Imaging the delivery of drug-loaded, iron-stabilized micelles

Nanoparticle drug carriers hold potential to improve current cancer therapy by delivering payload to the tumor environment and decreasing toxic side effects. Challenges in nanotechnology drug delivery include plasma instability, site-specific delivery, and relevant biomarkers. We have developed a triblock polymer comprising a hydroxamic acid functionalized center block that chelates iron to form a stabilized micelle that physically entraps chemotherapeutic drugs in the hydrophobic core. The iron-imparted stability significantly improves the integrity of the micelle and extends circulation pharmacokinetics in plasma over that of free drug. Furthermore, the paramagnetic properties of the iron-crosslinking exhibits contrast in the tumors for imaging by magnetic resonance. Three separate nanoparticle formulations demonstrate improved anti-tumor efficacy in xenograft models and decreased toxicity. We report a stabilized polymer micelle that improves the tolerability and efficacy of chemotherapeutic drugs, and holds potential for non-invasive MRI to image drug delivery and deposition in the tumor.

Abstract 596: ABCG2 is upregulated in SN-38 resistant colorectal cancer cells

Irinotecan, a member of the camptothecin chemotherapeutic drug family, is a first and second line therapy for patients with colorectal cancer. However, as with most chemotherapeutic therapies, patients’ tumors eventually develop drug resistance. Therefore, identifying mechanisms of chemotherapeutic resistance will allow for the development of additional molecular therapeutic targets. In this study SN-38, the highly insoluble active metabolite of irinotecan, was used to investigate corollary resistance to irinotecan. SN-38 resistant HT-29 cells were generated and compared to parental untreated HT-29 cells. Cells were characterized following treatment with either DMSO soulubilized SN-38 or IVECT encapsulated SN-38, a triblock copolymer micelle, in aqueous solution. The ATP-binding cassette transmembrane transporter protein, ABCG2, was found to have more than 40-fold expression in the SN-38 resistant HT-29 cells compared to the parental line. The increased expression of ABCG2 protein correlated with increased resistance to SN-38 in HT-29 cells and also with increased cell efflux. Cytotoxicity studies demonstrated that SN-38 resistant HT-29 cells were affected in a similar manner by IVECT polymer encapsulated SN-38 micelles and DMSO dissolved free SN-38. Cell cycle analysis showed that SN-38 resistant cells had an abrogated S phase arrest compared to parental cells. Cell treatment with free SN-38 was limited by its solubility in addition to DMSO toxicity. Further, IVECT polymer encapsulation improved SN-38 aqueous solubility allowing for increased concentration administration. Efflux proteins such as ABCG2 have been found to be upregulated in numerous types of cancers by several classes of chemotherapeutic drugs. Since transporter proteins have an important role in cell efflux, ABCG2 overexpression could serve as an additional target for pharmacological modulation. Finally, the increased solubility of SN-38 by IVECT polymer encapsulation allows for potential in vivo clinical applications of SN-38, a molecule that is 1000 times more active than its prodrug irinotecan.

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 596. doi:10.1158/1538-7445.AM2011-596

Abstract 4453: Development of a crosslinked, daunorubicin-loaded micelle with superior pharmacokinetics compared to free daunorubicin and with tunable stability

Chemotherapeutic drugs are widely used for the treatment of cancer; however, use of these drugs is often associated with patient toxicity and poor delivery to the tumor. Poor delivery to the tumor can be attributed, in part, to rapid elimination of the drug by the reticuloendothelial system (RES), resulting in short circulation times. Nanoscopic drug carriers offer a promising approach to achieving improved delivery of chemotherapeutic drugs to tumors due to their size and ability to avoid RES uptake, but conventional nanoparticles are not stable in complex biological environments. This instability has resulted in little clinical success of conventional nanoparticles to date. Intezyne's IVECTTM Method, which utilizes triblock copolymers to form micelles that are stabilized to dilution in complex media, was used to encapsulate daunorubicin. The resulting daunorubicin loaded micelle's size was determined to be 60 nm by dynamic light scattering analysis. To generate stable micelles, iron (II) chloride was used to form pH-reversible iron-acetate crosslinking bonds in the outer core of the micelle. Release of daunorubicin from stabilized micelles was shown to be pH-dependent through the use of drug-release dialysis assays. Cytotoxicity studies in cancer cell lines revealed that the IC50 values of daunorubicin micelles were similar to free daunorubicin. In vivo, the AUC of daunorubicin released from stabilized daunorubicin micelles was up to 60-fold higher compared to free daunorubicin. Furthermore, the pharmacokinetic parameters were proportional to the iron (II) concentrations used for crosslinking. Repeated injections of daunorubicin micelles in rats showed little to no change in the pharmacokinetic parameters and did not exhibit accelerated blood clearance based on rat IgM ELISA measurements. These data report the development of a stabilized daunorubicin micelle that exhibits pH-dependent release and superior pharmacokinetics based on tunable crosslinking chemistry.

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 4453. doi:10.1158/1538-7445.AM2011-4453