Pharmacokinetics and splenic accumulation of N-acetylamino-3-chloro-N-(2-diethylamino-ethyl) benzamide after a single administration to rats.

The purpose of this study was to measure the pharmacokinetics and tissue accumulation of N-acetylamino-3-chloro-N-(2-diethylamino-ethyl) benzamide (NACPA) after oral or intravenous administration at a single dose of 25 mg/kg to female W/Fu rats. The serum pharmacokinetics of NACPA were characterized by rapid absorption, distribution and elimination. However, in comparison with its parent compound, 4-amino-3-chloro-N-(2-diethylamino-ethyl) benzamide (3-CPA), NACPA displayed a higher Cmax (mean+/-SD, 201+/-21 vs 33.6+/-0.5 nmol/ml, p < 0.05), and a longer elimination half-life (50+/-0.8 vs 36.6+/-1.1 min, p < 0.05) following intravenous administration. Bioavailability of NACPA was significantly greater than that of 3-CPA (50% compared with 14%, p < 0.05). The tissue accumulation of NACPA was generally higher than that of 3-CPA. NACPA was deposited at higher concentrations in the spleen than in the kidney and liver. Cellular pharmacokinetics indicated that NACPA accumulated more readily in lymphocyte related cells than in liver related cells. Furthermore, incubation of human peripheral lymphocytes with NACPA resulted in inhibition of lymphocyte proliferation, INF-gamma production and chemotaxis. All these results suggest that NACPA may be a good candidate drug for oral administration for immune modulation.

Combretastatin family member OXI4503 induces tumor vascular collapse through the induction of endothelial apoptosis.

The mechanism of tumor cell killing by OXI4503 was investigated by studying vascular functional and morphological changes post drug administration. SCID mice bearing MHEC5-T hemangioendothelioma were given a single dose of OXI4503 at 100 mg/kg. Tumor blood flow, measured by microsphere fluorescence, was reduced by 50% at 1 hr, and reached a maximum level 6-24 hr post drug treatment. Tumor vascular permeability, measured by Evan's blue and hemoglobin, increased significantly from 3 hr and peaked at 18 hr. The elevated tumor vessel permeability was accompanied by an increase in vascular endothelial growth factor (VEGF) from 1 hr post drug treatment. Immunohistochemical staining for CD31 and laminin showed that tumor blood vessels were affected as early as 3 hr but more prominent from 6 hr. From 12 hr, the vessel structure was completely destroyed. Histopathological and double immunohistochemical staining showed morphological change and induction of apoptosis in endothelial cells at 1-3 hr, followed by tumor cell necrosis from 6-72 hr. There were no statistically significant changes of Evan's blue and hemoglobin contents in liver tissue over the time course. These results suggest that OXI4503 selectively targets tumor blood vessels, and induces blood flow shutdown while it enhances tumor blood vessel permeability. The early induction of endothelial cell apoptosis leads to functional changes of tumor blood vessels and finally to the collapse of tumor vasculature, resulting in massive tumor cell necrosis. The time course of the tumor vascular response observed with OXI4503 treatment supports this drug for development as a stand alone therapy, and also lends support for the use of the drug in combination with other cancer therapies.

Oxi4503, a novel vascular targeting agent: effects on blood flow and antitumor activity in comparison to combretastatin A-4 phosphate.

Oxi4503, which is the diphosphate prodrug of combretastatin A1, is a novel vascular targeting agent from the combretastatin family. Another member of this family, Combretastatin A-4 phosphate (CA4P), is a well-characterized vascular targeting agent already being evaluated in clinical trials. The potential for tumor vascular targeting by Oxi4503 was assessed in a mouse system. This approach aims to shut down the established tumor vasculature, leading to the development of extensive tumor cell necrosis. The vascular effects of Oxi4503 were assessed in the s.c. implanted MDA-MB-231 adenocarcinoma and the MHEC5-T hemangio-endothelioma in SCID mice and in a range of normal tissues. Blood flow was measured by i.v. injection of fluorescence beads, while quantitative fluorescence microscopy was used to measure the spatial heterogeneity of blood flow in tumor sections. Oxi4503 induced the shutdown of tumor blood vessels in a dose-dependent pattern with an ED50 at 3 mg/kg in contrast to 43 mg/kg of CA4P. Quantitative fluorescence microscopy showed that Oxi4503 increased the spatial heterogeneity in tumor blood flow. Oxi4503 affected peripheral tumor regions less than central regions, although this was not as pronounced as seen with CA4P, where only central regions were affected. The vascular shutdown induced by administration of Oxi4503 at a dose of 6 mg/kg resulted in extensive cell loss 24 hours following treatment, which translated into a significant effect on tumor growth. Tumor growth was completely repressed at doses above 12.5 mg/kg of Oxi4503, while doses above 25 mg/kg showed tumor regression and even complete regression in some animals. These results are promising for the use of Oxi4503 as a tumor vascular targeting agent. Moreover the potent antitumor effect when administered as a single agent suggests a different activity profile than CA4P.

Synthesis, in vitro, and in vivo evaluation of phosphate ester derivatives of combretastatin A-4.

Combretastatin A-4 disodiumphosphate (CA4P), a prodrug formulation of the natural product combretastatin A-4 (CA4), is currently in clinical investigation for the treatment of cancer. In vivo, CA4P is rapidly enzymatically converted to CA4, a potent inhibitor of tubulin polymerization (IC(50)=1-2 microM), and rapidly causes bloodflow shutdown in tumor tissues. A variety of alkyl and aryl di- and triesters of CA4P have been synthesized and evaluated as potential CA4 prodrugs and/or stable CA4P analogues.