Inhibiting PNP for the therapy of hyperuricemia in Lesch–Nyhan disease: Preliminary in vitro studies with analogues of immucillin‐G

Abstract

Lesch-Nyhan disease (LND) is a rare X-linked genetic disorder, with complete hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency, uric acid (UA), hypoxanthine and xanthine accumulation, and a devastating neurologic syndrome. UA excess, causing renal failure, is commonly decreased by xanthine oxidoreductase (XOR) inhibitors, such as allopurinol, yielding a xanthine and hypoxanthine increase. Xanthine accumulation may result in renal stones, while hypoxanthine excess seems involved in the neurological disorder. Inhibition of purine nucleoside phosphorylase (PNP) represents a different strategy for lowering urate. PNP catalyzes the cleavage of purine ribo-and d-ribo-nucleosides into ribose/deoxyribose phosphate and free bases, starting catabolism to uric acid. Clinical trials demonstrated that PNP inhibitors, initially developed as anticancer drugs, lowered UA in some gouty patients, in association or not with allopurinol. The present study tested the reliability of an analogue of immucillin-G (C1a), a PNP inhibitor, as a therapy for urate, hypoxanthine, and xanthine excess in LND patients by blocking hypoxanthine production upstream. The therapeutic aim is to limit the administration of XOR inhibitors to LND patients by supplying the PNP inhibitor in low doses, avoiding d-nucleoside toxicity. We report studies conducted in primary cultures of skin fibroblasts from controls and LND patients grown in the presence of the PNP inhibitor. Cell viability, oxypurine release in culture medium, and endocellular nucleotide pattern have been monitored in different growth conditions (inhibitor concentration, time, added inosine). Our results demonstrate effective PNP inhibition by low inhibitor concentration, with reduced hypoxanthine release, and no appreciable toxicity in control or patient cells, suggesting a new therapeutic strategy for LND hyperuricemia. K E Y W O R D S

Agents for the Treatment of Gout: Current Advances and Future Perspectives

“…Besides XO inhibitors, purine nucleoside phosphorylase (PNP) inhibitors have been found to exhibit a potency to reduce the production of UA. 115 However, reports for PNP inhibitors are limited at present. BCX4208 is currently under an early stage of evaluation for hyperuricemia treatment.…”

“…The side effects of febuxostat and topiroxostat have resulted in some patients avoiding XO inhibitors. Besides XO inhibitors, purine nucleoside phosphorylase (PNP) inhibitors have been found to exhibit a potency to reduce the production of UA . However, reports for PNP inhibitors are limited at present.…”

Inborn Errors of Purine Salvage and Catabolism

“…Rasburicase, a recombinant urate oxidase converting UA into allantoin, is also sporadically used for the rapid prevention of renal failure. Alternative treatments avoiding hypoxanthine accumulation have been recently proposed, based on recombinant enzyme therapy restoring the uricolytic pathway [ 46 ], or on upstream PNP inhibition to slower purine breakdown [ 47 ]. Treatment with allopurinol or other hypouricemic drugs has no effect on the neurological or behavioral manifestations of the disease.…”