| The main hurdle to efficacious treatment of diseases such as ovarian cancer with low molecular weight chemotherapeutics is their rapid clearance from the body and indiscriminate uptake into normal tissues, which prevents their accumulation in the tumor. When suitable means are harnessed to aid drug localization to the tumor, the development of multidrug resistance or lack of specificity diminishes intracellular drug concentration at its subcellular target, rendering it ineffective.;This research addresses these issues by combining two potent moieties: water-soluble polymers [such as those based on N-(2-hydroxypropyl) methacrylamide (HPMA)] and cell-penetrating peptides (such as the Tat peptide), to yield drug delivery carriers with superior cellular as well as subcellular targeting capabilities. HPMA copolymers will lead to an altered biodistribution of the drug and promote its preferential accumulation in the tumor. As macromolecules are lysosomotropic, a cell-penetrating peptide needs to be incorporated to facilitate vesicular escape and assist the drug in reaching its subcellular destination.;In the first study, the subcellular distribution of HPMA copolymer-Tat conjugates in A2780 human ovarian carcinoma cells was determined to be endocytotic and cytoplasmic, with significant affinity for the plasma membrane. In the second study, HPMA copolymer-Tat conjugates bearing the photosensitizer Mce 6 bound to the polymer backbone via a lysosomally degradable glycylphenylalanylleucylglycine (GFLG) spacer or a disulfide spacer were evaluated for photodynamic therapy. HPMA copolymer-Mce6-Tat conjugates exhibited greater cytotoxicities as compared to control polymers. Further, the mode of cell death shifted from apoptosis to necrosis in a concentration dependent manner. In the third study, the mechanism of internalization of the HPMA copolymer-Tat conjugate was confirmed as macropinocytosis. Based on these findings, HPMA copolymers with the Tat peptide bound to the polymer backbone via either the GFLG or nondegradable glycylglycine linkers were investigated as carriers for antisense oligonucleotide (ASON) delivery. The data suggested that these carriers improve the intracellular targeting of ASON.;This investigation imparts a basic understanding of the mechanism of uptake of HPMA copolymer-Tat conjugates and illustrates their potential as carriers for enhancing intracellular targeting and delivery of low MW (Mce 6) and high MW (ASON) therapeutics. |
