Three
aniline derivatives
melphalan (
L-PAM),
chlorambucil (CHL) and 4-[bis(2-chloroethyl)amino]
benzoic acid (BAM) have been compared on the basis of their in vitro cytotoxicities,
DNA interstrand crosslinking ability and DNA sequence selectivity. Cytotoxicity was assessed in the human colonic
adenocarcinoma LS174T and leukaemic K562 cell lines using the sulpho-
rhodamine B and tetrazolium
dye reduction assays. The order of cytotoxicities was
L-PAM greater than CHL greater than BAM in both cell lines with K562 being less sensitive than LS174T. This was different from the order CHL greater than
L-PAM greater than BAM which would be predicted from simple chemical reactivity or rate of hydrolysis, parameters which have been used previously as indicators of
biological potency for aromatic
nitrogen mustards.
DNA interstrand crosslinking in cells as determined by alkaline elution showed a correlation with IC50 values. The ranking order of activity was further predicted by the ability of the agents to produce interstrand crosslinks in isolated
DNA. The extent of
guanine N-7 alkylation, assessed using a modified
DNA sequencing technique, mirrored cytotoxicity and crosslinking ability, but at equivalent levels of alkylation there was no significant difference in DNA sequence selectivity. These data demonstrates that simple chemical reactivity or hydrolysis rate is not a good
indicator of
DNA reactivity or cytotoxicity for a number of
aniline mustards, whereas
DNA interstrand crosslinking ability either measured directly in cells or in isolated
DNA, gives a good indication of
biological activity.