Synergistic effect of a retinoid X receptor-selective ligand bexarotene (LGD1069, Targretin) and paclitaxel (Taxol) in mammary carcinoma

We have previously shown that the retinoid X receptor (RXR) ligand bexarotene (LGD1069, Targretin) is efficacious as a chemopreventive and chemotherapeutic agent in rat N-nitroso-N-methylurea (NMU)-induced mammary carcinomas (Cancer Res 58: 479-484, 1998). To determine additional role for bexarotene in breast cancer treatment, we evaluated the effect of bexarotene on the efficacy of paclitaxel (Taxol) treatment in a rat NMU-derived mammary tumor cell line, NMU-417, in vitro and in rat NMU-induced mammary tumors in vivo. Our growth inhibition results showed that the bexarotene/paclitaxel combination produced a concentration-dependent synergy in NMU-417 tumor cell line. Synergistic growth inhibition by the combination was associated with an increase in cell death induced by both agents. In rat NMU-induced mammary tumor model in vivo, the benefit of combination therapy was observed as early as 1 week after treatment and increased as treatment continued. At the end of 6 weeks of treatment, the bexarotene/paclitaxel combination produced an overall objective response rate of 94% compared with a rate of 12% in paclitaxel-treated and 58% in bexarotene-treated animals, an effect that was more than the additive effects produced by single agents. Although both bexarotene alone and the bexarotene/paclitaxel combination reduced tumor multiplicity to similar extent, the combination regimen produced a statistically significant decrease in total tumor burden compared to single agents and untreated controls (two-tailed, p < 0.05). Combination therapy did not further alter body weight nor increase toxicity when compared to single agents. In summary, our results demonstrated the potential of using a RXR selective ligand in combination with chemotherapy for the treatment of breast cancer.

Cutaneous T-cell lymphoma treatment using bexarotene and PUVA: A case series

BACKGROUND

Mycosis fungoides, the most common form of cutaneous T-cell lymphoma, often presents as chronic eczematous or psoriasiform patches and plaques that can be resistant to a variety of single-agent treatment modalities, necessitating combination therapy.

OBJECTIVE

To evaluate the efficacy of combination therapy with bexarotene and psoralen plus ultraviolet A (PUVA) in treating patients with cutaneous T-cell lymphoma (CTCL) that recurred following monotherapy with multiple agents, including electron-beam irradiation, interferon, PUVA, and topical steroids. This was done by retrospective chart review.

METHODS

Retrospective chart review analysis of eight patients with CTCL ranging from stage Ia to IIb who failed multiple single-agent treatment regimens treated with low-dose oral bexarotene and PUVA combination therapy.

RESULTS

We noted an initial response in all eight patients and complete remission in five of the patients treated, with pruritus being the most common adverse event.

CONCLUSION

In view of its good safety profile, combination therapy with bexarotene and PUVA may be considered for patients with treatment resistant CTCL refractory to monotherapy.

Systemic treatment of psoriatic patients with bexarotene decreases epidermal proliferation and parameters for inflammation, and improves differentiation in lesional skin

BACKGROUND

Bexarotene, a novel synthetic retinoid X receptor (RXR)-selective retinoid, has been reported to have antiproliferative and apoptotic stimulating effects in cutaneous T-cell lymphoma. In benign, hyperproliferative, and retinoid sensitive disorders, such as psoriasis, bexarotene has not been evaluated so far and no information on these parameters is available.

OBJECTIVE

In the present study, immunohistochemical parameters for proliferation, differentiation, inflammation, and apoptosis were investigated in a group of bexarotene-treated psoriatic patients.

METHODS

Twenty-nine patients with plaque-type psoriasis were treated for 12 weeks with oral bexarotene in four dose-defined treatment panels. Treatment was initiated in the following consecutive order: 1.0 mg/kg/day, 2.0 mg/kg/day, 0.5 mg/kg/day, and 3.0 mg/kg/day. Biopsies for immunohistochemical analysis were taken at the baseline and after 12 weeks of treatment.

RESULTS

Significant reductions in Ki-67, keratin 16, transglutaminase, dermal CD4, epidermal CD8, and inflammation scores were seen after bexarotene treatment in combination with a significant increase in keratin 10. No induction of keratin 13 and 19 and no alterations in apoptosis associated p53 expression were observed. Apart from a weak significant dose-response effect for Ki-67, no other significant dose-response effects were seen.

CONCLUSION

We have demonstrated efficacy of oral bexarotene in psoriasis in doses up to 3.0 mg/kg/day during 12 weeks of treatment for proliferation, differentiation, and inflammation parameters. Studies investigating higher doses of bexarotene in a larger number of patients are necessary to reveal potentially dose-related immunohistochemical effects of this new rexinoid and to elucidate the role of RXR-signaling in retinoid-associated keratin expression.

A phase II multicenter clinical trial of systemic bexarotene in psoriasis

BACKGROUND

Bexarotene, a novel and unique synthetic P, RXR-selective retinoid, is available as a treatment for cutaneous T-cell lymphoma. In psoriasis, a common retinoid-sensitive disease, no data are available on bexarotene treatment.

OBJECTIVE

In this phase II study we investigated the safety, tolerability, and effectiveness of bexarotene in psoriasis at doses of 0.5 to 3.0 mg/kg/day.

METHODS

Fifty patients with moderate to severe plaque-type psoriasis were treated with bexarotene in 4 sequential dose-defined panels of 12-13 patients at doses of 1.0, 2.0, 0.5, and 3.0 mg/kg/day for 12-24 weeks. Patients were monitored for safety and clinical efficacy.

RESULTS

No serious adverse events related to the drug occurred. Bexarotene was well tolerated in most patients. Most frequently observed adverse events related to bexarotene were hypertriglyceridaemia (56%) and a decrease in free T4 serum levels (54%). Significant improvement of psoriasis after bexarotene at all doses was confirmed by a modified psoriasis area and severity index (mPASI), plaque elevation (PEL), and physician's global assessment (PGA). Overall response rates (> or =50% improvement) for mPASI, PEL, and PGA were 22%, 52%, and 36%, respectively. No significant dose-response effect was established for these parameters.

CONCLUSION

The present study indicates an anti-psoriatic effect of bexarotene. Further studies are necessary to assess the optimal dose and the potential for bexarotene as a new therapy for psoriasis.

Bexarotene: a clinical review

Bexarotene (Targretin, Ligand Pharmaceuticals Inc.) is a synthetic retinoid analog with specific affinity for the retinoid X receptor and belongs to a group of compounds called rexinoids. Early clinical trials of this drug demonstrated activity in cutaneous T-cell lymphoma. Subsequent Phase II/III trials have demonstrated a greater than 50% response rate in patients with all stages of cutaneous T-cell lymphoma who were refractory or intolerant to the previous therapy. The principal toxicities of bexarotene include central hypothyroidism, xeroderma and elevation of cholesterol and triglycerides. These toxicities can be managed with dose attenuation or addition of atorvastatin (Lipitor, Pfizer) or fenofibrate (TriCor, Abbott Laboratories). Since bexarotene has little bone marrow toxicity, it is an excellent candidate for combination therapy with other modalities useful in the treatment of cutaneous T-cell lymphoma. These include ultraviolet B irradiation, psoralen and ultraviolet A photochemotherapy, interferons, denileukin diftitox (Ontak, Ligand Pharmaceuticals Inc.) and cytotoxic chemotherapy. Bexarotene has also been investigated in the treatment of breast cancer and non-small cell carcinoma of the lung with promising early results.

The Novel Synthetic Oleanane Triterpenoid CDDO (2-cyano-3, 12-dioxoolean-1, 9-dien-28-oic acid) Induces Apoptosis in Mycosis Fungoides/Sézary Syndrome Cells

The novel synthetic oleanane triterpenoid CDDO (2-cyano-3, 12-dioxoolean-1, 9-dien-28-oic acid) can serve as a ligand for the peroxisome proliferator activator receptor-gamma (PPAR-gamma) and has been shown to inhibit cell proliferation, and to induce differentiation and apoptosis in tumor cell lines. Bexarotene is an RXR-selective retinoid that can induce apoptosis of mycosis fungoides (MF) and Sézary syndrome (SS) cells. Since the PPAR-gamma and RXR receptors can form heterodimers, we studied the effects of CDDO and its synergism with bexarotene on apoptosis in MF/SS cell lines (MJ, Hut78, and HH) and freshly isolated peripheral blood lymphocytes (PBL) from SS patients with circulating atypical T cells (CD4+CD26-). CDDO treatment at 1-5 microM for 48 h caused a concentration-dependent apoptosis in three MF/SS cell lines and patients' PBL compared to vehicle controls. Bexarotene augmented CDDO-induced apoptosis in these cells. PPAR-gamma was expressed but decreased by 47% in MJ, 42% in Hut78, and 77% in HH cells following CDDO treatment. The anti-apoptotic protein bcl-xL, but not bcl-2, was decreased by 69% in MJ, 31% in Hut78, and 59% in HH cells and caspase-3 was activated following CDDO treatment. Interestingly, the PPAR-gamma antagonist T007 did not block CDDO-induced apoptosis, and the more potent PPAR-gamma agonist rosiglitazone required much higher concentrations (>50 microM) than CDDO to induce apoptosis in MF/SS cells. In summary, CDDO induces apoptosis that is further enhanced by bexarotene and decreases the PPAR-gamma and bcl-xL proteins in MF/SS cells. CDDO's effects on MF/SS cells may be at least partly mediated through a PPAR-gamma-independent mechanism. Our findings suggest the rationale for further investigation of the clinical potential of CDDO, either alone or in combination with bexarotene for MF/SS patients.

Potentiation of the teratogenic effects induced by coadministration of retinoic acid or phytanic acid/phytol with synthetic retinoid receptor ligands

Previous studies in our laboratory identified retinoid-induced defects that are mediated by RAR-RXR heterodimerization using interaction of synthetic ligands selective for the retinoid receptors RAR and RXR in mice (Elmazar et al. 1997, Toxicol Appl Pharmacol 146:21-28; Elmazar et al. 2001, Toxicol Appl Pharmacol 170:2-9; Nau and Elmazar 1999, Handbook of experimental pharmacology, vol 139, Retinoids, Springer-Verlag, pp 465-487). The present study was designed to investigate whether these RAR-RXR heterodimer-mediated defects can be also induced by interactions of natural and synthetic ligands for retinoid receptors. A non-teratogenic dose of the natural RXR agonist phytanic acid (100 mg/kg orally) or its precursor phytol (500 mg/kg orally) was coadministered with a synthetic RARalpha-agonist (Am580; 5 mg/kg orally) to NMRI mice on day 8.25 of gestation (GD8.25). Furthermore, a non-teratogenic dose of the synthetic RXR agonist LGD1069 (20 mg/kg orally) was also coadministered with the natural RAR agonist, all- trans-retinoic acid (atRA, 20 mg/kg orally) or its precursor retinol (ROH, 50 mg/kg orally) to NMRI mice on GD8.25. The teratogenic outcome was scored in day-18 fetuses. The incidence of Am580-induced resorptions, spina bifida aperta, micrognathia, anotia, kidney hypoplasia, dilated bladder, undescended testis, atresia ani, short and absent tail, fused ribs and fetal weight retardation were potentiated by coadministration of phytanic acid or its precursor phytol. Am580-induced exencephaly and cleft palate, which were not potentiated by coadministration with the synthetic RXR agonists, were also not potentiated by coadministration with either phytanic acid or its precursor phytol. LGD1069 potentiated atRA- and ROH-induced resorption, exencephaly, spina bifida, aperta, ear anotia and microtia, macroglossia, kidney hypoplasia, undescended testis, atresia ani, tail defects and fetal weight retardation, but not cleft palate. These results suggest that synergistic teratogenesis can be induced by coadministration of a natural RXR ligand (phytanic acid) with a synthetic RAR agonist (Am580). Thus, certain potentially useful therapeutic agents or nutritional factors such as phytanic acid should be tested for teratogenic risk by coadministration with other retinoid receptor agonists.

Comparison of selective retinoic acid receptor– and retinoic X receptor–mediated efficacy, tolerance, and survival in cutaneous t-cell lymphoma

Primary cutaneous T-cell lymphomas are non-Hodgkin's lymphomas with varied clinical presentation and prognosis. The most common subtypes of cutaneous T-cell lymphomas are the epidermotropic variants mycosis fungoides and Sézary syndrome. Treatment of mycosis fungoides has encompassed a variety of modalities including the use of retinoids with several studies evaluating their efficacy. The reported benefits and duration of response have varied in published data. The biological effect of retinoids is mediated by specific receptor families, retinoic acid receptor (RAR) and retinoic X receptor (RXR), with subsequently altered gene expression. There are no data available on cutaneous T-cell lymphomas that compare RAR and RXR retinoids. The objective of our retrospective, nonrandomized, single-center study was to compare the response, survival outcomes, and toxic effects in our phase II trial of the RAR-specific retinoid, all-trans retinoic acid, with clinical use of the RXR-specific retinoid, bexarotene, in patients with mycosis fungoides/Sézary syndrome who have relapsed. There was no statistical difference in response rates (12% vs 21%), response duration (20.5 vs 7.3 months), event-free survival time (4 vs 5 months), or median survival when corrected for length of follow-up. Both have favorable toxicity profiles that can be managed with medications. The toxicity profile caused by bexarotene seems to be more limited to laboratory values and better tolerated, although generally associated with more severe grades of toxicity. In conclusion, both retinoids have modest objective response rates and, therefore, most likely will have limited impact as monotherapeutic agents. However, the immunomodulatory effects of RAR and RXR retinoids provide a rational basis for using retinoids in combination with other biologic immune response modifiers, phototherapy, or cytotoxic chemotherapy.

Sustained remission of treatment-resistant cutaneous T-cell lymphoma with oral bexarotene

Cutaneous T-cell lymphomas (CTCL) encompass a spectrum of clinical and histologic variants, characterized by malignant CD4+ T lymphocytes in the skin and visceral organs. This is a case report of a 74-year-old man with CTCL, including ulcerative lesions, resistant to multiple systemic therapies. Treatment with oral bexarotene resulted in rapid and sustained remission of both cutaneous and systemic symptoms.

How retinoids regulate breast cancer cell proliferation and apoptosis

Breast cancer still remains a major problem in its incidence, morbidity and mortality; therefore, more effective strategies for its prevention are urgently needed. Retinoids, natural and synthetic derivatives of vitamin A, possess antiproliferative and proapoptotic properties, making them a promising class of chemopreventive agents against breast cancer. The efficacy of all-trans retinoic acid, 9-cis-retinoic acid, LGD1069 (Targretin, bexarotene), and N-(4-hydroxyphenyl)retinamide (fenretinide) as breast cancer chemopreventive agents is being studied. A better understanding of the molecular mechanisms of action of these agents should lead to improvements in their clinical application. In this review, we discuss the mechanisms by which retinoids exert their antiproliferative and apoptotic effects in breast cancer cells.

Novel treatment of chronic severe hand dermatitis with bexarotene gel

BACKGROUND

Hand dermatitis is an eczematous inflammation of the hands that is related to occupation or to routine activities. It often becomes chronic, and in some patients may become severe and disabling. Topical corticosteroids are effective treatment, particularly for milder forms, but they often lose effectiveness with time and can produce skin atrophy.

OBJECTIVES

To evaluate bexarotene gel topical therapy for safety, tolerability and efficacy in patients with chronic hand dermatitis.

METHODS

A phase I-II open-label randomized clinical study of bexarotene gel, alone and in combination with a low- and a mid-potency steroid, was conducted in 55 patients with chronic severe hand dermatitis at two academic clinics.

RESULTS

Patients using bexarotene gel monotherapy reached a 79% response rate for > or = 50% clinical improvement and a 39% response rate for > or = 90% clearance of hands. Adverse events possibly related to treatment in all patients were stinging or burning (15%), flare of dermatitis (16%) and irritation (29%). Thirteen patients (24%) withdrew early, including two for related adverse events and five for inadequate response.

CONCLUSIONS

Bexarotene gel appears to be safe, tolerated by most patients, with useful therapeutic activity in chronic severe hand dermatitis.

Potential Nonhormonal Therapeutics for Medical Treatment of Leiomyomas

Uterine leiomyomas are a common disorder resulting in significant morbidity for women and substantial economic impact on the health care system. Current therapies include conservative surgery, hysterectomy, and hormonal therapy. Conservative surgical therapy often fails because of recurrence, and hysterectomy dramatically limits reproductive options. Radiologic therapies are associated with considerable risk of morbidity and mortality and are not likely to be compatible with reproduction. Hormonal therapies such as gonadotropin-releasing hormone (GnRH) analogues or progestins with or without estrogen are utilized by many patients, but long-term use of either is often responsible for unacceptable morbidity and hormonal therapies are not compatible with reproduction. Newer hormonal alternatives such as progesterone antagonists and selective agonists as well as "add-back" estrogen therapy in addition to GnRH analogues have been developed and show promise. However, no hormonal therapy that significantly alters estrogen and progesterone production or function is likely to be compatible with reproduction. Thus, it is important to develop novel nonhormonal therapies for medical treatment of leiomyomas. Other laboratories have evaluated pirfenidone, halofuginone, heparin, and interferon-alpha (IFN-alpha). Recent work in our laboratory suggests potential use of two additional classes of compounds, thiazolidinediones and tocopherol analogs. The rationale, evidence, and potential for the use of each of these compounds in the treatment of leiomyomas are discussed.

Follicular mycosis fungoides: successful treatment with oral bexarotene

Follicular mycosis fungoides, a subtype of cutaneous T-cell lymphoma, is often difficult to treat. We present a case of a female with follicular mycosis fungoides who showed an excellent response to low-dose (150 mg/m2) oral bexarotene (Targretin). To our knowledge, this is the first reported case of follicular mycosis fungoides demonstrating a response to bexarotene.

Low-dose oral bexarotene in combination with low-dose interferon alfa in the treatment of cutaneous T-cell lymphoma: clinical synergism and possible immunologic mechanisms

BACKGROUND

For nearly 2 decades clinicians have been treating cutaneous T-cell lymphoma (CTCL) with regimens that combine interferon alfa with retinoid compounds. In December 1999 a new retinoid, bexarotene, was approved by the US Food and Drug Administration for the treatment of CTCL. At the manufacturer's recommended dose of bexarotene (300 mg/m(2) of body surface area), it has proven to be a highly effective therapy for all stages of CTCL. Nevertheless, this dose is typically associated with adverse effects including severe hyperlipidemia. Furthermore, there appears to be no standardization of dosing among physicians who treat CTCL.

OBSERVATIONS

We present 3 representative patients, 2 with erythrodermic CTCL and 1 with follicular mycosis fungoides, who experienced the rapid clearing of skin disease while being treated with a combination of low-dose bexarotene and low-dose recombinant interferon alfa.

CONCLUSIONS

Combining low-dose bexarotene with low-dose interferon alfa was well tolerated and led to rapid improvement in our patients. We review the clinical and biologic basis for this approach.

Retinoid signalling and gene expression in neuroblastoma cells: RXR agonist and antagonist effects on CRABP-II and RARbeta expression

9-cis Retinoic acid (RA) induces gene expression in neuroblastoma cells more effectively and with different kinetics than other RA isomers, and could be acting in part through Retinoid X Receptors (RXRs). The aim of this study was to characterise the effects of an RXR agonist and RXR homodimer antagonist on the induction of cellular RA binding protein II (CRABP-II) and RA receptor-beta (RARbeta) in neuroblastoma cells in response to different retinoids. The RXR agonist, LDG1069, was as effective as all-trans RA in inducing gene expression, but less effective than 9-cis RA. The RXR-homodimer antagonist, LG100754, inhibited the induction of CRABP-II mRNA in SH-SY5Y neuroblastoma cells by 9-cis RA or the RXR-specific agonist LGD1069, but had no effect when used with all-trans RA. Conversely, LG100754 did not inhibit induction of RARbeta mRNA by 9-cis or all-trans RA, or by LGD1069. RAR- and RXR-specific ligands used together induced CRABP-II and RARbeta as effectively as 9-cis RA. These results demonstrate the value of combining RXR- and RAR-specific ligands to regulate RA-inducible gene expression. The possibility that RXR-homodimers mediate, in part, the induction of CRABP-II by 9-cis RA and RXR-specific ligands is discussed.

[Standard and experimental therapy of cutaneous T-cell lymphoma]

Cutaneous T-cell lymphoma represent a heterogeneous group of diseases characterized by skin invasion of monoclonal T-lymphocytes. These cutaneous T-cell lymphomas are divided into 3 groups based on clinical, histological and immunohistological characteristics: Indolent with a survival time of over 10 years, aggressive with a survival time less than 10 years and provisional (EORTC classification). Standard treatments such as PUVA, total skin electron beam, methotrexate, polychemotherapy regimens, retinoids and photopheresis have been used for years. Bexarotene is a newly registered drug. To achieve better response rates, several new drugs are being evaluated in clinical trails, including imiquimod, denileukon-diftitox, liposomal doxorubicin, adeno-interferon-gamma and various combination approaches.

Topical bexarotene therapy for patients with refractory or persistent early-stage cutaneous T-cell lymphoma: results of the phase III clinical trial

OBJECTIVES

We sought to determine the safety and efficacy of topical bexarotene (Targretin; Ligand Pharmaceuticals, La Jolla, Calif) gel 1% in patients with refractory or persistent early-stage cutaneous T-cell lymphoma.

METHODS

We conducted a multinational, open-label, phase III study of 50 patients with stage IA to IIA cutaneous T-cell lymphoma. The primary end point classification was the overall complete and partial response rate by the higher of 2 measures: the Physician's Global Assessment of Clinical Condition or the Composite Assessment of Index Lesion Disease Severity.

RESULTS

The overall response rates for the Physician's Global Assessment of Clinical Condition, Composite Assessment of Index Lesion Disease Severity, and primary end point classification were 44%, 46%, and 54%, respectively. The most common adverse events possibly related to study medication were mild to moderate irritant dermatitis, pruritus, pain (ie, primarily burning at application site), and skin disorder (eg, skin inflammation, excoriation, and new lesions). There were no serious treatment-related adverse events.

CONCLUSIONS

Topical bexarotene gel was generally well tolerated and demonstrated substantial efficacy in patients with refractory or persistent early-stage cutaneous T-cell lymphoma.

Mycosis fungoides with follicular mucinosis displaying aggressive tumor-stage transformation : successful treatment using radiation therapy plus oral bexarotene combination therapy

Follicular mucinosis is a tissue reaction pattern characterized by mucin deposition with follicular sebaceous units and is found as an idiopathic, primary, benign process (alopecia mucinosa), or as a secondary process due to inflammatory and neoplastic disorders (mycosis fungoides). When associated with follicular mucinosis, mycosis fungoides commonly pursues an aggressive course, often undergoing large-cell transformation, which is associated with resistance to therapy and poor prognosis. We present a case of mycosis fungoides with follicular mucinosis that was treated with incomplete courses of interferon, isotretinoin, and polychemotherapy with subsequent rapid progression to tumor-stage mycosis fungoides with large cell transformation and nodal and bone marrow involvement. In this setting, the patient was treated with local radiation therapy, total-skin electron beam therapy, and therapy and maintenance with the oral retinoid-X-receptor retinoid bexarotene, and achieved a durable complete remission.

Bexarotene - an alternative therapy for progressive cutaneous T-cell lymphoma? First experiences

BACKGROUND

A standard therapy for advanced cutaneous T-cell lymphomas has not yet been defined. Bexarotene is a new retinoid x receptor-specific retinoid that has been approved for systemic second-line therapy for cutaneous T-cell lymphomas in the USA and Europe. In order to evaluate the efficacy of bexarotene in cutaneous T-cell lymphomas, a pilot trial was initiated.

PATIENTS AND METHODS

In a pilot project 10 patients with advanced cutaneous T-cell lymphomas, who had received a variety of previous treatments, were treated with bexarotene at the departments of dermatology in Münster, Minden and Charité Berlin, Germany. The patients received bexarotene at a dose of 300 mg/m2 body surface daily. According to the percentage of tumour reduction and affected body surface, the response rates were divided in complete and partial remission, stable disease and progressive disease. Laboratory parameters i.e. cholesterol, triglycerides transaminases, T3, T4, and TSH were screened regularly.

RESULTS

In 2 patients a short partial remission was achieved; however, after a few weeks progression followed. In 4 patients a lasting stabilisation was obtained. The other 4 patients showed a progressive disease during therapy. 6 patients developed hypertriglyceridemia with levels up to 2000 mg/dl; therapy had to be suspended in 3 patients because of these adverse drug events.

CONCLUSION

Weighing benefits and risks, bexarotene can at present not be recommended as standard therapy in the treatment of patients with progressive cutaneous lymphomas.

Responsiveness to the retinoic acid receptor-selective retinoid LGD1550 correlates with abrogation of transforming growth factor alpha/epidermal growth factor receptor autocrine signaling in head and neck squamous carcinoma cells

PURPOSE

The use of retinoids to prevent and/or treat cancers, including head and neck squamous cell carcinoma (HNSCC), has been limited by the development of resistance and unwanted side effects. Receptor-selective retinoids are potentially less toxic than nonselective compounds. The present investigation was undertaken to determine the mechanism of responsiveness to an retinoic acid receptor-selective retinoid (LGD1550) that has shown antitumor efficacy in a xenograft model of HNSCC.

EXPERIMENTAL DESIGN

A series of HNSCC cell lines were characterized with respect to proliferation and apoptosis after LGD1550 treatment. Relative responsiveness to LGD1550 was examined with respect to modulation of epidermal growth factor receptor (EGFR) signaling pathways.

RESULTS

Cells were either growth inhibited and underwent apoptosis or were resistant to treatment with this compound. Retinoids have been shown to decrease the gene transcription rates of transforming growth factor (TGF)-alpha and EGFR in HNSCC. LGD1550 responsiveness was accompanied by decreased expression of TGF-alpha, EGFR, and modulation of EGFR signaling pathways, including signal transducers and activators of transcriptions and mitogen-activated protein kinase. In contrast, EGFR autocrine signaling pathways were not altered in HNSCC cells that were resistant to the growth inhibitory effects of LGD1550.

CONCLUSIONS

These results suggest that there is a correlation between the efficacy of receptor-selective retinoids and modulation of TGF-alpha/EGFR signaling in HNSCC. Therefore, alterations of these signaling pathways may serve as a biomarker of clinical response.

A multiparameter flow cytometric analysis of the effect of bexarotene on the epidermis of the psoriatic lesion

BACKGROUND

A new retinoid, bexarotene (Targretin), was recently investigated in a large multicentre trial for its efficacy and safety in psoriasis. Bexarotene is a novel retinoid X receptor (RXR)-selective ligand.

OBJECTIVES

The aim was to study the effect of bexarotene in psoriasis by analysing markers for epidermal differentiation, proliferation and inflammation in epidermal single cell suspensions from lesions of patients with psoriasis treated with various doses of bexarotene.

METHODS

Thirty-four patients with moderate to severe plaque psoriasis participated in this study and were assigned in sequence to four different dose regimens: 0.5, 1, 2 and 3 mg kg-1 once daily. Before and after 12 weeks of bexarotene treatment, punch biopsies were taken from lesional skin from which epidermal single cell suspensions were prepared using an optimized thermolysin protocol. A sum of scores was determined for each biopsy site, based on a four-point scale for erythema, induration and desquamation. An improved multiparameter flow cytometric assay was used that enabled simultaneous assessment of epidermal proliferation, various aspects of differentiation and epidermal inflammation. The following variables were measured simultaneously: relative DNA content, relative cell size, keratin (K) 10, K6 and vimentin expression.

RESULTS

The psoriasis area and severity index (PASI) and sum of scores for the individual psoriatic lesion each showed a statistically significant decrease of 28% after 12 weeks of bexarotene treatment (P < 0.001). However, no significant dose-response effect was found. The total percentage of K10+ cells showed a significant increase of 43% (P < 0.01). The total population of K6 expressing cells did not show significant changes. Regarding the subpopulations of K6 single, K10 single and K6 and 10 co-expressing cells, a significant increase of 77% was seen in the K10+ K6- cells (P < 0.05), a significant decrease of 33% in K10- K6+ cells (P < 0.01), and no significant changes in the remaining population of K10+ K6+ cells. After 12 weeks of treatment with bexarotene no significant changes in epidermal proliferation and inflammation were shown.

CONCLUSIONS

The present study indicates a direct effect of RXR activation by bexarotene on the transition of proliferation-associated keratinization into normal keratinization. Although no direct effect of bexarotene on DNA content in the total K10- cells was shown, further studies on subpopulations within the germinative layer such as stem cells and transit amplifying cells might be worthwhile.