Tamoxifen Sensitivity-Testing of Glioblastomas: Comparison of in Vitro and in Vivo Results

Summary

 Background. Only less than half of the patients with malignant gliomas respond to a continuous high dose Tamoxifen (TAM) and/or Carboplatin (CP)-treatment. Therefore, a method for predicting the efficacy of TAM-treatment would be desirable.

 Methods. Paralleling a clinical study, the predictive value of in vitro-sensitivity testing of TAM and TAM's metabolite 4-OH-TAM in primary cultures of tumour explants from 15 of a total of 50 patients was examined. Additionally, the influence of TAM, 4-OH-TAM, and CP on the proliferation of established glioblastoma cell lines and of those explanted from athymic nude mice and re-established in cell culture was investigated. Human glioblastomas xenotransplanted subcutaneously into athymic nude mice and subsequently treated with TAM and/or CP were examined in a parallel in vivo-study.

 Findings. TAM-chemosensitivity-testing of glioblastomas failed to predict the clinical response to TAM-treatment in our patients and did not correlate with the in vivo-TAM-response of tumours xenotransplanted into nude mice. TAM's and 4-OH-TAM's ability to inhibit growth of various glioblastoma cell lines in vitro in very similar concentrations was shown to be a consistent phenomenon which seems to be independent of the in vivo response in either patients or mice as previous hosts. However, CP's antiproliferative effect on glioblastomas in vivo was paralleled by respective in vitro results. Whereas TAM showed to mediate its in vitro antiproliferative effect by inducing apoptosis in most cell lines examined, CP-treatment lead to necrosis of cells.

 Interpretation. Combining the results obtained from our human and mouse studies, it has to be postulated that host factors other than the sensitivity to TAM of the individual cell, determine the efficacy of TAM-treatment in vivo.