A cytidine deaminase biodegrader sensitises multiple cancer types to deoxycytidine analogue-based chemotherapies

Deoxycytidine (dC) analogues are widely used to treat solid tumours and blood cancers. However, their clinical efficacy is often limited by resistance mediated by cytidine deaminase (CDA), which converts these drugs into inactive metabolites. Existing CDA inhibitors have limited efficacy and off-target effects, highlighting the need for alternative approaches. Here, we show the development of a CDA biodegrader, an intracellular anti-CDA VHH fused to the SPOP E3 ubiquitin ligase, enabling specific CDA degradation. It effectively depletes CDA in pancreatic, lung, and acute myeloid leukaemia cancer cell lines, increasing sensitivity to dC analogues in vitro. Combined with gemcitabine, the CDA biodegrader inhibits pancreatic and lung tumour growth in vivo. Importantly, mRNA encoding the biodegrader delivered using virus-like particles achieves efficient sensitisation to gemcitabine in vitro and in vivo. This proof-of-concept study establishes targeted CDA degradation as a feasible strategy to enhance the therapeutic efficacy of dC analogues.