Resistance to the atypical retinoid ST1926 in SK-N-AS cells selected the subline rAS-ST with enhanced sensitivity to ATRA mediated by not conventional mechanisms: DNA damage, G2 accumulation and late telomerase inhibition.

BACKGROUND AND PURPOSE: 13-cis-Retinoic acid represents a well-established clinical strategy for the management of minimal residual disease of high risk neuroblastoma (NB) patients. However, the clinical efficacy on the overall survival of these patients remains limited, addressing the issue of better understanding the molecular mechanisms and intracellular pathways mediating Retinoic Acid (RA) clinical effects. EXPERIMENTAL APPROACH: This work investigates the mechanism underlying the sensitivity/resistance to RA in NB by taking advantage of the paired SK-N-AS/rAS-ST cells showing different responsivity to ATRA. The subline rAS-ST was selected by inducing resistance to the novel retinoid ST1926 in the NB SK-N-AS cell line. KEY RESULTS: Resistance to ST1926 was neither dependent on cellular uptake nor on multi-drug resistance phenotype. Rather, both delayed/lower DNA damage and apoptosis appeared involved in reduced sensitivity of rAS-ST cells to ST1926. This subline showed enhanced responsivity to ATRA compared to the wt counterpart, that was associated with enhanced RARα/ß expression, DNA damage, G2 accumulation, PI3K/AKT pathway inhibition, cellular differentiation and delayed telomerase inhibition, without involvement of either p27/p53 or caspase-mediated apoptosis. CONCLUSIONS AND IMPLICATIONS: The present data add important information to the understanding of RA sensitivity in NB, providing further insights towards a more efficacious clinical use of this drug.

Interfacing Sca-1(pos) mesenchymal stem cells with biocompatible scaffolds with different chemical composition and geometry.

An immortalized murine mesenchymal stem cell line (mTERT-MSC) enriched for Lin(neg)/Sca-1(pos) fraction has been obtained through the transfection of MSC with murine TERT and single-cell isolation. Such cell line maintained the typical MSC self-renewal capacity and continuously expressed MSC phenotype. Moreover, mTERT-MSC retained the functional features of freshly isolated MSC in culture without evidence of senescence or spontaneous differentiation events. Thus, mTERT-MSC have been cultured onto PLA films, 30 and 100 microm PLA microbeads, and onto unpressed and pressed HYAFF-11 scaffolds. While the cells adhered preserving their morphology on PLA films, clusters of mTERT-MSC were detected on PLA beads and unpressed fibrous scaffolds. Finally, mTERT-MSC were not able to colonize the inner layers of pressed HYAFF-11. Nevertheless, such cell line displayed the ability to preserve Sca-1 expression and to retain multilineage potential when appropriately stimulated on all the scaffolds tested.

The unique biological features of the marine product Yondelis (ET-743, trabectedin) are shared by its analog ET-637, which lacks the C ring.

It was previously suggested that the peculiar mechanism of action of the novel anticancer drug Yondelis (ET-743, trabectedin) was due to part of the molecule, units A and B, binding to DNA in the minor groove, causing an alkylation at the N2 of guanine, while unit C protrudes out of DNA, possibly interacting with transcription factors or other DNA binding proteins. To test this hypothesis, we have compared the biological activity and the mode of action of Yondelis with its analogue ET-637, which has the same chemical structure except for the lack of the C ring. Yondelis and ET-637 showed similar cytotoxic potency and cell cycle perturbations. As already reported for Yondelis, the UV-96 cell line, deficient in ERCC-1, was less sensitive to ET-637 than the parental cell line. The binding of Yondelis or ET-637 to DNA-oligonucleotides was demonstrated by gel shift assay and SDS did not reverse the binding. Both compounds blocked the temperature-induced activation of the HSP40 promoter in the range of 1-10 nM. This study indicates that ET-637 acts similarly to Yondelis and demonstrates that the C ring of Yondelis may not be required for its biological activity.

Cellular and molecular aspects of drugs of the future: oxaliplatin.

Oxaliplatin (Eloxatine) is a third-generation platinum compound which has shown a wide antitumour effect both in vitro and in vivo, a better safety profile than cisplatin and a lack of cross-resistance with cisplatin and carboplatin. In this scenario, oxaliplatin may represent an innovative and challenging drug extending the antitumour activity in diseases such as gastrointestinal cancer that are not usually sensitive to these coordination complexes. Oxaliplatin has a non-hydrolysable diaminocyclohexane (DACH) carrier ligand which is maintained in the final cytotoxic metabolites of the drug. Like cisplatin, oxaliplatin targets DNA producing mainly 1,2-GG intrastrand cross-links. The cellular and molecular aspects of the mechanism of action of oxaliplatin have not yet been fully elucidated. However, the intrinsic chemical and steric characteristics of the DACH-platinum adducts appear to contribute to the lack of cross-resistance with cisplatin. To date, mismatch repair and replicative bypass appear to be the processes most likely involved in differentiating the molecular responses to these agents.

The abnormal cytotoxicities of 2,5-diaziridinyl-1,4-benzoquinone-3-phenyl esters.

Several derivatives of 2,5-diaziridinyl-3-phenyl-1,4-benzoquinone have been synthesized and their cytotoxicities in six different human cancer cell lines (H460, H596, HT29, BE, K562 and A2780) have been determined. It was observed that certain phenol-ester derivatives were significantly more cytotoxic in all of the cell lines investigated. These esters were shown to be cleaved by esterases to form a stable meta-phenol and an unstable para-phenol. The meta-phenol was also highly cytotoxic. Several of these compounds were studied in detail using DNA cross-linking, clonogenic, apoptosis and flow cytometry assays. It is proposed that although the phenol-esters and the phenols can efficiently cross-link DNA, this mechanism alone is not sufficient to explain the toxicities of these compounds.