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
- ADPKD: Genetic and Model Studies
October 25, 2018 | Location: Exhibit Hall, San Diego Convention Center
Abstract Time: 10:00 AM - 12:00 PM
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) | pAKT | pS6 | FLUX | p62 | Cyst area % | p4EBP1 | |
| PKD VEH | 2.6±0.1 | 63±2 | 0.8±0.2 | 1.3±0.1 | 0.02±0.1 | 1.03±0.05 | 31.6±3.2 | 0.7±0.1 |
| PKD TORK | 2.1±0.2* | 41±4* | 0.3±0.1* | 1.0±0.2 | 0.82±0.2* | 0.88±0.02 | 22.1±4.8 | 0.4±0.1 |
| PKD SIR | 2.3±0.02* | 39±4* | 0.2±0.1* | 0.7±0.04* | 0.10±0.2 | 0.86±0.01 | 20.2±3.2 | 0.4±0.1 |
*p<0.05 vs VEH, n=4
Funding
- Other U.S. Government Support