Gregory Czarnota

Research Synopsis

Dr. Czarnota is conducting research focused on using ultrasound imaging and spectroscopy at conventional- and high-frequencies to detect apoptosis and other forms of cell death in response to chemotherapy and radiation therapy. In addition to being a Scientist in the Imaging Division he is an M.D in the Department of Radiation Oncology with applied research in breast cancer patients. His basic-science research interests include studies in biochemistry, chromatin biology, biophysics, medicine and oncology.

Dr. Czarnota, along with his collaborator Dr. Michael Kolios, discovered that ultrasound can be used to detect apoptosis (Figure 1). We have since applied this finding to important questions in oncology and organ transplantation. Our research group has demonstrated that this special form of cell death may be detected using ultrasound imaging and spectroscopy in vitro, in situ, and in vivo. The use of ultrasound to detect apoptosis and other forms of cell death has numerous applications listed below.

Projects for interested students may be arranged in any of the following topics.

(A) Cell and Molecular Biology

Despite the use of medical ultrasound for decades the features inside cells that contribute to ultrasound backscatter at conventional- and high-frequencies remain unknown. We are systematically probing how subcellular constituents such as DNA, RNA, protein and lipids contribute to backscatter. In particular we are interested in how nuclear and chromatin structure affects ultrasound signals since we have found it to be a dominant structure in the formation of backscatter signals.

(B) Image and Spectroscopic Analysis

We are collaboratively investigating a number of spectroscopic parameters for characterizing tumours and tumour responses to chemotherapy and radiation therapy at conventional and high-frequencies. We are developing these methods to generate colour-coded ultrasound parameteric maps to aid in assessing tumour responses to therapy. Since these spectroscopic signals are potentially linked to nuclear structure and chromatin structure which differs between normal and neoplastic tissue there is potential to develop our spectroscopic methods not only into a method to track tumour responses but a potentially important diagnostic tool.

(C) Clinical Evaluations of Ultrasound Imaging and Spectroscopy

We are instituting a number of clinical evaluations of our spectroscopic detection of cell death. Our main investigational site is breast cancer patients with large ‘locally-advanced” breast cancers who receive neoadjuvant combined chemotherapy and radiation therapy.

We hope to be able to rapidly ascertain responding tumours from those that are non-responding so that the latter may be treated with different chemotherapy regimens or with radiation sensitizers in order to hopefully improve outcomes.

Figure 1. Results of ultrasound imaging of apoptotic cells. Each panel is a representative ultrasound scan of a pellet of acute myeloid leukaemia cells. The bottom of each ultrasound scan is at the bottom of each frame. Pellets are immersed in buffered saline. From left to right, panels correspond to cells treated with cisplatinum for 0, 6, 12, 24 and 48 h to induce varying degrees of apoptosis. A bar at the bottom right of the figure indicates the colour map used in this image, the left of the bar indicating the colour that corresponds to pixel values of 0 and the right giving the colour that corresponds to a pixel value of 256. At 0, 6, 12, 24 and 48 h histological analysis indicated that 1.6, 2, 36, 87 and 93% of all cells showed nuclear fragmentation, respectively. At the 6-h time point, 72% of the cells exhibited prominent nuclear condensation changing from a nuclear diameter 70% of the cellular diameter before addition of the drug, to a diameter 40% of the cellular diameter at 6 hours. After the 6-h time point, 95% of all cells exhibited nuclear condensation or fragmentation. The speckle pattern is characteristic of ultrasound images. The scale bar indicates 1 mm. From Czarnota et al, 1999.

Appointments

Professor, Department of Radiation Oncology, University of Toronto
Professor, Department of Medical Biophysics, University of Toronto
Clinician Scientist, Department of Radiation Oncology and Imaging Research, Sunnybrook Health Sciences Centre