Combination of calcineurin B subunit (CnB) and 5-fluorouracil reverses 5-fluorouracil-induced immunosuppressive effect and enhances the antitumor activity in hepatocellular carcinoma.

Five-fluorouracil (5-FU) is a widely used chemotherapeutic agent for digestive system tumors; however, continuous use of 5-FU may cause severe side effects, including myelosuppression and immunosuppression. Our previous study revealed that calcineurin B subunit (CnB), an innovative genetic engineering antitumor protein, possesses tumor-suppressive effects with low toxicity. CnB can bind to and activate integrin αM on macrophages, subsequently promoting the expression, and secretion of TNF-related apoptosis-inducing ligand, a specific proapoptotic cytokine. In the present study, whether the combined use of CnB and 5-FU can reverse the myelosuppression, and immunosuppressive effects of 5-FU by reactivating the immune system thus increasing antitumor efficacy, was investigated. It was demonstrated that combined treatment of 5-FU and CnB led to increased tumor-suppressive effects, as indicated by reduced tumor volume and weight when compared with 5-FU or CnB treatment alone in a hepatoma xenograph model. In addition, it was demonstrated that combined treatment inhibited the proliferation of hepatoma cells. Notably, the addition of CnB to 5-FU-based therapy completely reversed the immunosuppressive effect of 5-FU. The spleen index and total number of white blood cells in the combination group were higher compared with that of the 5-FU alone group. Furthermore, pathological examinations indicated that CnB attenuated 5-FU-induced organ damage. Based on these findings, it is proposed that CnB may serve as a novel and promising drug candidate for the improvement of 5-FU-based chemotherapy.