Antitumor activity of a membrane lytic peptide cyclized with a linker sensitive to membrane type 1-matrix metalloproteinase

Membrane lytic peptides are a novel class of anticancer agents that have the potential to overcome drug resistance. The limited selectivity against cancer cells, however, presents a major hurdle for the application. We aim to exploit the proteolytic activity of tumor-associated matrix metalloproteinases (MMP) to mediate the cytotoxicity of these peptides. We designed a membrane lytic peptide cyclized with a linker cleavable by membrane type 1-MMP (MT1-MMP). We showed that the cyclic peptide could be restored to the linear state on MT1-MMP digestion, and it preferentially killed MMP-overexpressing cells above a threshold concentration. Circular dichroism indicated that cyclization resulted in a more rigid structure, making it more difficult for the lytic peptide to transit from random coil to alpha-helix in a membrane-mimicking environment. Selective membrane activity of the cyclic peptide was shown by comparing cytotoxicity results on RBC and two human breast cancer cell lines of different malignancy and MT1-MMP expression: highly invasive MDA-MB-435 and noninvasive MCF-7. Above a concentration of 5 mu mol/L, suppressed activity to MCF-7 and RBC was observed, whereas the toxicity against MDA-MB-435 was maintained. MMP inhibition experiments further showed that the membrane-lysing activity was enzyme dependent.