p53 in hepatic differential stress response

Current therapies for hepatocellular carcinoma (HCC) are proven less effective than those against other cancer types and HCC patients frequently become resistant to treatment. Therefore, novel strategies which will aid the current treatments of HCC are imperative. Short-term fasting is suggested to exhibit a protective effect on normal, non-transformed cells while it sensitizes transformed (cancer) cells during high-dose chemotherapy (CT). This phenomenon is termed differential stress resistance (DSR) and its underlying mechanisms are unclear. The tumor suppressor p53 is a transcription factor whose main activities are aimed to inhibit cancer development. Recent results obtained by the applicants lab showed that fasting activates the p53 pathway in liver of normal (wild type) mice. Based on these results, we hypothesize that the protective (in normal cells) or sensitizing (in cancer cells) effects of fasting during high-dose CT are regulated via p53. Differential effects could be mediated via different mechanisms which will be explored in the proposed research. Therefore, animal models (inducible, liver-specific p53 knock-out mice and xenografts) and liver cell lines (normal and transformed cell lines with different p53 activities) will be used, specifically probing glucose metabolism, oxidative stress, and autophagy with focused and global (RNA-seq, metabolomics) approaches. We will also investigate whether DSR involves modifications in the metastatic potential of transformed hepatocytes in relation to their p53 status by analyzing extracellular matrix-degrading proteinases. Hence, the overall aim of this proposal is to elucidate the role of p53 in fasting-induced DSR to chemotherapy in liver and HCC-derived cells. We expect that the results obtained will unveil novel cellular mechanisms which, in a clinical perspective, might help to improve current therapeutic measures against HCC by exploiting fasting as supportive treatment via inducing wild-type p53 activity.

Hepatocellular carcinoma (HCC) is inherently difficult to treat rendering it as one of the deadliest cancers with increasing global incidence. Sorafenib (trade name: Nexavar) has long been the sole first-line treatment for late-stage unresectable HCC but efficacy has been limited due to the development of therapy resistance. Suggesting a clinically actionable method of improving sorafenib efficacy, we report a combinatorial effect of nutrient restriction (i.e. intermittent fasting) with sorafenib. We show that the fasting/sorafenib combination can sensitize resistant HCC cells to sorafenib in culture and in xenografts, as well as in patient- derived HCC organoids. Furthermore, we show an improvement of the therapeutic effect of sorafenib in a non-resistant HCC model upon co-treatment with intermittent fasting. Cancer cells can provide energy for their proliferative demands either by mitochondrial respiration or through increased glucose consumption. We show that sorafenib acts to inhibit mitochondrial activity and nutrient restriction curtails the cancer cells shift to glucose consumption. In combination this kills cancer cells through blocking the two main energy generating pathways. Moreover, in both the sorafenib-resistant and -sensitive models, the tumor suppressor protein p53 is necessary for the combined effect of fasting and sorafenib. This finding is of clinical relevance considering that about a third of HCC patients are deficient for p53 and therefore might not benefit from adjuvant fasting, while the other two thirds might. This is important for the implementation of personalized medicine-driven interventions in HCC and in other cancers with mutated p53. Overall, our results could be clinically exploited bearing in mind that fasting was previously shown to be safe for cancer patients. If generalizable to other cancers, our findings may constitute a paradigm shift for development of novel combination treatments that target both mitochondrial activity and glucose consumption. Further, studies are currently testing if this approach to metabolic combination therapy is generalizable to other drugs, fasting modalities and cancer types.