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

Class IIb HDAC Inhibition Enhances the Inhibitory Effect of Am80, a Synthetic Retinoid, in Prostate Cancer

Combination therapy is often an effective strategy to treat cancer. In this study, we examined the growth-inhibitory effects of Am80 (tamibarotene), a specific retinoic acid receptor (RAR) α/β agonist, in combination with a histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA), or a DNA methyl transferase (DNMT) inhibitor, 5-aza-2'-deoxycytidine, on androgen receptor (AR)-positive and AR-negative prostate cancer cell lines (LNCaP and PC-3, respectively). We found that the combination therapy of SAHA and Am80 showed an enhanced growth-inhibitory effect on LNCaP cells. Further studies with various HDAC isotype-selective inhibitors showed that SAHA and KD5170 (a selective class I and II HDAC inhibitor) each increased the RARα protein level in LNCaP cells. Our results indicate that the target of the enhancing effect belongs to the Class IIb HDACs, especially HDAC6. Dual targeting of Class IIb HDAC and RARα may be a candidate therapeutic strategy for prostate cancer.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Phase 2 trial of paclitaxel, 13-cis retinoic acid, and interferon alfa-2b in the treatment of advanced stage or recurrent cervical cancer

OBJECTIVE

Overexpression of bcl-2 is a mechanism of drug resistance in cervical cancer. Agents that down-regulate bcl-2 may decrease tumor cell threshold and sensitize tumor cells to chemotherapy. The objective of this multi-institutional phase 2 trial was to evaluate the efficacy and toxicity of paclitaxel and bcl-2 modulators (13-cis retinoic acid and interferon alfa-2b) in patients with advanced-stage or recurrent cervical cancer.

MATERIALS AND METHODS

Patients had biopsy-proven metastatic, first relapse, or persistent cervical cancer with no prior chemotherapy except for chemosensitizing agents. The treatment consisted of oral 13-cis retinoic acid, 1 mg/kg, and subcutaneous interferon alfa-2b, 6 mU/m, days 1 to 4, and intravenous paclitaxel, 175 mg/m, day 4 until disease progression or adverse events prohibited treatment. The primary endpoint was overall response rate.

RESULTS

Thirty-three patients were enrolled between March 2001 and June 2009. Thirty-one patients were eligible for evaluation of treatment response. Twenty-seven patients (82%) received prior concurrent chemoradiation or radiotherapy alone before study enrollment. The overall response rate was 30% (6 complete responses and 4 partial responses). Furthermore, 7 patients (21%) had stable disease. Grade 3 or 4 adverse events included neutropenia (n =16 [48%]), febrile neutropenia (n = 1 [3%]), and anemia (n = 1 [3%]). There were no treatment-related deaths. The median progression-free survival was 3.4 months (95% confidence interval, 2.0-7.4 months), and overall survival was 11.2 months (95% confidence interval, 7.5-26.2 months). Of 6 patients with complete responses, 5 patients survived more than 2 years.

CONCLUSIONS

Combination therapy with paclitaxel, 13-cis retinoic acid, and interferon alfa-2b is feasible and safe in treating patients with advanced and recurrent cervical 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.

Retinoic Acid Induces Apoptosis of Prostate Cancer DU145 Cells through Cdk5 Overactivation

Retinoic acid (RA) has been believed to be an anticancer drug for a long history. However, the molecular mechanisms of RA actions on cancer cells remain diverse. In this study, the dose-dependent inhibition of RA on DU145 cell proliferation was identified. Interestingly, RA treatment triggered p35 cleavage (p25 formation) and Cdk5 overactivation, and all could be blocked by Calpain inhibitor, Calpeptin (CP). Subsequently, RA-triggered DU145 apoptosis detected by sub-G1 phase accumulation and Annexin V staining could also be blocked by CP treatment. Furthermore, RA-triggered caspase 3 activation and following Cdk5 over-activation were destroyed by treatments of both CP and Cdk5 knockdown. In conclusion, we report a new mechanism in which RA could cause apoptosis of androgen-independent prostate cancer cells through p35 cleavage and Cdk5 over-activation. This finding may contribute to constructing a clearer image of RA function and bring RA as a valuable chemoprevention agent for prostate cancer patients.

Up-regulation of platelet-derived growth factor-A is responsible for the failure of re-initiated interferon alpha treatment in hepatocellular carcinoma

BACKGROUND

Postoperative interferon-α(IFN-α) treatment delays hepatocellular carcinoma(HCC) recurrence and prolongs patient survival, and may thus be an effective form of adjuvant therapy. However, clinical observations found that HCC recurs in some patients within 8 months of IFN-α treatment being discontinued. We investigated whether HCC regrowth appears after IFN-α is discontinued, whether re-initiated IFN-α is effective, and the underlying mechanisms of IFN-α treatment.

METHODS

The human HCC nude mouse model LCI-D20 was used to study the effects of IFN-α treatment, discontinued IFN-α treatment, and re-initiated IFN-α treatment on tumor growth. Tumor weight, microvessel density(MVD), serum vascular endothelial growth factor (VEGF), and tumor cell apoptosis were analyzed. Angiogenesis-related factors were studied using cDNA microarray in different tumor samples and confirmed using reverse transcription-polymerase chain reaction(RT-PCR) and Western blotting assays. Finally, imatinib was added with re-initiated IFN-α treatment to improve efficacy.

RESULTS

IFN-α (1.5 × 107 U/kg/day for 20 days) suppressed HCC growth by 60.3% and decreased MVD by 52.2% compared with the control. However, tumor regrowth occurred after IFN-α was discontinued, and re-initiated IFN-α treatment was not effective for inhibiting tumor growth or reducing MVD compared with a saline-treated group. cDNA microarray showed VEGF was down-regulated while platelet-derived growth factor-A (PDGF-A) was up-regulated when IFN-α treatment was re-initiated. These findings were further confirmed with RT-PCR and Western blotting assay. The combination of imatinib with re-initiated IFN-α reduced HCC weight by 30.7% and decreased MVD by 31.1% compared with IFN-α treatment only (P=0.003 and 0.015, respectively).

CONCLUSION

Tumor regrowth occurred after IFN-α treatment was discontinued. Re-initiated IFN-α treatment was not effective and was associated with up-regulation of PDGF-A, while the VEGF remained suppressed. The combination of a PDGF-receptor inhibitor with IFN-α improved the effect of the re-initiated treatment.

Vitamin A and retinoid derivatives for lung cancer: a systematic review and meta analysis

BACKGROUND

Despite reported antiproliferative activity of vitamin A and its common use for cancer, there is no comprehensive synthesis of its safety and efficacy in lung cancers. To address this issue we conducted a systematic review of the safety and efficacy of vitamin A for the treatment and prevention of lung cancers.

METHODS AND FINDINGS

Two independent reviewers searched six electronic databases from inception to July 2009 for clinical, observational, and preclinical evidence pertaining to the safety and efficacy of vitamin A and related retinoids for lung cancers. 248 studies were included for full review and analysis. Five RCTs assessed treatment of lung cancers, three assessed primary prevention, and three looked at secondary prevention of lung cancers. Five surrogate studies, 26 phase I/II, 32 observational, and 67 preclinical studies were also included. 107 studies were included for interactions between vitamin A and chemo- or radiation-therapy. Although some studies demonstrated benefits, there was insufficient evidence overall to support the use of vitamin A or related retinoids for the treatment or prevention of lung cancers. Retinyl palmitate combined with beta carotene increased risk of lung cancer in smokers in the large CARET trial. Pooling of three studies pertaining to treatment and three studies on secondary prevention revealed no significant effects on response rate, second primary tumor, recurrence, 5-year survival, and mortality. There was a small improvement in event free survival associated with vitamin A compared to controls, RR 1.24 (95% CI 1.13-1.35). The synthetic rexinoid bexarotene increased survival significantly among a subset of patients in two RCTs (p<0.014, <0.087).

CONCLUSIONS

There is a lack of evidence to support the use of naturally occurring retinoids for the treatment and prevention of lung cancers. The rexinoid bexarotene may hold promise for use among a subset of patients, and deserves further study.

A randomized phase II trial of mitoxantrone, estramustine and vinorelbine or bcl-2 modulation with 13-cis retinoic acid, interferon and paclitaxel in patients with metastatic castrate-resistant prostate cancer: ECOG 3899

BACKGROUND

To test the hypothesis that modulation of Bcl-2 with 13-cis retinoic acid (CRA)/interferon-alpha2b (IFN) with paclitaxel (TAX), or mitoxantrone, estramustine and vinorelbine (MEV) will have clinical activity in men with metastatic castrate-resistant prostate cancer (CRPC).

METHODS

70 patients were treated with either MEV (Arm A) in a 3-week cycle or CRA/IFN/TAX with an 8-week cycle (Arm B). Patients were assessed for response, toxicity, quality of life (QOL), and the effect of treatment on Bcl-2 levels in peripheral blood mononuclear cells (PBMC).

RESULTS

The PSA response rates were 50% and 23%, measurable disease response rates (CR+PR) 14% and 15%, and median overall survival 19.4 months and 13.9 months on Arm A and Arm B respectively. Transient grade 4 neutropenia occurred in 18 and 2 patients, and grade 3 to 4 thrombosis in 7 patients and 1 patient in Arm A and Arm B respectively. Patients on Arm B reported a clinically significant decline in QOL between baseline and week 9/10 (.71 s.d.), and a significantly lower level of QOL than Arm A (p = 0.01). As hypothesized, Bcl-2 levels decreased with CRA/IFN therapy only in Arm B (p = 0.03).

CONCLUSIONS

Treatment with MEV was well tolerated and demonstrated clinical activity in patients with CRPC. Given the adverse effect of CRA/IFN/TAX on QOL, the study of other novel agents that target Bcl-2 family proteins is warranted. The feasibility of measuring Bcl-2 protein in a cooperative group setting is hypothesis generating and supports further study as a marker for Bcl-2 targeted therapy.

TRIAL REGISTRATION

CLINICAL TRIALS REGISTRATION NUMBER

CDR0000067865.

Bcl-2 modulation to activate apoptosis in prostate cancer

Apoptosis resistance is a hallmark of cancer linked to disease progression and treatment resistance, which has led to the development of anticancer therapeutics that restore apoptotic function. Antiapoptotic Bcl-2 is frequently overexpressed in refractory prostate cancer and increased following standard hormonal therapy and chemotherapy; however, the rationally designed Bcl-2 antagonist, ABT-737, has not shown single agent apoptosis-promoting activity against human prostate cancer cell lines. This is likely due to the coordinate expression of antiapoptotic, Bcl-2-related Mcl-1 that is not targeted by ABT-737. We developed a mouse model for prostate cancer in which apoptosis resistance and tumorigenesis were conferred by Bcl-2 expression. Combining ABT-737 with agents that target Mcl-1 sensitized prostate cancer cell lines with an apoptotic block to cell death in vitro. In mice in vivo, ABT-737 showed single agent efficacy in prostate tumor allografts in which tumor cells are under hypoxic stress. In human prostate cancer tissue, examined using a novel tumor explant system designated Tumor Tissue Assessment for Response to Chemotherapy, combination chemotherapy promoted efficient apoptosis. Thus, rational targeting of both the Bcl-2 and Mcl-1 mechanisms of apoptosis resistance may be therapeutically advantageous for advanced prostate cancer.

Retinoic acid receptors and GATA transcription factors activate the transcription of the human lecithin:retinol acyltransferase gene

Lecithin:retinol acyltransferase (LRAT) catalyzes the esterification of retinol (vitamin A). Retinyl esters and LRAT protein levels are reduced in many types of cancer cells. We present data that both the LRAT and retinoic acid receptor beta(2) (RARbeta(2)) mRNA levels in the human prostate cancer cell line PC-3 are lower than those in cultured normal human prostate epithelial cells (PrEC). The activity of the human LRAT promoter (2.0 kb) driving a luciferase reporter gene in PC-3 cells is less than 40% of that in PrEC cells. Retinoic acid (RA) treatment increased this LRAT promoter-luciferase activity in PrEC cells, but not in PC-3 cells. Deletion of various regions of the human LRAT promoter demonstrated that a 172-bp proximal promoter region is essential for LRAT transcription and confers RA responsiveness in PrEC cells. This 172-bp region, contained within the 186 bp pLRAT/luciferase construct, has five putative GATA binding sites. Cotransfection of RARbeta(2) or RARgamma and the transcription factor GATA-4 increased LRAT (pLRAT186) promoter activity in both PrEC and PC-3 cells. In addition, we found that both retinoic acid and retinol induced transcripts for the STRA6 gene, which encodes a membrane receptor involved in retinol (vitamin A) uptake, in PrEC cells but not in PC-3 cells. In summary, our data show that the transcriptional regulation of the human LRAT gene is aberrant in human prostate cancer cells and that GATA transcription factors are involved in the transcriptional activation of LRAT in PrEC cells.

Interferon-gamma reduces cell surface expression of annexin 2 and suppresses the invasive capacity of prostate cancer cells

The effect of interferon-gamma (IFNgamma) treatment on cell surface protein expression was studied in the human prostate cancer cell line 1542CP3TX. IFNgamma increased both the number and abundance of proteins in membrane fractions. In contrast, the expression of annexin 2 and its binding partner p11 decreased by 4-fold after 24 h of exposure, with the remaining anx2(t) complexes localized to lipid rafts. Within the same time scale, IFNgamma reduced the abundance of the peripherally attached, anx2(t)-associated proteases procathepsin B and plasminogen. The invasive capacity of the cancer cells was reduced by treatment with IFNgamma or antibody to annexin 2 in 1542CP3TX cells, but not in LNCaP, an annexin 2-negative prostate cancer cell line. Expression of annexin 2 in LNCaP cells increased their invasiveness. IFNgamma induced calpain expression and activation and increased the phosphorylation and degradation of the calpain substrate ABCA1 in 1542CP3TX cancer cells. Surface expression of annexin 2 was reduced in cells treated with glyburide, an ABCA1 inhibitor, whereas inhibition of calpain abrogated IFNgamma-induced annexin 2 down-regulation and suppression of Matrigel invasion. The findings suggest annexin 2 externalization is coupled to lipid efflux in prostate epithelium and that IFNgamma induces down-regulation of the protease-binding anx2(t) scaffold at the cell surface and consequently acts to suppress invasiveness through calpain-mediated degradation of the lipid transporter ABCA1.

A phase I, pharmacokinetic and pharmacodynamic dose escalation trial of weekly paclitaxel with interferon-α2b in patients with solid tumors

PURPOSE

Paclitaxel and interferon have demonstrated anti-angiogenic activity in vitro and in vivo. The toxicity, pharmacokinetics, and pharmacodynamics of paclitaxel with interferon-alpha2b (IFN-alpha2b) were assessed in patients with solid tumors to assess the feasibility of this novel anti-angiogenic regimen.

METHODS

IFN-alpha2b (1 million units) was administered twice daily by subcutaneous injection. Paclitaxel was given weekly over 1 h starting at 30 mg/m2 and increased to 50 mg/m2. Cycles were repeated every 4 weeks.

RESULTS

Nineteen patients with a variety of solid tumors were enrolled. Dose-limiting toxicity in cycle 1 was observed at 50 mg/m2. Eleven patients were treated at 40 mg/m2 with no undue toxicity. Pharmacokinetic parameter comparison studies were completed in 11 patients who received days 1 and 29 paclitaxel. Mean paclitaxel clearance and area under the curve (0-infinity) were not statistically different from days 1 to 29. There was a 50% increase in the average Cmax from days 1 to 29. There was also a 73% decrease of matrix metalloproteinase-9 (MMP-9) levels in these 11 patients from days 1 to 29 (p < 0.0005). All three patients with cutaneous angiosarcomas experienced clinically meaningful remissions. In addition, minor responses were observed in one patient with heavily pretreated ovarian cancer and another with adrenocortical carcinoma.

CONCLUSION

This trial details the inability to dose escalate to the maximum tolerated dose of weekly paclitaxel when combined with low-dose interferon. However, this low-dose regimen caused a significant decrease in MMP-9 and demonstrated anti-cancer activity in cutaneous angiosarcomas.

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.

Alterations in expression of retinoid receptor beta and p53 in oral submucous fibrosis

OBJECTIVE

Knowledge of the molecular pathogenesis of oral submucous fibrosis (OSF), a potentially malignant condition with high risk of transition to oral cancer, is meagre. Alterations in the expression of retinoic acid receptor beta (RARbeta) and tumor suppressor gene, p53 are early events in oral tumorigenesis. The aim of this study was to investigate the alterations in the expression of RARbeta and p53 in OSF lesions and determine their association with disease pathogenesis.

METHODS

The expression of RARbeta and p53 proteins was analyzed by immunohistochemistry in 50 cases of OSF and 30 histologically normal oral tissues.

RESULTS

No detectable RARbeta expression was observed in 35 of 50 (70%) OSF cases. p53 protein accumulation was observed in 24 of 50 (48%) OSF cases analyzed. Thirty-six percent OSF lesions showed loss of RARbeta and p53 overexpression. Interestingly, 41 of 50 (82%) of OSF lesions showed altered expression of at least one of these two proteins.

CONCLUSION

Altered expression of either RARbeta or p53 in majority of OSF lesions suggests their association with disease pathogenesis and warrants follow-up to determine whether OSF lesions harboring concomitant alterations in RARbeta and p53 are at a high risk of transition to malignancy.

mTOR inhibition reverses Akt-dependent prostate intraepithelial neoplasia through regulation of apoptotic and HIF-1-dependent pathways

Loss of PTEN function leads to activation of phosphoinositide 3-kinase (PI3K) signaling and Akt. Clinical trials are now testing whether mammalian target of rapamycin (mTOR) inhibition is useful in treating PTEN-null cancers. Here, we report that mTOR inhibition induced apoptosis of epithelial cells and the complete reversal of a neoplastic phenotype in the prostate of mice expressing human AKT1 in the ventral prostate. Induction of cell death required the mitochondrial pathway, as prostate-specific coexpression of BCL2 blocked apoptosis. Thus, there is an mTOR-dependent survival signal required downstream of Akt. Bcl2 expression, however, only partially restored intraluminal cell growth in the setting of mTOR inhibition. Expression profiling showed that Hif-1 alpha targets, including genes encoding most glycolytic enzymes, constituted the dominant transcriptional response to AKT activation and mTOR inhibition. These data suggest that the expansion of AKT-driven prostate epithelial cells requires mTOR-dependent survival signaling and activation of HIF-1 alpha, and that clinical resistance to mTOR inhibitors may emerge through BCL2 expression and/or upregulation of HIF-1 alpha activity.

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.

Ectopic p21sdi1 gene transfer induces retinoic acid receptor beta expression and sensitizes human cancer cells to retinoid treatment

The biological effects of retinoic acid (RA) are mediated by nuclear retinoic acid receptors (RARs) that function as ligand-activated transcriptional factors. The response of human cancer cells to RA is known to be associated with the expression of RARbeta. Recent studies have demonstrated that the loss of RARbeta expression is involved in the development of a variety of human malignancies. We show that recombinant adenovirus-mediated p21(sdi1) gene transfer enhances RARbeta mRNA expression as well as protein expression and induces the sensitivity to all-trans RA (ATRA) in human cancer cells. Semi-quantitative reverse transcription-polymerase chain reaction analysis demonstrated that infection with adenovirus carrying human p21(sdi1) gene (Ad5CMV-p21), which encodes a cyclin-dependent kinase inhibitor, induced RARbeta mRNA and protein expression in H1299 human non-small cell lung cancer cells and DLD-1 human colorectal cancer cells. We also found that exogenous introduction of the p21(sdi1) gene transcriptionally activated the upstream promoter function of the RARbeta gene. Treatment with 1 microM of ATRA showed no significant inhibitory effects on the growth of H1299 and DLD-1 cells; after Ad5CMV-p21 infection, however, cells underwent apoptosis with ATRA treatment at the same concentration, suggesting that p21(sdi1) gene transfer sensitized H1299 and DLD-1 cells, presumably, through RARbeta upregulation. We also demonstrated the efficacy of intratumoral injection of Ad5CMV-p21 in combination with systemic administration of ATRA in a nude mice xenograft model. Our results indicate that recombinant adenovirus-mediated p21(sdi1) gene transfer could be potentially useful for the local induction of RA sensitivity in human premalignant and malignant lesions lacking appropriate RARbeta expression.

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.

Mutational analysis of human thioredoxin reductase 1. Effects on p53-mediated gene expression and interferon and retinoic acid-induced cell death

The interferon (IFN)-beta and all-trans-retinoic acid combination suppresses tumor growth by inducing apoptosis in several tumor cell lines. A genetic technique permitted the isolation of human thioredoxin reductase (TR) as a critical regulator of IFN/all-trans-retinoic acid-induced cell death. Our recent studies have shown that TR1:thioredoxin 1-regulated cell death is effected in part through the activation of p53-dependent responses. To understand its death regulatory function, we have performed a mutational analysis of TR. Human TR1 has three major structural domains, the FAD binding domain, the NADPH binding domain, and an interface domain (ID). Here, we show that the deletion of the C-terminal interface domain results in a constitutive activation of TR-dependent death responses and promotes p53-dependent gene expression. TR mutant without the ID still retains its dependence on thioredoxin for promoting these responses. Thus, our data suggest that TR-ID acts as a regulatory domain.

Novel polyphenol molecule isolated from licorice root (Glycrrhiza glabra) induces apoptosis, G2/M cell cycle arrest, and Bcl-2 phosphorylation in tumor cell lines

Herbal therapies are commonly used by patients with cancer, despite little understanding about biologically active chemical derivatives. We recently demonstrated that the herbal combination PC-SPES, which contains licorice root, had anti-prostate cancer activity attributable to estrogen(s) that produced a chemical castration. A recent study also demonstrated that licorice root alone decreased circulating testosterone in men. Other studies demonstrated antitumor activity of PC-SPES in vitro associated with decreased expression of the anti-apoptotic protein Bcl-2 and in patients independent of chemical castration, suggesting that other mechanisms of antitumor activity exist separate from chemical castration. In the present study, we assessed licorice root extract for effects on Bcl-2 to identify novel cytotoxic derivatives. Licorice root extract induced Bcl-2 phosphorylation as demonstrated by immunoblot and G2/M cell cycle arrest, similarly to clinically used antimicrotubule agents such as paclitaxel. Bioassay-directed fractionations resulted in a biologically active fraction for Bcl-2 phosphorylation. HPLC separation followed by mass spectrometry and NMR identified 6 compounds. Only one molecule was responsible for Bcl-2 phosphorylation; it was identified as 1-(2,4-dihydroxyphenyl)-3-hydroxy-3-(4'-hydroxyphenyl) 1-propanone (beta-hydroxy-DHP). The effect on Bcl-2 was structure specific, because alpha-hydroxy-DHP, 1-(2,4-dihydroxyphenyl)-2-hydroxy-3-(4'-hydroxyphenyl) 1-propanone, in contrast to beta-hydroxy-DHP, was not capable of Bcl-2 phosphorylation. Pure beta-hydroxy-DHP induced Bcl-2 phosphorylation in breast and prostate tumor cells, G2/M cell cycle arrest, apoptosis demonstrated by Annexin V and TUNEL assay, decreased cell viability demonstrated by a tetrazolium (MTT) assay, and altered microtubule structure. Therefore, these data demonstrate that licorice root contains beta-hydroxy-DHP, which induced Bcl-2 phosphorylation, apoptosis, and G2/M cell cycle arrest, in breast and prostate tumor cells, similarly to the action of more complex (MW >800) antimicrotubule agents used clinically.

Phase II and biologic study of interferon alfa, retinoic acid, and cisplatin in advanced squamous skin cancer

PURPOSE

The purpose of this study was to test interferon alfa (IFNalpha), 13-cis-retinoic acid (13cRA), and cisplatin biochemotherapy in advanced squamous cell carcinoma (SCC) of the skin.

PATIENTS AND METHODS

Patients with advanced skin SCC received IFNalpha (5 x 10(6) IU/m(2), subcutaneous injection, three times a week), 13cRA (1 mg/kg, orally, daily), and cisplatin (20 mg/m(2), intravenous injection, weekly) in a phase II trial. The growth inhibition, cell-cycle, and apoptosis activity of these agents was evaluated in two skin SCC cell lines (SRB1-m7 and SRB12-p9).

RESULTS

Thirty-nine patients were enrolled. All were assessable for survival, 35 for response and toxicity (median follow-up was 38 months). The overall and complete response rates were 34% and 17%, respectively, with median durations of 9 and 35.4 months, respectively. The response rate was higher in locally advanced (67%) than metastatic (17%) disease (P =.007). Median survival was 14.6 months. One-, 2-, and 5-year survival rate estimates were 58%, 32%, and 21%, respectively. Toxicity included generally mild to moderate fatigue and mucocutaneous dryness, moderate to severe neutropenia (38%), and neutropenic fever (6%). There were no treatment-related deaths. In vitro growth inhibition and apoptosis effects of cisplatin were differential and inversely associated with those of retinoic acid and especially IFNalpha in two skin SCC lines.

CONCLUSION

The rising incidence, morbidity, and mortality of advanced skin SCC are a major challenge for clinical oncologists. Combined 13cRA, IFNalpha, and cisplatin was clinically active in extensive locally advanced disease. Each agent had independent, non-cross-resistant biologic effects in vitro, which may account for the combination's clinical activity.

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.

Paclitaxel and docetaxel in prostate cancer

Although their ultimate value in prostate cancer therapy remains to be defined in randomized trials, docetaxel and paclitaxel are active agents in HRPC. Combination therapies using either of these taxanes plus oral EMP show reproducible antitumor activity that appears to be greater and more durable than that of single-agent treatment. Although the optimal combination and schedule have not been determined, weekly paclitaxel and EMP and docetaxel given every 3 weeks or by weekly infusion with EMP are useful treatment options for patients with progressive HRPC. The gastrointestinal toxicity of EMP has been reduced by intermittent rather than continuous administration, and other toxicities may be reduced further by use of intravenous EMP. Although there has been progress, the median time to progression of 5 to 6 months for current taxane-based therapies suggests that they will not have major impact on overall survival for patients with HRPC. Greater benefit may be possible earlier in the course of prostate cancer, and the activity of the taxane-EMP combinations is sufficient to justify clinical trials of adjuvant or neoadjuvant chemotherapy for selected groups of patients with locally advanced and poor-prognosis tumors. Armed with many new molecularly targeted agents that may interact favorably with taxanes, it should be possible to build on current antimicrotubule regimens to improve activity in HRPC. Taxane-EMP combinations provide a platform on which to test additional agents that may enhance the apoptotic response or circumvent cellular stress adaptations that confer drug resistance. Further elucidation of signaling pathways that regulate microtubule dynamics and programmed cell death after exposure to microtubule inhibitors would provide a more rational guide for integrating specific inhibitors of signal transduction with current taxane-based therapies. Pharmacokinetic and pharmacodynamic studies will play a key role in the development of future taxane-based therapies for prostate cancer.

Molecular mechanisms of resistance to taxanes and therapeutic implications

The mechanism of resistance to taxanes has not been fully elucidated. Since Taxol is a substrate for P-glycoprotein, overexpression of this transport system is recognized as a relevant mechanism of resistance. Additional mechanisms include changes of microtubule structure and/or composition resulting in reduced drug binding to the target. Current efforts are directed at clarifying the role of cellular response to drug-induced damage to cytoskeleton and mitotic spindle. Downstream events, such as control of cell cycle progression and regulation of cell death pathways, are likely to play a relevant role in cellular sensitivity to antimicrotubule agents. The identification of resistance factors and critical determinants of antitumor efficacy of microtubule-stabilizing agents is essential to (i) improve their therapeutic efficacy; and (ii) to design non-cross-resistant compounds. The present review discusses the possible therapeutic implications of the recent progress in the field of resistance to taxanes. Copyright 1999 Harcourt Publishers Ltd.