Synthesis and Biological Evaluation of RGD and isoDGR-Monomethyl Auristatin Conjugates Targeting Integrin (V3)

This work reports the synthesis of a series of small molecule-drug conjugates containing the αVβ3-integrin ligand cyclo[DKP-RGD] or cyclo[DKP-isoDGR], a lysosomally cleavable Val-Ala (VA) linker or an "uncleavable" version devoid of this sequence, and monomethyl Auristatin E (MMAE) or F (MMAF) as cytotoxic agent. The conjugates were obtained via a straightforward synthetic scheme taking advantage of a copper-catalyzed azide-alkyne cycloaddition as key-step. The conjugates were tested for their binding affinity to the isolated αvβ3 receptor, and shown to retain nanomolar IC50 values, in the same range of the free ligands. The cytotoxic activity of the conjugates was evaluated in cell viability assays with αvβ3 integrin over-expressing human glioblastoma (U87) and human melanoma (M21) cells. The conjugates possess a markedly lower cytotoxic activity compared to the free drugs, which is consistent with an inefficient integrin-mediated internalization. In almost all cases the conjugates featuring isoDGR as integrin ligand exhibited higher potency than their RGD counterparts. In particular, cyclo[DKP-isoDGR]-VA-MMAE conjugate has low nanomolar IC50 values in cell viability assays with both cancer cell lines tested (U87: 11.50 ± 0.13 nM; M21: 6.94 ± 0.09 nM) and is therefore a promising candidate for in vivo experiments.

This work reports the synthesis of a series of small-molecule–drug conjugates containing the α V β 3 -integrin ligand cyclo[DKP-RGD] or cyclo[DKP-isoDGR], a lysosomally cleavable Val-Ala (VA) linker or an “uncleavable” version devoid of this sequence, and monomethyl auristatin E (MMAE) or F (MMAF) as the cytotoxic agent. The conjugates were obtained via a straightforward synthetic scheme taking advantage of a copper-catalyzed azide–alkyne cycloaddition as the key step. The conjugates were tested for their binding affinity for the isolated α v β 3 receptor and were shown to retain nanomolar IC 50 values, in the same range as those of the free ligands. The cytotoxic activity of the conjugates was evaluated in cell viability assays with α v β 3 integrin overexpressing human glioblastoma (U87) and human melanoma (M21) cells. The conjugates possess markedly lower cytotoxic activity than the free drugs, which is consistent with inefficient integrin-mediated internalization. In almost all cases the conjugates featuring isoDGR as integrin ligand exhibited higher potency than their RGD counterparts. In particular, the cyclo[DKP-isoDGR]-VA-MMAE conjugate has low nanomolar IC 50 values in cell viability assays with both cancer cell lines tested (U87: 11.50±0.13 nm; M21: 6.94±0.09 nm) and is therefore a promising candidate for in vivo experiments.