Regulation of the Opioid Growth Factor-Opioid Growth Factor Receptor Axis in the Progression of Triple Negative Breast Cancer and its Potential as a Therapeutic Agent

Open Access
Author:
Worley, Beth Lorraine
Graduate Program:
Anatomy
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 02, 2015
Committee Members:
  • Patricia J Mc Laughlin, Thesis Advisor
Keywords:
  • triple negative breast cancer
  • breast cancer
  • MDA-MB-231
  • MCF-7
  • opioid growth factor
  • OGF
  • opioid growth factor receptor
  • OGFr
Abstract:
Triple negative breast cancer (TNBC) is an extremely aggressive form of breast cancer characterized by tissues lacking estrogen receptors (ER), progesterone receptors (PR), and human epidermal growth factor receptor (HER2). TNBC accounts for approximately 15% of all breast cancers diagnosed worldwide, and frequently affects younger women, women of color, and those from lower socioeconomic countries. TNBC has an increased likelihood of recurrence and a twofold greater mortality risk compared to other types of breast cancer, as well as a tendency to metastasize outside the breast. The financial burden for patients with TNBC is considerable, as costs are increased by 50% compared to other breast cancers. The median survival rate for patients with metastatic TNBC is only 13 months. Lack of hormone receptors and frequent de novo or acquired chemotherapy resistance renders almost all therapies ineffective. Thus, there is a critical need to develop TNBC treatments that target the underlying biology of tumor growth. A novel biological pathway has been studied in a wide variety of human cancers that may provide knowledge on progression of TNBC and serve as an effective treatment. The opioid growth factor – opioid growth factor receptor axis is a determinant of cell proliferation in both normal cells and neoplasia. OGF inhibits cell proliferation by upregulating the cyclin dependent inhibitory kinases p16 and p21, arresting cells in the transition from G0/G1 phase to S phase of the cell cycle and halting DNA synthesis. The proposed experiments investigated the presence of the OGF-OGFr axis in MDA-MB-231 TNBC cells in vitro and in vivo and assessed whether expression of peptide or receptor changes with cancer progression, and whether OGF serves as an effective treatment for TNBC. For cell culture studies, log phase cells were compared with confluent and post-confluent cultures to mimic early and advanced stages of cancer growth. Semi-quantitative immunohistochemistry and western blot analysis comparing log phase and confluent cells, as well as small and large tumors, revealed that both OGF and its receptor are significantly reduced in advanced stages of squamous cell carcinoma of the head and neck, as well as ovarian, cancers. These observations were extended and confirmed in human breast cancer using MDA-MB-231 and MCF-7 cancer cell lines grown in vitro and in vivo. A mechanism of action involving OGF inhibition of growth was demonstrated utilizing BrdU incorporation that indicated a decrease in DNA synthesis in TNBC cells treated with OGF. Confluent cells were less responsive to OGF treatment than log phase cells. The data suggest that OGFr expression is reduced in TNBC with tumor progression, and that tumor progression may lead to deficits in the OGF-OGFr axis. Nonetheless, OGF was shown to significantly decrease cell growth relative to controls, indicating its potential as an effective biological treatment for TNBC.