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Ligand targeted drug conjugates. (A) General representation of ligand conjugated to cytotoxic payload via a peptide linker. The circle represents the cholecystokinin 2 receptor (CCK2R) binding ligand, whereas the linker is represented by an oval. The cytotoxic drug, or payload, is indicated by a rectangle. The solid black line represents a covalent bond between the ligand and the linker, and the dotted line symbolizes a cleavable self-immolative bond. (B) Chemical structures of the CCK2R ligand CRL conjugated to the cytotoxic antimicrotubule agents desacetyl vinblastine hydrazide and tubulysin B hydrazide via a hydrophilic peptide linker.
Source publication
Cholecystokinin 2 receptor (CCK2R) is over expressed on many cancers of lungs, pancreas, liver and GI tract (esophagus, colon and GIST), whereas its expression in normal tissues is limited to epithelial cells of the GI tract and brain. This restricted expression pattern renders CCK2R an excellent candidate for use in tumor-targeted drug delivery. H...
Contexts in source publication
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... A related strategy to achieve tumor-selective drug delivery involves the use of low molecular weight targeting ligands that can similarly deliver attached drugs specifically to cancer cells. Low molecular weight ligand−drug conjugates ( Figure 1A) also target receptors that are overexpressed on malignant cells, and their much smaller sizes may permit more thorough tumor penetration. 17−20 In this paper, Z-360, 21 a low molecular weight ligand of the cholecystokinin 2 receptor (CCK2R), is modified to deliver two of the more potent antimicrotubule agents currently available (desacetyl vinblastine monohydrazide and tubulysin B hydrazide). ...
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... CCK2R ligand (Z-360) was synthesized as previously described 21 and abbreviated CRL to be consistent with previous publications. 30 The peptide spacer was prepared using Fmoc-protected solid phase peptide synthesis as outlined in Scheme 1 (Supporting Information (SI), Figure 1) and named L1. As shown in Scheme 1 (SI, Figure 1), CRL was coupled to the peptide spacer on the solid phase and cleaved from the resin using a standard cleavage cocktail solution. ...
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... The peptide spacer was prepared using Fmoc-protected solid phase peptide synthesis as outlined in Scheme 1 (Supporting Information (SI), Figure 1) and named L1. As shown in Scheme 1 (SI, Figure 1), CRL was coupled to the peptide spacer on the solid phase and cleaved from the resin using a standard cleavage cocktail solution. Crude CRL-L1 was purified by preparative RP-HPLC [A = 2 mM ammonium acetate buffer (pH 5.0), B = CH 3 CN, solvent gradient: 5% B to 80% B in 25 min] to yield the requisite product. ...
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... of Nontargeted Desacetyl Vinblastine Hydrazide (L1-DAVBH) and Nontargeted Tubulysin Hydrazide (L1- TubBH). L1-DAVBH and L1-TubBH were synthesized from activated DAVBH and TubBH, respectively, following the procedure outlined for the synthesis of CRL-L1-DAVBH (SI, Figure 1 and 3). Each compound was then purified by reverse phase HPLC [A = 2 mM ammonium acetate buffer (pH 7.0), B = CH 3 CN, solvent gradient: 5% B to 80% B in 25 min] to yield the requisite product. ...
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... design of a ligand-targeted chemotherapeutic agent requires (i) selection of a high affinity ligand with good selectivity for a cancer-enriched receptor, (ii) identification of a therapeutic agent with sufficient potency to kill cancer cells when captured by a cancer-specific receptor, and (iii) construction of a linker that will enable delivery and release of the attached drug preferentially within the targeted cells. Because cholecystokinin receptor ligand (CRL) has been shown to exhibit high affinity (0.47 nM) and strong selectivity for CCK2R (>600-fold specificity over CCK1R 29 ), it was selected for exploration as a targeting ligand for drug delivery to CCK2R-expressing cancer cells ( Figure 1B). 21,30 To avoid nonspecific adsorption to CCK2R negative cells, we incorporated a water-soluble peptide spacer, 31 referred to as L1, between the ligand and its therapeutic payload ( Figure 1B). ...
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... cholecystokinin receptor ligand (CRL) has been shown to exhibit high affinity (0.47 nM) and strong selectivity for CCK2R (>600-fold specificity over CCK1R 29 ), it was selected for exploration as a targeting ligand for drug delivery to CCK2R-expressing cancer cells ( Figure 1B). 21,30 To avoid nonspecific adsorption to CCK2R negative cells, we incorporated a water-soluble peptide spacer, 31 referred to as L1, between the ligand and its therapeutic payload ( Figure 1B). Previous results from our lab have shown only a slight loss of affinity with no effect on specificity when CRL is conjugated to its payload via hydrophilic linkers. ...
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... complete tumor remission was not achieved at a dose of 2 μg/kg with CRL-L1-DAVBH, we elected to develop a more potent CCK2R-targeted conjugate. For this purpose, tubulysin B hydrazide (TubBH), a microtubule inhibitor with ∼10× the potency of DAVBH, was conjugated to CRL via the same L1 linker (Figure 1, SI Figures 2 and 3). As shown in Figure 5A, free tubulysin B hydrazide was found to be very potent in vitro, exhibiting an IC 50 of 2.7 nM on HEK 293- CCK2R cells. ...
