Platelet factor 4: A Marker For Malignant Breast Tumors

Institution: La Jolla Institute for Molecular Medicine
Investigator(s): Per Borgstrom, Ph.D. -
Award Cycle: 1995 (Cycle I) Grant #: 1IB-0493 Award: $95,380
Award Type: IDEA
Research Priorities
Detection, Prognosis and Treatment>Imaging, Biomarkers, and Molecular Pathology: improving detection and diagnosis

Initial Award Abstract (1995)
Angiogenesis, a fundamental process by which new blood vessels are formed, is rare in adults under normal physiological conditions. However, in pathophysiological conditions like cancer, unrestrained angiogenesis occurs. Rapid tumor growth is dependent on angiogenesis to support the metabolic need of the fast-growing transformed tumor cells and the growth of the tumor beyond a certain size requires angiogenesis. In breast cancer there is a significant association between the density of vessels in the tumor (a consequence of the angiogenic process) and overall survival as well as relapse-free survival in both node-negative and node-positive patients. Since the density of vessels in a tumor is an independent prognostic indicator in breast cancer, specific markers suitable for imaging of angiogenesis could contribute to the early detection of malignant breast tumors. We have previously shown that platelet factor 4 (PF4) selectively binds to newly formed vessels, i.e., sites of angiogenesis, and the overall goal of this project is to investigate the potential of PF4 as an imaging marker for breast cancer angiogenesis.

Our first goal is to characterize a suitable human breast cancer cell line using our newly developed in vivo video-microscopy technique. Our technique allows detailed repeated in vivo real time observations of tumor microvasculature, and permits quantitative evaluation of tumor growth and tumor angiogenesis in vivo. Currently there is no reliable information on in vivo angiogenic behavior of breast cancer, and the results from this investigation will inevitably provide new and important results which are a prerequisite for the evaluation of PF4 as an angiogenesis marker.

Our second goal is to investigate binding characteristics of systemically injected fluorescently labeled PF4 (FITC-PF4) to the microvasculature of human breast tumors. In the present investigation, we are using video-microscopy and fluorescently labeled PF4 which will allow us to characterize in detail the binding characteristics of intravascular PF4 which is a prerequisite for future use of other PF4 conjugates in clinical screening techniques. To the extent that we find that FITC-PF4 selectively labels the vessels of human breast cancer cell lines, such results would lend strong support for the use of PF4 as an in vivo marker for breast cancer angiogenesis. The proposed studies provide a systematic approach to evaluate the potential of PF4 as an imaging marker for breast cancer angiogenesis and thus could be an important step towards the development of novel screening techniques to improve the early detection of malignant breast tumors.

Final Report (1996)
We have investigated the potential of platelet factor 4 (PF4) as a marker for early detection of breast cancer using an in vivo model of human breast carcinoma. Results from these experiments showed that fluorescent PF4 labeled intensely and specifically capillaries growing into implanted breast tumors. The process of tumor capillary growth (angiogenesis) is a prognostic indicator of malignant tumor progression and therefore imaging tumor blood vessels has great diagnostic and therapeutic potential.

Our results indicate that human breast cancer cell lines possess considerable angiogenic activity. Furthermore, our results show that PF4 preferentially binds to regions of active angiogenesis in vivo, lending strong support for the concept of using PF4-conjugated to contrast imaging molecules for identification, screening, prognosis, detection, or monitoring of early stages of breast cancer in patients.

The conclusions of this in vivo preclinical study were accomplished using a recently developed intravital microscopic technique developed in this laboratory which allows us to study growth of small tumors (tumor spheroids) and progress of tumor angiogenesis. Our first goal was to investigate if breast cancer cell lines possess angiogenic activity, using our in vivo system. To accomplish this, we tested four human breast cancer cell lines, namely; MCF-7, ZR-75, SK-BR-3, and BT-20. The cell line MCF-7 was found to possess the most intense angiogenic activity, and also to be the fastest growing cancer line. Results from these experiments indicate that a variety of breast cancer cell lines all possess considerable angiogenic activity, and that markers for tumor angiogenesis could facilitate early detection of breast cancer. Our second goal was to investigate binding characteristics of systemically injected fluorescently labeled PF4 to tumor capillaries. For these experiments we chose to use tumor spheroids of the MCF-7 cell line. The results showed that PF4 rapidly localizes at sites of active tumor growth and selectively images the tumor blood vessels while leaving normal vessels unlabeled. We conclude that PF4 has potential as a tumor marker for diagnostic detection and monitoring of patients with malignant breast cancers.