Retinoid mechanisms and cyclins

Phase I trial of belinostat in combination with 13-cis-retinoic acid in advanced solid tumor malignancies: a California Cancer Consortium NCI/CTEP sponsored trial

PURPOSE

The reported maximum tolerated dose (MTD) of single-agent belinostat is 1000 mg/m² given days 1-5, every 21 days. Pre-clinical evidence suggests histone deacetylase inhibitors enhance retinoic acid signaling in a variety of solid tumors. We conducted a phase I study of belinostat combined with 50-100 mg/m²/day 13-cis-retinoic acid (13-cRA) in patients with advanced solid tumors.

METHODS

Belinostat was administered days 1-5 and 13-cRA days 1-14, every 21 days. Dose-limiting toxicity (DLT) was defined as cycle 1 hematologic toxicity grade ≥ 3 not resolving to grade ≤ 1 within 1 week or non-hematologic toxicity grade ≥ 3 (except controlled nausea and vomiting and transient liver function abnormalities) attributable to belinostat.

RESULTS

Among 51 patients, two DLTs were observed: grade 3 hypersensitivity with dizziness and hypoxia at 1700 mg/m²/day belinostat with 100 mg/m²/day 13-cRA, and grade 3 allergic reaction at 2000 mg/m²/day belinostat with 100 mg/m²/day 13-cRA. The MTD was not reached. Pharmacokinetics of belinostat may be non-linear at high doses. Ten patients had stable disease, including one with neuroendocrine pancreatic cancer for 56 cycles, one with breast cancer for 12 cycles, and one with lung cancer for 8 cycles. Partial responses included a patient with keratinizing squamous cell carcinoma of the tonsils, and a patient with lung cancer.

CONCLUSIONS

The combination of belinostat 2000 mg/m² days 1-5 and 13-cRA 100 mg/m² days 1-14, every 21 days, was well-tolerated and an MTD was not reached despite doubling the established single-agent MTD of belinostat.

Retinoic acid promotes primary fetal alveolar epithelial type II cell proliferation and differentiation to alveolar epithelial type I cells

Retinoic acid (RA) plays an important role in lung development and maturation. Many stimuli can induce alveolar epithelial cell damage which will result in the injury of lung parenchyma. The aim of this study was to observe the effect of RA on the proliferation and differentiation of primary fetal alveolar epithelial type II cells (fAECIIs). Primary fAECIIs were isolated from fetal rats at 19 d of gestation and purified by a differential centrifugation and adhesion method. The cells were randomly divided into control (dimethyl sulfoxide, DMSO) and RA groups. Cell proliferation, viability, apoptosis, cycle, and expression of target protein were examined at 24, 48, and 72 h. We found that the proliferation and viability of cells in the RA-exposed group significantly increased compared with the DMSO control group. The proportion (%) of cells in the G2 and S phases in the RA group was significantly higher than that in control group cells. The proportion (%) of both early apoptotic cells and late apoptotic cells decreased significantly in cells exposed to RA compared with cells exposed to DMSO. RA significantly enhanced the expression of aquaporin 5 (AQP5). The expression level of pulmonary surfactant C (SPC) was elevated after cells were exposed to RA for 24 and 72 h but was inhibited when cells were exposed to RA for 48 h. These results suggest that RA promotes fAECII proliferation by improving cell viability, promoting S phase entry and inhibiting apoptosis and RA promotes fAECIIs differentiation to alveolar epithelial type I cells (AECIs).

Anti-tumor effects of a novel retinoic acid metabolism blocking agent VN/14-1 in the N-methyl-N-nitrosourea-induced rat mammary carcinoma model and its effects on the uterus

VN/14-1 [4-(±)-(1H-Imidazol-1-yl)-(E)-retinoic acid], a novel retinoic acid metabolism blocking agent (RAMBA), works by inhibiting the breakdown of all-trans-retinoic acid. The purpose of this study was to evaluate the anti-tumor effects of VN/14-1 on the N-methyl-N-nitrosourea (MNU)-induced rat mammary carcinoma model, and peripheral organ effects on the uteri of immature ovariectomized (OVX) rats. In tumor burden experiments, after 56 days of administration of VN/14-1 5, 10, and 20 mg/kg/day, significant tumor reductions in mean tumor weight of 19.1, 34.4, and 44.3%, compared to tumors in control animals occurred. Cumulative tumor growth was also significantly slower in a dose-dependent manner in groups receiving 5, 10, and 20 mg/kg/day of VN/14-1 compared to growth rates in the control group. Tumor apoptosis was significant increases in animals treated with 5, 10, and 20 mg/kg/day of VN/14-1. In uterotrophic experiments, immature OVX rats given VN/14-1 significantly reduced uterine weight and blocked endometrial stimulation induced by unopposed β-estradiol (E2). In both rat models, adverse toxicities included weakness, anorexia, and reduction in body weight in the groups given the highest dose of 20 mg/kg/day. In summary, VN/14-1 inhibited tumor growth in the MNU-induced estrogen receptor (ER)-positive rat mammary tumor model, and antagonized the stimulatory effect of estrogens on the uterus. The studies suggest that VN/14-1 may be a useful novel therapy for ER-positive breast cancer.

Effect of all-trans retinoic acid on renal expressions of matrix metalloproteinase-2, matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 in rats with glomerulosclerosis

In kidney injury the accumulation of extracellular matrix (ECM) plays an important role and precedes the development of glomerulosclerosis (GS). There is great interest in agents that may interfere with such accumulation of ECM. Therefore, a rat model of GS was established to investigate the effect of all-trans retinoic acid (ATRA) on the renal expressions of matrix metalloproteinase-2 (MMP-2), matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1). Eighty Wistar rats were randomly divided into four groups: sham operation group (SHO), GS model group without treatment (GS), GS model group treated with benazepril (GB) and GS model group treated with ATRA (GA), n = 20, respectively. The disease was established in the GS rats by uninephrectomy and adriamycin (5 mg/kg) injection through the tail vein. Serum creatinine (Scr), blood urea nitrogen (BUN) and urine protein (Upro) were measured. Renal abnormality was evaluated at the end of 12 weeks. Immunohistochemical analysis was performed on renal tissue to detect the expression of collagen IV (Col-IV), fibronectin (FN), MMP-2, MMP-9 and TIMP-1 protein. MMP-2 and MMP-9 activity was detected by gelatin zymography. Real-time reverse transcription polymerase chain reaction (real-time RT-PCR) was used to detect the expression of MMP-2, MMP-9, and TIMP-1 mRNA. In comparison with group GS, group GA and group GB exhibited levels of BUN and 24 h urinary protein and a glomerulosclerosis index (GSI) that were significantly reduced (P < 0.05); the level of Scr in group GA was reduced too (P < 0.05). ATRA and benazepril also significantly down-regulated Col-IV, FN expression and TIMP-1 expression (protein and mRNA) (P < 0.05). In contrast, the expressions of MMP-2, MMP-9 mRNA and protein, and activity in groups GA and GB were enhanced (P < 0.05). However, there were no significant differences in MMP-2, MMP-9 mRNA and protein expression, or activity, between the ATRA and GB groups (P > 0.05). In conclusion, ATRA may protect renal function and step down the progression of GS by reducing the expression of TIMP-1, enhancing the expression and activity of MMP-2 and MMP-9, and regulating the ratio of MMPs/TIMPs to dynamic balance, so as to reduce the accumulation of ECM.

Novel retinoic acid metabolism blocking agents have potent inhibitory activities on human breast cancer cells and tumour growth

Antitumour effects of retinoids are attributed to their influence on cell proliferation, differentiation, apoptosis and angiogenesis. In our effort to develop useful agents for breast cancer therapy, we evaluated the effects of four representative retinoic acid metabolism blocking agents (RAMBAs, VN/14-1, VN/50-1, VN/66-1 and VN/69-1) on growth inhibition of oestrogen receptor positive (ER +ve, MCF-7 and T-47D) and oestrogen receptor negative (ER −ve, MDA-MB-231) human breast cancer cells. Additionally, we investigated the biological effects/molecular mechanism(s) underlying their growth inhibitory properties as well as their antitumour efficacies against MCF-7 and MCF-7Ca tumour xenografts in nude mice. We also assessed the effect of combining VN/14-1 and all-trans-retinoic acid (ATRA) on MCF-7 tumuor xenografts. The ER +ve cell lines were more sensitive (IC₅₀ values between 3.0 and 609 nM) to the RAMBAs than the ER −ve MDA-MB-231 cell line (IC₅₀=5.6–24.0 μM). Retinoic acid metabolism blocking agents induced cell differentiation as determined by increased expression of cytokeratin 8/18 and oestrogen receptor-α (ER-α). Similar to ATRA, they also induced apoptosis via activation of caspase 9. Cell cycle analysis indicated that RAMBAs arrested cells in the G1 and G2/M phases and caused significant downregulation (>80%) of cyclin D1 protein. In vivo, the growth of MCF-7 mammary tumours was dose-dependently and significantly inhibited (92.6%, P<0.0005) by VN/14-1. The combination of VN/14-1 and ATRA also inhibited MCF-7 breast tumour growth in vivo (up to 120%) as compared with single agents (P<0.025). VN/14-1 was also very effective in preventing the formation of MCF-7Ca tumours and it significantly inhibited the growth of established MCF-7Ca tumours, being as effective as the clinically used aromatase inhibitors, anastrozole and letrozole. Decrease in cyclin D1 and upregulation of cytokeratins, Bad and Bax with VN/14-1 may be responsible for the efficacy of this compound in inhibiting breast cancer cell growth in vitro and in vivo. Our results suggest that our RAMBAs, especially VN/14-1 may be useful novel therapy for breast cancer.

Murine toxicology and pharmacokinetics of novel retinoic acid metabolism blocking agents

PURPOSE

Novel potent C-4 azolyl retinoic acid metabolism blocking agents (RAMBAs)-VN/14-1, VN/50-1, VN/66-1, VN/67-1, and VN/69-1, have been synthesized and investigated for their in vitro and in vivo effects against breast and prostate cancers. These RAMBAs, in addition to being potent inhibitors of all-trans-retinoic acid (ATRA) metabolism have potent anti-cancer properties and in vivo anti-tumor efficacies as characterized in breast and prostate cancer models. Here we determined the toxicity and pharmacokinetics (PK) of these various RAMBAs.

METHODS

Preliminary acute toxicity studies of these RAMBAs were carried out using Swiss NIH mice. The toxicity profile of the RAMBAs was evaluated relative to ATRA. Three different doses (8.3, 33, and 100 micromol/kg/day) of ATRA and RAMBAs were administered on a daily basis subcutaneously for 14 days to the mice. Clinical signs of toxicity alopecia, scaly skin, and loss of body weight in the mice were observed during the study and the maximum tolerated dose was determined. PK of selected agents (VN/14-1, VN/50-1, and VN/66-1) was studied in Balb/C mice after a single dose subcutaneous administration. Plasma concentrations of the agents were quantitatively determined using a high-performance liquid chromatographic method with ultraviolet detection. Plasma concentration versus time profiles were fit to various PK structural models and relevant PK parameters were estimated.

RESULTS

VN/66-1 and VN/69-1 were found to be the least toxic even at the highest doses when compared to the other RAMBAs and ATRA. VN/66-1 had the longest half-life, the slowest clearance, and the greatest exposure.

CONCLUSIONS

Based on PK characteristics and toxicity studies, VN/66-1 appeared to be the most favorable agent. However, both VN/14-1 and VN/66-1 are our leads based on the fact that VN/14-1 has been found to be highly effective in endocrine-sensitive and -resistant breast cancer cells and tumors with little toxicity. Our findings provide valuable information that will be used to select RAMBAs and establish therapeutic regimens that provide optimal efficacy with minimal toxicity.

Role of retinoid signaling in the regulation of spermatogenesis

While the need for vitamin A for the normal progression of male germ cell differentiation has been known for many years, the molecular mechanisms underlying this requirement are poorly understood. This review will explore the aspects of the effects on spermatogenesis of dietary deprivation of vitamin A, in particular as to how they compare to the male sterility that results from the genetic ablation of function of the retinoid receptor RARalpha. The effects of other genes involved with retinoid synthesis, transport, and degradation are also considered. The possible cellular mechanisms that may be affected by the lack of retinoid signaling are discussed, in particular, cell cycle regulation and cell-cell interaction, both of which are critical for normal spermatogenesis.

Retinoid-X-receptor alpha (RXRalpha) expression during laryngeal carcinogenesis: detrimental or beneficial event?

RXRalpha is an obligatory heterodimerization partner in many signal transducing pathways. To evaluate RXRalpha expression during laryngeal carcinogenesis, immunohistochemistry was performed on laryngeal epithelial specimens of 154 patients with normal-appearing, hyperplastic, dysplastic laryngeal epithelium and squamous cell carcinoma. RXRalpha up-regulation was detected from the early stages of laryngeal carcinogenesis compared with normal epithelium. Statistical analysis and correlation of the intensity of nuclear immunostaining among the various histologic entities revealed statistically significant results. We pose that RXRalpha overexpression might represent an early protective effect in the process of laryngeal carcinogenesis that might be overwhelmed by an epigenetic disability in forming heterodimers with PPARgamma.

Linkage between retinoid and fatty acid receptors: implications for breast cancer prevention

Certain dietary retinoids and polyunsaturated fatty acids (PUFAs) consistently inhibit progression of mammary carcinogenesis both in animal studies and cell culture, but clinically, their effect is inconsistent. New evidence of synergistic interaction between the nuclear receptors for the two groups of nutritional agents suggests that appropriate selective ligands from each group might be combined in breast cancer chemoprevention studies. Peroxisome proliferator-activated receptor (PPAR) gamma is a nuclear receptor that is activated by PUFAs, eicosanoids and antidiabetic agents such as troglitazone. Such activation can cause growth inhibition in human mammary cancer cells in culture and the effect is enhanced by ligands of retinoic acid receptor (RAR) and retinoid X receptor (RXR). In mouse mammary tissue in organ culture, an RXR-selective ligand has been shown to enhance the effect of troglitazone in suppressing carcinogen-induced pre-neoplastic changes. A PPAR/RXR heterodimer is involved in tumour growth inhibition and has been shown to bind directly to nuclear oestrogen response elements (ERE) independently of oestrogen receptor (ER) activity. A combination of an RXR-selective retinoid with either troglitazone or else a long-chain n-3 PUFA, is proposed for a short-term study in postmenopausal women after primary surgery for intraductal breast cancer. The resulting activation of PPAR/RXR expression may increase response to retinoid administration, especially in the presence of obesity and insulin resistance, because of the ability of PPAR gamma ligands to reduce insulin-like growth factor I (IGF-I) concentrations. Serial core biopsies of breast tissue over a short term are proposed to identify changes in phenotype, which may influence progression to invasiveness. In addition to cytomorphological criteria, expression of ER alpha and beta, RAR alpha and beta, and IGF-I receptor in the nucleus should be examined.

Classical and novel retinoids: their targets in cancer therapy

Retinoids are important mediators of cellular growth and differentiation. Retinoids modulate the growth of both normal and malignant cells through their binding to retinoid nuclear receptors and their subsequent activation. While retinoids have demonstrated therapeutic efficacy in the treatment of acute promyelocytic leukemia, their spectrum of activity remains limited. Other agents such as histone deacetylase inhibitors may significantly increase retinoid activity in a number of malignant cell types. The novel retinoids N-(4-hydroxyphenyl) retinamide (4-HPR) and 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437; AHPN) induce apoptosis in a wide variety of malignant cells. Their mechanism(s) of action remain unclear, although a number of potential targets have been identified. Whether the retinoid receptors are involved in 4-HPR and CD473/AHPN mediated apoptosis remains unclear. Both 4-HPR and CD437/AHPN display significant potential as therapeutic agents in the treatment of a number of premalignant and malignant conditions.