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

Development of flexible-heteroarotinoids for kidney cancer

Potential chemopreventive and therapeutic value of the lead Flexible Heteroarotinoid (Flex-Het), SHetA2, was indicated by growth inhibition of multiple cancer cell lines. The objective of this study was to evaluate the SHetA2 mechanism and in vivo activity in kidney cancer. SHetA2 induced apoptosis in the Caki-1 kidney cancer cell line through reduction of Bcl-2 protein and induction of PARP-1 and caspase 3 cleavages, whereas normal kidney epithelial cells exhibited resistance. Both normal and cancerous cells underwent G(1) arrest and loss of Cyclin D1. Tubule differentiation was induced in organotypic cultures and xenograft tumors in association with increases in E-Cadherin mRNA and protein expression. SHetA2 repressed activity of nuclear factor-κB, a transcription factor that regulates apoptosis, Bcl-2, growth, Cyclin D1, differentiation, and E-Cadherin in the opposite manner as SHetA2. Glutathione binding and generation of reactive oxygen species were not required for these activities. Oral SHetA2 inhibited growth in one of two renal cancer xenograft models without causing mortality or weight loss. Structure function analysis of related Flex-Hets for potential improvement of SHetA2 pharmaceutical properties showed that compounds with increased hydrophilicity slightly reduced the growth inhibition efficacy, but retained the differential effect on cancer over normal cells. Flex-Hets and metabolites were not mutagenic in the Ames test. In conclusion, SHetA2 regulates growth, differentiation, and apoptosis in kidney cancer cells through multiple molecular events downstream of nuclear factor-κB repression. Increasing the hydrophilicity of Flex-Hets does not attenuate the differential effect on cancer cells over normal cells, thus offering alternatives for improvement of therapeutic value.

Phase II studies of antiangiogenic four drug regimens for the treatment of advanced renal cell carcinoma: FUNIL-retinoid and the FUNIL-thalidomide protocols

BACKGROUND AND PURPOSE

The objective of these studies was to determine the activity of two alternative 4- drug combinations using cis-retinoic acid or thalidomide administered with a previously developed combination of 5 fluorouracil, interferon-alpha, and interleukin 2 (FUNIL), for patients with metastatic renal cell carcinoma (RRC).

METHODS

Patients enrolled in these studies had progressive measurable metastatic renal cell cancer and signed an informed consent. Treatments included continuous infusions of 5-fluorouracil, interferon-alpha, 6 MIU/m2 given subcutaneous on days 1, 3, and 5 every week, interleukin-2 6 MIU/m2/day given by continuous infusion days 2 to 5 every week, and either cis-retinoic acid at a dose of 1 mg/kg/day orally in two divided doses or thalidomide given at an initial dose of 200 mg per day. Each cycle consisted of 6 or 4 weeks of the combinations, respectively, followed by a 2-week rest. Patients were evaluated for response prior to each successive cycle. A 2-step mini-max statistical design was used.

RESULTS

In the cis-retinoid study, 20 patients were enrolled. One patient was ineligible. There were 1 complete and 2 partial responses (one confirmed and one unconfirmed) (15.8%), 1 stable disease, and 15 disease progression. In the thalidomide combination study, 20 patients were enrolled, but only 19 are assessable. One patient progressed early and was never treated. There were 2 partial responses (10.5%), 4 stable disease, and 13 progressive disease.

CONCLUSION

Neither the FUNIL-cis-retinoid nor the FUNIL-thalidomide regimens met their primary objective first step endpoint of 3 confirmed responses. Both regimens had significant adverse effects and neither is considered promising for further study.

Phase 1/2 Clinical Trial of Interferon α2b and Weekly Liposome-encapsulated All-trans Retinoic Acid in Patients With Advanced Renal Cell Carcinoma

To evaluate the feasibility, efficacy, and biologic effects of weekly liposome-encapsulated all-trans retinoic acid (ATRA-IV) plus interferon alpha2b (IFN) in patients with advanced renal cell carcinoma (RCC). Twenty-six patients with metastatic RCC were treated on a phase 1/2 trial with weekly ATRA-IV and IFN SQ daily 5 d/wk. Twelve patients received ATRA-IV at three dose levels (60, 75, and 90 mg/m2) according to phase 1 methodology, and 14 additional patients received 90 mg/m2. Response was assessed according to an intention-to-treat analysis. Serum retinoic acid (RA) concentrations were assayed and peripheral blood mononuclear cell mRNA expression of RA and IFN-inducible genes (RARalpha, RARbeta2, IRF1, CRABP2, and TRAIL) were examined. No dose limiting toxicities occurred at 60 mg/m2; grade 3 leukopenia affected 1/6 patients at 75 mg/m2, whereas 3 patients received 90 mg/m2 without a dose limiting toxicities. Fourteen additional patients received 90 mg/m2 ATRA-IV without grade 3/4 toxicity. Five of 26 (19%) patients achieved a major response, with a median duration of 14 months (range 9 to 23); 9 additional patients (41%) demonstrated stable disease or minor response lasting > or =4 months. No significant differences in serum (RA) after ATRA infusion were detected between weeks 1 and 8 of treatment. Peripheral blood mononuclear cell mRNA expression did not correlate with clinical response. The addition of weekly ATRA-IV to IFN therapy is feasible and well tolerated, resulting in sustainable increased serum (RA). This regimen demonstrates antitumor activity in metastatic RCC, and suggests ATRA-IV augments IFN therapy.

Expression and functional influence of cellular retinoic acid-binding protein II in renal cell carcinoma

INTRODUCTION

Retinoic acid (RA) and its derivates possess antiproliferative and tumor-suppressive abilities and are successfully used in the treatment of various malignancies. However, in metastatic renal cell carcinoma (RCC), its application did not meet first expectations. As the exact mechanisms of RA action and especially the role of the cellular retinoic acid-binding proteins (CRABP) still remain unclear, we studied the expression of CRABP-II and its potential influence on RA response in RCC.

MATERIALS AND METHODS

We used the real-time RT-PCR methodology to investigate CRABP-II expression in 12 RCC samples and corresponding normal kidney tissue. Moreover, CRABP-II was cloned and overexpressed in CAKI-2 RCC cells. CRABP-II (un)transfected CAKI-2 cells were stimulated with all-trans RA (ATRA) and 9-cis RA, and their antiproliferative effects were evaluated using 3H-thymidine-proliferation assays.

RESULTS

Using RPS9 and RPLP0 to normalize its expression, the median tumor/kidney ratio for CRABP-II expression was 0.16 and 0.12, respectively. Using proliferation assays, CRABP-II overexpressing CAKI-2 cells did not exhibit a significant change in RA sensitivity, but appeared to be less sensitive toward RA-stimulation compared to CAKI-2 cells expressing naturally low levels of CRABP-II (maximum difference, 59% at 3 microM ATRA).

CONCLUSIONS

We were able to demonstrate a downregulation of CRABP-II expression in primary RCC tumor samples compared to the corresponding normal kidney tissue. However, CRABP-II overexpression in CAKI-2 RCC cells did not significantly influence RA associated antiproliferative actions. Further experiments are necessary to define the exact role of CRABP-II and its downregulation in RCC including its influence and dependence on other molecules involved in RA signalling and metabolism.

Second-line strategies for metastatic renal cell carcinoma: classics and novel approaches

OBJECTIVES

Renal cell carcinoma is an aggressive malignancy with a high propensity for both early and metachronous regional and distant metastasis. While surgical resection is the mainstay of therapy for patients with localized disease, the prognosis for patients with distant metastasis is poor with a 5-year survival rate of less than 10%. Response rates to first-line immunotherapy or immunochemotherapy range from 10-35%; responses achieved are predominantly partial remissions of short duration. Until today, there is no standard therapeutic procedure for the growing number of patients who relapse following first-line therapy and desire further active treatment.

MATERIALS AND METHODS

This article reviews classic and recent publications about second- and third-line approaches, their potential efficacy and toxicity.

RESULTS

Several novel approaches have raised well-founded hope. Especially the application of monoclonal antibodies targeting VEGF signalling as well as different receptor tyrosine kinase inhibitors have the potential to change the face of second-line treatment of patients with metastatic RCC. Both groups of agents are focused in current phase III trials, either as mono- and/or combination therapy.

CONCLUSIONS

Until today, second-line treatment of patients with metastatic RCC progressing under therapy with biological response modifiers remains an unresolved issue. The results of ongoing clinical trials evaluating novel targeted approaches can be expected with suspense.

Cellular retinoic acid binding protein I: expression and functional influence in renal cell carcinoma

Despite the known anti-proliferative and tumor-suppressive effects seen with retinoic acid (RA), treatment of metastatic renal cell carcinoma (RCC) failed to meet the initial expectations. As the exact mechanisms of action of RA and especially the role of the cellular RA binding proteins (CRABP) have not been elucidated yet, we investigated the expression of CRABP-I and its potential influence on RA response in RCC. Real-time RT-PCR analysis disclosed a significant lack of CRABP-I expression in four RCC cell lines and 12 primary RCC samples; in contrast, high expression levels were found in the respective adjacent normal kidney tissue. To further investigate the impact of CRABP-I on RA response in RCC, A-498 RCC cells were employed as a cellular model system. CRABP-I was stably transfected into A-498 cells which consequently displayed substantial resistance to all-trans (ATRA) and 9-cis RA compared to vector controls lacking CRABP-I. Comparison of gene expression profiles of ATRA-treated CRABP-I-expressing A-498 cells and vector controls revealed specific regulation of 54 of approximately 20,000 genes tested on a selected human CodeLink UniSet Bioarray, with a prominent modulation of genes involved in transcriptional control, signaling, apoptosis, cell cycle regulation and metabolism. The genetic changes reported here contribute to a better understanding of the role of RA in RCC. They also provide new insights into CRABP-I-mediated signaling and gene expression.