of chemotherapy and/or molecularly targeted agents with radiation is under study to determine if tumors can be made more sensitive or normal tissues more resistant to radiation treatment. The central aim is to identify approaches that will result in a net therapeutic gain, thus improving cancer treatment with radiation. One goal of the project is to define and better understand those aspects of tumor physiology, including cellular and molecular processes and the influence of the tumor microenvironment on treatment response. The ability to enhance the response of the tumor to radiation, without enhancing normal tissue within a given treatment field is desirable. We finished initial pre-clinical studies of a novel HSP90 inhibitor and a CDK4/6 inhibitor as a radiation sensitizers (in vitro and in vivo). Significant in vitro radiation dose modification factors have been observed with both agents and xenograft studies indicate that the combination of the drug with fractionated radiation results in enhanced radiosensitivity. Further, we have identified molecular biomarkers that will be helpful in assessing treatment efficacy for both agents. Both agents have potential of being translated into human clinical trials. A new discovery, initially made using the CDK4/6 inhibitor (abemaciclib) was confirmed to be operational with a completely different agent, the HSP90 inhibitor (AT13387). When combined with radiation both agents inhibited tumor vasculogenesis, which is a process following radiation that resupplies the tumor with blood vessels resulting in tumor regrowth. We have placed a major emphasis this past year on defining the mechanism of vasculogenesis inhibition which we have found that both agents inhibit HIF-1alpha and SDF-1. We are currently conducting studies to determine the mechanism of this inhibition. We continue to evaluate a number of metabolic inhibitors as radiation modifiers under the working hypothesis that inhibition of metabolism (for example, decreased ATP production) will diminish the repair of radiation-induced DNA damage. In vitro studies have shown that a novel lactate dehydrogenase inhibitor (LDHAi) enhances the radiosensitivity of human pancreatic carcinoma cells. Preliminary xenograft studies with this agent have shown a significant tumor growth delay with drug alone, but no enhancement of the radiation response. This finding has prompted us to obtain an inhibitor of oxidative phosphorylation with the idea of using both agents (LDHAi and OxPhos inhibitior) combined with radiation to determine the impact on tumor response. We have shown that the combination of LDHAi and the OxPhos inhibitor when combined with radiation provides more radiosensitization than is observed for each agent alone with radiation. We are also conducting non-invasive monitoring of tumor metabolism using 13C-pyruvate MRI to assess changes in tumor metabolism as well as MRI studies that address tumor blood flow and hypoxia status. The OxPhos inhibitor clearly results in less oxygen consumption in tumors thereby decreasing the hypoxic fraction in tumors. These pre-clinical studies will provide the necessary information to consider these agents in a clinical human trial for tumor radiosensitization. Collectively, we have identified a number of pre-clinical approaches to initiate human radiation oncology clinical trials for modulation of radiation effects on tumors.