The effect of monofunctional or difunctional platinum adducts and of various other associated DNA damage on the expression of transfected DNA in mammalian cell lines sensitive or resistant to difunctional agents

The effects of introducing various DNA damage into pSV2gpt DNA on the subsequent expression of xanthine guanine phosphoribosyltransferase (XGPRT), after its transfection into two Walker 256 cell lines, one which is inherently sensitive only to difunctional agents while the other shows a normal sensitivity, have been examined. Both the sensitive (WS) and the relatively resistant (WR) cell lines were shown to be equally capable of both ligation of DNA double-strand breaks (although the efficiency varied with the actual site of the break) introduced into pSV2gpt and homologous recombination of pSV2gpt fragments (recombination events are thought to be important in the repair of DNA-DNA interstrand crosslinks). Reacting the plasmid with either the difunctional platinum compound, Cisplatin, or the monofunctional reacting Pt(Dien) caused a dose-dependent decrease in the subsequent expression of XGPRT. This decrease was about the same with either agent in either cell line when expressed as a function of dose of drug. However, when the actual binding of platinum to DNA by these compounds was measured, a large difference (due to the higher specific binding of Pt(Dien) to DNA) in the effects of the difunctional, as opposed to the monofunctional agent, was apparent and this was a reflection of the relative cytotoxicities of these compounds towards mammalian cells. Although at doses of Cisplatin equitoxic to WS and WR cells 20-fold less Pt is bound to the DNA of WS cells, no significant difference was seen on the expression of pSV2gpt, reacted with this agent, between WS or WR cells. Based upon a knowledge of the proportions of adducts formed in DNA reacted with Cisplatin, the lesion that inactivates expression of XGPRT was probably the intrastrand crosslink and it was calculated that due to the size of the plasmid, the interstrand crosslink was unlikely to be present at these inactivating doses. It is suggested that the inherent sensitivity of WS cells only to difunctional agents is due to their response to such relatively rare lesions such as a DNA-DNA interstrand crosslink.

Antagonism of mu-opioid receptor-mediated inhibitions of nociceptive neurones by U50488H and dynorphin A1-13 in the rat dorsal horn

We have studied the effects of two highly selective kappa-opioid receptor agonists, U50488H and dynorphin A1-13 on the powerful inhibitions of rat dorsal horn nociceptive neurones produced by the potent mu-opiate receptor agonist, Tyr-D-Ala-Gly-Me-Phe-Gly-ol (DAGO). Extracellular single unit recordings were made from 35 convergent neurones which could be excited by impulses in A beta- and C-fibre afferents following transcutaneous electrical stimulation of the ipsilateral hind paw. The mu- and kappa-agonists were applied directly onto the surface of the spinal cord. DAGO (0.19, 0.48 and 1.9 nmol) dose-dependently inhibited C-fibre evoked responses with little effect on A beta-evoked activity. The spinal application of dynorphin A1-13 (6.2 nmol) and U50488H (28 nmol) rapidly reversed the spinal inhibitory effect of DAGO indicating that these kappa-ligands are likely to act as mu-receptor antagonists in the rat dorsal horn.

CB 1954 (2,4-dinitro-5-aziridinyl benzamide) becomes a DNA interstrand crosslinking agent in Walker tumour cells

Walker tumour cells were shown to be uniquely sensitive to CB 1954 when compared with other cells in vitro. CB 1954 forms DNA-DNA interstrand crosslinks in a time-dependent manner in Walker tumour but not Chinese hamster cells. The absence of interstrand crosslinks in hamster cells was not due to a lack of uptake of drug but rather to a failure to convert (probably by bioreduction) CB 1954 to the required reactive difunctional intermediate.

Mechanism of cytotoxicity of anticancer platinum drugs: evidence that cis-diamminedichloroplatinum(II) and cis-diammine-(1,1-cyclobutanedicarboxylato)platinum(II) differ only in the kinetics of their interaction with DNA

The kinetics of the aquation reactions of cisplatin and carboplatin and their subsequent reactions with DNA, both in vitro and in vivo, have been measured. The results have been extrapolated to indicate the expected cytotoxicity of these compounds in cells obtained from human cancer patients. Rate constants for the aquation at 37 degrees C of cisplatin and carboplatin of 8 X 10(-5) and 7.2 X 10(-7) s-1, respectively, were calculated from the half-life of these compounds in phosphate buffer, pH 7. This difference in their rate of activation was matched by their rates of binding to DNA. By use of a 14C-labeled ligand, carboplatin was shown to bind monofunctionally to DNA, after which there was a time-dependent formation of difunctional interstrand cross-links, formed from some of these initially monofunctional adducts. A similar, although faster, accumulation of cross-links was seen when cisplatin was bound to DNA. The loss of the 14C-CBDCA ligand of carboplatin was calculated to occur with a rate constant of 1.3 X 10(-5) s-1 which was similar to that for the rate of formation of interstrand cross-links and faster than that for the monofunctional reaction with DNA. It was concluded therefore that the CBDCA ligand becomes a more labile leaving group once carboplatin has been monoaquated. In contrast, both chloro-ligands of cisplatin were shown to leave at similar rates. The fact that other difunctional lesions were formed to the same extent, by equal bound doses of cisplatin or carboplatin, was indicated by the unwinding of supercoiled plasmid DNA. The effects of cisplatin and carboplatin on this DNA were the same once bound to the same extent. About a 100-fold larger dose of carboplatin was, as predicted by their rates of aquation, required to produce equivalent binding to plasmid DNA. In vivo, equal binding of the two drugs to DNA of various cell systems resulted in equal cytotoxicity. Again a much larger dose (20- to 40-fold) of carboplatin was required to produce this equal binding. In general a DNA bound platinum level of about 20 nmol/g reduced cell survival by 90%, although certain cell lines were shown to be much more sensitive to DNA bound platinum. Similar binding values, to those above, were obtained in the DNA extracted from cells of human cancer patients treated with cisplatin. It was inferred that the cytotoxic effect of this level of platinum on DNA would be (unless the cells were of a sensitive phenotype) about 90%.(ABSTRACT TRUNCATED AT 400 WORDS)

Photosensitive interaction of RSU 1069 with DNA

RSU 1069 is a 2-nitroimidazole radiosensitizer with an aziridine-containing side chain. In light (360 nm) the absorbance maximum of the nitro group at 325 nm disappears, which is accompanied by expulsion of the nitro group as the nitrite ion. We suggest an intramolecular cyclization of the aziridine side chain and the C2 of the imidazole ring as a possible explanation. This photosensitive effect was used to determine separately the damage to DNA induced by the reduced nitro group and the alkylating property of the aziridine. The aziridine-induced DNA damage is maximized in the dark when the nitro group is either absent (electrolytically reduced prior to the addition of DNA) or non functional (unreduced). In the light, damage is reduced. Typical DNA damage includes helix disruption leading to single strand breaks and the release of thymidine. Alkaline filter elution studies show evidence only for strand breakage and none for cross-linking indicating the drug is capable of mono-functional alkylation only.

The mechanism of nitroimidazole damage to DNA: coulometric evidence

A high resolution coulometric technique has been developed to measure the electron requirement for reduction of 12 nitroimidazoles, both in the presence and absence of DNA. The cytotoxic species is shown to be a light sensitive intermediate of drug reduction and a common mechanism of cytotoxicity proposed which involves electron transfer from DNA to the one-electron radical anion (R-NO2-).

Studies on the action of nitroimidazole drugs. The products of nitroimidazole reduction

The electron requirements for the electrolytic reduction of misonidazole, metronidazole and 4(5)-nitroimidazole have been measured using high-resolution coulometry. Eleven of the labelled final reduction products of metronidazole (a 5-nitroimidazole) have been separated by high-performance liquid chromatography and identified. These appear to be formed without the prior generation of a stable intermediate. In contrast, the reduction products of misonidazole (a 2-nitroimidazole) show little similarity to those of metronidazole but are likely to be formed via the four-electron hydroxylamine derivative. None of the final reduction products show toxicity towards Clostridium bifermentans or Escherichia coli suggesting that the short-lived cytotoxic agent of nitroimidazoles is a reduction product formed by the addition of not more than three electrons.

Synergistic growth stimulation of corneal fibroblasts by components of mesodermal growth factor from murine submaxillary glands

Recycled mesodermal growth factor (R-MGF) is a pool of proteins of 26,000 molecular weight obtained by recycling gel chromatography of male murine submaxillary gland extracts. R-MGF strikingly accelerates corneal stromal wound healing in vivo, fibroblast growth and migration in cultured corneal buttons and is showing here to stimulate stromal fibroblast growth and division in tissue culture. Chromatographic fractionation of R-MGF has yielded several components, none of which has a greater biological potency than the parent R-MGF. In contrast, two components, MGF-I and -II, when recombined synergistically stimulate fibroblast response in tissue culture and organ culture in excess of those obtained with the parent R-MGF. Three MGF components (I, III, and IV) have been purified and are inactive at 10-15 micrograms/ml in organ culture but potently stimulate fibroblast responses when combined in pairs containing 7.5 micrograms of each component. The striking synergism in organ culture suggests that the stimulation of wound healing by R-MGF in vivo may also reflect synergistic action of more than one R-MGF component. Procedures for isolating gram quantities of R-MGF and for the purification of different R-MGF components by ion exchange chromatography are detailed.

Structure-cytotoxicity relationships of nitroimidazoles in an in vitro system

Correlations of cytotoxicity of nitroimidazoles and their electron affinity depend upon the degree of reduction of the drugs. If the end-point chosen to assess cytotoxicity is one at which incomplete reduction has occurred the slope of the correlation is positive, with respect to E71, but if measurements are taken after complete reduction of the drugs the slope is a negative one. The production of nitrite ion by 5-nitroimidazoles depends on the base composition of DNA suggesting that the active agent responsible for cytotoxicity is the one-electron radical anion, R--NO2-.

Interaction of nitroimidazole drugs with DNA in vitro: structure-activity relationships

An electrolytic reduction system has been developed to model the cytotoxic action of a range of nitroimidazole drugs against DNA hypoxic cells or anaerobic microorganisms. THe degree of damage induced by these drugs (measured as the release of [14C]-dT from DNA) and their relative rates of reduction have been correlated with their redox potentials. The results show that the correlation of drug-induced damage and electron affinity is related to the amount of drug reduced, and supports the hypothesis that at the molecular level the cytotoxic mechanism of reduced nitroimidazoles is identical in hypoxic mammalian cells, bacteria and protozoa.

Acceleration of healing of rabbit corneal endothelium by mesodermal growth factor

Freeze-thaw injuries of rabbit corneas were treated with mesodermal growth factor (MGF) in organ culture and the repair of the endothelium followed by light microscopic examination of endothelial whole mounts. MGF-treated corneas showed an increased number of mitotic figures. In addition, MGF accelerated the rate of cell hypertrophy, formation of spindle-shaped cells, and the rate of their migration into the killed zone so that Descemet's was covered more rapidly than was that of the controls. In MGF-treated corneas, the cells lost their fibroblast-like appearance and became endothelial-like in appearance sooner than did the untreated corneas. A short period of treatment (6 hr) was sufficient to stimulate the repair processes described above. The healing responses obtained in organ culture for control eyes approximately those described in the literature for freeze-thaw injuries to the rabbit endothelium in vivo. The data presented also show that it is possible to accelerate endothelial regeneration in wound healing.

Red cell aging. II. Anomalous electrophoretic properties of neuraminidase treated human erythrocytes

Desialylation of human red blood cells (RBC) by Vibrio cholerae neuraminidase (VCN) was found to produce cells with electrophoretic properties which were inconsistent with the view of simple loss of N-acetylneuraminic acid (NANA) as the sole effect of VCN treatment. Modification of human RBC with 50--350 U VCN/10(10) RBC for one hour at 37 degrees C releases 90-100% of the NANA and produces a progressive decrease towards zero in their electrophoretic mobilities when measured in 0.15 M NaCl (pH 7.2) at 25 degrees C. The appearance of positive groups on the desialylated cells was indicated by the VCN-treated cells displaying positive mobilities below approximately pH 5.5 and increased negative mobilities at approximately pH 9 as well as substantial increases in their mobility at neutral pH following treatment with formaldehyde. Adsorption of about 95% of the VCN activity at 0 degrees C to the RBC did not produce any significant change in their electrophoretic mobilities thus indicating that the observed changes in the electrophoretic properties of the RBC following VCN treatment could not be attributable to adsorption of VCN. These studies indicate that the cationic charge groups which appear at the electrophoretic surface of the RBC after VCN treatment are probably of endogenous origin. It is suggested that this alteration rather than simple NANA release may operate to shorten the in vivo survival time of desialylated red cells.

Analytical particle electrophoresis applied to immunologic research

The technique of analytical particle electrophoresis has been applied to the study of membrane phenomena associated with lectin stimulation of lymphocytes. It has been observed that such treatment results in a significant increase in the electrophoretic mobility of murine T-cells. Moreover, it has been demonstrated that the mobility changes in most cells are attributable to the release of a factor from relatively few cells. Preliminary evidence suggests that the murine factor has a comparatively low relative molecular mass, is heat-labile, and will alter the mobility of cultured human T-cells.

Analytical particle electrophoresis applied to immunologic research

The technique of analytical particle electrophoresis has been applied to the study of membrane phenomena associated with lectin stimulation of lymphocytes. It has been observed that such treatment results in a significant increase in the electrophoretic mobility of murine T-cells. Moreover, it has been demonstrated that the mobility changes in most cells are attributable to the release of a factor from relatively few cells. Preliminary evidence suggests that the murine factor has a comparatively low relative molecular mass, is heat-labile, and will alter the mobility of cultured human T-cells.