WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• The prodrug cyclophosphamide requires bioactivation by liver CYP enzymes.• Controversy exists about which CYP isoforms are important in the in vitro bioactivation of this drug.• Recent clinical studies have highlighted a role for either CYP2C19 or CYP2B6 in the therapeutic response to cyclophosphamide in lupus patients. • However, the role of these isoforms in the bioactivation of cyclophosphamide in lupus patients has not been previously demonstrated. WHAT THIS STUDY ADDS• Low bioactivation of cyclophosphamide by human liver appears to be dependent on a combination of both CYP2C19 and CYP2B6 loss of function variants.• In a preliminary study of lupus patients poor bioactivation of cyclophosphamide was also observed in those individuals who had at least one loss of function allele at either CYP2C19 or CYP2B6. AIMSThe role of CYP pharmacogenetics in the bioactivation of cyclophosphamide is still controversial. Recent clinical studies have suggested a role for either CYP2C19 or CYP2B6. The aim of this study was to clarify the role of these pharmacogenes. METHODSWe used a combined in vitro-in vivo approach to determine the role of these pharmacogenes in the bioactivation of the prodrug to 4-hydroxy cyclophosphamide (4-OHCP). Cyclophosphamide metabolism was determined in a human liver biobank (n = 14) and in patients receiving the drug for treatment of lupus nephritis (n = 16) RESULTSIn livers of known CYP2C19 and CYP2B6 genotype and protein expression we observed that there was a combined role for both CYP2C19 and CYP2B6 in the bioactivation of cyclophosphamide in vitro. The presence of at least one loss of function (LoF) allele at either CYP2C19 or CYP2B6 resulted in a significant decrease in both Vmax (P = 0.028) and CLint (P = 0.0017) compared with livers with no LoF alleles. This dual genotype relationship was also observed in a preliminary clinical study, with patients who had Ն1 LoF allele at either CYP2C19 or CYP2B6 also displaying significantly (P = 0.0316) lower bioactivation of cyclophosphamide. The mean 4-OHCP : CP bioactivation ratio was 0.0014 (95% CI 0.0007, 0.002) compared with 0.0071 (95% CI 0.0001, 0.014) in patients with no LoF alleles at either of these genes. CONCLUSIONSThe presence of Ն1 LoF allele(s) at either CYP2B6 or CYP2C19 appeared to result in decreased bioactivation of cyclophosphamide both in vitro and in patients. Further clinical studies to confirm this relationship are warranted.

This study shows for the first time that DMXAA has significant in vivo antitumour activity against non-transplanted autochthonous tumours and in a host species other than the mouse.

Acquired loss of CYP2C19 activity occurs in a substantial proportion of patients with multiple myeloma. This indicates that the previously reported phenomenon is not limited to patients with solid tumours. Thus, measurement of CYP2C19 activity rather than CYP2C19 genotype may be more clinically relevant for the determination of whether loss of CYP2C19 function adversely influences the toxicity and efficacy of certain drugs used in medical oncology.

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ABSTRACT:The dinitrobenzamide mustards are a class of bioreductive nitroaromatic anticancer prodrugs, of which a phosphorylated analog (PR-104) is currently in clinical development. They are bioactivated by tumor reductases to form DNA cross-linking cytotoxins. However, their biotransformation in normal tissues has not been examined. Here we report the aerobic in vitro metabolism of three N-(2 hydroxyethyl)-3,5-dinitrobenzamide 2-mustards and the corresponding nonmustard analog in human, mouse, rat, and dog hepatic S9 preparations. These compounds have a range of mustard structures (-N(CH 2 CH 2 X) 2 where X ‫؍‬ H, Cl, Br, or OSO 2 Me). Four metabolic routes were identified: reduction of either nitro group, N-dealkylation of the mustard, plus O-acetylation, and O-glucuronidation of the hydroxyethyl side chain. Reduction of the nitro group ortho to the mustard resulted in intramolecular alkylation and is considered to be an inactivation pathway, whereas reduction of the nitro group para to the mustard generated potential DNA cross-linking cytotoxins. N-Dealkylation inactivated the mustard moiety but may result in the formation of toxic acetaldehyde derivatives. Increasing the size of the nitrogen mustard leaving group abrogated the ortho-nitroreduction and N-dealkylation routes and thereby improved overall metabolic stability but had little effect on aerobic para-nitroreduction. All four compounds underwent O-glucuronidation of the hydroxyethyl side chain and further studies to elucidate the relative importance of this pathway in vivo are in progress.