Synergistic antitumor effects of immune checkpoint inhibitors and targeted therapy in an orthotopic RCC mouse model

With the development of checkpoint inhibitors and immunotherapy treatment for Renal cell carcinoma (RCC), syngeneic orthotopic mouse models are advantageous as suitable preclinical models due to the presence of immune system. Orthotopic renal subcapsular inoculation tumor models are challenging and offer strong clinical relevance by closely mimicking the native tumor microenvironment. The In Vivo Imaging System (IVIS) further enhances these studies by enabling non-invasive, real-time tracking of tumor growth/regression during the study period without interim animal sacrifice. In the present study, we have evaluated the preclinical efficacy of anti-PD1, anti-CTLA-4 antibody and Cabozantinib and Bevacizumab as standalone and combination regimen in orthotopic renal cell carcinoma (RCC) model of immunocompetent BALB/c mice. Subcutaneous tumor was generated in donor mice by inoculation of RenCa luciferase reporter cell line. Tumor fragments (1mm 3 ) harvested from the donor mice were orthotopically implanted into the sub-renal capsule (SRC) space of the fresh batch of mice. Tumor growth was monitored twice weekly by IVIS optical imaging system. Mice were randomized based on total flux signal intensity (1-2 X 10 6 photons/second). Standalone and combination treatment was initiated with Cabozantinib at 10mg/kg; p.o; QD for 2 weeks and Bevacizumab at 5mg/kg; i.p; Q4Dx4 dose, anti-PD-1 at 10mg/kg; i.p; Q4Dx4 dose and Anti-CTLA4 at 10mg/kg; i.p; Q4Dx4 dose. Total flux (photons/second), changes in body weight, clinicals signs, mortality were monitored twice weekly up to 3 weeks. At the study's endpoint, tumors were excised and both ex-vivo bioluminescence signal intensity and tumor mass were quantified to assess treatment efficacy. In the current, orthotopic renal cell carcinoma model, treatment with standalone anti-PD1, anti-CTLA-4, and Cabozantinib and Bevacizumab resulted in moderate tumor regression. Whereas combination of anti-PD1 and anti-CTLA-4 with Cabozantinib and Bevacizumab demonstrated in improved efficacy when compared with individual treatments which was evident from the reduction in signal intensity, organ metastasis and resulted in prolonged survival. The findings of this study indicate that combining targeted therapy with immune checkpoint inhibitors can effectively suppress tumor progression and potentially overcome therapeutic resistance. This combinatorial strategy represents a promising multimodal translational approach to enhance the efficacy of chemotherapy in renal cancer. Assessing treatment outcomes in preclinical orthotopic tumor models using IVIS imaging offers a valuable, non-invasive method for accurate and longitudinal monitoring of tumor growth over time.