Pharmacokinetic study of low- versus high-dose medroxyprogesterone acetate (MPA) in women

Cross-reactivity of steroid hormone immunoassays: clinical significance and two-dimensional molecular similarity prediction

Background

Immunoassays are widely used in clinical laboratories for measurement of plasma/serum concentrations of steroid hormones such as cortisol and testosterone. Immunoassays can be performed on a variety of standard clinical chemistry analyzers, thus allowing even small clinical laboratories to do analysis on-site. One limitation of steroid hormone immunoassays is interference caused by compounds with structural similarity to the target steroid of the assay. Interfering molecules include structurally related endogenous compounds and their metabolites as well as drugs such as anabolic steroids and synthetic glucocorticoids.

Methods

Cross-reactivity of a structurally diverse set of compounds were determined for the Roche Diagnostics Elecsys assays for cortisol, dehydroepiandrosterone (DHEA) sulfate, estradiol, progesterone, and testosterone. These data were compared and contrasted to package insert data and published cross-reactivity studies for other marketed steroid hormone immunoassays. Cross-reactivity was computationally predicted using the technique of two-dimensional molecular similarity.

Results

The Roche Elecsys Cortisol and Testosterone II assays showed a wider range of cross-reactivity than the DHEA sulfate, Estradiol II, and Progesterone II assays. 6-Methylprednisolone and prednisolone showed high cross-reactivity for the cortisol assay, with high likelihood of clinically significant effect for patients administered these drugs. In addition, 21-deoxycortisol likely produces clinically relevant cross-reactivity for cortisol in patients with 21-hydroxylase deficiency, while 11-deoxycortisol may produce clinically relevant cross-reactivity in 11β-hydroxylase deficiency or following metyrapone challenge. Several anabolic steroids may produce clinically significant false positives on the testosterone assay, although interpretation is limited by sparse pharmacokinetic data for some of these drugs. Norethindrone therapy may impact immunoassay measurement of testosterone in women. Using two-dimensional similarity calculations, all compounds with high cross-reactivity also showed a high degree of similarity to the target molecule of the immunoassay.

Conclusions

Compounds producing cross-reactivity in steroid hormone immunoassays generally have a high degree of structural similarity to the target hormone. Clinically significant interactions can occur with structurally similar drugs (e.g., prednisolone and cortisol immunoassays; methyltestosterone and testosterone immunoassays) or with endogenous compounds such as 21-deoxycortisol that can accumulate to very high concentrations in certain disease conditions. Simple similarity calculations can help triage compounds for future testing of assay cross-reactivity.

Combined bezafibrate and medroxyprogesterone acetate have efficacy without haematological toxicity in elderly and relapsed acute myeloid leukaemia (AML)

Acute myeloid leukaemia (AML) causes life-threatening deficits of functional blood cells that require management using red cell and platelet transfusion and aggressive treatment of neutropenic infections. Current cytotoxic chemotherapy further worsens the problem of reduced haemopoiesis and two-thirds of patients are too frail to tolerate intensive chemotherapy at all. Median survival amongst these patients remains at <3 months emphasizing the urgent need for anti-AML therapies that do not suppress haemopoiesis. Our laboratory studies showed combined Bezafibrate and Medroxyprogesterone acetate (BaP) had activity against AML without toxicity to normal stem cells. Here we report the safety and efficacy of BaP in 20 patients (19 AML, 1 high-risk myelodysplasia) for whom intensive chemotherapy was not an option. No patient exhibited haematological toxicity from BaP. Eleven patients took BaP alone for >4 weeks. One reverted from high risk myelodysplasia and remains transfusion independent after 201 weeks of therapy. Three AML patients gained major haematological improvements for 22-30 weeks; in one, marrow was available to document a partial AML response. Thus, this trial indicates that BaP therapy has potential for treatment of elderly and relapsed AML.

Metabolism of medroxyprogesterone acetate (MPA) via CYP enzymes in vitro and effect of MPA on bleeding time in female rats in dependence on CYP activity in vivo

Medroxyprogesterone acetate (MPA) is a drug commonly used in endocrine therapy for advanced breast cancer, although it is known to cause thrombosis as a serious side effect. Recently, we found that cytochrome P450 3A4 (CYP3A4) mainly catalyzed the metabolism of MPA via CYP in human liver microsomes. However, the metabolic products of MPA in humans and rats have not been elucidated. In addition, it is not clear whether thrombosis could be induced by MPA itself or by its metabolites. In this study, we determined the overall metabolism of MPA as the disappearance of the parent drug from an incubation mixture, and identified the enzymes catalyzing the metabolism of MPA via CYP in rats. Moreover, the effects of CYP-modulators on MPA-induced hypercoagulation in vivo were examined. Intrinsic clearance of MPA in rat liver microsomes was increased by treatment with CYP3A-inducers. The intrinsic clearance of MPA in liver microsomes of rats treated with various CYP-inducers showed a significant correlation with CYP3A activity, but not CYP1A activity, CYP2B activity or CYP2C contents. Among the eight recombinant rat CYPs studied, CYP3A1, CYP3A2 and CYP2A2 catalyzed the metabolism of MPA. However, since CYP3A2 and CYP2A2 are male-specific isoforms, CYP3A1 appears to be mainly involved in the metabolism of MPA in liver microsomes of female rats. In an in vivo study, pretreatment of female rats with SKF525A, an inhibitor of CYPs including CYP3A1, significantly (p < 0.05) enhanced MPA-induced hypercoagulation, whereas pretreatment with phenobarbital, an inducer of CYPs including CYP3A1, reduced it. These findings suggest that CYP-catalyzed metabolism of MPA is mainly catalyzed by CYP3A1 and that MPA-induced hypercoagulation is predominantly caused by MPA itself in female rats.