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In vivo biodistribution and small animal PET of (64)Cu-labeled antimicrobial peptoids.

ABSTRACT: Peptoids are a rapidly developing class of biomimetic polymers based on oligo-N-substituted glycine backbones, designed to mimic peptides and proteins. Inspired by natural antimicrobial peptides, a group of cationic amphipathic peptoids has been successfully discovered with potent, broad-spectrum activity against pathogenic bacteria; however, there are limited studies to address the in vivo pharmacokinetics of the peptoids. Herein, (64)Cu-labeled DOTA conjugates of three different peptoids and two control peptides were synthesized and assayed in vivo by both biodistribution studies and small animal positron emission tomography (PET). The study was designed in a way to assess how structural differences of the peptidomimetics affect in vivo pharmacokinetics. As amphipathic molecules, major uptake of the peptoids occurred in the liver. Increased kidney uptake was observed by deleting one hydrophobic residue in the peptoid, and (64)Cu-3 achieved the highest kidney uptake of all the conjugates tested in this study. In comparison to peptides, our data indicated that peptoids had general in vivo properties of higher tissue accumulation, slower elimination, and higher in vivo stability. Different administration routes (intravenous, intraperitoneal, and oral) were investigated with peptoids. When administered orally, the peptoids showed poor bioavailability, reminiscent of that of peptide. However, remarkably longer passage through the gastrointestinal (GI) tract without rapid digestion was observed for peptoids. These unique in vivo properties of peptoids were rationalized by efficient cellular membrane permeability and protease resistance of peptoids. The results observed in the biodistribution studies could be confirmed by PET imaging, which provides a reliable way to evaluate in vivo pharmacokinetic properties of peptoids noninvasively and in real time. The pharmacokinetic data presented here can provide insight for further development of the antimicrobial peptoids as pharmaceuticals.

SUBMITTER: Seo J

PROVIDER: S-EPMC3410980 | biostudies-literature | 2012 May

REPOSITORIES: biostudies-literature

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In vivo biodistribution and small animal PET of (64)Cu-labeled antimicrobial peptoids.

Seo Jiwon J Ren Gang G Liu Hongguang H Miao Zheng Z Park Minyoung M Wang Yihong Y Miller Tyler M TM Barron Annelise E AE Cheng Zhen Z

Bioconjugate chemistry 20120419 5

Peptoids are a rapidly developing class of biomimetic polymers based on oligo-N-substituted glycine backbones, designed to mimic peptides and proteins. Inspired by natural antimicrobial peptides, a group of cationic amphipathic peptoids has been successfully discovered with potent, broad-spectrum activity against pathogenic bacteria; however, there are limited studies to address the in vivo pharmacokinetics of the peptoids. Herein, (64)Cu-labeled DOTA conjugates of three different peptoids and t ...[more]

PMID: 22486390

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Project description:The ability to detect and quantify macrophage accumulation can provide important diagnostic and prognostic information for atherosclerotic plaque. We have previously shown that LyP-1, a cyclic 9-amino acid peptide, binds to p32 proteins on activated macrophages, facilitating the visualization of atherosclerotic plaque with PET. Yet, the in vivo plaque accumulation of monomeric [(18)F]FBA-LyP-1 was low (0.31 ± 0.05%ID/g). To increase the avidity of LyP-1 constructs to p32, we synthesized a dendritic form of LyP-1 on solid phase using lysine as the core structural element. Imaging probes (FAM or 6-BAT) were conjugated to a lysine or cysteine on the dendrimer for optical and PET studies. The N-terminus of the dendrimer was further modified with an aminooxy group in order to conjugate LyP-1 and ARAL peptides bearing a ketone. Oxime ligation of peptides to both dendrimers resulted in (LyP-1)4- and (ARAL)4-dendrimers with optical (FAM) and PET probes (6-BAT). For PET-CT studies, (LyP-1)4- and (ARAL)4-dendrimer-6-BAT were labeled with (64)Cu (t1/2 = 12.7 h) and intravenously injected into the atherosclerotic (ApoE(-/-)) mice. After two hours of circulation, PET-CT coregistered images demonstrated greater uptake of the (LyP-1)4-dendrimer-(64)Cu than the (ARAL)4-dendrimer-(64)Cu in the aortic root and descending aorta. Ex vivo images and the biodistribution acquired at three hours after injection also demonstrated a significantly higher uptake of the (LyP-1)4-dendrimer-(64)Cu (1.1 ± 0.26%ID/g) than the (ARAL)4-dendrimer-(64)Cu (0.22 ± 0.05%ID/g) in the aorta. Similarly, subcutaneous injection of the LyP-1-dendrimeric carriers resulted in preferential accumulation in plaque-containing regions over 24 h. In the same model system, ex vivo fluorescence images within aortic plaque depict an increased accumulation and penetration of the (LyP-1)4-dendrimer-FAM as compared to the (ARAL)4-dendrimer-FAM. Taken together, the results suggest that the (LyP-1)4-dendrimer can be applied for in vivo PET imaging of plaque and that LyP-1 could be further exploited for the delivery of therapeutics with multivalent carriers or nanoparticles.

Project description:Current noninvasive imaging methods for monitoring immune response were largely developed for interrogation of the local reaction. This study developed the radiotracer 64Cu-labeled anti-CD11b (64Cu-αCD11b) for longitudinal assessment of local and systemic immune response involving mobilization of CD11b+ myeloid cells by small-animal PET/CT. Methods: Acute or chronic inflammation in the ears of BALB/c mice was induced by 12-o-tetradecanoylphorbol-13-acetate. Acute lung inflammation was induced by intratracheal lipopolysaccharide inoculation. αCD11b was conjugated with p-SCN-Bn-DOTA followed by labeling with 64Cu. PET/CT and biodistribution were evaluated at different times after intravenous injection of 64Cu-αCD11b. Cell populations from bone marrow (BM) and spleen were analyzed by flow cytometry. Results: 64Cu-αCD11b was primarily taken up by BM and spleen in control mice. In comparison, 64Cu-αCD11b uptake was significantly reduced in the BM and spleen of CD11b-knockout mice, indicating that 64Cu-αCD11b selectively homed to CD11b+ myeloid cells in vivo. In mice with ear inflammation, for the local inflammatory response, 64Cu-αCD11b PET/CT revealed significantly higher 64Cu-αCD11b uptake in the inflamed ears in the acute inflammation phase than the chronic phase, consistent with markedly increased infiltration of CD11b+ cells into the inflammatory lesions at the acute phase. Moreover, imaging of 64Cu-αCD11b also showed the difference in mouse systemic response for different inflammatory stages. Compared with uptake in control mice, BM 64Cu-αCD11b uptake in mice with ear inflammation was significantly lower in the acute phase and higher in the chronic phase, reflecting an initial mobilization of CD11b+ cells from the BM to the inflammatory foci followed by a compensatory regeneration of CD11b+ myeloid cells in the BM. Similarly, in mice with lung inflammation, 64Cu-αCD11b PET/CT readily detected acute lung inflammation and recruitment of CD11b+ myeloid cells from the BM. Immunohistochemistry staining and flow cytometry results confirmed the noninvasive imaging of PET/CT. Conclusion: 64Cu-αCD11b PET/CT successfully tracked ear and pulmonary inflammation in mice and differentiated acute from chronic inflammation at the local and systemic levels. 64Cu-αCD11b PET/CT is a robust quantitative method for imaging of local and systemic immune responses.

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In vivo biodistribution and small animal PET of (64)Cu-labeled antimicrobial peptoids.

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In vivo biodistribution and small animal PET of (64)Cu-labeled antimicrobial peptoids.

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