Nuclear Medicine Aids Early Diagnosis Of Pulmonary Anthrax

The JNM Newsline reports that the Food and Drug Administration (FDA) has approved a protocol for a clinical trial to assess the efficacy of a 99mTc-labeled monoclonal antibody in imaging early-stage inhalation anthrax infection.

According to the representatives of the company that has developed the monoclonal antibody, the technique offers the unique ability to detect the earliest stages of involvement, before any other laboratory or radiographic diagnostic tests can detect the presence of infection and well before the more serious symptoms of inhalation anthrax infection are apparent. Newsline reports that the technique promises not only to identify and begin treatment for patients in the earliest stages of infection but to provide a means by which patients can be definitively identified as disease free and taken off long-term wide-spectrum antibiotic treatment.

According to Newsline, the protocol, developed by Robert Bridwell, MD, Associate Professor of Nuclear Medicine and Radiology and the Uniformed Services University of the Health Sciences (Bethesda, MD) and staff physician at Walter Reed Army Medical Center (WRAMC; Washington, DC), is designed to identify asymptomatic patients who have experienced “credible exposure” to anthrax spores. Information from Bridwell obtained by SNM after the article went to press, indicated that all patients exposed will be assessed and that for ethical reasons there will not be a control group. The trial will be undertaken with patients that are on active military duty, their spouses, or retired individuals.

Bridwell is quoted in the Newsline article as stating, “Once anthrax spores were discovered in the United States, there was a real urgency to scour the various methods that currently exist to determine whether any offered promise in the early diagnosis of anthrax infection.” As of the date of this press release, no patients have been imaged. “The good news is we currently don’t have patients who need to be part of this protocol,” said Bridwell. “The better news is that we have additional testing opportunities to try should the need arise.”

Newsline notes that an Investigational New Drug (IND) approval was granted for the trial in two to three weeks, which may be record time. Individuals from academic medicine, the military, government agencies, and industry worked together to secure the IND.

Palatin Technologies (Princeton, NJ) is the maker of the radiolabeled antibody product, Leutech™, that will be used in the WRAMC investigation and is the company to which the IND was granted. Newsline notes that Palatin is a development-stage biopharmaceutical company that began work with what would become known by the trade name of LeuTech in 1996. The 99mTc-labeled monoclonal antibody binds with high affinity and specificity to a carbohydrate antigen, CD-15, on human polymorphonuclear leukocytes in vivo. This ability means that, once a small amount of the radiolabeled antibody is injected, it binds to white blood cells congregating at the site of even the earliest infections and makes them apparent on nuclear medicine imaging. The technique has been tested successfully in functional imaging of other infections, including appendicitis, osteomyelitis, bowel infections, and postsurgical infection.

In the article, Mathew Thakur, PhD, Professor of Diagnostic Radiology and Nuclear Medicine at Thomas Jefferson University (Philadelphia PA), notes that “With its high specificity and affinity––and a number of other advantages––this technique provides a logical and promising approach to early diagnosis, which assumes critical importance in an entity as life-threatening as anthrax and where criminal activity may be involved.” Thakur was the earliest nuclear medicine practitioner to work with this radiolabeled antibody.

Bridwell agrees, noting that “this technique also reinforces nuclear medicine’s growing importance in providing fast and reliable functional information at the cellular diagnostic level.”

According to the article, should the initial results of this clinical trial demonstrate the monoclonal antibody’s utility in the diagnosis of inhalation anthrax, Palatin will initiate discussions with the FDA to provide the agent to other medical institutions caring for patients with credible exposure to anthrax.