“I don’t know what I don’t know” #gradschool
Emily Ehlerding graduated from Manchester University in North Manchester, IN in May 2014 with a B.S. in both chemistry and physics. During her sophomore year, she was an NSF-REU intern at Purdue University in the BioPhysics department studying photosystem II protein under Dr. Yulia Pushkar. The next summer, she held an NSF-REU position at the University of Chicago in the High Energy Physics group under Dr. Henry Frisch, and worked on the development of time-of-flight detectors for positron emission tomography (PET). She joined the Medical Physics department at the University of Wisconsin – Madison in August 2014, at which time she also became a member of Dr. Weibo Cai’s Molecular Imaging and Nanotechnology lab. There, she is developing radiolabeled antibody-based tracers for noninvasive imaging of cancer using PET, specifically for applications within immunotherapy treatments. She is also conducting a five-year study to determine the best cheese curds in the state of Wisconsin. She wants to teach and help undergrads everywhere discover the greatness of physics.
CTLA-4 is expressed on the surface of activated T cells and some cancer cells, and is the target of the clinically-approved monoclonal antibody Ipilimumab. Ipilimumab is only successful in a small subset of patients, making neoadjuvant patient selection crucial. In this study, we employ radiolabeled Cu-DOTA-Ipilimumab to monitor CTLA-4 expression levels in subcutaneous lung cancer xenografts using positron emission tomography (PET).
Ipilimumab was conjugated with the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) for radiolabeling with Cu (half-life = 12.7 h). Western blot, ELISA, and flow cytometry were employed to determine the CTLA-4 expression levels of three lung cancer cell lines: A549, H460, and H358. Longitudinal PET studies following intravenous injection of Cu-DOTA-Ipilimumab into mice bearing xenografts of the aforementioned lung cancer cells allowed for tracer uptake to be quantified up to 48 h post-injection. Ex vivo biodistribution and histological studies were employed to verify PET results.
By in situ analysis, A549 was found to have the highest CTLA-4 expression level, and H358 the lowest. PET quantification verified these results, with A549 tumor uptake peaking at 14.6 ± 3.2 %ID/g, H460 at 10.5 ± 1.6 %ID/g, and H358 at 7.7 ± 0.75 %ID/g, 48 h p.i. A549-blocked mice also displayed decreased tracer uptake values at 8.1 ± 1.0 %ID/g. Ex vivo analysis following the terminal imaging timepoint also corroborated these findings.
Radiolabeled Cu-DOTA-Ipilimumab is able to differentiate tumors based on their CTLA-4 expression levels noninvasively using PET. Thus, this antibody holds promise to be employed in small doses prior to immunotherapy treatment to predict the success of such anti-CTLA-4 therapy and aid in patient selection.