Roland Löser

Preclinical data for Droloxifene

The new antiestrogen Droloxifene has a 10-60-fold higher binding affinity to the estrogen receptor (ER) compared to the related compound Tamoxifen. A similar relationship was found in growth inhibition studies which showed that Droloxifene inhibited the different ER positive human breast cancer cells more effectively than Tamoxifen, predominantly in drug concentrations which are found in humans during therapy. As another consequence of the high stability of the complex formed by Droloxifene binding to the ER, intermittent exposures with clinically relevant concentrations of Droloxifene brought about effective growth inhibition of human ER positive tumor cells even after short-term application. Droloxifene was found, like Tamoxifen, to block human breast cancer cells in G1-phase of the cell cycle. Moreover, cell-cycle data confirmed the superior growth-inhibiting potency of Droloxifene compared to Tamoxifen. Droloxifene was also found to effectively induce expression of the negative growth factor TGF-beta, to inhibit IGF-I stimulated cell growth and to prevent estrogen-stimulated proto-oncogene c-myc expression. Unlike Tamoxifen, Droloxifene is a potent inhibitor of protein biosynthesis in ER-positive breast cancer cells at physiologically relevant concentrations. Lower estrogenic and higher antiestrogenic effects on immature rat uterus indicate a higher therapeutic index for Droloxifene compared to Tamoxifen. In vivo, Droloxifene displayed increased growth inhibition of different tumors of animal (R3230AC and 13762) and human origin (T61). Furthermore, it was found that the two structurally similar drugs differ in their toxicologic characteristics in the following important respects: Droloxifene is devoid of any in vivo or in vitro carcinogenic or mutagenic effects, whereas Tamoxifen causes liver tumors in rats, induces DNA adduct formation in rats and hamsters and shows transforming activity in SHE-cells (Syrian hamster embryo fibroblasts). Considerably less toxicity and a lower level of intrinsic estrogenicity was observed even after maximum long-term exposure of different animal species to Droloxifene, in comparison with Tamoxifen. Therefore, it can be assumed that Droloxifene may represent an important step forward in the treatment of mammary carcinomas in women through its better tolerability and increased efficacy compared with Tamoxifen. For long-term adjuvant or preventive treatment of breast cancer, Droloxifene may well be the safer choice.

Flow cytometric analysis of virus-infected cells and its potential use for screening antiviral agents.

Virus-infected cells were analyzed using multiparameter flow cytometry. Two virus-cell systems were investigated: HSV-1-infected VF cells and influenza C virus JHB/1/66-infected MDCK cells. Analysis included the measurement of the appearance of virus specific antigens. On individual cells, with polyclonal antibodies, antigens were first detected at 12 h p.i., and the numbers of labeled cells were followed up to 96 h p.i. The efficacy of four antiviral agents was tested with this system. The results were in good agreement with those of plaque reduction tests and indicated that this new method may be extremely useful for the correlation of viral and cellular events with antiviral activity. Finally, it was demonstrated that infected cells in both systems have a considerably greater volume than non-infected cells.