Potentiation of Radioimmunotherapy with Response-Selective Peptide Agonist of Human C5a

Potentiation of Radioimmunotherapy with Response-Selective Peptide Agonist of Human C5a

Takashi Kurizaki, MD, PhD¹, Shinji Okazaki, MD¹, Sam D. Sanderson, PhD², David Colcher, PhD³, Charles A. Enke, MD¹, Margaret A. Tempero, MD⁴ and Janina Baranowska-Kortylewicz, PhD¹

¹ Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, Nebraska
² Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, Nebraska
³ Corixa, South San Francisco, California
⁴ UCSF Cancer Center, University of California at San Francisco, San Francisco, California

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FIGURE 1. Effects of AP (C5aAP) on uptake of macromolecular tracer in normal tissues of athymic (nu/nu) mice. Dose-dependent changes in uptake of ¹²⁵I-IgG in various tissues and blood of athymic mice were measured 30 min after intravenous administration of 0.37 MBq ¹²⁵I-IgG. Mice were given simultaneous injection of ¹²⁵I-IgG and indicated doses of AP through tail vein. Results are reported as average (n = 4) ± SD. Relative uptake of ¹²⁵I-IgG is calculated by dividing uptake of ¹²⁵I-IgG coinjected with AP by uptake of ¹²⁵I-IgG in absence of AP.

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FIGURE 2. Uptake kinetics of ¹²⁵I-B72.3 by LS174T xenografts in athymic mice treated intravenously with one 0.1-mg dose of AP at indicated time points before administration of ¹²⁵I-B72.3. For example, 3 h on x-axis indicates that AP was administered 3 h before dose of radiotracer. Biodistribution was conducted 72 h after injection of ¹²⁵I-B72.3. Data are expressed as average ± SD (*3-h vs. 6-h uptake, P > 0.2 at 0.05 level of significance; **3-h vs. 24-h uptake, 0.05 > P > 0.02 at 0.05 level of significance).

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FIGURE 3. Uptake of ¹²⁵I-B72.3 in tumor-bearing mice 72 h after injection of radiotracer. ¹²⁵I-B72.3 was administered 3 h after first dose of AP. Each point is average ± SE of 6 mice.

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FIGURE 4. Native PAGE of sera recovered from normal and AP-immunized mice reacted ex vivo with ¹²⁵I-AP. Mice were given 0.1 mg AP through intradermal or intravenous route once daily for 3 d. Two weeks after last injection, mice were euthanized. Sera collected from mice were incubated with ¹²⁵I-AP overnight and examined by electrophoresis on native PAGE gel. Lanes: 1, control, C57BL/6 mouse serum; 2, control, Swiss Albino mouse serum; 3, immunized mouse serum, Swiss Albino, intradermal; 4, immunized mouse serum, Swiss Albino, intradermal; 5, immunized mouse serum, Swiss Albino, intravenous; 6, immunized mouse serum, Swiss Albino, intravenous.

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FIGURE 5. Clearance curves for ¹²⁵I-AP (0.1 mg) administered intravenously in LS174T-bearing athymic mice. Each symbol represents average ± SD (n = 5); SDs are omitted when they are <5%. Sm Int = small intestine; Lg Int = large intestine.

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FIGURE 6. Relative growth of LS174T colon cancer xenografts after RIT treatment (n = 9). Tumor size changes are expressed relative to tumor volume 10 d after tumor implantation on day of ¹³¹I-B72.3 treatment (day 0). (A) AP (0.1 mg) without RIT. Solid lines represent kinetics of tumor growth for each mouse treated with AP; dotted line is mean tumor growth curve in control mice that received no treatment. (B) RIT with 9.25 MBq ¹³¹I-B72.3 alone. (C) Combination RIT with 9.25 MBq ¹³¹I-B72.3 and 0.1 mg AP.

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FIGURE 7. Autoradiogram of 5%–20% gradient SDS-PAGE gel of serum samples indicating no difference in processing of ¹³¹I-B72.3 in serum of AP-treated mice compared with ¹³¹I-B72.3 alone. Lanes: 1, ¹³¹I-B72.3 stored 22 d at 4°C; 2, ¹³¹I-B72.3 with AP; 3, ¹³¹I-B72.3 alone. All radioactivity recovered in serum 22 d after dosing is in form of ¹³¹I-B72.3. HPLC analyses on TSK G2000SW-TSK G3000SW columns confirmed this finding. MW = molecular weight.

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FIGURE 8. Microautoradiography of 5-µm tumor sections harvested 22 d after administration of 9.25 MBq ¹³¹I-B72.3. (A) Section of tumor from mouse treated with ¹³¹I-B72.3. (B) Section of tumor from mouse treated with 0.1 mg AP followed 3 h later by treatment with ¹³¹I-B72.3.