Design and Synthesis of an RGD Peptidomimetic-Paclitaxel Conjugate Targeting αvβ3 Integrin for Tumour-Directed Drug Delivery

Abstract

Abstract. A 1,2,3-triazole-based RGD peptidomimetic having nanomolar affinity for αvβ3 integrin was conjugated to the potent antimitotic paclitaxel via an oxime heterobifunctional linker. The resulting construct maintained nanomolar binding concentration to αvβ3 integrin and showed 11-fold selectivity in terms of cytotoxicity towards highly αvβ3 expressing U87MG cancer cells relative to non αvβ3 expressing MCF7 cells, indicating promising cancer cell targeting capacity. RGD, peptidomimetic, integrin, paclitaxel, click, cytotoxicity, cancer The efficacy of chemotherapeutic agents clinically used for the treatment of malignant tumours is generally limited by their non-specific toxicity against off-target cells, especially those characterised by a high proliferation rate, resulting in a reduced therapeutic index and serious side effects (e.g. alopecia, nausea, vomiting and immunosuppression). Several strategies have been developed over the years in order to overcome these problems and achieve a tumour-targeted delivery of cytotoxic agents. 1 An attractive approach is represented by hybrid compounds, containing a cytotoxic drug bound to a moiety that specifically identifies protein markers overexpressed on cancer cells. Thanks to the development of phage display technologies, several peptide sequences capable of recognising tumour markers have been discovered and extensively investigated as valuable tools for tumour-targeted delivery of chemotherapeutics. 1-2 RGD-containing peptides targeting αvβ3 integrin belong to this class of tumourhoming vectors. The overexpression of αvβ3 on solid tumours, along with its capacity to be internalised via endocytosis after binding of ligands such as RGD peptides, makes it an attractive target for tumour delivery of anticancer agents. 3 A number of cytotoxic drugs have been conjugated to tumour-homing peptides containing the RGD motif and the resulting constructs assessed in animal models. Several studies in this field provided experimental evidence that RGDbased strategies contribute to reduce the toxicity and augment the therapeutic window of existing chemotherapeutics. 1,4,5 Key words

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

“…Along a similar strategy, Zanda and colleagues [55] proposed the synthesis and in vitro evaluation of hybrid compound 20 (Scheme 6), where PTX was conjugated to a nonpeptidic RGD mimic ligand (depicted in red, Scheme 6) through robust oxime ligation. The triazole‐based peptidomimetic 15 , featuring nanomolar affinity toward the isolated α V β 3 integrin receptor, [56] was selected as the α V β 3 ‐targeting ligand, and was anchored to the remaining conjugate at its triazole core, based on molecular modeling studies that revealed its suitability for functionalization without presumably impacting on the integrin recognition capability.…”

5-Iodo-1H-1,2,3-triazoles as Versatile Building Blocks

“…The latter was linked to the triazole fragment via another bifunctional linker (orange), in which the terminal triple bond, in turn, was linked to the 5-iodotriazole by Sonogashira coupling. 109 The resulting hybrid maintained nanomolar binding concentration to  v  3 integrin and showed 11-fold selectivity in terms of cytotoxicity towards highly  v  3 expressing U87MG cancer cells relative to non  v  3 expressing MCF7 cells, indicating promising cancer cell targeting capacity.…”

A Brief Guide to Preparing a Peptide–Drug Conjugate

“…[59] Oxime/hydrazone ligation can be conducted both in aqueous and organic solvents, without metal catalysts; they generally show high selectivity and compatibility with other functional groups in PDCs chemistry. [60][61][62] Additionally, efficient oxime ligation variations have been reported at late stage of peptide synthesis (e. g., on histidine residues). [56] Oxime condensation is usually performed at pH 4.5-5.5, so that to catalyse the reaction by protonating the carbonyl oxygen, making the carbon more electrophilic.…”

“…Oxime/hydrazone ligation can be conducted both in aqueous and organic solvents, without metal catalysts; they generally show high selectivity and compatibility with other functional groups in PDCs chemistry [60‐62] . Additionally, efficient oxime ligation variations have been reported at late stage of peptide synthesis (e. g., on histidine residues) [56] …”