Bioinspired Membrane-Disruptive Macromolecules as Drug-Free Therapeutics

Membrane-disruptive, drug-free macromolecular therapeutics may help overcome cancer drug-resistance. Their inability to distinguish cancerous from normal cells, however, results in significant off-target toxicity. Note that the tumor has a slightly acidic microenvironment (pH 6.5-6.8) in contrast to the alkaline microenvironment in normal tissues (pH 7.4) and that host-defense peptides (HDPs) and their synthetic mimetics need to be net cationic to be membrane-disruptive. We herein endow polymer mimetics of HDPs with acid-triggered cationicity, to make them membrane-disruptive at only tumor pH. For these polymer mimetics, there exists a maximal threshold of chain length that determines whether the micelle of a mimetic inherits its pH-sensitive activity. Using the most and least active micelles as representatives, we find that their distinct potency in disrupting membranes arises because of their striking tendency to dissociate upon exposure to tumor pH. As expected, these micelles exhibit in vitro cytotoxicity profiles that correlate with their membrane-disruptive activity profiles. When administered intravenously, these micelles-irrespective of their distinct activity profiles-unanimously exhibit long systemic circulation as do PEGylated micelle nanoparticles, despite of their lacking stealth materials, owing to the zwitterionic nature of their surfaces at blood pH. Nevertheless, the pH-sensitive micelle achieves significantly higher tumor uptake and strikingly better therapeutic efficacy than its completely inactive analogue. More important, the pH-sensitive micelle exhibits undetectable off-target toxicity, owing to its pH-sensitivity. Clearly, making HDPs and their mimetics sensitive to tumor-characteristic cues (e.g., acidic pH) is efficient in minimizing their off-target toxicity, thereby offering membrane-disruptive, drug-free macromolecular therapeutics for fighting against cancer drug-resistance.