Carbidopa, an activator of aryl hydrocarbon receptor, suppresses IDO1 expression in pancreatic cancer and decreases tumor growth.

IDO1 is an immunomodulatory enzyme responsible for tryptophan catabolism. Its expression in immune cells, especially the DCs, has attracted attention because it leads to tryptophan depletion at the immunological synapse, thereby causing T-cell anergy and immune evasion by the tumor cells. Cancer cells also overexpress IDO1. Immunotherapy targeting IDO1 has been one of the focus areas in cancer biology, but lately studies have identified non-immune related functions of IDO1 leading to a paradigm shift with regard to IDO1 function in the context of tumor cells. In this study, we show that PDAC tissues and PDAC cells overexpress IDO1. The expression level is reciprocally related to overall patient survival. We further show that carbidopa, an FDA-approved drug for Parkinson's disease as well as an AhR agonist, inhibits IDO1 expression in PDAC cells. Using athymic nude mice, we demonstrate that carbidopa-mediated suppression of IDO1 expression attenuates tumor growth. Mechanistically, we show that AhR is responsible for carbidopa-mediated suppression of IDO1, directly as a transcription factor and indirectly by interfering with the JAK/STAT pathway. Overall, targeting IDO1 not only in immune cells but also in cancer cells could be a beneficial therapeutic strategy for PDAC and potentially for other cancers as well and that carbidopa could be repurposed to treat cancers that overexpress IDO1.

Deletion of Slc6a14 reduces cancer growth and metastatic spread and improves survival in KPC mouse model of spontaneous pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is lethal. There is a dire need for better therapeutic targets. Cancer cells have increased demand for sugars, amino acids, and lipids and therefore up-regulate various nutrient transporters to meet this demand. In PDAC, SLC6A14 (an amino acid transporter (AAT)) is up-regulated, affecting overall patient survival. Previously we have shown using in vitro cell culture models and in vivo xenograft mouse models that pharmacological inhibition of SLC6A14 with α-methyl-l-tryptophan (α-MLT) attenuates PDAC growth. Mechanistically, blockade of SLC6A14-mediated amino acid transport with α-MLT leads to amino acid deprivation, eventually inhibiting mTORC1 signaling pathway, in tumor cells. Here, we report on the effect of Slc6a14 deletion on various parameters of PDAC in KPC mice, a model for spontaneous PDAC. Pancreatic tumors in KPC mice show evidence of Slc6a14 up-regulation. Deletion of Slc6a14 in this mouse attenuates PDAC growth, decreases the metastatic spread of the tumor, reduces ascites fluid accumulation, and improves overall survival. At the molecular level, we show lower proliferation index and reduced desmoplastic reaction following Slc6a14 deletion. Furthermore, we find that deletion of Slc6a14 does not lead to compensatory up-regulation in any of the other amino transporters. In fact, some of the AATs are actually down-regulated in response to Slc6a14 deletion, most likely related to altered mTORC1 signaling. Taken together, these results underscore the positive role SLC6A14 plays in PDAC growth and metastasis. Therefore, SLC6A14 is a viable drug target for the treatment of PDAC and also for any other cancer that overexpresses this transporter.

PEPT1 is essential for the growth of pancreatic cancer cells: a viable drug target.

PEPT1 is a proton-coupled peptide transporter that is up-regulated in PDAC cell lines and PDXs, with little expression in the normal pancreas. However, the relevance of this up-regulation to cancer progression and the mechanism of up-regulation have not been investigated. Herein, we show that PEPT1 is not just up-regulated in a large panel of PDAC cell lines and PDXs but is also functional and transport-competent. PEPT2, another proton-coupled peptide transporter, is also overexpressed in PDAC cell lines and PDXs, but is not functional due to its intracellular localization. Using glibenclamide as a pharmacological inhibitor of PEPT1, we demonstrate in cell lines in vitro and mouse xenografts in vivo that inhibition of PEPT1 reduces the proliferation of the cancer cells. These findings are supported by genetic knockdown of PEPT1 with shRNA, wherein the absence of the transporter significantly attenuates the growth of cancer cells, both in vitro and in vivo, suggesting that PEPT1 is critical for the survival of cancer cells. We also establish that the tumor-derived lactic acid (Warburg effect) in the tumor microenvironment supports the transport function of PEPT1 in the maintenance of amino acid nutrition in cancer cells by inducing MMPs and DPPIV to generate peptide substrates for PEPT1 and by generating a H+ gradient across the plasma membrane to energize PEPT1. Taken collectively, these studies demonstrate a functional link between PEPT1 and extracellular protein breakdown in the tumor microenvironment as a key determinant of pancreatic cancer growth, thus identifying PEPT1 as a potential therapeutic target for PDAC.

Chronic exposure to excess iron promotes EMT and cancer via p53 loss in pancreatic cancer.

Based on the evidence that hemochromatosis, an iron-overload disease, drives hepatocellular carcinoma, we hypothesized that chronic exposure to excess iron, either due to genetic or environmental causes, predisposes an individual to cancer. Using pancreatic cancer as our primary focus, we employed cell culture studies to interrogate the connection between excess iron and cancer, and combined in vitro and in vivo studies to explore the connection further. Ferric ammonium citrate was used as an exogenous iron source. Chronic exposure to excess iron induced epithelial-mesenchymal transition (EMT) in normal and cancer cell lines, loss of p53, and suppression of p53 transcriptional activity evidenced from decreased expression of p53 target genes (p21, cyclin D1, Bax, SLC7A11). To further extrapolate our cell culture data, we generated EL-KrasG12D (EL-Kras) mouse (pancreatic neoplastic mouse model) expressing Hfe+/+ and Hfe-/- genetic background. p53 target gene expression decreased in EL-Kras/Hfe-/- mouse pancreas compared to EL-Kras/Hfe+/+ mouse pancreas. Interestingly, the incidence of acinar-to-ductal metaplasia and cystic pancreatic neoplasms (CPN) decreased in EL-Kras/Hfe-/- mice, but the CPNs that did develop were larger in these mice than in EL-Kras/Hfe+/+ mice. In conclusion, these in vitro and in vivo studies support a potential role for chronic exposure to excess iron as a promoter of more aggressive disease via p53 loss and SLC7A11 upregulation within pancreatic epithelial cells.