Enhanced Tumor Targeting and Antitumor Activity of Methylated β-Cyclodextrin-Threaded Polyrotaxanes by Conjugating Cyclic RGD Peptides

We previously reported that acid-degradable methylated beta-cyclodextrins (Me-beta-CDs)-threaded polyrotaxanes (Me-PRXs) can induce autophagic cell death through endoplasmic reticulum (ER) stress-related autophagy, even in apoptosis-resistant cells. Hence, Me-PRXs show great potential as anticancer therapeutics. In this study, peptide-supermolecule conjugates were designed to achieve the targeted delivery of Me-PRX to malignant tumors. Arg-Gly-Asp peptides are well-known binding motifs of integrin alpha v beta 3, which is overexpressed on angiogenic sites and many malignant tumors. The tumor-targeted cyclic Arg-Gly-Asp (cRGD) peptide was orthogonally post-modified to Me-PRX via click chemistry. Surface plasmon resonance (SPR) results indicated that cRGD-Me-PRX strongly binds to integrin alpha v beta 3, whereas non-targeted cyclic Arg-Ala-Glu (cRGE) peptide conjugated to Me-PRX (cRGE-Me-PRX) failed to interact with integrins alpha v beta 3. In vitro, cRGD-Me-PRX demonstrated enhanced cellular internalization and antitumor activity in 4T1 cells than that of unmodified Me-PRX and non-targeted cRGE-Me-PRX, due to its ability to recognize integrin alpha v beta 3. Furthermore, cRGD-Me-PRX accumulated effectively in tumors, leading to antitumor effects, and exhibited excellent biocompatibility and safety in vivo. Therefore, cRGD conjugation to enhance selectivity for integrin alpha v beta 3-positive cancer cells is a promising design strategy for Me-PRXs in antitumor therapy.