Preparation, biological evaluation, and pharmacokinetics of the human anti-HER1 monoclonal antibody panitumumab labeled with 86Y for quantitative PET of carcinoma

Abstract

Panitumumab, a human monoclonal antibody that binds to the epidermal growth factor receptor (HER1), was approved by the Food and Drug Administration in 2006 for the treatment of patients with HER1-expressing carcinoma. In this article, we describe the preclinical development of (86)Y-CHX-A''-diethylenetriaminepentaacetic acid (DTPA)-panitumumab for quantitative PET of HER1-expressing carcinoma. Panitumumab was conjugated to CHX-A''-DTPA and radiolabeled with (86)Y. In vivo biodistribution, PET, blood clearance, area under the curve, area under the moment curve, and mean residence time were determined for mice bearing HER1-expressing human colorectal (LS-174T), prostate (PC-3), and epidermoid (A431) tumor xenografts. Receptor specificity was demonstrated by coinjection of 0.1 mg of panitumumab with the radioimmunoconjugate.

Results: (86)Y-CHX-A''-DTPA-panitumumab was routinely prepared with a specific activity exceeding 2 GBq/mg. Biodistribution and PET studies demonstrated a high HER1-specific tumor uptake of the radioimmunoconjugate. In mice bearing LS-174T, PC-3, or A431 tumors, the tumor uptake at 3 d was 34.6 +/- 5.9, 22.1 +/- 1.9, and 22.7 +/- 1.7 percentage injected dose per gram (%ID/g), respectively. The corresponding tumor uptake in mice coinjected with 0.1 mg of panitumumab was 9.3 +/- 1.5, 8.8 +/- 0.9, and 10.0 +/- 1.3 %ID/g, respectively, at the same time point, demonstrating specific blockage of the receptor. Normal organ and tumor uptake quantified by PET was closely related (r(2) = 0.95) to values determined by biodistribution studies. The LS-174T tumor had the highest area under the curve (96.8 +/- 5.6 %ID d g(-1)) and area under the moment curve (262.5 +/- 14.9 %ID d(2) g(-1)); however, the tumor mean residence times were identical for all 3 tumors (2.7-2.8 d).

Conclusion: This study demonstrates the potential of (86)Y-CHX-A''-DTPA-panitumumab for quantitative noninvasive PET of HER1-expressing tumors and represents the first step toward clinical translation.

Figure 1

Biodistribution of ⁸⁶Y-CHX-A″-DTPA-panitumumab in selected organs of female athymic (NCr) nu/nu mice bearing human colorectal carcinoma LS-174T (A) and human prostate carcinoma PC-3 (B) tumor xenografts. Biodistribution data were obtained at 1, 2, 3 and 4 d after i.v. injection of ⁸⁶Y-CHX-A″-DTPA-panitumumab. All values are expressed as % ID/g. Data represent the mean value ± SEM from at least four determinations.

Figure 2

Receptor-meditated uptake of ⁸⁶Y-CHX-A″-DTPA-panitumumab in selected organs of female athymic (NCr) nu/nu mice bearing human colorectal carcinoma LS-174T (A), human prostate carcinoma PC-3 (B) and human epidermoid carcinoma A431 tumor xenografts (C). Biodistribution data were obtained at 3 d after injection. All values are expressed as % ID/g. Data represent the mean value ± SEM from at least three determinations. ^*Receptor blocking studies were performed by co-injecting 0.1 mg panitumumab with the radiotracer.

Figure 3

Representative reconstructed and processed maximum intensity projections (top panel) and transverse slices (bottom panel) of female athymic (NCr) nu/nu mouse bearing human colorectal carcinoma LS-174T (3A and 3B) and human epidermoid carcinoma A431 tumor xenografts (3C and 3D). Mice represented in 3A and 3C were injected i.v. via tail vein with 1.8–2.0 MBq of ⁸⁶Y-CHX-A″-DTPA-panitumumab, and mice represented in 3B and 3D were co-injected i.v. via tail vein with 1.8–2.0 MBq of ⁸⁶Y-CHX-A″-DTPA-panitumumab and 0.1 mg Panitumumab for blocking HER1. The tumors are indicated with a white arrow. The scale represents % maximum and minimum threshold intensity. ^*Receptor blocking studies were performed by co-injecting 0.1 mg panitumumab with the radiotracer.

Figure 4

(A) Time-activity curve and uptake values of ⁸⁶Y-CHX-A″-DTPA-panitumumab in selected organs of female athymic (NCr) nu/nu mice bearing human colorectal carcinoma LS-174T xenografts assessed through quantitative small animal PET imaging. (B) Comparative time-activity curves of ⁸⁶Y-CHX-A″-DTPA-panitumumab in female athymic (NCr) nu/nu mice bearing LS-174T, A431 and PC-3 tumor xenografts. (C) Correlation between organ % ID/g values assessed through in vivo biodistribution studies and quantitative small animal PET imaging. All uptake values derived from PET studies are expressed as % ID/cc. Data represent the mean value ± SEM from three determinations. ^*Receptor blocking studies performed by co-injecting 0.1 mg panitumumab with the radiotracer.