Synthesis and in vitro anti-tumor activity of novel HPMA copolymer-drug conjugates with potential cell surface targeting property for carcinoma cells

In several groups of malignant tumors including head and neck tumors, a protein named Hsp47/CBP2 leaked from the cell was expressed on the tumor cell surface. Several synthetic peptides have been identified as effective ligands for binding to Hsp47/CBP2. This study has focused on the synthesis and in vitro characterization of a targeting delivery system of 5-fluorouracil (5-FU) to human head and neck squamous cell carcinoma (HNSCC) in order to improve anti-cancer efficacy and reduce dose-limiting toxicity of 5-FU. An N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer, with Hsp47/CBP2 binding peptide sequence (namely WHYPWFQNWAMA) as a targeting ligand, was synthesized by a novel and simplified synthetic route. Under the controlled synthetic conditions, 1,3-dimethylol-5-FU, derived from 5-FU, was attached to the HPMA copolymer backbone via the lysosomally degradable GFLG linker, while the WHYPWFQNWAMA was conjugated via a non-degradable Gly-Gly (GG) linker. A control polymer without targeting moiety was also synthesized (P-FU). The in vitro cytotoxicity, internalization and apoptosis assays of the polymeric conjugates were evaluated. The characteristic apoptotic morphological changes were also assessed. Compared to 5-FU and P-FU, the HPMA copolymer containing the Hsp47/CBP2 binding peptide (P-FU-peptide) exhibited the highest cytotoxic efficacy to cell line of human head and neck squamous cell carcinoma (p < 0.05) and was internalized much faster than P-FU, especially after being incubated for 30 min. Both of the morphology and apoptosis analyses demonstrated that the treatment of P-FU-peptide resulted in more apoptotic and necrotic induction of tumor cells than P-FU. Meanwhile, the rate of apoptosis induced by P-FU-peptide was higher than that of necrosis. In summary, the HPMA copolymer-Hsp47/CBP2 binding peptide conjugates showed a promising future for the treatment of HNSCC with improved efficacy.