Suppression of hepatocellular carcinoma growth in mice via leptin, is associated with inhibition of tumor cell growth and natural killer cell activation.

BACKGROUND/AIMS Leptin exerts potent immune modulatory properties. The aim of this study was to determine leptin's anti-tumor effect in a murine model of hepatocellular carcinoma (HCC). METHODS In vivo, athymic nude mice were transplanted with Hep3B cells, followed by daily leptin administration for 6 weeks. RESULTS Leptin administration induced a significant reduction in tumor size, improved survival rate, and was associated with a significant increase in peripheral natural killer (NK) cell number. Splenocytes from leptin-treated mice featured decreased expression of CIS mRNA. SCID mice featured a similar leptin-associated tumor suppression. In contrast, NK-deficient SCID-beige mice developed larger tumors which were unresponsive to leptin. NK cells incubated in vitro with increasing doses of leptin demonstrated increased cytotoxicity and proliferation. Incubation of leptin with hepatoma cells induced a dose-dependent reduction in proliferation, suggesting a direct anti-tumor effect. Leptin induced increased mRNA expression of STAT2 and SOCS1 on HCC cell lines. CONCLUSIONS Leptin administration induces a significant suppression of human HCC. This effect is mediated by induction of natural killer cell proliferation and activation, along with direct inhibition of tumor growth. Decreased NK expression of inhibitory CIS and over-expression of the antiproliferative STAT2 and SOCS1 proteins in HCC lines may underline the anti-cancerous effects of leptin.