Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the presence of innumerous fluid filled cysts that progressively enlarge, leading nephron loss and the progressive decline in renal function. Aberrant proliferation of the cyst-lining epithelial cells and the accumulation of fluid within the cysts du to Cl-dependent fluid secretion are responsible for the growth of the cysts. During the past fifteen years, there has been enormous amounts information gained from PKD research; however there is still a lack of understanding on how to effectively treat the disease. Tolvaptan, a vasopressin V2 receptor antagonist, was highly effective in animals models of PKD and significantly slow PKD progression in patients of the TEMPO trial; however, the drug caused liver complications is some patients and was not approved by the FDA for treatment of PKD. mTOR inhibitors, such as rapamycin, are also being considered as potential disease modifying therapies, however, clinical trials of these agents have been disappointing. One concern is that circulating concentrations of the drug at concentrations that are tolerated relatively well may not be sufficient to inhibit mTOR in the kidneys. Recently, folate-conjugated rapamycin was shown to specifically target the kidney since the pro drug was taken up by the folate receptor-mediated endocytosis and cleaved releasing the active rapamycin within the kidney cells. NovaTarg, in collaboration with the Kidney Institute at the University of Kansas Medical Center, has identified an innovative approach to inhibit cyst growth. Taking advantage of the focused medicinal chemistry program at NovaTarg and the expertise of the PKD investigators at KUMC, we have developed kidney-specific AMPK activators that inhibit ADPKD cell proliferation through p53 and the mTOR pathway, and fluid secretion driven by CFTR mediated Cl- secretion. Our approach is based on the synthesis of novel biguanides, analogues of metformin that utilize the kidney specific organic cation transporter 2 (OCT2) to enter kidney cells and to activate AMPK in the cyst-lining cells. Biguanides are very basic compounds which require OCTs for cellular entry, but metformin itself does not discriminate between OCT1 (liver) and OCT2 (kidney). An important complication of the use of metformin in patients with chronic kidney disease is the development of lactic acidosis due to the accumulation of the drug in the liver. Thus NovaTarg has synthesized >130 biguanide analogues of metformin to identify biguanides that are selectively transported by OCT2 to target kidney cells. An early lead compound, NT1021 activated AMPK in human ADPKD cells, leading to inhibition of mTOR- mediated cell proliferation and transepithelial Cl secretion. In addition, NT1021 blocked in vitro cyst formation of ADPKD cells cultured within a collagen matrix and the expansion of cyst-like structures in Pkd-/- mouse embryo kidneys ex vivo. We think that highly OCT2 selective biguanides will avoid liver uptake by OCT1 and display the safety profile required for this population of patients. During Phase 1 of the SBIR, NovaTarg discovered a highly OCT2-selective biguanide NT1096 that has higher selectivity for OCT2 than NT1021, but is not quite as potent. In Phase 2, we will synthesis derivatives of NT1096 for hit-to-lead optimization and evaluate the drug in preclinical studies and prepare for testing the drug is a proof-of-principal clinical trial.
Autosomal dominant polycystic kidney disease is a life-threatening condition affecting 12 million people worldwide for which there are no treatments. Approximately, half of the patients progress to end-stage renal disease (ESRD) by the sixth decade of life. The medical and economic costs of ADPKD are considerable: PKD is responsible for ~10% of all patients requiring renal transplantation and dialysis, costing >$2B/year in the US alone. NovaTarg has discovered a novel kidney selective treatment that offers the possibility of disease modifying drug therapy for PKD.
