An Investigation of the Chemotactic Role of Osteoclasts in Breast Cancer Metastasis in Bone

Open Access
Author:
Pursnani, Richa
Area of Honors:
Biochemistry and Molecular Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Andrea Marie Mastro, Thesis Supervisor
  • Craig Eugene Cameron, Honors Advisor
  • Daniel J Cosgrove, Honors Advisor
  • Richard John Frisque, Faculty Reader
Keywords:
  • breast cancer
  • metastasis
  • osteoclasts
  • osteoblasts
  • chemoattraction
  • bone
Abstract:
Four out of five women diagnosed with progressive breast cancer will suffer from metastasis and metastasis-related symptoms. Metastasis, trafficking and growth of cancer cells in specific target organs, is one of the leading causes of death associated with cancer. Some of the most prevalent forms of cancer, including breast cancer, are known to aggressively metastasize to the bone. Bone maintains homeostasis by means of a repair and renewal process called “bone remodeling” executed by osteoblasts (OBs), or bones building cells, and osteoclasts (OCs), or bone resorbing cells. This constant dynamic activity creates a pre-metastatic niche which facilitates the invasion of breast cancer cells that disseminate from the primary tumor In osteolytic breast cancer metastasis, the delicate balance of bone remodeling is set askew causing excess bone resorption which leads to detrimental clinical symptoms in cancer patients such as bone pain, fracture, hypercalcaemia, and spinal cord compression. Previous data from this laboratory by Krishnan [1] highlighted a potential relationship between OCs and the invasion of cancer cells in the bone. We postulated that OCs chemoattract metastatic breast cancer cells to sites of active bone remodeling and resorption. Once located in the bone microenvironment, cancer cells trigger the production of certain osteoclastogenic factors such as RANKL, VEGF, and M-CSF that enhance the formation and activity of OCs, causing massive bone degradation. The aim of this study was to classify the mechanism of the chemoattractant between primary OCs and MDA-MB-231-GFP metastatic breast cancer cells as involving either a soluble matrix factor created by bone-resorbing OCs or a soluble OC-specific factor. It was hypothesized that conditioned medium from OCs actively resorbing an OB-derived matrix and yielding soluble matrix factors would elicit more migration of cancer cells than conditioned media from differentiated OCs growing without OB-derived matrix. Primary OCs were derived from the bone marrow of DsRed mice. The OCs were treated with macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor kappa B ligand (RANKL). Cancer migration was determined by quantitative analysis of green fluorescent protein (GFP)-expressing cancer cells that migrated through a porous membrane. Conditioned medium from OCs growing on a plastic surface, or on a decellularized matrix, or cellularized matrix had no significant effect on migration of MDA-MB-231breast cancer cells. Thus, the potential chemoattractant may not be a soluble factor but rather a ligand factor that requires cell to cell contact. The development of effective therapies that would eliminate or ameliorate bone metastasis is currently hindered due to a limited understanding of the molecular and cellular mechanisms behind the growth and spread of breast cancer cells in the bone. Further work in this realm of bone metastasis would help in the synthesis of drugs and with treatments targeted at halting cancer cell chemoattraction to OCs in the bone.