Regulus Therapeutics Announces Successful Completion of its Phase 1b MAD Clinical Trial for Autosomal Dominant Polycystic Kidney Disease Treatment

Regulus Therapeutics Inc. recently announced positive topline results from all patients in the fourth cohort in its Phase 1b MAD study of farabursen for the treatment of ADPKD.

The Phase 1b MAD study is a double-blind, placebo-controlled trial which evaluated the safety, tolerability, pharmacokinetics and pharmacodynamics (PK/PD) of farabursen in adult patients with ADPKD. The study evaluated farabursen treatment for three months followed by one month of follow up across three weight-based dose levels (1, 2 and 3 mg/kg) and one fixed dose level (300 mg). Primary endpoints were changes in urinary PC1 and PC2, with an exploratory examination of change in htTKV growth rate. PC1 and PC2 are the protein products of the PKD1 and PKD2 genes and their levels have been shown to inversely correlate with disease severity; htTKV has been shown to inversely correlate with kidney function.

In the fourth cohort, 26 subjects received a fixed dose of 300 mg of farabursen every other week for three months.  Consistent with the previously announced interim analysis of efficacy data from the first 14 subjects of this fixed-dose cohort, the full cohort of 26 patients demonstrated similar mechanistic response based on urinary PC1 and PC2 levels as well as a mean halting of htTKV growth over the four-month study period.

Cohort 4 data highlights:

• Increases in urinary PC1 and PC2 levels were similar to cohort 3 and reached a similar level of statistical significance compared to placebo (PC1 p=0.026; PC2 p=0.014).
• Mean htTKV growth rate over 4 months was 0.05% (SE -0.86% to +0.92%) while placebo subjects in the trial experienced a mean growth rate of 2.58% (SE +1.09% to +4.10%).
• Changes in htTKV were highly correlated with changes in renal cyst volume, suggesting farabursen directly impacts disease progression by limiting abnormal cyst growth.
• In an exploratory analysis, the combination of patients treated with 3 mg/kg or 300 mg fixed dose farabursen (n=35) were compared to a combined historical control group of placebo-treated patients from prior pivotal ADPKD trials (n=550). Farabursen-treated patients experienced mean reduction in htTKV growth rate (-0.14%) compared to a mean increase of (+1.87%) in placebo-treated patients (p=0.0056).
• Farabursen at 300 mg demonstrated a favorable safety and tolerability profile in this study, consistent with earlier cohorts.

“We are pleased that the results of cohort 4 demonstrate a level of mechanistic response, as measured by urinary PC1 and PC2, that indicates maximal anti-miR-17 activity. Along with the observed favorable safety and tolerability profile, these results give us confidence that 300 mg provides optimal target exposure and is the appropriate dose to take forward into Phase 3,” said Preston Klassen, M.D., President and Head of Research & Development of Regulus Therapeutics. “Even more encouraging is the repeated demonstration across multiple cohorts in the trial that, on average, growth of the kidney in ADPKD patients is halted after only a relatively short treatment period with farabursen. Based on exploratory analysis of Cohorts 3 & 4, which deliver overlapping drug exposures, we are confident that the htTKV effects seen with farabursen in this trial are clinically meaningful and provide important insight into the probability of success for the 12-month htTKV endpoint in the planned Phase 3 trial.”

“With full data from cohort 4 now analyzed, we are pleased with the positive results, in line with our expectations based on previous cohorts. These data suggest that farabursen has the potential to be an important addition to the limited therapeutic options for patients with ADPKD,” said Jay Hagan, CEO of Regulus Therapeutics. “I would like to thank all the patients, physicians, and support staff who have been vital to the ongoing development of farabursen. We are excited to move forward with initiation of the pivotal Phase 3 trial later this year.”

In January, the Company announced that it held a meeting with U.S. Food and Drug Administration (FDA) and had confirmed alignment with the FDA on the acceptability of the program’s CMC, non-clinical and clinical pharmacology plans and the key elements of a Phase 3 trial design as a single pivotal study, including a 12-month htTKV endpoint planned to support Accelerated Approval and a 24-month eGFR endpoint to support Full Approval.

More information about the MAD clinical trial is available at clinicaltrials.gov (NCT05521191).

Autosomal dominant polycystic kidney disease (ADPKD), caused by 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. Approximately 160,000 individuals are diagnosed with the disease in the United States alone, with an estimated global prevalence of 4 to 7 million.

Farabursen is a novel, next generation oligonucleotide for the treatment of ADPKD designed to inhibit miR-17 and to preferentially target the kidney. Administration of farabursen has shown clear improvements in kidney function, size, and other measures of disease severity in preclinical models. Regulus announced completion of the Phase 1 SAD study in September 2022. The Phase 1 SAD study demonstrated that farabursen has a favorable safety and PK profile. Farabursen was well-tolerated with no serious adverse events reported and plasma exposure was approximately linear across the four doses tested. In the Phase 1b MAD study, Regulus announced topline data from the first cohort of patients in September 2023, from the second cohort of patients in March 2024, from the third cohort of patients in June 2024, and from the fourth cohort in March 2025. Patients in the fourth cohort received an open-label 300 mg fixed dose of farabursen which was administered every other week for three months. Review of complete safety data from all cohorts demonstrated that farabursen was well tolerated.

Regulus Therapeutics Inc. (Nasdaq: RGLS) is a biopharmaceutical company focused on the discovery and development of innovative medicines targeting microRNAs. Regulus has leveraged its oligonucleotide drug discovery and development expertise to develop a pipeline complemented by a rich intellectual property estate in the microRNA field. Regulus maintains its corporate headquarters in San Diego, CA. For more information, visit https://www.regulusrx.com/.