The effect of alkylating agents on the activity of adenosine 3',5'-monophosphate-dependent protein kinase in Walker carcinoma cells

A comparative analysis of drug-induced DNA effects in a nitrogen mustard resistant cell line expressing sensitivity to nitrosoureas

In the Walker 256 rat mammary carcinoma cell line, WR, resistance to nitrogen mustards (NM) is accompanied by collateral sensitivity to chloroethylnitrosoureas (CENUs). DNA-interstrand cross-links, DNA-protein cross-links, and sister chromatid exchange (SCE) induction were assayed in WR and the parent cell line (WS) after treatment with nitrogen mustard (HN2), phosphoramide mustard (PM), chlorozotocin (CLZ) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU). Treatment of cells with HN2 caused extensive levels of cross-links, approximately 50% of which were DNA-interstrand, equal in both WR and WS, whereas PM caused no detectable cross-links in either cell line. CLZ induced low levels of DNA-interstrand cross-links, similar in WR and WS, but no DNA-interstrand cross-links could be detected in either cell line after treatment with CCNU. Both CLZ and CCNU induced low levels of DNA-protein cross-links in both cell lines, though higher in WR than WS. There was no difference in the rate of removal of HN2-induced DNA-interstrand or DNA-protein cross-links or total CLZ-induced cross-links by the two cell lines, suggesting that differential repair was not relevant to the expression of resistance. Both HN2 and PM caused more SCEs in WS than in WR, whereas CLZ and CCNU induced more SCEs in WR. Thus, NM-induced SCEs were related to cell killing but not cross-linking, whilst CENU-induced SCEs were related to cell killing and DNA-protein but not DNA-interstrand cross-links. Furthermore, the collateral sensitivity of WR cells to CENUs was not due to the differential induction of DNA-interstrand cross-links or repair of total cross-links, or repair of total cross-links, although higher levels of DNA-protein cross-links occurred in WR, and these may be either a cause or a consequence of increased susceptibility of these cells to CENUs. Presumably NMs and CENUs have several distinct and separate macromolecular targets which result in differential cell killing. It is concluded that a range of lesions occurred after treatment of WR and WS cells with either NMs or CENUs and that, in these cell lines, there is no simple correlation between drug-induced cross-linking, SCE induction and cytotoxicity.

Poly(adenosine diphosphate-ribosylation) of nuclear matrix proteins in alkylating agent resistant and sensitive cell lines

Using Walker 256 breast carcinoma cell lines either with or without acquired resistance to alkylating agents, the structural framework proteins of the nucleus, the nuclear matrix proteins, were found to be effective acceptors for poly(ADP-ribose). Incubation of isolated nuclei with nicotinamide adenine [32P] dinucleotide ([32P] NAD), followed by the isolation of the nuclear matrix, demonstrated that two polypeptides of approximate molecular weight (Mr) 105 000 and 116 000 were extensively poly(ADP-ribosylated). By an in vitro [32P] NAD assay, the nuclear matrix fraction was found to maintain approx. 15% of the total nuclear matrix activity of poly(ADP-ribose) polymerase. Confirmation that the trichloroacetic acid (TCA) precipitable material represented ADP-ribose units was achieved by enzymatic digestion of the nuclear matrix preparation with snake venom phosphodiesterase (SVP). Within 15 min, greater than 85% of the 32P label was digested by SVP and the final digestion products were found to be phosphoribosyl-AMP (PR-AMP) and adenosine 5'-monophosphate (5'-AMP) by thin layer chromatographic analysis. The average polymer chain length was estimated to be 6-7 ADP-ribose units. Because poly(ADP-ribose) polymerase has a putative role in DNA repair, a comparison of the nuclear matrix fractions from Walker resistant and sensitive tumor cell lines was made. In both cell lines, the quantitative and qualitative patterns of the nuclear matrix associated poly(ADP-ribosylation) were similar.

Guanosine 3',5'-monophosphate and the action of alkylating agents

The intracellular level of guanosine 3',5'-monophosphate (cGMP) has been measured in Walker carcinoma cells in tissue culture after treatment with various alkylating agents. At concentrations which caused a rise in the level of adenosine 3',5'-monophosphate (cAMP) chlorambucil and 5-(1-aziridinyl)-2,4-dinitrobenzamide (CB 1954) produced only a small (35%) elevation of cGMP, while merophan had no such effect. This suggests that any effect of cAMP will not be outweighed by an equivalent rise in cGMP. Sepcific cytosolic binding of cGMP decreased with increasing resistance of Walker cells to alkylating agents, while the dissociation constant, KD, for binding increased. This was also observed with cAMP binding which suggests that the same protein in responsible for binding both nucleotides.