(448e) Lytic Peptide-Polymer Conjugate with Enhanced Potency and Sensitivity to Tumor-Associated Protease

Lytic peptides are a group of cationic peptides capable of lysing cell membranes with quick action. They widely exist as natural antibiotic, and recently are being explored as anticancer agents for the unique property in overcoming drug resistance. However, there remain two major obstacles: 1) Relatively high local concentration and minimal length are required for effectiveness; 2) The lack of selectivity for cancer cells may cause serious side effect. To tackle these problems, we synthesized a polyvalent peptide-polymer conjugate, which significantly enhanced the anticancer potency of a short lytic peptide. The conjugate was further engineered with selectivity for cancer cells by targeting a tumor-associated protease.

Multiple copies of a hexopeptide KWKWKW ((KW)₃ for short) of mild membrane lysing activity were conjugated to 70kDa dextran with “click” chemistry to yield the polyvalent conjugate Dex-(KW)₃. All the reactions were monitored with NMR. The peptide loading was measured to be 0.05 mmol/g. The zeta potential of conjugate in pH 7.4 buffer was about 8 mV.The anticancer activity of polyvalent Dex-(KW)₃ was examined and compared with free (KW)₃ peptide. The potency of conjugate was significantly enhanced, with LC₅₀ lower by three orders of magnitude than free peptide in two different cancer cell lines MCF-7 and PC-3. The same trend was observed in multi-drug resistant cancer cell line MES-SA/Dx5, suggesting the potential in overcoming MDR. In isothermal titration, the polyvalent conjugate showed stronger capability of membrane binding and disturbing than free peptide, which are attributed to the increased order and elevated local concentration of lytic peptides by polyvalent design.

To obtain a tumor targeted conjugate, an anionic quencher was fused to lytic peptide via a linker labile to MT1-MMP, a membrane protease actively involved in cancer progression. Since the positive charge mediates the first step of membrane binding and therefore critical to the activity of lytic peptides, the activity of conjugate should be neutralized until the removal of quenchers by MT1-MMP in tumor region. Preliminary data have shown the adjacent negative charge were capable of suppressing the cytotoxicity of conjugate. The protease specificity is being examined.

Novel lytic peptide-polymer conjugates with enhanced potency, tumor-targeted activity and improved pharmacokinetic properties were constructed. The work should contribute to the further development of an emerging class of promising anticancer agents.

REFERENCES

1. J. Zhong, Y. Chau, Bioconjugate Chemistry, 21, 2055-2064, 2010.