Regulus Therapeutics Inc. announced that it has completed enrollment of the first cohort of patients into its Phase 1b clinical study of RGLS4326. The Phase 1b is an adaptive design, open-label, multiple dose study in up to three cohorts of patients with ADPKD. The study is designed to evaluate the safety, pharmacokinetics, and changes in levels of polycystin 1 (PC1) and polycystin 2 (PC2) in patients with ADPKD administered RGLS4326 every other week for a total of four doses. The dose level for the first cohort is 1mg/kg of RGLS4326 and the dose level for the second cohort is 0.3mg/kg. The third and final cohort will be dosed at a level to be determined based on the results of the first two cohorts. Concurrent with completion of enrollment in the first cohort and based on the review of the available interim safety data, the first patient of the second cohort has received the first dose of RGLS4326. ADPKD, caused by the mutations in the PKD1 or PKD2 genes, is among the most common human monogenic disorders and a leading cause of end-stage renal disease. The disease is characterized by the development of multiple fluid filled cysts primarily in the kidneys, and to a lesser extent in the liver and other organs. Excessive kidney cyst cell proliferation, a central pathological feature, ultimately leads to end-stage renal disease in approximately 50% of ADPKD patients by age 60. RGLS4326 is a novel oligonucleotide designed to inhibit miR-17 and designed to preferentially target the kidney. Preclinical studies with RGLS4326 have demonstrated direct regulation of Pkd1 and Pkd2, reduction of cyst growth in human in vitro ADPKD models, and attenuation of cyst proliferation and improvement of kidney function in mouse models of ADPKD. The RGLS4326 IND is currently on a Partial Clinical Hold for treatment of extended duration by FDA until the second set of requirements outlined by the agency have been satisfactorily addressed. The Company will use information from the Phase 1 clinical studies, including the first cohort of the Phase 1b together with information from the recently completed additional nonclinical studies generated in 2020, in its plan to address the second set of requirements outlined in the Partial Clinical Hold letter to support studies of extended duration. Regulus plans to discuss its approach to addressing the remaining Partial Clinical Hold requirements with FDA in mid-2021. RGLS4326 has received orphan drug designation from FDA in July 2020.