| Summary: | OBJECTIVE To explore the biodistribution and anti-tumor activity of 131I labeled rituximab injected intratumorally or intraperitoneally in vivo in nude mice bearing Raji human Burkit ’s lymphoma xenograts.METHODS The rituximab and the mouse IgG were labeled with Na131 I using the IODO-GEN method. BALB/C nude mice were xenograt ed with 131 I-Rituximab or 131I-IgG and killed on the 1st, 3rd, 7th, and 15th day after injection. The tumor/non-tumor ratio (T/NT) and the dose injected in each gram of the tissue (%ID/g) from 12 organs or tissues of interest, e.g. tumor, blood, were calculated. The long and short axes of each tumor were measured by calipers at 2-3-day intervals a t er treatment, and the growth inhibition of the tumor was calculated using the MIRD formula. RESULTS When comparing intraperitoneal injection (IP) and intratumoral injection (IT) of 131I-IgG, intratumoral injection of 131I-rituximab produced a significantly higher tumor/non-tumor ratio in all tissues and organs of interest on the 1st, 3rd, and 7th day, respectively (P < 0.05). The %ID/g of tumor was 1.4-1.7-fold and 1.5-3.7-fold in the IP and IgG IT groups, respectively, but the %ID/g of non-tumors was significantly lower in the IP group and IgG IT group.Similarly, the tumor growth was greatly inhibited by intratumoral injection of the 131I-rituximab, whereas it was less inhibited by other forms of the treatment (P < 0.05). However 131I-rituximab injected intratumorally inhibited tumor growth in a dose-dependent manner. The inhibition rate was less with a low dose (75 μ Ci) and greater with a high dose (150 μ Ci), yet the difference was not signifi cant ( P > 0.05). CONCLUSION Tumors can absorb the highest amount of the radiolabelled antibodies, and the tumor/non-tumor ratios in the group with intratumoral injection of the 131 I-rituximab resulted in the optimal anti-tumor activity.
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