[Combination chemotherapy of HO-221, a derivative of benzoylphenylurea with various anticancer agents against human cancer xenografts in nude mice].

: Antitumor effect of HO-221, a derivative of benzoylphenylurea, has been previously studied against seven human cancer xenografts in nude mice established and maintained in our laboratory. In this study, the effect of combination chemotherapy was examined with six of the above seven human cancer cell lines. These consisted of four gastric cancers (H-55, H-111, H-81 and H-154), one breast cancer (H-31) and one pancreatic cancer (H-48). HO-221 was used in combination with one of the following widely used anticancer drugs; mitomycin (MMC), adriamycin (ADM), CDDP, VP-16 and 5-fluorouracil (5-FU). When the tumor growth inhibition rate (IR) by combination of two drugs (at 1/2 MTD for each drug) exceeded both of IR obtained separately with single drug at 1/2 MTD, the combination regimen was rated as showing an additive effect. When IR by combination of two drugs at the same dose level exceeded both of IR obtained separately by MTD of each single drug, the regimen was rated as showing a synergistic effect. Histological changes and side-effects were also taken into consideration for the evaluation of the drug. Combination of HO-221 and MMC produced an additive effect against H-55 and H-111, a synergistic effect against H-81. In the treatment of H-31 which was highly susceptible to these drugs, a remarkable effect was shown in both IR and cellular changes even by combination using 1/2 MTD and 1/4 MTD doses. Combination with ADM at 1/2 MTD for both produced an additive effect against H-111 and H-48. Combination at MTD produced a marked antitumor effect against H-111 and a strikingly remarkable combination effect was confirmed. Combination with CDDP produced an additive effect against H-81 and a synergistic effect against H-154. Moreover, the weight loss by this combination regimen was far less than that by single administration of CDDP at MTD. An additive effect was demonstrated by combination with VP-16. Combination with 5-FU produced minimal combination effect. HO-221 was thus found to have a high antitumor effect by combination with various anticancer agents that are at present widely used clinically. HO-221 is expected to be a promising anticancer drug in its clinical application.