Serial fractional doses of mAb B3 and paclitaxel improve accumulation and penetration of B3 due to apoptosis of tumor cells

1376 Objectives To test if the greater accumulation and deeper penetration of mAb B3 in solid tumor achieved by serial fractional doses of B3 and paclitaxel (Taxol) could be explained by the distribution pattern of apoptotic cells (ACs). Methods Nude mice (n=6/group) with Ley positive A431 tumors (~200mm3) were injected as follows: 1) a single dose of 150 or 300µg Alexa B3 (IV) on D0 followed by a single dose of 40 or 70mg/kg Taxol (IP) on D1, and 2) serial fractional doses of 150µg Alexa B3 on D0, 40mg/kg Taxol on D1, 150µg Alexa B3 on D3, and 30mg/kg Taxol on D4, and 3) 150 or 300µg Alexa B3 (IV) on D0 as a control. The mice were euthanized 2 days after Alexa B3 injection. Tumor slices (8µm) were stained with the TUNEL assay to assess the apoptotic cell distributions by ScanScope FL. Alexa B3 intensity was plotted vs the distance and the B3 accumulation to 1 mm distance from tumor surface was calculated by AUC analysis. Results Regimen 1) produced apoptotic cells primarily in tumor periphery (P) (~50µm from tumor surface) with the apoptotic intensity depending on Taxol dose. The intensity and distribution of ACs showed a positive correlation with the accumulation and distribution of B3, indicating that the apoptosis decreased tumor cell density and improved the accumulation (% ID) of B3 in both P and tumor core (C). Although the single Taxol injection improved the accumulation of B3 by 75% compared to the control, it did not drastically improve the C/P ratio of B3 (0.25~0.32 vs 0.34~0.39 for the control). In contrast, regimen 2) produced very dense patches of ACs in P with areas of sparse ACs in C. This distribution of ACs resulted in deeper penetration of B3 toward C with its peak intensity shown at 1 mm from the surface with the C/P ratio of 1.54. Conclusions These findings indicate that regimen 2) improved the accumulation and penetration of B3 toward tumor core due to lowering of interstitial fluid pressure and overcoming binding-site barrier by extensive apoptotic cells in tumor periphery. Research Support Clinical Center, NIH and NCI Contract No. HHSN261200800001E.