New drugs in prostate cancer

Acetyl-lupeolic acid inhibits Akt signaling and induces apoptosis in chemoresistant prostate cancer cells in vitro and in vivo

The triterpenoid acetyl-lupeolic acid (ac-LA) isolated from the oleogum resin of Boswellia carterii reduced the viability of a panel of cancer cell lines more efficiently than lupeol. There was no detectable intracellular conversion of ac-LA to lupeol and vice versa. In contrast to docetaxel, ac-LA did not induce selection of treatment-resistant cancer cells. By various parameters including DNA fragmentation, ac-LA was shown to induce apoptosis in androgen-independent PC-3 cells, whereas in MDA-MB-231 breast cancer cells, ac-LA led to cell accumulation in the G₂/M phase of the cell cycle, but not to apoptosis. In silico docking combined with in vitro kinase assays implied that ac LA potently inhibits Akt mainly by direct binding to the pleckstrin homology domain. Consistently, an Akt1 mutant deficient of the PH domain afforded partial resistance to ac-LA and complete resistance to lupeol and the Akt inhibitor III. Ac-LA inhibited phosphorylation of downstream targets of the Akt signaling pathway, which was followed by inhibition of the mTOR target p70 ribosomal six protein kinase and the nuclear accumulation of p65/NF-κB, β-catenin, and c-myc, as well as loss of the mitochondrial membrane potential. Ac-LA exhibited antiproliferative, proapoptotic, and antitumorigenic effects on PC-3-tumors xenografted either on chick chorioallantoic membranes or in nude mice. Ac-LA exhibited a clearly better safety profile than docetaxel or lupeol during chronic administration in vivo. In contrast to lupeol, ac-LA also inhibited release of vascular endothelial growth factor in vitro and accordingly angiogenesis in vivo. Thus, ac-LA deserves further exploration as a potential new antitumor compound.

Randomized phase II study of nintedanib in metastatic castration-resistant prostate cancer postdocetaxel

This open-label, phase II trial assessed the efficacy and safety of two doses of nintedanib, a triple angiokinase inhibitor targeting vascular endothelial growth factor, fibroblast growth factor, and platelet-derived growth factor signaling, in patients with metastatic castration-resistant prostate cancer (mCRPC) following progression on docetaxel-based regimens. Patients were randomized to nintedanib 150 mg (arm A, n=40) or 250 mg (arm B, n=41) twice daily for 6 months unless disease progression or adverse events (AEs) led to discontinuation. The primary endpoint was the prostate-specific antigen (PSA) response rate (confirmed PSA decline of ≥20% from baseline). Eighty-one patients were enrolled. The PSA response rate was 0% (0/32) in arm A versus 11.1% (4/36) in arm B (P=0.12); 5.6% of patients (2/36) in arm B showed a PSA reduction of at least 50%. In arm B, the rate of PSA increase was significantly decelerated on treatment versus before treatment (P=0.002). The median progression-free survival was 73.5 and 76.0 days for arm A and arm B, respectively (P=0.3). AEs included gastrointestinal disorders, asthenia, hypertension, and reversible elevated transaminases. The incidence of drug-related serious AEs (no drug-related deaths) was 20.0% (arm A) and 24.4% (arm B). The primary endpoint was not met. Nintedanib (250 mg) showed only modest activity with manageable AEs in patients with mCRPC post-docetaxel.

The hurdle of antiandrogen drug resistance: drug design strategies

INTRODUCTION

Prostate cancer is the second most common cancer death in men after lung cancer, due to distant metastases. While distant prostate cancer is typically castrate resistant, it is not necessarily androgen independent. For this reason, a review of the literature regarding the pathways involved in androgen signaling and therapeutic regimens to treat distant metastases is beneficial to increasing the survival rate of prostate cancer patients.

AREAS COVERED

In this article, the author reviews the literature from the past decade covering metastatic hormone refractory prostate cancer with the aim to examine and identify pathways, therapeutic targets and current therapies for treating castrate-resistant disease. As this area is lacking, the author aims to provide the reader with knowledge of the molecular consequences of castrate resistant prostate cancer, the current treatment paradigms and future directions.

EXPERT OPINION

While there have been advances in the treatment of castrate resistant prostate cancer, only minimal advances have been made in overall survival rate. Due to aberrant mutations and activation in the androgen receptor gene, and the complexity of cell signaling within prostate cancer, the androgen receptor should remain a main target for drug discovery efforts. This author believes that designing compounds that will reduce the activation of the androgen receptor may hold the key to a cure in the future.

Effect of diallyl disulfide on insulin-like growth factor signaling molecules involved in cell survival and proliferation of human prostate cancer cells in vitro and in silico approach through docking analysis

PURPOSE

Diallyl Disulfide (DADS) is one of the major components of garlic, which inhibits the proliferation of various cancer cells. Our previous studies showed that DADS inhibits cell growth and induces apoptosis on prostate cancer cells. Insulin like growth factor signaling pathway plays a significant role on prostate cancer cell growth and survival and it's over expression also identified in human prostate cancers. The molecular mechanism of IGF mediated PI3K/Akt signaling remains to be elucidated. The present study was designed to evaluate the effects of diallyl disulfide on IGF signaling in androgen independent prostate cancer cells (PC-3).

METHODS

DADS (10-50 μM) caused dose-dependent inhibition of PC-3 cells, were analyzed by MTT, IC50 value of PC-3 cells was 40 μM for 24h. Interestingly, DADS also altered the mRNA and protein expressions of IGF signaling and apoptotic molecules which were confirmed by semi quantitative PCR and western blot method. Further the docking study of DADS with IGF receptor was carried out by Ligand Fit of Discovery studio. Accord Excel Package was used for the prediction of ADME properties of the compound.

RESULTS

The results suggests that DADS decreases the survival rate of androgen independent prostate cancer cells by modulating the expression of IGF system, which leads to inhibition of phosphorylation of Akt, thereby inhibits cell cycle progression and survival by lowering the expression of cyclin D1, NFkB and anti-apoptotic Bcl-2 molecule and increasing the level of pro-apoptotic (Bad and Bax) signaling molecules which leads to apoptosis.

CONCLUSION

The present investigation showed downregulation of Akt and a concomitant increase in apoptosis in DADS treated prostate cancer cells. Since inhibition of this Akt pathway by DADS leads to inhibition in cancer cell progression, it is highly suggested that DADS has the potential use as a therapy for prostate cancer.

Pharmacological and functional properties of TRPM8 channels in prostate tumor cells

Prostate cancer (PC) is a major health problem in adult males. TRPM8, a cationic TRP channel activated by cooling and menthol is upregulated in PC. However, the precise role of TRPM8 in PC is still unclear. Some studies hypothesized that TRPM8-mediated transmembrane Ca(2+) fluxes play a key role in cellular proliferation of PC cells. In contrast, other findings suggest that high TRPM8 levels may reduce the metastatic potential of PC cells. A detailed understanding of the response of TRPM8 channels to pharmacological modulators of their activity is relevant when considering potential therapies, targeting this ion channel to treat PC. We characterized the pharmacological and functional properties of native TRPM8 channels in four human prostate cell lines, PNT1A, LNCaP, DU145, and PC3, commonly used as experimental models of PC. PNT1A is a non-tumoral prostate cell line while the other three correspond to different stages of PC. Here, we show that cold- and agonist-evoked [Ca(2+)](i) responses in PC cells are much less sensitive to well-characterized agonists (menthol and icilin) and antagonists (BCTC, clotrimazole, and DD01050) of TRPM8 channels, compared to TRPM8 channels in other tissues, suggesting a different molecular composition and/or spatial organization. In addition, the forced overexpression of human TRPM8 facilitated the trafficking of TRPM8 channels residing in the endoplasmic reticulum to the plasma membrane, leading to a marked potentiation in the efficacy of the different blockers. These results predict that blockers of canonical TRPM8 channels may be less effective in halting proliferation of PC cells than expected.

Tirucallic acids are novel pleckstrin homology domain-dependent Akt inhibitors inducing apoptosis in prostate cancer cells

Activation of the serine/threonine kinase Akt is associated with aggressive clinical behavior of prostate cancer. We found that the human prostate cancer cell lines LNCaP and PC-3 express predominantly Akt1 and Akt2. Selective down-regulation of Akt1, but not Akt2, by short-hairpin RNA reduced the viability of prostate cancer cells. In addition, structurally different Akt inhibitors were cytotoxic for the prostate cancer cells, confirming that the Akt pathway is indispensable for their viability. We have purified the tetracyclic triterpenoids 3-oxo-tirucallic acid, 3-alpha-acetoxy-tirucallic acid, and 3-beta-acetoxy-tirucallic acid from the oleogum resin of Boswellia carterii to chemical homogeneity. The acetoxy-derivatives in particular potently inhibited the activities of human recombinant Akt1 and Akt2 and of constitutively active Akt immunoprecipitated from PC-3 cells, whereas inhibitor of nuclear factor-kappaB kinases remained unaffected. Docking data indicated that these tetracyclic triterpenoids form hydrogen bonds within the phosphatidylinositol binding pocket of the Akt pleckstrin homology domain. Accordingly, 3-beta-acetoxy-tirucallic acid did not inhibit the activity of Akt1 lacking the pleckstrin homology domain. In the prostate cancer cell lines investigated, these compounds inhibited the phosphorylation of cellular Akt and the Akt signaling pathways, including glycogen synthase kinase-3beta and BAD phosphorylation, nuclear accumulation of p65, the androgen receptor, beta-catenin, and c-Myc. These events culminated in the induction of apoptosis in prostate cancer, but not in nontumorigenic cells. The tirucallic acid derivatives inhibited proliferation and induced apoptosis in tumors xenografted onto chick chorioallantoic membranes and decreased the growth of pre-established prostate tumors in nude mice without overt systemic toxicity. Thus, tirucallic acid derivatives represent a new class of Akt inhibitors with antitumor properties.

Emerging drugs for prostate cancer

Prostate cancer mortality usually occurs as a result of castrate resistant disease. Many approaches are currently being evaluated to improve the treatment of this condition. These include drugs that induce androgen deprivation, that is, LHRH antagonists; more active or less toxic chemotherapy agents; immunologic approaches, including passive and active immunization; drugs that target the androgen receptor and/or androgen synthesis; drugs that target specific pathways, including tyrosine kinase inhibitors, angiogenesis inhibitors, endothelin antagonists and matrix metalloproteinase inhibitors; and antioxidants and cell cycle inhibitors. Many of these agents seem promising. The rationale, biologic activity and therapeutic results of these emerging drugs are reviewed.

Ligand-independent androgen receptor variants derived from splicing of cryptic exons signify hormone-refractory prostate cancer

Suppression of androgen production and function provides palliation but not cure in men with prostate cancer (PCa). Therapeutic failure and progression to hormone-refractory PCa (HRPC) are often accompanied by molecular alterations involving the androgen receptor (AR). In this study, we report novel forms of AR alteration that are prevalent in HRPC. Through in silico sequence analysis and subsequent experimental validation studies, we uncovered seven AR variant transcripts lacking the reading frames for the ligand-binding domain due to splicing of "intronic" cryptic exons to the upstream exons encoding the AR DNA-binding domain. We focused on the two most abundantly expressed variants, AR-V1 and AR-V7, for more detailed analysis. AR-V1 and AR-V7 mRNA showed an average 20-fold higher expression in HRPC (n = 25) when compared with hormone-naive PCa (n = 82; P < 0.0001). Among the hormone-naive PCa, higher expression of AR-V7 predicted biochemical recurrence following surgical treatment (P = 0.012). Polyclonal antibodies specific to AR-V7 detected the AR-V7 protein frequently in HRPC specimens but rarely in hormone-naive PCa specimens. AR-V7 was localized in the nuclei of cultured PCa cells under androgen-depleted conditions, and constitutively active in driving the expression of canonical androgen-responsive genes, as revealed by both AR reporter assays and expression microarray analysis. These results suggest a novel mechanism for the development of HRPC that warrants further investigation. In addition, as expression markers for lethal PCa, these novel AR variants may be explored as potential biomarkers and therapeutic targets for advanced PCa.

Current perspectives in the treatment of advanced prostate cancer

Prostate cancer (PC) continues to be an important world health problem for men. Patients with locally confined PC are treated with either radiotherapy or surgery. However, treatment of more advanced stages of the disease is problematic. Initially, androgen deprivation offers a period of clinical stability, which is however invariably followed by progression to non-responsiveness to hormonal manipulation. Current management of patients with androgen-independent prostate cancer (AIPC) displays modest response rates and achieves only short-term benefit. Recently, knowledge in the complex pathophysiology of advanced PC has led to the identification of mechanisms and target molecules permitting the introduction of new therapies. Consequently, many investigational treatments are ongoing for AIPC in Phase-II and Phase-III trials aiming at the combination of chemotherapeutic regimens along with immunotherapy targeting PC-associated antigens. Other attractive options are gene therapy, as well as the targeting of survival signaling, differentiation, and apoptosis of the malignant PC cells. Further treatment modalities are directed against the tumor microenvironment, bone metastasis, or both. Collectively, the aforementioned efforts introduce a new era in the management of advanced PC. Novel pharmaceutical compounds and innovative approaches, integrated into the concept of individualized therapy will hopefully, during the next decade, improve the outcome and survival for hundreds of thousands of men worldwide.

[Promising new treatment options for metastatic androgen-independent prostate cancer]

OBJECTIVE

Review the recent advances in the treatment of androgen independent prostate cancer (AIPC).

METHODS

Review recent abstracts and literature utilizing Medline/PubMed using key words: androgen independent/hormone refractory prostate cancer, novel treatment options, Phase II, III trials and meeting abstracts/presentations.

CONCLUSION

Two pivotal trials SWOG (Southwest Oncology Group) study 9916 and Taxotere 327 have shown that survival can be improved in this population by administration of chemotherapy with docetaxel every three weeks intravenously. An overall survival of 19 months could be achieved with docetaxel/prednisone compared to 16 months with mitoxantrone/prednisone. Despite this, there is a need to improve on this survival benefit because the relapse free survival among responders is often short (6 months) and patients often would have progression of their cancer leading to death. Satraplatin, a novel platinum analogue had been found to provide an additional 1.5 week progression free survival benefit in this population in the second line setting. There is however, a need to develop less toxic drugs that would improve survival significantly.

Bevacizumab plus 5-fluorouracil induce growth suppression in the CWR-22 and CWR-22R prostate cancer xenografts

Prostate cancer is the most common malignancy in men. Although patients with metastatic prostate cancer can benefit from androgen ablation, most of them will die of prostate cancer progression to an androgen-refractory state. In the present study, the effects of docetaxel, bevacizumab, 5-fluorouracil (5-FU), bevacizumab plus docetaxel, and bevacizumab plus 5-FU on the growth of human CWR-22 (androgen-dependent) and CWR-22R (androgen-independent) prostate carcinoma xenografts were investigated. We report that i.p. administration of 10 mg/kg docetaxel at 1-week interval, 5 mg/kg/ bevacizumab once every 2 weeks, or 12.5 mg/kg 5-FU, bevacizumab/docetaxel, or bevacizumab/5-FU weekly to severe combined immunodeficient mice bearing prostate cancer xenografts (12 mice per treatment group) for 21 days resulted in 22.5 +/- 8%, 23 +/- 7%, 31 +/- 8%, 22 +/- 6%, and 81 +/- 5% growth inhibition, respectively. Greatest growth suppression was observed in bevacizumab/5-FU treatment. Bevacizumab/5-FU-induced growth suppression was associated with reduction in microvessel density, inhibition of cell proliferation; up-regulation of phosphatase and tensin homologue, p21(Cip1/Waf1), p16(INK4a), and p27(Kip1); hypophosphorylation of retinoblastoma protein; and inhibition of Akt/mammalian target of rapamycin pathway. Our data indicate that bevacizumab/5-FU effectively inhibits angiogenesis and cell cycle progression and suggest that bevacizumab/5-FU may represent an alternative treatment for patients with prostate cancer.

Prostate cancer: Re-focusing on androgen receptor signaling

Prostate cancer is the most common, non-dermatologic cancer in men. Since prostate cancer is highly associated with increased age, the incidence of this disease is expected to increase as the population ages. In its initial stages prostate cancer depends upon the actions of androgen, and androgen deprivation therapy induces tumor regression. Currently, androgen deprivation is achieved by either surgical or chemical androgen blockade. Unfortunately, nearly all prostate cancer patients develop tumors that grow despite androgen blockade and ultimately relapse. Many alterations in prostate cancer cells contribute to this state. Although chemotherapy induces short remissions in some patients, there are no curative therapies for metastatic disease. This review summarizes our current understanding in androgen signaling and the mechanisms that allow tumor cells to bypass androgen manipulation therapy. The identification of novel survival pathways and effector molecules that drive androgen independent growth is necessary to develop effective therapies for advanced prostate cancers.

Allogeneic retrovirally transduced, IL-2- and IFN-γ-secreting cancer cell vaccine in patients with hormone refractory prostate cancer—a phase I clinical trial

BACKGROUND

The purpose of this vaccine study was to determine the safety and feasibility of vaccination with an allogeneic prostate carcinoma cell line, LNCaP, expressing recombinant interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) and to evaluate the efficacy of inducing tumor-specific immune responses in HLA-A2-matched patients with hormone refractory prostate cancer (HRPC).

METHODS

In a dose-escalating phase I study, HLA-A2-matched HRPC patients received four vaccinations of irradiated allogeneic LNCaP cells retrovirally transduced to secrete IL-2 and IFN-gamma at study day 1, 15, 29 and 92 and subsequently every 91 days unless tumor progression was evident.

RESULTS

Three patients receiving the first dose level (7.5 million cells) showed no evidence of dose-limiting toxicity or vaccine-related adverse events including autoimmunity. One of three patients receiving the second dose level (15 million cells) developed a transient self-limiting grade 3 local injection site reaction (ulceration) after the eighth vaccination. Vaccine-induced immune responses against a broad array of prostate tumor associated antigens were detected in all six patients. Two of the three patients receiving the higher dose showed a decline in serum prostate-specific antigen (PSA) values of more than 50%, with one patient remaining on protocol for 3 years.

CONCLUSIONS

Immunisation with the allogeneic LNCaP/IL-2/IFN-gamma vaccine is safe and feasible without any dose-limiting toxicity or autoimmunity. A 50% PSA decline was achieved in two of the six patients. This encouraging data provides the scientific rationale for further investigation of the vaccine in a phase II trial.

Pharmacoeconomics of available treatment options for metastatic prostate cancer

The resources devoted to managing metastatic prostate cancer are enormous, yet little attention has been given to directly measuring the economic consequences of treatment alternatives. The purpose of this article was to evaluate the pharmacoeconomics of available treatments for metastatic prostate cancer, including hormone-sensitive disease, androgen-independent prostate cancer and locally advanced/progressive disease. We identified 58 articles addressing economic issues related to metastatic prostate cancer. Treatment alternatives with considerably different costs are available in many areas of disease management, most notably, medical androgen deprivation therapy (ADT) versus surgical castration; combined androgen blockage (CAB) versus monotherapy for initial treatment of hormone-sensitive disease; as well as bisphosphonates and bone-targeted radioisotopes for palliation. The few available pharmacoeconomic studies indicate that the additional costs are not supported by clear and compelling evidence of differences in survival or quality-of-life (QOL) outcomes. Our review revealed that authors often use considerably different assumptions about efficacy and survival outcomes in their analyses, which may be due to the inconsistency of available clinical evidence. Although there have been many clinical trials comparing various therapies, we identified only three trials that included economic assessments. Thus, few sources of economic data are available and most pharmacoeconomic studies rely on information mined from indirect sources. We note that, while there has been considerable enthusiasm about the role of docetaxel regimens in the past 2 years, no study has yet examined the costs of these therapies. Survival remains poor for metastatic disease, thus QOL is the primary consideration for many therapies. However, QOL for treatment of metastatic disease is poorly measured and, in most analyses, the impact of therapy on QOL was inferred based on speculation by the authors. Given the large cost burdens of these treatments, it is essential that we more fully understand the true QOL gains potentially offered by more expensive therapies. The economic studies of advanced prostate cancer highlight several aspects of clinical care that are filled with considerable uncertainty and remain guided by forces other than optimal resource allocation. It is essential that we address the weaknesses in our understanding of the economic consequences of therapies for prostate cancer, and find ways to include economic information into the process of determining optimal therapy.

The ageing male reproductive tract

Ageing of the male reproductive system is characterized by changes in the endocrine system, hypogonadism, erectile dysfunction and proliferative disorders of the prostate gland. Stochastic damage accumulating within ageing leads to progressive dysregulation at each level of the hypothalamic-pituitary-gonadal (HPG) axis and in local auto/paracrine interactions, thereby inducing morphological changes in reproductive target organs, such as the prostate, testis and penis. Despite age-related changes in the HPG axis, endocrine functions are generally sufficient to maintain fertility in elderly men. Ageing of the male reproductive system can give rise to clinically relevant manifestations, such as benign prostatic hyperplasia (BPH), prostate cancer (PCa) and erectile dysfunction (ED). In this review, we discuss morphological/histological changes occurring in these organs and current views and concepts of the underlying pathology. Moreover, we emphasize the molecular/cellular pathways leading to reduced testicular/penile function and proliferative disorders of the prostate gland.

Novel targets in prostate cancer

Despite recent advances in the understanding of the cellular and molecular biology of prostate cancer, new options for the treatment of prostate cancer remain elusive. Targeted therapies have shown promising activities in many solid tumours and the growing number of targets and targeted agents is creating numerous opportunities for clinical research in advanced prostate cancer. At ASCO 2006 in Atlanta, a clinical science symposium on novel targets in prostate cancer was presented. It consisted of three abstracts, each of which was followed by a discussant who reviewed the work and placed it in the overall context of current approaches to treating prostate cancer. The three abstracts were a discussion of a new method for quantification of the androgen receptor; the impact of high-dose vitamin D plus chemotherapy on hormone refractory disease and on the risk of thromboembolic disease; and the paradoxical effects seen with the raf-kinase and vascular endothelial growth factor inhibitor sorafenib, which produced improvement in bone scans in the absence of any prostate-specific antigen responses.