Temozolomide Delivery to Tumor Cells by a Multifunctional Nano Vehicle Based on Poly(β-L-malic acid)
Authors: Muungo Lungwani 
Published: June 2020

Malignant gliomas are the most common (60–70%) of all CNS/brain tumors. Annually, thereare approximately five cases of malignant gliomas per 100,000 people, and over 14,000 newcases are diagnosed each year in the United States (1,2). Surgery remains the standard therapyfor primary brain tumors. Although surgery may be combined with radiation therapy and/orfollowed with chemotherapy to destroy remaining cancer cells, patients still have a poorsurvival (3-5). In recent years, Temozolomide (TMZ, Temodar®), a prodrug which undergoesspontaneous conversion to the active alkylating agent (Charts 1 and 2) has emerged as a potentchemotherapeutic agent (6). In combination with radiotherapy, it has been shown tosubstantially increase median survival compared with radiotherapy alone (7). However, TMZhas considerable toxicity, which prevents therapeutic dosage increase. Moreover, anotherlimiting factor of TMZ treatment is tumor resistance to the drug (8-10).Recently, efforts have been made to develop delivery systems for conventionalchemotherapeutic drugs. Polymer-based delivery systems are less immunogenic than proteinbased,e.g. viral vectors, and allow repetitive treatments without acute or chronic host immuneresponse (11-14). Compared with most chemotherapeutic molecules, macromolecules offerseveral advantages, including tumor targeting, increased solubility, enhanced accumulation insolid tumors, decreased general toxicity, increased maximum tolerated doses, circumventionof multidrug resistance and enhanced apoptosis induction (15,16). Nanodrugs can selectivelyaccumulate in tumor through a passive targeting mechanism known as enhanced permeabilityand retention (EPR) effect (17-19). Targeting efficiency is substantially enhanced bycombining nanodrugs with specific antibodies that allow targeting by binding to antigens onthe tumor cell surface (20-22).To avoid systemic side effects by orally administered TMZ, targeting to brain tumor would behighly important. Recently, Brem (23) and Akbar (24) have administered a solid mixture ofbiodegradable polymer and TMZ directly into the brain tumor in animal models. The drug wasprogressively released during degradation of the embedding polymer material and significantlyprolonged the survival time of experimental animals. These methods are invasive, and the drugis applied at the time of surgery. Moreover, gliomas are tumors with the ability to developrecurrences; thus, systemic and targeted delivery of TMZ would be a more beneficial treatmentapproach.Following I.V. administration, we have delivered antisense oligonucleotides specifically tobrain tumor using the targeted nanoconjugate delivery system, Polycefin (21). Thenanoconjugate platform, poly(β-L-malic acid) (PMLA), is biodegradable, non-toxic and nonimmunogenic,containing numerous pendant carboxyl groups suitable for the covalentattachment of prodrugs and other useful molecules. For the delivery into the cytoplasm ofrecipient glioma cells, we conjugated TMZ in its hydrazide form with PMLA along with antitransferrinreceptor (TfR) monoclonal antibody (mAb) for tumor targeting by receptormediatedendocytosis (21) and pH-sensitive trileucine (LLL) for disruption of endosomalmembranes.