Retinoic acids induce growth inhibition and apoptosis in adult T-cell leukemia (ATL) cell lines

Deep learning for detecting and elucidating human T-cell leukemia virus type 1 integration in the human genome

Human T-cell leukemia virus type 1 (HTLV-1), a retrovirus, is the causative agent for adult T cell leukemia/lymphoma and many other human diseases. Accurate and high throughput detection of HTLV-1 virus integration sites (VISs) across the host genomes plays a crucial role in the prevention and treatment of HTLV-1-associated diseases. Here, we developed DeepHTLV, the first deep learning framework for VIS prediction de novo from genome sequence, motif discovery, and cis-regulatory factor identification. We demonstrated the high accuracy of DeepHTLV with more efficient and interpretive feature representations. Decoding the informative features captured by DeepHTLV resulted in eight representative clusters with consensus motifs for potential HTLV-1 integration. Furthermore, DeepHTLV revealed interesting cis-regulatory elements in regulation of VISs that have significant association with the detected motifs. Literature evidence demonstrated nearly half (34) of the predicted transcription factors enriched with VISs were involved in HTLV-1-associated diseases. DeepHTLV is freely available at https://github.com/bsml320/DeepHTLV.

Next-generation retinoid X receptor agonists increase ATRA signaling in organotypic epithelium cultures and have distinct effects on receptor dynamics

Retinoid X receptors (RXRs) are nuclear transcription factors that partner with other nuclear receptors to regulate numerous physiological processes. Although RXR represents a valid therapeutic target, only a few RXR-specific ligands (rexinoids) have been identified, in part due to the lack of clarity on how rexinoids selectively modulate RXR response. Previously, we showed that rexinoid UAB30 potentiates all-trans-retinoic acid (ATRA) signaling in human keratinocytes, in part by stimulating ATRA biosynthesis. Here, we examined the mechanism of action of next-generation rexinoids UAB110 and UAB111 that are more potent in vitro than UAB30 and the FDA-approved Targretin. Both UAB110 and UAB111 enhanced ATRA signaling in human organotypic epithelium at a 50-fold lower concentration than UAB30. This was consistent with the 2- to 5- fold greater increase in ATRA in organotypic epidermis treated with UAB110/111 versus UAB30. Furthermore, at 0.2 μM, UAB110/111 increased the expression of ATRA genes up to 16-fold stronger than Targretin. The less toxic and more potent UAB110 also induced more changes in differential gene expression than Targretin. Additionally, our hydrogen deuterium exchange mass spectrometry analysis showed that both ligands reduced the dynamics of the ligand-binding pocket but also induced unique dynamic responses that were indicative of higher affinity binding relative to UAB30, especially for Helix 3. UAB110 binding also showed increased dynamics towards the dimer interface through the Helix 8 and Helix 9 regions. These data suggest that UAB110 and UAB111 are potent activators of RXR-RAR signaling pathways but accomplish activation through different molecular responses to ligand binding.

Retinoic acid receptor agonist as monotherapy for early-stage mycosis fungoides: does it work?

BACKGROUND

Retinoids exert their biologic effects by binding to intracellular retinoic-acid receptors (RARs) and/or retinoid X receptors (RXRs). Early-stage mycosis fungoides (MF) has been effectively treated with bexarotene, an RXR-agonist, with overall response (OR) rates 54-67% and complete response (CR) rates 7-27%. Data on RAR-agonist monotherapy are limited.

OBJECTIVE

To analyze the effectiveness of RAR-agonist monotherapy for early-stage MF.

METHODS

Data on patients with early-stage MF treated with acitretin/isotretinoin monotherapy at a tertiary cutaneous lymphoma clinic in 2010-2017 were collected retrospectively from the medical files.

RESULTS

Thirty-five patients (26 males) of median age 50 years (range 8-83) with early-stage MF (IA 9, IB 26) underwent 37 treatment events: 25 acitretin and 12 isotretinoin at a median dosages of 0.3 mg/kg (range 0.2-0.9) and 0.2 mg/kg (range 0.1-0.7), respectively. Median time to maximal response was 6 months for both (range 1-10 for acitretin, 3-16 for isotretinoin); median treatment duration was 10 months (range 3-46) for acitretin, and 9 months (range 3-55) for isotretinoin. OR was 64% for acitretin and 80% for isotretinoin, and CR, 4% and 8%, respectively. Side-effect profiles were as previously reported for retinoids.

CONCLUSIONS

Early-stage MF patients may benefit from low dose RAR-agonist monotherapy, although the CR rate is low.

Retinoid X Receptor Agonists Upregulate Genes Responsible for the Biosynthesis of All-Trans-Retinoic Acid in Human Epidermis

UAB30 is an RXR selective agonist that has been shown to have potential cancer chemopreventive properties. Due to high efficacy and low toxicity, it is currently being evaluated in human Phase I clinical trials by the National Cancer Institute. While UAB30 shows promise as a low toxicity chemopreventive drug, the mechanism of its action is not well understood. In this study, we investigated the effects of UAB30 on gene expression in human organotypic skin raft cultures and mouse epidermis. The results of this study indicate that treatment with UAB30 results in upregulation of genes responsible for the uptake and metabolism of all-trans-retinol to all-trans-retinoic acid (ATRA), the natural agonist of RAR nuclear receptors. Consistent with the increased expression of these genes, the steady-state levels of ATRA are elevated in human skin rafts. In ultraviolet B (UVB) irradiated mouse skin, the expression of ATRA target genes is found to be reduced. A reduced expression of ATRA sensitive genes is also observed in epidermis of mouse models of UVB-induced squamous cell carcinoma and basal cell carcinomas. However, treatment of mouse skin with UAB30 prior to UVB irradiation prevents the UVB-induced decrease in expression of some of the ATRA-responsive genes. Considering its positive effects on ATRA signaling in the epidermis and its low toxicity, UAB30 could be used as a chemoprophylactic agent in the treatment of non-melanoma skin cancer, particularly in organ transplant recipients and other high risk populations.

Tazarotene 0.1% Cream as Monotherapy for Early-Stage Cutaneous T-Cell Lymphoma

BACKGROUND

Numerous treatments are available for cutaneous T-cell lymphoma (CTCL), including systemic retinoids. Very few data are available on topical retinoids.

OBJECTIVES

The aim of this study was to evaluate the safety and efficiency of tazarotene as monotherapy for early-stage CTCL.

METHODS

An open-label, prospective study of tazarotene as monotherapy for stages IA to IIA CTCL was conducted. Index lesions on 10 patients were followed for 6 months on treatment, plus at least 6 months off treatment.

RESULTS

Six patients (60%) showed complete response (CR). Erythema, scaling, thickness, and lesion area decreased progressively throughout treatment. The mean time to CR was 3.8 months; CR was durable for at least 6 months in 83%. Of the 4 patients (40%) without CR, 2 (20%) had stable disease and 2 (20%) stopped the medication because of local side effects; none showed progression.

CONCLUSIONS

This is the first Canadian trial providing evidence that topical tazarotene has excellent potential as a monotherapy agent for stages I to IIA CTCL.

DNA fragmentation induced by all-trans retinoic acid and its steroidal analogue EA-4 in C2 C12 mouse and HL-60 human leukemic cells in vitro

We have recently shown that retinoic acid induces micronucleation mainly via chromosome breakage (Alakhras et al. Cancer Lett 2011; 306: 15-26). To further study retinoic acid clastogenicity and evaluate DNA damaging potential we investigated the ability of (a) all-trans retinoic acid and its steroidal analogue EA-4 to induce DNA fragmentation by using Comet assay under alkaline unwinding and neutral condition electrophoresis, and (b) the retinoids under study to induce small (0-1 kb) DNA fragments. Two cell lines, C2C12 mouse cells and HL-60 human leukemic cells were used in this study. We found that all-trans retinoic acid and its steroidal analogue EA-4 (a) provoke DNA migration due to DNA fragmentation as it is shown by the increased values of Comet parameters, and (b) induce significantly small-size fragmented genomic DNA as indicated by the quantification of necrotic/apoptotic small DNA segments in both cell systems. A different response between the two cell lines was observed in relation to retinoid ability to increase the percentage of DNA in the tail as well as break DNA in to small fragments. Our findings confirm the ability of retinoic acid to provoke micronucleation by disrupting DNA into fragments, among which small pieces of double-stranded DNA up to 1 kb are identified.

Cell death signaling and anticancer therapy

For a long time, it was commonly believed that efficient anticancer regimens would either trigger the apoptotic demise of tumor cells or induce a permanent arrest in the G₁ phase of the cell cycle, i.e., senescence. The recent discovery that necrosis can occur in a regulated fashion and the increasingly more precise characterization of the underlying molecular mechanisms have raised great interest, as non-apoptotic pathways might be instrumental to circumvent the resistance of cancer cells to conventional, pro-apoptotic therapeutic regimens. Moreover, it has been shown that some anticancer regimens engage lethal signaling cascades that can ignite multiple oncosuppressive mechanisms, including apoptosis, necrosis, and senescence. Among these signaling pathways is mitotic catastrophe, whose role as a bona fide cell death mechanism has recently been reconsidered. Thus, anticancer regimens get ever more sophisticated, and often distinct strategies are combined to maximize efficacy and minimize side effects. In this review, we will discuss the importance of apoptosis, necrosis, and mitotic catastrophe in the response of tumor cells to the most common clinically employed and experimental anticancer agents.

Genotoxicity of all-trans retinoic acid (ATRA) and its steroidal analogue EA-4 in human lymphocytes and mouse cells in vitro

The aim of our study is to: (a) investigate whether ATRA and its steroidal analogue EA-4 enhance micronucleation in human lymphocytes and mouse cells in vitro and clarify the micronucleation mechanism by FISH and CREST analysis respectively, and (b) analyze their effect on spindle organization by immunofluorescence of β- and γ-tubulin in mouse cells. We found that they: (a) induce micronucleation mainly via chromosome breakage and chromosome delay in a lesser extent, (b) disturb microtubule network, chromosome orientation and centrosome duplication/separation, (c) accumulate cell cycle at ana-telophases, which exert micronucleation, multiple γ-tubulin signals, nucleoplasmic bridges and multinucleation, and (d) generate multinucleated and multimicronucleated interphase cells.

HTLV-1 and apoptosis: role in cellular transformation and recent advances in therapeutic approaches

A universal cellular defense mechanism against viral invasion is the elimination of infected cells through apoptotic cell death. To counteract host defenses many viruses have evolved complex apoptosis evasion strategies. The oncogenic human retrovirus HTLV-1 is the etiological agent of adult-T-cell leukemia/lymphoma (ATLL) and the neurodegenerative disease known as HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The poor prognosis in HTLV-1-induced ATLL is linked to the resistance of neoplastic T cells against conventional therapies and the immuno-compromised state of patients. Nevertheless, several studies have shown that the apoptotic pathway is largely intact and can be reactivated in ATLL tumor cells to induce specific killing. A better understanding of the molecular mechanisms employed by HTLV-1 to counteract cellular death pathways remains an important challenge for future therapies and the treatment of HTLV-1-associated diseases.

Treatment of adult T-cell leukemia/lymphoma: past, present, and future

Adult T-cell leukemia/lymphoma (ATLL) is a peripheral T-cell malignancy caused by human T-cell lymphotrophic virus type I. Clinical manifestations of ATLL range from smoldering to chronic, lymphoma and acute. Patients with acute and lymphoma type ATLL require therapeutic intervention. Conventional chemotherapeutic regimens used against other malignant lymphoma have been administered to ATLL patients, but the therapeutic outcomes of acute and lymphoma type ATLL remain very poor. Promising results of allogeneic stem cell transplantation (SCT) for ATLL patients have recently been reported and the treatment outcome might be improved for some ATLL patients. Besides conventional chemotherapy and SCT, interferon, zidovudine, arsenic trioxide, targeted therapy against surface molecule on ATLL cells, retinoid derivatives, and bortezomib have been administered to ATLL patients in pilot or phase I/II studies. Further studies are required to confirm the clinical benefits of these novel therapeutics. This article reviews the current status and future directions of ATLL treatment.

Induction of cell cycle arrest and apoptosis by a combined treatment with 13-cis-retinoic acid, interferon-α2a, and α-tocopherol in squamous cell carcinoma of the head and neck

BACKGROUND

We have previously conducted phase II trials with a combination of 13-cis-retinoic acid (13-cRA), interferon-alpha2a (IFN-alpha2a), and alpha-tocopherol (alpha-TF) in patients with advanced oral premalignant lesions and locally advanced head and neck cancer in the adjuvant settings and achieved promising outcomes. The present study was conducted in vitro to elucidate the mechanisms of anti-tumor activity of this 3-drug combination in squamous cell carcinoma of the head and neck (SCCHN).

METHODS

Five SCCHN cell lines were treated with 13-cRA, IFN-alpha2a, and alpha-TF as single agents or 2- to 3-drug combinations for 72 hours. Inhibition of cell growth and cell cycle progression and induction of apoptosis by the treatments were evaluated.

RESULTS

Our results demonstrated that although each single-agent and 2-drug combination showed a certain level of cell growth inhibition, the 3-drug combination apparently further inhibited cell growth in comparison to any single agents and 2-drug combinations in the 5 SCCHN cell lines. Cell cycle analysis on Tu212 and 886LN cells by flow cytometry exhibited significant accumulation of the cells at S phase in the 3-drug combination. On the other hand, Annexin-V binding assay demonstrated that the 3-drug combination induced more profound apoptosis than any of the single agents or 2-drug combinations. In parallel, proteolytic cleavages of pro-caspase-8, -9, -3 and poly (ADP ribose) polymerase as well as caspase-3 activity induced by the 3-drug treatment were observed.

CONCLUSIONS

Our data suggests that 3-drug combination biochemopreventive regimen has cooperative inhibitory effect on the growth of SCCHN cells. Both cell cycle arrest and apoptosis contribute to cell growth inhibition of this 3-drug combination therapy.

Topical and systemic retinoid therapy for cutaneous T-cell lymphoma

Because curative therapies for CTCL are not yet available, short of TSEB in patients who have early-stage disease and allogeneic bone marrow transplantation in patients who have more advanced disease, the goal of current therapies is to prevent progression of MF and to preserve quality of life. The overall conclusion drawn from the studies reported in the literature, is that retinoids as monotherapy, or in combination with other nonaggressive treatment modalities, represent a low-risk treatment alternative that is especially suitable for controlling early stages of MF and other CTCL. A combination of therapies may be more effective in controlling CTCL as shown with IFN-alpha plus retinoids, and, recently, IFN-alpha with bexarotene and other modalities. For example, isotretinoin, followed by TSEB (for stage I to II disease) or preceded by chemotherapy (for stage II and IV disease) and bexarotene plus PUVA or photopheresis plus IFN, gave overall response rates of 82% and 69% in patients who had MF and SS, respectively. Retinoids as monotherapy may induce complete remissions, but usually these responses are of short duration and relapses are common. Clinical response is not identical to histologic clearance. Even in cases with clinically complete clearance of skin lesions, lymphoid infiltrates persisted, which are most likely the source of recurrences. The new generation of retinoids, the RXR selective agonists like bexarotene, represent a promising approach for refractory or persistent MF that is unresponsive to first-line therapies. Individual differences in response to retinoids may be due to different expression of retinoid receptors, functional polymorphisms in metabolizing retinoids, or resistance to some retinoids. In the future, pharmacogenomic studies are needed to clarify the mechanisms that underlie the differing response rates of patients who have CTCL to retinoids. In addition, new agonists of RAR and RXR, either selective or pan agonists, will become available and will enlarge the spectrum of vitamin A analogs that have antitumoral properties.

Ham-Wasserman Lecture

Conventional treatment of acute leukemia involves the use of cytotoxic agents (chemotherapy), but other strategies have been explored. All-trans retinoic acid (ATRA) and arsenic have clearly been effective in the treatment of acute promyelocytic leukemia (APL), which creates the possibility that other types of acute leukemia can be conquered by selectively inducing differentiation and/or apoptosis. A great number of investigations have been performed to elucidate the mechanisms and search for effective agents in the treatment of other types of acute leukemia by these new strategies. Progress at the molecular level has been achieved in explaining the mechanisms of action of ATRA and arsenic compounds, and several new agents have emerged, although their clinical effectiveness remains to be confirmed. Mechanism-/gene-based targeted therapy and a combination of different strategies will improve the treatment of acute leukemia.

Ham-Wasserman Lecture

Conventional treatment of acute leukemia involves the use of cytotoxic agents (chemotherapy), but other strategies have been explored. All-trans retinoic acid (ATRA) and arsenic have clearly been effective in the treatment of acute promyelocytic leukemia (APL), which creates the possibility that other types of acute leukemia can be conquered by selectively inducing differentiation and/or apoptosis. A great number of investigations have been performed to elucidate the mechanisms and search for effective agents in the treatment of other types of acute leukemia by these new strategies. Progress at the molecular level has been achieved in explaining the mechanisms of action of ATRA and arsenic compounds, and several new agents have emerged, although their clinical effectiveness remains to be confirmed. Mechanism-/gene-based targeted therapy and a combination of different strategies will improve the treatment of acute leukemia.

Superior effect of 9-cis retinoic acid (RA) compared with all-trans RA and 13-cis RA on the inhibition of clonogenic cell growth and the induction of apoptosis in OCI/AML-2 subclones: is the p53 pathway involved?

In the present study, the effects of 9-cis retinoic acid (RA) and 13-cis RA on acute myeloblastic leukaemia (AML) cell growth and the induction of apoptosis as well as its relationship with bcl-2 and p53 were compared with those of all-trans RA (ATRA). The study was performed with the subclones of the retinoid-sensitive OCI/AML-2 cell line. The most prominent inhibitory effect on clonogenic cell growth and morphological apoptosis was shown by 9-cis RA. In addition, Western blotting revealed the most obvious translocation of p53 from cytosol to nucleus in the case of 9-cis RA, which was the only retinoid able to change the conformation of p53 from mutational to wild type, as demonstrated by flow cytometry. There was no difference between the retinoids in the downregulation of bcl-2 as analysed by Western blotting and flow cytometry. The RA receptor (RAR)-alpha antagonist had no effect on apoptosis in any of the three retinoids studied using the annexin V method. In conclusion, this study shows that 9-cis RA was a more potent agent than ATRA or 13-cis RA in inducing growth arrest and apoptosis in the OCI/AML-2 subclones. The effect was associated with the downregulation of bcl-2 and was hardly mediated through the RAR-alpha receptor, but might be related to the activation of p53.

Arsenic trioxide induces apoptosis in human T-cell leukemia virus type 1- and type 2-infected cells by a caspase-3-dependent mechanism involving Bcl-2 cleavage

Treatment of patients with adult T-cell leukemia-lymphoma (ATLL) using conventional chemotherapy has limited benefit because human T-cell leukemia virus type 1 (HTLV-1) cells are resistant to most apoptosis-inducing agents. The recent report that arsenic trioxide induces apoptosis in HTLV-1-transformed cells prompted investigation of the mechanism of action of this drug in HTLV-1 and HTLV-2 interleukin-2-independent T cells and in HTLV-1-immortalized cells or in ex vivo ATLL samples. Fluorescence-activated cell sorter analysis, fluorescence microscopy, and measures of mitochondrial membrane potential (Delta Psi m) demonstrated that arsenic trioxide alone was sufficient to induce programmed cell death in all HTLV-1 and -2 cells tested and in ATLL patient samples. I kappa B-alpha phosphorylation strongly decreased, and NF-kappa B translocation to the nucleus was abrogated. Expression of the antiapoptotic protein Bcl-X(L), whose promoter is NF-kappa B dependent, was down-regulated. The collapse of Delta Psi m and the release of cytochrome c to the cytosol resulted in the activation of caspase-3, as demonstrated by the cleavage of PARP. A specific caspase-3 inhibitor (Ac-DEVD-CHO) could reverse this phenotype. The antiapoptotic factor Bcl-2 was then cleaved, converting it to a Bax-like death effector. These results demonstrated that arsenic trioxide induces apoptosis in HTLV-1- and -2-infected cells through activation of the caspase pathway.

Treatment of adult T-cell leukaemia/lymphoma: current strategy and future perspectives

Human T-cell leukaemia virus type I (HTLV-I) associated adult T-cell leukaemia/lymphoma (ATL) carries a very poor prognosis due to an intrinsic resistance of leukaemic cells to conventional or even high doses of chemotherapy and to an associated severe immunosuppression. Therefore, the potential role of conventional chemotherapy, high dose chemotherapy with autologous or allogeneic bone marrow transplantation remains to be defined. Important progress was achieved in the treatment of ATL with the combination of zidovudine (AZT) and interferon-alpha (IFN) which produces a high response rate in ATL patients with minimal side effects. This treatment seems to prolong the survival of patients much more than intensive chemotherapy. The success of this potentially anti-retroviral approach in the treatment of ATL suggests the existence of continuous HTLV-I replication in vivo. These encouraging results may be improved by the use of higher doses of AZT and IFN combined with other anti-retroviral agents. However, since cure seems still elusive, new therapeutic approaches or new combinations are required. For example, biological mediators such as retinoid acid, which induces apoptosis of ATL cells in vitro, may reduce drug resistance and stimulates immunity to restore anti-tumour activity against ATL cells. Alternatively, immunotherapy with anti-interleukin-2 receptor monoclonal antibodies or injection of cytotoxic T-cells directed against virus antigens could be interesting approaches which may merit further investigations in the near future. Finally, the recent demonstration that the combination of arsenic trioxide (As) and IFN induces a specific degradation of the viral transactivator Tax followed by cell cycle arrest and apoptosis of HTLV-I positive cells may constitute a valuable addition to ATL treatment.

Retinoid therapy of childhood cancer

In vitro studies that showed RA could cause growth arrest and differentiation of myelogenous leukemia and neuroblastoma led to clinical trials of retinoids in APL and neuroblastoma that increased survival for both of those diseases. In the case of APL, ATRA has been the drug of choice, and preclinical and clinical data support direct combinations of ATRA with cytotoxic chemotherapy. For neuroblastoma, a phase I study defined a dose of 13-cis-RA, which was tolerable in patients after myeloablative therapy, and a phase III trial that showed postconsolidation therapy with 13-cis-RA improved EFS for patients with high-risk neuroblastoma. Preclinical studies in neuroblastoma indicate that ATRA or 13-cis-RA can antagonize cytotoxic chemotherapy and radiation, so use of 13-cis-RA in neuroblastoma is limited to maintenance after completion of cytotoxic chemotherapy and radiation. A limitation on the antitumor benefit of ATRA in APL is the marked decrease in drug levels that occurs during therapy as a result of induction of drug metabolism, resulting in a shorter drug half-life and decreased plasma levels. Although early studies sought to overcome the pharmacologic limitations of ATRA therapy in APL, the demonstration that ATO is active against APL in RA-refractory patients has led to a focus on studies employing ATO. Use of 13-cis-RA in neuroblastoma has avoided the decreased plasma levels seen with ATRA. It is likely that recurrent disease seen during or after 13-cis-RA therapy in neuroblastoma is due to tumor cell resistance to retinoid-mediated differentiation induction. Studies in neuroblastoma cell lines resistant to 13-cis-RA and ATRA have shown that they can be sensitive, and in some cases collaterally hypersensitive, to the cytotoxic retinoid fenretinide. Fenretinide induces tumor cell cytotoxicity rather than differentiation, acts independently from RA receptors, and in initial phase I trials has been well tolerated. Clinical trials of fenretinide, alone and in combination with ceramide modulators, are in development.

13cis- and all-trans retinoic acid have antiproliferative effects on CML cells and render IFN alpha antiproliferative potency after combined treatment in vitro

The treatment of CML with IFN alpha is limited due to resistance against this substance. Recent studies with different cells than chronic myelogenous leukemic cells revealed a synergistic effect of a combined use of Retinoids (RA) and IFN alpha. The purpose of the study was to detect possible interactions of IFN alpha and RA in CML considering also the effect of the BCR-ABL gene-product. Therefore, we investigated three CML cell lines in their proliferation after incubation with IFN alpha and Retinoids alone and in combination. We measured low susceptibility to IFN alpha but a marked influence of the Retinoids. In combination, the growth inhibition was enhanced potentially in response to an increased efficacy of IFN alpha. Even solely, ineffective concentrations of both substances lead to decreased proliferation.

Recent advances in the use of vitamin A (retinoids) in the prevention and treatment of cancer

Vitamin A, its physiologic metabolites, and synthetic derivatives (retinoids) have been shown to have protective effects against the development of certain types of cancer. In addition, pharmacologic amounts of retinoids have been used with some success in the treatment of a few human tumors. The chemoprevention effect of retinoids is most likely exerted at the tumor-promotion phase of carcinogenesis. Retinoids block tumor promotion by inhibiting proliferation, inducing apoptosis, inducing differentiation, or a combination of these actions. Clinically, isotretinoin (13-cis-retinoic acid) significantly decreases the incidence of second primary tumors in patients with head-and-neck cancer and reduces appearance of non-melanoma skin cancer in patients with xeroderma pigmentosum. Retinoic acid has proved to be an effective treatment for promyelocytic leukemia. However, retinoid resistance limits its use as a single agent. Clinical trials are in progress to determine the efficacy of retinoids in treating other types of cancer such as neuroblastoma and breast carcinoma. The development of receptor-selective retinoids and selective inhibitors of retinoid metabolism may lead to further use of retinoids in both chemoprevention and treatment of cancer.

Historical perspective on the use of retinoids in cutaneous T-cell lymphoma (CTCL)

Vitamin A and its analogues influence differentiation and proliferation and may also alter immune responses. Limited clinical efficacy of these compounds given alone or as part of a combination therapy has been shown in various types of cutaneous T-cell lymphoma (CTCL), including mycosis fungoides, Sézary syndrome, and prelymphomatous disorders such as parapsoriasis en plaques. Compounds used mostly in small, nonrandomized trials are isotretinoin (13-cis-retinoic acid), etretinate, acitretin, and all-trans-retinoic acid. Clinical responses have been found despite persistent residual disease with atypical lymphocytes in various compartments. The exact mechanism of action of retinoids in CTCL is unclear and depends on the presence of retinoid receptors on the tumor cells, which is variable in different forms of CTCL. Therapies combining retinoids with psoralen-ultraviolet A or with interferons may have a synergistic effect, which deserves confirmation through randomized trials in the future.

Effect of retinoic acid on apoptosis and DNA repair in human keratinocytes after UVB irradiation

BACKGROUND

Skin cancer is extremely common. Epidemiological studies indicated that ultraviolet radiation (UV) is the primary cause for skin cancers, and that retinoic acid (RA) is able to inhibit this UV-induced skin carcinogenesis; however, the molecular mechanism of the anti-UV action of RA is unclear.

OBJECTIVE

The purpose of this study is to investigate if RA enhances the removal of UV-induced DNA damage.

METHODS

The effect of RA on UV-induced apoptosis and DNA repair was investigated by ELISA apoptosis assay and CAT assay.

RESULTS

Both all-trans-RA and 9-cis-RA did not promote UV-induced apoptosis nor the repair of UV-damaged DNA in human keratinocytes. Furthermore, RA did not induce the expression of p53.

CONCLUSION

The inhibition of RA on skin carcinogenesis is not due to enhanced removal of UV-damaged DNA. Therefore, RA does not inhibit skin cancer development at the initiation stage, but possibly at the promotion and progression stages.