EFFECTS OF SIROLIMUS ON DISEASE PROGRESSION IN PATIENTS WITH AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DISEASE AND SEVERE RENAL INSUFFICIENCY

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common hereditary renal disease, responsible for the 8% to 10% of the cases of end-stage renal disease (ESRD) in Western Countries.

ADPKD shows genetic heterogeneity, with at least three different genes implicated: the PKD1 gene (85% of the cases), the PKD2 (15% of the cases), and probably a PDK3 gene not yet identified. Recently, it has been reported that PC1 tail interacts with tuberin, the product of the TSC2 gene. The main function of the tuberin is to inactivate the Ser/Thr kinase mTOR, whose activity has been linked to increased cell growth, proliferation, apoptosis and differentiation. In ADPKD experimental animal models, researchers have shown that cyst lining epithelial cells exhibited very high mTOR activity; thus, they hypothesized that PC1 normally suppresses mTOR activity, and that defects in PC1 (and other proteins) may lead to aberrant mTOR activation. Studies in rat models of ADPKD have shown that short-term treatment with sirolimus (SRL) resulted in the dramatic reduction of the kidney size.

Recently we have documented that in ADPKD patients with normal kidney function or moderate renal dysfunction a short-course of SRL halted cyst growth and increased parenchyma volume. At this effective SRL dose (target trough blood level 5-10 ng/ml) the only relevant adverse effect observed in some patients was the development of aphthous stomatitis, relieved with topical treatment alone using a mouthwash.

Interestingly a retrospective study in a small number of SRL-treated ADPKD transplant patients showed that the treatment significantly reduced native kidney volumes over an average of 24 month follow-up. This reduction was three times higher than that reported in a control group of ADPKD transplant recipients not given SRL over a 40 month period. These results suggested that SRL may have a similar beneficial effect in humans as in experimental animals.

Overall, these findings are the basis for designing this study in ADPKD patients with severe renal dysfunction (GFR 40-15 ml/min/1.73m2) aimed to assess the safety and the efficacy of SRL in slowing renal function decline as compared to conventional therapy.