Abiraterone, Orteronel, Enzalutamide and Docetaxel: Sequential or Combined Therapy?

Objective: To summarize the current therapeutic status using chemotherapeutic agent docetaxel and endocrine therapeutic agents (ARAT, abiraterone, orteronel or enzalutamide) for the treatment of metastatic castration-resistant prostate cancer (mCRPC), including sequential therapy and combined therapy, to promote the consensus on the optimal regimen for achieving superior treatment efficacy.

Methods: Through literature search in PubMed, articles with the following relevant keywords were collected and anlyzed: CRPC, abiraterone, orteronel and enzalutamide, median survival, overall survival, prostate specific antigen (PSA), PSA response rate and median radiologic progression-free survival.

Results: Fifty-eight articles were obtained and analyzed in this review. These articles included androgen axis-targeting agents after docetaxel, docetaxel after androgen axis-targeting agents, Triple sequential and combination therapy, covering four current drugs for mCRPC treatment: docetaxel, abiraterone, orteronel, and enzalutamide. It was found that there may be some cross-resistance between androgen axis-targeting agents, which will reduce the efficacy of subsequent drug treatment. Although neither of the studies of using combination therapy showed serious drug toxicity, the efficacy of sequential therapy was not as good as expected. Most adverse reactions after treatment were reported to be level 1–2.

Conclusion: Based on the results of the current studies, abiraterone followed by enzalutamide treatment is the best sequential treatment for most docetaxel-naïve patients. This treatment achieves not only good OS, but also PFS and PSA response rates. In addition, for patients who have previously failed docetaxel treatment, enzalutamide is the best choice as the subsequent treatment.

The clinical benefit of sequential therapy with androgen receptor axis-targeted agents alone in patients with castration-resistant prostate cancer: A propensity score-matched comparison study

BACKGROUND

The optimal sequential therapy for castration-resistant prostate cancer (CRPC) remains unknown. In recent years, some doubts have emerged regarding the clinical benefit of sequential therapy with androgen receptor axis-targeted agents (ART) such as abiraterone (ABI) or enzalutamide (ENZ) for patients with CRPC. We compared the effect of ART-to-ART (AA) sequential therapy after castration resistance with that of docetaxel (DTX)-combined sequential therapy (ART to DTX or DTX to ART) in patients with CRPC.

METHODS

We retrospectively identified and analyzed the data of 315 patients with CRPC treated in our seven affiliated institutions between 2009 and 2019. All patients received either DTX or ART (ABI or ENZ) as the first- or second-line therapy after castration resistance. We compared the overall survival (OS) and the second progression-free survival (PFS2), calculated from the initiation of first-line therapy after castration resistance, between the AA sequence group and the DTX-combined sequence group. PFS2 was defined as the period from the start of first-line treatment after castration resistance to progression on second-line treatment. To minimize selection bias from possible confounders, we performed propensity score matching using one-to-one nearest neighbor matching without replacement.

RESULTS

Overall, 106 and 209 patients were administered the AA sequential therapy and DTX-combined sequential therapy, respectively. The clinicopathological variables of patients were well balanced after propensity score matching, and there were no significant differences between the two groups. In the propensity score-matched cohort, OS was not significantly different between the two groups (median, 37.9 vs. 45.4 months; hazard ratio [HR], 1.10; 95% confidence interval [CI], 0.68-1.79; p = .701), while PFS2 was significantly shorter in the AA group than in the DTX-combined group (median, 12.9 vs. 21.6 months; HR, 1.70; 95% CI, 1.16-2.48; p = .007).

CONCLUSIONS

Certain patients with CRPC can benefit from ART-to-ART sequential therapy in a daily clinical setting.

Comparison of Oncologic Outcomes Between Two Alternative Sequences with Abiraterone Acetate and Enzalutamide in Patients with Metastatic Castration-Resistant Prostate Cancer: A Systematic Review and Meta-Analysis

Sequential treatment of androgen receptor axis targeted agents (ARAT), abiraterone acetate (ABI) and enzalutamide (ENZA), in metastatic castration-resistant prostate cancer (mCRPC) demonstrated some positive effects, but cross-resistances between ABI and ENZA that reduce activity have been suggested. Therefore, we conducted a meta-analysis to compare oncologic outcomes between the treatment sequences of ABI-ENZA and ENZA-ABI in patients with mCRPC. The primary endpoint was a combined progression-free survival (PFS), and the secondary endpoint was overall survival (OS). A total of five trials on 553 patients were included in this study. Each of the included studies was retrospective. In two studies including both chemo-naïve and post-chemotherapy mCRPC patients, for ABI-ENZA compared with ENZA-ABI, pooled hazard ratios (HRs) for PFS and OS were 0.37 (p < 0.0001; 95% confidence intervals (CIs), 0.23–0.60) and 0.64 (p = 0.10; 95% CIs, 0.37–1.10), respectively. In three studies with chemo-naïve mCRPC patients only, for ABI-ENZA compared with ENZA-ABI, pooled HRs for PFS and OS were 0.57 (p = 0.02; 95% CIs, 0.35–0.92) and 0.86 (p = 0.39; 95% CIs, 0.61–1.21), respectively. The current meta-analysis revealed that ABI-ENZA had a significantly more favorable oncological outcome, but the level of evidence was low. Therefore, large-scale randomized trials may be needed.

Inhibition of TAMs improves the response to docetaxel in castration-resistant prostate cancer

For men with castration-resistant prostate cancer (CRPC), androgen-deprivation therapy (ADT) often becomes ineffective requiring the addition of docetaxel, a proven effective chemotherapy option. Tumor-associated macrophages (TAMs) are known to provide protumorigenic influences that contribute to treatment failure. In this study, we examined the contribution of TAMs to docetaxel treatment. An increased infiltration of macrophages in CRPC tumors was observed after treatment with docetaxel. Prostate cancer cells treated with docetaxel released more macrophage colony-stimulating factor (M-CSF-1 or CSF-1), IL-10 and other factors, which can recruit and modulate circulating monocytes to promote their protumorigenic functions. Inhibition of CSF-1 receptor kinase signaling with a small molecule antagonist (PLX3397) in CRPC models significantly reduces the infiltration of TAMs and their influences. As such, the addition of PLX3397 to docetaxel treatment resulted in a more durable tumor growth suppression than docetaxel alone. This study reveals a rational strategy to abrogate the influences of TAMs and extend the treatment response to docetaxel in CRPC.

Radium 223 dichloride for prostate cancer treatment

Prostate cancer is the most common malignant disease in men. Several therapeutic agents have been approved during the last 10 years. Among them, radium-223 dichloride (Xofigo^®) is a radioactive isotope that induces irreversible DNA double-strand breaks and consequently tumor cell death. Radium-223 dichloride is a calcium-mimetic agent that specifically targets bone lesions. Radium-223 dichloride has been approved for the treatment of metastatic castration-resistant prostate cancer with symptomatic bone metastases, without known visceral metastases. In this review, first we summarize the interplay between prostate tumor cells and bone microenvironment; then, we discuss radium-223 dichloride mechanism of action and present the results of the available clinical trials and future developments for this new drug.

Inhibition of the PI3K/AKT/mTOR pathway activates autophagy and compensatory Ras/Raf/MEK/ERK signalling in prostate cancer

The PI3K/AKT/mTOR pathway is frequently activated in advanced prostate cancer, due to loss of the tumour suppressor PTEN, and is an important axis for drug development. We have assessed the molecular and functional consequences of pathway blockade by inhibiting AKT and mTOR kinases either in combination or as individual drug treatments. In established prostate cancer cell lines, a decrease in cell viability and in phospho-biomarker expression was observed. Although apoptosis was not induced, a G1 growth arrest was observed in PTEN null LNCaP cells, but not in BPH1 or PC3 cells. In contrast, when the AKT inhibitor AZD7328 was applied to patient-derived prostate cultures that retained expression of PTEN, activation of a compensatory Ras/MEK/ERK pathway was observed. Moreover, whilst autophagy was induced following treatment with AZD7328, cell viability was less affected in the patient-derived cultures than in cell lines. Surprisingly, treatment with a combination of both AZD7328 and two separate MEK1/2 inhibitors further enhanced phosphorylation of ERK1/2 in primary prostate cultures. However, it also induced irreversible growth arrest and senescence.

Ex vivo treatment of a patient-derived xenograft (PDX) of prostate cancer with a combination of AZD7328 and the mTOR inhibitor KU-0063794, significantly reduced tumour frequency upon re-engraftment of tumour cells.

The results demonstrate that single agent targeting of the PI3K/AKT/mTOR pathway triggers activation of the Ras/MEK/ERK compensatory pathway in near-patient samples. Therefore, blockade of one pathway is insufficient to treat prostate cancer in man.