Introduction  

Ovarian tumors exhibit irregular vasculature due to excessive pro-angiogenic stimuli leading to disorganized blood vessel networks. These chaotic vasculature patterns have numerous implications, including elevated interstitial fluid pressure (IFP), tissue hypoxia, and poor tissue perfusion. With high IFP, therapeutic compounds and immune cells infiltrating the tumor are significantly impeded. Immunotherapies are emerging as novel therapeutic approaches; however, the tumor microenvironment (TME) has hindered success. Our lab has developed a fusion protein that connects two segments (3TSR) of a potent anti-angiogenic compound, thrombospondin-1 (TSP-1), with a non-immunostimulatory human IgG domain. This compound, Fc3TSR, normalizes vasculature. We hypothesize that Fc3TSR will remodel the TME to improve the uptake and efficacy of immunotherapies.

Methods  

Ovarian tumors were induced with an injection of 1 x 10^6 ID8 cells under the ovarian bursa in syngeneic C57BL6 mice and allowed to develop to an advanced stage characterized by a primary tumor, secondary lesions, and ascites. At this phase, mice were administered PBS or Fc3TSR (0.158mg/kg) once a week for two weeks before intraperitoneal injection of anti-CTLA-4 (25ug) and anti-PD-L1 (25ug) for the following two weeks. At endpoint, tumors and inguinal lymph nodes were collected.

Results 

The Fc3TSR treatment group alone led to tumor regression and combining Fc3TSR with anti-CTLA-4 and anti-PD-L1 resulted in a further substantial decrease in tumor weight. Immunofluorescence staining demonstrated Fc3TSR significantly reduced hypoxic tissue, and co-localization staining for aSMA and CD31 revealed Fc3TSR-induced vascular normalization. The combination group exhibited significantly more CD68, CD11c, and CD3 staining within the tumor and inguinal lymph node.

Conclusion 

This study introduces a strategy for remodeling the TME and facilitating migration of immune cells into the tumor and tumor-draining lymph node.