Restoring Tumour Selectivity of the Bioreductive Prodrug PR-104 by Developing an Analogue Resistant to Aerobic Metabolism by Human Aldo-Keto Reductase 1C3

• Published in: Pharmaceuticals (Basel, Switzerland) Switzerland), 2021-11, Vol.14 (12), p.1231
• Main Authors: Abbattista, Maria R, Ashoorzadeh, Amir, Guise, Christopher P, Mowday, Alexandra M, Mittra, Rituparna, Silva, Shevan, Hicks, Kevin O, Bull, Matthew R, Jackson-Patel, Victoria, Lin, Xiaojing, Prosser, Gareth A, Lambie, Neil K, Dachs, Gabi U, Ackerley, David F, Smaill, Jeff B, Patterson, Adam V
• Format: Article
• Language: English
• Subjects: Acids; aldo-keto reductase 1C3; bioreductive prodrug; Bone marrow; Cell cycle; Clinical trials; Cytotoxicity; Enzymes; Granulocytes; Hypoxia; hypoxia-activated prodrug; Metabolism; Metabolites; myelotoxicity; Neutropenia; orthologues; Phosphate esters; PR-104; Radiation therapy; Thrombocytopenia; Toxicology; Tumors
• ISSN: 1424-8247; 1424-8247
• DOI: 10.3390/ph14121231

PR-104 is a phosphate ester pre-prodrug that is converted in vivo to its cognate alcohol, PR-104A, a latent alkylator which forms potent cytotoxins upon bioreduction. Hypoxia selectivity results from one-electron nitro reduction of PR-104A, in which cytochrome P450 oxidoreductase (POR) plays an important role. However, PR-104A also undergoes 'off-target' two-electron reduction by human aldo-keto reductase 1C3 (AKR1C3), resulting in activation in oxygenated tissues. AKR1C3 expression in human myeloid progenitor cells probably accounts for the dose-limiting myelotoxicity of PR-104 documented in clinical trials, resulting in human PR-104A plasma exposure levels 3.4- to 9.6-fold lower than can be achieved in murine models. Structure-based design to eliminate AKR1C3 activation thus represents a strategy for restoring the therapeutic window of this class of agent in humans. Here, we identified SN29176, a PR-104A analogue resistant to human AKR1C3 activation. SN29176 retains hypoxia selectivity in vitro with aerobic/hypoxic IC ratios of 9 to 145, remains a substrate for POR and triggers γH2AX induction and cell cycle arrest in a comparable manner to PR-104A. SN35141, the soluble phosphate pre-prodrug of SN29176, exhibited superior hypoxic tumour log cell kill (>4.0) to PR-104 (2.5-3.7) in vivo at doses predicted to be achievable in humans. Orthologues of human AKR1C3 from mouse, rat and dog were incapable of reducing PR-104A, thus identifying an underlying cause for the discrepancy in PR-104 tolerance in pre-clinical models versus humans. In contrast, the macaque AKR1C3 gene orthologue was able to metabolise PR-104A, indicating that this species may be suitable for evaluating the toxicokinetics of PR-104 analogues for clinical development. We confirmed that SN29176 was not a substrate for AKR1C3 orthologues across all four pre-clinical species, demonstrating that this prodrug analogue class is suitable for further development. Based on these findings, a prodrug candidate was subsequently identified for clinical trials.