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Critical regulation of bile acid (BA) pool size and composition occurs via an intensive molecular crosstalk between the liver and gut, orchestrated by the combined actions of the nuclear Farnesoid X receptor (FXR) and the enterokine fibroblast growth factor 19 (FGF19) with the final aim of reducing hepatic BA synthesis in a negative feedback fashion. Disruption of BA homeostasis with increased hepatic BA toxic levels leads to higher incidence of hepatocellular carcinoma (HCC). While native FGF19 has anti-cholestatic and anti-fibrotic activity in the liver, it retains peculiar pro-tumorigenic actions. Thus, novel analogues have been generated to avoid tumorigenic capacity and maintain BA metabolic action. Here, using BA related Abcb4−/− and Fxr−/− mouse models of spontaneous hepatic fibrosis and HCC, we explored the role of a novel engineered variant of FGF19 protein, called FGF19-M52, which fully retains BA regulatory activity but is devoid of the pro-tumoral activity. Expression of the BA synthesis rate-limiting enzyme Cyp7a1 is reduced in FGF19-M52-treated mice compared to the GFP-treated control group with consequent reduction of BA pool and hepatic concentration. Treatment with the non-tumorigenic FGF19-M52 strongly protects Abcb4−/− and Fxr−/− mice from spontaneous hepatic fibrosis, cellular proliferation and HCC formation in terms of tumor number and size, with significant reduction of biochemical parameters of liver damage and reduced expression of several genes driving the proliferative and inflammatory hepatic scenario. Our data bona fide suggest the therapeutic potential of targeting the FXR-FGF19 axis to reduce hepatic BA synthesis in the control of BA-associated risk of fibrosis and hepatocarcinoma development.

Tumor evolution is shaped by many variables, potentially involving external selective pressures induced by therapies1. After surgery, estrogen receptor (ERα) positive breast cancer (BCa) patients are treated with adjuvant endocrine therapy2 including selective estrogen receptor modulators (SERMs) and/or aromatase inhibitors (AIs)3. However, over 20% of patients relapse within 10 years and eventually progress to incurable metastatic disease4. Here we demonstrate that the choice of therapy has a fundamental influence on the genetic landscape of relapsed diseases: in this study, 21.5% of AI-treated, relapsed patients had acquired CYP19A1 gene (aromatase) amplification (CYP19A1amp). Relapsed patients also developed numerous mutations targeting key breast cancer genes including ESR1 and CYP19A1. Strikingly, CYP19A1amp cells also emerge in vitro but only in AI resistant models. CYP19A1 amplification causes increased aromatase activity and estrogen-independent ERα binding to target genes resulting in CYP19A1amp cells displaying decreased sensitivity to AI treatment. Collectively these data suggest that AI treatment itself selects for acquired CYP19A1 amplification and promotes local autocrine estrogen signalling in AI resistant metastatic patients.