Inhibition of dopamine receptor D1 signaling promotes human bile duct cancer progression via WNT signaling.

Bile duct cancer (BDC) frequently invades the nerve fibers, making complete surgical resection difficult. A single tumor mass contains cells of variable malignancy and cell-differentiation states, with cancer stem cells (CSCs) considered responsible for poor clinical outcomes. This study aimed to investigate the contribution of autosynthesized dopamine to CSC-related properties in BDC. Sphere formation assays using 13 commercially available BDC cell lines demonstrated that blocking dopamine receptor D1 (DRD1) signaling promoted CSC-related anchorage-independent growth. Additionally, we newly established four new BDC patient-derived organoids (PDOs) and found that blocking DRD1 increased resistance to chemotherapy and enabled xenotransplantation in vivo. Single-cell analysis revealed that the BDC PDO cells varied in their cell-differentiation states and responses to dopamine signaling. Further, DRD1 inhibition increased WNT7B expression in cells with bile duct-like phenotype, and it induced proliferation of other cell types expressing Wnt receptors and stem cell-like signatures. Reagents that inhibited Wnt function canceled the effect of DRD1 inhibition and reduced cell proliferation in BDC PDOs. In summary, in BDCs, DRD1 is a crucial protein involved in autonomous CSC proliferation through the regulation of endogenous WNT7B. As such, inhibition of the DRD1 feedback signaling may be a potential treatment strategy for BDC.