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Kidney Week

Abstract: TH-PO675

Head-to-Head Study of Sirolimus and an mTOR Kinase Inhibitor (TORK) in a Hypomorphic Model of Polycystic Kidney Disease

Session Information

Category: Genetic Diseases of the Kidney

  • 1001 Genetic Diseases of the Kidney: Cystic

Authors

  • Brown, Carolyn Nicole, UC Denver Anschutz Medical Campus, Aurora, Colorado, United States
  • Holditch, Sara, UC Denver Anschutz Medical Campus, Aurora, Colorado, United States
  • Atwood, Daniel, UC Denver Anschutz Medical Campus, Aurora, Colorado, United States
  • Edelstein, Charles L., UC Denver Anschutz Medical Campus, Aurora, Colorado, United States
Background

Sirolimus indirectly inhibits mTORC1 and reduces but does not completely inhibit cyst growth in rodent models of autosomal dominant polycystic kidney disease (ADPKD). Sirolimus was not effective in human PKD and was associated with side effects. The novel ATP competitive mTOR kinase inhibitors (TORKs) e.g. Torin2 directly inhibit mTOR kinase that results in inhibition of both mTORC1 and 2. TORKs, which increase liver enzymes, have a different side effect profile to sirolimus, which causes mucositis. We report a head-to-head comparison of Torin2 versus sirolimus in a hypomorphic mouse model of PKD.

Methods

C57Bl/6 Pkd1 p.R3277C (PKD) mice were treated with 0.5mg/kg sirolimus (SIR) or 10mg/kg Torin2 (TORK) daily from 50 to 120 days of age. Serum BUN was analyzed using an enzymatic assay. Cyst area was quantified from H&E stained kidneys. Kidneys were immunoblotted for mTORC1 substrates, pS6 and p4E-BP1 (S65), mTORC2 substrate, pAkt (S473), LC3-II (autophagosome marker), and p62 (autophagy-specific ubiquitin-binding protein). Autophagic flux was defined as the difference between LC3-II before and after administration of the lysosomal inhibitor bafilomycin.

Results

Kidney weight and serum BUN were significantly decreased in TORK- and SIR-treated mice compared to vehicle (VEH). CVD showed a tendency to decrease with both TORK and SIR. pAKT was decreased in both TORK and SIR treatments. pS6 was significantly decreased in SIR-treated mice only. TORK significantly increased autophagic flux (FLUX). No side effects were noted on gross examination in either treatment group.

Conclusion

For the first time, we have shown in a head-to-head study that the TORK, Torin2, is as effective as sirolimus in decreasing kidney size and serum BUN in a hypomorphic ADPKD mouse model. Both drugs inhibited pAKT. SIR had a better effect on pS6 than TORK. Interestingly, TORK resulted in a significant increase in autophagic flux. As Torin2 has a short half-life (~1 hr), further studies are warranted to determine whether more frequent dosing of Torin2 will be more effective than sirolimus.

Table 1
 KW/BW(%)BUN (mg/dL)pAKTpS6FLUXp62Cyst area %p4EBP1
PKD VEH2.6±0.163±20.8±0.21.3±0.10.02±0.11.03±0.0531.6±3.20.7±0.1
PKD TORK2.1±0.2*41±4*0.3±0.1*1.0±0.20.82±0.2*0.88±0.0222.1±4.80.4±0.1
PKD SIR2.3±0.02*39±4*0.2±0.1*0.7±0.04*0.10±0.20.86±0.0120.2±3.20.4±0.1

*p<0.05 vs VEH, n=4

Funding

  • Other U.S. Government Support