Antitumor activity of the combination of synthetic retinoid ST1926 and cisplatin in ovarian carcinoma models

BACKGROUND

The novel adamantyl retinoid ST1926 is a potent inducer of apoptosis in ovarian carcinoma cells. Since the pro-apoptotic effect is associated with activation of p53, in this study we have investigated the efficacy of combination of ST1926 with cisplatin, a DNA-damaging agent that is known to induce p53-dependent apoptosis.

MATERIALS AND METHODS

The efficacy of ST1926 and its combination with cisplatin was evaluated in human ovarian carcinoma models, including resistant tumors.

RESULTS

Oral treatment with ST1926 alone caused a marginal tumor growth inhibition (<50%), but the combination with cisplatin resulted in an improved efficacy, most evident in terms of tumor growth delay without a substantial increase of toxicity. The combination therapy achieved the best effects against the HOC18 ovarian carcinoma tumor, resulting in an appreciable number of animals without evidence of disease at the end of the experiment. In contrast to the marginal effect of ST1926 alone against the subcutaneous-growing tumors, loco-regional (intraperitoneal) treatment achieved a marked increase of survival of animals with ascitic IGROV-1 tumor.

CONCLUSIONS

The present results document the efficacy of the combination of cisplatin with ST1926 and provide a rational basis for the design of novel, well-tolerated platinum-based treatment approaches in human ovarian carcinoma.

DNA accessibility to minor groove ligands in core nucleosome and chromatosome

Using the circular dichroism spectra induced in the visible by the binding to the minor groove of DNA, we found that Hoechst 33258 is able to occupy its specific sites even when these are located inside the nucleosome structure. This high accessibility of the DNA in the nucleosome is not modified by the removal of the amino-terminal domains of the octamer histones and is not reduced by the presence of linker histone. Interesting and reasonable differences were found in the association constants.

Chromatin accessibility to DNA minor groove ligands in vitro: role of linker histones and amino-terminal domains of octamer histones

Using the circular dichroism spectra, induced in the visible range by the binding of minor groove ligands to DNA, we found that two drugs, DAPI and Hoechst 33258, are able to occupy their specific sites even when these are located inside the nucleosome structure. This high accessibility of the binding sites in the nucleosome is not modified by the removal of the amino-terminal domains of the octamer histones and, surprisingly, it is not reduced by the presence of linker histone. Interesting and reasonable differences were found in the association constants, that reveal the "reluctance" of the ligands to bind the DNA-minor groove when the histones are present.