KW-2149 (7-N-[2-[gamma-L-glutamylamino]ethyldithioethyl] mitomycin C): DNA interactions and drug uptake following serum activation

7-N-[2-[gamma-L-glutamylamino]ethyldithio-ethyl] mitomycin C (KW-2149) is a mitomycin-C analogue currently being evaluated in clinical trials. It has been shown that KW-2149 is unusual in that it is activated by serum, resulting in an increase in potency of up to 200-fold. To investigate the mechanism by which KW-2149 is activated, the abilities of mitomycin-C, KW-2149 and its metabolites M-18 (symmetrical disulphide dimer) and M-16 (methyl sulphide form) to interact with DNA were compared, and the influence of serum and glutathione on the sequence-specificity of KW-2149-DNA interactions was determined. Following reduction by glutathione both KW-2149 and M-18 are more efficient crosslinking agents of naked DNA, with the metabolite M-18 showing superior activity. The efficiency of DNA interstrand crosslinking in cells by KW-2149 was also increased by the addition of serum. Using the potassium/SDS precipitation method it was found that KW-2149 and M-18 crosslink protein to DNA whilst mitomycin C and M-16 do not. All four compounds produced almost identical patterns of adducts. Serum and glutathione did not alter the pattern of DNA adducts, but did increase the efficiency of adduct formation. Our earlier studies had indicated that the mechanism of activation of KW-2149 by serum is related to cellular uptake, and we therefore studied the effects of certain metabolic inhibitors, temperature and competitive inhibition on drug uptake. The results suggest that uptake is passive, and this indicates that a component in serum modifies KW-2149 to a form that passively enters cells more rapidly.