BACKGROUND:Autosomal dominant polycystic kidney disease (ADPKD) is the most common life-threatening genetic disease in humans, affecting approximately 1 in 500 people. ADPKD is characterized by cyst growth in the kidney leading to progressive parenchymal damage and is the underlying pathology in approximately 10% of patients requiring hemodialysis or transplantation for end-stage kidney disease. The two proteins that are mutated in ADPKD, polycystin-1 and polycystin-2, form a complex located on the primary cilium and the plasma membrane to facilitate calcium ion release in the cell. There is currently no Food and Drug Administration (FDA)-approved therapy to cure or slow the progression of the disease. Rodent ADPKD models do not completely mimic the human disease, and therefore preclinical results have not always successfully translated to the clinic. Moreover, the toxicity of many of these potential therapies has led to patient withdrawals from clinical trials.RESULTS:Here, we review compounds in clinical trial for treating ADPKD, and we examine the feasibility of using a kidney-targeted approach, with potential for broadening the therapeutic window, decreasing treatment-associated toxicity and increasing the efficacy of agents that have demonstrated activity in animal models. We make recommendations for integrating kidney- targeted therapies with current treatment regimes, to achieve a combined approach to treating ADPKD.CONCLUSION:Many compounds are currently in clinical trial for ADPKD yet, to date, none are FDA-approved for treating this disease. Patients could benefit from efficacious pharmacotherapy, especially if it can be kidney-targeted, and intensive efforts continue to be focused on this goal.

Background: Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the formation of fluid-filled cysts in the kidney and end stage renal disease by the fourth or fifth decade of life. Mutations in the PKD1 gene account for 85% of all cases of ADPKD. No curative therapy exists for patients affected by this disease and an underexplored avenue for the treatment of ADPKD is the targeting of epigenetic changes that occur during cystogenesis. Limited data exists on alterations in DNA methylation that are associated with ADPKD. Given the similarities between cyst growth and neoplasia, and the fact that 2 DNA methylation inhibitors are already Food and Drug Administration-approved for the treatment of myelodysplastic syndrome, we hypothesized that global DNA methylation patterns in ADPKD would parallel that observed in neoplasia, and which may provide an opportunity to treat ADPKD with epigenetic inhibitors. To address this hypothesis, we undertook a global DNA methylation analysis of human ADPKD kidney. Methods: We generated single nucleotide resolution methylomes of cortical kidney tissue from individuals with ADPKD, and from non-ADPKD kidney tissue, using reduced representation bisulfite sequencing. Using quantitative reverse transcription polymerase chain reaction, we investigated expression of the PKD1 gene in both ADPKD and non-ADPKD kidney. Results: We have shown that ADPKD-derived genomic DNA exhibits global hypomethylation when compared with non-ADPKD kidney, a pattern commonly observed in DNA methylation studies of tumor-derived tissue. We have also identified 13 discrete regions that are significantly differentially methylated in ADPKD compared to non-ADPKD, and 8 of these are gene specific. The PKD1 gene shows an increase in methylation at the 3′ end of the gene body, but in contrast to previously published data, this is not associated with a decrease in PKD1 mRNA expression. Conclusion: This genome-scale single nucleotide resolution analysis of DNA methylation in human polycystic kidneys suggests that DNA methylation differences at specific loci are associated with ADPKD. Further exploration into the significance of these preliminary results may shed light on the disease process, and potentially reveal new therapeutic possibilities.