Evaluation of combretastatin A-4 prodrug in a non-Hodgkin's lymphoma xenograft model: Preclinical efficacy

Combretastatin A-4 prodrug (CA4P) is a new antitubulin agent currently in phase I/II clinical trials against solid tumors. We have previously reported on the in vitro activity of CA4P against a panel of malignant human B-lymphoid cell lines. In this study, we investigated the antitumor and the antiangiogenic activity of CA4P in our diffuse large cell lymphoma WSU-DLCL₂-SCID mouse model. WSU-DLCL₂ cells (10⁷) were injected s.c. into 5-week-old female ICR-SCID mice. Tumor-bearing mice were treated at the CA4P maximum tolerated dose (MTD) of 800 mg/kg in different dose/schedules. CA4P showed significant antitumor activity against this lymphoma model. Best results were seen when MTD was given in two and four divided doses (400 and 200 mg/kg, respectively). CA4P given in four divided doses (4 × 200 mg/kg) showed a log₁₀ kill of 1.01, T/C of 11.7% and T-C of 12 days. Immunohistochemical staining using anti-CD31 antibody after 6, 24, 48 and 120 h treatment revealed a significant decrease in the number of tumor blood vessels after 24 h (about 80%). Only the periphery of treated tumors revealed the presence of blood vessels. Morphological examination of the tumors after tetrachrome staining showed a necrotic center in tumors of CA4P-treated animals. New blood vessel formation was noted to emerge in tumor tissues as early as 48 h following a single dose of CA4P. The G₂/M arrest observed in vitro was not detected in vivo indicating predominance of the antiangiogenic effects with regard to antitumor efficacy in vivo. We conclude that CA4P has antiangiogenic activity in this lymphoma model and the use of this agent should be explored clinically in the treatment of non-Hodgkin's lymphoma.