PHASE II STUDY OF ALL-TRANS RETINOIC ACID ADMINISTERED INTERMITTENTLY FOR HORMONE REFRACTORY PROSTATE CANCER

Comprehensive Review on Recent Strategies for Management of Prostate Cancer: Therapeutic Targets and SAR

Prostate cancer is a disease that is affecting a large population worldwide. Androgen deprivation therapy (ADT) has become a foundation for the treatment of advanced prostate cancer, as used in most clinical settings from neo-adjuvant to metastatic stage. In spite of the success of ADT in managing the disease in the majority of men, hormonal manipulation fails eventually. New molecules are developed for patients with various hormone-refractory diseases. Advancements in molecular oncology have increased understanding of numerous cellular mechanisms which control cell death in the prostate and these insights can lead to the development of more efficacious and tolerable therapies for carcinoma of the prostate. This review is focused on numerous therapies that might be a boon for prostate therapy like signaling inhibitors, vaccines, and inhibitors of androgen receptors. Along with these, various bioactive molecules and their derivatives are highlighted, which act as potential antiprostate cancer agents. This article also emphasized the recent advances in the field of medicinal chemistry of prostate cancer agents.

All-trans retinoic acid in anticancer therapy: how nanotechnology can enhance its efficacy and resolve its drawbacks

Introduction: All-trans retinoic acid (ATRA, tretinoin) is the main drug used in the treatment of acute promyelocytic leukemia (APL). Despite its impressive activity against APL, the same could not be clinically observed in other types of cancer. Nanotechnology can be a tool to enhance ATRA anticancer efficacy and resolve its drawbacks in APL as well as in other malignancies.Areas covered: This review covers ATRA use in APL and non-APL cancers, the problems that were found in ATRA therapy and how nanoencapsulation can aid to circumvent them. Pre-clinical results obtained with nanoencapsulated ATRA are shown as well as the two ATRA products based on nanotechnology that were clinically tested: ATRA-IV® and Apealea®.Expert opinion: ATRA presents interesting properties to be used in anticancer therapy with a notorious differentiation and antimetastatic activity. Bioavailability and resistance limitations impair the use of ATRA in non-APL cancers. Nanotechnology can circumvent these issues and provide tools to enhance its anticancer activities, such as co-loading of multiple drug and active targeting to tumor site.

Is There a Standard Chemotherapeutic Regimen for Hormone-Refractory Prostate Cancer? Present and Future Approaches in the Management of the Disease

Prostate cancer that no longer responds to hormonal manipulation can be defined as hormone-refractory prostate cancer. Until recently, there has been no standard chemotherapeutic approach for hormone-refractory prostate cancer. The major benefits of chemotherapy in the treatment of the disease are palliative in nature, in terms of reduction of pain and use of analgesics and improvement of performance status, as followed in the most recent trials. Phase III studies are necessary to better evaluate the efficacy of the different regimens, because several old studies suffer for methodological deficits. There is a promising activity of new drug combinations, such as vinca alkaloids and taxanes. Phase I and II trial are testing combinations of classic chemotherapeutic agents and biologic drugs, and the first results appear interesting. In this article, recent advances in the treatment of hormone-refractory prostate cancer using chemotherapeutic regimens are critically reviewed.

Retinoic acid and cancer treatment

Retinoic acid which belongs to the retinoid class of chemical compounds is an important metabolite of vitamin A in diets. It is currently understood that retinoic acid plays important roles in cell development and differentiation as well as cancer treatment. Lung, prostate, breast, ovarian, bladder, oral, and skin cancers have been demonstrated to be suppressed by retinoic acid. Our results also show that low doses and high doses of retinoic acid may respectively cause cell cycle arrest and apoptosis of cancer cells. Also, the common cell cycle inhibiting protein, p27, and the new cell cycle regulator, Cdk5, are involved in retinoic acid’s effects. These results provide new evidence indicating that the molecular mechanisms of/in retinoic acid may control cancer cells’ fates. Since high doses of retinoic acid may lead to cytotoxicity, it is probably best utilized as a potential supplement in one’s daily diet to prevent or suppress cancer progression. In this review, we have collected numerous references demonstrating the findings of retinoic acid in melanoma, hepatoma, lung cancer, breast cancer, and prostate cancer. We hope these observations will shed light on the future investigation of retinoic acid in cancer prevention and therapy.

A phase 2 trial of all-trans-retinoic acid in combination with interferon-alpha2a in children with recurrent neuroblastoma or Wilms tumor: A Pediatric Oncology Branch, NCI and Children's Oncology Group Study

BACKGROUND

The combination of the antiproliferative and differentiation-inducing effects of retinoids together with the antiproliferative, immunostimulatory, and differentiation-potentiating effects of interferon-alpha (IFN-alpha) were the basis for the development of this combination in pediatric patients with refractory neuroblastoma or Wilms tumor.

PROCEDURE

A phase 2 trial of all-trans-retinoic acid (ATRA), administered orally at a dose of 90 mg/m(2)/day in three divided doses for 3 consecutive days per week, and IFN-alpha2a, administered subcutaneously daily at a dose of 3 x 10(6) U/m(2)/day for 5 consecutive days per week, in 4 week cycles was performed. A two-stage design was used for each disease stratum.

RESULTS

Seventeen patients (16 evaluable) with neuroblastoma, median age 9 years, and 15 patients (14 evaluable) with Wilms tumor, median age 6 years, were enrolled. Overall, the combination was well tolerated, with headache being the most common toxicity observed. There were no complete or partial responses. The median number of cycles administered was 1 (range 1-9). Four patients with neuroblastoma had stable disease for 12 or more weeks.

CONCLUSIONS

The combination of ATRA and IFN-alpha2a was inactive in children with relapsed or refractory neuroblastoma and Wilms tumor. The lack of activity with this combination in children with refractory neuroblastoma is similar to the disappointing phase 2 results of single agent 13-cis-retinoic-acid (13cRA) and does not support further development of ATRA for children with relapsed neuroblastoma.

Transcriptional regulation of the homeobox geneNKX3.1 by all-trans retinoic acid in prostate cancer cells

NKX3.1 is a homeobox gene, expression of which is largely restricted to the adult prostatic epithelium. Loss of NKX3.1 expression has been linked to prostate carcinogenesis and disease progression and occurs in the absence of mutations in the coding region of the NKX3.1 gene. In this study, we have characterized regulation of NKX3.1 expression by all-trans retinoic acid (tRA), a naturally occurring vitamin A metabolite that is accumulated at high levels in the prostate. Using the prostate cancer cell line LNCaP, Western blot analysis revealed a approximately twofold induction of NKX3.1 protein levels following tRA exposure, with sequential analysis of NKX3.1 protein levels in cycloheximide co-treated cells indicating that tRA does not alter NKX3.1 protein turnover. The approximately 1.6-fold increase in NKX3.1 mRNA levels detected in tRA-treated LNCaP cells also occurred independently of new protein synthesis and was not mediated by changes in NKX3.1 mRNA stability. In contrast, nuclear run-on assays indicated that tRA treatment increased NKX3.1 transcription. To identify retinoid responsive regions of the NKX3.1 gene, DNA sequences encompassing approximately 2 kb of the NKX3.1 promoter or the entire 3'untranslated region (UTR) were cloned into luciferase reporter plasmids. Analysis of induced luciferase activity following transfection of these constructs into prostate cancer cells did not identify tRA responsiveness, however the 3'UTR was found to be strongly androgen responsive. These studies demonstrate that the NKX3.1 gene is a direct target of retinoid receptors and suggest that androgen regulation of NKX3.1 expression is mediated in part by the 3'UTR.

Interaction of nuclear receptor ligands with the Vitamin D signaling pathway in prostate cancer

A number of hormonal ligands and/or the nuclear receptors that mediate their actions have been targeted for prostate cancer therapy. Androgens, the ligands for the androgen receptor (AR), are critical for the growth of prostate cancer. Inhibition of androgen production has been the mainstay of treatment for advanced prostate cancer for decades. Other more recently tested targets include retinoid receptors (RAR and RXR), glucocorticoid receptors (GR), estrogen receptors (ER) and peroxisome proliferator-activated receptors (PPAR). Calcitriol, acting through the Vitamin D receptor (VDR), has many tumor suppressive activities in the prostate, including inhibition of proliferation, induction of apoptosis and/or differentiation, and reduction of cellular invasion. Because of these properties, calcitriol and its less hypercalcemic analogs are being evaluated as agents to prevent or treat prostate cancer. Androgens, retinoids, glucocorticoids, estrogens and agonists of PPAR directly or indirectly impact Vitamin D signaling pathways, and vice versa. In order to design the most effective strategies to use calcitriol to prevent or treat prostate cancer, the interactions of other nuclear receptors and their ligands with the Vitamin D signaling pathway need to be considered.

Retinoic acid slows progression and promotes apoptosis of spontaneous prostate cancer

BACKGROUND

All-trans retinoic acid (ATRA) promotes terminal differentiation in epithelial cells and anti-angiogenesis and thus, may have beneficial effects in an intervention therapy for prostate cancer.

METHODS

We used the autochthonous spontaneous transgenic adenocarcinoma of the mouse prostate (TRAMP) model system to test the ability of ATRA to prevent initiation and progression of prostate cancer in a pre-clinical setting.

RESULTS

Initial studies demonstrated that exposure of TRAMP-derived C2N prostate tumor cells to ATRA in vitro decreased total viable cell numbers with a concomitant decrease in the fraction of cells in S phase. When TRAMP mice were treated in vivo with ATRA for either 6 or 8 weeks at low, medium, or high dose, mice on average presented with lower grade and more differentiated tumors. However, ATRA therapy conferred no significant protection on incidence of tumors or frequency of metastasis at any dose. Nevertheless, we were able to observe a significant decrease in the expression of synaptophysin, a marker of neuroendocrine differentiation, in tumors of mice receiving the highest dose of ATRA. As well, expression of the cell cycle inhibitor p21 was found to be elevated only in well-differentiated tumors of mice, treated with ATRA while expression of p27, was found to be elevated only in the poorly differentiated tumors.

CONCLUSIONS

Collectively, our in vitro and in vivo data demonstrates that ATRA was able to slow prostate tumor cell proliferation, induce apoptosis, and block the emergence of the neuroendocrine phenotype. Furthermore, our study suggests the differential regulation of p21 and p27 as a molecular mechanism whereby ATRA intervention therapy can inhibit the natural history of spontaneous prostate cancer.

Application of retinoids in the treatment of renal cell carcinoma–a futile effort?

The therapeutic benefit of adding retinoids such as all-trans retinoic acid (RA), 9-cis-RA or 13-cis-RA to established single-agent or combination immuno/chemotherapy regimens for the treatment of metastatic renal cell carcinoma (RCC) has been extensively investigated during the last decade. However, at present results are contradictory and their application controversial. Moreover, recent studies indicated a significantly higher incidence of toxic side-effects in patients treated with retinoids in addition to established bio/chemotherapy. This Commentary summarizes preclinical and clinical trials investigating efficacy and toxicity of retinoids in the treatment of RCC.

Quantitative RARβ2 Hypermethylation

Retinoic acid receptor beta2 (RARbeta2) is a tumor suppressor gene frequently hypermethylated in several human neoplasms. To further characterize this epigenetic alteration in prostate cancer progression, we examined tumor tissue from 118 patients with prostate carcinoma (PCa), 38 paired high-grade prostatic intraepithelial neoplasias (HGPIN), and non-neoplastic prostate tissue from 30 patients with benign prostate hyperplasia (BPH), using quantitative methylation-specific PCR. We found RARbeta2 hypermethylation in 97.5% of PCa, 94.7% of HGPIN, and 23.3% of BPH. Methylation levels were significantly higher in PCa compared with HGPIN and BPH (P < 0.00001). By establishing an empiric cutoff value, we were able to discriminate between neoplastic and non-neoplastic tissue, with 94.9% sensitivity and 100% specificity. Moreover, RARbeta2 methylation levels correlated with higher pathological stage (r = 0.30, P = 0.0009). This quantitative assay represents a novel and promising molecular marker that may augment current approaches for prostate cancer detection.

Decreased Retinoid X Receptor-α Protein Expression in Basal Cells Occurs in the Early Stage of Human Prostate Cancer Development

The development of prostatic intraepithelial neoplasia (PIN)-like lesions in the prostate-specific retinoid X receptor-α (RXRα) null mouse suggests that RXRα may protect against neoplasia. The purpose of this study was to characterize RXRα protein expression in human prostate to determine if RXRα is altered in early stages of tumor progression. Immunohistochemistry with anti-RXRα antibody was performed on 138 fresh frozen prostate specimens collected from 27 noncarcinomatous prostates and 111 radical prostatectomy samples of prostate adenocarcinoma (CA). The RXRα signal intensity was scored using a scale of 0–3. In normal glands, RXRα was expressed strongly in basal cells and only weakly in secretory epithelial cells. This finding was confirmed by double immunofluorescence labeling of RXRα and Keratin-903, a basal cell marker, followed by confocal microscopic examination. In basal cells, a gradual decrease of RXRα expression was noted from normal glands of noncarcinomatous prostate (3.0 ± 0) to “normal” glands distant to CA (2.13 ± 0.44) to “normal” glands adjacent to CA (1.25 ± 0.53) and high-grade PIN (0.56 ± 0.58). While nearly all “normal” glands from 138 specimens were positive for RXRα in basal cells, only 48% (13 of 27) of the high-grade PIN glands appeared positive. Moreover, basal cell expression of RXRα in “normal” tissue was less in specimens with poorly differentiated tumor (Gleason score ≥ 8; 1.83 ± 0.36) compared with well-differentiated tumor (Gleason score &lt; 6; 2.35 ± 0.34; P = 0.04). Thus, a decrease of RXRα in the basal cells may serve as a marker for prostate CA-associated field change, which may represent an early event in the prostate carcinogenic process. These findings suggest that chemoprevention strategies with retinoids may be most effective if applied during the early stages of transformation.

Vitamin A, Retinoids and Carotenoids as Chemopreventive Agents for Prostate Cancer

PURPOSE

Evidence is examined for the use of vitamin A, retinoids and carotenoids as chemopreventive agents for prostate cancer.

MATERIALS AND METHODS

Studies in in vitro and animal experimental models as well as in human observational (epidemiologic) and experimental studies are reviewed.

RESULTS

There is little evidence that dietary vitamin A is associated with prostate cancer risk and, thus, it is unlikely that vitamin A or retinyl palmitate, the form most often used in dietary supplements, would be useful as chemoprevention agents. Several pharmaceutical formulations of retinoids show cancer prevention properties in animal experimental models but their high toxicity makes them unlikely candidates for cancer prevention. There is also currently no evidence that dietary carotenoids (except for lycopene and possibly other bioactive compounds found in tomato products) will be useful for prostate cancer prevention. Epidemiological and experimental studies show no association of beta-carotene with prostate cancer risk. There is inconsistent though intriguing evidence from epidemiological studies that tomato products and/or lycopene is associated with reduced prostate cancer risk. However, animal experimental studies of lycopene and prostate cancer are not strongly supportive, and the results of human experimental studies are not interpretable due to poor design.

CONCLUSIONS

There is currently no evidence that vitamin A, synthetic retinoids or carotenoids can be used as prostate cancer chemopreventive agents. Experimental studies are needed to determine whether lycopene or other compounds in tomatoes have chemopreventive properties.

[Current multidisciplinary treatment of metastatic prostatic cancer]

Prostate cancer is one of the commonest causes of cancer-related death in the western world. The morbi-mortality associated is usually a direct consequence of metastatic spread to bone, in up to 50% of patients at first presentation. The aim of treatment of metastatic patients is to alleviate and to prevent the distressing symptoms. The approach include hormone-therapy, radiotherapy, radio-nuclides, surgery, chemotherapy, bisphosphonates and new drugs (agents that inhibit angiogenesis, immunotherapy and therapies that affect the differentiation). Decisions about therapy must also take into consideration the androgen-dependent or independent, so hormone-therapy is the first step of the treatment; the number and location of bone metastases; the severity of symptoms; the available of therapies; the status performance of patient; the prognosis and the cost-effect relationship. Some treatments have established indications whereas others are still in process of study in order to determinate their efficacy, their model of treatment and their indications. This article revises and updates these treatments.

Chemotherapy in advanced androgen-independent prostate cancer 1990-1999: a decade of progress?

BACKGROUND AND PURPOSE

A great number of clinical research studies have been reported in the field of chemotherapy for advanced androgen-independent prostate cancer during the last ten years. The aims of the present review were to assess their impact on management of the disease and on survival of patients.

METHODS

The review of full published reports was facilited by the use of a MEDLINE computer search.

RESULTS

Clinical research studies have focused on defining guidelines for eligibility criteria and accurate endpoints for patients to be enrolled onto clinical trials and developing new agents or combination of drugs including estramustine phosphate. Any combination of current chemotherapy has no impact on overall survival of patients. Among drugs in development, only the promising activity observed with docetaxel deserves randomized trials to assess its impact on survival. The major innovative advance of the 90s is the demonstration of the impact of chemotherapy (mitoxantrone + prednisone) on quality of life as compared to prednisone alone. A greater and longer-lasting improvement in quality of life along with a concomitant decrease in costs was observed.

CONCLUSIONS

At the present time, chemotherapy should be considered as a palliative treatment in patients with symptomatic androgen-independent disease. The enrollment of patients into clinical trials dealing with quality of life as primary endpoint is strongly solicited. A standard methodology should be used in phase II trials with a primary goal of selection of agents which should progress to randomized trials using survival as an endpoint. Hopefully new specific strategies targeted to reverse the molecular changes that underlie prostate tumorigenesis should rapidly impact the multimodality management of AIPC in the third millenium.