Influence of protein properties and protein modification on biodistribution and tumor uptake of anticancer antibodies, antibody derivatives, and non-Ig scaffolds.

Newly developed protein drugs that target tumor-associated antigens are often modified in order to increase their therapeutic effect, tumor exposure, and safety profile. During the development of protein drugs, molecular imaging is increasingly used to provide additional information on their in vivo behavior. As a result, there are increasing numbers of studies that demonstrate the effect of protein modification on whole body distribution and tumor uptake of protein drugs. However, much still remains unclear about how to interpret obtained biodistribution data correctly. Consequently, there is a need for more insight in the correct way of interpreting preclinical and clinical imaging data. Summarizing the knowledge gained to date may facilitate this interpretation. This review therefore provides an overview of specific protein properties and modifications that can affect biodistribution and tumor uptake of anticancer antibodies, antibody fragments, and nonimmunoglobulin scaffolds. Protein properties that are discussed in this review are molecular size, target interaction, FcRn binding, and charge. Protein modifications that are discussed are radiolabeling, fluorescent labeling drug conjugation, glycosylation, humanization, albumin binding, and polyethylene glycolation.

Rapid optical imaging of human breast tumour xenografts using anti-HER2 VHHs site-directly conjugated to IRDye 800CW for image-guided surgery.

PURPOSE: Molecular optical imaging using monoclonal antibodies is slow with low tumour to background ratio. We used anti-HER2 VHHs conjugated to IRDye 800CW to investigate their potential as probes for rapid optical molecular imaging of HER2-positive tumours by the determination of tumour accumulation and tumour to background levels. METHODS: Three anti-HER2 VHHs (11A4, 18C3, 22G12) were selected with phage display and produced in Escherichia coli. Binding affinities of these probes to SKBR3 cells were determined before and after site-specific conjugation to IRDye 800CW. To determine the potential of VHH-IR as imaging probes, serial optical imaging studies were carried out using human SKBR3 and human MDA-MB-231 xenograft breast cancer models. Performance of the anti-HER2 VHH-IR was compared to that of trastuzumab-IR and a non-HER2-specific VHH-IR. Image-guided surgery was performed during which SKBR3 tumour was removed under the guidance of the VHH-IR signal. RESULTS: Site-specific conjugation of IRDye 800CW to three anti-HER2 VHHs preserved high affinity binding with the following dissociation constants (KD): 11A4 1.9 ± 0.03, 18C3 14.3 ± 1.8 and 22G12 3.2 ± 0.5 nM. Based upon different criteria such as binding, production yield and tumour accumulation, 11A4 was selected for further studies. Comparison of 11A4-IR with trastuzumab-IR showed ∼20 times faster tumour accumulation of the anti-HER2 VHH, with a much higher contrast between tumour and background tissue (11A4-IR 2.5 ± 0.3, trastuzumab-IR 1.4 ± 0.4, 4 h post-injection). 11A4-IR was demonstrated to be a useful tool in image-guided surgery. CONCLUSION: VHH-IR led to a much faster tumour accumulation with high tumour to background ratios as compared to trastuzumab-IR allowing same-day imaging for clinical investigation as well as image-guided surgery.

VEGF-PET imaging is a noninvasive biomarker showing differential changes in the tumor during sunitinib treatment.

Non-invasive imaging of angiogenesis could ease the optimization of antiangiogenesis treatments for cancer. In this study, we evaluated the role of VEGF-PET as a biomarker of dynamic angiogenic changes in tumors following treatment with the kinase inhibitor sunitinib. The effects of sunitinib treatment and withdrawal on the tumor was investigated using the new VEGF-PET tracer (89)Zr-ranibizumab as well as (18)F-FDG PET, and (15)O-water PET in mouse xenograft models of human cancer. The obtained imaging results were compared with tumor growth, VEGF plasma levels and immunohistologic analyzes. In contrast to (18)F-FDG and (15)O-water PET, VEGF-PET demonstrated dynamic changes during sunitinib treatment within the tumor with a strong decline in signal in the tumor center and only minimal reduction in tumor rim, with a pronounced rebound after sunitinib discontinuation. VEGF-PET results corresponded with tumor growth and immunohistochemical vascular- and tumor- markers. Our findings highlight the strengths of VEGF-PET imaging to allow serial analysis of angiogenic changes in different areas within a tumor.