Combination adriamycin and suramin induces apoptosis in bcl-2 expressing prostate carcinoma cells

Treatment Options in Hormone-refractory Metastatic Prostate Carcinoma

Prostate cancer represents one of the most important health problems in industrialized countries. It is the second leading cause of cancer-related death in the United States. Therapeutic options are different according to the stage of the disease at the diagnosis. Patients with localized disease may be treated with surgery or radiation, whereas the treatment for patients with a metastatic disease is purely palliative. Hormonal treatment represents the standard therapy for stage IV prostate cancer, but patients ultimately become unresponsive to androgen ablation and are classified as hormone-refractory prostate cancer patients. The molecular mechanisms involved in progression in hormone resistance are characterized by mutations, down and up-regulation in the androgen receptor gene, mutations in p53 and over-expression of Bcl2 and other alterations in genes and in gene expression. The important thing is that we understand these mechanisms to define potential therapeutic agents for the treatment of hormone-refractory prostate cancer patients. Conventional options for patients with hormone-refractory prostate cancer include secondary hormone therapy, radiotherapy and cytotoxic chemotherapy. The commonest antineoplastic agents are mitoxantrone, estramustine and taxanes. Despite an improvement In the palliative benefit, none of these agents has demonstrated a beneficial impact on the overall survival of patients. Therefore, there is no standard therapy for these patients, thus we need new approaches which should be studied in clinical trials. The evaluation and incorporation of new agents into current treatment regimens could have a role in the treatment of hormone-refractory prostate cancer, but their efficacy has not yet been demonstrated.

Treatment of hormone-refractory prostate cancer

Objective. An increasing number of patients with prostate cancer develop hormone-refractory disease after standard treatment modalities. In these patients, early clinical trials with chemotherapy produced disappointing response rates. However, clinical trials that employ response criteria such as prostate-specific antigen (PSA) and clinical benefit response have produced encouraging responses. This article reviews current and future treatment options for the management of hormone-refractory prostate cancer.

Data Sources. A MEDLINE search for the years 1978 to 1998 was completed. The following terms were used in our search: prostate cancer, hormone-refractory, treatment, and chemotherapy. Relevant articles referenced in the literature obtained in our MEDLINE search were reviewed.

Study Selection. Randomized and nonrandomized clinical trials were used in our review. Clinical trials using prostate-specific antigen or a palliation of symptoms as primary criteria for response were given priority.

Data Synthesis. Several genetic alterations, including the overexpression of bcl-2 or mutations in p53, may lead to the development of hormone-refractory prostate cancer. Agents such as estramustine and taxanes, which affect microtubule function and potentially modulate bcl-2, appear to be particularly active in the treatment of hormone-refractory prostate cancer. In addition, mitoxantrone as well as other agents has been shown to be beneficial in improving the quality of life in patients with hormone-refractory prostate cancer.

Conclusion. Hormone-refractory prostate cancer is not a chemotherapy-resistant disease as once believed; significant progress in the treatment of hormone-refractory prostate cancer has been made with new combinations of chemotherapy agents. Promising new treatments are currently under evaluation to assess their potential benefit over the standard treatment modalities that are currently available.

Inhibition of autophagy promotes apoptosis and enhances anticancer efficacy of adriamycin via augmented ROS generation in prostate cancer cells

The interplay between autophagy and apoptosis response to chemotherapy is still a subject of intense debate in recent years. More efforts have focused on the regulation effects of apoptosis on autophagy, whereas how autophagy affects apoptosis remains poorly understood. In this study performed on prostate cancer cells, we investigated the role of autophagy in adriamycin-induced apoptosis, as well as the mechanisms mediating the effects of autophagy on apoptosis response to adriamycin (ADM). The results show that ADM not only inhibited cell viability and enhanced apoptosis, but also promoted autophagy via PI3K/Akt(T308)/mTOR signal pathway. Inhibition of autophagy by either pharmacological inhibitor chloroquine (CQ) or RNA interference of Atg5 increased ADM-induced apoptosis and enhanced the chemosensitivity of prostate cancer cells. Moreover, blockade of autophagy augmented reactive oxygen species (ROS) generation induced by ADM. Scavenging of ROS by antioxidant N-acetyl-cysteine (NAC) reversed the strengthened effects of CQ on ADM-induced apoptosis and rescued the cells from apoptosis. The results identified ROS as a potential mediator directing the modulation effects of the protective autophagy on apoptosis response to ADM. Suppression of the protective autophagy might provide a promising strategy to increase the anticancer efficacy of agents in the treatment of prostate cancer.

Interferon alpha plus 13-cis-retinoic acid modulation of BCL-2 plus paclitaxel for recurrent small-cell lung cancer (SCLC): an Eastern Cooperative Oncology Group study (E6501)

BACKGROUND

Patients with recurrent small-cell lung cancer (SCLC) have dismal outcomes. The failure of salvage therapy is due to the possible development of resistance mechanisms, such as the upregulation of the anti-apoptosis protein, Bcl-2. We conducted a phase II study to evaluate if modulation of Bcl-2 with 13-cis-retinoic acid (13-CRA) and interferon alpha could improve response rates when combined with paclitaxel in patients with recurrent SCLC.

METHODS

Patients with recurrent SCLC and measurable disease were treated with interferon alpha at 6 million units/m² subcutaneously and 13-CRA 1 mg/kg orally on days 1 and 2 and paclitaxel 75 mg/m² intravenously on day 2 of each week for 6 weeks of an 8-week treatment cycle. Treatment was continued until disease progression, development of unacceptable toxicity, or withdrawal of consent. The primary endpoint was response rate with secondary endpoints of progression-free survival (PFS) and overall survival (OS). Bcl-2 levels were assessed in peripheral blood mononuclear cells (PBMCs).

RESULTS

Thirty-seven patients were enrolled; 34 were included in the intention-to-treat analysis as 3 patients were ineligible for the study. There were 3 partial responses (9 %), and 5 patients had stable disease (15 %) as best response. The median PFS was 2 months, and median OS was 6.2 months. Although mean Bcl-2 protein levels decreased with therapy in PBMCs, there was no association between Bcl-2 levels and response rate or survival.

CONCLUSION

Despite sound pre-clinical evidence, the addition of 13-CRA and interferon alpha to paclitaxel did not improve outcomes for recurrent SCLC.

A novel epoxypropoxy flavonoid derivative and topoisomerase II inhibitor, MHY336, induces apoptosis in prostate cancer cells

Here, we reported the synthesis of a novel topoisomerase II inhibitor, MHY336, which that has strong topoisomerase-mediated anticancer activity but fewer side effects than other topoisomerase II inhibitors. The catalytic activity of MHY336 on the topoisomerase II enzyme was the same as that of the etoposide. In a cell-free system, MHY336 exhibited a potent activity on scavenging of reactive oxygen species against 3-morpholinosydnonimine hydrochloride (SIN-1)-induced oxidative stress. An in vitro cell-based assay demonstrated that MHY336 significantly inhibited the proliferation of three prostate cancer cell lines, LNCaP, PC-3, and DU145 cells. Notably, the cytotoxicity of MHY336 was more potent in LNCaP cells (IC(50)=1.39 μM) than in DU145 (IC(50)=2.94 μM) and PC3 cells (IC(50)=3.72 μM). Furthermore, MHY336 treatment induced similar levels of cytotoxicity compared to doxorubicin treatment (IC(50)=1.55 μM) in LNCap cells. Also, MHY336 significantly down-regulated topoisomerase II alpha expression and up-regulated p53 expression in LNCaP cells (wild-type p53), whereas it up-regulated the topoisomerase II alpha protein in both DU145 and PC3 cells (p53 mutated or deleted). MHY336 induced G2/M or S phase arrest in LNCaP cells through a well-documented topoisomerase II-dependent mechanism. Further studies using Annexin V-FITC binding assay, DAPI staining, and Western blot analyses illustrated that MHY336 markedly induced apoptotic cell death via the mitochondria-mediated intrinsic pathway in LNCaP cells. These results suggest that MHY336 is an attractive chemotherapeutic agent because of its topoisomerase II-mediated anti-tumour activity in human prostate cancer.

Combination of 2-methoxyestradiol (2-ME2) and eugenol for apoptosis induction synergistically in androgen independent prostate cancer cells

Lack of effective treatment options for the management of hormone refractory prostate cancer (PCA) reinforce the great need to develop novel compounds that act singly or in combination. 2-Methoxyestradiol (2-ME(2)) is an endogenous estrogenic metabolite that has been reported to work as an antiproliferative agent in various tumor models including prostate. Recently conducted clinical trial in hormone refractory prostate cancer (HRPC) patients concluded that 2-ME(2) was safe and well tolerated. However this study identified bioavailability of 2-ME(2) as a limiting factor. Here we report the ability of a combination of 2-ME(2) and eugenol (4-allyl-2-methoxyphenol) as an approach for enhancing anticancerous activities in prostate cancer cells. Combining 2-ME(2) with eugenol (i) inhibited growth of prostate cancer cells and induced apoptosis at lower concentrations than either single agent alone; (ii) analysis of the data using combination index (CI) showed CI values of 0.4 indicating strong synergistic interaction; (iii) increased population of cells G(2)/M phase by 4.5-fold (p=0.01); (iv) significantly reduced expression of antiapoptotic protein Bcl-2 and enhanced expression of proapoptotic protein Bax. Combination induced apoptosis was not affected in PC-3 cells that over-express or lack Bcl-2 but was associated with loss of mitochondrial membrane potential. Since 2-ME(2) was well tolerated in phase II trail in patients with HRPC; and eugenol is consumed by humans in the form of spices, the combination of 2-ME(2) with eugenol may offer a new clinically relevant treatment regimen. Combining these agents may allow ameliorating any adverse effects of either 2-ME(2) or eugenol alone by reducing their individual concentrations should these two agents be developed for human use.

The role of doxorubicin and epirubicin in the treatment of patients with metastatic hormone-refractory prostate cancer

Advanced hormone-refractory prostate cancer (HRPC) is characterized by prevalently osteoblastic bone metastases which are what mostly affect these patients' quality of life and make the assessment of response to treatment particularly difficult by commonly used criteria. HRPC cannot be cured by any available therapeutic option, and chemotherapy has to be still considered as a palliative treatment. The anthracyclines doxorubicin (Dox) and epirubicin (Epi), alone or in combination with other agents, have been extensively used in the treatment of HRPC, but controversial results have been reported. The majority of reviewed studies reported a pain reduction in >50% of patients receiving Dox or Epi, suggesting a substantial palliative effect by their use in metastatic HRPC. The weekly schedule of anthracyclines seemed to achieve similar results to the 3-weekly schedule but with a better toxicity profile. Although the toxic adverse effects were usually manageable when anthracyclines were combined with other agents, toxicity was severe by a number of aggressive regimens. Docetaxel is today approved for the treatment of HRPC, and must be considered the standard platform on which new agents may be combined. Given that HRPC includes a heterogeneous group of patients with variable rates of tumour growth, the combination of docetaxel with active agents such as anthracyclines may deserve further clinical investigation.

Oblimersen combined with docetaxel, adriamycin and cyclophosphamide as neo-adjuvant systemic treatment in primary breast cancer: final results of a multicentric phase I study

BACKGROUND

Combining the Bcl-2 down-regulator oblimersen with cytotoxic treatment leads to synergistic antitumor effects in preclinical trials. This multicentric phase I study was carried out to evaluate maximum tolerated dose (MTD), safety and preliminary efficacy of oblimersen in combination with docetaxel, adriamycin and cyclophosphamide as neo-adjuvant systemic treatment (NST) in primary breast cancer (PBC).

METHODS

Previously untreated patients with PBC T2-4a-c N0-3 M0 received one cycle of docetaxel 75 mg/m(2), adriamycin 50 mg/m(2) and cyclophosphamide 500 mg/m(2) administered on day 5 combined with escalating doses of oblimersen as a 24-h continuous infusion on days 1-7 followed by five cycles of combination of docetaxel, adriamycin and cyclophosphamide (TAC) without oblimersen every 3 weeks. Prophylactic antibiotic therapy and granulocyte colony-stimulating factor administration were used in all six cycles. Blood serum samples were taken throughout the treatment period for pharmacokinetic analysis.

RESULTS

Twenty-eight patients were enrolled (median age, 50 years; ductal-invasive histology, 68%; tumorsize 2-5 cm, 61%; grade 3, 43%; hormone receptor negative, 36%; Her2 positive 18%) and received oblimersen in a dose of 3 mg/kg/day (cohort I, nine patients), 5 mg/kg/day (cohort II, nine patients) and 7 mg/kg/day (cohort III, 10 patients) respectively. No dose-limiting toxicity occurred. Following oblimersen combined with TAC, the most severe toxicity was neutropenia [National Cancer Institute-Common Toxicity Criteria (NCI-CTC) grades 1-2/3/4] which developed in 0/0/56% of patients (cohort I), 11/0/56% of patients (cohort II) and 20/20/50% of patients (cohort III). No febrile neutropenia occurred. Most common adverse events (all NCI-CTC grade < or = 2) were fatigue, nausea, alopecia, headache and flue-like symptoms observed in 78% (cohort I), 89% (cohort II) and 90% (cohort III) of patients. With increasing dose of oblimersen, a higher incidence of grade IV leukopenia and neutropenia was noted. At the MTD of 7 mg/kg/day of oblimersen, serious adverse events occurred in 40% of the patients.

CONCLUSION

Oblimersen up to a dose of 7 mg/kg/day administered as a 24-h infusion on days 1-7 can be safely administered in combination with standard TAC on day 5 as NST in patients with PBC. The safety and preliminary efficacy warrants further evaluation of oblimersen in combination with every cycle of the TAC regimen in a randomized trial.

Eradication of therapy-resistant human prostate tumors using a cancer terminator virus

Terminal prostate cancer is refractory to conventional anticancer treatments because of frequent overexpression of antiapoptotic proteins Bcl-2 and/or Bcl-x(L). Adenovirus-mediated delivery of melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24), a secreted cytokine having cancer-selective apoptosis-inducing properties, profoundly inhibits prostate cancer cell growth. However, forced overexpression of Bcl-2 or Bcl-x(L) renders prostate cancer cells resistant to Ad.mda-7. We constructed a conditionally replication-competent adenovirus in which expression of the adenoviral E1A gene, necessary for replication, is driven by the cancer-specific promoter of progression elevated gene-3 (PEG-3) and which simultaneously expresses mda-7/IL-24 in the E3 region of the adenovirus (Ad.PEG-E1A-mda-7), a cancer terminator virus (CTV). This CTV generates large quantities of MDA-7/IL-24 as a function of adenovirus replication uniquely in cancer cells. Infection of Ad.PEG-E1A-mda-7 (CTV) in normal prostate epithelial cells and parental and Bcl-2- or Bcl-x(L)-overexpressing prostate cancer cells confirmed cancer cell-selective adenoviral replication, mda-7/IL-24 expression, growth inhibition, and apoptosis induction. Injecting Ad.PEG-E1A-mda-7 (CTV) into xenografts derived from DU-145-Bcl-x(L) cells in athymic nude mice completely eradicated not only primary tumors but also distant tumors (established in the opposite flank), thereby implementing a cure. These provocative findings advocate potential therapeutic applications of this novel virus for advanced prostate cancer patients with metastatic disease.

Future directions in the treatment of androgen-independent prostate cancer

The rationale for evaluating the taxanes in hormone-refractory prostate cancer (HRPC) is strong. Preclinical data demonstrate that docetaxel is a potent inhibitor of bcl-2, an antiapoptotic gene implicated in the progression of HRPC and the development of chemotherapy resistance. The results of early clinical trials with docetaxel suggested that it could improve survival; trials in which docetaxel was combined with estramustine appeared even more promising. The Southwest Oncology Group intergroup trial (SWOG 9916) phase III was developed to compare the combination of docetaxel and estramustine to mitoxantrone-prednisone in men with HRPC. A total of 684 eligible patients were enrolled. Median survival was significantly improved with docetaxel-estramustine (17.5 months vs 15.6 months with mitoxantrone-prednisone, P = .02), and the relative risk of death was reduced by 20%. Progression-free survival was improved from 3.2 months with mitoxantrone-prednisone to 6.3 months with docetaxel-estramustine (P < .001). Significantly more patients treated with docetaxel-estramustine had a prostate-specific antigen response decline of at least 50% compared with those treated with mitoxantrone-prednisone (50% vs 27%, P < .001). Toxicity was more common in the docetaxel-estramustine arm, likely due to estramustine. Other docetaxel-based regimens under investigation include combinations with calcitriol, thalidomide, or bevacizumab. With docetaxel/prednisone approved by the US Food and Drug Administration (FDA) as first-line treatment of HRPC, ongoing and future trials will build on its success by evaluating a number of docetaxel-based combinations in various prostate cancer settings. Other novel agents, including the oral platinum analog satraplatin, are being investigated as second-line treatment for HRPC.

A phase I trial of a Bcl-2 antisense (G3139) and weekly docetaxel in patients with advanced breast cancer and other solid tumors

PURPOSE

Expression of the Bcl-2 protein confers resistance to various apoptotic signals. G3139 [oblimersen sodium (Genasense)] is a phosphorothioate antisense oligodeoxynucleotide that targets Bcl-2 mRNA, downregulates Bcl-2 protein translation, and enhances the antitumor effects of subtherapeutic doses of docetaxel (Taxotere).

PATIENTS AND METHODS

We performed a phase I trial to determine the maximum tolerated dose (MTD) and safety profile of combined therapy with G3139 and weekly docetaxel in patients with advanced Bcl-2-positive solid tumors. Cohorts of three to six patients were enrolled to escalating doses of G3139 and a fixed dose of weekly docetaxel using either of two schedules. In part I, G3139 was administered by continuous infusion for 21 days (D1-22), and docetaxel (35 mg/m2) was given weekly on days 8, 15 and 22. In part II, G3139 was given by continuous infusion for 5 days before the first weekly dose of docetaxel, and for 48 h before the second and third weekly docetaxel doses. For both schedules, cycles were repeated every 4 weeks.

RESULTS

Twenty-two patients were enrolled. Thirteen patients were treated on the part I schedule with doses of G3139 escalated from 1 to 4 mg/kg/day. Nine patients were on the part II schedule of shorter G3139 infusion at G3139 doses of 5-9 mg/kg/day. Hematologic toxicities were mild, except for one case of persistent grade 3 thrombocytopenia in part I. The most common adverse events were cumulative fatigue and transaminase elevation, which prevented further dose escalation beyond 4 mg/kg/day for 21 days with the part I schedule. In part II of the study, using the abbreviated G3139 schedule, even the highest daily doses were tolerated without dose-limiting toxicity or the need for dose modification. Objective tumor response was observed in two patients with breast cancer, including one whose cancer previously progressed on trastuzumab plus paclitaxel. Four patients had stable disease. Pharmacokinetic results for G3139 were similar to those of other trials.

CONCLUSIONS

G3139 in combination with standard-dose weekly docetaxel was well tolerated. The shortened and intermittent G3139 infusion had less cumulative toxicities and still allowed similar total G3139 delivery as the longer infusion. Further studies should examine the molecular effect of the regimen, as well as clinical activities in malignancies for which taxanes are indicated.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

Bcl-2 and Bcl-x(L) differentially protect human prostate cancer cells from induction of apoptosis by melanoma differentiation associated gene-7, mda-7/IL-24

Subtraction hybridization identified melanoma differentiation associated gene-7, mda-7, in the context of terminally differentiated human melanoma cells. Based on its structure, cytokine-like properties and proposed mode of action, mda-7 has now been classified as IL-24. When expressed by means of a replication-incompetent adenovirus, Ad.mda-7 induces apoptosis in a broad range of cancer cells, without inducing harmful effects in normal fibroblast or epithelial cells. These unique properties of mda-7/IL-24 suggest that this gene will prove beneficial for cancer gene therapy. We now demonstrate that Ad.mda-7 decreases viability by induction of apoptosis in hormone-responsive (LNCaP) and hormone-independent (DU-145 and PC-3) human prostate carcinomas, without altering growth or survival in early-passage normal human prostate epithelial cells (HuPEC). Ad.mda-7 causes G(2)/M arrest and apoptosis in LNCaP (p53-wildtype), DU-145 (p53 mutant, Bax-negative) and PC-3 (p53-negative) prostate carcinomas, but not in HuPEC. Apoptosis induction correlated with changes in the ratio of pro- to antiapoptotic Bcl-2 protein family members. A potential functional role for changes in bcl-2 family gene expression in Ad.mda-7-induced apoptosis was suggested by the finding that forced overexpression of bcl-x(L) or bcl-2 differentially diminished the apoptotic effect of Ad.mda-7 in prostate carcinomas. These results confirm that induction of apoptosis by the mda-7/IL-24 gene in prostate cancer cells is Bax- and p53-independent and is mediated by mitochondrial pathways involving bcl-2 family gene members. The mda-7/IL-24 gene represents a new class of cancer-specific apoptosis-inducing genes with obvious potential for the targeted gene-based therapy of human prostate cancer.

State-of-the-art treatment of metastatic hormone-refractory prostate cancer

Initial therapy for advanced prostate cancer includes androgen ablation by surgical or medical castration. Still, nearly all men with metastases will progress to hormone-refractory prostate cancer (HRPC). Current U.S. Food and Drug Administration-approved agents for the treatment of HRPC include mitoxantrone and estramustine, although the vinca alkaloids and the taxanes have shown promising activity in single-agent phase II trials. Combinations of these agents induce a biochemical response in greater than 50% of patients, but the median duration of response is approximately 6 months. Overall survival of patients treated with these combinations is approximately 18-24 months. Studies are ongoing to develop novel therapies that target specific molecular pathways or mechanisms of chemotherapy resistance. Novel agents under development include growth factor receptor inhibitors, antisense oligonucleotides, bisphosphonates, and cell differentiating agents. Evaluation and incorporation of these agents into existing treatment regimens will guide us in the development of more active regimens in the treatment of HRPC.

Suramin-induced neuropathy in an animal model

Suramin is being used either alone, or in combination with other chemotherapeutic agents, in the treatment of hormone-refractory or metastatic prostate cancer. Use of this potentially valuable chemotherapy is limited by a dose-dependent polyneuropathy. It has been difficult in human studies to characterize peripheral suramin toxicity separately from cancer-related neuropathy. To characterize suramin-induced neuropathy in a rat model, adult rats were given either a single dose of 500 mg/kg (high dose) or 50 mg/kg (low dose) weekly suramin for 2 months. Electrophysiology and peroneal/sural nerve morphometry were performed. In high dose animals, neuropathy developed within 2 weeks, most severe in the digital sensory responses (DSR) (p<0.05) and tail and hind limb compound muscle action potential (p<0.001). Histologically, there was evidence of axonal degeneration and axon atrophy. With low dose suramin, the DSR (p<0.05) and tail distal sensory and motor responses (p<0.01) were most severely affected at 2 months. Axonal degeneration was seen in teased fibers from most animals. With TEM, there were abundant characteristic lysosomal inclusion bodies in DRG and Schwann cells. Electrophysiological and histological evidence of peripheral demyelination was rare, being observed in only one animal. Suramin induced a length, dose and time-dependent axonal sensorimotor polyneuropathy associated with axonal degeneration, atrophy, and accumulation of glycolipid lysosomal inclusions.

PTEN induces chemosensitivity in PTEN-mutated prostate cancer cells by suppression of Bcl-2 expression

The tumor suppressor gene PTEN (MMAC1/TEP1) is lost frequently in advanced prostate cancer (PCa). However, the function of PTEN in tumorigenesis is not understood fully. In this study, we demonstrate that expression of Bcl-2 in prostate tumors correlates with loss of the PTEN protein. This finding was verified by studies in the PCa cell lines DU145, PC-3, LNCaP, and an androgen-refractory subline of LNCaP. Transient transfection of PTEN into the PTEN-null cells resulted in decreased levels of Bcl-2 mRNA and protein. These effects appear to be mediated at the level of gene transcription, since a Bcl-2 promoter-reporter construct was down-regulated by ectopic expression of PTEN in LNCaP cells. The inhibition of Bcl-2 required the lipid-phosphatase activity of PTEN and was blocked by overexpression of a constitutively active form of Akt. Moreover, the transcription-regulatory protein cAMP-response element-binding protein (CREB) may be involved, since decreased phosphorylation of CREB at Ser(133) was detected following PTEN expression, and ectopic expression of CREB repressed completely the PTEN-induced inhibition of Bcl-2 promoter activity. Furthermore, cotransfection of Bcl-2 and PTEN expression vectors rescued PTEN-induced cell death but not G(1) cell cycle arrest. Finally, forced expression of PTEN sensitized LNCaP cells to cell death induced by staurosporine, doxorubicin, and vincristine, and this chemosensitivity was attenuated by exogenous expression of Bcl-2. Taken together, these data demonstrate that loss of PTEN leads to up-regulation of the bcl-2 gene, thus contributing to survival and chemoresistance of PCa cells. These findings suggest that the PTEN gene and its regulated pathway are potential therapeutic targets in prostate cancer.

Mitoxantrone in patients with prostate specific antigen progression after local therapy for prostate carcinoma

BACKGROUND

Molecular mechanisms of chemotherapy resistance are present in prostate carcinoma, some of which increase after androgen ablation (AA) therapy. Therefore, the authors hypothesized that chemotherapy in patients with prostate specific antigen (PSA) progression after local therapy, before androgen ablation therapy, will have greater antitumor activity.

METHODS

Twenty-three hormone-naive patients with PSA progression after prostatectomy or radiation therapy were registered in this study. Twenty-two were treated with 10 mg/m(2) of mitoxantrone initially, followed by 12 mg/m(2) every 3 weeks for a maximum of 8 cycles. Prostatectomy specimens were assessed, when possible, for topoisomerase II alpha, multidrug resistance protein MRP, and bcl-2 by immunohistochemistry.

RESULTS

Twenty-two patients received a total of 131 cycles of therapy. Three patients had transient Grade 3 or 4 neutropenia without fever. During treatment, 10 of 22 patients showed a decrease in PSA, without an associated decrease in testosterone. In this group of 10 patients, the mean PSA decrease was 29% at 3 months and 43% at 6 months. Overall, 4 of 22 patients had a decrease in PSA of greater than or equal to 50%. The PSA decreased in three of seven patients whose cancer overexpressed MRP and in three of seven patients who overexpressed bcl-2. No patient with overexpression of topoisomerase II alpha (n = 4) had a decrease in PSA during the study.

CONCLUSIONS

To the authors' knowledge, this is the first reported study of mitoxantrone in patients with hormone-naive prostate carcinoma and PSA progression after local therapy; mitoxantrone was safe and biochemically active, similar to prior studies in hormone refractory prostate carcinoma, suggesting that critical molecular mechanisms of chemotherapy resistance are present independent of AA. Further studies are warranted to determine whether pharmacogenomic assessment of topoisomerase II, MRP, or bcl-2 may predict for response to mitoxantrone.

BCL2 antisense transcripts decrease intracellular Bcl2 expression and sensitize LNCaP prostate cancer cells to apoptosis-inducing agents

Prostate cancer (CaP) is the most commonly diagnosed cancer of aging men and the second leading cause of male cancer death in the United States. At present, no effective therapy is available for treating hormone independent CaP. Since Bcl2 is believed to play a role in protecting CaP cells from apoptosis, we investigated the effects of down-regulating Bcl2 expression on CaP cells. Genetically engineered LNCaP sublines were established by stably transfecting LNCaP cells with BCL2 antisense (BCL2-AS) transcript-expressing plasmids. Western blotting analysis showed that intracellular Bcl2 protein was decreased by 50-60% in BCL2-AS-transfected LNCaP cells. Expression of the antisense transcripts resulted in 50% growth inhibition of LNCaP cells in response to androgen withdrawal and markedly sensitized these cells to Adriamycin-induced apoptosis. These results suggest that down-regulation of Bcl2 protein using BCL2-AS transcripts could be exploited for improved treatment of advanced CaP.

Targeting apoptosis in prostate cancer

The understanding of apoptotic pathways provides new insights into cancer therapy. Therapies that modulate these pathways may induce apoptosis or sensitize tumor cells to other agents. Because many of the components of these pathways are altered in tumor cells compared with normal cells, therapies that target these abnormal apoptotic proteins may be more selective than traditional cytotoxic agents. Difficulties include the translation of the knowledge of these pathways into clinical trials and monitoring the predicted biologic effects in patients. The continued study of new targets, agents capable of modulating these targets, and markers of biologic effect in patients should improve clinical results.

Targeting ceramide metabolism--a strategy for overcoming drug resistance

Inherent or acquired drug resistance, which frequently characterizes cancer cells, is caused by multiple mechanisms, including dysfunctional metabolism of the lipid second messenger ceramide. Ceramide, the basic structural unit of the sphingolipids, plays a role in activating cell death signals initiated by cytokines, chemotherapeutic agents, and ionizing radiation. Recent discoveries about the metabolism of ceramide suggest that this agent may have an important influence on the effectiveness of various cancer therapeutics. In particular, the cytotoxic effect of chemotherapy is decreased when generation of ceramide is impaired but is increased when the degradation of ceramide is blocked. Herein, we review the mechanisms of resistance to chemotherapeutic agents in terms of ceramide metabolism.

Chemotherapy for advanced hormone refractory prostate cancer

Men with metastatic prostate cancer treated with androgen ablation respond rapidly and often dramatically to therapy, with improvement of bone pain, regression of soft tissue metastases, and declines in serum prostate-specific antigen (PSA). Unfortunately, few treatment options are available to men who progress after hormone therapy. Recent studies in the mechanism of anticancer drug action have focused on the proteins that regulate apoptosis or programmed cell death as a target for the treatment of hormone-resistant prostate cancer. New treatments are now being designed with both resistance and apoptotic pathways in mind. US Food and Drug Administration (FDA) approval of the combination of mitoxantrone and prednisone for the palliation of bone pain in men with hormone refractory prostate cancer demonstrates that chemotherapy can be effective. Two randomized trials have demonstrated the superiority of mitoxantrone combined with a corticosteroid over corticosteroid therapy in alleviating bone pain. The combination of estramustine with vinblastine, or VP-16, is commonly used in clinical practice with both regimens demonstrating significant PSA declines. When estramustine is combined with either paclitaxel or docetaxel in vitro, greater than additive in vitro cytotoxicity is noted. Phase I and II studies of taxane-based therapy in hormone refractory prostate cancer demonstrate improved survival when compared with historical controls, but phase III studies are necessary to confirm these preliminary observations.

Suramin in combination with weekly epirubicin for patients with advanced hormone-refractory prostate carcinoma

BACKGROUND

Suramin and epirubicin are both active agents in the treatment of patients with hormone-refractory advanced prostate carcinoma, with demonstrated antitumor synergism in vitro on human prostate carcinoma cells and different dose-limiting toxicities. The authors conducted this Phase II study to determine the feasibility, toxicity, and antitumor activity of suramin in combination with epirubicin.

METHODS

Only patients with hormone-independent advanced prostate carcinoma who had progressive disease after the last therapeutic maneuver they had undergone, including antiandrogen withdrawal, entered the study. Suramin was administered initially as a 6-day continuous infusion for 10 consecutive weeks and then for 6 days every 28 days for a maximum of 6 months. Doses were determined by a computer-assisted dosing system that used Bayesian pharmacokinetics to maintain suramin plasma concentrations of 200-250 microg/mL. Cortisone acetate 25 mg, administered at 8 a.m. and 8 p.m. daily, was begun 4 weeks after the initiation of suramin therapy. Epirubicin 25 mg/m2 was given as a weekly intravenous bolus beginning on Day 1 and was continued for a maximum of 6 months.

RESULTS

Twenty-six patients entered the study. Toxicities mainly included World Health Organization Grade 1-2 nausea, fatigue, anorexia, neutropenia, peripheral neuropathy, creatinine elevation, proteinuria, and prolonged prothrombin time, whereas Grade 3 toxicities were uncommon. Among 11 patients with measurable disease, 3 (27%) demonstrated an objective response. Among 24 patients evaluated for prostate specific antigen (PSA) response, 8 (33%; 95% confidence interval 16-55%) had a > or =50% decrease in PSA levels, which lasted a median of 32 (range, 8-52) weeks. Median progression free and overall survival were both 8 months.

CONCLUSIONS

The combination of suramin and epirubicin used in the current study is feasible, is associated with moderate toxicities, and has antitumor activity in advanced hormone-refractory prostate carcinoma. However, the results obtained with this combination do not represent major improvements in the treatment of patients with this disease, compared with suramin or epirubicin alone or other available treatments.

Phase I clinical and pharmacologic study of 13-cis-retinoic acid, interferon alfa, and paclitaxel in patients with prostate cancer and other advanced malignancies

PURPOSE

Recent studies demonstrate that retinoids decrease expression of the anti-apoptotic protein bcl-2, enhance the effect of chemotherapy, and act synergistically with interferon alfa (IFNalpha) to inhibit tumor cell growth in vitro. A phase I trial of 13-cis-retinoic acid (CRA), IFNalpha, and paclitaxel (TAX) was conducted to determine the toxicity and recommended phase II dose of this combination. Pharmacodynamic studies were performed to determine whether CRA and IFNalpha could modulate bcl-2 expression in vitro and in patients.

PATIENTS AND METHODS

Twenty-two patients with prostate cancer or other advanced malignancies were treated with CRA/IFNalpha and escalating doses of TAX. The effect of CRA/IFNalpha on TAX pharmacokinetics was analyzed in both patients and human liver microsomes. The effect of CRA/IFNalpha on bcl-2 expression was assessed in vitro and in peripheral-blood mononuclear cells (PBMCs) by immunoblotting.

RESULTS

CRA 1 mg/kg on days 1 to 4, IFNalpha 6 MU/m(2) subcutaneously on days 1 to 4, and TAX 175 mg/m(2) on day 3 was well tolerated. Pharmacokinetic studies demonstrated that CRA/IFNalpha caused a 33% decrease in TAX clearance and a 23% decrease in the area under the concentration-time curve values of the TAX metabolite 6-alfa-hydroxytaxol (6-HT). CRA alone reduced conversion of TAX to 6-HT by 41% in human liver microsomes. CRA/IFNalpha decreased bcl-2 expression in vitro and in PBMCs.

CONCLUSION

CRA/IFNalpha and TAX is a well-tolerated regimen. CRA/IFNalpha increases TAX area under the concentration-time curve through an inhibitory effect of CRA on the metabolism of TAX to 6-HT. CRA/IFNalpha can modulate bcl-2 expression in vitro and demonstrates similar biologic activity in patients. Further studies will determine the activity of CRA/IFNalpha/TAX and validate the assessment of bcl-2 in PBMCs as a marker of tumor response.

Activation of Rb and decline in androgen receptor protein precede retinoic acid-induced apoptosis in androgen-dependent LNCaP cells and their androgen-independent derivative

Androgen ablation-induced prostate cancer regression is transient and ends with the regrowth of androgen-independent (AI) tumors. To mimic this evolution in culture, we chronically deprived an androgen-dependent (AD) prostate cancer cell line (LNCaP) of androgen, generating an AI derivative which retained limited hormone proliferative responsiveness and a barely detectable prostate-specific antigen (PSA) mRNA level. While the cytokeratin 8 (CK8) level was low, the androgen receptor (AR) protein in AI cells was on average tenfold greater than in AD cells. When challenged for susceptibility to undergo apoptosis, the AI cells were more resistant than AD cells to all-trans retinoic acid (tRA) and two chemotherapeutic agents, Taxol and Adriamycin, requiring higher doses and longer periods of treatment to achieve similar effects. Compared to AD cells, the partially apoptosis-resistant AI cells expressed four times more Bcl-2 protein and undetectable levels of p21/WAF1. Induction of apoptosis by tRA in both cell types did not affect their expression but was preceded by the activation of Rb and a pronounced reduction of AR protein level. The kinetics of the Rb activation and AR downmodulation in both cell types matched their tRA sensitivity, suggesting that these events may be required for tRA-induced apoptosis. The results show that the apoptotic pathway in AI cells, although more difficult to induce, is not irrevocably lost and that targeted reduction of the AR protein level with retinoids in combination with androgen ablation therapy may prolong remissions in advanced prostate cancer patients.

Role of ceramide in suramin-induced cancer cell death

Suramin is an experimental antineoplastic agent which is currently being tested in clinical trials for its utility in treating breast and prostate cancer. Recent in vitro studies from our laboratory report a disruption in glycolipid metabolism and cell death in suramin-treated neurons. Evidence presented in this study proposes to consolidate the neurotoxic and cytotoxic effects of suramin. Electron microscopic studies, bis-benzimide staining and DNA gel electrophoresis of suramin and C2-ceramide treatment revealed apoptotic cells in human breast, prostate and rat neuron like cell lines. Apoptotic cell death was preceded by an elevation in intracellular ceramide.

Regulation of lipid signaling pathways for cell survival and apoptosis by bcl-2 in prostate carcinoma cells

Compelling evidence indicates that activation of the JNK/SAPK signaling pathway is obligatory for apoptosis induction by multiple cell stresses that activate the sphingomyelin cycle. Moreover, ectopic expression of bcl-2 can impair apoptosis signaling by most of the cell stresses that activate the ceramide/JNK pathway. Here we show that enforced expression of bcl-2 protects prostate carcinoma cells against the induction of apoptosis by exogenous C2-ceramide. Moreover, enforced bcl-2 expression blocked the capacity of C2-ceramide to activate JNK1, indicating bcl-2 functions at the level of JNK1 or upstream of JNK1 in the ceramide/JNK pathway. The contribution of bcl2 to the regulation of the arachidonate pathway for prostate carcinoma cell survival was also investigated using highly selective inhibitors of arachidonate metabolism. Our results indicate bcl-2 can protect cells against diminished availability of arachidonic acid, 12-HETE, and 15-HETE. Finally, arachidonic acid substantially suppresses the induction of apoptosis by C2-ceramide, providing evidence for the opposing influences of these lipid signaling pathways in the mediation of prostate carcinoma cell survival. These results provide evidence for opposing influences of the ceramide and arachidonate signaling pathways in the mediation of cell death and cell survival, respectively, in prostate carcinoma cells and suggest a dual role for bcl-2 in this context.

Suramin/epidoxorubicin association in hormone-refractory prostate cancer: preliminary results of a pilot phase II study

PURPOSE

Previous studies indicate that suramin may be an active agent for treating hormone-refractory prostate cancer. However, antitumour responses were observed in initial experiments only when plasma suramin concentrations were maintained in excess of 250 micrograms/ml. Dose-limiting toxicity, especially neurological toxicity, is directly related to the duration of exposure and sustained plasma drug concentrations of 300 micrograms/ml or more. Combination with other agents such as epidoxorubicin, a drug with demonstrable activity in metastatic prostatic carcinoma, could be more effective and allow reduced suramin doses, while maintaining the suramin antitumor effect; this could make suramin therapy more feasible. On the basis of preclinical synergistic activity for combined suramin/doxorubicin in prostate cancer cell lines, a pilot study in patients with metastatic hormone refractory prostate cancer was performed.

MATERIALS AND METHODS

Ten patients with hormone-refractory prostate cancer received a fixed dosing scheme of suramin infusion in combination with weekly epidoxorubicin at 25 mg/m2. Therapy was discontinued for dose-limiting toxicity or progressive disease.

RESULTS

None of the ten patients achieved a prostate-specific antigen reduction of more than 50% and no objective responses were observed in any patient. Dose-limiting toxicity was observed in four patients: grade 3 neurotoxicity was observed in three patients and grade 3 nephrotoxicity in one patient.

CONCLUSIONS

Suramin/epidoxorubicin association, despite the encouraging preclinical results, was not able to improve the antitumour activity of suramin and showed significant toxicity. The results achieved in our study, although in a small number of patients, seem to suggest that this regimen cannot be recommended for use in the treatment of metastatic hormone-refractory prostate cancer.