Inhibition of CHOP Chemotherapy‐stimulated Hematological Tumor Growth with Resolvins

Background Current therapeutic approaches for non‐Hodgkin lymphoma, such as CHOP chemotherapy (cyclophosphamide, doxorubicin, vincristine, prednisone), reduce tumor burden by inducing tumor cell death thereby creating tumor cell debris. This debris can stimulate inflammation in the tumor microenvironment contributing to tumor growth, making cytotoxic therapies a double‐edged sword . A new direction in inflammation research has emerged with the discovery of a novel genus of endogenous anti‐inflammatory and pro‐resolving lipid‐autacoid mediators derived from omega‐3 polyunsaturated fatty acids, including resolvins , which have potent novel inflammation clearing (‘pro‐resolution’) activity without being immunosuppressive. We hypothesize that (1) the failure of endogenous clearance of tumor cell debris can promote hematological cancer progression (2) resolvins represent a novel modality in cancer treatment by enhancing endogenous clearance of tumor debris by macrophage phagocytosis. Results Flow cytometry confirmed chemotherapy‐generated apoptotic and necrotic cell death (debris) in a dose‐ and time‐dependent manner. Vincristine‐generated EL4 lymphoma debris stimulated growth of EL4 tumors by over 100‐fold. Increasing the amount of vincristine‐generated EL4 debris (1×10 5 , 3×10 5 , 9×10 5 , or 1.8×10 6 dead cells) co‐injected with a subthreshold inoculum of 1×10 4 living EL4 tumor cells resulted in progressive acceleration of tumor growth. Tumor cell debris alone did not produce tumors, even at 250 days post‐injection. Vincristine‐generated EL4 debris also stimulated tumor growth in 3 other tumor types (LLC, B16F10, or PancOH7). Similarly, doxorubicin‐generated lymphoma (EL4) debris stimulated primary tumor growth. In addition, debris from cultures of non‐tumorigenic cells (NIH‐3T3 fibroblasts or MelaC melanocytes) generated by vincristine stimulated primary EL4 tumor growth. While systemic administration of vincristine inhibited the growth of 1 × 10 6 EL4 living cells, vincristine stimulated the growth of a subthreshold inoculum of 1×10 4 EL4 living cells in mice. Co‐injection of phosphatidylserine (PS) liposomes stimulated EL4 tumor growth in a dose‐dependent manner in comparison to phosphatidylcholine (PC) liposomes utilized as a control. Blocking PS in the cell debris using recombinant annexin V protein suppressed debris‐stimulated tumor growth in a dose‐dependent manner, with complete suppression of tumor growth until day 12 post‐injection. Both doxorubicin and vincristine‐generated tumor cell debris stimulated pro‐inflammatory cytokine production by macrophages. Resolvins inhibited debris‐stimulated tumor growth via stimulating macrophage phagocytosis of chemotherapy‐induced tumor cell debris. Conclusions The clearance of CHOP therapy‐induced tumor cell debris via resolvins provides a novel approach to hematological cancer therapy. Understanding the mechanisms including PS‐dependent debris‐stimulated tumor growth is critical to improving hematological cancer treatment. Support or Funding Information R01‐170549