Development of Targeted, Enzyme-Activated, Dendrimer-Drug Nano-Conjugates for Hepatic Cancer Therapy

Primary liver cancer is the 4th most common malignancy worldwide, accounting for >600,000 deaths/year globally. Loco-regional chemotherapy fails to deliver anticancer drugs specifically to hepatic cancer cells resulting in low anticancer activity and severe toxicities. This dissertation describes development of targeted nanoparticles that can deliver and release chemotherapeutic agents selectively to the cytoplasm of hepatic cancer cells. Specifically, we conjugate doxorubicin (DOX) chemotherapeutic molecules to generation 5 (G5) poly(amidoamine) dendrimers via aromatic azo-linkers to prepare G5-DOX conjugates. We engineered these azo-linkers to be cleaved by liver-specific azoreductase enzymes, with tunable DOX release achieved by modulating the linker's enzyme affinity via increased azo-bond electronegativity, indicated by decreasing Hammett values (a). We synthesized four G5-L(x)-DOX conjugates incorporating azolinkers LI -L4 with decreasing a values and evaluated their cleavage by human liver microsomal (HLM) enzymes, HepG2 hepatic cancer cell and rat cardiomyocyte S9 enzyme fractions, or control proteins. This resulted in selective cleavage of G5-L(x)-DOX by azoreductase enzymes with increased DOX release rates observed as azo-linker a value decreased, achieving 100% DOX release from G5-L4-DOX conjugates by HLM enzymes. We evaluated the anticancer activity of G5-L(x)-DOX towards hepatic cancer cells using a clonogenic cell survival assay. Results showed increased cytotoxicity of G5-L(x)-DOX which matched their DOX release rank order, reaching a similar IC50 for G5-L4-DOX and free DOX in HepG2 cells at equivalent drug concentrations. Hepatic cancer cell-specific delivery of G5 dendrimers was achieved by surface functionalization with N-acetylgalactosamine (NAcGal) sugars, resulting in binding and receptor-mediated endocytosis of G5-NAcGal by the liver-specific asialoglycoprotein receptor. Biodistribution of G5-NAcGal in liver-tumor bearing mice showed a 2-fold increase in tumor-specific carrier accumulation versus non-targeted dendrimers, while attachment of poly(ethylene glycol) (PEG) to the G5 surface limited carrier distribution to healthy liver tissue. This prompted synthesis of G5-PEG carriers displaying the targeting ligand at the PEG terminus, leading to selective carrier internalization into HepG2 cells while avoiding opsonization and subsequent uptake into liver macrophages and rat hepatocytes. By combining this targeting approach with tunable G5-DOX conjugates we expect to achieve specific delivery of free DOX to hepatic cancer cells for effective liver cancer therapy with minimal side effects.