Although several approaches for making antibody-drug conjugates (ADC) have been developed, it has yet to be reported that an antibody binding peptide such as Z33 from protein A is utilized as the pivotal unit to generate the noncovalent-type ADC (NC-ADC). Herein we aim to establish a novel probe for NC-ADC by synthesizing the Z33-conjugated antitumor agent, plinabulin. Due to the different solubility of two components, including hydrophobic plinabulin and hydrophilic Z33, an innovative method with a solid-supported disulfide coupling reagent is required for the synthesis of the target compounds with prominent efficiency (29% isolated yield). We demonstrate that the synthesized hybrid exhibits a binding affinity against the anti-HER2 antibody (Herceptin) and the anti-CD71 antibody (6E1) (Kd = 46.6 ± 0.5 nM and 4.5 ± 0.56 μM, respectively) in the surface plasmon resonance (SPR) assay. In the cell-based assays, the hybrid provides a significant cytotoxicity in the presence of Herceptin against HER2 overexpressing SKBR-3 cells, but not against HER2 low-expressing MCF-7 cells. Further, it is noteworthy that the hybrid in combination with Herceptin induces cytotoxicity against Herceptin-resistant SKBR-3 (SKBR-3HR) cells. Similar results are obtained with the 6E1 antibody, suggesting that the synthesized hybrid can be widely applicable for NC-ADC using the antibody of interest. In summary, a series of evidence presented here strongly indicate that NC-ADCs have high potential for the next generation of antitumor agents.
Chemical conjugation between hydrophilic and hydrophobic components is difficult because of their extremely different solubility. Herein, we report a new versatile method with a solid-phase-assisted disulfide ligation to overcome the difficulty of conjugation attributed to solubility. The method involves two steps in a one-pot process: 1) loading of a hydrophobic molecule onto a resin in an organic solvent, and 2) release of the solid-supported hydrophobic molecule as a conjugate with a hydrophilic molecule into an aqueous solvent. This strategy allows the use of a suitable solvent system for the substrates in each step. Conjugates of a water-insoluble drug, plinabulin, with hydrophilic carriers that could not be prepared by solution-phase reactions were obtained in moderate yields (29-45 %). This strategy is widely applicable to the conjugation of compounds with solubility problems.
Chemical conjugation between hydrophilic and hydrophobic components is difficult because of their extremely different solubility. Herein, we report a new versatile method with a solid‐phase‐assisted disulfide ligation to overcome the difficulty of conjugation attributed to solubility. The method involves two steps in a one‐pot process: 1) loading of a hydrophobic molecule onto a resin in an organic solvent, and 2) release of the solid‐supported hydrophobic molecule as a conjugate with a hydrophilic molecule into an aqueous solvent. This strategy allows the use of a suitable solvent system for the substrates in each step. Conjugates of a water‐insoluble drug, plinabulin, with hydrophilic carriers that could not be prepared by solution‐phase reactions were obtained in moderate yields (29–45 %). This strategy is widely applicable to the conjugation of compounds with solubility problems.
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