Abiraterone

Abiraterone (17-(3-pyridyl)androsta-5,16-dien-3β-ol) is a potent small-molecule inhibitor of CYP17 complex (17 alpha-monooxygenase) which is a member of the cytochrome P450 family consisting of 17 alpha-hydroxylase and C17,20-lyase and catalyzing the 17 alpha-hydroxylation of intermediates of steroid biosynthesis involved in testerone sysnthesis. Abiraterone inhibits CYP17 complex by binding to the haem iron of CYP17A1, which forms a 60^o angle above the haem plane and packs against the central I helix with 3β-OH interacting with aspargine 202 in the F helix. Abiraterone is currently being investigated to treat late stage prostate cancer, in which it consistently suppresses testosterone levels, leads to significant reduction in PSA level, and prolong life in patients with castration-resistant prostate cancer (CRPC).

Reference

Natasha M. DeVore and Emily E. Scott. Structures of cytochrome P450 17A1 with prostate cancer drugs abiraterone and TOK-001. Nature 2012; 482: 116-120

Farshid Dayyani, Gary E. Gallick, Christopher J. Logothetis, Paul G. Corn. Novel therapies for metastatic castrate-resistant prostate cancer. JNCI J Natl Cancer Inst (2011); 103(22): 1665-1675

Analytical challenges in quantifying abiraterone with LC-MS/MS in human plasma.[Pubmed:28370076]

Biomed Chromatogr. 2017 Nov;31(11).

A method was developed and validated to quantify Abiraterone in human plasma. During assay development, several analytical challenges were encountered: limited stability in patient samples, adsorption to glass, coelution with metabolites and carry-over issues. Limited stability (2 h) was found for Abiraterone in fresh plasma as well as whole blood at ambient temperature. When kept at 2-8 degrees C, Abiraterone in plasma was stable for 24 h and in whole blood for 8 h. Adsorption of Abiraterone to glass materials was addressed by using polypropylene throughout the method. Carry-over was reduced to acceptable limits by incorporating a third mobile phase into the gradient. The chromatographic separation of Abiraterone with its multiple metabolites was addressed by using a longer analytical column and adjusting the gradient. Abiraterone was extracted by protein precipitation, separated on a C18 column with gradient elution and analyzed with tandem quadrupole mass spectrometry in positive ion mode. A stable deuterated isotope was used as the internal standard. The assay ranges from 1 to 500 ng/mL. Within- and-between-day precisions and accuracies were below 13.4% and within 95-102%. This bioanalytical method was successfully validated and applied to determine plasma concentrations of Abiraterone in clinical studies and in regular patient care for patients with metastatic castration-resistant prostate cancer.

Potential drug-drug interactions with abiraterone in metastatic castration-resistant prostate cancer patients: a prevalence study in France.[Pubmed:28361167]

Cancer Chemother Pharmacol. 2017 May;79(5):1051-1055.

PURPOSE: Abiraterone acetate combined with prednisone improves survival in metastatic castration-resistant prostate cancer (mCRPC) patients. This oral anticancer agent may result in drug-drug interactions (DDI). We aimed to evaluate the prevalence of DDI with Abiraterone and the possible determinants for the occurrence of these DDI. METHODS: We performed a single centre retrospective review from electronic medical records of mCRPC patients treated with Abiraterone from 2011 to 2015. Potential DDI with Abiraterone were identified using Micromedex and were categorized by a 4-point scale severity. RESULTS: Seventy-two out of ninety-five mCRPC pts (median age: 77 years [68-82]) had comorbidities. The median number of drugs used per patient was 7 [5-9]. 66 potential DDI with Abiraterone were detected in 49 patients (52%): 39 and 61% were classified as major and moderate DDI, respectively. In the univariate analysis, pain (p < 0.0001), hypo-albuminemia (p = 0.032), and higher ECOG performance status (PS) (p = 0.013) were significantly associated with a higher risk of DDI with Abiraterone. Pain (p < 0.0001) and PS (p = 0.018) remained significant in the multivariate analysis. CONCLUSIONS: Polypharmacy is an issue among mCRPC patients. In our study, half of the patients have potential DDI with Abiraterone. Patients with pain and poor PS are at higher risk of DDI with Abiraterone. A medication review by a pharmacist is of crucial importance to prevent DDI with Abiraterone.

Abiraterone Acetate for Metastatic Prostate Cancer in Patients With Suboptimal Biochemical Response to Hormone Induction.[Pubmed:28358937]

JAMA Oncol. 2017 Nov 9;3(11):e170231.

Importance: Men with metastatic prostate cancer who have a poor response to initial androgen-deprivation therapy (ADT), as reflected by a prostate-specific antigen (PSA) level higher than 4.0 ng/mL after 7 months of ADT, have a poor prognosis, based on historical controls. Objective: To determine the efficacy of Abiraterone acetate with prednisone in these high-risk patients with a suboptimal response to hormonal induction. Design, Setting, and Participants: A phase 2 single-arm study was conducted through the National Clinical Trials Network-Southwest Oncology Group. Eligible patients had metastatic prostate cancer and a PSA level higher than 4.0 ng/mL between 6 and 12 months after starting ADT. The PSA level could be rising or falling at the time of enrollment, but had to be higher than 4.0 ng/mL. No previous chemotherapy or secondary hormonal therapies were allowed, except in patients receiving a standard, first-generation antiandrogen agent with a falling PSA level at the time of enrollment; this therapy was continued in this cohort. Abiraterone acetate, 1000 mg, once daily with prednisone, 5 mg, twice daily was administered to all participants. A total of 41 men were enrolled between the trial's activation on August 9, 2011, and closure on August 1, 2013. Data analysis was conducted from March 21 to November 29, 2016. Interventions: Abiraterone acetate, 1000 mg, once daily by mouth with prednisone, 5 mg, by mouth twice daily. Main Outcomes and Measures: The primary end point was a PSA level of 0.2 ng/mL or lower within 12 months of starting Abiraterone acetate plus prednisone. A partial response (PR) was a secondary end point, defined as a PSA level reduction to lower than 4.0 ng/mL but higher than 0.2 ng/mL. Results: Of the 41 men enrolled, 1 did not receive any protocol treatment and was excluded from analysis. The median (range) age of the 40 participants was 66 (39-85) years. Five (13%) patients achieved a PSA level of 0.2 ng/mL or lower (95% CI, 4%-27%). Thirteen (33%) additional patients achieved a partial response, with a reduction in the PSA level to lower than 4.0 ng/mL but higher than 0.2 ng/mL. Sixteen (40%) patients had no PSA response and 6 (15%) were not assessable and assumed to be nonresponders. The median progression-free survival was 17.5 months (95% CI, 8.6-25.0 months) and the median overall survival was 25.8 months (95% CI, 15.7-25.8 months). There was 1 incident each of grade 4 adverse events of alanine aminotransferase level elevation and rectal hemorrhage. Eleven patients reported grade 3 adverse events. Conclusions and Relevance: This study did not reach its prescribed level of 6 PSA responses of 0.2 ng/mL or lower, although 5 responses were observed. The overall survival and progression-free survival rates observed in this trial are encouraging compared with historical controls. The therapy was generally well tolerated, without any clear signal of any unexpected adverse effects.

Abiraterone is a potent and irreversible CYP17A1 inhibitor with antiandrogen activity, which inhibits both the 17α-hydroxylase and 17,20-lyase activity of the cytochrome p450 enzyme CYP17 with IC50s of 2.5 nM and 15 nM, respectively.

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