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Biomedical subjects

T G Johns

Publications and source records attributed to T G Johns.

5 recordsLinked to original sources
PubMed1992

Antiproliferative potencies of interferons on melanoma cell lines and xenografts: higher efficacy of interferon beta.

BACKGROUND: Human melanomas have shown only limited responsiveness to clinical therapy with interferon (IFN). PURPOSE: Our aim was to determine the most effective class of IFN for inhibiting growth of melanoma cells and to establish whether variation exists in response of various cell lines to different IFNs. METHODS: We compared the direct antiproliferative effects of the type I IFN alpha-2b, IFN alpha-4a, and IFN-beta and the type II IFN-gamma on eight melanoma cell lines grown in vitro. We did this comparison by determining the concentration of each IFN that resulted in 50% growth inhibition, using the MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium tetrazolium bromide] dye uptake method. We also tested IFN alpha-2a and IFN-beta for their ability to inhibit the growth of xenografts of the LiBr melanoma cell line in vivo in nude mice. Receptor binding was determined using [35S]methionine-labeled IFN alpha-4a, in competition with unlabeled IFN alpha-2b, IFN alpha-4a, and IFN-beta. RESULTS: The melanoma cell lines differed markedly in their sensitivity to the IFNs tested: Five were sensitive to low concentrations (less than 30 pM) of IFN-beta, only one was sensitive to similar concentrations of IFN alpha-2b, and none were sensitive to IFN alpha-4a at concentrations up to 920 pM. For all cell lines, the antiproliferative potency of the type I IFNs was IFN-beta greater than IFN alpha-2b greater than IFN alpha-4a. IFN-gamma was less active than IFN-beta on all except one of the cell lines. Similarly, IFN-beta was more potent than IFN alpha-2a in inhibiting the growth of the LiBr xenograft in nude mice. Labeled IFN alpha-4a bound with high specificity in all four melanoma lines tested, and competitive binding experiments showed that the order of binding affinity (IFN-beta greater than IFN alpha-2b greater than IFN alpha-4a) correlated with the order of antiproliferative potency. CONCLUSION: The finding that melanoma cell lines differ intrinsically in their sensitivity to IFNs may explain differences in clinical response. Our results suggest that IFN-beta may be the most effective IFN in the treatment of melanoma, although confirmation will require clinical trials involving large numbers of patients.

Animals↗
PubMed1992

Validation of the MTT dye assay for enumeration of cells in proliferative and antiproliferative assays.

Increasing use is being made of colorimetric assays to quantitate viable cells, e.g., the cellular reduction of the tetrazolium salt, MTT, to formazan by mitochondrial succinate dehydrogenase. We validated this assay for cell proliferation in mixed lymphocyte cultures as compared with 3H-thymidine uptake, and for inhibition of cell proliferation induced by interferon with results compared by direct cell counting. We also found that cells do not, as previously assumed, require functional mitochondria: there were no differences in formazan production by normal cells or respiratory defective cells in which mitochondria had been poisoned by the nucleic acid toxin, ethidium bromide. The high reproducibility of MTT metabolism by lymphoblasts and various cultured cell lines establishes the reliability and versatility of this method for quantitating cell numbers.

Animals↗
PubMed1979

The pharmacological profile of a potential hypnotic compound RU 31158.

RU 31158, 6-(orthochlorophenyl)-1, 2-dihydro-2 (N-methylpiperazine-1-yl) methylene-8-nitro-IH, 4H-imidazo [1,2-a] [1,4] benzodiazepin-1-one methanesulphonate, demonstrated potent hypnotic activity compared to diazepam when examined in the mouse and rat. RU 31158 potentiated minimal hypnosis in mice induced by both hexobarbital and chlorprothixene with ED50 values of 2.15 (1.53-3.01) and 0.69 (0.46-1.02) mg/kg p.o. respectively; these compared to values for diazepam of 17.00 (11.25-25.67) and 3.60 (2.25-5.76) mg/kg p.o. RU 31158 also potentiated hexobarbital in the rat with an ED50 value of 1.2 (0.7-2.0) mg/kg p.o. as compared to 32.0 (27.5-38.5) mg/kg p.o. for diazepam. Sleep studies in the rat confirmed the hypnotic properties of RU 31158, and also showed that the duration of action at 8.0 and 16.0 mg/kg p.o. was not longer than 9 hours. RU 31158 also showed potent minor tranquilizer, anxiolytic, and anti-convulsant properties in a series of pharmacological tests.

Animals↗
PubMedDate not supplied

Natural killer cell activity against cultured melanoma cells: a dye-reduction technique with studies on augmented activity by interferon subtypes.

We assessed natural killer (NK) cell activity against cultured melanoma cells using a novel method, with observations on the comparative effects of interferons (IFNs) in NK-stimulating and anti-proliferative assays. Since the tumour cells tested were adherent, a semi-automated colorimetric MTT dye reduction assay was developed to assess NK activity. The three adherent human melanoma cell lines Sk-Mel-28, MM418 and MM96 were shown to be suitable targets for determining NK activity. Also, these were representative of the range of sensitivities of melanoma cells to the anti-proliferative action of type 1 IFNs. The dose-dependent stimulation of NK activity by type 1 IFNs was confirmed in this alternative assay system. IFN-alpha 2b and IFN-beta ser had equivalent stimulatory activities, and IFN-alpha 4 proved less effective, as with assays using the classical K562 system. Augmented NK cytotoxicity did not correlate with anti-proliferative effects of IFN. In anti-proliferative assays, the hierarchy of activity is IFN-beta greater than IFN-alpha 2 greater than IFN-alpha 4, whereas, in the NK augmentation assay IFN-beta and IFN-alpha 2 were of equivalent activity. Interestingly, MM96 was the cell line most resistant to the direct anti-proliferative action of IFN, yet it was the most susceptible of the melanoma cell lines to cytotoxicity by NK cells, whether stimulated or unstimulated by IFN.

Cytotoxicity, Immunologic↗