#966 Targeting cAMP in ADPKD by small molecule activation of long form PDE4 enzymes
Authors: Rowley Adele , Henderson David , Adam Julia , Wang Xiaofang , LI Jiang , Irfan Jaazba , Whitworth Claire , Omar Faisa , Kelleher Catherine , Torres Vicente 
Published: May 2024

Abstract

Background and Aims
Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common hereditary kidney disorder, affecting over 12 million people worldwide. ADPKD is characterized by the uncontrolled growth of fluid-filled cysts in the kidney that can lead to kidney enlargement, loss of function, and associated complications. Currently, there are limited treatment options for ADPKD patients. By activating long form PDE4 enzymes and increasing cAMP hydrolysis, Mironid®’s first-in-class small molecule LoAc® compounds [1] directly target the increased kidney cAMP levels that are known to drive cyst formation in ADPKD, resulting in decreased cyst growth in vitro and in vivo. Here we present translational data demonstrating that LoAc® compound MR-L22 lowers renal cAMP after single or multiple doses and delivers efficacy in the Pkd1RC/RC mouse model of ADPKD, alongside favourable differentiation from tolvaptan, the only therapy approved for ADPKD patients.

Method
To demonstrate cAMP lowering in urine, male Han Wistar rats (n = 6) were dosed p.o. with 100 mg/kg MR-L22 or vehicle (1% methylcellulose, 0.2% Tween 80) either once, or on 7 consecutive days. Urine was collected on Day 1 or Day 7. To assess the ability of MR-L22 to ameliorate disease progression alone, or in combination with tolvaptan, doses of MR-L22 (60 mg/kg) and tolvaptan (0.1% in chow), both expected to be individually sub-maximally efficacious, were administered singly, or in combination in F1 hybrid progeny Pkd1RC/RC mice (8 m and 8f/group), from 4-16 weeks of age. Urine measurements were taken after 8 weeks of dosing. Total kidney volume (TKV) was measured by MRI prior to randomisation and termination. cAMP in urine and kidney tissue were measured by ELISA.

Results
A 100 mg/kg oral dose of MR-L22 in rat resulted in a &gt;40% decrease in cAMP in urine compared to vehicle. This effect was maintained over multiple days of dosing demonstrating that urinary cAMP can be used as a biomarker of LoAc® target engagement. Consistent with the mechanism of action, a small increase in urine production and commensurate decrease in urine osmolality was observed. To assess the ability of MR-L22 to ameliorate disease progression in an in vivo model of ADPKD, and to determine whether additive or synergistic effects might be seen in combination with tolvaptan, MR-L22 (60 mg/kg) and tolvaptan (0.1% in chow) were dosed individually and in combination in the Pkd1RC/RC mouse model of ADPKD. Alongside a reduction in urinary cAMP, MR-L22 delivered reductions in TKV/Bw (Fig. 1), urinary and tissue cAMP, cystic index, terminal blood urea nitrogen (BUN) and creatinine, as well as trending reductions in urinary NGAL.

Conclusion
We have shown that in rat, acute or multiple dosing, of LoAc® compound MR-L22 results in a significant reduction of urinary cAMP and a small, but measurable, increase in urine production and commensurate decrease in urine osmolality. Furthermore, we have demonstrated that significantly reduced urinary and kidney cAMP levels correlate with reductions in TKV, cystic index, Kw/Bw, BUN and urinary NGAL in the Pkd1RC/RC model of ADPKD. In these studies, we have demonstrated beneficial differentiation vs tolvaptan on limiting aquaretic effects but been unable to conclusively demonstrate additive or synergistic effects of MR-L22 combined with tolvaptan due to experimental limitations; Further experiments will be needed to answer this question. Looking forwards, measurements of urine cAMP and urine osmolality will be measured as supportive of target engagement in phase 1 studies. Positive effects on TKV, seen in vivo in the Pkd1RC/RC model, will be assessed in a phase 2 clinical trial. By directly targeting cAMP, LoAc® compounds have the potential to slow renal disease progression, and to delay or prevent the need for dialysis, offering a potential new treatment option for ADPKD patients.