Targeting Bcl-2 with oblimersen for patients with hormone refractory prostate cancer

Phosphoprotein phosphatase 1-interacting proteins as therapeutic targets in prostate cancer

Prostate cancer is a major public health concern worldwide, being one of the most prevalent cancers in men. Great improvements have been made both in terms of early diagnosis and therapeutics. However, there is still an urgent need for reliable biomarkers that could overcome the lack of cancer-specificity of prostate-specific antigen, as well as alternative therapeutic targets for advanced metastatic cases. Reversible phosphorylation of proteins is a post-translational modification critical to the regulation of numerous cellular processes. Phosphoprotein phosphatase 1 (PPP1) is a major serine/threonine phosphatase, whose specificity is determined by its interacting proteins. These interactors can be PPP1 substrates, regulators, or even both. Deregulation of this protein-protein interaction network alters cell dynamics and underlies the development of several cancer hallmarks. Therefore, the identification of PPP1 interactome in specific cellular context is of crucial importance. The knowledge on PPP1 complexes in prostate cancer remains scarce, with only 4 holoenzymes characterized in human prostate cancer models. However, an increasing number of PPP1 interactors have been identified as expressed in human prostate tissue, including the tumor suppressors TP53 and RB1. Efforts should be made in order to identify the role of such proteins in prostate carcinogenesis, since only 26 have yet well-recognized roles. Here, we revise literature and human protein databases to provide an in-depth knowledge on the biological significance of PPP1 complexes in human prostate carcinogenesis and their potential use as therapeutic targets for the development of new therapies for prostate cancer.

Bcl-2 family of proteins as therapeutic targets in genitourinary neoplasms

INTRODUCTION

Overexpression of antiapoptotic B-cell lymphoma (Bcl-2) proteins confers the dysregulation of apoptosis and results in drug resistance in a variety of cancers, including those of the genitourinary tract. Inhibitors that target prosurvival Bcl-2 proteins are in preclinical and clinical development. The objective of this review is to assess the involvement of Bcl-2 proteins as well as the preclinical and clinical activity of Bcl-2 inhibitors under evaluation for genitourinary neoplasms.

MATERIALS AND METHODS

PubMed was used with both medical subject heading terms and free search to identify the relevant literature. Information on clinical trials was obtained using http://Clincaltrials.gov, EU Clinical Trials Register, and meeting abstracts of the American Society of Clinical Oncology.

RESULTS

To date, 2 Bcl-2 inhibitors have been evaluated in clinical trials for genitourinary tumors (oblimersen and AT-101 (R-(-)-gossypol)). Both agents demonstrated some success in early stages of development, but their clinical activity did not meet expectations. Preclinical studies are under way for other Bcl-2 inhibitors including ABT-737, HA14-1, and Bcl-2 homology 3 inhibitors.

CONCLUSION

Antiapoptotic Bcl-2 proteins are potential molecular targets in genitourinary cancers. Bcl-2 inhibitors might be effective as single agents or in combination with conventional therapies. However, the biology of the Bcl-2 family in genitourinary cancers remains poorly understood and robust preclinical studies are needed to inform clinical development. Such studies should aim to identify: (1) pharmacodynamic markers that could help guide patient selection for treatment with Bcl-2 inhibitors, and (2) optimal combinations of Bcl-2 inhibitors with other anticancer agents for future clinical investigation.

Vitamin D(3) cryosensitization increases prostate cancer susceptibility to cryoablation via mitochondrial-mediated apoptosis and necrosis

OBJECTIVES

To investigate the effect and molecular mechanisms of action of Vitamin D(3) (VD(3) ) as a neo-adjunctive agent before cryosurgery in an effort to increase treatment efficacy for prostate cancer (CaP). To eliminate the potential for disease recurrence that exists at the periphery of the freeze lesion, where temperatures may be insufficient to destroy both androgen-sensitive (AS) and androgen-insensitive (AI) CaP.

METHODS

Human CaP cells, LNCaP, were each genetically altered to express the AS and AI phenotypes and subjected to VD(3) treatment and freezing in an in vitro and tissue-engineered model. Cell viability, caspase inhibitor and western blot studies were used to determine the basis of the different responses of AI and AS cells to VD(3) cryosensitization.

RESULTS

VD(3) was found to be a highly effective cryosensitizer, resulting in a >50% overall increase in cell death after -15 °C freezing. Fluorescence microscopy, western blot analysis and caspase protease assays confirmed that the increased activation of apoptosis was modulated through a mitochondrial-mediated pathway. Caspase inhibition studies showed that apoptosis played an integral role in cell death, with VD(3) cryosensitivation-induced apoptotic events responsible for >30% of the overall cell death after -15 °C freezing.

CONCLUSIONS

The present study suggests that the use of VD(3) as a cryosensitizer increases cryoablation efficacy through the increased activity of apoptosis as well as through necrosis. The data show that through VD(3) treatment the overall level of AI CaP cell tolerance to freezing is reduced to a level similar to that of AS CaP. VD(3) pre-treatment in conjunction with cryoablation may increase treatment efficacy and reduce disease recurrence for CaP patients.

Targets for molecular therapy in esophageal squamous cell carcinoma: an immunohistochemical analysis

Neoadjuvant chemotherapy may improve the outcome of esophageal cancer after esophagectomy, but is accompanied by considerable toxicity by collateral destruction of normal cells. Such side effects may be avoided by developing therapies that specifically target molecular characteristics of tumors. The aim of the present study was to determine the proportion of esophageal squamous cell carcinoma (ESCC) patients that could possibly benefit from (a combination of) currently available targeted therapies, by assessing the frequency of immunohistochemical expression of their target molecular markers in ESCC tissues. Sections from a validated tissue microarray comprising 108 ESCCs were immunohistochemically stained for Bcl-2, c-KIT, cyclo-oxygenase-2 (COX-2), cyclin D1, estrogen receptor (ER), epidermal growth factor receptor (EGFR), Her-2/neu, progesterone receptor (PR), and vascular endothelial growth factor (VEGF). VEGF, cyclin D1, EGFR, and COX-2 could be detected in 55, 42, 40, and 40%, respectively. Her-2/neu, Bcl-2, and c-KIT were detected in 12, 11, and 10% of the tumors, respectively. No nuclear expression of ER or PR was noticed. Concurrent expression of two markers was noticed in 28% of ESCCs, whereas 25% of ESCCs showed concurrent expression of three markers. The concurrent expression of two of the most frequently expressed markers (VEGF, cyclin D1, EGFR, and COX-2) ranged from 11 (COX-2 and EGFR) to 26% (cyclin D1 and VEGF). The expression of all of these four markers was seen in 5% of ESCCs. Promising targets for molecular therapy in ESCC appear to be COX-2, VEGF, EGFR, and cyclin D1, as they are frequently overexpressed. Phase II clinical studies on these molecular markers may therefore be warranted. The role for targeted therapy against ER, PR, Her-2/neu, c-KIT, or Bcl-2 in ESCC seems limited.

Divergent effects of castration on prostate cancer in TRAMP mice: possible implications for therapy

PURPOSE

Divergent responses to androgen deprivation have been found in patients and in animal models of prostate cancer. The molecular basis for these different outcomes is unknown. Our aim was to identify the molecular responses of prostate cancer with divergent outcomes to androgen deprivation in TRAMP mice.

EXPERIMENTAL DESIGN

Castrated and noncastrated B6xFVB TRAMP mice were evaluated for survival, tumor development, pathology, and expressions of specific proteins at different time points.

RESULTS

TRAMP mice responded differentially to androgen deprivation. In the majority, primary tumors regressed after castration (positive response), whereas in others the tumors grew even more aggressively than in the noncastrated mice (negative response). Mice with regressed tumors had the highest survival rates. Androgen receptor was elevated in all tumors from castrated mice despite significant differences in tumor sizes. In positively responding tumors, expressions of Bcl-2 and Grp78 were greatly increased by 10 weeks after castration, whereas expressions of Bax, Bcl-xl, SV40 T antigen, and c-myc were lower. These tumors also showed a reduction in proliferating cells compared with noncastrates and negatively responding tumors. Most of these changes disappeared 20 weeks after castration, by which time there was an increase in the size of primary tumors as well as in distant metastasis.

CONCLUSIONS

In TRAMP prostate cancer that responded positively to castration, different expression patterns of proteins involved in cellular apoptosis, stress, and proliferation occur approximately 10 weeks after castration. This may be an optimal time for targeting Bcl-2, and perhaps Grp78, to enhance the antitumor effects of androgen deprivation.

Progress in understanding androgen-independent prostate cancer (AIPC): a review of potential endocrine-mediated mechanisms

This review is triggered by recent developments that offer new explanations for the mechanism of progression of prostate cancer to androgen independence. Established and hypothetical mechanisms, which have been described in the past, are put into perspective with recent progress in the field. A total of seven mechanisms can be identified that relate to progression to androgen independence. Five of those are dependent on the androgen receptor, which is present or over-expressed in androgen-independent prostate cancer tissue. Probably due to selective pressure, AIPC cells have the capability to escape from the effect of castration and antiandrogens; exclusion of the androgen receptor activity by inhibition of dimerisation or inhibition of DNA binding seem to be the logical next steps. Although androgen levels and androgen synthesis are suppressed in prostatic tissues during the phase of response to endocrine treatment, androgen levels and, specifically, 5-alpha-dihydrotestosterone (DHT) were elevated in tissues derived from metastases of AIPC. In addition, all enzymes needed to synthesise androgens from the level of pregnenolone on are present or over-expressed in such tissue. This offers new potential for treatment.

Sphingolipids and the sphingosine kinase inhibitor, SKI II, induce BCL-2-independent apoptosis in human prostatic adenocarcinoma cells

BACKGROUND

Elevated BCL-2 is one mechanism of therapeutic resistance in prostate cancer (PC), and new approaches are needed to overcome such resistance.

METHODS

We evaluated the effects of BCL-2 over-expression in human prostatic adenocarcinoma cells on their susceptibility to sphingolipids (SLs) and to the sphingosine kinase (SpK) inhibitor, SKI II.

RESULTS

In survival assays, no significant differences were observed in the responses to sphingosine or ceramide among parental PC-3 cells lacking detectable BCL-2 and BCL-2 over-expressing PC-3 transfectants; similarly, the responses to dimethyl-sphingosine (DMSP) of parental LNCaP cells and a BCL-2 over-expressing LNCaP transfectant were equivalent. SKI II induced protracted, BCL-2-independent survival loss in both PC-3 and LNCaP parental/transfectant pairs; in contrast, DMSP induced rapid cell shrinkage, caspase activation and caspase-dependent DNA fragmentation. DMSP-induced DNA fragmentation and loss of mitochondrial membrane potential were equivalent in BCL-2 transfectants and parental PC-3 cells and were not associated with BCL-2 downregulation. DMSP-mediated cytotoxicity was not associated with the enhanced production of reactive oxygen intermediates. SL analyses of parental and transfectant PC-3 cells did not reveal increased levels of sphingosine-1-phosphate in the BCL-2 transfectants; further, there only a modest early shift, corresponding to apoptotic onset, in pro- versus anti-apoptotic SLs in response to DMSP treatment.

CONCLUSIONS

Thus, in contrast to the inhibitory effects of BCL-2 on apoptosis induced by various agents in tumor cells, SKI II and selected pro-apoptotic SLs appear atypical in their independence from such inhibition, and may have merits as new candidates for treatment of AI PC.

Androgen-independent prostate cancer

Androgen-independent or hormone-refractory prostate cancer (AIPC) is prostate cancer that progresses after primary androgen-ablation therapy--either orchiectomy or a gonadotropin-releasing hormone (LHRH) agonist, followed by addition and subsequent withdrawal of an antiandrogen. In the majority of patients, AIPC appears after a median time of 18 months of hormone deprivation. Patients with AIPC have a median survival between 10 and 20 months and the prognosis can be defined by using nomograms. Standard treatment is continued castration by LHRH agonists in combination with docetaxel-containing chemotherapy. Other treatment options to palliate symptoms are hormones, other chemotherapeutic agents, radioisotopes or radiotherapy and bisphosphonates. New targeted drugs and vaccination strategies are evaluated in the treatment of AIPC.

Photodynamic therapy of cerebral glioma – A review Part I – A biological basis

Photodynamic therapy (PDT) has been investigated extensively in the laboratory for decades, and for over 25 years in the clinical environment, establishing it as a useful adjuvant to standard treatments for many cancers. A combination of both photochemical and photobiological processes occur that lead to the eventual selective destruction of the tumour cells. It is a potentially valuable adjuvant therapy that can be used in conjunction with other conventional therapies for the treatment of cerebral glioma. PDT has undergone extensive laboratory studies and clinical trials with a variety of photosensitizers (PS) and tumour models of cerebral glioma. Many environmental and genetically based factors influence the outcome of the PDT response. The biological basis of PDT is discussed with reference to laboratory and preclinical studies.

First- and second-line chemotherapy with docetaxel or mitoxantrone in patients with hormone-refractory prostate cancer

BACKGROUND

Docetaxel and mitoxantrone are considered first-line chemotherapeutic options in patients with hormone-refractory prostate cancer (HRPC), but their clinical effectiveness in a second-line setting is unknown. Therefore, the authors conducted a population-based retrospective study to establish activity and tolerability of second-line docetaxel or mitoxantrone in HRPC.

METHODS

The study included 68 patients who had failed androgen ablation therapy and who received docetaxel and mitoxantrone in either sequence. Clinical efficacy in terms of median overall survival (OS), progression-free survival (PFS), posttreatment prostate-specific antigen (PSA) decline of > or = 50% and treatment-related toxicity were evaluated.

RESULTS

Of 68 patients, 35 received docetaxel followed by mitoxantrone, and 33 received mitoxantrone followed by docetaxel. Both groups were comparable for recognized pretreatment prognostic factors. Patients who received docetaxel first-line had a trend toward longer median OS compared with patients treated with second-line docetaxel after mitoxantrone failure (22 mos, 95% confidence interval [CI], 17.2-26.8 mos vs. 15 mos, 95% CI, 10.4-19.6 mos). Median number of second-line chemotherapy cycles was 3 and median PFS survival was 2-3 months in both groups. Second-line docetaxel produced a higher PSA response compared with mitoxantrone (38% vs. 12%, P = 0.012), but this did not translate to a survival benefit. Both second-line docetaxel and mitoxantrone were associated with a high frequency of treatment-related adverse events that resulted in dose reduction, delay, or discontinuation (64% and 46% of patients, respectively).

CONCLUSIONS

Study results favored docetaxel given up-front for patients with HRPC considered suitable for further chemotherapy. Second-line docetaxel or mitoxantrone had limited efficacy and tolerability. Patients who are candidates for second-line chemotherapy, should be enrolled into clinical trials.