Suppression of prostate tumor cell survival by antisense oligonucleotide-mediated inhibition of AR-V7 mRNA synthesis

One of the mechanisms by which advanced prostate cancer develops resistance to androgen deprivation therapy is the elevated expression of C-terminally truncated androgen receptor (AR) variants. These variants, such as AR-V7, originate from aberrant splicing of the AR pre-mRNA and the inclusion of a cryptic exon containing a premature stop codon in the mRNA. The resulting loss of the ligand-binding domain allows AR-V7 to act as a constitutively active transcription factor. Here, we designed two antisense oligonucleotides (AONs) directed against cryptic splicing signals within the AR pre-mRNA. These two AONs, AON-ISE and AON-ESE, demonstrated high efficiency in silencing AR-V7 splicing without affecting full-length AR expression. The subsequent downregulation of AR-V7-target gene UBE2C was accompanied by inhibition of androgen-independent cell proliferation and induction of apoptosis in castration-resistant prostate cancer (CRPC)-derived cell line models 22Rv1, DuCaP, and VCaP. Our results show that splicing-directed AONs can efficiently prevent expression of AR-V7, providing an attractive new therapeutic option for the treatment of CRPC.

Clusterin as a therapeutic target

INTRODUCTION

Clusterin (CLU) is a stress-activated, ATP-independent molecular chaperone, normally secreted from cells, that is up-regulated in Alzheimer disease and in many cancers. It plays important roles in protein homeostasis/proteostasis, inhibition of cell death pathways, and modulation of pro-survival signalling and transcriptional networks. Changes in the CLU gene locus are highly associated with Alzheimer disease, and many therapy-resistant cancers over-express CLU. The extensive post-translational processing and heterogeneous oligomerization of CLU have so far prevented any definitive structure determination. This in turn has meant that targeting CLU with small molecule inhibitors is challenging. Therefore, inhibiting CLU at the gene-expression level using siRNA or antisense is a valid approach to inhibit its function. Areas covered: This article reviews recent advances regarding the role of CLU in proteostasis, cellular trafficking, human diseases, and signalling pathways involved in oncogenesis. It addresses the rationale for CLU as a therapeutic target in cancer, and the current status of pre-clinical and clinical studies using CLU antisense inhibitor OGX011. Expert opinion: Discusses challenges facing the therapeutic targeting of CLU including rapid changes in the treatment landscape for prostate cancer with multiple new FDA approved drugs, selection of windows of intervention, and potential side effects when silencing CLU expression.

Cabazitaxel for the second-line treatment of metastatic hormone-refractory prostate cancer: a NICE single technology appraisal

The National Institute for Health and Clinical Excellence (NICE) invited the manufacturer of cabazitaxel (Jevtana®, sanofi-aventis, UK) to submit evidence of its clinical and cost effectiveness for the second-line treatment of metastatic hormone-refractory prostate cancer (mHRPC). The School of Health and Related Research Technology Appraisal Group (ScHARR-TAG) at the University of Sheffield was commissioned to act as the independent Evidence Review Group (ERG). The ERG produced a critical review of the evidence for the clinical and cost effectiveness of the technology based upon the manufacturer's submission to NICE. Clinical evidence was derived from a multinational randomized open-label phase III trial of cabazitaxel plus prednisone or prednisolone in men with mHRPC that had progressed during or following treatment with docetaxel. The comparator was mitoxantrone plus prednisone or prednisolone. Use of cabazitaxel was associated with a statistically significant improvement in overall survival, median progression-free survival and time to tumour progression. However, it was also associated with an increased incidence of adverse events such as neutropenia. Utility data were based on interim results from the early access programme for cabazitaxel. Data were only available for a small number of patients with stable disease, resulting in great uncertainty as to the effect of cabazitaxel on quality of life. For their economic evaluation, the manufacturer estimated that the use of cabazitaxel was associated with an incremental cost of £74,908 per QALY gained. However, the ERG disagreed with the manufacturer over two key methodological points. The first concerned modelling and extrapolating survival; the second point was concerned with the choice of patient population. The ERG altered the manufacturer's evaluation to take into account these two points of disagreement. The resulting cost per QALY gained was £82,950. The NICE Appraisal Committee believed the analysis presented by the ERG to be more plausible, and likely to be an underestimate of the cost per QALY. They concluded that whilst the clinical effectiveness of cabazitaxel had been proven, it was not likely to represent a cost-effective use of NHS resources and so its use could not be recommended.

Castration-resistant prostate cancer: new science and therapeutic prospects

There is a growing number of new therapies targeting different pathways that will revolutionize patient management strategies in castration-resistant prostate cancer (CRPC) patients. Today there are more clinical trial options for CRPC treatment than ever before, and there are many promising agents in late-stage clinical testing. The hypothesis that CRPC frequently remains driven by a ligand-activated androgen receptor (AR) and that CRPC tissues exhibit substantial residual androgen levels despite gonadotropin-releasing hormone therapy, has led to the evaluation of new oral compounds such as abiraterone and MDV 3100. Their results, coupled with promising recent findings in immunotherapy (eg sipuleucel-T) and with agents targeting angiogenesis (while awaiting the final results of the CALGB trial 90401) will most probably impact the management of patients with CRPC in the near future. Other new promising agents need further development. With our increased understanding of the biology of this disease, further trial design should incorporate improved patient selection so that patient populations are those who may be most likely to benefit from treatment.

Pathways of chemotherapy resistance in castration-resistant prostate cancer

Chemotherapy remains the major treatment option for castration-resistant prostate cancer (CRPC) and limited cytotoxic options are available. Inherent chemotherapy resistance occurs in half of all patients and inevitably develops even in those who initially respond. Docetaxel has been the mainstay of therapy for 6 years, providing a small survival benefit at the cost of significant toxicity. Cabazitaxel is a promising second-line agent; however, it is no less toxic, whereas mitoxantrone provides only symptomatic benefit. Multiple cellular pathways involving apoptosis, inflammation, angiogenesis, signalling intermediaries, drug efflux pumps and tubulin are implicated in the development of chemoresistance. A thorough understanding of these pathways is needed to identify biomarkers that predict chemotherapy resistance with the aim to avoid unwarranted toxicities in patients who will not benefit from treatment. Until recently, the search for predictive biomarkers has been disappointing; however, the recent discovery of macrophage inhibitory cytokine 1 as a marker of chemoresistance may herald a new era of biomarker discovery in CRPC. Understanding the interface between this complex array of chemoresistance pathways rather than their study in isolation will be required to effectively predict response and target the late stages of advanced disease. The pre-clinical evidence for these resistance pathways and their progress through clinical trials as therapeutic targets is reviewed in this study.

Management of metastatic castration-resistant prostate cancer after first-line docetaxel

Although chemotherapy, based on docetaxel, is now established in the management of metastatic castration-resistant prostate cancer (mCRPC), until recently, there has been no treatment licensed for use in the second line in men whose disease progresses during or after docetaxel therapy. This article reviews the classes of agents that have shown potential in this setting, notably chemotherapy drugs, hormonal therapies, immunotherapies, anti-angiogenic drugs, and clusterin-targeted therapy.

Novel targeted agents on the horizon for castration-resistant prostate cancer

Androgen deprivation treatment in prostate cancer patients is well established; however, resistance to such treatment manifests itself by progression to castration-resistant prostate cancer (CRPC). Despite significant advances in treatment options for patients with CRPC, their prognosis remains poor. Resistance results from multiple processes that facilitate cancer cell growth and survival. Mechanisms underlying the shift to castrate resistance have been attributed to a complex interplay of clonal selection, reactivation of the androgen receptor axis despite castrate levels of serum testosterone, stress-induced prosurvival genes and cytoprotective chaperone networks and alternative mitogenic growth factor pathways. This article discusses several pathways involved in the development of CRPC, with a particular focus on those mechanisms that have led to the development of new targeted therapies.

Drug resistance in metastatic castration-resistant prostate cancer

Docetaxel in combination with prednisone is the standard of care in men with symptomatic castration-resistant prostate cancer (CRPC). However, a substantial proportion of men with CRPC do not benefit from docetaxel or other systemic therapy and those who do benefit invariably progress and die of (or with) prostate cancer. Resistance to chemotherapy in metastatic CRPC is a result of cellular mechanisms of drug resistance intrinsic to prostate cancer and general mechanisms common to different tumor types. Continued signaling from the androgen receptor, activation of oncogenic survival pathways by various receptor tyrosine kinases and crosstalk between the androgen receptor and these oncogenic survival pathways are hallmarks of progression of CRPC. General mechanisms of drug resistance include the existence of subpopulations of cancer cells with cellular mechanisms of resistance, resistance related to interactions between prostate cancer cells and their surrounding microenvironment and impaired drug delivery to the cancer cells. New therapeutics targeting these mechanisms are under evaluation in clinical trials. Drug resistance in metastatic CRPC is multifactorial and complex and development of new medical therapies remains challenging.

Randomized phase II study of docetaxel and prednisone with or without OGX-011 in patients with metastatic castration-resistant prostate cancer

PURPOSE

To determine the clinical activity of OGX-011, an antisense inhibitor of clusterin, in combination with docetaxel/prednisone in patients with metastatic castration-resistant prostate cancer.

PATIENTS AND METHODS

Patients were randomly assigned 1:1 to receive docetaxel/prednisone either with (arm A) or without (arm B) OGX-011 640 mg intravenously weekly. The primary end point was the proportion of patients with a prostate-specific antigen (PSA) decline of ≥ 50% from baseline, with the experimental therapy being considered of interest if the proportion of patients with a PSA decline was more than 60%. Secondary end points were objective response rate, progression-free survival (PFS), overall survival (OS), and changes in serum clusterin.

RESULTS

Eighty-two patients were accrued, 41 to each arm. OGX-011 adverse effects included rigors and fevers. After cycle 1, median serum clusterin decreased by 26% in arm A and increased by 0.9% in arm B (P < .001). PSA declined by ≥ 50% in 58% of patients in arm A and 54% in arm B. Partial response occurred in 19% and 25% of patients in arms A and B, respectively. Median PFS and OS times were 7.3 months (95% CI, 5.3 to 8.8 months) and 23.8 months (95% CI, 16.2 months to not reached), respectively, in arm A and 6.1 months (95% CI, 3.7 to 8.6 months) and 16.9 months (95% CI, 12.8 to 25.8 months), respectively, in arm B. Baseline factors associated with improved OS on exploratory multivariate analysis were an Eastern Cooperative Oncology Group performance status of 0 (hazard ratio [HR], 0.27; 95% CI, 0.14 to 0.51), presence of bone or lymph node metastases only (HR, 0.45; 95% CI, 0.25 to 0.79), and treatment assignment to OGX-011 (HR, 0.50; 95% CI, 0.29 to 0.87).

CONCLUSION

Treatment with OGX-011 and docetaxel was well tolerated with evidence of biologic effect and was associated with improved survival. Further evaluation is warranted.

Castration-resistant prostate cancer: current and emerging treatment strategies

Until very recently, docetaxel was the only approved agent in castration-resistant prostate cancer (CRPC) and other effective therapeutic options are urgently needed. In recent years, several new agents with promising activity and a favourable toxicity profile have been developed and clinically investigated in the fields of hormonal, cytotoxic, targeted and immune therapy. In particular, recent results from two large phase III trials of sipuleucel-T and cabazitaxel show that these two agents significantly prolong overall survival in CRPC. Indeed, sipuleucel-T has recently been approved by the US FDA for the treatment of CRPC. Many other pharmaceuticals, which are presented in this review, have been investigated recently or are being investigated in phase III trials and might prove to be effective in the future. Reviewed articles are discussed in light of the innovations in study design brought by the Prostate Cancer Clinical Trials Working Group (PCWG2), which updated the Prostate-Specific Antigen Working Group (PCWG1) guidelines, in order to allow better identification of potentially active drugs in clinical trials.

Novel targeted therapies for prostate cancer

This article reviews the concepts and rationale behind targeted agents that are currently in clinical testing for patients with castration resistant prostate cancer (CRPC). Advances in our understanding of the molecular mechanisms underlying prostate cancer progression has translated into a variety of treatment approaches. Agents targeting androgen receptor activation and local steroidogenesis, angiogenesis, apoptosis, chaperone proteins, the insulinlike growth factor pathway, RANK ligand, endothelin receptors, and Src family kinases are entering, or have recently completed, accrual to phase III trials for patients with CRPC. There has also been interest generated by data from early-phase studies evaluating multitargeted tyrosine kinase inhibitors, agents effecting signal transduction pathways, and novel cytotoxics.

Targeting the cytoprotective chaperone, clusterin, for treatment of advanced cancer

Many strategies used to kill cancer cells induce stress-responses that activate survival pathways to promote emergence of a treatment resistant phenotype. Secretory clusterin (sCLU) is a stress-activated cytoprotective chaperone up-regulated by many varied anticancer therapies to confer treatment resistance when overexpressed. sCLU levels are increased in several treatment recurrent cancers including castrate resistant prostate cancer, and therefore sCLU has become an attractive target in cancer therapy. sCLU is not druggable with small molecule inhibitors, therefore nucleotide-based strategies to inhibit sCLU at the RNA level are appealing. Preclinical studies have shown that antisense oligonucleotide (ASO) or siRNA knockdown of sCLU have preclinical activity in combination with hormone- and chemotherapy. Phase I and II clinical trial data indicate that the second generation ASO, custirsen (OGX-011), has biologic and clinical activity, suppressing sCLU expression in prostate cancer tissues by more than 90%. A randomized study comparing docetaxel-custirsen to docetaxel alone in men with castrate resistant prostate cancer reported improved survival by 7 months from 16.9 to 23.8 months. Strong preclinical and clinical proof-of-principle data provide rationale for further study of sCLU inhibitors in randomized phase III trials, which are planned to begin in 2010.

The role of docetaxel based therapy for prostate cancer in the era of targeted medicine

Docetaxel based chemotherapy has been shown to modestly extend life, relieve pain and improve the quality of life in patients with metastatic castration-resistant prostate cancer. Current trials are attempting to build on the backbone of docetaxel by combining it with novel biological agents. Trials are also investigating the role of docetaxel for earlier stages of prostate cancer. No standard second-line systemic therapy exists and such patients are candidates for clinical trials. The increased understanding of the mechanisms of progressive castration-resistant prostate cancer is being translated into an increasing pipeline of novel therapies.

Clinical cancer advances 2008: major research advances in cancer treatment, prevention, and screening--a report from the American Society of Clinical Oncology

A message from ASCO'S president: Nearly 40 years ago, President Richard Nixon signed the National Cancer Act, mobilizing the country's resources to make the "conquest of cancer a national crusade." That declaration led to a major investment in cancer research that has significantly improved cancer prevention, treatment, and survival. As a result, two thirds of people diagnosed with cancer today will live at least 5 years after diagnosis, compared with just half in the 1970s. In addition, there are now more than 12 million cancer survivors in the United States--up from 3 million in 1971. Scientifically, we have never been in a better position to advance cancer treatment. Basic scientific research, fueled in recent years by the tools of molecular biology, has generated unprecedented knowledge of cancer development. We now understand many of the cellular pathways that can lead to cancer. We have learned how to develop drugs that block those pathways; increasingly, we know how to personalize therapy to the unique genetics of the tumor and the patient. Yet in 2008, 1.4 million people in the United States will still be diagnosed with cancer, and more than half a million will die as a result of the disease. Some cancers remain stubbornly resistant to treatment, whereas others cannot be detected until they are in their advanced, less curable stages. Biologically, the cancer cell is notoriously wily; each time we throw an obstacle in its path, it finds an alternate route that must then be blocked. To translate our growing basic science knowledge into better treatments for patients, a new national commitment to cancer research is urgently needed. However, funding for cancer research has stagnated. The budgets of the National Institutes of Health and the National Cancer Institute have failed to keep pace with inflation, declining up to 13% in real terms since 2004. Tighter budgets reduce incentives to support high-risk research that could have the largest payoffs. The most significant clinical research is conducted increasingly overseas. In addition, talented young physicians in the United States, seeing less opportunity in the field of oncology, are choosing other specialties instead. Although greater investment in research is critical, the need for new therapies is only part of the challenge. Far too many people in the United States lack access to the treatments that already exist, leading to unnecessary suffering and death. Uninsured cancer patients are significantly more likely to die than those with insurance, racial disparities in cancer incidence and mortality remain stark, and even insured patients struggle to keep up with the rapidly rising cost of cancer therapies. As this annual American Society of Clinical Oncology report of the major cancer research advances during the last year demonstrates, we are making important progress against cancer. But sound public policies are essential to accelerate that progress. In 2009, we have an opportunity to reinvest in cancer research, and to support policies that will help ensure that every individual in the United States receives potentially life-saving cancer prevention, early detection, and treatment. Sincerely, Richard L. Schilsky, MD President American Society of Clinical Oncology.