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Biomedical subjects

R K Ralph

Publications and source records attributed to R K Ralph.

At least 37 records · Page 2Linked to original sources
PubMed1986

Potentiation of 4'-(9-acridinylamino)methanesulphon-m-anisidine) action by verapamil.

Verapamil was shown to increase growth inhibition and decrease viability of PY815 mastocytoma cells treated with the anti-cancer drug mAMSA 4'-(9-acridinylamino)methanesulphon-m-anisidide (mAMSA) or its normally inactive congener, 4'-(9-acridinylamino)methanesulphon-o-anisidide (oAMSA). Verapamil also potentiated the effect of sub-optimal concentrations of mAMSA or oAMSA on DNA scission in intact cells. Uptake of [14C]mAMSA by PY815 cells was considerably enhanced, while efflux of [14C]mAMSA from precharged cells was inhibited by verapamil. It is concluded that verapamil potentiates the action of mAMSA on PY815 cells in culture by reducing efflux of drug from the cells. The possibility that verapamil may affect systems that sequester or metabolize AMSA drugs is suggested.

Aminoacridines↗
PubMed1985

Transport of AMSA drugs into cells.

The uptake and efflux of radioactive 4'-(9-acridinylamino)methanesulphon-m-anisidide (mAMSA) and its inactive congener 4'-(9-acridinylamino)methanesulphon-o-anisidide (oAMSA) by PY815 mastocytoma cells were investigated. Both drugs were readily taken up by intact cells although only mAMSA caused DNA scission and is actively cytotoxic to PY815 cells. The microsomal enzyme inhibitors cimetidine or SKF525A increased drug uptake and decreased drug efflux suggesting that drug metabolism could explain the different activities of oAMSA and mAMSA.

Aminoacridines↗
PubMed1985

Cyclic AMP and c-myc gene expression in PY815 mouse mastocytoma cells.

The possibility was examined that inhibition of growth of PY815 mouse mastocytoma cells by N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate (DB cyclic AMP) results from inhibition of c-myc gene expression. Temporary increases in c-myc RNA which occurred soon after DB cyclic AMP treatment and upon removal of the drug were not consistent with direct inhibition of c-myc gene expression by DB cyclic AMP. The increases in c-myc RNA coincided with the passage through, or accumulation of cells in late G1-early S phase. It is proposed that cyclic AMP may stimulate c-myc gene expression which normally occurs only in late G1-early S phase in PY815 cells and that cyclic AMP prevents c-myc expression in cells at other phases of the cell cycle by inhibiting their progression past a cyclic AMP-sensitive restriction point in early G1 phase.

Animals↗
PubMed1985

Cyclic AMP, nuclear protein kinase and the PY815 cell cycle.

A substantial increase in cyclic AMP-dependent protein kinase activity occurred in nuclei of PY815 mastocytoma cells during G1 phase growth arrest by DB cyclic AMP and the increased nuclear protein kinase was accompanied by changes in nuclear protein phosphorylation. However, there was no obligatory association between the rise in nuclear cyclic AMP-dependent protein kinase in G1 phase and growth arrest because nuclear cyclic AMP-dependent protein kinase also increased during G1 phase in cycling PY815 cells synchronized with amethopterin. These observations suggest that maintenance of high cyclic AMP levels during G1 phase may cause growth arrest by activating a cyclic AMP-dependent protein kinase that normally increases in PY815 cell nuclei during G1 phase.

Animals↗
PubMed1985

Chromosomol DNA fragments from mouse cells exposed to an intercalating agent contain a 175-kdalton terminal polypeptide.

A 175 kdalton (kDa) polypeptide is bound covalently to the chromosomal DNA fragments from mouse cells exposed to the intercalating agent 4'-[(9-acridinyl)-amino]methansulphon-m-anisidide. Electron microscopy shows a terminal protein on the DNA fragments, whose 5'-termini are blocked. Since the relative molecular mass of topoisomerase II polypeptide chains is also about 175 kDa and topoisomerase II inhibitors prevent intercalator-induced DNA fragmentation, we propose that the polypeptide bound covalently to the 5'-terminus of the DNA fragments is a polypeptide derived from frequently integrated topoisomerase II operating to normalize torsional stress resulting from intercalation.

Aminoacridines↗
PubMed1984

Chlorpromazine: a potential anticancer agent?

The antipsychotic drug chlorpromazine causes scission of the DNA in PY815 mouse mastocytoma cells or isolated PY815 cell nuclei and the broken DNA reseals when chlorpromazine is removed from nuclei. These properties suggest that chlorpromazine interferes with topoisomerase action as do several other DNA-intercalating anti-cancer drugs. However, protein is not associated with the broken DNA after chlorpromazine treatment suggesting a different mode of action on the topoisomerase. Reasons why chlorpromazine may have potential as anti-cancer agent are considered.

Aminoacridines↗
PubMed1984

Dibutyryl cyclic AMP effects on calcium metabolism by mouse mastocytoma cells.

The ability of mouse mastocytoma cells to take up 45Ca2+ was measured in normal growth medium. As previously observed in physiological buffers with succinate and Pi, cells grown for 18h with N6,O2'-dibutyryladenosine 3',5' cyclic monophosphate (DB cyclic AMP) to inhibit growth took up more 45Ca2+ than untreated cells. However 45Ca2+ uptake by cells in growth medium was less sensitive to respiratory inhibitors or uncouplers than 45Ca2+ uptake in physiological buffer. Increased 45Ca2+ uptake by 18h cyclic nucleotide-treated cells was not a result of tighter mitochondrial coupling since mitochondria prepared from cyclic nucleotide-treated cells were less coupled than those from untreated cells. Nevertheless studies with uncouplers suggested that the bulk of the intracellular Ca2+ was associated with mitochondria. DB cyclic AMP-treated cells contained less total Ca2+ than untreated cells indicating that net Ca2+ efflux occurred during the 18h period of drug treatment. These observations suggest that Ca2+ fluxes increase in DB cyclic AMP-treated PY815 cells and that a net efflux of Ca2+ occurs during growth inhibition by the cyclic nucleotide.

Animals↗
PubMed1983

Cyclic AMP, calcium and control of cell growth.

The role of cyclic AMP and calcium in the control of normal and tumour cell growth is considered in relation to the question whether cyclic AMP is a true mitogen or co-mitogen. It is proposed that cyclic AMP normally controls the cell cycle at a point in G1 phase only by virtue of its ability to exclude calcium required by cells to progress past this point into S phase. Therefore increased influx of calcium by other routes induced by various factors can bypass the inhibitory effect of cyclic AMP and stimulate growth. In these circumstances cyclic AMP or calcium may or may not facilitate further progress into S phase according to the metabolic requirements of individual cells. The relevance to cancer cells is considered.

Animals↗
PubMed1983

Evidence that mAMSA induces topoisomerase action.

Evidence is presented that the topoisomerase inhibitors novobiocin and coumermycin inhibit the production of double-strand breaks in mouse mastocytoma cell nuclear DNA by the anticancer drug 4'[(9-acridinyl)amino]-methanesulphon-m-anisidide (mAMSA). Novobiocin did not inhibit resealing of DNA breaks induced by mAMSA. It is suggested that mAMSA intercalation into DNA induces the action of a type II topoisomerase. mAMSA and oAMSA were equally effective in breaking the DNA in isolated nuclei.

Aminoacridines↗
PubMed1983

Blocked 5'-termini in the fragments of chromosomal DNA produced in cells exposed to the antitumor drug 4'-[(9-acridinyl)-amino]methanesulphon-m-anisidide (mAMSA).

Comparison of the sensitivity of DNA isolated from untreated and mAMSA-treated PY815 mouse mastocytoma cells to hydrolysis by E.coli 3'-exonuclease III and phage lambda or phage T7 5'-exonucleases show that the fragments of chromosomal DNA produced by mAMSA treatment have free 3'-OH termini and blocked 5'-termini.

Aminoacridines↗
PubMed1982

A reassessment of the mechanism of action of 4'-[(9-acridinyl)-amino]methanesulphon-m-anisidide.

The conclusion that treating cells with 4'-[(9-acridinyl)- amino]methanesulphon-m-anisidide (mAMSA) causes an alkali-dependent decrease in the size of their DNA was reinvestigated. Evidence is presented that alkali is not needed to detect an effect of mAMSA on the sedimentation rate of DNA released from mAMSA-treated PY815 cells and that mAMSA causes double-strand breaks in cellular DNA.

Aminoacridines↗
PubMed1981

The control of growth of mouse mastocytoma cells by N6,O2'-dibutyryladenosine cyclic 3',5'-monophosphate.

Addition of N6,O2'-Dibutyryladenosine cyclic 3',5'-monophosphate (DB cyclic AMP) plus theophylline or transfer to medium containing 0.2% serum slowed the growth of cultured mouse mastocytoma cells and eventually arrested their growth in G1 phase. Examination of the properties of cells arrested by either procedure suggested that the drugs arrested cells in G1 phase 1.5-2 h after the point of low serum arrest. Cycloheximide prevented the recovery of cell growth after low serum or drug-induced arrest demonstrating that protein synthesis was necessary to pass either growth restriction point. Cordycepin also prevented drug-arrested cells from progressing into cycle indicating a requirement for RNA synthesis to overcome the drug-induced growth arrest. Evidence is also presented that DB cyclic AMP prevented the cells receiving a pulse of calcium necessary to proceed past the DB cyclic AMP-sensitive growth restriction point. It is suggested that high cyclic AMP levels prevent mastocytoma cells from receiving a surge of calcium in G1 phase that is necessary if the cells are to proceed to S phase and eventually divide.

Animals↗
PubMed1980

Changes in motochondrial calcium metabolism after treating mastocytoma cells with N6,O2'-dibutyryladenosine 3',5' cyclic monophosphate.

Comparison of Ca2+ uptake by isolated mouse liver mitochondria, and mitochondria prepared from mastocytoma cells grown with and without N6,O2'-dibutyryladenosine 3',5' cyclic monophosphate (DB cyclic AMP) and theophylline showed several differences in their capacity to take up and retain calcium. In particular mitochondria from DB cyclic AMP-treated mastocytoma cells took up more Ca2+ than mitochondria from untreated mastocytoma cells. Ca2+ uptake by mitochondria from DB cyclic AMP-treated cells was also increased in the presence of oxalate whereas oxalate did not affect Ca2+ uptake by mitochondria from untreated mastocytoma cells and it reduced Ca2+ uptake by mouse liver mitochrondria. The results suggest that inhibiting the growth of mastocytoma cells with DB cyclic AMP alters their mitochondrial Ca2+ metabolism.

Animals↗