Imaging Technology News - October 2008 - (Page 35)

> > special report Pretargeting Hones in on Cancer Pretargeting attacks colorectal, breast and lung cancers and helps predict treatment outcome. by Amy Ballard, MEd, director of research, Arkansas Urology A Pretargeting yields more precise images. dvances in molecular imaging, specifically through the discovery of new molecular imaging agents and developments in the technologies that enable their visualization have opened up new possibilities for the early detection of disease as well as personalized medicine. In conventional radioimmunoimaging (RAII), radioisotopes are bound with therapeutic antibodies and are administered concurrently to targets of disease. Delivering both the imaging and therapeutic agents together lowers the sensitivity and the selectivity of the radioimmunoimaging due to the antibody taking more time to leave the body, resulting in less accurate images and less lethal doses of radiation to the tumor. In contrast, pretargeting yields more precise images due to a high signal with very low background noise and a more toxic radioactive dose to the tumor while sparing healthy tissue. More predictable treatments The breakthrough technique, pretargeting, shows much hope for the effective and early treatment of cancer. Otto Boerman, Ph.D., professor in the department of nuclear medicine at Radbound University Nijmegen Medical Center, Nijmegen, The Netherlands, led a study examining the potential of pretargeting which was recently presented at the Society of Nuclear Medicine’s 55th Annual Meeting. Pretargeting “decouple(s) the delivery of the bispecific antibody that seeks out the disease-carrying cells from the delivery of the imaging or therapeutic radioisotope. During the few-day-waiting period between the delivery of the bispecific antibody and the delivery of the radioisotope, the unbound antibody clears from the body, leaving only the tumor-bound antibody behind. This ensures that the radioisotope binds only to the tumor cells and not to the other bystander tissues in the body, thus improving the tumor-to-nontumor ratio of the radioisotope greater than 100-fold compared to the directly labeled antibodies,” according to Boerman. According to Boerman, in this process a bispecific monoclonal antibody (bsMAb), with one arm that recognizes a tumor-associated antigen and another arm that recognizes a peptide carrying an imaging agent, is given as a first injection. When the non-tumor-bound bsMAb has substantially cleared non-target tissues and has reached a maximum level in the tumor, the bsMAb-recognizable imaging agent is given. The latter agent either targets the bsMAb localized at the tumor or is rapidly removed in the urine. Because the delivery of imaging isotopes is rapid and is separated from the long antibody delivery process, radioisotope uptake in the tumor is sigThe Discovery VUEPoint HD by GE Healthcare is a PET/CT nificantly higher than in the system that aims to improve contrast-to-noise of moving lesions blood, making pretargetup to 60 percent vs. static acquisition. ing RAII an attractive alternative to traditional RAII. “Because the same bispecific antibody can be used with both imaging and therapeutic isotopes, this approach lends itself to use in personalized medicine, where the sequence of steps would be as follows — delivery of the bispecific antibody, delivery of imaging isotope, imaging to confirm targeting of the tumor by the antibody and delivery of the therapeutic isotope. In this sequence, the imaging step serves as a predictive tool for the success of the therapeutic step, making the approach highly attractive to patients, physicians and managed care organizations,” Boerman explained. Traditional monoclonal antibody treatments cost over $20,000 per treatment cycle but achieve results in less than 50 percent of cases. Because of the inability of this technique to appropriately target disease, pretargeting offers a way to predict whether a certain antibody will appropriately target the cancer. Several new pretargeting agents for cancer have been developed, according to Boerman, including an anti-CEA agent that attaches to colorectal, breast and lung cancers; an anti-CD20 agent that attaches to leukemia and lymphoma cells; and an anti-MUC1 agent that very specifically attaches to the pancreatic cancer cells. These pretargeting agents can be used with any type of imaging tool such as PET, ultrasound, MRI and fluorescence. Clearer vision of angiogenesis Other molecular imaging advances have been underway at GE Healthcare where researchers are using molecular agents to visualize angiogenesis, the formation of new blood vessels created by cancer — a product GE is calling “f-angio.” Since cancer cells have the ability to form new blood vessels, particularly the more aggressive types of cancer, targeting the formation of new blood vessels would reveal the metabolism and the propensity of growth of a tumor and be able to detect lesions that are extremely small. Jean Luc Vanderheyden, Ph.D., global molecular imaging leader for GE Healthcare explained that clinical trials are currently being conducted using “f-angio” and said, “I’m just reporting anecdotal results here, but the ability to see breast metastases that are very small, hardly defined by CT but can be seen by MI [molecular imaging] techniques, have been reported by researchers.” Along with the discovery of these new molecular agents, new imaging tools have been created to enhance their visualization. The ultimate endpoint in this endeavor has been achieving motion-free image acquisition. Breathing itself or the heart beating is enough to blur images of small tumors, so a new approach is to separate the focus of the image from the background. “If you are affecting things that are very small, it is important to have the equipment that is capable of separating these areas from the background and that is where technology has taken place; where we have developed MotionFree software, which is not just software but is a way to acquire the data and render it in 4D mode,” Vanderheyden explained. The ability to track a tumor over time has implications in the area of radiation therapy where the motion of a tumor may hinder treatment if not taken into account in the treatment planning. Using the latest VUE Point HD high-definition imaging with crystal technology by GE Healthcare in combination with other MotionFree techniques helps improve lesion detectability, treatment planning and quantitative accuracy, improving contrast-to-noise of moving lesions up to 60 percent versus static acquisition for overall better clinical confidence. Also enabling better visualization of molecular imaging agents is the Pretargeting Cancer continued on page 36 October 2008 > special report > 35 http://new.reillycomm.com/imaging/special-report-b.php

Table of Contents Feed for the Digital Edition of Imaging Technology News - October 2008

Imaging Technology News - October 2008 Contents RSNA Low-Field MRI Systems Contrast Media Injectors AM-LCDs Special Report - Agents Target Neurological Diseases and Disorders IT Laser Imagers Monitors Meet Radiology Suite Needs MR Guides Ultrasound in Outpatient Treatments Replacing a Legacy PACS PACS SAs: Titles and Salaries

Imaging Technology News - October 2008

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