Polymer-dual drug conjugates targeted to HER2 overexpressing breast cancer

Abstract

Current FDA approved treatments for Human epidermal growth factor receptor type 2 (HER2) overexpressing breast cancers include a humanized monoclonal antibody, Trastuzumab (TRZ) and small molecule tyrosine kinase inhibitors (TKIs). However, TRZ develops rapid drug resistance while TKIs and their metabolites cause hepatotoxicity due to nonselective distribution. To overcome these limitations of each agent it is essential to develop novel strategies to increase efficacy and reduce toxicity. This dissertation evaluates the potential of using conjugates of water soluble, N-(2-hydroxypropylmethacrylamide) (HPMA) copolymers with TRZ and TKI for targeted delivery of dual drugs to HER2 overexpressing tumors. Comb-like random and star-like semitelechelic (ST) HPMA copolymers (PHPMA) and their conjugates to TRZ were synthesized and characterized. Star-like conjugate system showed narrower size distribution, more potent and prolonged anticancer activity in HER2 overexpressing breast cancer cell lines (BT-474 and SK-BR-3) compared to comb-like conjugates. Therefore, the star-like conjugate system was selected to additionally conjugate a second anticancer agent for targeted combination drug delivery. Also fluorescence microscopy studies with Alexa488 labeled star-like conjugate demonstrated cellular internalization. The combination drug delivery system was successfully synthesized by covalently conjugating PKI166 (a model TKI) and TRZ to ST-PHPMA backbone. PKI166 release from the conjugate was observed in the presence of lysosomal enzyme cathepsin B. The polymer dual-drugs conjugate showed synergistic anticancer activity on HER2 overexpressing BT-474 and SK-BR-3 cells. The conjugate also exhibited prolonged anticancer activity up to 72 h by inhibiting the phosphorylation of MAPK and Akt when compared to free TRZ and free PKI166. The in vivo antitumor activity of the conjugates was evaluated in a pilot study in mice bearing SK-BR-3 tumor xenografts. The conjugates showed concentration dependent and synergistic antitumor activity over a 3 weeks treatment. The conjugates also showed no apparent indications of toxicity in non-tumor bearing mice. The results demonstrate the potential of HPMA copolymer based dual mode of action drugs conjugate as a novel combination drug delivery system that could i) prolong anticancer efficacy, ii) synergistically enhance anticancer effects of the drug combination and iii) reduce non-specific toxicity by way of cancer cell specific targeting and synergistic activity.