Inhibiting PNP for the therapy of hyperuricemia in Lesch-Nyhan disease:
preliminary in vitro studies with analogues of immucillin-G
Received: 2 October 2017 /Revised: 2 May 2018 /Accepted: 4 May 2018
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.
Lesch-Nyhan disease (LND) is a rare X-linked genetic disease
due to hypoxanthine-guanine phosphoribosyltransferase
(HGPRT, EC 22.214.171.124) deficiency, with hyperuricaemia and a
peculiar severe neurological dysfunction (Lesch and Nyhan
1964; Kelley et al 1969; Torres and Puig 2007).
Alterations in the HPRT1 gene may cause various degrees
of deficiency, all resulting in marked uric acid (UA) overpro-
duction due to oxidation of unrecycled hypoxanthine by
xanthine oxido-reductase (XOR: XDH, E.C. 126.96.36.199; XO,
E.C. 188.8.131.52) and increased de novo purine synthesis.
Depending on residual HGPRT activity, severe (LND full
syndrome) or milder (LND variants, LNV) neurological dis-
ability occurs (Anderson and Ernst 1994;Jinnahetal2006;
Jinnah et al 2010). The fine connection between the neurolog-
ical syndrome and HGPRT deficiency is still unclear (Micheli
et al 2011).
Hyperuricemia, often leading to renal failure, is usually
treated by XOR inhibitors (allopurinol, febuxostat) effectively
lowering UA, but accumulating hypoxanthine and xanthine,
the latter forming stones (Torres et al 2007; Terkeltaub et al
2006). Moreover, increased hypoxanthine and xanthine con-
centrations in LND cerebrospinal fluid have been related to
the neurological manifestation (Palmour et al 1989; Torres and
Puig 2015; Biasibetti-Brendler et al 2017;Gedye1992).
Alternative treatments based on uricolysis have been recently
proposed (Ronda et al 2017).
Lowering the activity of purine nucleoside phosphorylase
(PNP, E.C. 184.108.40.206) is expected to decrease hypoxanthine pro-
duction while accumulating inosine, d-inosine, guanosine,
Communicated by: Bruce A Barshop
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s10545-018-0196-x) contains supplementary
material, which is available to authorized users.
* Gabriella Jacomelli
Department of Biotechnology, Chemistry and Pharmacy, University
of Siena, Via A. Moro 2, 53100 Siena, Italy
Journal of Inherited Metabolic Disease