BACKGROUND: The marked difference in metabolism observed between tumor and normal cells could contribute to the development of invasive and metastatic forms of breast cancer. The problem is that while patients diagnosed with invasive forms of breast cancer may be initially responsive to treatment, a significant number develop relapsing and even metastatic disease. There is a critical unmet need to develop new therapeutic approaches for patients diagnosed with invasive forms of breast cancer that are effective given the unique metabolism of tumor cells. METHODS: We examined the cytotoxic properties of a novel peptide, CT20p, derived from the C-terminus of Bax. For delivery to cells, the amphipathic nature of CT20p allowed it to be encapsulated in polymeric nanoparticles (NPs). NPs were made using aliphatic hyperbranched polyester (HBPE) that incorporated surface carboxylic groups and interior hydrophobic cavities for encapsulation of CT20p. To examine the cytotoxic potential and targeting capacity of CT20p-HBPE-NPs, we treated MDA-MB-231 breast cancer cells and MCF-10A breast epithelial cells with the peptide-nanoparticle combination and measured changes in mitochondrial function, cell metabolism and induction of apoptotic and non-apoptotic cell death. The ability of CT20p-NP-HBPE to cause tumor regression was examined by subcutaneously implanting MDA-MB-231 cells in nude mice. RESULTS: Initial studies showed that CT20p caused the release of calcein from mitochondrial-like lipid vesicles, without disrupting vesicle integrity, and, when expressed as a fusion protein in cells, localized to mitochondria. While the peptide alone had little effect upon intact cells, likely not penetrating the plasma membrane, when encapsulated and delivered by nanoparticles, CT20p-HBPE-NPs proved an effective killer of breast cancer cells. CT20p-HBPE-NPs initiated non-apoptotic cell death within 3 hours of treatment by targeting mitochondria and deregulating cellular metabolism. Nanoparticles alone or nanoparticles encapsulating a control peptide had minimal effects. The cytotoxicity of CT20p-HPBE-NPs was most pronounced in breast cancer cells, sparing normal, epithelial cells. In implanted breast tumors, CT20p-HBPE-NPs accumulated in tumors within 24 hours and reduced tumor burden by 50-80%. CONCLUSION: These results reveal the innovative features of CT20p that allow nanoparticle-mediated delivery to tumors and the potential application in combination therapies that target the unique metabolism of cancer cells. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-04-13.

Metastatic breast cancer is a uniformly fatal disease with a 5-year survival rate of 15 percent. To date there are no effective approaches for targeted therapy. To develop a treatment for metastatic cancer, our group discovered a novel cytotoxic peptide, CT20p, and developed a nanotechnology-based platform to deliver and concentrate CT20p in breast tumors. CT20p was derived from Bax, a member of the Bcl-2 family. Unlike the parent protein, CT20p does not cause apoptosis and its cytotoxicity is independent of caspases and Bcl-2 overexpression. Rather, the intracellular target of CT20p is a protein called chaperonin-containing T-complex (CCT), which is required for the folding of actin and tubulin into their native forms. Inhibition of CCT activity by CT20p, indicated by decreased F-actin and tubulin, impaired the polymerization of microfilaments and microtubules, causing loss of cell migration and adhesion that promoted breast cancer cell death. In contrast, normal, non-transformed cells were resistant to the cytotoxicity of CT20p. On its own, CT20p is not membrane-permeable. To deliver the peptide to cells, we used nanoparticles formed with a novel aliphatic hyperbranched polyester polymer (HBPE-NPs). The surface of HBPE-NPs retains carboxylic acid groups for labeling of targeting ligands to enable accumulation in tumors. To concentrate on breast cancer, we functionalized the HBPE-NPs with either folate (FOL) or glutamate (GLU), which target the folate receptor (FR) or the metabotropic glutamate receptor (GRM-1) respectively. FR and GRM-2 are essential metabolic components that are highly expressed in solid tumors like breast cancer. In vitro targeting studies using triple negative breast cancer cell (TNBC) lines established that folate FOL or GLU-HBPE-NPs loaded with fluorescent dyes were readily up taken at high efficiency by TNBC cells. HBPE-NPs also contain unique hydrophobic cavities especially suited for encapsulating CT20p. We found that once the CT20p-HBPE-NPs were taken up by cancer cells, the peptide was released inside cells under acidic conditions (e.g. endosomes) and directly interacted with its intracellular target, CCT. Studies using primary cells derived from human breast tumors confirmed the targeted uptake of HBPE-NPs as well as demonstrated the cancer-specific cytotoxicity of CT20p. We treated a murine TNBC xenograft model with nanomolar amounts of FOL-CT20p-HBPE-NPs and achieved 100% regression of established tumors as well as prevented tumor growth. These studies indicated that CT20p is a potent and specific anti-cancer agent due to its inhibition of CCT, an essential molecular complex highly expressed in cancer cells, and that the peptide can be efficiently delivered to tumor sites using HBPE-NPs decorated with ligands to receptors, such FR or GRM-1, found on tumor cells. Citation Format: Vishnubhotla P, Khaled AR, Khaled AS, Perez JM, Bassiouni R, Flores O, Nierenberg D. The dynamic duo: A breast cancer-targeting nanoparticle loaded with a cytotoxic peptide as a treatment for metastatic disease. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-03-02.