Radiation following chemotherapy for mediastinal Hodgkin's disease: the outcome of various doses for bulky tumors.

Twenty-one patients with bulky mediastinal disease responding to chemotherapy received consolidation with low-dose mediastinal radiation (19.8-25.2 Gy). Their 5-year mediastinal failure rate (10%) was equivalent to that of 10 similar patients who received higher doses of 30-44 Gy (20%). Low-dose radiation may be appropriate for these patients. Prospective studies are required to verify these findings.

Fraction size and dose parameters related to the incidence of pericardial effusions.

PURPOSE: The influence of treatment parameters, such as (a) fraction size and (b) average and maximum dose (as derived from three-dimensional (3D) distributions), on the incidence of pericarditis was analyzed. To understand and predict the dose and volume effect on the pericardium, a normal tissue-complication probability model was tested with these complication data. METHODS AND MATERIALS: Patients (n = 57) entered in 3 consecutive University of Michigan protocols of combined modality for treatment of localized esophageal carcinoma, and having 3D treatment planning for radiation therapy were the subject of this study. Univariate and multivariate analyses were performed to determine the significance of the effect of fraction size and dose parameters on the development of any grade of pericarditis. Dose distributions were corrected for the biological effect of fraction size using the linear-quadratic method. Normal tissue complication probability (NTCP) was calculated with the Lyman model. RESULTS: Nonmalignant pericardial effusions occurred in 5 of the 57 patients; all effusions were in patients who received treatment with 3.5 Gy daily fractions. On multivariate analysis, no dose factor except fraction size predicted pericarditis, until the dose distributions were corrected for the effect of fraction size ("bio"-dose). Then, both "bio-average" and "bio-maximum" dose were significant predictive factors (p = 0.014). NTCPs for the patients with pericarditis range from 62% to 99% for the calculations with the "bio"-dose distributions vs. 0.5% to 27% for the uncorrected distributions. DISCUSSION: A normal tissue complication probability (NTCP) model predicts a trend towards a high incidence of radiation pericarditis for patients who have high complication probabilities. It is important to correct the dose distribution for the effects of fractionation, particularly when the fraction size deviates greatly from standard (2.0 Gy) fractionation.

Enhanced expression of thymidine kinase in human cells following ionizing radiation.

PURPOSE: We investigated the induction of thymidine kinase transcription and enzymatic activity, and the activation of transcription factors binding to the thymidine kinase promoter, in human normal compared to tumor cells in culture before and after ionizing radiation. METHODS AND MATERIALS: Northern blot, dot-blot, and thymidine kinase enzyme assays were used to observe thymidine kinase transcript and enzymatic changes before and after radiation. Temporal expression of thymidine kinase transcripts following an optimal induction dose of radiation was also studied. Gel mobility shift assays were performed using a 95-base pair fragment of the thymidine kinase promoter (containing the CCAAT box) to analyze transcription factor binding. RESULTS: Thymidine kinase transcript and enzymatic levels were higher in human tumor compared to normal cells. In contrast, levels of x-ray-activated thymidine kinase transcription factors were not significantly different in human neoplastic compared to normal cells. CONCLUSIONS: Elevated x-ray-induced thymidine kinase transcripts, enzymatic levels, and transcription factors are consistent with the loss of stringent cell growth regulation associated with neoplastic cells. The induction of thymidine kinase following ionizing radiation may be exploited in chemotherapeutic strategies which use halogenated pyrimidines and/or in various gene therapy strategies.

Alterations in transcription factor binding in radioresistant human melanoma cells after ionizing radiation.

We analyzed alterations in transcription factor binding to specific, known promoter DNA consensus sequences between irradiated and unirradiated radioresistant human melanoma (U1-Mel) cells. The goal of this study was to begin to investigate which transcription factors and DNA-binding sites are responsible for the induction of specific transcripts and proteins after ionizing radiation (Boothman et al., Proc. Natl. Acad. Sci. USA 90, 7200, 1993). Transcription factor binding was observed using DNA band-shift assays and oligonucleotide competition analyses. Confluence-arrested U1-Mel cells were irradiated (4.5 Gy) and harvested at 4 h. Double-stranded oligonucleotides containing known DNA-binding consensus sites for specific transcription factors were used. Increased DNA-binding activity after ionizing radiation was noted with oligonucleotides containing the CREB, NF-kappa B and Sp1 consensus sites. Increased DNA binding activity after ionizing radiation was noted with oligonucleotides containing the CREB, NF-kappa B and Sp1 consensus sites. No changes in protein binding to AP-1, AP-2, AP-3 or CTF/NF1, GRE or Oct-1 consensus sequences were noted. X-ray activation of select transcription factors, which bind certain consensus sites in promoters, may cause specific induction or repression of gene transcription.

Isolation of an X-ray-responsive element in the promoter region of tissue-type plasminogen activator: potential uses of X-ray-responsive elements for gene therapy.

Tissue-type plasminogen activator (t-PA) was induced over 50-fold after X irradiation in radioresistant human melanoma cells (Boothman et al., Cancer Res. 51, 5587-5595, 1991). Activities of t-PA were induced 14-fold in ataxia telangiectasia, 9-fold in Bloom's syndrome and 6-fold in Fanconi's anemia cells, compared to normal human fibroblasts (Fukunaga et al., Int. J. Radiat. Oncol. Biol. Phys. 24, 949-957, 1992). X-ray-inducible synthesis of the protease, t-PA, may play a role(s) in damage-inducible repair processes in mammalian cells, similar to the SOS repair systems in lower eukaryotes and prokaryotes. DNA band shift and DNase I footprinting assays were used to determine binding if transcription factors to a previously unknown X-ray-responsive element (XRE) in the t-PA promoter. The major goals of our research with XREs are to understand (a) which transcription factor(s) regulates t-PA induction after X rays, and (b) the role(s) of t-PA in DNA repair, apoptosis or other responses to X rays. The purpose of this paper is to discuss the potential use of an XRE, such as the one in the t-PA promoter, for gene radiotherapy. Several gene therapy strategies are proposed.

Role of the neural retina in newt (Notophthalmus viridescens) lens regeneration in vitro.

Removal of the lens from the eye of an adult newt (Notophthalmus viridescens) is followed by regeneration of a new lens from the dorsal iris epithelial cells at the pupillary margin. This process is dependent upon the neural retina for its normal completion in vivo and in vitro. To examine the relationship between the retina and lens regeneration, we have conducted experiments that delimit the time period during which the retinal presence is critical (in vivo) and have investigated the influence of extracts of the retina on the progress of regeneration (in vitro). In vivo, removal of the retina at day 11 seriously retards further progression of regeneration while removal of the retina at day 15 does not retard regeneration significantly. This defines a "critical period" in regeneration of the lens during which the retina is required. Explantation of regenerates 11 or 12 days after lentectomy to organ culture medium enriched with either crude retinal homogenate or extracts prepared from chick or bovine retinas according to Courty et al. ('85, Biochimie, 67:265-269) reveals that the progress of regeneration can be supported in culture by the crude extract. This is the first demonstration of complete iris-lens transformation in culture in the presence of retinal extract. It is possible that the retina acts indirectly by promoting passage of the iris epithelial cells through the critical number of mitoses required before redifferentiation into lens cells can occur (as proposed by Yamada, '77, Monogr. Dev. Biol., 13:126). It is also possible that the retina acts by directly instructing the iris cells to redifferentiate.(ABSTRACT TRUNCATED AT 250 WORDS)