Functional identification of the C-terminal domain of rhCNB

Recombinant human Calcineurin B subunit (rhCNB) has emerged as a promising antitumour candidate. Its antitumour activity is mediated by the secretion of proinflammatory cytokines and chemokines from both innate and adaptive immune cells, thereby enhancing their antigen-presenting capacity. Moreover, rhCNB is rapidly internalized by various tumour cells, demonstrating specific tumour-targeting properties. Previous studies have revealed that the C-terminal domain is responsible for the internalization and targeting ability of rhCNB; however, the precise antitumour functional domain remains unexplored. To address this, we engineered a truncated variant (designated DC, comprising amino acids 85–169 of rhCNB). Functional characterization revealed that DC promoted the maturation and differentiation of bone marrow-derived dendritic cells (BMDCs), stimulated the production of cytokines by BMDCs, were internalized into tumour cells, accumulated at tumour sites, and synergistically enhanced the tumoricidal activity of paclitaxel. Administration of the same dose (5 mg/kg) of DC and rhCNB to H22 tumour-bearing mice resulted in tumour growth inhibition rates of 40.5% and 53.73%, respectively, with no statistically significant difference between the two treatments. Collectively, these findings identify DC as the core functional domain responsible for the antitumour effects of rhCNB.