The pharmacological properties of 3-arm or 4-arm DOTA constructs for conjugation to α-melanocyte-stimulating hormone analogues for melanoma imaging

PLoS One. 2019 Mar 22;14(3):e0213397. doi: 10.1371/journal.pone.0213397. eCollection 2019.

Abstract

Background: Although a 3-arm DOTA construct, which has three carboxylic acids, h has been applied for conjugation to many peptides, we investigated if a 4-arm DOTA construct conjugated to peptides improves chemical properties for melanoma imaging of the melanocortin 1 receptor compared to 3-arm DOTA-conjugated peptides.

Methods: Specific activities, radiolabeling efficiencies, and partition coefficients were evaluated using 111In-labeled 3-arm and 4-arm DOTA-α-melanocyte-stimulating hormone (MSH). For assessment of MC1-R affinity and accumulation in tumor cells in vitro, B16-F1 melanoma and/or 4T1 breast cancer cells were incubated with 111In-labeled 3-arm and 4-arm DOTA-α-MSH with and without α-MSH as a substrate. The stability was evaluated using mouse liver homogenates and plasma. Biological distribution and whole-body single photon emission computed tomography imaging of 111In-labeled 3-arm and 4-arm DOTA-α-MSH were obtained using B16-F1 melanoma-bearing mice.

Results: Specific activities and radiolabeling efficiencies of both radiotracers were about 1.2 MBq/nM and 90-95%, respectively. The partition coefficients were -0.28 ± 0.03 for 111In-labeled 3-arm DOTA-α-MSH and -0.13 ± 0.04 for 111In-labeled 4-arm DOTA-α-MSH. Although accumulation was significantly inhibited by α-MSH in B16-F1 cells, the inhibition rate of 111In-labeled 4-arm DOTA-α-MSH was lower than that of 111In-labeled 3-arm DOTA-α-MSH. 111In-labeled 4-arm DOTA-α-MSH was taken up early into B16-F1 cells and showed higher accumulation than 111In-labeled 3-arm DOTA-α-MSH after 10 min of incubation. Although these stabilities were relatively high, the stability of 111In-labeled 4-arm DOTA-α-MSH was higher than that of 111In-labeled 3-arm DOTA-α-MSH. Regarding biological distribution, 111In-labeled 4-arm DOTA-α-MSH showed significantly lower average renal accumulation (1.38-fold) and significantly higher average melanoma accumulation (1.32-fold) than 111In-labeled 3-arm DOTA-α-MSH at all acquisition times. 111In-labeled 4-arm DOTA-α-MSH showed significantly higher melanoma-to-kidney, melanoma-to-blood, and melanoma-to-muscle ratios than 111In-labeled 3-arm DOTA-α-MSH.

Conclusions: The 4-arm DOTA construct has better chemical properties for peptide radiotracers than the 3-arm DOTA construct.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line, Tumor
  • Coordination Complexes* / chemical synthesis
  • Coordination Complexes* / chemistry
  • Drug Stability
  • Female
  • Heterocyclic Compounds, 1-Ring* / chemical synthesis
  • Heterocyclic Compounds, 1-Ring* / chemistry
  • Indium Radioisotopes
  • Male
  • Melanoma, Experimental / diagnostic imaging*
  • Mice
  • Mice, Inbred C57BL
  • Molecular Structure
  • Radiopharmaceuticals* / chemical synthesis
  • Radiopharmaceuticals* / chemistry
  • Tomography, Emission-Computed, Single-Photon
  • alpha-MSH / analogs & derivatives*
  • alpha-MSH / chemistry

Substances

  • Coordination Complexes
  • Heterocyclic Compounds, 1-Ring
  • Indium Radioisotopes
  • Radiopharmaceuticals
  • indium-111-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid
  • alpha-MSH

Grants and funding

This study was partly funded by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (Nos. 15K09949 and 16KK0020 for Masato Kobayashi and 15K15452 for Keiichi Kawai), the Program of the Network-type Joint Usage/Research Center for Radiation Disaster Medical Science of Hiroshima University, Nagasaki University, and Fukushima Medical University, and the Nakatani Foundation for measuring technologies in biomedical engineering. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.