Transient Metabolic Alterations Induced by Chemotherapeutics in Cancer Persisters

Acquired drug tolerance has been a major challenge in cancer therapy. Recent evidence has revealed the existence of slow-cycling persister cells that survive drug treatments and give rise to multi-drug tolerant mutants in cancer. The mechanisms associated with persister phenotypes are highly diverse and complex, and many aspects of persister cell physiology remain to be explored. In this study, we aim to characterize the metabolic profiles of cancer persister cells mediated by cancer therapeutics, as epigenetic changes induced by drugs can lead to a transient metabolic rewiring of persister cells that can be associated with the phenotypic switch between normal and persister cell state. Determining the metabolic mechanisms underlying persister cell survival and maintenance will facilitate the development of novel treatment strategies that target persisters and enhance cancer therapy. In our first project, we treated melanoma cells with various conventional chemotherapeutic agents and showed that melanoma persister cells are not necessarily preexisting dormant cells. In fact, our data indicate they may be induced by cancer chemotherapeutics. Furthermore, with the use of untargeted metabolomics and phenotype microarrays, we demonstrated a transient upregulation in Krebs cycle metabolism in persister cells. We verified that targeting mitochondrial activity can significantly reduce melanoma persister levels. The reported metabolic remodeling feature seems to be a conserved characteristic of melanoma persistence, as it has been observed in various melanoma persister subpopulations derived from a diverse range of chemotherapeutics. In the next project, we explored metabolic alterations in melanoma cells mediated by Vemurafenib (VEM), a BRAF inhibitor. Co-treatment with BRAF inhibitors is a common treatment strategy for melanoma cancer. However, how a BRAF inhibitor itself alters melanoma cell metabolism and mediates persister survival is not well understood. Our findings demonstrate that metabolites associated with phospholipid synthesis, pyrimidine, one-carbon metabolism, and branched-chain amino acid metabolism are significantly altered in vemurafenib persister cells when compared to the bulk cancer population. Our data also show that vemurafenib persisters have higher lactic acid consumption rates as well as higher cell viability in a medium with lactate as the primary carbon source compared to control cells, further validating the existence of a unique metabolic reprogramming in these drug-tolerant cells. In the final project, we aim to elucidate the signaling pathways that link the therapeutic treatments to the observed metabolic reprogramming in melanoma persister cells. Using a high throughput assay with commercially available antibody arrays and western blotting, we identified that the cJUN pathway was transiently upregulated in cultures treated with chemotherapeutic agents. We further show that co-treatment with a cJUN inhibitor, JNK-In-8, resulted in an increased survival rate in cancer cells in the presence of chemotherapeutic agents. Furthermore, we highlighted that the phenomenon associated with cJUN was predominantly active in cultures treated with antimetabolites that act as a nucleoside analog for deoxycytidine. Overall, these results lead us to believe that cJUN, which is at the crossroads for both cell survival and apoptotic pathways, plays a significant role in persister physiology.