Heptaplatin, cis-malonato [(4R,5R)-4,5-bis 
(amino-methyl)-2-isopropyl-1,3-dioxolane] platinum(II) (SKI-2053R, Sunpla) is a 
new platinum derivative with anti-tumor activity comparable to cisplatin on 
various cancer cell lines. Preclinical studies suggest that it is less 
nephrotoxic than cisplatin. This study was undertaken to examine the combined 
effect of heptaplatin and ionizing radiation on two established human squamous 
carcinoma cell lines (NCI-H520, SQ20B). The cytotoxic activity of heptaplatin 
was concentration-dependent in both cell lines. When low dose heptaplatin was 
combined with high dose ionizing radiation, there was an additive cytotoxic 
effect on NCI-H520 cells (P < 0.05), while a moderate dose of heptaplatin and a 
low dose of ionizing radiation had an additive cytotoxic effect on the growth of 
SQ20B cells (P < 0.05). FACS analysis and DAPI staining showed that their 
additive cytotoxic effects were correlated with the induction of apoptosis. 
Further studies are warranted using heptaplatin and ionizing radiation in 
squamous cell carcinoma as a substitute for cisplatin.