Chemoprevention of hepatocellular carcinoma. Proof of concept in animal models

Abstract

In the present work, we have evaluated the possibility of preventing liver carcinogenesis in rats at two stages of development. In the first series of experiments, we induced foci of altered hepatocytes, (FAH) which represent the first events in rodent liver carcinogenesis, using the chemical mutagens diethylnitrosamine (DEN) and acetylaminofluorene (AAF). In the second part of the work, we used repeated weekly injections of DEN only that gave rise to significant fibrosis at 11 weeks and the development of malignant tumours at 16 weeks. We chose to assess the chemopreventive effect of three different drugs: pioglitazone, lanreotide and S-trans-trans-farnesylthiosalicylic acid (FTS). Pioglitazone (PGZ) is an agonist of peroxisome proliferator-activated receptor gamma (PPARg), itself a member of the nuclear receptor superfamily, responsible for the modulation of a number of metabolic pathways, including cell differentiation, metabolism of lipids and inflammation. Lanreotide (LAN) is a somatostatin analogue that has an inhibitory effect on the release of several hormones, such as growth hormone and serotonine. FTS is a specific antagonist of the protoocogene Ras, tested here based on the rationale that Ras is activated in many hepatocellular carcinomas (HCC). We showed that both PGZ and LAN were efficient in the first, pre-neoplastic model, by reducing the size of FAH, decreasing proliferation specifically in FAH by interacting with proteins of the cell cycle. We could also demonstrate that LAN increased apoptosis. In the second model, LAN was able to diminish the number of established HCC by decreasing proliferation, in parallel with an anti-fibrotic action. Furthermore, enhanced apoptosis and antiangiogenic effects were observed when LAN was given from the start of the carcinogenic induction by DEN. The cellular mechanisms leading to its effects warrant further investigations. FTS also strongly inhibited the appearance of FAH and HCC in the second model, through a complete inhibition of Ras activation and the induction of pro-apoptotic pathways. On the contrary, PGZ did not prevent the appearance of neoplastic lesions. For these reasons, we did not analyse further its mechanism of action in the second model. Altogether, the results we obtained demonstrate an activity of both LAN and FTS, at the early onset of liver carcinogenesis, and later on when advanced fibrosis, cirrhosis and HCC are induced. These anti-tumoural effects could be complementary and will be tested in combination in the future.