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Biomedical subjects

P M Naha

Publications and source records attributed to P M Naha.

At least 19 recordsLinked to original sources
PubMed1981

Cytotoxicity of L-canavanine in vitro.

Cytotoxicity of L-canavanive, a structural analogue of L-arginine, was tested by means of (1) inhibition of DNA synthesis in Balb/c-3T3 cell line and (2) inhibition of mitosis in peripheral blood lymphocytes in culture. The cytostatic nature of inhibition caused by L-canavanine was indicated by the complete recovery of cells after withdrawal of the drug.

Animals↗
PubMed1980

Reappraisal of L-canavanine as an anti-tumour agent.

L-canavanine, an analogue of L-arginine, is known to have a toxic effect on pathogens. In experiments performed on a specialised epithelial-like cell system which is conditionally transformable, L-canavanine appeared to exhibit (1) a reversible 'static' effect on exponentially growing cells at optimal concentration, and (2) a selectively toxic effect on proliferating cells. The capacity to recognise 'tumour cells' in a heterogeneous population of cells is of potential interest in cancer chemotherapy.

Animals↗
PubMed1980

An experimental model for selective inhibition of proliferating cells by chemotherapeutic agents.

Conditionally transformable cells of primate origin in which 'untransformed' and 'transformed' cells derived from the same source grow in culture, has been used as an experimental system for testing selective inhibition of proliferating cells by chemotherapeutic agents. The cytotoxic agents Adriamycin and Mitomycin C fail to recognise "tumour cells" in a heterogenous population and thus differ from the non-toxic and non-carcinogenic agent L-canavanine.

Animals↗
PubMed1980

Biochemical controls of the G1 phase of a mammalian cell cycle. I. Analysis of chromatin proteins in temperature-sensitive variants.

Chromatin proteins of Balb/c-3T3 cell line and its temperature sensitive variants A83 and A8, arrested in G1 phase of the cell cycle at the restricted temperature, were analysed on SDS-polyacrylamide gel by electrophoresis to detect major alterations that could be related to the G1 arrest. Appearance of two additional proteins (mol. wt. 80,000 and 20,000) and disappearance of another (mol.wt. 14,000) were thought to be significant. The protein of mol.wt. 20,000 was absent in the G1- derivatives, suggesting a possible relationship to the appearance of the G1 phase.

Animals↗
PubMed1979

Conditional expression of the transformed phenotype in an "epithelial-like" cell line.

A subclone of ts 14/MNU/2, derived from a heteroploid (epithelial) monkey kidney cell line of BSC-1 and transformed in vitro by methylnitrosourea, expressed the transformed phenotype only at the elevated temperature of 39.5(0)C. Compared to the growth characteristics at 33(0)C, the transformed property was exhibited in the (1) high efficiency of plating at low cell densities, (2) colony morphology, (3) growth in absence of serum and (4) alterations in the quality and the quantity of chromosomal proteins in presence of low concentrations of serum. Such experimental systems may provide an effective control for studying molecular mechanisms related to transformation and neoplasia.

Animals↗
PubMed1979

Complementation of G1-phase variants of a mammalian cell cycle.

Complementation between temperature-sensitive (ts) variants of Balb/c-3T3 defective in the G1 phase of its cell cycle was measured in the [3H]thymidine-labeling indices of the multinucleated cells during incubation at the restricted temperature (38 degrees C) following cell fusion. One ts variant from each group along the length of the G1 phase was tested for complementation. Varying degrees of complementation were observed between the 4 ts variants tested, judging by the time of entry into S-phase and the degree of synchrony attained. At least 3 complementation groups were discernible.

Animals↗
PubMed1979

Induction of G1- cells at high frequency.

Experimental conditions are reported on the induction of G1- cells at high frequency by ultraviolet irradiation of temperature-sensitive cells arrested in G1 phase at the restricted temperature. Neither the wild type cells of Balb/C-3T3 nor the temperature-sensitive derivative of tsA83 grown at the permissive temperature could be 'mutated' under similar conditions. One such 'mutant' (RI8) was 'inducible' from a G1+ phenotype at 33 degrees C to G1- state at 38 degrees C within one cell generation time. The 'inducible' property of RI8 from G1+ to G1- lends support to the theory that the duration of the G1+ phenotype is determined by the level of precursors for DNA synthesis. Since the G1- variants were isolated from revertants, the frequency of 'mutagenesis' appeared to be artifically high.

Animals↗
PubMed1975

Temperature sensitive cells in the study of carcinogenic transformation.

Two temperature sensitive variants (ts13 and ts14) of an African green monkey tetraploid kidney cell line (epithelial), carrying temperature sensitive lesions in thymidine metabolism, were transformed by methylnitrosourea (MNU) at the permissive temperature of 33 degrees C, nor was there any transformation in the wild type parental cell line of BSC-1 at these temperatures under similar conditions. A comparative study of the cell cycle and metabolic efficiency in the 3 cell lines was performed in order to get an understanding of the physiology of the "target cells" in culture. Compared with the parental cell line of BSC-1, ts13 and ts14 cells were blocked in the G1 phase of the cell cycle during the time that the cell were in contact with the carcinogen (MNU); the variant cells also had higher mitotic indices at this time. The cells of ts13 which showed 50% more transformation than those of ts14 differed from the latter in having larger numbers of viable cells arrested in mitosis over the G1 period. The results were interpreted to indicate that there were other factors, besides cells arrested being in G1, which contributed to the difference in the frequency of transformation between the variant cell lines which had an otherwise similar physiology. Using gel electrophoresis a new protein was located in the nuclei of the transformed cells of ts13 and ts14 which was absent in the wild type cell line of BSC-1 or in the variants ts13 and ts14 at 39-5 degrees C.

Cell Fusion↗
PubMed1974

On the theory of clonal selection in carcinogenic transformation.

A temperature sensitive variant (ts13) of African green monkey kidney cell line, carrying a temperature sensitive lesion in thymidine metabolism, was transformed by 40 μg/ml of methylnitrosourea (MNU) at the restricted temperature of 39·5°C, whereas the same cell line was not transformed by MNU at the permissive temperature of 33°C. Results presented in this paper raise the possibility that clones of cells carrying a biochemical lesion might possibly contribute to carcinogenesis with respect to certain chemical carcinogens.

Cell Line↗