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Many p53 mutants found in human cancer have an altered ability to bind DNA and transactivate gene expression. Re-expression of functional p53 in cells in which the endogenous TP53 gene is inactivated has been demonstrated to restore a non-tumorigenic phenotype. Pharmacological modulation of p53 mutant conformation may therefore represent a mechanism to reactivate p53 function and consequently improve response to radio- and chemotherapy. We have recently reported that the radio- and chemoprotector Amifostine (WR2721, Ethyol®) activates wild-type p53 in cultured mammalian cells. In the present study, we have used a yeast functional assay to investigate the effect of WR2721 on the transcriptional activity of p53. WR2721 restored this activity in a temperature-sensitive mutant V272M (valine to methionine at codon 272) expressed at the non-permissive temperature and it also partially restored the transcriptional activity of several other conformationally flexible p53 mutants. The results indicate that the yeast functional assay may be used to identify compounds that modulate p53 activity, with potential therapeutic implications. Oncogene (2001) 20, 3533–3540. [ABSTRACT FROM AUTHOR]

The relationship between P-glycoprotein expression and malignancy is controversial. We have recently found that, in osteosarcoma, multidrug resistance (MDR) is associated with a less aggressive behavior, both in vitro and in clinical settings. In this study, we evaluated whether P-glycoprotein overexpression has a cause-effect relationship with the reduced metastatic potential of MDR cells, or rather reflects a more complex phenotype. MDR1 gene-transfected osteosarcoma cell clones, showing different levels of P-glycoprotein expression, were analysed for their in vitro characteristics and their tumorigenic and metastatic ability in athymic mice. Apart from the different levels of P-glycoprotein, no significant change in the expression of surface antigens or in the differentiative features were observed in the MDR1 gene transfectants compared to the parental cell lines or control clones, obtained by transfection with neo gene alone. In contrast to controls, however, MDR1 transfectants showed a significantly lower ability to grow in semi-solid medium and were completely unable to grow and give lung metastases in athymic mice. These findings indicate that P-glycoprotein overexpression is causally associated with a low malignant potential of osteosarcoma cells, and open new insights on the role and functions of P-glycoprotein activity. [ABSTRACT FROM AUTHOR]

The reliability of a simple method evaluating the pattern of subcellular binding of Adriamycin (Adriamycin binding assay, ABA) as an index of sensitivity was demonstrated in different primary cultures and in sensitive and resistant cell lines of human osteosarcoma. After exposure to Adriamycin (10 μg/ml for 30 min at 37°C), living sensitive cells showed selective intranuclear uptake of the drug, whereas in resistant cells no distinct subcellular distribution was observed. The binding pattern of Adriamycin in sensitive and in highly resistant cells was inversely related to the expression of P-glycoprotein. However, low levels of resistance in vitro, not detectable by increased levels of expression of P-glycoprotein, were revealed by ABA. The use of ABA in combination with the estimate of P-glycoprotein expression is recommended in clinical practice as an accurate means for predicting the sensitivity of osteosarcoma to Adriamycin. [ABSTRACT FROM AUTHOR]