Polymeric Combination Therapy Based on Host Defence Peptides Targeting Cancer Cells

摘要

Chemotherapy combinations have being the mainstays in the treatment of most types of cancer in the past half century [1]. Multi-drug therapies may circumvent mechanisms of tumour resistance to single agents and potentially provide greater therapy benefits if the selected agents act synergistically in combination. The aim of the project is to develop a multi component drug delivery system by combining a classical cytotoxic drug, doxorubicin (DOX), and a host defence peptide (P18) to a polymeric carrier [2]. A polymer of ethylene glycol (PEG) was chosen as the carrier because of its non-toxic and non-immunogenic properties. Pegylation of a peptide can also improve its pharmacokinetic properties and enhance its accumulation in tumour tissue by the "enhanced permeability and retention (EPR) effect". A method for the reversible pegylation of P18 (H-kwkflkklpflkhalkkf-NHi), a hybrid sequence of cecropin A (1-8) and magainin 2 (1-12) with known anticancer activity and its conjugation and/or combination with a classical anticancer agent was originally developed. In this approach, the P18 sequence assembled from D-amino acids is elongated at its N-tenninus by a short peptide linker Gly-L-Phe-L-Leu-Gly. This GFLG sequence is a substrate of the endo-lysosomal cathepsin B enzyme, a protease over-expressed in cancer cells. The N-terminal amino group of this linker is amidated with a bi-functional PEG (H2N-PEG-COOH) in which the amino group is modified with a hydrazide linker for conjugation of doxorubicin via a hydrazone bond. The latter is stable at neutral pH, but can be hydrolysed in the lysosome at pH < 4.5. Pegylation of doxorubicin can be used to prevent its toxicity and target its delivery to malignant cells by the EPR effect. Following passive accumulation in the tumour and cellular uptake by endocytosis, it is proposed that release of the anticancer peptide and classical agent could occur in the lysosome of cancer cells, thereby allowing their combined and selective delivery. While the synthetic feasibility study for the production of these conjugates was successfully completed, the linear multi-step synthetic strategy implemented was not amenable to convenient scale-up. Furthermore, the design of these polymeric prodrugs limit their application to a 1:1 doxorubicin-peptide ratio, which might not be adequate due to the significant difference in the anticancer activities of these two candidates (nanomolar range for doxorubicin, micromolar range for P18). An alternative approach based on the combination of individually pegylated peptide and doxorubicin was therefore developed to study their potential synergistic/additive effects.