PubMed · 8220754
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
S Beck. 1993. Multiplex DNA sequencing.. https://doi.org/10.1385/0-89603-248-5%3A225
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
PURPOSE: The purpose of the present study was to investigate if there were differences between U715 spheroids and single cells in the radiotoxic effect of 67Ga on cell growth and clonogenic capacity in vitro and to generate dosimetric approaches for the multicellular tumor model. METHODS AND MATERIALS: Human lymphoma U715 cells were cultured in vitro as single cells and multicellular spheroids, grown with the use of a combination of fibrin clot technique, spinner flasks, and liquid-overlay culture. Cells were incubated with 2.96-8.88 MBq/ml 67Gallium for 4 days. Spheroids were dispersed to single cells by treatment with plasmin. Residual proliferative and clonogenic capacity after 67Ga incubation were assayed using the MTT-test and clonogenic test, respectively. Autoradiography was performed with 1 microm sections and Ilford L4 liquid photographic emulsion. Dosimetric approaches were made, based on the MIRD-approach. RESULTS: During 67Ga incubation proliferation was inhibited. The residual proliferative or clonogenic capacity was inhibited by 8.88 MBq/ml for 39 and 88%, respectively. For single cells with 6.66 MBq/ml these inhibitions were 64 and 96%, respectively. Autoradiography showed an homogeneous distribution of 67Ga in spheroids and single cells. In single cells a 2.1-3.5 times higher 67Ga uptake/cell than in spheroids produced an equitoxic effect. The uptake parameters were implemented in new dosimetric approaches and showed that the efficacy of intracellular 67Ga was two times higher in spheroid clusters than in single cells due to energy deposition of internal conversion electrons within the cell clusters with a mean diameter size of nine cells. Both for proliferative and clonogenic capacity the exponential survival curves were superimposed. CONCLUSIONS: With the new approaches made in our dosimetric model the discrepancy found between 67Ga accumulation and radiotoxic effect in spheroids as compared to single cells can be explained by additional effects of the crossfire of internal conversion electrons within clusters of about nine cells in diameter in spheroids. Only twice as much 67Ga was needed to reach equitoxic absorbed doses in spheroids than was needed in single cells. Such might be important for the use of 67Ga treatment of small metastasis of malignant lymphoma.
Development of drug resistance is a major problem in attempts to control the growth of neoplastic cell populations. The resistance can he either inherent or acquired by an exposure to a chemotherapeutic drug. The available models for study of these phenomena have not led to major improvements in the therapy for human cancers. Therefore, in order to develop a new model for such studies, we have exposed human myeloid leukemia cells HL60 to increasing concentrations of 1,25-dihydroxyvitamin D3 (1,25D3) and characterized the emerging new phenotypes of these cells over a period of 4 years. During the stepwise development of resistance only cells which did not adhere to the flask walls were passaged. Beginning at 30 nM 1,25D3 the sublines became resistant to the differentiation-inducing and growth-retarding properties of 1,25D3 even at 400 nM. Also, their growth rates in 1,25D3-free media increased. In addition, beginning at 40 nM 1,25D3 the sublines acquired resistance to 5-beta-D-arabinocytosine (araC) due to the lack of expression of the deoxycytidine kinase gene. The araC-resistant sublines were also near-tetraploid, as judged by their DNA content. When grown in 1,25D3-free long-term culture the phenotype was essentially stable. The development of cross-resistance to araC during growth in the presence of an unrelated compound (i.e., 1,25D3) shows that in some instances an apparently inherent drug resistance may in fact he due to a metabolic defect resulting from an exposure to another agent.
Influenza virus utilizes a unique mechanism for initiating the transcription of viral mRNA. The viral transcriptase ribonucleoprotein complex hydrolyzes host cell transcripts containing the cap 1 structure (m7GpppG(2'-OMe)-) to generate a capped primer for viral mRNA transcription. Basic aspects of this viral endonuclease reaction are elucidated in this study through the use of synthetic, radiolabeled RNA substrates and substrate analogs containing the cap 1 structure. Unlike most ribonucleases, this viral endonuclease is shown to catalyze the hydrolysis of the scissile phosphodiester, resulting in 5'-phosphate- and 3'-hydroxyl-containing fragments. Nevertheless, the 2'-OH adjacent to the released ribosyl 3'-OH is shown to be important for catalysis. In addition, while the endonuclease steady-state turnover rate is measured to be 2 h(-1), phosphodiester bond hydrolysis is not rate-limiting. The direct generation of a free 3'-OH and the subsequent slow release of this product are consistent with the viral need for efficient use of the capped primer in subsequent reactions of the influenza transcriptase complex.