Pharmacokinetics, pharmacodynamics and clinical efficacy of abiraterone acetate for treating metastatic castration-resistant prostate cancer

Synthesis and Biological Evaluation of Methoxypolyethylene-Glycol-Substituted Abiraterone Derivatives as Potential Antiprostate Cancer Agents

Globally, prostate cancer is the most commonly diagnosed tumor and a cause of death in older men. Abiraterone, an orally administered irreversible CYP17 inhibitor, is employed to treat prostate cancer. However, abiraterone has several clinical limitations, such as poor water solubility, low dissolution rate, low bioavailability, and toxic side effects in the liver and kidney. Therefore, there is a need to identify high-efficiency and low-toxicity water-soluble abiraterone derivatives. In this work, we aimed to design and synthesize a series of abiraterone derivatives by methoxypoly(ethylene glycol) (mPEG) modification. Their antitumor activities and toxicology were analyzed in vitro and in vivo. The most potent compound, 2e, retained the principle of action on the CYP17 enzyme target and significantly improved the abiraterone water solubility, cell permeability, and blood safety. No significant abnormalities were observed in toxicology. mPEG-modification significantly improved abiraterone's antitumor activity and efficiency while reducing the associated toxic effects. The finding will provide a theoretical basis for future clinical application of mPEG-modified abiraterone.

Effect of food and polymorphisms in SLCO2B1, CYP3A4 and UGT1A4 on pharmacokinetics of abiraterone and its metabolites in Chinese volunteers

AIMS

Abiraterone acetate, a prodrug of abiraterone (ABI), provides an efficient therapeutic option for metastatic castration-resistant prostate cancer patients. ABI undergoes extensive metabolism in vivo and is transformed into active metabolites Δ4 -abiraterone and 3-keto-5α-abiraterone as well as inactive metabolites abiraterone sulfate and abiraterone N-oxide sulfate. We aimed to examine the effect of polymorphisms in SLCO2B1, CYP3A4 and UGT1A4 on the pharmacokinetics of ABI and its metabolites.

METHODS

In this study, 81 healthy Chinese subjects were enrolled and divided into 2 groups for fasted (n = 45) and fed (n = 36) studies. Plasma samples were collected after administering a 250 mg abiraterone acetate tablet followed by liquid chromatography-tandem mass spectrometry analysis. Genotyping was performed on a MassARRAY system. The association between SLCO2B1, CYP3A4, UGT1A4 genotype and pharmacokinetic parameters of ABI and its metabolites was assessed.

RESULTS

Food effect study demonstrated high fat meal remarkedly increased systemic exposure of ABI and its metabolites. The geometric mean ratio and 90% confidence interval of area under the plasma concentration-time curve from time 0 to the time of the last quantifiable concentration (AUC0-t ) and maximum plasma concentration (Cmax ) of ABI in fed state vs. fasted state were 351.64% (286.86%-431.04%) and 478.45% (390.01%-586.94%), respectively, while the corresponding results were ranging from 145.11% to 269.42% and 150.10% to 478.45% for AUC0-t and Cmax of ABI metabolites in fed state vs. fasted state, respectively. The SLCO2B1 rs1077858 had a significant influence on AUC0-t and Cmax , while 7 other SLCO2B1 variants prolonged half-life of ABI under both fasted and fed conditions. As for ABI metabolites, the systemic exposure of Δ4 -abiraterone, abiraterone sulfate and abiraterone N-oxide sulfate as well as the elimination of 3-keto-5α-abiraterone were significantly affected by SLCO2B1 polymorphisms. Polymorphisms in CYP3A4 and UGT1A4 did not significantly affect pharmacokinetics of ABI and its metabolites.

CONCLUSION

Polymorphisms in SLCO2B1 were significantly related to the pharmacokinetic variability of ABI and its metabolites under both fasted and fed conditions.

Pharmacokinetics of Darolutamide in Mouse - Assessment of the Disposition of the Diastereomers, Key Active Metabolite and Interconversion Phenomenon: Implications to Cancer Patients

BACKGROUND

Darolutamide is recently approved for the treatment of non-metastatic castrate resistance prostate cancer. Hitherto, no stereoselective pharmacokinetic data have been published pertaining to darolutamide and its diastereomers in animals or humans. The key aims of the experiment were to examine darolutamide, S,S-darolutamide and S,R-darolutamide with respect to (a) assessment of in vitro metabolic stability and protein binding and (b) characterization of in vivo oral and intravenous pharmacokinetics in mice.

METHODS

In vitro (liver microsomes stability and protein binding) and in vivo experiments (oral/intravenous dosing to mice) were carried out using darolutamide, S,S-darolutamide and S,Rdarolutamide. Besides, tissue levels of darolutamide, S,S-darolutamide and S,R-darolutamide were measured following oral and intravenous dosing. Appropriate plasma/tissue samples served to determine the pharmacokinetics of various analytes in mice. Liquid chromatography in tandem with mass spectrometry procedures enabled the delineation of the plasma pharmacokinetics, in vitro and tissue uptake data of the various analytes.

RESULTS

Chiral inversion was absent in the metabolic stability study. However, darolutamide showed profound stereoselectivity (S,S-darolutamide greater than S,R-darolutamide) after either intravenous or oral dosing. S,R-darolutamide but not S,S-darolutamide showed conversion to its antipode post oral and intravenous dosing to mice. Regardless of oral or intravenous dosing, active keto darolutamide formation was evident after administration of darolutamide, S,S-darolutamide or S,R- darolutamide. Tissue data supported the observations in plasma; however, tissue exposure of darolutamide, S,Sdarolutamide and S,R-darolutamide was much lower as compared to plasma.

CONCLUSION

In lieu of the human pharmacokinetic data, although the administration of diastereomeric darolutamide was justified, it is proposed to delineate the clinical pharmacokinetics of S,Rdarolutamide and S,S-darolutamide relative to darolutamide in future clinical pharmacology studies.

[Adverse drug reactions profiles for abiraterone and enzalutamide: A pharmacovigilance descriptive analysis]

OBJECTIVE

The aim of this study was to describe the profile of adverse drug reactions (ADRs) observed with abiraterone and enzalutamide, based on cases registered in the French regional pharmacovigilance centres to identify potential pharmacovigilance signals.

METHODS

We extracted from the French pharmacovigilance database all cases of ADRs or drug interactions involving abiraterone or enzalutamide from the time they market authorization date until December 31st, 2017. Signal detection results have been transmitted by the French Agency for Health Products (ANSM). The data were compared with those of the risk management plans for each drug and the literature.

RESULTS

Among the 233 observations analyzed, nearly 62% involved abiraterone as a suspect drug and 38% involved enzalutamide; only 1 case involved both drugs. The ADRs profile is different between the drugs. Abiraterone is mostly associated with expected cardiac diseases (heart failure, and QT prolongation), expected with the drug. Also described, several cases of hepatotoxicity have been reported, however some cases with fatal outcome suggest that despite a follow-up of the liver function tests, it is difficult to anticipate this risk. Signals concerning acute renal failure and ischemic stroke have arisen. Enzalutamide is more particularly associated with various neurological disorders (convulsions, hallucinations, fatigue, and memory impairment) expected with the drug. While ischemic heart disease is also expected, signals of heart failure and atrial fibrillation have arisen. A potential hepatotoxicity of the molecule is discussed because of cases of cholestatic hepatitis.

CONCLUSION

The analysis of the French pharmacovigilance database cases allows to confirm an expected and monitored risk profile in the risk management plan for both drugs. Several signals have arisen, some of which will be investigated through a pharmacoepidemiology study.

Computational modelling of resistance and associated treatment response heterogeneity in metastatic cancers

Metastatic cancer patients invariably develop treatment resistance. Different levels of resistance lead to observed heterogeneity in treatment response. The main goal was to evaluate treatment response heterogeneity with a computation model simulating the dynamics of drug-sensitive and drug-resistant cells. Model parameters included proliferation, drug-induced death, transition and proportion of intrinsically resistant cells. The model was benchmarked with imaging metrics extracted from 39 metastatic prostate cancer patients who had ¹⁸F-NaF-PET/CT scans performed at baseline and at three cycles into chemotherapy or hormonal therapy. Two initial model assumptions were evaluated: considering only inter-patient heterogeneity and both inter-patient and intra-patient heterogeneity in the proportion of intrinsically resistant cells. The correlation between the median proportion of intrinsically resistant cells and baseline patient-level imaging metrics was assessed with Spearman's rank correlation coefficient. The impact of model parameters on simulated treatment response was evaluated with a sensitivity study. Treatment response after periods of six, nine, and 12 months was predicted with the model. The median predicted range of response for patients treated with both therapies was compared with a Wilcoxon rank sum test. For each patient, the time was calculated when the proportion of disease with a non-favourable response outperformed a favourable response. By taking into account inter-patient and intra-patient heterogeneity in the proportion of intrinsically resistant cells, the model performed significantly better ([Formula: see text]) than by taking into account only inter-patient heterogeneity ([Formula: see text]). The median proportion of intrinsically resistant cells showed a moderate correlation (ρ  =  0.55) with mean patient-level uptake, and a low correlation (ρ  =  0.36) with the dispersion of mean metastasis-level uptake in a patient. The sensitivity study showed a strong impact of the proportion of intrinsically resistant cells on model behaviour after three cycles of therapy. The difference in the median range of response (MRR) was not significant between cohorts at any time point (p   >  0.15). The median time when the proportion of disease with a non-favourable response outperformed the favourable response was eight months, for both cohorts. The model provides an insight into inter-patient and intra-patient heterogeneity in the evolution of treatment resistance.

Inter- and intra-patient variability in pharmacokinetics of abiraterone acetate in metastatic prostate cancer

PURPOSE

This study examined the inter- and intra-patient variability in pharmacokinetics of AA and its metabolites abiraterone and Δ(4)-abiraterone (D4A), and potential contributing factors.

METHODS

AA administered daily for ≥4 weeks concurrently with androgen deprivation therapy (ADT) for mCRPC were included. Pharmacokinetic evaluation was performed at two consecutive visits at least 4 weeks apart. Plasma samples were collected 24 h after last dose of AA to obtain drug trough level (DTL) of two active metabolites, abiraterone and D4A.

RESULTS

39 plasma samples were obtained from 22 patients, with 17 patients had repeat DTL measurement. Considerable inter-patient variability in DTL was seen, with initial DTL for abiraterone ranging between 1.5 and 25.4 ng/ml (CV 61%) and for D4A between 0.2 and 2.5 ng/ml (CV 61%). Intra-patient variability in DTL for abiraterone varied between 0.85 and 336% and for D4A between 1.14 and 199%. There was no increase in AA exposure with use of dexamethasone (n = 5; DTL 13.9) compared with prednisone (n = 17; DTL 11.0 p = 0.5), dosing in fasted state (n = 13, DTL 12.1) compared to dosing in fed state (n = 9; DTL 11.1, p = 0.8), or chemotherapy-exposed (n = 10; DTL 8.9) compared to chemotherapy naïve (n = 12; DTL 14.0, p = 0.1).

CONCLUSIONS

Our cohort demonstrated high inter- and intra-patient variability in both abiraterone and D4A with fixed dosing of AA, with no effect from choice of corticosteroids, prior use of chemotherapy, or dosing in fasting state. Monitoring DTL of AA may be necessary to minimise risk of patients being under-dosed and earlier development of resistance.

Management of anticoagulation in patients with metastatic castration-resistant prostate cancer receiving abiraterone + prednisone

PURPOSE

Abiraterone has been proven to be an effective agent used in the management of metastatic castration-resistant prostate cancer, significantly improving overall and progression-free survival. Due to the pharmacodynamic and pharmacokinetic properties of abiraterone, concurrent use with anticoagulation may pose a challenge for clinicians. Thrombosis within the cancer setting continues to increase patient mortality; therefore, appropriate anticoagulation through the use of a management algorithm can reduce adverse events and increase quality of life.

METHODS

A review of the literature was preformed by a medical oncologist, haematologist and pharmacists to identify relevant randomized controlled trials, meta-analyses and retrospective studies. Major society guidelines were reviewed to further aid in developing the anticoagulation protocol for non-valvular atrial fibrillation and venous thromboembolism within this patient population. After reviewing the literature, a clinical framework was designed to aid clinicians in the management of those patients receiving abiraterone concurrently with an anticoagulant.

RESULTS

In this review, we describe the potential interactions between abiraterone and various anticoagulants and provide management strategies based on the most recent literature for atrial fibrillation, venous thromboembolism and mechanical heart valves to avoid potential drug-drug interactions.

CONCLUSION

Abiraterone therapy has become a mainstay of the management of advanced prostate cancer and is often used over prolonged years. In this review, we have summarized a framework of how to use abiraterone in men with prostate cancer on anticoagulants. Evidence available to date suggests that patients with an indication for anticoagulation such as atrial fibrillation, venous thromboembolism and mechanical heart valves can be treated safely with abiraterone in the appropriate setting, with appropriate monitoring.

Heterocyclic sterol probes for live monitoring of sterol trafficking and lysosomal storage disorders

The monitoring of intracellular cholesterol homeostasis and trafficking is of great importance because their imbalance leads to many pathologies. Reliable tools for cholesterol detection are in demand. This study presents the design and synthesis of fluorescent probes for cholesterol recognition and demonstrates their selectivity by a variety of methods. The construction of dedicated library of 14 probes was based on heterocyclic (pyridine)-sterol derivatives with various attached fluorophores. The most promising probe, a P1-BODIPY conjugate FP-5, was analysed in detail and showed an intensive labelling of cellular membranes followed by intracellular redistribution into various cholesterol rich organelles and vesicles. FP-5 displayed a stronger signal, with faster kinetics, than the commercial TF-Chol probe. In addition, cells with pharmacologically disrupted cholesterol transport, or with a genetic mutation of cholesterol transporting protein NPC1, exhibited strong and fast FP-5 signal in the endo/lysosomal compartment, co-localizing with filipin staining of cholesterol. Hence, FP-5 has high potential as a new probe for monitoring cholesterol trafficking and its disorders.

Identification of Galeterone and Abiraterone as Inhibitors of Dehydroepiandrosterone Sulfonation Catalyzed by Human Hepatic Cytosol, SULT2A1, SULT2B1b, and SULT1E1

Galeterone and abiraterone acetate are antiandrogens developed for the treatment of metastatic castration-resistant prostate cancer. In the present study, we investigated the effect of these drugs on dehydroepiandrosterone (DHEA) sulfonation catalyzed by human liver and intestinal cytosols and human recombinant sulfotransferase enzymes (SULT2A1, SULT2B1b, and SULT2E1) and compared their effects to those of other antiandrogens (cyproterone acetate, spironolactone, and danazol). Each of these chemicals (10 μM) inhibited DHEA sulfonation catalyzed by human liver and intestinal cytosols. Enzyme kinetic analysis showed that galeterone and abiraterone acetate inhibited human liver cytosolic DHEA sulfonation with apparent K_i values at submicromolar concentrations, whereas cyproterone acetate, spironolactone, and danazol inhibited it with apparent K_i values at low micromolar concentrations. The temporal pattern of abiraterone formation and abiraterone acetate depletion suggested that the metabolite abiraterone, not the parent drug abiraterone acetate, was responsible for the inhibition of DHEA sulfonation in incubations containing human liver cytosol and abiraterone acetate. Consistent with this proposal, similar apparent K_i values were obtained, regardless of whether abiraterone or abiraterone acetate was added to the enzymatic incubation. Abiraterone was more effective than abiraterone acetate in inhibiting DHEA sulfonation when catalyzed by human recombinant SULT2A1 or SULT2B1b. In conclusion, galeterone and abiraterone are novel inhibitors of DHEA sulfonation, as determined in enzymatic incubations containing human tissue cytosol (liver or intestinal) or human recombinant SULT enzyme (SULT2A1, SULT2B1b, or SULT1E1). Our findings on galeterone and abiraterone may have implications in drug-drug interactions and biosynthesis of steroid hormones.

Androgen deprivation therapy for the treatment of prostate cancer: a focus on pharmacokinetics

INTRODUCTION

Medical therapy has undergone many changes as our understanding of prostate cancer cell biology has improved. Androgen deprivation therapy (ADT) remains the mainstay of therapy for metastatic disease. Metastatic castrate-resistant prostate cancer (CRPC) is an important concern since we are unable to stop progression with currently available agents. Areas covered: Pharmacologic ADT is the most commonly used treatment for metastatic prostate cancer. Multiple agents are available for both first-line and second-line use: antiandrogens, estrogens, luteinizing hormone-releasing hormone agonists/antagonists, and CYP17 inhibitors. With adoption of these drugs, it is important to consider their pharmacokinetic and pharmacodynamic properties. Many undergo metabolism through cytochrome P450. Levels may be altered with co-administration of drugs acting as enzyme inhibitors or inducers. Understanding mechanism of action, metabolism, and excretion of these drugs allows clinicians to provide the best therapeutic care while minimizing adverse events. Expert opinion: Many men with metastatic prostate cancer will progress to castration resistance. An understanding of resistance mechanisms at the cellular level has revealed new drug targets with hopes of halting or reversing progression of metastatic disease. Second-line agents, traditionally reserved for CRPC, are being studied in metastatic castrate-sensitive prostate cancer, and may offer practice-changing evidence supporting their use.

Drug-drug interactions in older patients with cancer: a report from the 15th Conference of the International Society of Geriatric Oncology, Prague, Czech Republic, November 2015

Drugs taken for cancer can interact with each other, with agents taken as part of supportive care, with drugs taken for comorbid conditions (which are particularly common in the elderly patients), and with herbal supplements and complementary medicines. We tend to focus on the narrow therapeutic window of cytotoxics, but the metabolism of tyrosine kinase inhibitors by the cytochrome P450 3A4 enzyme (CYP3A4) makes some TKIs particularly prone to interference with or from other agents sharing this pathway. There is also potential for adverse pharmacokinetic interactions with new hormonal agents used in advanced prostate cancer.