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Biomedical subjects

J J Roberts

Publications and source records attributed to J J Roberts.

At least 55 records · Page 3Linked to original sources
PubMed1983

Synthesis and accumulation of an extremely stable high-energy phosphate compound by muscle, heart, and brain of animals fed the creatine analog, 1-carboxyethyl-2-iminoimidazolidine (homocyclocreatine).

A new creatine analog, 1-carboxyethyl-2-iminoimidazolidine (homocyclocreatine), has been synthesized and compared with other synthetic analogs of creatine as a substrate for creatine kinase under both in vitro and in vivo conditions. Reactivity with rabbit muscle creatine kinase at 2 mM and pH 7.0 occurred in the order: creatine greater than cyclocreatine (1-carboxymethyl-2-iminoimidazolidine) greater than N-ethylguanidinoacetate greater than N-propylguanidinoacetate greater than guanidinoacetate greater than N-methyl-3-guanidinopropionate greater than 3-guanidinopropionate greater than homocyclocreatine. Homocyclocreatine was 10,000-fold less active than creatine. In the reverse direction at 0.2 mM and pH 7.0: creatine-P greater than N-ethylguanidinoacetate-P greater than cyclocreatine-P much greater than homocyclocreatine-P. Homocyclocreatine-P was 200,000-fold less active than creatine-P. The phosphoryl group transfer potential of homocyclocreatine-P was estimated to be 2 kcal/mol lower than that of creatine-P. Chicks fed 5% homocyclocreatine for 16 days synthesized and accumulated homocyclocreatine-P in breast muscle (32 mumol/g wet wt), leg muscle (24 mumol/g), heart (7 mumol/g), intestine (8.5 mumol/g), and brain (2.4 mumol/g). During ischemia homocyclocreatine-P was utilized by muscle much more slowly for the regeneration of ATP than was creatine-P or cyclocreatine-P. Our results suggest that in tissues of homocyclocreatine-fed animals subjected to a sudden large increase in work load or to ischemia, the residual creatine-P system would rapidly equilibrate with the adenylate system at the new lower cytosolic phosphorylation potential, whereas in the same cytosol the (homocyclocreatine-P)/(homocyclocreatine) ratio would exhibit a hysteresis or memory effect and reflect for a considerable period of time the earlier higher (ATP)/(free ADP) ratio rather than the actual lower (ATP)/(free ADP) ratio.

Animals↗
PubMed1982

Toxicity of cisplatin and hydroxymalonatodiammine platinum (II) towards mouse bone marrow and B16 melanoma in relation to DNA binding in vivo.

The antitumour selectivity of cisplatin and hydroxymalonatodiammine platinum II (Pt[OHmal(NH3)2]), a second generation platinum drug, was evaluated in C57B1/Cbi mice bearing advanced intramuscular B16 melanoma. At maximally tolerated doses, Pt[OHmal(NH3)2] produced greater inhibition of growth of the advanced B16 melanoma than did cisplatin. Comparison of dose-response curves for survival of B16 lung colony-forming cells and bone marrow stem cells treated in vivo indicated that selective killing of B16 cells was achieved with Pt[OHmal(NH3)2], whereas cisplatin was relatively nonselective. The extent of reaction of platinum with DNA at doses producing measurable levels of survival in tumour and marrow in vivo was similar to values previously observed in cultured cells treated with cisplatin in vitro. Studies of the amount of platinum bound to DNA in tumour and marrow following administration of the two drugs revealed that the improved selectivity of Pt[OHmal(NH3)2] was associated with a selective increase in the amount of platinum bound to tumour DNA, relative to cisplatin. In addition, platinum lesions produced in DNA by Pt[OHmal(NH3)2] appeared to be more effective in producing tumour cell killing than those produced by cisplatin. No significant excision of total DNA-bound platinum from tumour was observed up to 48 h after administration of either drug.

Animals↗
PubMed1982

The frequency of interstrand cross-links in DNA following reaction of cis-diamminedichloroplatinum(II) with cells in culture or DNA in vitro: stability of DNA cross-links and their repair.

DNA that had been reacted in vitro with cis-diamminedichloroplatinum(II) (cisplatin) had the same frequency of interstrand cross-linking (namely, approx. 1 cross-link per 150 platinum reaction) as that found in the DNA isolated from cells in culture immediately after their treatment with cisplatin. Incubation of both the in vitro and in vivo platinum-reacted DNA in sodium citrate buffer for 24 h at 37 degrees C resulted in up to a 5-fold increase in cross-link frequency.

Animals↗
PubMed1981

Quantitative aspects of the formation and loss of DNA interstrand crosslinks in Chinese hamster cells following treatment with cis-diamminedichloroplatinum(II) (cisplatin). I. Proportion of DNA-platinum reactions involved in DNA crosslinking.

The presence of interstrand crosslinks in the DNA of cis-diamminedichloroplatinum(II) (cisplatin)-treated Chinese hamster cells was demonstrated by the formation of a species of hybrid-labelled DNA in cells that had been density and radioactively prelabelled with a combination of [3H]thymidine and 2'-deoxy-5-bromouridine (BrdUrd) prior to treatment. The extent of crosslinking and of total binding of platinum to the DNA increased linearly with dose over a wide range of concentrations of cisplatin. Simultaneous measurement of the size of co-isolated 14C-labelled DNA from untreated cells permitted an estimate of the size of the crosslinked DNA and hence of the proportion of bound platinum involved in a crosslinking reaction. No increase in the proportion of crosslinking reactions occurred during several hours post treatment incubation of cells when crosslinks were measured by this technique, in contrast to other studies using different techniques to measure DNA interested crosslinking in cis-platin treated cells (see following paper, Pera, M.F., Jr., Rawlings, C.J., Shackleton, J. and Roberts, J.J (1981) Biochim. Biophys, Acta 655, 152--166). The enforced high concentrations of cisplatin required by this method to detect crosslinks precludes studies of their possible repair.

Animals↗
PubMed1981

Quantitative aspects of the formation and loss of DNA interstrand crosslinks in Chinese hamster cells following treatment with cis-diamminedichloroplatinum(II) (cisplatin). II. Comparison of results from alkaline elution, DNA renaturation and DNA sedimentation studies.

The formation of interstrand crosslinks in the DNA of cis-diamminedichloroplatinum(II) (cisplatin)-treated Chinese hamster cells has been demonstrated by three independent, highly sensitive techniques: namely those of alkaline elution, renaturation of crosslinked DNA and alkaline sucrose gradient velocity sedimentation. Simultaneous measurement of DNA break frequency by the first two methods and a computer model combined with the third enabled the calculation of crosslink frequency after application of low doses of cisplatin. Good agreement was found between the values obtained by the three methods used here, and also with those obtained by direct measurement of the amount of crosslinked hybrid DNA in density-labelled cells treated with higher doses of cis-platin (Roberts, J.J. and Friedlos, F. (1981) Biochim. Biophys, Acta 655, 146--151). When measured by all three methods described here, crosslinking was found to increase during several hours after treatment and then to decrease with a half-life of between 12 and 24 h. For low initial levels of crosslinking, this was largely attributed to an excision repair process, since the formation of breaks in DNA was only minimal.

Animals↗
PubMed1980

DNA repair mechanisms and cytotoxicity of antitumour alkylating agents and neutral platinum complexes.

There are many indications that the cytotoxic action of a number of different antitumour agents, including chlorambucil and cis-platinum (II) diammine dichloride, is due to their ability to react with DNA and thereby inactivate it as a template for DNA replication. Moreover, the sensitivity of cells to these agents is related to their ability, either to remove the damage from DNA by some form of excision repair process, or to circumvent the lesions during DNA replication by so-called post-replication repair.

Alkylating Agents↗
PubMed1979

The excision of N-methyl-N-nitrosourea-induced lesions from the DNA of Chinese hamster cells as measured by the loss of sites sensitive to an enzyme extract that excises 3-methylpurines but not O6-methylguanine.

An enzyme extract from Micrococcus luteus excises 3-methyladenine and 3-methylguanine but not O6-methylguanine, 7-methylguanine, 1-methyladenine or 7-methyladenine from DNA reacted with N-methyl-N-nitrosourea. The extract was used to detect lesions in the DNA of Chinese hamster cells treated in culture with N-methyl-N-nitrosourea. It was concluded that 3-methyladenine is excised from these cells with a half-life of about 2.3 h.

Animals↗
PubMed1979

Excision repair of cis-diamminedichloroplatinum(II)-induced damage to DNA of Chinese hamster cells.

Platinum was lost from the DNA of cis-diamminedichloroplatinum(II) [cis-Pt(II)]-treated exponentially growing Chinese hamster V79-379A cells with a half-life of 28 hr. By contrast, platinum was lost from the DNA of cells treated in stationary-phase culture with a half-life of 4 days. Cells treated in and allowed to remain as a stationary-phase culture maintained an intact and apparently viable appearance. When the stationary-phase culture was diluted with fresh medium, cell division occurred, and cell survival, as measured by colony-forming ability, could be determined. Dilution of cells immediately after treatment with 40 micron cis-Pt(II) resulted in 0.19% control survival. There was an increase in the ability of the stationary-phase cells to survive cis-Pt(II) damage with time after treatment. Thus, after 3 days, the survival had increased from 0.19 to 15.9%. We demonstrate that this increased ability of stationary-phase cells to survive with time after treatment is due to DNA excision repair and hence that survival is inversely related to the extent of reaction of cis-Pt(II) with the DNA.

Animals↗