Peptide-Targeted Polyglutamic Acid Doxorubicin Conjugates for the Treatment of α_vβ₆-Positive Cancers

Abstract

Most chemotherapeutics exert their effects on tumor cells as well as their healthy counterparts, resulting in dose limiting side effects. Cell-specific delivery of therapeutics can increase the therapeutic window for treatment by maintaining the therapeutic efficacy while decreasing the untoward side effects. We have previously identified a peptide, named H2009.1, which binds to the integrin αvβ6. Here, we report the synthesis of a peptide targeted polyglutamic acid polymer in which the high affinity αvβ6-specific tetrameric H2009.1 peptide is incorporated via a thioether at the N-terminus of a 15 amino acid polymer of glutamic acid. Doxorubicin is incorporated into the polymer via an acid-labile hydrazone bond. Payloads of four doxorubicin molecules per targeting agent are achieved. The drug is released at pH 4.0 and 5.6 but the conjugate is stable at pH 7.0. The conjugate is selectively internalized into αvβ6 positive cells as witnessed by flow cytometric analysis and fluorescent microscopy. Cellular uptake is mediated by the H2009.1 peptide, as no internalization of the doxorubicin-PG polymer is observed when it is conjugated to a scrambled sequence control peptide. Importantly, the conjugate is more cytotoxic toward a targeted cell than a cell line that does not express the integrin.

Tumor Targeting via Integrin Ligands

“…For instance, the high affinity αvβ6-specific 20-mer peptide H2009.1 (75) was conjugated as a tetramer to a poly-glutamic acid polymer carrying DOX, and was shown to specifically target αvβ6-expressing cells in vitro (76). In another work, the selectivity of this peptide toward αvβ6 was exploited to guide fluorescent quantum dots to lung adenocarcinoma cell line H2009 in vitro (68).…”

Carbon-Based Nanomaterials for Targeted Drug Delivery and Imaging

“…Primarily, the polymeric conjugates exert their effect through enhanced permeability and retention, owing to their stealth macromolecular structure, which enables them to selectively accumulate in tumor tissue. Along with this, pathophysiologic factors at the tumor site, namely, enhanced permeability, poor venous drainage, acidic pH, and relatively high temperature enhance the pharmacological profi le of PDC [ 35 ]. Conjugating CNTs with other moieties is a signifi cant challenge owing to lack of homogeneity of dispersions and subsequent characterization of conjugates, but nevertheless are being explored for improvement in the cancer therapy.…”

Peptide‐mediated targeted drug delivery

“…This indicates that the structural properties of the molecules have important influence in final drug efficacy. 42 Interestingly, cytotoxicity of nontargeting DOX-HPMA copolymer was increased by 150-fold after conjugation of high affinity E-selectin binding peptide (Esbp) to DOX-HPMA in human immortalized vascular endothelial cells. DOX was conjugated to one end of HPMA using hydrazide linkage while cysteine-containing Esbp (CDITWDQLWDLMK) was conjugated to the other end of HPMA using amide linkage.…”