Xiankai Sun, Ph.D.
Xiankai Sun, Ph.D., and his colleagues are developing new nuclear imaging probes for use in positron emission tomography (PET) and single photon emission computed tomography (SPECT). In PET, a biologically active radioactive tracer is injected into the body and its tissue concentration mapped by detecting pairs of gamma rays that arise from tracer-emitted positrons annihilating with electrons. While SPECT also involves detecting gamma rays, they are directly emitted by a different type of radioactive tracer. In both techniques, mapping of emissions enables construction of images showing real-time tracer distribution in vivo.
Dr. Sun's aim is to create versatile molecular "scaffolds" that carry a PET or SPECT radiolabel, onto which could be attached a variety of biomolecules of interest that target a particular cell or biological process. Importantly, these scaffolds could be designed to be multivalent, carrying more than one copy of the targeting molecule to enhance specific binding to the target. Such targeted tracers could offer higher specificity and sensitivity for PET and SPECT.
The molecular basis for these scaffolds could be organic compounds called chelators that can hold radiometal tracers tightly, dendrimers, which are branched organic molecules with defined structures, or nano-sized organic or inorganic particles.
The most widely used tracer for PET is 18F-labeled fluorodeoxyglucose (FDG), an analog of glucose. However, FDG has limitations in imaging prostate cancer because prostate cancer cells are dormant in terms of glucose utilization, and FDG is excreted from the body through the bladder, which is in the proximity of the prostate. In one project, he is seeking to develop more specific probes for prostate cancer detection. He is also seeking to develop PET tracers that could specifically reveal prostate cancer metastases. Such tracers could help oncologists determine the prognostic category of an individual's cancer.
In another project, he and his colleagues are developing imaging agents specific for imaging the pancreatic beta-cells. His aim is to create imaging agents what would enable non-invasive and longitudinal monitoring of the progression of diabetes and its treatment. Such monitoring would enable clinicians to diagnose diabetes earlier for the early stage disease reversal or more efficient treatment. The molecular target for these imaging agents is the receptor for glucagon-like peptide-1 (GLP-1), which is highly expressed on the pancreatic beta-cells. The researchers are developing targeted imaging agents based on chemical analogues of GLP-1 for PET or SPECT imaging of beta-cells.
Dr. Sun’s lab is also working to develop hybrid agents that could be used for PET and computerized tomography (CT), or for PET and MRI. Such hybrid agents would enable clinicians to superimpose the two images to map clearly the biochemical information available with PET onto the high-resolution tissue images enabled by CT or MRI and would find applications in imaging a wide array of diseases, including pancreatic and prostate cancers, and diabetes.
For publication information please view Dr. Sun's faculty profile.