Pharmacologic inducers of the uric acid exporter ABCG2 as potential drugs for treatment of gouty arthritis

Uric acid is the end product of purine catabolism and its plasma levels are maintained below its maximum solubility in water(6–7 mg/dl).The plasma levels are tightly regulated as the balance between the rate of production and the rate of excretion,the latter occurring in urine(kidney),bile(liver)and feces(intestinal tract).Reabsorption in kidney is also an important component of this process.Both excretion and reabsorption are mediated by specific transporters.Disruption of the balance between production and excretion leads to hyperuricemia,which increases the risk of uric acid crystallization as monosodium urate with subsequent deposition of the crystals in joints causing gouty arthritis.Loss-of-function mutations in the transporters that mediate uric acid excretion are associated with gout.The ATP-Binding Cassette exporter ABCG2 is important in uric acid excretion at all three sites:kidney(urine),liver(bile),and intestine(feces).Mutations in this transporter cause gout and these mutations occur at significant prevalence in general population.However,mutations that are most prevalent result only in partial loss of transport function.Therefore,if the expression of these partially defective transporters could be induced,the increased number of the transporter molecules would compensate for the mutation-associated decrease in transport function and hence increase uric acid excretion.As such,pharmacologic agents with ability to induce the expression of ABCG2 represent potentially a novel class of drugs for treatment of gouty arthritis.

The amino acid transporter SLC6A14 in cancer and its potential use in chemotherapy

Tumor cells have an increased demand for glucose and amino acids to support their rapid growth,and also exhibit alterations in biochemical pathways that metabolize these nutrients.Transport across the plasma membrane is essential to feed glucose and amino acids into these tumor cell-selective metabolic pathways.Transfer of amino acids across biological membranes occurs via a multitude of transporters;tumor cells must upregulate one or more of these transporters to satisfy their increased demand for amino acids.Among the amino acid transporters,SLC6A14 stands out with specific functional features uniquely suited for the biological needs of the tumor cells.This transporter is indeed upregulated in tumors of epithelial origin,including colon cancer,cervical cancer,breast cancer,and pancreatic cancer.Since normal cells express this transporter only at low levels,blockade of this transporter should lead to amino acid starvation selectively in tumor cells,thus having little effect on normal cells.This offers a novel,yet logical,strategy for the treatment of cancers that are associated with upregulation of SLC6A14.In addition,a variety of amino acid-based prodrugs are recognized as substrates by SLC6A14,thus raising the possibility that anticancer drugs can be delivered into tumor cells selectively via this transporter in the form of amino acid prodrugs.This strategy allows exposure of SLC6A14-positive tumor cells to chemotherapy with minimal off-target effects.In conclusion,the amino acid transporter SLC6A14 holds great potential not only as a direct drug target for cancer therapy but also for tumor cell-selective delivery of anticancer drugs.

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.