Abstract P5-03-02: The dynamic duo: A breast cancer-targeting nanoparticle loaded with a cytotoxic peptide as a treatment for metastatic disease

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.

Abstract P5-04-04: Cutting the ties that bind: Targeting chaperonin-containing T-complex (CCT) for therapeutic intervention in the treatment of advanced stage breast cancer

Metastatic disease is a principal cause of death from breast cancer. This is due in part to the development of resistance to current therapeutics and the often debilitating side effects that impair quality of life. The challenge is to therapeutically target an essential physiological function of cancer cells not found in normal, non-transformed cells. To this end, we discovered CT20p, a therapeutic peptide that causes cancer-specific death in human breast tumor cells and tumor regression in xenograft models of breast cancer. Using a proteomics approach, we found that CT20p directly binds to multiple subunits of a type II chaperonin called chaperonin containing T-complex or CCT. CCT forms a large macromolecular complex composed of 8 subunits (CCTα, CCTβ, CCTγ, CCTδ, CCTϵ, CCTζ, CCTη, CCTω). Each subunit contains an ATP binding site as well as substrate binding sites. Inhibition of CCT by CT20p depletes the pool of native actin and tubulin (obligate clients of CCT), impairing the polymerization of cytoskeletal elements needed to support cell adhesion and motility. As a result cancer cells lose the ability to migrate and die from loss of substrate survival signals. We found that expression levels of CCT varied among different triple negative breast cancer (TNBC) cell lines, with the highest expression occurring in those of the mesenchymal stem-like (MSL) subtype with metastatic potential. Lowest levels of CCT were found in normal breast epithelial cells. Sensitivity to killing by CT20p thus correlated with levels of CCT, with cancer cells expressing high amounts of CCT being the most susceptible. Using tissue microarrays (TMAs) of breast cancer progression, we developed an immunohistochemistry staining procedure for CCTβ. Results were interpreted on a scale of 1 to 4 (with 4 being the strongest staining). CCTβ expression was statistically higher in invasive ductal carcinoma (IDC) as compared to normal and cancer adjacent tissue (CAT) (p<0.0001). Within the types of IDC, CCTβ was highest in tumors that exceeded 5 cm across (T3), grew in chest wall or skin and in inflammatory breast cancer (T4) (p<0.05). Examining CCTβ levels in different molecular types showed little correlation with estrogen receptor (ER) positivity but strong correlation with ER and progesterone receptor (PR) positivity or PR alone (p>0.001). Statistical correlations were also observed with Her2 positivity (p>0.05). However, no statistically significant correlations were observed with TNBC tissues, with CCTβ staining ranging from the strongest staining (4) to lowest (1). These results are similar to that observed with the TNBC cell lines and indicate that CCT expression may reflect the heterogeneity of TNBC. These results suggest that CCT is a promising target for therapeutic intervention due to its increased expression in advanced stage breast cancer, independence of molecular identity and dependence by cancer cells to support essential cytoskeletal changes associated with the metastatic stem-like phenotype.

Citation Format: Khaled AS, Vishnubhotla P, Khaled AR, Bassiouni R. Cutting the ties that bind: Targeting chaperonin-containing T-complex (CCT) for therapeutic intervention in the treatment of advanced stage breast cancer. [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 P5-04-04.

Abstract P6-04-13: Preclinical testing using a novel CT20p peptide-nanoparticle combination in breast cancer

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.

A comparison of DXA and CT based methods for estimating the strength of the femoral neck in post-menopausal women

The study goal was to compare simple two-dimensional (2D) analyses of bone strength using dual energy x-ray absorptiometry (DXA) data to more sophisticated three-dimensional (3D) finite element analyses using quantitative computed tomography (QCT) data. DXA- and QCT-derived femoral neck geometry, simple strength indices, and strength estimates were well correlated.

INTRODUCTION

Simple 2D analyses of bone strength can be done with DXA data and applied to large data sets. We compared 2D analyses to 3D finite element analyses (FEA) based on QCT data.

METHODS

Two hundred thirteen women participating in the Study of Women's Health Across the Nation (SWAN) received hip DXA and QCT scans. DXA BMD and femoral neck diameter and axis length were used to estimate geometry for composite bending (BSI) and compressive strength (CSI) indices. These and comparable indices computed by Hip Structure Analysis (HSA) on the same DXA data were compared to indices using QCT geometry. Simple 2D engineering simulations of a fall impacting on the greater trochanter were generated using HSA and QCT femoral neck geometry; these estimates were benchmarked to a 3D FEA of fall impact.

RESULTS

DXA-derived CSI and BSI computed from BMD and by HSA correlated well with each other (R=0.92 and 0.70) and with QCT-derived indices (R=0.83-0.85 and 0.65-0.72). The 2D strength estimate using HSA geometry correlated well with that from QCT (R=0.76) and with the 3D FEA estimate (R=0.56).

CONCLUSIONS

Femoral neck geometry computed by HSA from DXA data corresponds well enough to that from QCT for an analysis of load stress in the larger SWAN data set. Geometry derived from BMD data performed nearly as well. Proximal femur breaking strength estimated from 2D DXA data is not as well correlated with that derived by a 3D FEA using QCT data.