A peptide-doxorubicin 'prodrug' activated by prostate-specific antigen selectively kills prostate tumor cells positive for prostate-specific antigen in vivo

We covalently linked doxorubicin with a peptide that is hydrolyzable by prostate-specific antigen. In the presence of prostate tumor cells secreting prostate-specific antigen, the peptide moiety of this conjugate, L-377,202, was hydrolyzed, resulting in the release of leucine-doxorubicin and doxorubicin, which are both very cytotoxic to cancer cells. However, L-377,202 was much less cytotoxic than conventional doxorubicin to cells in culture that do not secrete prostate-specific antigen. L-377,202 was approximately 15 times more effective than was conventional doxorubicin at inhibiting the growth of human prostate cancer tumors in nude mice when both drugs were used at their maximally tolerated doses. Nude mice inoculated with human prostate tumor cells secreting prostate-specific antigen showed considerable reductions in tumor burden with minimal total body weight loss when treated with L-377, 202. This improvement in therapeutic index correlated with the selective localization of leucine-doxorubicin and free doxorubicin in tissues secreting prostate-specific antigen after exposure to L-377,202.     

Treatment options for hormone-refractory prostate cancer

Hormone-refractory prostate cancer is a disease that includes a variety of patients and represents a treatment dilemma for the practicing physician. Because of the diversity of this group, management strategies must be targeted to the clinical situations of the individual patients and their wishes. This article outlines a logical progression of treatment choices that currently exist in this rapidly evolving field, and the landmark chemotherapy trials involving docetaxel (SWOG 9916 and TAX 327) are reviewed. Although significant progress has been made in understanding and treating hormone-refractory prostate cancer, current treatments do not yet provide a cure, and important clinical trials continue to recruit patients.     

Substrate specificity of prostate-specific membrane antigen

A series of putative dipeptide substrates of prostate-specific membrane antigen (PSMA) was prepared that explored alpha- and beta/gamma-linked acidic residues at the P1 position and various chromophores at the P2 position, while keeping the P1' residue constant as L-Glu. Four chromophores were examined, including 4-phenylazobenzoyl, 1-pyrenebutyryl, 9-anthracenylcarboxyl-gamma-aminobutyryl, and 4-nitrophenylbutyryl. When evaluating these chromophores, it was found that a substrate containing 4-phenylazobenzoyl at the P2 position was consumed most efficiently. Substitution at the P1 position with acidic residues showed that only gamma-linked L-Glu and D-Glu were recognized by the enzyme, with the former being more readily proteolyzed. Lastly, binding modes of endogenous substrates and our best synthetic substrate (4-phenylazobenzoyl-Glu-gamma-Glu) were proposed by computational docking studies into an X-ray crystal structure of the PSMA extracellular domain.     

前列腺特异性抗原在前列腺癌诊断中的应用进展

已经证明,前列腺特异性抗原（PSA）是一种有价值的前列腺癌（PCa)肿瘤标记物,血清PSA的广泛使用提高了前列腺癌的检出率,使晚期癌患得明显减少。然而,PSA对PCa的检测缺乏特异性,由于其高的假阳性率,引起许多不必要的活检。为了提高PSA对PCa诊断的特异性,降低不必要的活检,众多学正在探讨与PSA相关的几项参数的临床应用价值,本就此作一综述。     

Selective gene therapy for prostate cancer cells using liposomes conjugated with IgM type monoclonal antibody against prostate-specific membrane antigen

Prostate cancer cells express prostate-specific membrane antigen (PSMA). We developed an IgM type monoclonal antibody against PSMA. The antibody was coupled to poly-L-lysine and thereafter this conjugate was mixed with cationic liposomes containing plasmid DNA. The antibody-liposome complex was tested whether it could deliver the gene of interest selectively to the PSMA positive cells. As assessed by beta-galactosidase reporter gene, the transfection efficiency was 13.2% with anti-PSMA-liposome complex as compared to 4% with control IgM liposome complex. In contrast, no such differences were observed in PSMA negative PC-3, DU145 and T24 cells. Furthermore, in the suicide gene therapy in vitro with thymidine kinase gene plus ganciclovir system, anti-PSMA liposome complex demonstrated a selective growth inhibitory effect on PSMA positive LNCaP cells but not on PSMA negative cell lines.     

The role of the urologist in treating patients with hormone-refractory prostate cancer

Objectives: To ascertain what percentage of urologists' oncology practice is dedicated to the care of prostate cancer patients and to determine urologists' attitudes towards the treatment of patients with metastatic and hormone-refractory prostate cancer (HRPC). An additional objective is to determine urologists' interest in administering various types of chemotherapy in HRPC patients.Materials and Methods: The American Urological Association (AUA) directory of practicing urologists was obtained, and 3000 randomly selected members of the AUA, as well as the complete list of 168 Society of Urologic Oncology (SUO) members, were chosen for the mailing of a 16-item questionnaire. The urologists were asked about how many of their patients have prostate cancer, how many have metastatic disease, and how many have HRPC and are currently receiving intravenous (IV) chemotherapy. In addition, the urologists were queried regarding their level of interest in learning about chemotherapy options as well as learning how to administer chemotherapy.Results: A total of 654 survey questionnaires were completed and returned for tabulation, resulting in a 21% effective response rate. Sixty-four percent of the responding urologists' cancer patients had prostate cancer, 21% had metastatic disease, and 19% had HRPC; only 4% of the urologists currently administer IV chemotherapy themselves. When asked to describe their interest in learning how to deliver and be reimbursed for IV chemotherapy, 26% expressed an extremely low level of interest, 23% a low level of interest, 31% a high level of interest, and 17% an extremely high level of interest. The results of other questions are presented and correlated with the number of years the urologists have been in practice and other demographic data.Conclusions: The management of prostate cancer comprises a major portion of urologists' practices. Almost one half (48%) of the urologists in this survey were interested in administering and being reimbursed for IV chemotherapy. Several chemotherapy regimens have been shown to improve quality of life in patients with HRPC, yet only about 30% of these patients were referred for chemotherapy. If more urologists were able to deliver these drugs, then the number of patients referred for chemotherapy would likely increase, as would accrual to important clinical trials in HRPC. The results of this survey suggest that methods to implement the training and reimbursement of urologists in the use of chemotherapy regimens should be investigated.     

Docetaxel for the treatment of hormone-refractory prostate cancer

Chemotherapy has historically proven toxic and ineffective for the treatment of metastatic hormone-refractory prostate cancer (HRPC), a disease with substantial morbidity and mortality. Progress has been made in symptom relief, and the combination of mitoxantrone and prednisone is considered the palliative standard of care. The effects of a variety of chemotherapeutic agents, both alone and in combination, on prostate-specific antigen decline rates, measurable disease response, and survival have been examined in numerous phase I and II trials. Results suggest that combining vinblastine or paclitaxel with estramustine confers a survival advantage over either agent alone. In addition, docetaxel-based therapy has been found to be effective and well tolerated, and phase III trials will soon determine whether docetaxel-based therapy should replace mitoxantrone-based therapy as the standard of care for HRPC.     

Differential responsiveness of prostatic acid phosphatase and prostate-specific antigen mRNA to androgen in prostate cancer cells

Androgens regulate the expression of both human prostatic acid phosphatase (PAcP) and prostate-specific antigen (PSA), two major prostate epithelium-specific differentiation antigens. Due to the important role of these two enzymes as prostate epithelium differentiation markers, we investigated their regulation of expression at the mRNA level in LNCaP human prostate carcinoma cells. Interestingly, phenol red, a pH indicator in the culture medium, promoted cell growth. To eliminate this non-specific effect, a phenol red-free, steroid-reduced medium was utilized. When high-density cells were grown in that medium, 5alpha-dihydrotestosterone (DHT) suppressed PAcP but stimulated PSA. However, tumor promoter phorbol ester 12-o-tetradecanoyl phorbol-13-acetate (TPA) functioned as a potent inhibitor of both PAcP and PSA expression. Prolonged treatment with DHT as well as TPA resulted in a similar down-regulation of protein kinase C and cellular PAcP activities. Thus, the levels of PAcP and PSA mRNA are differentially regulated by androgens in LNCaP cells.     

Beyond prostate-specific antigen: new serologic biomarkers for improved diagnosis and management of prostate cancer

The use of total prostate-specific antigen (tPSA) measurement has dramatically improved the ability to detect prostate cancer at earlier stages. However, as the number of men presenting with advanced disease (and high tPSA levels) has decreased, and given the fact that tPSA is highly reflective of benign prostatic hyperplasia, the need has emerged for novel biomarkers specifically associated with prostate cancer in order to improve predictive models. Several new biomarkers have shown promise, and studies continue to investigate the role of these markers in the detection, staging, and prognosis of prostate cancer. As new useful biomarkers continue to emerge, guidelines for their employment, as well as coordination of further research studies, are needed; a systematic, phased, nomogram-based model is a rational way to manage these efforts.     

Different glycan structures in prostate-specific antigen from prostate cancer sera in relation to seminal plasma PSA

Prostate-specific antigen (PSA), the tumor marker currently used for prostate cancer (PCa), is not specific enough to distinguish between PCa and benign prostate hyperplasia (BPH). Glycan processing is normally perturbed in tumors, therefore we investigated whether changes in glycosylation of PSA could be useful diagnostic indicators. Previously we determined that the glycosylation of PSA secreted by the tumor prostate cell line LNCaP differs significantly from that of PSA from seminal plasma (normal control). We therefore undertook a detailed glycan analysis of PSA derived from sera from PCa patients and, importantly, established that the glycosylation of the PCa serum PSA was significantly different from the PSA from the LNCaP cell line. In comparison with seminal plasma PSA, the fucose content of PSA from the PCa patient serum was significantly lower and there was a decrease in alpha2,3-linked sialic acid. Differences in the glycosylation of PSA derived from PCa patients' sera, seminal plasma, and LNCaP cells were further established by lectin detection, glycosylation immunosorbent assay, and two-dimensional electrophoresis. We also investigated whether the impact of glycosylation changes initiated by the tumor was reflected in the serum glycome. By comparing the glycans released from the total glycoproteins in PCa patient serum with those of normal serum we found an increase in the proportion of sialyl-Lewis x structures. Further analysis of the glycosylation of PSA from PCa and BPH sera will be required in order to determine the utility of these glycan differences to discriminate specifically between benign and malignant prostate states.     

Evaluation and treatment of men with biochemical prostate-specific antigen recurrence following definitive therapy for clinically localized prostate cancer

Early detection and monitoring by serum prostate-specific antigen (PSA) measurement has increased the number of men presenting with potentially curable prostate cancer. Most will choose radical prostatectomy or some form of radiation therapy for treatment, but some will have evidence of biochemical disease recurrence following therapy, shown by a rising PSA level without other clinical evidence of disease. Radical prostatectomy involves the removal of all prostate tissue, causing the serum PSA to decline to undetectable levels within four to six weeks following surgery; a subsequent rise in the serum PSA to a detectable level indicates disease recurrence. Patients should be evaluated to assess whether rising PSA levels indicate local recurrence or early metastatic disease. The advantages of salvage radiation, endocrine therapy, and other treatment modalities in local disease recurrence must be weighed against potential side effects and the resulting decrease in quality of life. Radiation therapy does not immediately eradicate all PSA-producing cells; therefore the persistence of a detectable PSA does not necessarily imply residual cancer, but rising PSA levels indicate treatment failure. Salvage surgery can be performed after radiotherapy for the purpose of removing all viable cancer cells, but should be weighed against a higher incidence of surgical complications; cryoablation offers a less invasive therapeutic modality.     

Polyamine-reduced diet in metastatic hormone-refractory prostate cancer (HRPC) patients

Polyamine (PA) deprivation is effective in prostate carcinoma models. We have assessed the observance by patients, tolerance and side effects of a PA-reduced diet (PRD) and intestinal decontamination (ID), in order to reduce PA dietary and intestinal bacterial pools, in metastatic, hormone-refractory prostate cancer (HRPC) patients. A total of 13 volunteers (mean age, 67+/-10 years) with metastatic HRPC were proposed for PRD and ID (0.75 g/day of oral neomycin every other week). The mean time from HRPC diagnosis to the start of the diet was 12+/-8 months. Of the total 13, seven patients had received prior chemotherapy or Estramustine phosphate. PRD was obtained after HPLC assessment of PA contents in current foods and given 5 days a week. Toxicity, performance and pain status were assessed according to the World Health Organisation and EORTC scales. Prostatic specific antigen (PSA), blood counts, ionograms, transaminases and erythrocyte PA spermidine (Spd) and spermine (Spm; assessed by HPLC) were evaluated regularly. Mean observance was 8+/-7 months (range, 2-26 months). One case of grade II toxicity to neomycin was observed. Cancer-specific survival (after the diet) was 14+/-7 months, and two patients are still alive. All the other patients have died of their cancer at 12+/-6 months (range, 4-20 months). Cancer-specific survival after hormonal escape was 27+/-11 months (range, 9-45 months). Performance status was improved during the regimen and deteriorated 3 months after stopping. Pain score was improved (1.3 versus 0.6; P =0.04) during the diet and increased (2.1 versus 0.3) 3 months after stopping. Erythrocyte Spd (11.6+/-7 versus 7.7+/-2 nmol/8 x 10(9) erythrocytes; P =0.036) and Spm (7+/-6 versus 3.9+/-1.6 nmol/8 x 10(9) erythrocytes; P =0.036) levels were significantly reduced at 3 months. One patient had a >50% reduction in PSA, three patients had PSA stabilization for 6 months. PSA progression was observed in all other patients. No significant modification of other studied biological parameters was noted. Reducing PA dietary intake and ID is a well-observed and tolerated regimen and seems to be beneficial for patient quality of life and pain control. Patients with low initial PSA can experience durable stabilization. These encouraging results in such an aggressive disease certainly warrant further investigation.     

Mitotic catastrophe and apoptosis induced by docetaxel in hormone-refractory prostate cancer cells

Studies performed in different experimental and clinical settings have shown that Docetaxel (Doc) is effective in a wide range of tumors and that it exerts its activity through multiple mechanisms of action. However, the sequence of events induced by Doc which leads to cell death is still not fully understood. Moreover, it is not completely clear how Doc induces mitotic catastrophe and whether this process is an end event or followed by apoptosis or necrosis. We investigated the mechanisms by which Doc triggers cell death in hormone-refractory prostate cancer cells by analyzing cell cycle perturbations, apoptosis-related marker expression, and morphologic cell alterations. Doc induced a transient increase in G2/M phase followed by the appearance of G0/1 hypo- and hyperdiploid cells and increased p21 expression. Time- and concentration-dependent apoptosis was induced in up to 70% of cells, in concomitance with Bcl-2 phosphorylation, which was followed by caspase-2 and -3 activation. In conclusion, Doc would seem to trigger apoptosis in hormone-refractory prostate cancer cells via mitotic catastrophe through two forms of mitotic exit, in concomitance with increased p21 expression and caspase-2 activation.