MANAGEMENT OF HORMONE REFRACTORY PROSTATE CANCER: CURRENT STANDARDS AND FUTURE PROSPECTS

Bisphosphonate induces apoptosis and inhibits pro-osteoclastic gene expression in prostate cancer cells

AIM

Bisphosphonates are well established for the management of cancer-induced skeletal complications. Recent studies suggest that bisphosphonates promote apoptosis of cancer cells as well as osteoclasts in bone metastatic sites. To determine the direct effects of bisphosphonate on prostate cancer, we examined the effects of minodronate on prostatic cancer cell growth and the expression of apoptosis-related proteins and osteoclastogenic factors.

METHODS

PC-3, DU145 and LNCaP cells were treated with amino-bisphosphonate minodronate. Then proliferation, apoptosis and expression of bcl-2, bax, poly (ADP)-ribose polymerase (PARP), caspase-3, receptor activator of nuclear factor-kappaB ligand (RANKL), osteoprotegerin (OPG), matrix metalloproteinases-2 (MMP-2), and parathyroid hormone related protein (PTHrP) were assessed.

RESULTS

The proliferation of prostatic cancer cells was inhibited by minodronate. DNA fragmentation and TUNEL-positive nuclei were observed in minodronate-treated PC-3 cells. Minodronate decreased bcl-2 expression and induced bax expression, caspase-3 activity and degradation of PARP in DU145 and PC-3 cells. Minodronate decreased expression of RANKL, PTHrP and MMP-2 in PC-3 cells.

CONCLUSIONS

Our results suggest that bisphosphonate not only promotes apoptosis directly but also decreases pro-osteoclastic gene expression in prostate cancer cells.

Antisense oligodeoxynucleotide therapy targeting clusterin gene for prostate cancer: Vancouver experience from discovery to clinic

BACKGROUND

The objective of this study was to review our experience in the development of antisense (AS) oligodeoxynucleotide (ODN) therapy for prostate cancer targeting antiapoptotic gene, clusterin.

METHODS

We initially summarized our data demonstrating that clusterin could be an optimal therapeutic target for prostate cancer, then presented the process of developing AS ODN therapy using several preclinical animal models. Finally, the preliminary data of the recently completed phase I clinical trial using AS clusterin ODN as well as the future prospects of this therapy are discussed.

RESULTS

Expression of clusterin was highly up-regulated after androgen withdrawal and during progression to androgen-independence, but low or absent in untreated tissues in both prostate cancer animal model systems and human clinical specimens. Introduction of the clusterin gene into human prostate cancer cells confers resistance to several therapeutic stimuli, including androgen ablation, chemotherapy and radiation. AS ODN targeting the translation initiation site of the clusterin gene markedly inhibited clusterin expression in prostate cancer cells in a dose-dependent and sequence-specific manner. Systemic treatment with AS clusterin ODN enhanced the effects of several conventional therapies through the effective induction of apoptosis in prostate cancer xenograft models. Based on these findings, a phase I clinical trial was completed using AS clusterin ODN incorporating 2'-O-(2-methoxy)ethyl-gapmer backbone (OGX-011), showing up to 90% suppression of clusterin in prostate cancer.

CONCLUSIONS

The data described above identified clusterin as an antiapoptotic gene up-regulated in an adaptive cell survival manner following various cell death triggers that helps confer a phenotype resistant to therapeutic stimuli. Inhibition of clusterin expression using AS ODN technology enhances apoptosis induced by several conventional treatments, resulting in the delay of AI progression and improved survival. Clinical trials using AS ODN confirm potent suppression of clusterin expression and phase II studies will begin in early 2005.

Phase I/II study of 19-nor-1alpha-25-dihydroxyvitamin D2 (paricalcitol) in advanced, androgen-insensitive prostate cancer

PURPOSE

We assessed the safety and efficacy of the vitamin D analogue, 19-nor-1alpha-25-dihydroxyvitamin D2 (paricalcitol), in patients with androgen-independent prostate cancer.

EXPERIMENTAL DESIGN

Patients received paricalcitol i.v. three times per week on an escalating dose of 5 to 25 microg (3-15 microg/m2). The primary end point was prostate-specific antigen (PSA) response. Secondary end points were characterization of toxicity in this population, changes in serum parathyroid hormone (PTH), and survival.

RESULTS

A total of 18 patients were enrolled. No patient showed a sustained 50% drop in serum PSA, despite several large declines in PSA (e.g., 1,300 ng/mL). Paricalcitol was well tolerated. One instance of significant hypercalcemia, a serum calcium of 14.3 mg/dL, was observed at the highest dose (25 microg). At entry into the study, seven (41%) of the patients had elevated serum levels of PTH, which were significantly reduced by paricalcitol. Higher levels of serum PTH at study entry were significantly and negatively associated with survival (P<0.01).

CONCLUSION

No objective responses were seen in the primary end point. However, elevated serum levels of PTH, a common feature of advanced prostate cancer, were reduced by paricalcitol. Because elevated PTH is associated with increased cardiovascular and skeletal morbidity, including an increased risk for pathologic fracture, further evaluation of paricalcitol in the reduction of skeletal morbidity in advanced prostate cancer is warranted.

Efficacy of nilutamide as secondary hormonal therapy in androgen-independent prostate cancer

OBJECTIVE

To evaluate the activity of nilutamide as secondary hormonal therapy in patients with androgen-independent prostate cancer (AIPC), as treatment options are limited for these patients and secondary hormonal therapy with antiandrogens has advantages, including low toxicity, oral administration and high patient acceptance.

PATIENTS AND METHODS

We retrospectively identified 45 patients with AIPC who were treated with nilutamide as secondary hormonal therapy in two institutions. The decrease in prostate-specific antigen (PSA) levels, side-effects of treatment, and the relationship between baseline characteristics, type and duration of previous therapy and response to nilutamide were assessed. Most patients received oral nilutamide at 150 mg/day.

RESULTS

Eighteen of 45 evaluable patients (40%) had a PSA level decrease of > or = 50%. Responders (PSA decline > or = 50%) had a median (range) time to progression of 4.4 (0.31-44.7) months. There were responses to nilutamide whether used as the second to fifth line of hormonal therapy. There were no differences in response to nilutamide based on clinical stage, type of local therapy, PSA level at diagnosis or initiation of nilutamide, or type of previous antiandrogen therapy. Responders were more likely to have received monotherapy with luteinizing hormone-releasing hormone analogues or orchidectomy as first-line hormonal treatment (P = 0.02). The most common reversible adverse effects were mild to moderate visual adaptation effects, reported in 20% of patients.

CONCLUSIONS

Nilutamide appears to be an effective secondary hormonal therapy in patients with AIPC and is associated with a mild toxicity profile.

Clinical outcome of maximum androgen blockade using flutamide as second-line hormonal therapy for hormone-refractory prostate cancer

OBJECTIVES

To investigate the efficacy of maximum androgen blockade (MAB) using flutamide as second-line hormonal therapy for advanced hormone-refractory prostate cancer (HRPC).

PATIENTS AND METHODS

The study included 55 patients with HRPC who were treated with MAB using flutamide (375 mg daily) as second-line hormonal therapy. All patients had previously received bicalutamide combined with either surgical or medical castration as first-line hormonal therapy, which failed. The effect of the second-line therapy was evaluated by serum prostate-specific antigen (PSA) level alone, and the response defined as a decrease of >50% from the baseline PSA at the start of second-line therapy.

RESULTS

On initiating second-line hormonal therapy there was a reduction in the PSA level in 25 of the 55 patients (45%), among whom 12 (22%) were regarded as responders, while the PSA level continued to increase in the remaining 30 (55%). The median (range) duration of the PSA response was 6 (1-13) months. During the observation period there were no severe side-effects from the second-line MAB therapy. Patients without bone metastases or whose disease progressed >1 year after first-line therapy had a significantly higher incidence of PSA response to second-line therapy, despite no significant effect of other factors examined on the PSA response to second-line therapy. Furthermore, the cause-specific survival in responders to second-line therapy was significantly better than that in nonresponders; however, multivariate analysis showed that no factors, including response to second-line therapy, could be used as independent predictors of cause-specific survival.

CONCLUSIONS

MAB using flutamide as second-line hormonal therapy can give a comparatively favourable PSA response with no severe side-effects; therefore, this therapy may be suitable for patients with HRPC after primary MAB using bicalutamide has failed, particularly in those with no bone metastases or whose disease has progressed for >1 year after first-line therapy.

Chemohormonal therapy as primary treatment for metastatic prostate cancer: a randomized study of estramustine phosphate plus luteinizing hormone-releasing hormone agonist versus flutamide plus luteinizing hormone-releasing hormone agonist

BACKGROUND

The present study was undertaken mainly to investigate whether chemohormonal therapy with estramustine phosphate plus luteinizing hormone-releasing hormone (LHRH) agonist has a more beneficial effect than the hormonal therapy with flutamide plus LHRH agonist for newly diagnosed patients with metastatic prostate cancer.

METHODS

A total of 57 patients with metastatic prostate cancer aged 59-80 years (median 74 years) were entered in the study and were randomized to the treatment of estramustine phosphate (560 mg/day) plus LHRH agonist (estramustine group) or flutamide (375 mg/day) plus LHRH agonist (flutamide group) with stratification for the degree of performance status, histological differentiation and bone metastasis.

RESULTS

Both of the treatment regimens were well tolerated with similar incidences of adverse drug reactions. The overall response rates (complete response plus partial response) at 12 weeks after treatment in the estramustine and flutamide groups were 76 and 55%, respectively. The median time to objective progression for the estramustine group (25.4 months) was longer than that of the flutamide group (14.6 months). The serum levels of follicle stimulating hormone and testosterone were significantly lower in the estramustine group.

CONCLUSIONS

Chemohormonal therapy with estramustine phosphate plus LHRH agonist showed longer clinical progression-free survival than the hormonal therapy with flutamide plus LHRH agonist (P = 0.03), although there was no significant difference in the overall survival. A larger-scaled trial with more statistical power is required to clarify that the former regimen is more beneficial than the latter for newly diagnosed patients with advanced prostate cancer.

Phase II study of repeated single 24-hour infusion of low-dose 5-fluorouracil for palliation in symptomatic hormone-refractory prostate cancer

BACKGROUND

To assess the efficacy and toxicity of repeated single 24-hour infusion of low-dose 5-fluorouracil for symptomatic hormone-refractory prostate cancer using relevant endpoints of palliation and biological response.

PATIENTS AND METHODS

25 patients with histologically confirmed prostatic adenocarcinoma and symptomatic progressive disease despite one or several hormonal treatments and chemotherapy were included in the study. Treatment consisted of a single 24-hour infusion of 500 mg/m(2) 5-fluorouracil (5-FU) to be repeated on day 21. This regimen was continued until either progression or serious toxicity occurred. Response was assessed by serial measurements of serum prostate-specific antigen (PSA) as well as by health-related quality-of-life instruments (EORTC QLQ-C30 and McGill-Melzack Present Pain Intensity Scale) every 3 weeks. In 10 patients with bidimensionally measurable metastases, objective responses were assessed every 3 months.

RESULTS

A mean number of four courses of repeated single 24-hour infusion of 5-FU was administered (range 2-6). Toxicity was absent or mild, and no patient had to be withdrawn from therapy. All patients required analgesics prior to treatment and only 3 patients experienced a significant reduction in pain for 9 weeks, the remaining patients experienced no deterioration for a mean duration of 12 weeks (6-18 weeks). Five patients (20%) demonstrated a biological response of a 50% or greater decrease in PSA from baseline, including 2 (12%) with a 75% or greater decline for 10 weeks (range 6-16 weeks). One partial remission was observed among 10 patients with measurable lesions lasting 12 weeks; 4 patients had stable disease with a mean duration of 12 weeks. Mean survival time from the onset of treatment with 5-FU was 7 months (2-12 months).

CONCLUSIONS

Though less toxic than other 5-FU regimens, repeated single low-dose 24-hour infusion is of no significant benefit in patients with symptomatic hormone-refractory prostate cancer.

Prostate-specific antigen levels and prognosis in patients with hormone-refractory prostate cancer treated with low-dose dexamethasone

OBJECTIVE

The efficacy of low-dose dexamethasone (DXM) therapy in patients with hormone-refractory prostate cancer (HRPC) was evaluated.

PATIENTS AND METHODS

Prostate-specific antigen (PSA) response and survival following DXM therapy were analyzed in 27 Japanese patients exhibiting HRPC. Concurrent therapies and antiandrogen withdrawal syndrome, which may affect PSA levels and palliative effects, were excluded from the study. A dose of 1.5 mg of DXM was administered, and androgen deprivation therapy was maintained during DXM therapy. A decline in PSA levels of at least 50% from baseline was considered a significant PSA response. Prognostic factors for PSA response and survival were examined by univariate and multivariate analyses.

RESULTS

A significant PSA response was observed in 16 of the 27 cases (59.3%). Median survival period of patients exhibiting significant PSA response was 15.9 months and was significantly longer than that of patients demonstrating a decline in PSA of less than 50% (median 7.7 months, p < 0.0001). Effect on pain control also correlated with the significant PSA response. No meaningful prognostic factors for PSA response were detected; however, a PSA decline of greater than 50% was the prognostic factor for survival.

CONCLUSION

DXM therapy remains one of the most beneficial treatment modalities in patients with HRPC.

Novel therapeutic strategy for advanced prostate cancer using antisense oligodeoxynucleotides targeting anti-apoptotic genes upregulated after androgen withdrawal to delay androgen-independent progression and enhance chemosensitivity

Progression to androgen-independence remains the main obstacle to improving survival for patients with advanced prostate cancer. In this review, findings are summarized that have recently been demonstrated to establish novel therapeutic strategy targeting several genes playing functionally important roles after androgen withdrawal and during androgen-independent progression. The authors initially characterized changes in gene expression after androgen withdrawal in the androgen-dependent Shionogi and LNCaP tumor models using cDNA arrays. Based on these results, they focused on genes highly upregulated after androgen ablation (i.e. bcl-2, bcl-xL, TR.PM-2, IGFBP-5), which have anti-apoptotic or mitogenic activities, and thereby confer a resistance to androgen withdrawal as well as cytotoxic chemotherapy. The authors further demonstrated the efficacy of an antisense oligodeoxynucleotide (ODN) strategy for patients with advanced prostate cancer through the inhibition of target gene expression, resulting in a delay in the progression to androgen-independence by enhancing apoptotic cell death induced by androgen ablation and chemotherapy. The authors also showed the effectiveness of combined antisense ODN therapy and cytotoxic chemotherapy by achieving additive or synergistic effects. These findings provide a basic significance for the design of clinical studies using antisense ODN either alone or in combination with chemotherapeutic agents in patients with advanced prostate cancer.

Mechanisms of drug resistance in chemotherapy for urogenital carcinoma

Cancer chemotherapy is the principal approach for urogenital cancers. However, the acquisition of resistance to anticancer agents is a critical factor that limits the successful treatment of malignancies. The multidrug resistant (MDR) phenotype has been widely recognized in cancer chemotherapy in urogenital tumors and the mechanisms underlying MDR have also been extensively studied. One of the principle mechanisms in MDR is caused by the overexpression of P-glycoprotein (P-gp), encoded by the multidrug resistance gene (MDR1). It functions as an ATP-dependent active efflux pump of chemotherapeutic agents in human cancer cells. Recently, other drug resistance proteins, including multidrug resistance-associated protein (MRP1) and cMOAT (or MRP2), were also identified from multidrug resistant cells. A functional analysis of MRP1 has shown that MRP1 may have the potential to act as a transporter of glutathione conjugates, which has been known as a central detoxification pathway in anticancer agents. Furthermore, several other resistance-related proteins (e.g. glutathione S-transferase, metallothionein, thioredoxin, topoisomerase I, II, O6-alkylguanine-DNA methyltransferase, etc.) have been found to be up- or down-regulated in resistant cells and these molecules are believed to contribute to the resistant phenotype as well. Based on the molecular characteristics identified in MDR, several experimental and clinical approaches have been studied to overcome MDR. One of these strategies is to reverse MDR by using such P-gp inhibitors as verapamil and cyclosporine A. In this review, we summarize the recent advances in MDR-related molecules and clinical trials to circumvent MDR in urogenital carcinomas.

Local and systemic therapy of human prostate adenocarcinoma with the conditionally replicating herpes simplex virus vector G207

Prostate adenocarcinoma is the most common nonskin malignancy in males and the second most common cause of cancer death in the United States (Landis et al., 1998). Initial treatments of surgery or radiotherapy may cause impotence and/or incontinence from neural damage (Eastham and Scardino, 1998; Porter et al., 1998). When extraprostatic or metastatic disease develops, castration or pharmaceutical androgen ablation is utilized (Catalona, 1994). Androgen-resistant recurrence indicates a poor prognosis and justifies experimental chemotherapy (Oh and Kantoff, 1998). G207 (Mineta et al., 1995; Yazaki et al., 1995) is a multimutated herpes simplex virus 1 (HSV) vector that replicates within cancer cells, causing cellular death; however, replication is limited in normal cells, including those of the nervous system. In vitro, G207 at a low multiplicity of infection (MOI of 0.01) is oncolytic for multiple human prostate cancer cells. In athymic mice, a single intraneoplastic inoculation of G207 completely eradicates >22% of established subcutaneous human prostate cancer tumors irrespective of hormonal responsiveness. Two intraneoplastic inoculations of G207 completely eradicated two of three recurrent previously irradiated tumors and two intravenous administration of G207 induced tumor regression in distant subcutaneous tumors and completely eradicated one-fourth of the tumors.