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Solid-Phase Synthesis of Heterobivalent Ligands Targeted to Melanocortin and Cholecystokinin Receptors

  • Jatinder S. Josan
  • Josef Vagner
  • Heather L. Handl
  • Rajesh Sankaranarayanan
  • Robert J. Gillies
  • Victor J. HrubyEmail author
Article

Abstract

Heteromultivalency provides a route to increase binding avidity and to high specificity when compared to monovalent ligands. The enhanced specificity can potentially serve as a unique platform to develop diagnostics and therapeutics. To develop new imaging agents based upon multivalency, we employed heterobivalent constructs of optimized ligands. In this report, we describe synthetic methods we have developed for the preparation of heterobivalent constructs consisting of ligands targeted simultaneously to the melanocortin receptor, hMC4R, and the cholecystokinin receptors, CCK-2R. Modeling data suggest that a linker distance span of 20–50 Å is needed to crosslink these two G-protein coupled receptors (GPCRs). The two ligands were tethered with linkers of varying rigidity and length, and flexible polyethylene glycol based PEGO chain or semi-rigid [poly(Pro-Gly)] linkers were employed for this purpose. The described synthetic strategy provides a modular way to assemble ligands and linkers on solid-phase supports. Examples of heterobivalent ligands are provided to illustrate the increased binding avidity to cells that express the complementary receptors.

Keywords

Solid-phase peptide synthesis Multivalency Heterobivalent ligands Heterodimers Linkers Receptor combination approach Targeted agents 

Abbreviations

GPCR

G-protein coupled receptor

hMC4R

Human melanocortin-4 receptor

CCK-2R

Cholecystokinin-2 receptor

α-MSH

α-Melanocortin stimulating hormone

MSH-7

Ac-Ser-Nle-Glu-His-DPhe-Arg-Trp-

CCK-6

-Nle-Gly-Trp-Nle-Asp-Phe-NH2

PEGO

19-Amino-5-oxo-3,10,13,16-tetraoxa-6-azanonadecan-1-oic acid

Fmoc

9-Fluorenylmethyloxycarbonyl

Boc

Tert-butyloxycarbonyl

HOBt

1-Hydroxybenzotriazole

HOCt

6-Chloro-1-hydroxybenzotriazole

HBTU

o-[1H-Benzotriazol-1-yl)(dimethylamino)methylene]uranium hexafluorophosphate N-oxide

DIC

Diisopropylcarbodiimide

DIEA

Diisopropylethylamine

Pbf

2,2,4,6,7-Pentamethyldihydrobenzofuran-5-yl sulfonyl

Trt

Triphenylmethyl (trityl)

TFA

Trifluoroacetic acid

MALDI-TOF

Matrix assisted laser desorption ionization-time of flight

ESI-MS

Electrospray ionization-mass spectrometry

FT-ICR

Fourier transform-ion cyclotron resonance

Hek-293 cells

Human embryonic kidney cells

TRF

Time-resolved fluorescence

Notes

Acknowledgements

We thank Ms. Lucinda Begay and Mrs. Renata Patek for HPLC and technical assistance. This work was supported by grants R01 CA 123547 and RO1 CA097360 from the National Cancer Institute and Grant ABRC06-006 from the Arizona Biomedical Research Commission.

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Copyright information

© Springer Science+Business Media, LLC 2008

Authors and Affiliations

  • Jatinder S. Josan
    • 1
  • Josef Vagner
    • 2
  • Heather L. Handl
    • 3
  • Rajesh Sankaranarayanan
    • 1
  • Robert J. Gillies
    • 2
    • 3
    • 4
    • 5
  • Victor J. Hruby
    • 1
    • 2
    • 3
    Email author
  1. 1.Department of ChemistryThe University of ArizonaTucsonUSA
  2. 2.BIO5 Institute, The University of ArizonaTucsonUSA
  3. 3.Department of Biochemistry and Molecular BiophysicsThe University of ArizonaTucsonUSA
  4. 4.Department of RadiologyThe University of ArizonaTucsonUSA
  5. 5.H. Lee Moffitt Cancer CenterTampaUSA

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