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Our study focused on the influence of herpes simplex virus thymidine kinase (HSV-tk) expression and ganciclovir (GCV) treatment on the sensitivity of C6 glioma cells to frequently used chemotherapeutic drugs, i.e. adriamycin (ADR), cisplatin (CDDP), 5-fluorouracil (5-FU), and methotrexate (MTX). Transfection with HSV-tk revealed an increased sensitivity to GCV and CDDP and a decreased sensitivity to ADR and MTX. No significant differences were found in sensitivity to 5-FU. Combined treatment in a HSV-tk negative cell line revealed an additive effect when GCV was combined with ADR, whereas an antagonistic effect was found when GCV was combined with CDDP, 5-FU, or MTX. Comparable results were obtained in an HSV-tk positive cell line, apart from CDDP, which showed an additive effect. In conclusion, both HSV-tk transfection and subsequent GCV treatment can influence the sensitivity of tumor cells to various chemotherapeutic drugs in an antagonistic manner. Therefore, combining HSV-tk/GCV gene therapy with chemotherapy might not always be beneficial.

Background: Cornea-derived transcript 6 (CDT6 = AngX) has been shown to have an anti-tumor effect., Materials and Methods: We transfected the murine melanoma cell line B16-F10 with the CDT6 gene and compared the sensitivity to cytostatic drugs of the resulting cell line, B16-CDT6, to that of the empty vector-transfected control cell line B16-CMV., Results: The B16-CDT6 line showed a significantly increased sensitivity to doxorubicin as well as a tendency towards a decreased sensitivity to cisplatin. To further resolve the mechanism of the increase in sensitivity to doxorubicin, we also tested the cytotoxic agents vincristine, etoposide and taxol. However no difference in sensitivity for these drugs was found between the B16-CDT6 and the control cell line., Conclusion: CDT6 increased the sensitivity to doxorubicin in a mechanism probably not related to interference with the efflux pumps MRP, Pgp or the DNA-associated target enzyme topoisomerase II. Altered gene expression induced by gene therapy might influence tumor sensitivity to chemotherapy.

Cisplatin (CDDP) is an extremely active drug in the treatment of germ-cell tumours. Earlier, we found an unexpected inverse correlation between the total amount of sulfhydryl groups and CDDP sensitivity in a panel of 3 human germ-cell-tumour and 3 colon-carcinoma cell lines. Major components of the sulfhydryl groups are glutathione and metallothionein (MT). We further investigated a possible role of MT in the CDDP sensitivity of germ-cell tumours. MT levels and functionality of the germ-cell-tumour and colon-carcinoma cell lines were found to be inversely correlated with CDDP sensitivity. No difference in sub-cellular localization of MT could be observed among the types of cell lines. In agreement with the in vitro data, immunohistochemical detection of MT was high in 11/14 primary human germ-cell tumours and low in 7/7 human colon carcinomas. MT-protein expression in primary germ-cell tumours did not discriminate between responding and non-responding patients. As compared with the primary tumours, MT-protein expression decreased in 5/7 post-chemotherapy residual vital tumours or remained undetectable (2/7). MT-protein expression in the germ-cell tumours was not related to total p53-protein expression. In summary, over-expression of MT was found in germ-cell tumours, both in cell lines and in human tumours. Although MT-protein over-expression seems to be associated with the CDDP sensitivity of germ-cell tumours, MT-protein expression in primary germ-cell tumours did not differ between responding and non-responding patients and therefore cannot be used to predict response to chemotherapy., (Copyright 2000 Wiley-Liss, Inc.)

In this study, the mechanism(s) by which heat increases cis-diamminedichloroplatinum (cisplatin, cDDP) sensitivity in cDDP-sensitive and -resistant cell lines of murine as well as human origin were investigated. Heating cells at 43 degrees C during cDDP exposure was found to increase drug accumulation significantly in the cDDP-resistant cell lines but had little effect on drug accumulation in the cDDP-sensitive cell lines. DNA adduct formation, however, was significantly increased in all cell lines studied. Furthermore, ongoing formation of platinum (Pt)-DNA adducts after the end of cDDP treatment was enhanced and/or adduct removal was decreased in heated cells, resulting in relatively more DNA damage remaining at 24 h after the end of cDDP exposure. Correlation plots with survival revealed weak correlations with cellular Pt accumulation (r2 = 0.59) and initial Pt-DNA adduct formation (r2 = 0.64). Strong correlations, however, were found with Pt-DNA adducts at 6 h (r2 = 0.97) and 24 h (r2 = 0.89) after the incubation with the drug. In conclusion, the mechanism by which heat sensitizes cells for cDDP action seems to be the sum of multiple factors, which comprise heat effects on accumulation, adduct formation and adduct processing. This mechanism did not seem to differ between cDDP-sensitive and -resistant cells, emphasizing the potential of hyperthermia to reduce cDDP resistance.