The effect of chemotherapy on the exposure-response relation of abiraterone in metastatic castration-resistant prostate cancer

Feasibility and efficacy of therapeutic drug monitoring of abiraterone in metastatic castration resistant prostate cancer patients

BACKGROUND

Previous studies demonstrated better outcomes for mCRPC (metastatic castration resistant prostate cancer) patients with higher abiraterone exposure (minimal plasma concentration (Cmin) > 8.4 ng/mL), but around 40% of patients experience exposure below this target. Pharmacokinetic (PK)-guided interventions following Therapeutic Drug Monitoring (TDM) could optimise exposure and outcomes. We aimed to evaluate the feasibility and effect on treatment outcomes of abiraterone TDM.

METHODS

Patients with low exposure levels (Low-group, Cmin < 8.4 ng/mL) got a PK-guided intervention. We compared exposure, adverse event (AE) incidence, time on treatment (ToT) and Prostate-Specific Antigen response rate (PSArr) between the Low-group and Adequate-group.

RESULTS

We included 167 mCRPC patients, with 56 in the Adequate-group and 111 in the Low-group. Interventions were successful 86% of the time. Exposure between groups became corresponding (Low-group: 7.95 to 20.5 ng/mL, Adequate-group: 20.8 ng/mL, p = 0.72) with comparable AE incidence (17% vs. 23%, p = 0.4). Median ToT and PSArr were similar (351 vs. 379 days, p = 0.35; 61.3% vs. 67.9%, p = 0.51).

CONCLUSIONS

PK-guided interventions improved above target exposure from 33.5% to 81.4% of patients without additional AEs. While historically, low exposure patients had significantly shorter survival, PK-guided interventions eliminated this disparity. As interventions are effective, low-cost and safe, TDM for abiraterone should be considered to enhance treatment outcomes.

Long-Term Pharmacokinetic Follow-Up of Abiraterone Acetate in Patients with Metastatic Castration-Resistant Prostate Cancer

This ABIGENE pharmacokinetic (PK) study sought mainly to characterize the unchanged drug PK during long-term abiraterone acetate (AA) administration in advanced prostate cancer patients (81 patients). It was observed that individual AA concentrations remained constant over treatment time, with no noticeable changes during repeated long-term drug administration for up to 120 days. There was no correlation between AA concentrations and survival outcomes. However, a significant association between higher AA concentrations and better clinical benefit was observed (p = 0.041). The safety data did not correlate with the AA PK data. A significant positive correlation (r = 0.40, p < 0.001) was observed between mean AA concentration and patient age: the older the patient, the higher the AA concentration. Patient age was found to impact steady-state AA concentration: the older the patient, the higher the mean AA concentration. Altogether, these data may help to guide future research and clinical trials in order to maximize the benefits of AA metastatic castration-resistant prostate cancer patients.

Cortisol as Biomarker for CYP17-Inhibition is Associated with Therapy Outcome of Abiraterone Acetate

BACKGROUND

Abiraterone acetate is an irreversible 17α-hydroxylase/C17, 20-lyase (CYP17) inhibitor approved for the treatment of metastatic castration-resistant prostate cancer (mCRPC) patients. Inhibition of this enzyme leads to low testosterone and cortisol levels in blood. There is growing evidence that clinical efficacy of abiraterone is related to the rate of suppression of serum testosterone. However, quantification of very low levels of circulating testosterone is challenging. We therefore aimed to investigate whether circulating cortisol levels could be used as a surrogate biomarker for CYP17 inhibition in patients with mCRPC treated with abiraterone acetate.

PATIENTS AND METHODS

mCRPC patients treated with abiraterone acetate were included. Abiraterone and cortisol levels were measured with a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS). On treatment cortisol and abiraterone concentrations were related to treatment response and progression free survival.

RESULTS

In total 117 patients were included with a median cortisol concentration of 1.13 ng/ml (range: 0.03 - 82.2) and median abiraterone trough concentration (Cmin) of 10.2 ng/ml (range: 0.58 - 92.1). In the survival analyses, abiraterone Cmin ≥ 8.4 ng/mL and cortisol  < 2.24 ng/mL were associated with a longer prostate-specific antigen (PSA) independent progression-free survival than patients with an abiraterone concentration  ≥ 8.4 ng/mL and a cortisol concentration ≥ 2.24 ng/mL (13.8 months vs. 3.7 months).

CONCLUSION

Our study shows that cortisol is not an independent predictor of abiraterone response in patients with mCRPC, but it is of added value in combination with abiraterone levels, to predict a response on abiraterone.

Clinical Pharmacokinetics and Pharmacodynamics of the Next Generation Androgen Receptor Inhibitor-Darolutamide

Darolutamide is a next-generation androgen receptor signaling inhibitor (ARSI) currently approved for the treatment of nonmetastatic castration-resistant prostate cancer (nmCRPC) and metastatic hormone sensitive prostate cancer (mHSPC). Studies suggest that darolutamide also has the potential to be used to treat other stages of prostate cancer (PC), suggesting that its indications will broaden in the near future. Since ARSIs show similar efficacy for the treatment of PC, pharmacokinetic properties of these drugs and patient characteristics could help physicians decide which drug to select. This review provides an overview of the pharmacokinetic and pharmacodynamic properties of darolutamide. One of the most important pharmacological advantages of darolutamide is its low brain distribution and therefore limited seizure potential and central nervous system adverse effects. In addition, darolutamide has little drug-drug interaction potential and is unlikely to alter the exposure of other cytochrome P450 or P-glycoprotein substrates. Nevertheless, it may significantly increase the exposure of breast cancer resistant protein (BCRP) substrates. The limited solubility and bioavailability of darolutamide increases when taken together with food, regardless of the fat content. Darolutamide is excessively metabolized by oxidation and glucuronidation and excreted in the urine and feces. For this reason, dose reduction is required in patients with moderate and severe renal or severe hepatic impairment. Although no exposure-response relationship was observed with darolutamide, less advanced stages of PC showed better PSA response on treatment. Overall, darolutamide has some advantageous pharmacological properties that may lead to its preferred use, when broader registered, in selected patients across different disease stages.

Validation of an LC-MS/MS method for simultaneous quantification of abiraterone, enzalutamide and darolutamide in human plasma

Currently, several oral androgen receptor signalling inhibitors are available for the treatment of advanced prostate cancer. Quantification of plasma concentrations of these drugs is highly relevant for various purposes, such as Therapeutic Drug Monitoring (TDM) in oncology. Here, we report a liquid chromatography/tandem mass spectrometric (LC-MS/MS) method for the simultaneous quantification of abiraterone, enzalutamide, and darolutamide. The validation was performed according to the requirements of the U.S. Food and Drug Administration and European Medicine Agency. We also demonstrate the clinical applicability of the quantification of enzalutamide and darolutamide in patients with metastatic castration-resistant prostate cancer.