Calorie restriction has proven, potent benefits in terms of delaying cancer progression, but long-term calorie restriction is difficult to translate into human use. For this reason, calorie restriction mimetics (CRM) are being developed to replicate the beneficial effects of calorie restriction without the need for significant caloric limitation. Recently, the use of CRM has been shown to enhance chemotherapeutic efficacy by: 1) inducing autophagy in tumor cells, 2) increasing CD8 T cells infiltration into tumors, and 3) reducing localized tumor burdens. However, no study has yet tested the effects of CRM use in a pre-clinical model of spontaneous tumor metastasis, and the effects of CRM use + immunotherapy have not been evaluated at all. Immunotherapy is one of the most promising clinical treatment modalities available today for patients with metastatic disease, but clinical response rates remain <50%. If CRM use could act as adjuvant to boost immunotherapy-induced anti-tumor immunity, this could represent a major advance in clinical management of advanced cancer patients. We have been studying acarbose, an FDA-approved anti-diabetic drug and CRM, to better understand its effects on host metabolism, tumor outgrowth, and the immune system. Here, we investigate the ability of acarbose to enhance the efficacy of a CD8 T cell-based immunotherapy in the context of spontaneously metastasizing murine renal tumors. Our study of acarbose in tumor-free mice illustrates its action as a CRM: despite increased food intake, male and female mice have decreased fat mass, decreased leptin, and equal or diminished weight gain. In the absence of tumor growth, acarbose produced no significant changes in splenic leukocyte composition, but following orthotopic renal tumor challenge, acarbose markedly enhanced CD8 T cell infiltration into tumors (p = 0.04). One drawback was that tumor-bearing mice fed an acarbose-containing diet exhibited weight loss that was not seen in tumor-challenged mice on control diet (p = .001). This same type of adverse event was reported previously in mice treated with CRM+chemotherapy. Thus, despite increasing CD8 T cell infiltration into tumors, CRM use may trigger significant adverse events that could limit clinical translation. For these reasons, pre-clinical studies are needed to understand how best to use CRMs safely in the context of immunotherapy. We hypothesize that CRM use will synergize with CD8 T cell-based immunotherapy to facilitate tumor eradication in a majority of mice, permitting the identification of specific biologic and physiologic biomarkers that correlate with treatment success. The goals of this proposal are two-fold: 1) assess CRM effects on immunotherapeutic outcomes in a relevant pre-clinical model of metastatic renal cancer; and 2) identify local and systemic metabolic, inflammatory, and cellular immune biomarkers that could be used to evaluate both treatment success and adverse events such as weight loss in future clinical studies on CRM+ immunotherapy use in advanced cancer patients.
Renal tumors are immunogenic and responsive to T cell-based immunotherapies. Despite this, clinical response rates remain <30% and combinatorial approaches are being developed to improve immunotherapeutic efficacy. As caloric restriction mimetics were recently shown to enhance chemotherapy outcomes in a T cell-dependent manner, we propose to investigate the use of calorie restriction mimetics + immunotherapy in a pre-clinical model of advanced renal cancer, for the purpose of identifying therapeutic benefits and drawbacks that will inform translation into future clinical practice.
