LU 79553 is a novel bis-naphthalimide which is highly cytotoxic in vitro with EC50 (concentration required for 50% inhibition of growth) ranging from 2 x 10(-7) to 5 x 10(-10) M. A number of studies were conducted to examine its antitumor activity in human xenograft models. In addition, we wanted to explore the possible schedule dependency of LU 79553 cytotoxicity in these xenograft models. Complete regression of MX-1 (mammary carcinoma) xenografts was observed when LU 79553 was administered i.v. daily for 5 doses at 20 mg/kg (2 cycles starting on Days 6 and 20) or every 3 days for 2 doses at 55 mg/kg (2 cycles starting on Days 6 and 13) or every 7 days for 4 doses. Complete regression was also seen in the MX-1 model when tumors were staged at 1-2 g prior to the initiation of treatment. Regressions (complete or partial) were observed in the LX-1 (lung), CX-1 (colon), DLD (colon), and LOX (melanoma) xenograft models. A significant increase in the median survival time of OVCAR-3- (ovarian carcinoma) bearing mice was noted in LU 79553-treated animals (treated/control = 195%). The excellent activity of this compound in such a wide variety of tumor types suggests LU 79553 merits further investigation in clinical trials.