- New Predictors of Patient Survival after Neoadjuvant Chemotherapy
- Cytoskeletal Control of Mammary Epithelial Morphogenesis and Tumorigenesis
- Center of Excellence Highlights
- Legubicin, a Tumor-Activated Prodrug for Breast Cancer Therapy
- Nestin: A Selective Marker for Basal Epithelial Breast Tumors
- Understanding the Breast Cancer Metastatic Process in Bone
Pathologic complete response (pCR) is often defined as having no evidence of viable, invasive tumor cells remaining in a surgical specimen. In breast cancer, pCR is associated with prolonged patient survival and has been utilized as the primary surrogate end point in clinical trials of neoadjuvant chemotherapy. However, the definitions used to measure pCR versus residual disease (RD) are not uniform and do not consistently include various disease states or tumor characteristics, such as the presence of nodal metastasis, tumor cellularity, and residual in situ carcinoma. The broad range of actual tumor responses may extend beyond the categories of pCR and RD to provide the strong prognostic information needed in neoadjuvant chemotherapy trials.
Supported by a Fiscal Year 2001 Breast Cancer Research Program Clinical Bridge Award, Dr. W. Fraser Symmans and colleagues at the M. D. Anderson Cancer Center sought to develop a new, predictive model that integrates the relevant pathological characteristics of RD into a composite index called residual cancer burden (RCB). RCB combines pathological measurements of primary tumor size and tumor bed cellularity with the number and size of nodal metastases to predict distant relapse in a multivariate model. Dr. Symmans examined pathologic tissues and reports from 382 breast cancer patients in two different neoadjuvant treatment cohorts (paclitaxel followed by fluorouracil, doxorubicin, and cyclophosphamide [T-FAC], or FAC alone). Other parameters that were evaluated in the T-FAC and FAC cohorts included the hormone receptor status and whether or not the patients had undergone adjuvant hormone therapy. The researchers found that RCB was strongly predictive of patient relapse and survival, and accounted for the wide range of RD characteristics in the treatment groups. The 5-year prognosis for patients with minimal RD (RCB-I) was similar to that of patients with pCR (RCB-0), suggesting that the subset of patients who would benefit from neoadjuvant chemotherapy may be better identified using the RCB classification model. Patients with extensive RD (RCB-III) had a poor prognosis, irrespective of their hormone receptor status or adjuvant hormone therapy. Interestingly, the prognosis of patients with moderate RD (RCB-II) was improved in the group that had undergone adjuvant hormone treatment. These findings demonstrate the capacity for RCB classification to identify the important subsets of patients who are or are not likely to benefit from neoadjuvant chemotherapy. Further validation of the prognostic value of RCB in predicting distant relapse may lead to more accurate surrogate end points for neoadjuvant chemotherapy in breast cancer.
Symmans WF, Peintinger F, Hatzis C, et al. 2007. Measurement of residual breast cancer burden to predict survival after neoadjuvant chemotherapy. Journal of Clinical Oncology 25(28):4414-4422.
Dr. Celeste Nelson of the Lawrence Berkeley National Laboratory, recipient of a Fiscal Year 2003 Breast Cancer Research Program Postdoctoral Traineeship Award, has been studying the cytoskeletal control of mammary epithelial morphogenesis and tumorigenesis. The normal development of the mammary gland depends on the protein epimorphin, also known as syntaxin-2, which regulates epithelial-mesenchymal interactions and epithelial cell morphogenesis and activation. One of the hallmark changes in tissue structure during cancer development is the loss of apical-basal epithelial cell polarity. The researcher's main goal in this study is to delineate the involvement of the cytoskeleton in epimorphin-induced differentiation, and to determine how this signaling differs between normal mammary cells and breast cancer cells. These studies have the potential to unlock general principles underlying the process of morphogenesis in the mammary gland, and they may increase our understanding of what goes awry in earlier stages of breast cancer. To define the role of positional context, Dr. Nelson and colleagues developed a membrane-based cell culture system that can independently isolate and control the apical, lateral, and basal surfaces of mammary epithelial cells. She also developed imaging protocols using spinning disk confocal microscopy to image and track individual cells undergoing morphogenetic movements in three-dimensional cultures over 24-48 hours. Dr. Nelson's data suggest epimorphin and growth factors work together to affect the activity of ROCK (part of the Rho GTPase signaling pathway that controls cellular shape and rigidity), which directs the branching morphogenesis of breast cells. By revealing that the normal signaling pathway is disrupted in malignant cells, Dr. Nelson's study has provided new insights into cancer development while identifying potential new targets for therapeutic treatments. The success of this postdoctoral training award led partly to Dr. Nelson's faculty appointment as an Assistant Professor of Chemical Engineering at Princeton University.
Itoh M, Nelson CM, Myers CA, et al. 2007. Rap1 integrates tissue polarity, lumen formation, and tumorigenic potential in human breast epithelial cells. Cancer Research 67:4759-4766.
LeBeyec J, Xu R, Moon Lee SY, et al. 2007. Cell shape regulates global histone acetylation in human mammary epithelial cells. Experimental Cell Research 313: 3066-3075.
Hirai Y, Nelson CM, Yamazaki K, et al. 2007. The non-classical export of epimorphin and its adhesion to alpha-v-integrin for regulation of epithelial morphogenesis. Journal of Cell Science 120:2032-2043.
Liu H, Radisky DC, Nelson CM, et al. 2006. Mechanism of Akt1 inhibition of breast cancer cell invasion reveals a protumorigenic role for TSC2. Proceedings of the National Academy of Sciences of the United States of America 103:4134 4139.
Kenny PA, Nelson CM, and Bissell MJ. 2006. The ecology of tumors. The Scientist 4:30 37.
Nelson CM, and Bissell MJ. 2006. Of extracellular matrix, scaffolds, and signaling: Tissue architecture regulates development, homeostasis, and cancer. Annual Review of Cell and Developmental Biology 22:287-309.
Nelson CM, and Bissell MJ. 2005. Modeling dynamic reciprocity: Engineering three-dimensional culture models of breast cancer architecture, function, and neoplastic transformation. Seminars in Cancer Biology 15:342-52.
Radisky DC, Levy, DD, Littlepage LE, et al. 2005. MMP3-induced Rac1b stimulates formation of ROS, causing EMT and genomic instability. Nature 436:123-7.
Alcaraz J, Nelson CM, and Bissell MJ. 2004. Biomechanical approaches for studying integration of tissue structure and function in mammary epithelia. Journal of Mammary Gland Biology and Neoplasia 9:361-374.
Legumain, also known as asparaginyl endopeptidase, is a conserved proteinase overexpressed in human and mouse breast cancer tissues. Overexpression of legumain activates other proteinases that modify surrounding tissues and cellular architecture, thereby facilitating increased cellular migration and invasion of tumor cells to surrounding sites. Dr. Cheng Liu, of The Scripps Research Institute, and his colleagues have developed a cell-impermeable, tumor-activated prodrug legubicin, as a therapeutic agent against breast cancer. Legubicin is a derivative of doxorubicin, a chemotherapeutic agent used in breast cancer treatment, which has been of limited usefulness because of its adverse systemic side effects on the heart and the immune system. However, when administered to tumor-bearing animal hosts, the peptide attached to legubicin is specifically recognized by legumain on the cell surfaces in the tumor microenvironment and then cleaved to release doxorubicin locally in the tumor tissues where effective cell killing occurs. Gene expression profiling and immunostaining of mouse breast tumor tissues showed that legumain is overexpressed in cells that make up the tumor microenvironment and are associated with tumor progression and metastasis. The higher levels of legumain in tumor tissues versus normal cells provide the specificity for activation of legubicin and allow normal cells to be largely spared from cell killing and cellular toxicity. Using mouse syngeneic and human xenograft models of breast cancer, Dr. Liu demonstrated that the prodrug legubicin significantly reduced spontaneous and experimental tumor metastases. Analysis of the pharmacodynamics of the prodrug suggests that it is an effective therapeutic agent. Further, in collaboration with Dr. Rong Xiang, Dr. Liu developed a legumain-based DNA vaccine and tested it in murine models of metastatic breast cancer. The vaccination-induced CD8 T cell immune response against tumor-associated macrophages resulted in a greater than 50% reduction in metastases and reduced expression of tumor growth factors and angiogenic factors without adversely affecting the classical M1 macrophages involved in antigen presentation and immune surveillance. In vitro studies identified the integrins such as αvβ3 and α5β1 as the specific cell surface receptor for legumain. Targeting the legumain-integrin complex with asparaginyl endopeptidase inhibitors (AEPIs) suppresses the activity of legumain and the activation of its physiologic substrates MMP-2 and cathepsin L, suggesting that legumain may regulate the pericellular proteolysis during tumor invasion and angiogenesis. Similarly, AEPIs have been shown to effectively block angiogenesis in mice by inhibiting FGF2-induced aortic vessel sprouts, in a dose-dependent manner, and by inhibiting vessel formation in an orthotopic human breast carcinoma xenograft murine model. The effectiveness of legubicin in arresting and preventing metastases without myelosuppression and cardiac toxicity, as well as evidence supporting its improved efficacy and safety over doxorubicin, support the clinical development of legubicin as a therapeutic agent for breast cancer.
Wu W, Luo Y, Sun C, et al. 2006. Targeting cell-impermeable prodrug activation to tumor microenvironment eradicates multiple drug-resistant neoplasms. Cancer Research 66(2):970-980.
Luo Y, Zhou H, Krueger J, et al. 2006. Targeting tumor-associated macrophages as a novel strategy against breast cancer. The Journal of Clinical Investigation 116(8):2132-2141.
The basal epithelial breast cancer subtype represents 17 to 37 percent of all breast cancers and is more common in premenopausal African-American women than in other demographic groups. Clinically, this form of human breast cancer is the most challenging to treat due to its aggressive nature, poor prognosis, and lack of molecular targets such as estrogen receptor alpha (ER alpha), progesterone receptor (PR), and Her2 overexpression. Dr. Hua Li of Dartmouth Medical School received a Fiscal Year 2004 Breast Cancer Research Program Multidisciplinary Postdoctoral Award to identify genes associated with self-renewing breast basal stem cells and progenitors, which have prognostic value and may enhance the ability of clinicians to design therapeutic strategies. Working in the laboratory of Dr. James DiRenzo, Dr. Li's main goal is to understand the etiology of breast cancer and to identify selective markers and therapeutic targets that might improve detection, diagnosis, and treatment of the basal epithelial breast cancer subtype. Dr. Li conducted the study on basal epithelial breast cancer subtype tumors that were negative for ER alpha, PR, and Her2, selected from the Tissue and Tumor Bank at Dartmouth Hitchcock Medical Center, and BRCA-1 mutated breast cancers from Chase Fox Cancer Center. Dr. Li discovered that nestin is overexpressed (expressed) in two morphologically and biochemically distinct populations within the basal/myoepithelial layers of the human mammary gland: one expressing cytokeratin 14 and p63 and another expressing desmin. Nestin is an intermediate filament protein that is expressed in neural stem cells and other cells with regenerative potential. Little is currently known about the function of nestin in stabilizing the structure of adult stem cells as they regenerate and divide into daughter cells. Dr Li found that normal breast basal epithelial tissue produces nestin, but nestin is robustly expressed in most basal epithelial breast tumors including BRCA-1 mutated breast cancers. Nestin was not detected in other breast cancer subtypes such as hormone receptor-positive or Her2-positive breast cancer, indicating selectivity for basal epithelial breast tumors. Therefore, nestin could be a useful selective marker for basal epithelial breast tumors, and further study could lead to a prospective target for the development of novel therapeutics. Nestin offers new avenues for treatment and for future development of the diagnostic tools for its detection in clinical samples.
Li H, Cherukuri P, Li N, et al. 2007. Nestin is expressed in the basal/myoepithelial layer of the mammary gland and is a selective marker of basal epithelial breast tumors. Cancer Research 67(2):501-510.
Breast cancer cells frequently leave the breast and metastasize to bone, where they can grow and cause bone destruction. Metastatic bone tumors are usually found at the ends (metaphyses) of the long bones in the arms and legs. Little is known about the early stages of the bone metastatic process, including the arrival, localization, and initial colonization of breast cancer cells. Dr. Andrea Mastro of Pennsylvania State University and recipient of a Fiscal Year 2002 Department of Defense Breast Cancer Research Program (DOD BCRP) Concept Award, has examined the traffic patterns of breast cancer cells in the bone marrow cavity and identified candidate factors that may attract the breast cancer cells to the metaphyseal regions of the bone. To facilitate tracking of the cells, Dr. Mastro and her collaborator, Danny Welch, University of Alabama-Birmingham, induced bone metastases in mice by intracardiac injection of MDA-MB-435 breast cancer cells tagged with green fluorescent protein. Femurs from the mice were then analyzed at times ranging from 1 hr to 6 weeks using fluorescence microscopy, immunohistochemistry, real-time PCR, flow cytometry, and histomorphometry. Infiltration patterns of the metastatic breast cancer cells were determined in the bone marrow collected from three different regions of the femur: proximal metaphysis, distal metaphysis, and shaft (diaphysis). Dr. Mastro's studies showed the early arrest of breast cancer cells in the metaphysis and minimal retention in the diaphysis, suggesting that breast cancer cells either move or are cleared from the diaphysis and migrate to grow in the metaphysis. Furthermore, she discovered that the cancer cells localized in the distal metaphysis before they were detected in the proximal end of the femur. Following the formation of a metaphyseal tumor mass, the breast cancer cells were found to extend throughout the diaphysis. These later-stage tumor cells influenced not only osteoclast function but also drastically reduced the number of functional osteoblasts, resulting in a restructured bone microenvironment that favors osteolysis. Additionally, Dr. Mastro found the metaphyseal bone rich in several cytokines and adhesion factors, as compared with the shaft of the bone, and she continues to characterize how these cytokines and adhesion factors might affect the distribution of metastases in the femur. Taken together, Dr. Mastro's studies are advancing our understanding of the bone metastatic process and may help to elucidate new methods of disrupting the localization and growth of breast cancer cells in the bone.
Phadke PA, Mercer RR, Harms JF, et al. 2006. Kinetics of metastatic breast cancer cell trafficking in bone. Clinical Cancer Research 12:1431-1440.