Specific treatments for Autosomal Dominant Polycystic Kidney Disease. A complerx biology and a long duration disease

Abstract

ADPKD is caused by mutations in the PKD1 and PKD2 genes. The two codified proteins, polycystins 1 and 2, are localized in the primary non-motil cilium and contribute through its mechanosensorial function to a normal signal process in the intracellular calcium (Ca2+) machinery. Renal cysts grow by a double epithelial process of increase in both fluid secretion and cell proliferation, fuelled both by a high intracellular cAMP. Along all these findings, it was also demonstrated in animal PKD models that an inhibitor of the endogenous vasopressin V2 receptor slowed the increase of renal volume and preserved the glomerular filtration rate (GFR). Besides this, the kinase-protein mTOR (mamalian target of rapamycin), that regulates multiple cellular functions and integrates information coming from a variety of growth factors and mitogens was also effective in ameliorating the course of the disease in animal PKD models. Upon all this data, a double-blind phase III clinical trial was started (TEMPO) with an inhibitor of the V2-vasopressin receptor OPC-31260 (Tolvaptan). No data are available at present on the influence of Tolvaptan on both renal volume and GFR. Similar approaches pointing to inhibit the AMPc intracellular content have been used in humans with somatostatin and its long-acting analogous octeotride, with preliminary benefits. Published results in humans with the mTOR inhibitors everolimus showed a slower pace in the growth rate of renal volume without concurrent changes in GFR. No beneficial changes were observed with the use of sirolimus. In summary, different animal models have provided a rational approach for planning clinical trials with different compounds. It is still necessary to get new data that permit the development of a new stage of carefully designed trials. This should permit to define questions as when to start treatment, how to evaluate the “biological” stage of the disease and which markers should be used to assess treatment effectiveness in a long-life disease as ADPKD.