Diphenylbutylpiperidine Antipsychotic Drugs Inhibit Prolactin Receptor Signaling to Reduce Growth of Pancreatic Ductal Adenocarcinoma in Mice

Abstract Background & Aims Prolactin (PRL) signaling is upregulated in hormone-responsive cancers. The PRL receptor (PRLR) is class I cytokine receptor that signals via the JAK–STAT and MAPK pathways to regulate cell proliferation, migration, stem-cell features, and apoptosis. Patients with pancreatic ductal adenocarcinoma (PDAC) have high plasma levels of PRL. We investigated whether PRLR signaling contributes to growth of pancreatic tumors in mice. Methods We used immunohistochemical analyses to compare levels of PRL and PRLR in multi-tumor tissue microarrays. We used structure-based virtual screening and fragment-based drug discovery to identify compounds likely to bind PRLR and interfere with its signaling. Human pancreatic cell lines (AsPC-1, BxPC-3, Panc-1, and MiaPaCa-2), with or without knockdown of PRLR (CRISPR or small-hairpin RNA), were incubated with PRL or penfluridol and analyzed in proliferation, spheroid formation. C57BL/6 mice were given injections of UNKC-6141 cells, with or without knockdown of PRLR, into pancreas, and tumor development was monitored for 4 weeks, with some mice receiving penfluridol treatment for 21 days. Human pancreatic tumor tissues were implanted into interscapular fat pads of NSG mice and mice were given injections of penfluridol daily for 28 days. Nude mice were given injections of Panc-1 cells, xenograft tumors were grown for 2 weeks, and mice were then given intraperitoneal penfluridol for 21 days. Tumors were collected from mice and analyzed by histology, immunohistochemistry, and immunoblots. Results Levels of PRLR were increased in PDAC compared with non-tumor pancreatic tissues. Incubation of pancreatic cell lines with PRL activated signaling via JAK2–STAT3 and ERK, as well as formation of pancospheres and cell migration; these activities were not observed in cells with PRLR knock down. Pancreatic cancer cells with PRLR knockdown formed significantly smaller tumors in mice. We identified several diphenylbutylpiperidine-class antipsychotic drugs as agents that decreased PRL-induced JAK2 signaling; incubation of pancreatic cancer cells with these compounds reduced their proliferation and formation of spheres. Injections of 1 of these compounds, penfluridol, slowed growth of xenograft tumors in the different mouse models, reducing proliferation and inducing autophagy of the tumor cells. Conclusions Levels of PRLR are increased in PDAC, and exposure to PRL increases proliferation and migration of pancreatic cancer cells. Antipsychotic drugs such as penfluridol block JAK2 signaling in pancreatic cancer cells to reduce their proliferation, induce autophagy, and slow growth of xenograft tumors in mice. These drugs might be tested in patients with PDAC.