Differential effects of retinoic acid and N-(4-hydroxyphenyl)retinamide on head and neck squamous cell carcinoma cells

The effect of retinoids on premalignant oral lesions: focus on topical therapy

BACKGROUND

Retinoids have been studied as chemopreventive treatment for patients with oropharyngeal carcinoma. Vitamin A modulates growth and differentiation of cells, and its deficiency enhances susceptibility to carcinogenesis. The chemopreventive mechanism of action of vitamin A is discussed, and a review of clinical results and side effects of the systemic use of vitamin A is included. The objective of the current report was to review the possible role of topical vitamin A and vitamin A derivatives in the management of patients with oral lesions with a risk of transformation to carcinoma.

METHODS

A Medline search was conducted and references identified within the identified papers were also reviewed.

RESULTS

Only four studies using topical vitamin A for patients with oral leukoplakia have been reported. A complete response was achieved in 10-27% of patients, and a partial response was achieved in 54-90% of patients; however, recurrence of leukoplakia was reported after withdrawing the medication in approximately 50% of patients. The side effects of the topical use were minimal.

CONCLUSIONS

Although the direct application of higher concentrations of retinoic acid results in suppression of oral leukoplakias only, its use in the treatment of patients with recurrent and persistent lesions may be justified for controlling lesions that otherwise may progress. Further controlled clinical studies are needed.

Heterocycle-containing retinoids. Discovery of a novel isoxazole arotinoid possessing potent apoptotic activity in multidrug and drug-induced apoptosis-resistant cells

In a search for retinoic acid (RA) receptor ligands endowed with potent apoptotic activity, a series of novel arotinoids were prepared. Because the stereochemistry of the C9-alkenyl portion of natural 9-cis-RA and the olefinic moiety of the previously synthesized isoxazole retinoid 4 seems to have particular importance for their apoptotic activity, novel retinoid analogues with a restricted or, vice versa, a larger flexibility in this region were designed and prepared. The new compounds were evaluated in vitro for their ability to activate natural retinoid receptors and for their differentiation-inducing activity. Cytotoxic and apoptotic activities were, in addition, evaluated. In general, these analogues showed low cytotoxicity, with the restricted structures being slightly more active than the more flexible ones. As an exception, however, the isoxazole retinoid 15b proved to be particularly able to induce apoptosis at concentrations <5 microM, showing a higher activity than the classical retinoids such as all-trans-RA, 13-cis-RA, and 9-cis-RA and the previously described synthetic retinoid 4. 15b also exhibited a good affinity for the retinoid receptors. Interestingly, another important property of 15b was its ability to induce apoptosis in the HL60R multidrug-resistant (MDR) cell line, at the same concentration as is effective in HL60. Therefore, 15b represents a new retinoid possessing high apoptotic activity in an MDR cell line. The ability of 15b to act on K562 and HL60R cells suggests that this compound may have important implications in the treatment of different leukemias, and its structure could offer an interesting model for the design of new compounds endowed with apoptotic activity on MDR- and retinoid-resistant malignancies.

4-(N-hydroxyphenyl)retinamide can selectively induce apoptosis in human epidermoid carcinoma cells but not in normal dermal fibroblasts

The retinoid 4-(N-hydroxyphenyl)retinamide (4HPR, fenretinide) has both growth inhibitory and apoptosis-inducing effects on a number of cancer cell lines in vitro and in vivo and has been entered into a number of oncological trials. However, little is known about its mechanism(s) of action or its effects on normal cells such as fibroblasts. In this study, the effects of fenretinide on both epidermoid carcinoma cells of vulva (cell line A431) and normal human dermal fibroblasts, both as monolayers and also grown in 3D cell culture systems, have been investigated. The 3D cell culture system contained normal human fibroblasts embedded in a type I collagen gel with the carcinoma cells seeded on top of the collagen gel, which mimics the epidermoid carcinoma. Fenretinide significantly inhibited the rate of DNA synthesis of carcinoma cells, while there was little effect on fibroblasts on monolayers, at 10(-6)-10(-5) M, which are clinically attainable doses. Fenretinide at 5 x 10(-6) M induced apoptosis characterised by cell shrinkage, membrane blebbing, nuclear condensation and/or fragmentation, and cell detachment in carcinoma cells, but not fibroblasts from monolayers. Fenretinide also reduced the viability of carcinoma cells in the 3D cell culture system without affecting fibroblasts. These data show that fenretinide may preferentially induce apoptosis in epidermoid carcinoma cells.

Effects of retinoids on cancerous phenotype and apoptosis in organotypic cultures of ovarian carcinoma

BACKGROUND

Retinoic acid analogues, called retinoids, have shown promise in clinical trials in preventing breast and ovarian cancers. Classic retinoids bind to retinoic acid receptors, which regulate cell growth. Some novel retinoids, such as fenretinide, i.e., N-(4-hydroxyphenyl)retinamide (4-HPR), induce apoptosis through retinoic acid receptor-independent mechanisms; however, they appear to do so only at concentrations above those achieved in clinical chemoprevention trials. At lower concentrations (< or =1 microM), 4-HPR acts like classic retinoids, by inducing differentiation through a receptor-dependent mechanism. Our goal was to compare the effects of novel receptor-independent (apoptotic) retinoids with those of classic growth-inhibitory retinoids at clinically achievable doses on growth, differentiation, and apoptosis in ovarian tissue.

METHODS

Four receptor-independent (apoptotic) and seven growth-inhibitory retinoids, including synthetic, low-toxicity compounds called heteroarotinoids, were administered at concentrations of 1 microM to organotypic cultures of ovarian primary and cancer cell lines: OVCAR-3, Caov-3, and SK-OV-3. After fixation, embedding, and sectioning, the growth fraction was quantified by measuring expression of the proliferation marker Ki-67/myb, differentiation was assessed by expression of mucin, and apoptosis was evaluated by the TUNEL assay. Spearman correlation analysis was performed on the data, and all P values were two-sided.

RESULTS

All 11 retinoids reversed characteristics associated with the cancerous phenotype in all neoplastic cultures. Glandular structures were observed consistently in retinoid-treated, but not in untreated, OVCAR-3 and Caov-3 cultures. All retinoids decreased growth fractions, and some increased mucin expression. All receptor-independent retinoids and two receptor-dependent retinoids induced apoptosis, and the induction correlated significantly with increased expression of the mucin MUC1 (r =.83; P =.03). Retinoids with ester-linking groups did not induce apoptosis but decreased the growth fraction in correlation with MUC1 induction (r = -.93; P =.02).

CONCLUSIONS

At clinically achievable concentrations, all retinoids tested decrease the growth fraction, induce differentiation and apoptosis. Induction of MUC1 expression is implicated in the mechanisms of action.

Heteroarotinoids inhibit head and neck cancer cell lines in vitro and in vivo through both RAR and RXR retinoic acid receptors

A class of less toxic retinoids, called heteroarotinoids, was evaluated for their molecular mechanism of growth inhibition of two head and neck squamous cell carcinoma (HNSCC) cell lines SCC-2 and SCC-38. A series of 14 heteroarotinoids were screened for growth inhibition activity in vitro. The two most active compounds, one that contained an oxygen heteroatom (6) and the other a sulfur heteroatom (16), were evaluated in a xenograph model of tumor establishment in nude mice. Five days after subcutaneous injection of 10(7) SCC-38 cells, groups of 5 nu/nu mice were gavaged daily (5 days/week for 4 weeks) with 20 mg/kg/day of all-trans-retinoic acid (t-RA, 1), 10 mg/kg/day of 6, 10 mg/kg/day of 16, or sesame oil. After a few days, the dose of t-RA (1) was decreased to 10 mg/kg/day to alleviate the side effects of eczema and bone fracture. No significant toxic effects were observed in the heteroarotinoid groups. All three retinoids caused a statistically significant reduction in tumor size as determined by the Student t-test (P < 0. 05). Complete tumor regression was noted in 3 of 5 mice treated with t-RA (1), 4 of 5 mice treated with 16, 1 of 5 mice treated with 6, and 1 of 5 mice treated with sesame oil. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to determine that the expression levels of RARalpha, RXRalpha, and RXRbeta were similar in the two cell lines, while RARbeta expression was higher in SCC-2 over SCC-38, and RARgamma expression was higher in SCC-38 over SCC-2. Receptor cotransfection assays in CV-1 cells demonstrated that 16 was a potent activator of both RAR and RXR receptors, while 6 was selective for the RXR receptors. Transient cotransfection assays in CV-1 cells using an AP-1 responsive reporter plasmid demonstrated that t-RA (1), 6, and 16 each inhibited AP-1-driven transcription in this cell line. In conclusion, the growth inhibition activity of the RXR-selective 6 and the more potent growth inhibition activity of the RAR/RXR pan-agonist 16 implicate both RARs and RXRs in the molecular mechanism of retinoid growth inhibition. Moreover, the chemoprevention activity and the lack of toxicity of heteroarotinoids demonstrate their clinical potential in head and neck cancer chemoprevention.

Fenretinide and its relation to cancer

Retinoids, natural or synthetic substances which have vitamin A activity, have a well-known reputation for their antitumour and differention-inducing activity in vitro and in vivo. More than 1500 retinoids have been tested so far but very few of them have been entered into clinical trials because of their side-effects. All-trans-N-(4-hydroxyphenyl)retinamide (4HPR or fenretinide) is a synthetic retinoid that is reported to have fewer side-effects compared to naturally occurring retinoids such as all-trans retinoic acid (ATRA) and 9-cis retinoic acid. In addition, fenretinide has been shown to induce cell death (apoptosis) even in ATRA-resistant cell lines. Although the mechanism by which fenretinide acts is not entirely known it is considered to be a promising drug and seems to induce apoptosis via different pathway(s) from classical retinoids. In this review, we discuss possible mechanisms of fenretinide action and summarize results of clinical trials.

Tumor growth inhibition and regression induced by photothermal vascular targeting and angiogenesis inhibitor retinoic acid

The effect of photothermal vascular targeting, alone and in combination with antiangiogenic therapy, was evaluated using tumors produced in mice by transplantation of KB cells. Tumor growth inhibition and regression followed vascular damage produced by pulsed dye laser (PDL) radiation. Administration of the antiangiogenic agent all-trans-retinoic acid (RA) was associated with smaller average tumor volumes in the presence and absence of PDL irradiation, but this effect was not statistically significant. The ability of PDL photothermal vascular targeting to cause regression of tumors without harming normal tissue may be a consequence of preferential damage to supplying vessels at the tumor periphery.

Fenretinide-induced apoptosis of human head and neck squamous carcinoma cell lines

BACKGROUND

Squamous cell carcinoma of the head and neck (HNSCC) has a high incidence of recurrence and associated second primary malignancy. The retinoid 13-cis-retinoic acid has been shown to be effective as both a chemopreventive and chemotherapeutic agent for HNSCC, but often with treatment-limiting toxicity. The synthetic retinoid fenretinide (N-(4-hydroxyphenyl)retinamide) (HPR) has significant antiproliferative activity against a number of animal and human malignancies and has been used in clinical trials as a chemopreventive agent in patients with breast and prostate cancer and oral leukoplakia. HPR has been shown to have a toxicity profile lower than that for other retinoids used in clinical trials.

PURPOSE

The aim of this study was to investigate the effect of HPR on the growth of HNSCC cell lines in vitro.

METHODS

Four HNSCC cell lines (JHU-011-SCC, JHU-020-SCC, JHU-022-SCC, and FaDu) were treated with a range of concentrations of HPR for various times. After HPR exposure, cell viability was determined by tetrazolium dye (MTT) colorimetric assay, comparing cell survival with that of untreated control cells. HPR-induced apoptosis was determined by flow-cytometric deoxyribonucleic acid cell-cycle analysis, ultrastructural analysis with electron microscopy, and deoxyribonucleic acid fragmentation detected by gel electrophoresis.

RESULTS

HPR caused significant growth inhibition in three of the four HNSCC cell lines in a dose- and time-dependent fashion. In two cell lines (JHU-011-SCC, JHU-020-SCC) a significant antiproliferative effect was achieved between 1 and 2.5 micromol/L HPR after 72 hours of treatment. By deoxyribonucleic acid cell-cycle analysis, electron microscopy, and gel electrophoresis, HPR was shown to induce apoptosis in the JHU-011-SCC and JHU-020-SCC cell lines, but not in the FaDu cell line, which was insensitive to the growth inhibitory effect of HPR.

CONCLUSIONS

This study has demonstrated that HPR reduces cell viability in HNSCC cells in vitro at clinically relevant doses, with the growth inhibition occurring through the induction of apoptosis.

The cloning and characterization of a novel cytochrome P450 family, CYP26, with specificity toward retinoic acid

A new family of cytochrome P450 enzymes, CYP26, has been cloned and characterized in zebra fish, human, and mouse tissues. CYP26 displays specificity toward retinoic acid and it may function as an important regulator or differentiation and a possible modulator of disease states by controlling retinoid concentration and homeostasis.