Phase I and Pharmacokinetic Study of XRP6258 (RPR 116258A), a Novel Taxane, Administered as a 1-Hour Infusion Every 3 Weeks in Patients with Advanced Solid Tumors

[How to manage patients with CRPC?]

Despite castrate levels of androgens, the androgen receptor (AR) remains active and continues to drive prostate cancer progression. Since the approval of docetaxel, four additional agents that show a survival benefit have been registered on the basis of randomized phase 3 trials. These have included enzalutamide and abiraterone, two agents designed specifically to affect the androgen axis, sipuleucel-T, which stimulates the immune system and cabazitaxel, a chemotherapeutic agent. Denosumab was shown to significantly delay skeletal-related events. Clinicians are challenged with a multitude of treatment options and potential sequencing of these agents that, consequently, make clinical decision making more complex. The induction of constitutively-active AR splice variants (AR-Vs) driving clonal proliferation of AR-negative and AR-independent metastases may be one major potential mechanism of resistance to new hormone therapies.

Sequencing of agents in castration-resistant prostate cancer

Until 2010, docetaxel was the only agent with proven survival benefit for castration-resistant prostate cancer. The development of cabazitaxel, abiraterone acetate, enzalutamide, radium-223, and sipuleucel-T has increased the number of treatment options. Because these agents were developed concurrently within a short period of time, prospective data on their sequential use efficacy are scarce. The challenge now is to reach a consensus on the best way to sequence effective treatments, ideally by the use of an approach specific to patient subgroups. However, the absence of robust surrogates of survival and the lack of predictive biomarkers makes data for the sequential use of these agents difficult to obtain and interpret.

The burden of different pathogens in acute diarrhoeal episodes among a cohort of Egyptian children less than five years old

Introduction

Diarrhoea continues to cause significant morbidity in Egypt.

Aim

To determine the frequency and distribution of different enteropathogens in acute diarrhoeal episodes, utilising an expanded testing regimen, and to correlate clinical signs and symptoms associated with the detected pathogens.

Material and methods

The case-control study enrolled 356 patients < 5 years old with acute diarrhoea and 356 age and sex-matched healthy controls. Both cases and controls underwent a full history and physical examination, and provided two rectal swab specimens and a stool sample. Laboratory analysis included stool culture, microscopy, and indirect methods.

Results

Rotavirus was detected in 11% of patients. Enterotoxigenic Escherichia coli (ETEC), Campylobacter, Shigella, and Salmonella were detected in 7%, 3.7%, 1.1%, and 1.4% of patients, respectively; and in 11.1%, 3.1%, 0.6%, and 0.6% of controls, respectively, with no significant statistical difference. Cryptosporidium was detected in 3.9% of cases. Mixed infection was detected in 5.9% of cases and 0.9% of controls, with a significant difference (p < 0.001). No pathogen was detected in 66.3% of cases and in 83.5% of controls. Rotavirus infection was associated with recurrent vomiting, dehydration, and hospitalisation. Bacterial diarrhoea was associated with vomiting (52%) in ETEC infections, fever (80%) in Salmonella infections, mucus (100%) and blood (50%) in stools of Shigella infections, and convulsions (15%) in Campylobacter infections.

Conclusions

Rotavirus is a prominent cause of diarrhoea among Egyptian children. Despite utilising an expanded testing regimen, more work is still needed for identification of other enteropathogens that constitute other causative agents of diarrhoea.

Clinical perspectives: practical insights from clinical experience with cabazitaxel in Australia

Prostate cancer, and in particular the management options for patients with metastatic castration-resistant prostate cancer (mCRPC), remains an important health issue. The approval of cabazitaxel provides a new treatment option for patients who have progressed despite docetaxel therapy. Clinical use of cabazitaxel in mCRPC is based on the results of the TROPIC study, which demonstrated an approximately 30% reduction in the risk of death compared with mitoxantrone. In this paper, we draw on accumulating clinical experience with cabazitaxel in Australia to discuss important questions such as how to select the right patient for treatment and how to proactively prevent and manage toxicities associated with this therapy. Recognizing the need for a multidisciplinary approach to patient care, opinion and insight has been sought from medical oncologists, nurses and pharmacists. While lack of trial data means that a number of questions remain unanswered, local clinical experience has helped to guide treatment decisions and refine management protocols. Appropriate patient selection, careful ongoing monitoring and proactive management of adverse events will ensure optimal treatment of patients. Nurses in particular play an important role in educating patients and identifying patients at increased risk of developing adverse events with cabazitaxel. The oncology team must work together to educate patients; taking a proactive approach to issues such as adverse events will help maximize the clinical outcome of cabazitaxel treatment and impact positively on the patient's quality of life.

Metastatic castration-resistant prostate cancer (CRPC): preclinical and clinical evidence for the sequential use of novel therapeutics

With five novel therapies shown to improve survival in metastatic castration-resistant prostate cancer (CRPC) in the last 3 years, patients are now living longer and experiencing better quality of life. Since docetaxel became standard of care for men with symptomatic metastatic CRPC, three artificial treatment "spaces" have emerged for prostate cancer drug development: pre-docetaxel, docetaxel combinations, and following docetaxel. Multiple therapies are currently under development in both early and late stage CRPC. Additionally, the novel agents abiraterone, radium-223, cabazitaxel, and enzalutamide have all been approved in the post-docetaxel setting. Strategies for patient selection and treatment sequencing are therefore urgently required. In this comprehensive review, we will summarize the preclinical and clinical data available with regards to sequencing of the novel treatments for CRPC.

Pharmaceuticals that contain polycyclic hydrocarbon scaffolds

This review comprehensively explores approved pharmaceutical compounds that contain polycyclic scaffolds and the properties that these skeletons convey.

Current and emerging therapies for bone metastatic castration-resistant prostate cancer

BACKGROUND

A paucity of therapeutic options is available to treat men with metastatic castration-resistant prostate cancer (mCRPC). However, recent developments in our understanding of the disease have resulted in several new therapies that show promise in improving overall survival rates in this patient population.

METHODS

Agents approved for use in the United States and those undergoing clinical trials for the treatment of mCRPC are reviewed. Recent contributions to the understanding of prostate biology and bone metastasis are discussed as well as how the underlying mechanisms may represent opportunities for therapeutic intervention. New challenges to delivering effective mCRPC treatment will also be examined.

RESULTS

New and emerging treatments that target androgen synthesis and utilization or the microenvironment may improve overall survival rates for men diagnosed with mCRPC. Determining how factors derived from the primary tumor can promote the development of premetastatic niches and how prostate cancer cells parasitize niches in the bone microenvironment, thus remaining dormant and protected from systemic therapy, could yield new therapies to treat mCRPC. Challenges such as intratumoral heterogeneity and patient selection can potentially be circumvented via computational biology approaches.

CONCLUSIONS

The emergence of novel treatments for mCRPC, combined with improved patient stratification and optimized therapy sequencing, suggests that significant gains may be made in terms of overall survival rates for men diagnosed with this form of cancer.

Chemotherapy and its evolving role in the management of advanced prostate cancer

Advanced prostate cancer has been recognized as being responsive to androgen deprivation since the 1940s when Charles Huggins first described the role of surgical castration in managing these patients. However, androgen deprivation only results in transient disease control for the vast majority of men, with those progressing in spite of castrate testosterone levels labeled as having castrate-resistant prostate cancer (CRPC). Until 2004, the therapeutic arena for these patients had remained stagnant, with no agent having shown a survival gain in the CRPC setting. Two landmark publications changed the prostate cancer treatment landscape by providing ‘level-1 evidence’ that docetaxel-based chemotherapy led to prolongation in overall survival (OS). This was followed by the approval of cabazitaxel in 2010 on the basis of Phase III data demonstrating its efficacy in patients pretreated with docetaxel. More recently, a number of next-generation androgen-directed agents (e.g. abiraterone and enzalutamide) have also been shown to lead to a survival benefit in men with CRPC. With so many new treatment options available, a number of questions remain. These include: how to best sequence chemotherapy with these newer hormonal agents, the clinical implication of cross-resistance between taxanes and androgen-directed agents and which subsets of patients may benefit most from early use of chemotherapy. This review will provide an overview of the evolving role of chemotherapy in the management of advanced prostate cancer in the current era.

A Phase I study of cabazitaxel in patients with advanced gastric cancer who have failed prior chemotherapy (GASTANA)

PURPOSE

This Phase I dose-escalation study (GASTANA) evaluated the safety, tolerability, pharmacokinetics and preliminary antitumor activity of cabazitaxel in Asian patients with advanced gastric adenocarcinoma failing two prior chemotherapy regimens.

METHODS

Cabazitaxel safety/tolerability was determined using a standard 3 + 3 dose-escalation design based on dose-limiting toxicities (DLTs) in Cycle 1. Three dose levels (DL) were planned: 20, 25 and 15 mg/m(2) (DL 1, DL 2 and DL -1).

RESULTS

Fifteen patients were evaluable for DLTs. At DL 1, no DLTs occurred in three patients. At DL 2, four patients were enrolled (one patient discontinued), with only one DLT observed [Grade 4 febrile neutropenia (FN)]; however, all four patients experienced FN, hence three more patients were enrolled at DL 1 who experienced two DLTs (Grade 4 neutropenia >7 days). In response, DL -1 was opened, with no DLTs observed in six patients. In the total population (n = 16), frequent Grade 3/4 toxicities included neutropenia (63%) and FN (38%), best overall responses included one partial response (6.3%; DL -1) and eight stable disease (50%), and median progression-free survival was 83 days.

CONCLUSIONS

No unexpected safety findings were observed. Significant toxicities included neutropenia and FN, potentially due to patients being heavily pretreated and the accumulated toxicity of prior taxane therapy.

Metabolism of the taxanes including nab-paclitaxel

INTRODUCTION

The classical taxanes (paclitaxel, docetaxel), the newer taxane cabazitaxel and the nanoparticle-bound nab-paclitaxel are among the most widely used anticancer drugs. Despite years of research, the optimal dosing regimen (weekly vs 3-weekly) and optimal dose is still controversial, as is the value of pharmacological personalization of taxane dosing.

AREAS COVERED

This review provides an overview of the pharmacological properties of the taxanes, including metabolism, pharmacokinetics-pharmacodynamics and aspects in the clinical use of taxanes. The latter includes the ongoing debate on the most active and safe regimen (paclitaxel, docetaxel, nab-paclitaxel), the recommended initial dose (cabazitaxel) and pharmacological dosing individualization.

EXPERT OPINION

Taxanes share the characteristics of extensive hepatic metabolism and biliary excretion, the need for dose adaptation in patients with liver dysfunction, and substantial pharmacokinetic variability even after taking into account known covariates. Data from clinical studies suggest that optimal scheduling of the taxanes is dependent not only on the specific taxane compound, but also on the tumor type and line of treatment. Finally, treating oncologists should be aware of the substantial risk for drug-drug interactions that is a direct consequence of the complex hepatic metabolism of the taxanes.

Preclinical profile of cabazitaxel

First-generation taxanes have changed the treatment paradigm for a wide variety of cancers, but innate or acquired resistance frequently limits their use. Cabazitaxel is a novel second-generation taxane developed to overcome such resistance. In vitro, cabazitaxel showed similar antiproliferative activity to docetaxel in taxane-sensitive cell lines and markedly greater activity in cell lines resistant to taxanes. In vivo, cabazitaxel demonstrated excellent antitumor activity in a broad spectrum of docetaxel-sensitive tumor xenografts, including a castration-resistant prostate tumor xenograft, HID28, where cabazitaxel exhibited greater efficacy than docetaxel. Importantly, cabazitaxel was also active against tumors with innate or acquired resistance to docetaxel, suggesting therapeutic potential for patients progressing following taxane treatment and those with docetaxel-refractory tumors. In patients with tumors of the central nervous system (CNS), and in patients with pediatric tumors, therapeutic success with first-generation taxanes has been limited. Cabazitaxel demonstrated greater antitumor activity than docetaxel in xenograft models of CNS disease and pediatric tumors, suggesting potential clinical utility in these special patient populations. Based on therapeutic synergism observed in an in vivo tumor model, cabazitaxel is also being investigated clinically in combination with cisplatin. Nonclinical evaluation of the safety of cabazitaxel in a range of animal species showed largely reversible changes in the bone marrow, lymphoid system, gastrointestinal tract, and male reproductive system. Preclinical safety signals of cabazitaxel were consistent with the previously reported safety profiles of paclitaxel and docetaxel. Clinical observations with cabazitaxel were consistent with preclinical results, and cabazitaxel is indicated, in combination with prednisone, for the treatment of patients with hormone-refractory metastatic prostate cancer previously treated with docetaxel. In conclusion, the demonstrated activity of cabazitaxel in tumors with innate or acquired resistance to docetaxel, CNS tumors, and pediatric tumors made this agent a candidate for further clinical evaluation in a broader range of patient populations compared with first-generation taxanes.

Phase I study of cabazitaxel plus cisplatin in patients with advanced solid tumors: study to evaluate the impact of cytochrome P450 3A inhibitors (aprepitant, ketoconazole) or inducers (rifampin) on the pharmacokinetics of cabazitaxel

PURPOSE

Cabazitaxel is primarily metabolized by CYP3A. This study evaluated the impact of moderate/strong CYP3A inhibitors [aprepitant (Study Part 2); ketoconazole (Study Part 3)] or strong CYP3A inducers [rifampin (Study Part 4)] on the pharmacokinetics of cabazitaxel.

METHODS

Adult patients received IV cabazitaxel/cisplatin 15/75 mg/m(2) on Day 1 of 3-week cycles (5/75 mg/m(2) in Cycles 1 and 2 of Part 3 to allow a safety margin to the cabazitaxel MTD). Patients received repeated oral doses of aprepitant, ketoconazole or rifampin before/during Cycle 2. Cabazitaxel clearance was the primary endpoint; clearance and area under the plasma concentration-time curve (AUC) were normalized to body surface area and dose, respectively.

RESULTS

The PK population included 13 (Part 2), 23 (Part 3) and 21 patients (Part 4). Repeated aprepitant administration did not affect cabazitaxel clearance [geometric mean ratio (GMR) 0.98; 90 % confidence interval (CI) 0.80-1.19]. Repeated ketoconazole administration resulted in 20 % decrease in cabazitaxel clearance (GMR 0.80; 90 % CI 0.55-1.15), associated with 25 % increase in AUC (GMR 1.25; 90 % CI 0.86-1.81). Repeated rifampin administration resulted in 21 % increase in cabazitaxel clearance (GMR 1.21; 90 % CI 0.95-1.53), associated with 17 % decrease in AUC (GMR 0.83; 90 % CI 0.65-1.05). The GMR of AUC0-24 with rifampin administration was 1.09 (90 % CI 0.9-1.33), suggesting that rifampin had a low impact during the initial phases of cabazitaxel elimination. Safety findings were consistent with previous results.

CONCLUSIONS

Cabazitaxel pharmacokinetics are modified by drugs strongly affecting CYP3A. Co-administration of cabazitaxel with strong CYP3A inhibitors or inducers should be avoided.

Advanced prostate cancer - patient survival and potential impact of enzalutamide and other emerging therapies

The advent of exponential growth of novel agents tested and approved for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) has brought about a need for understanding of the mechanism of action, side-effects, and clinical efficacy of these drugs as they relate to these patients. This review will provide a synopsis of the treatment landscape in mCRPC as varying agents such as abiraterone acetate, cabazitaxel, sipuleucel-T, radium, and selected emerging agents are presented. A distinct focus on the utilization of enzalutamide, its mechanism of action, key pivotal trials that brought about its US Food and Drug Administration approval, as well as patient-focused perspectives and clinical implications are discussed herein.

The role of cabazitaxel in the treatment of metastatic castration-resistant prostate cancer

For decades, cytotoxic therapy was considered ineffective for the treatment of metastatic castration-resistant prostate cancer (mCRPC). Earlier therapies such as estramustine and mitoxantrone received regulatory approval based upon improvement in palliative endpoints. In 2004, docetaxel became the first treatment to demonstrate a significant survival benefit in patients with mCRPC based on two randomized phase III studies, TAX327 and SWOG 99-16. Cabazitaxel, a third-generation taxane, was chosen for clinical development based on its decreased affinity for the drug efflux pump, p-glycoprotein, which is a frequent cause of drug resistance in docetaxel-resistant preclinical models. In 2010, cabazitaxel was approved by the US Food and Drug Administration as the first therapy to show a survival benefit for the treatment of patients with docetaxel-refractory mCRPC. This review summarizes the existing literature on the use of cabazitaxel, focusing on its efficacy and safety in combination with prednisone in the treatment of mCRPC, as well as its role in an era of new therapeutic options.

Cabazitaxel: A novel taxane for metastatic castration-resistant prostate cancer-current implications and future prospects

Recent advances in the management of prostate cancer have shown considerable development with time and many novel therapeutic agents have been approved over the past years. For patients with metastatic castration-resistant prostate cancer (mCRPC), initially docetaxel was the standard chemotherapy but once they became refractory to docetaxel, no treatment improved survival. This scenario changed in June 2010 when the US Food and Drug Administration (FDA) approved Cabazitaxel as a new therapeutic option for patients with mCRPC resistant to docetaxel. Cabazitaxel, being a novel tubulin-binding taxane with poor affinity for P-glycoprotein, decreases the chances of resistance. It has shown antitumor activity in preclinical, phase I, II and III clinical studies in docetaxel-resistant tumors. This article summarises the background, pharmacodynamic, kinetics and clinical development of cabazitaxel for the treatment of castration-resistant prostate cancer. Future development and rational use of this drug in other tumors is under therapeutic investigation.

Self-assembled micelles of novel amphiphilic copolymer cholesterol-coupled F68 containing cabazitaxel as a drug delivery system

Despite being one of the most promising amphiphilic block copolymers, use of Pluronic F68 in drug delivery is limited due to its high critical micelle concentration (CMC). In this study, we developed a novel F68 derivative, cholesterol-coupled F68 (F68-CHMC). This new derivative has a CMC of 10 μg/mL, which is 400-fold lower than that of F68. The drug-loading capacity of F68-CHMC was investigated by encapsulating cabazitaxel, a novel antitumor drug. Drug-loaded micelles were fabricated by a self-assembly method with simple dilution. The optimum particle size of the micelles was 17.5±2.1 nm, with an entrapment efficiency of 98.1% and a drug loading efficiency of 3.16%. In vitro release studies demonstrated that cabazitaxel-loaded F68-CHMC micelles had delayed and sustained-release properties. A cytotoxicity assay of S180 cells showed that blank F68-CHMC was noncytotoxic with a cell viability of nearly 100%, even at a concentration of 1,000 μg/mL. The IC₅₀ revealed that cabazitaxel-loaded F68-CHMC micelles were more cytotoxic than Tween 80-based cabazitaxel solution and free cabazitaxel. In vivo antitumor activity against S180 cells also indicated better tumor inhibition by the micelles (79.2%) than by Tween 80 solution (56.2%, P<0.05). Based on these results, we conclude that the F68-CHMC copolymer may be a potential nanocarrier to improve the solubility and biological activity of cabazitaxel and other hydrophobic drugs.

Drug delivery design for intravenous route with integrated physicochemistry, pharmacokinetics and pharmacodynamics: illustration with the case of taxane therapeutics

This review is aimed at combining the published data on taxane formulations into a generalized Drug Delivery approach, starting from the physicochemistry and assessing its relationships with the pharmacokinetics, the biodistribution and the pharmacodynamics. Owing to the number and variety of taxane formulation designs, we considered this class of cytotoxic anticancer agents of particular interest to illustrate the concepts attached to this approach. According to the history of taxane development, we propose a classification as (i) "surfactant-based formulations" first generation, (ii) "surfactant-free formulations" second generation and (iii) "modulated pharmacokinetics drug delivery systems" third generation. Since our objective was to make the link between (i) the physicochemistry of the drug and carrier and (ii) the efficacy and safety of the drug in preclinical animal models and (iii) in human, we focused on the drug delivery technologies that were tested in clinic.

An open-label study to investigate the cardiac safety profile of cabazitaxel in patients with advanced solid tumors

PURPOSE

This study assessed the cardiovascular safety of cabazitaxel, based on thorough evaluation of QT and non-QT variables, and the relationship between pharmacokinetic and pharmacodynamic electrocardiographic (ECG) profiles and the occurrence of Grade ≥3 cardiovascular adverse events.

METHODS

Patients with advanced solid tumors were treated with cabazitaxel 25 mg/m(2) every 3 weeks. Digital ECG recordings were obtained during Cycle 1 over 24 h after dosing. The primary end point was effect of cabazitaxel on QT interval corrected by the Fridericia formula (QTcF). Secondary end points were additional ECG parameters (QT, PR and QRS intervals, and heart rate), plasma pharmacokinetics of cabazitaxel and overall clinical safety.

RESULTS

The pharmacodynamic (ECG) population included 94 patients. In 63 patients with a full 24-h ECG evaluation, the maximum upper bound of 90 % confidence interval (CI) for mean QTcF change from baseline was 7.46 ms (mean 4.8 ms), occurring at 1 h 30 min post-infusion. The slope of QTcF change from baseline versus cabazitaxel concentration was slightly negative (-0.012 [95 % CI -0.017; -0.008], equivalent to a 1.2 ms decrease per 100 ng/mL increase in cabazitaxel concentration). For non-QT variables, no effect was noted. No Grade ≥3 cardiac adverse events were observed; Grade ≥3 hypotension and lymphocele occurred in two patients and one patient, respectively.

CONCLUSION

These results suggest that cabazitaxel has no clinically significant cardiovascular adverse effects in patients with advanced solid tumors.

Oncogenic protein interfaces: small molecules, big challenges

Historically, targeting protein-protein interactions with small molecules was not thought possible because the corresponding interfaces were considered mostly flat and featureless and therefore 'undruggable'. Instead, such interactions were targeted with larger molecules, such as peptides and antibodies. However, the past decade has seen encouraging breakthroughs through the refinement of existing techniques and the development of new ones, together with the identification and exploitation of unexpected aspects of protein-protein interaction surfaces. In this Review, we describe some of the latest techniques to discover modulators of protein-protein interactions and how current drug discovery approaches have been adapted to successfully target these interfaces.

Taxanes in the management of metastatic castration-resistant prostate cancer: efficacy and management of toxicity

Androgen deprivation is the therapy of choice in the majority of patients with metastatic prostate cancer. However, a state of castration resistance ultimately occurs after hormone therapy, thus defining metastatic castration-resistant prostate cancer (mCRPC). mCRPC has historically been considered a relatively chemoresistant tumor. However, due to its ability to improve survival and the quality of life in comparison with mitoxantrone, docetaxel has been established as the standard chemotherapeutic agent for first-line therapy since 2004. Moreover, recent results have shown that the novel taxane cabazitaxel is able to prolong the overall survival of patients with mCRPC previously treated with docetaxel. Even though these taxanes display a favorable toxicity profile, their routine use in clinical practice requires knowledge about the most frequent and distinct adverse events that may result from their administration.

Phase I dose-escalation and pharmacokinetic study (TED 11576) of cabazitaxel in Japanese patients with castration-resistant prostate cancer

PURPOSE

The purpose of the study is to analyze the pharmacokinetic (PK) profile of cabazitaxel and evaluate its safety and tolerability as a 1-h IV infusion every 3 weeks in Japanese patients with castration-resistant prostate cancer (CRPC).

METHODS

Seventeen patients were treated with cabazitaxel at doses of 20 and 25 mg/m(2) for PK analyses. Dose escalation was performed only in the absence of dose-limiting toxicity (DLT). The maximum tolerated dose (MTD) was the highest dose at which less than 33 % of the patients developed DLT.

RESULTS

Cabazitaxel exhibited a triphasic elimination profile with a long terminal half-life of 116 ± 29.0 or 113 ± 28.0 h after IV infusion of 20 or 25 mg/m(2) cabazitaxel, respectively. The major differences in the PK parameters of cabazitaxel and docetaxel were cabazitaxel's fairly high clearance rate, representing approximately half the hepatic flow, and its large volume of distribution at steady-state conditions. No DLT was observed during Cycle 1. Mild-to-moderate hematological adverse events (AEs), including neutropenia, and other AEs typically associated with taxanes were observed; all AEs were manageable. Cabazitaxel at 25 mg/m(2) every 3 weeks was selected as the MTD in Japanese patients.

CONCLUSIONS

The PK parameters of cabazitaxel in Japanese CRPC patients were comparable with those previously determined in Caucasian subjects. The safety and tolerability of cabazitaxel were also comparable in both ethnic populations.

Sequential use of novel therapeutics in advanced prostate cancer following docetaxel chemotherapy

In the last three years, five novel treatments have been shown to improve survival in metastatic castration-resistant prostate cancer (CRPC). These novel treatments have distinct mechanisms of action: tubulin-binding chemotherapy (cabazitaxel); immunotherapy (sipuleucel-T); CYP-17 inhibition (abiraterone); androgen receptor (AR) blockade (enzalutamide); and radioisotope therapy (radium-223). For a number of years, docetaxel was the only treatment with a proven survival benefit for patients with CRPC. Therefore, somewhat artificially, three treatment spaces for drug development in CRPC have emerged: pre-docetaxel; docetaxel combinations; and post-docetaxel. For patients progressing after docetaxel-based chemotherapy, treatment options available outside of clinical trials now include abiraterone, cabazitaxel and enzalutamide. Prospective data on how to best use these novel agents sequentially are not available. Clinicians face the difficult task of choosing between treatment options for individual patients to maximize patient benefit. Treatment evaluation in patients with CRPC remains challenging due to the predominance of bone metastatic disease and the lack of validated surrogate markers for survival. This review summarizes the data available with regards to sequencing of the novel treatments for CRPC.

New agents in the arsenal to fight castrate-resistant prostate cancer

Prior to 2010, the treatment options for castrate-resistant prostate cancer (CRPC) were limited. In the past 3 years, four new agents have been approved by the US Food and Drug Administration for use in CRPC. These four agents differ in their mechanisms of action and highlight the progress made in our understanding of CRPC, and more importantly, provide options with proven clinical benefit. This review examines the development, investigational evolution, adverse events, and future direction of: 1) the androgen receptor inhibitor, enzalutamide, 2) androgen biosynthesis inhibitor, abiraterone, 3) novel taxane chemotherapy, cabazitaxel, and 4) autologous immunotherapeutic agent, sipuleucel-T.

Evolution of the treatment paradigm for patients with metastatic castration-resistant prostate cancer

As recently as 2004, treatment options for men with metastatic castration-resistant prostate cancer (mCRPC) were limited, with docetaxel the only approved agent conferring a survival benefit. The therapeutic landscape is now very different, with several agents demonstrating prolonged survival since 2010. New agents for the treatment of mCRPC include sipuleucel-T, cabazitaxel, abiraterone acetate, enzalutamide and radium-223. All are now approved for use in this patient group, although the specific licensing terms vary between agents. In addition, denosumab may have utility in patients with bone metastases. A number of novel agents are also in development with promising initial results. However, because these treatment options have proliferated rapidly, there is currently a paucity of clinical evidence regarding their optimal sequencing. Selection of an appropriate treatment option should take into consideration disease characteristics, drug availability and patient choice. In summary, we discuss several new treatment options available for mCRPC and their integration into the current treatment paradigm.

New treatment options for castration-resistant prostate cancer

PURPOSE

Published efficacy and safety data from clinical trials of three recently approved agents for the management of metastatic castration-resistant prostate cancer (CRPC) are reviewed.

SUMMARY

Sipuleucel-T is approved by the Food and Drug Administration (FDA) for the treatment of asymptomatic or minimally symptomatic patients with CRPC. In a placebo-controlled Phase III clinical trial, the use of sipuleucel-T was associated with an average improvement in median overall survival of 4.1 months. Abiraterone acetate and cabazitaxel are approved by FDA as second-line treatments for patients with CRPC who experience disease progression during first-line docetaxel therapy. In Phase III trials, abiraterone acetate was associated with improved overall survival relative to placebo use (14.8 months versus 10.9 months), and cabazitaxel was found to confer an overall survival advantage over mitoxantrone therapy (median survival, 15.1 months versus 12.7 months), corresponding to a 30% reduction in the relative risk of death (hazard ratio, 0.7; 95% confidence interval, 0.59-0.83; p < 0.0001). The three agents range in cost from $40,000 to $93,000 for a full course of therapy. Sipuleucel therapy entails leukapheresis procedures for the collection of autologous cells used in dose preparation, requiring careful planning and coordination of care.

CONCLUSION

Sipuleucel-T, abiraterone acetate, and cabazitaxel offer new options for the treatment of patients with CRPC, including those with disease resistant to standard first-line therapies. The agents' varying administration requirements, as well as patient-specific factors and cost issues, are key considerations in the drug selection process.

Cabazitaxel: a guide to its use in hormone-refractory metastatic prostate cancer

The taxane derivative cabazitaxel (Jevtana(®)) is approved in the USA and the EU for use in combination with prednisone for the treatment of patients with hormone-refractory metastatic prostate cancer previously treated with a docetaxel-containing regimen. In the pivotal TROPIC trial, overall survival was significantly prolonged with cabazitaxel plus prednisone versus mitoxantrone plus prednisone in patients with metastatic castration-resistant prostate cancer who had progressed during or after docetaxel therapy. In addition, progression-free survival, the times to tumour progression and prostate specific antigen (PSA) progression, and tumour and PSA response rates were improved with cabazitaxel plus prednisone. Intravenous cabazitaxel had an acceptable tolerability profile, with haematological adverse events occurring most commonly, and diarrhoea being the most common nonhaematological adverse event.

Chemotherapeutic inhibitors in the treatment of prostate cancer

INTRODUCTION

Prostate cancer being the second leading cause of death in men in Western countries remains a major challenge in healthcare. Several novel agents targeting signaling pathways in prostate cancer have recently been approved by the US Food and Drug Administration (FDA) but there is still an unmet need for new treatment strategies for castration-resistant prostate cancer (CRPC).

AREAS COVERED

This review provides a broad overview of prostate cancer therapeutics and highlights key players in the biology of prostate cancer as well as first- and second-line treatments for CRPC. Keywords 'chemotherapeutic agents', 'prostate cancer', 'Phase III clinical trials' and 'US FDA approval' were used for search in PubMed and clinicalTrials.gov databases and the obtained literature was reviewed and summarized.

EXPERT OPINION

Owing to the advances in screening and diagnostic techniques, the majority of prostate cancer cases are diagnosed at an early stage resulting in an almost 100% 5-year survival rate. Recently FDA-approved novel agents (e.g., abiraterone acetate and enzalutamide) have provided new hope in the fight against prostate cancer. However, CRPC remains an incurable disease. Identification of mechanisms of resistance, new biomarkers, appropriate clinical trial end points and novel treatments holds the key for the future of prostate cancer therapy.

Phase I dose-finding study of cabazitaxel administered weekly in patients with advanced solid tumours

BACKGROUND

Cabazitaxel is approved in patients with metastatic hormone-refractory prostate cancer previously treated with a docetaxel-containing regimen. This study evaluated a weekly cabazitaxel dosing regimen. Primary objectives were to report dose-limiting toxicities (DLTs) and to determine the maximum tolerated dose (MTD). Efficacy, safety and pharmacokinetics were secondary objectives.

METHODS

Cabazitaxel was administered weekly (1-hour intravenous infusion at 1.5-12 mg/m² doses) for the first 4 weeks of a 5-week cycle in patients with solid tumours. Monitoring of DLTs was used to determine the MTD and the recommended weekly dose.

RESULTS

Thirty-one patients were enrolled. Two of six patients experienced DLTs at 12 mg/m², which was declared the MTD. Gastrointestinal disorders were the most common adverse event. Eight patients developed neutropenia (three ≥ Grade 3); one occurrence of febrile neutropenia was reported. There were two partial responses (in breast cancer) and 13 patients had stable disease (median duration of 3.3 months). Increases in C(max) and AUC(0-t) were dose proportional for the 6-12 mg/m² doses.

CONCLUSION

The MTD of weekly cabazitaxel was 12 mg/m² and the recommended weekly dose was 10 mg/m². The observed safety profile and antitumour activity of cabazitaxel were consistent with those observed with other taxanes in similar dosing regimens.

TRIAL REGISTRATION

The study was registered with ClinicalTrials.gov as NCT01755390.

Castrate-resistant prostate cancer: postdocetaxel management

PURPOSE OF REVIEW

Prior to 2010, docetaxel was the only treatment shown to prolong survival in metastatic castrate-resistant prostate cancer (CRPC). In the past 3 years, several therapeutic agents have demonstrated survival improvements for CRPC after the receipt of prior docetaxel, leading to multiple approvals by the US Food and Drug Administration.

RECENT FINDINGS

The development of these novel agents, each with a distinct mechanism of action, is the fruition of sedulous preclinical research and well designed clinical trials. Cabazitaxel, a next generation taxane, was the first Food and Drug Administration-approved drug for the postdocetaxel setting. The recognition of sustained androgen dependence of CRPC has led to the identification of more potent and selective inhibitors of androgen synthesis and androgen-receptor signaling, such as abiraterone and enzalutamide, respectively. Radium-223, an α-emitting radionuclide still under regulatory review, recently showed a significant survival benefit for CRPC. Finally, sipuleucel-T, a form of immunotherapy, may benefit a subset of patients in the postdocetaxel setting.

SUMMARY

Post-docetaxel management of CRPC has undergone a dramatic yet welcome paradigm change in the past 3 years. With multiple life-prolonging agents available, it now becomes imperative to coordinate how and when these new therapies should be used and sequenced to achieve optimal patient outcomes.

Management of patients with castration-resistant disease

The medical management of men with castration-resistant prostate cancer (CRPC) has changed dramatically in the last decade. Men can now access several agents developed to extend survival, delay morbidity caused by complications, and preserve quality of life. Strategies to extend survival include docetaxel and cabazitaxel, the CYP-inhibitor abiraterone acetate, the second-generation androgen receptor antagonist enzalutamide, sipuleucel-T immunotherapy, and the α-emitting radionuclide (223)radium. These novel therapies have fostered interest in translational science and a deeper understanding of the underlying biology of CRPC. This article summarizes clinical data and unresolved issues in the use of current and emerging CRPC therapies.

The novel toluidine sulphonamide EL102 shows pre-clinical in vitro and in vivo activity against prostate cancer and circumvents MDR1 resistance

Background:

Taxanes are routinely used for the treatment of prostate cancer, however the majority of patients eventually develop resistance. We investigated the potential efficacy of EL102, a novel toluidine sulphonamide, in pre-clinical models of prostate cancer.

Methods:

The effect of EL102 and/or docetaxel on PC-3, DU145, 22Rv1 and CWR22 prostate cancer cells was assessed using cell viability, cell cycle analysis and PARP cleavage assays. Tubulin polymerisation and immunofluorescence assays were used to assess tubulin dynamics. CWR22 xenograft murine model was used to assess effects on tumour proliferation. Multidrug-resistant lung cancer DLKPA was used to assess EL102 in a MDR1-mediated drug resistance background.

Results:

EL102 has in vitro activity against prostate cancer, characterised by accumulation in G2/M, induction of apoptosis, inhibition of Hif1α, and inhibition of tubulin polymerisation and decreased microtubule stability. In vivo, a combination of EL102 and docetaxel exhibits superior tumour inhibition. The DLKP cell line and multidrug-resistant DLKPA variant (which exhibits 205 to 691-fold greater resistance to docetaxel, paclitaxel, vincristine and doxorubicin) are equally sensitive to EL102.

Conclusion:

EL102 shows potential as both a single agent and within combination regimens for the treatment of prostate cancer, particularly in the chemoresistance setting.

Cabazitaxel-induced stabilization of microtubules enhances radiosensitivity in ovarian cancer cells

Background: Up to 40% of women with ovarian cancer have short disease-free intervals due to molecular mechanisms of chemotherapy resistance. New therapeutic strategies are sought. Ovarian cancers are sensitive to radiochemotherapy. The taxane cabazitaxel (XRP6258, Jevtana) promotes tubulin assembly and stabilizes microtubules against depolymerization in cells, acting similarly in mechanism to paclitaxel. Here, sequences of cabazitaxel-radiation co-administration are tested for drug-alone cytotoxicity and optimal radiosensitization.

Materials and Methods: SKOV3, OVCAR3, and TOV-112D ovarian cancer cells were administered cabazitaxel 24 h before (first), 18 h before (second), together (third), or 24 h after (fourth) a single radiation dose, and then, investigated by clonogenic assay and flow cytometric assays. Radiation dose-cell survival data were fitted by two-stage multivariate analyses of variance. High-content flow cytometry partitioned cabazitaxel effects into G2-phase versus M-phase events by DNA content, cyclin A2, and phospho-S10-histone H3 (PHH3). Paclitaxel served as a comparator.

Findings: Cabazitaxel cytotoxicity and radiosensitization were dose dependent. Cabazitaxel added 24 h before radiation was the most lethal schedule. DNA content measurements by flow cytometry showed that cabazitaxel-treated cells accumulated in the radiosensitive G2/M 4C DNA complement compartment. Cytometry also showed that surviving cabazitaxel-induced cell cycle arrested cells resolve the arrest by entering 4C or by 8C DNA complement cell cycles.

Interpretation: The radiosensitizing effect of cabazitaxel was schedule dependent, due to cell cycle redistribution, and best when cabazitaxel was given 24 h before radiation. Clinical trials of administering both cabazitaxel and radiation should be explored in women with chemoresistant ovarian cancer.

Tubulin: an example of targeted chemotherapy

Anticancer drugs directed against the microtubule, including taxanes and vinca alkaloids, have been the backbone of many chemotherapy regimes for decades. These drugs have, however, significant limitations, which have prompted the development of novel microtubule targeting agents (MTAs). This article will discuss MTAs for anticancer therapies and recent debates regarding their mechanisms of action. Furthermore, the limitations of taxanes, including hypersensitivity reactions, neurotoxicity, drug resistance and lack of validated biomarkers to guide therapy will be discussed, all of which have driven the development of novel agents. The mechanisms of action and drug development of new generations of MTAs will also be outlined. Agents demonstrating utility in Phase III clinical trials, including eribulin, ixabepilone, cabazitaxel and trastuzumab-DM1 will be highlighted, as well as novel agents currently in development and future directions for MTAs.

Castration-resistant prostate cancer: from new pathophysiology to new treatment

CONTEXT

Until recently, the only approved agent for metastatic castration-resistant prostate cancer (mCRPC) was docetaxel chemotherapy. But over the last 5 years, significant advances in the field have led to the approval of five new agents, each with different mechanisms of action and demonstrating improved overall survival in separate randomized phase 3 trials. Many of these novel agents are now also being evaluated in earlier stages of the disease, which may ultimately lead to even better outcomes.

OBJECTIVE

To summarize the current literature on the management of mCRPC with a particular focus on novel chemotherapy approaches, hormonal approaches, immunotherapy, and radiopharmaceuticals showing survival benefits in phase 3 clinical trials. Emerging therapies in late stages of development are also discussed briefly.

EVIDENCE ACQUISITION

A comprehensive search of PubMed, identified studies pertaining to novel therapies evaluated in mCRPC since the initial approval of docetaxel in 2004. Abstracts from major international meetings were hand searched to identify studies of novel agents in late stage development in mCRPC. The Clinical Trials.gov database was used to find ongoing clinical trials in the area of mCRPC. A detailed search of each new agent was also performed to ensure that additional trials of these agents in other stages of the disease were included where relevant.

EVIDENCE SYNTHESIS

The main agents discussed are the androgen synthesis inhibitor abiraterone acetate, the androgen receptor inhibitor enzalutamide, the novel taxane chemotherapy cabazitaxel, the immunotherapy sipuleucel-T, and the radiopharmaceutical radium 223. Other emerging agents and a brief discussion of negative phase 3 results are also included.

CONCLUSIONS

It is a very exciting time in the field of mCRPC, where therapeutic advances have improved outcomes in this disease, although once metastatic overall median survival remains a dismal 2-3 years. The key now will be to understand how best to use these new agents, understand the mechanisms of resistance to them, continue to develop novel treatment strategies, and ultimately test these agents earlier in the disease when cure may be possible.