Faculty Bibliography

PURPOSE: The promising chemotherapeutic agent, taxol, has been shown to sensitize the G18 line of human astrocytoma cells to ionizing radiation. The present studies were performed to identify specific changes in gene expression associated with this altered sensitivity. METHODS AND MATERIALS: The radioresistant, grade 3 human astrocytoma cell line, G18, was exposed for varying periods of time to treatment with taxol, tetradecanoyl phorbol acetate (TPA), serum, isoproterenol, dibutyryl cyclic adenosine monophosphate, or ionizing radiation alone or in combination with taxol pretreatment. Ribonucleic acid samples from the cells were monitored for the expression of a group of immediate early genes (IEGs), including c-fos, c-jun, TIS1, TIS7, TIS8, TIS11 and TIS21, by northern blot hybridization analysis. RESULTS: Transient immediate early gene induction was observed after treatment of G18 cells with tetradecanoyl phorbol acetate, serum, isoproterenol, or ionizing radiation, but not after treatment with taxol. Of the seven immediate early genes analyzed, all but TIS7 were found to be inducible by one or more of the treatments. Only TIS8 (also known as egr-1 or zif268) was significantly inducible by radiation, and this transient induction was decreased by at least four-fold by pretreatment for 24 hr with a dose of taxol that was previously shown to block 96.5% of the cells in G2/M and enhance radiosensitivity. CONCLUSION: The products of immediate early genes, which are induced transiently in cells in response to a variety of treatments, including growth factors, neurotransmitters, and irradiation with UV light or X rays, are thought to initiate a cascade of genetic responses to alterations in cellular environment. The present results demonstrate a dramatic attenuation in one immediate early gene response in association with a treatment that enhances radiosensitivity in a refractory human brain tumor line

PURPOSE: Prostate specific antigen density, previously described as a ratio of serum prostate specific antigen to the volume of the prostate, has been shown to be an important factor in the discrimination of patients with occult metastatic disease and patients with benign versus malignant prostatic disease. We undertook a retrospective study to determine if prostate specific antigen density was a predictor of outcome following definitive conformal radiation therapy. METHODS AND MATERIALS: Between January 1989 and August 1991, 86 patients with localized prostate cancer (confined to the prostate, periprostatic tissue, or seminal vesicles) were treated in the Department of Radiation Oncology, Columbia-Presbyterian Medical Center with definitive radiation therapy using computed tomography-guided conformal technique. Thirteen patients were excluded on the basis of prior prostatectomy, hormonal therapy, or no pretreatment prostate specific antigen measurement. Seventy-three patients were evaluable: 19% (14/73) American Urologic Association Stage A (T1), 41% (30/73) B (T2), and 40% (29/73) C (T3). Prostate specific antigen density was defined as the ratio of the pretreatment serum prostate specific antigen to the prostate volume as determined from computed tomography treatment planning scans. Pretreatment prostate specific antigen density was calculated for each patient and ranged from 0.04-3.85 with a mean and median value of 0.66 and 0.33, respectively. Prostate specific antigen failure was defined as a rise above normal level or, for patients whose nadir was above 4 ng/ml, an increase of greater than 10% above nadir. Mean prostate specific antigen follow-up was 13 months (range 2.3-31 months) by which time 66% of patients had normal prostate specific antigen (< or = 4 ng/ml) levels. RESULTS: Nine patients experienced prostate specific antigen failure. The mean prostate specific antigen density of patients with disease-free survival versus failures was 0.53 and 1.6, respectively (p < 0.05). Kaplan-Meier analysis showed that patients with a prostate specific antigen density < or = 0.3 (n = 30) had 100% actuarial disease-free survival at 30 months compared with 62% for patients with prostate specific antigen density > 0.3 (n = 43, p < 0.01). Patients with a prostate specific antigen density < or = 0.6 (n = 52) and > 0.6 (n = 21) had an 88% and 57% actuarial disease-free survival at > 24 months (p < 0.05). CONCLUSION: Prostate specific antigen density was an excellent predictor of disease-free survival (p < 0.01) and was superior to clinical stage (p > 0.05), Gleason's score (p > 0.05), and pretreatment prostate specific antigen (p < 0.05). These results suggest that patients with low prostate specific antigen density (< or = 0.3), including those with locally advanced clinical stage, high Gleason's score, or elevated pretreatment prostate specific antigen, do well with conventional radiation therapy and should not be subjected to high risk protocols. Further follow-up will be required to determine if patients with low prostate specific antigen density will have improved overall survival

Anti-taxol antibodies were generated in the rabbit using a taxol-bovine serum albumin conjugate prepared from 2'-succinyltaxol using a mixed anhydride procedure. Immunization with 2'-succinyltaxol-bovine serum albumin gave rise to polyclonal anti-taxol antibodies. By a radioimmunoassay using [3H]taxol, a standard curve gave a 50% inhibitory concentration of 1.0 nM. Taxol levels in human serum could be measured, with the lower limit of detection and measurement being 0.1 nM or 0.085 ng/ml. Two mouse monoclonal anti-taxol antibodies were isolated by immunizing BALB/c mice with the same antigen. One was an immunoglobulin G1 (69E4A8E) and the other was immunoglobulin M (29B7B3C). The specificity of these antibodies was determined by a competitive enzyme-linked immunosorbent assay with taxol and 10 different related derivatives and analogues. 29B7B3C had higher binding affinities for biologically active derivatives and markedly lower affinities for inactive derivatives; i.e., the specificity was consistent with the results of tubulin disassembly and cytotoxicity studies using the same taxol derivatives, making it suitable for screening for taxol or taxol-like compounds in extracts of natural products. 69E4A8E recognized the benzamidocarbamyl group at the C-3' position of taxol and had a lower affinity for other active compounds with different substitutions. Taxol levels in human serum could be detected and measured by 69E4A8E using a competitive enzyme-linked immunosorbent assay. The lower limit of measurement was about 50 nM or approximately 42 ng/ml. Similar measurements could be made by radioimmunoassay

The cytotoxic effects of Taxol and/or ionizing radiation were evaluated in four human tumor cell lines. The recognized antimicrotubular effects of the drug leading to transitory accumulations of cells in the G2/M phase of the cell cycle, the most radiosensitive phase of the cycle, prompted this assessment of the potential for Taxol to function as a cell-cycle, phase-specific radiosensitizer. Taxol alone was cytotoxic to all four cell lines at low (< 25 nM) concentrations. A Taxol concentration of 10 nM for 24 hours led to 48, 15, 8, and 4.4% of cells retaining clonogenic potential for melanoma, two cervical carcinomas, and astrocytoma, respectively. There were significant Taxol concentration-time-dependent differences in response between the cell lines. Cell lines also showed significant differences in their responses to ionizing radiation. Combined treatment resulted in a demonstration of radiation sensitization with the astrocytoma and melanoma cell lines but not with the cervical carcinoma cell lines. Sensitizer enhancement ratios at the 10% cell survival level were 1.8 for 10 nM Taxol for 24 hours with the astrocytoma cells and 1.2 for 40 nM Taxol for 24 hours with the melanoma cells. The cervical carcinoma cell lines showed an additive effect for radiation and Taxol at all drug concentrations; that is, combined treatments elicit an additive or supra-additive response with, however, no simple relationship between Taxol concentration, Taxol time of treatment, and radiation dose in optimizing cytotoxic effectiveness. Combined modality treatments using relatively low concentrations of Taxol and ionizing radiation can result in an enhanced response and, at the least, an additive response, which could be advantageous in a clinical setting