Targeting Integrin α_V β₃ with Theranostic RGD-Camptothecin Conjugates Bearing a Disulfide Linker: Biological Evaluation Reveals a Complex Scenario

Abstract

Theranostic RGD-camptothecin conjugates, possessing a disulfide linker and a fluorescent naphthalimide moiety, were synthesized and biologically evaluated. The conjugates showed nanomolar affinity for the purified a V b 3 -integrin receptor. For antiproliferative assays, the U87 human glioblastoma were chosen as a V b 3 -expressing cells, whereas a non a V b 3 -expressing clone (U87 b 3 -KO) was generated as negative control. Although the U87 b 3 -KO cells treated with the conjugates showed a statistically significant reduced fluorescence intensity (in the range 7-12 %) compared to the parental U87, internalization of the conjugates was clearly observed in both cell lines. Stability studies showed premature cleavage of the disulfide linker in the cell media, with consequent release of free camptothecin. Consistent with the results of the internalization and stability studies, the conjugates did not show significant selectivity against the U87 cells compared to the U87 b 3 -KO clone.

RGD Peptide‐Drug Conjugates as Effective Dual Targeting Platforms: Recent Advances

“…In 2017, Gennari and colleagues exploited the DKP-RGD peptidomimetic in the preparation of a "theranostic" platform (compound 36, Scheme 11) where the anticancer agent camptothecin (CPT), the RGD ligand and a fluorescent naphthalimide probe were joined together through a disulfide bridge, besides other amide, carbamate and carbonate linkages. [68] This type of reducible linker, though common in SMDCs, has been rarely used to build up integrin targeted conjugates, with the only exception given by Kim in 2012. [69] Conveniently, the S-S linkage can be selectively cleaved by intracellular exchange with free thiols of glutathione (GSH) or thioredoxin.…”

Synthesis and Evaluation of a Non-Peptide Small-Molecule Drug Conjugate Targeting Integrin αVβ3

“…The group of DeGrado designed and synthesized linear RGD mimetics with high affinity and high selectivity against integrin α 5 β 1 based on a diamine scaffold ( Corbett et al, 1997 ; Rockwell et al, 1999 ). Most notably, in the last years, the cyclic cRGDfK peptide and its analogs [e.g., cyclo( iso DGR) and cyclo(DKP-RGD)] have been used as integrin α V β 3 -addressing homing devices in SMDCs ( Figure 2 ) ( Pina et al, 2017 ; Anselmi et al, 2020 ; Battistini et al, 2021 ; Lerchen et al, 2022 ).…”

“… Structures of RGD containing SMDC with enzymatically cleavable linkers and paclitaxel ( Pina et al, 2017 ) as well as cryptophycin-55 ( Borbély et al, 2019a ) as payloads. …”

Conjugates of Cryptophycin and RGD or isoDGR Peptidomimetics for Targeted Drug Delivery

“…Importantly, the cyclo[DKP-RGD] 1 and cyclo[DKP-isoDGR] 3 (Figure 1) are selective integrin α v β 3 ligands with low nanomolar affinity. [24,25] Functionalized analogues 2 and 4 have been conjugated to different anticancer drugs, such as paclitaxel, [26][27][28][29][30][31] camptothecin [32] and α-amanitin [33] across different linkage systems including ester, ether, carbonate or carbamate bond, involving non-cleavable, disulfide, elastase cleavable NPV, and lysosomally cleavable ValÀ Ala, PheÀ Lys or GFLG linkers.…”