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

Synthetic Diphenylacetylene-Based Retinoids Induce DNA Damage in Chinese Hamster Ovary Cells without Altering Viability

All-trans-retinoic acid (ATRA), the active metabolite of vitamin A, plays a pivotal role in cell differentiation, proliferation and embryonic development. It is an effective therapy for dermatological disorders and malignancies. ATRA is prone to isomerization and oxidation, which can affect its activity and selectivity. Novel diphenylacetylene-based ATRA analogues with increased stability can help to overcome these problems and may offer significant potential as therapeutics for a variety of cancers and neurodegenerative diseases, including amyotrophic lateral sclerosis. Here, we investigated the effects of these retinoids on cell viability and genotoxicity in the widely used model system of the rapidly proliferating Chinese hamster ovary cell line. DC360 is a fluorescent ATRA analogue and DC324 is a non-active derivative of DC360. EC23, DC525, DC540, DC645, and DC712 are promising analogues with increased bioactivity. The cytotoxic activity of the compounds was evaluated by ATP assay and DNA damage was tested by comet assay. No cytotoxicity was observed in the 10⁻⁶–10⁻⁵ M concentration range. All compounds induced DNA migration similar to ATRA, but DC324, DC360 and EC23 did so to a greater extent, particularly at higher concentrations. We believe that retinoid receptor-independent genotoxicity is a general characteristic of these compounds; however, further studies are needed to identify the molecular mechanisms and understand their complex biological functions.

Cytotoxic and Genotoxic Effects of Cyanobacterial and Algal Extracts-Microcystin and Retinoic Acid Content

In the last decade, it has become evident that complex mixtures of cyanobacterial bioactive substances, simultaneously present in blooms, often exert adverse effects that are different from those of pure cyanotoxins, and awareness has been raised on the importance of studying complex mixtures and chemical interactions. We aimed to investigate cytotoxic and genotoxic effects of complex extracts from laboratory cultures of cyanobacterial species from different orders (Cylindrospermopsis raciborskii, Aphanizomenon gracile, Microcystis aeruginosa, M. viridis, M. ichtyoblabe, Planktothrix agardhii, Limnothrix redekei) and algae (Desmodesmus quadricauda), and examine possible relationships between the observed effects and toxin and retinoic acid (RA) content in the extracts. The cytotoxic and genotoxic effects of the extracts were studied in the human hepatocellular carcinoma HepG2 cell line, using the MTT assay, and the comet and cytokinesis-block micronucleus (cytome) assays, respectively. Liquid chromatography electrospray ionization mass spectrometry (LC/ESI-MS) was used to detect toxins (microcystins (MC-LR, MC-RR, MC-YR) and cylindrospermopsin) and RAs (ATRA and 9cis-RA) in the extracts. Six out of eight extracts were cytotoxic (0.04–2 mg_DM/mL), and five induced DNA strand breaks at non-cytotoxic concentrations (0.2–2 mg_DM/mL). The extracts with genotoxic activity also had the highest content of RAs and there was a linear association between RA content and genotoxicity, indicating their possible involvement; however further research is needed to identify and confirm the compounds involved and to elucidate possible genotoxic effects of RAs.

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.

Cytotoxic and genotoxic effects of acitretin, alone or in combination with psoralen-ultraviolet A or narrow-band ultraviolet B-therapy in psoriatic patients

Acitretin is currently used alone or combined with PUVA (psoralen + UVA) or with narrow-band ultraviolet B (NBUVB), to treat moderate and severe psoriasis. However, little is known about the potential genotoxic/carcinogenic risk and the cytostatic/cytotoxic effects of these treatments. Our aim was to study the cytotoxic and genotoxic effects of acitretin - alone or in combination with PUVA or NBUVB - by performing studies with blood from patients with psoriasis vulgaris who were treated with acitretin, acitretin+PUVA or acitretin+NBUVB for 12 weeks, and in vitro studies with blood from healthy volunteers, which was incubated with acitretin at different concentrations. The cytotoxic and genotoxic effects were evaluated by the cytokinesis-blocked micronucleus test and the comet assay. Our results show that psoriatic patients treated with acitretin alone or with acitretin+NBUVB, did not show genotoxic effects. In addition, these therapies reduced the rate of proliferation and induced apoptosis and necrosis of lymphocytes; the same occurred with lymphocyte cultures incubated with acitretin (1.2-20μM). The acitretin+PUVA reduced also the proliferation rate, and increased the necrotic lymphocytes. Our studies suggest that therapy with acitretin alone or combined with NBUVB, as used in psoriatic patients, does not show genotoxic effects, reduces the rate of proliferation and induces apoptosis and necrosis of lymphocytes. The combination of acitretin with PUVA also reduces the proliferation rate and increases the number of necrotic lymphocytes. However, as it induced slight genotoxic effects, further studies are needed to clarify its genotoxic potential.

Comparison of the aneugenic properties of nocodazole, paclitaxel and griseofulvin in vitro. Centrosome defects and alterations in protein expression profiles

We have comparatively investigated the aneugenic activity of two anticancer drugs, nocodazole (NOC) and paclitaxel (PTX), and the antifungal griseofulvin with promising role in cancer treatment (GF), which affect microtubule dynamics in different ways. The comparison was achieved in HFFF2 human fibroblasts, MCF-7 human breast cancer cells and C2C12 mouse myoblasts, and focused on three issues: (i) induction of chromosome delay by estimation of MN frequency using CREST analysis; (ii) disturbance of spindle organization with Aurora-A/β-tubulin immunofluorescence; and (iii) alterations in the expression of Aurora-A, β- and γ-tubulin by western blotting. They induced chromosome delay, provoked metaphase arrest and promoted microtubule disorganization, reflecting their common characteristic of generating aneuploidy. In particular, NOC induced mainly monopolar metaphases, although PTX induced only multipolar metaphases. GF generated different types of abnormal metaphases, exhibiting cell specificity. Additionally, NOC decreased the expression of Aurora-A and β-tubulin, while the opposite held true for PTX and GF. γ-Tubulin expression was not modulated owing to NOC treatment, whereas PTX and GF increased γ-tubulin expression. Our findings throw a light on the manifestation of the aneugenicity of the studied compounds through centrosome proliferation/separation and protein expression, reflecting their different effects on microtubule dynamics.