Abstract 378: Engineering Nanoplatforms based on hydrophobic derivatives of Poly(β, L-malic acid) for tumor drug delivery
Authors: Portilla-Arias Jose , Patil Rameshwar , Ding Hui , Muñoz-Guerra Sebastian , Black Keith L. , Ljubimova Julia Y. , Holler Eggehard 
Published: June 2012

Abstract
A new class of polymalic acid (PMLA) nanoconjugates is presented having built in membranolytic activity. It can be used for cytoplasmic drug delivery to brain and breast cancer. The polymer platform contains numerous pendant carboxyl groups for attachment of multiple pro-drugs and tissue/cell targeting molecules. (Poly)peptides, nucleotides and chemotherapeutic drugs can be immobilized on the platform and activated in the target cell while increasing specificity and reducing systemic toxicity.
Poly(β, L-malic acid) of microbial origin was methylated by controlled esterification with diazomethane. Methyl-PMLA was characterized by absolute molecular weight (Mw), size and ζ potential. Degradation in human plasma at 37 °C was followed by chloroform extraction and HPLC analysis. Membranolytic activity was measured using artificial liposomes. Cytotoxicity and cellular uptake were investigated for primary glioma cell lines U-87 MG, T98G and invasive breast carcinoma cell lines MDA-MB-231, MDA-MB-468.
Results: Methylated PMLA was prepared in a simple method with high yields. PMLA methylated at 25% and 50% of pendant carboxyl groups (coPMLA-Me25H75 and coPMLA-Me50H50) and absolute molecular weights of 32,600 Da and 33,100 Da, hydrodynamic diameters of 3.0 nm and 5.2 nm and zeta potentials of -15 mV and -8.25 mV disrupted the membranes of liposomes at pH 5.0 and pH 7.5 at concentrations exceeding 0.05 mg/mL. Copolymers were soluble in both PBS (half life of 40h) and human plasma (half life of 15h) but showed a tendency to aggregate at high levels of methylation. Fluorescent-labeled copolymers were internalized into MDA-MB-231 breast cancer cells and its efficiency increased with the degree of methylation. Viability of cultured brain and breast cancer cell lines indicated moderate toxicity that increased with the degree of methylation.
Conclusions: The new copolymers coPMLA-Me25H75 and coPMLA-Me50H50 are easily prepared and are active in membrane penetration and cellular uptake. They have half lives which would allow delivery of drugs to recipient cells, they are biodegradable and, as their parent compound PMLA, nontoxic and nonimmunogenic. The copolymers are endowed with membrane disrupting/penetrating activities which allow them to deliver drugs directly to intracellular targets by passing the plasma membrane. By raising the degree of methylation above 50%, the copolymers become insoluble and can be used as drug delivering nanoparticles. These results are in support of poly(β, L-malic acid) as a highly versatile material that can be used as a platform for drug delivery systems to treat cancer.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 378. doi:10.1158/1538-7445.AM2011-378