Early stimulation of acidification rate by novel cytotoxic pyridyl cyanoguanidines in human tumor cells: Comparison with m-iodobenzylguanidine

CHS 828, a newly recognized pyridyl cyanoguanidine, has shown promising ant itumor activity both in vitro and in vivo and is presently in early phase I clinical trial in collaboration with EORTC. In this study, the effects of CHS 828 and a series of analogues on extracellular acidification and cytoto xicity were compared with those of m-iodobenzylguanidine (MIBG) in human tu mor cells. The extracellular acidification rate was measured using the Cyto sensor microphysiometer, and determination of cytotoxicity and proliferatio n was [C-14] performed by the fluorometric microculture cytotoxicity assay (FMCA) and measurement of [C-14]thymidine and leucine uptake. CHS 828 signi ficantly increased the acidification rate during the first 15-24 hr in a co ncentration-dependent manner. This effect was abolished by removal of gluco se from the medium, substituted with 10 mM of pyruvate, indicating stimulat ed glycolysis as the source of the increased acidification rate. However, C HS 828 induced cytotoxicity at concentrations well below those that affecte d the rate of acidification; when a series of closely related pyridylguanid ine analogues were tested and compared, no apparent relationship between cy totoxicity and acidification could be discerned. Furthermore, comparable in creases in the acidification rate were evident in one subline with high-gra de resistance to the cytotoxic actions of CHS 828. The results indicate tha t CHS 828 may share the inhibitory actions of MIBG on mitochondrial respira tion with a subsequent increase in glycolysis and acidification rate. Howev er, this mechanism of action appears neither necessary nor sufficient to fu lly explain the cytotoxic actions of CHS 828 in human tumor cells, actions which remain to be mechanistically clarified. (C) 2000 Elsevier Science Inc .