01 May Granzyme B Probe Plus PET Scanning Helps Determine Response To Immunotherapy
Posted at 21:58h
in AACR, Author Interviews, Biomarkers, Brigham & Women's - Harvard, Cancer Research, Immunotherapy, Neurology, Radiology
MedicalResearch.com Interview with:
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Dr. Ben Larimer[/caption]
Ben Larimer, PhD research fellow in lab of
Umar Mahmood, MD, PhD
Massachusetts General Hospital
Professor, Radiology, Harvard Medical School
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: Although immunotherapies such as checkpoint inhibitors have revolutionized cancer treatment, unfortunately they only work in a minority of patients. This means that most people who are put on a checkpoint inhibitor will not benefit but still have the increased risk of side effects. They also lose time they could have spent on other therapies. The ability to differentiate early in the course of treatment patients who are likely to benefit from immunotherapy from those who will not greatly improves individual patient care and helps accelerate the development of new therapies.
The main purpose of our study was to find a way to separate immunotherapy responders from non-responders at the earliest time point possible, and develop an imaging probe that would allow us to distinguish this non-invasively.
Granzyme B is a protein that immune cells use to actually kill their target. They keep it locked up in special compartments until they get the right signal to kill, after which they release it along with another protein called perforin that allows it to go inside of tumor cells and kill them. We designed a probe that only binds to granzyme B after it is released from immune cells, so that we could directly measure immune cell killing. We then attached it to a radioactive atom that quickly decays, so we could use PET scanning to noninvasively image the entire body to see where immune cells were actively releasing tumor-killing granzyme B.
We took genetically identical mice and gave them identical cancer and then treated every mouse with checkpoint inhibitors, which we knew would result in roughly half of the mice responding, but we wouldn’t know which ones until their tumors began to shrink. A little over a week after giving therapy to the mice, and before any of the tumors started to shrink, we injected our imaging probe and performed PET scans. When we looked at the mice by PET imaging, they fell into two groups. One group had high PET uptake, meaning high levels of granzyme B in the tumors, the other group had low levels of PET signal in the tumors. When we then followed out the two groups, all of the mice with high granzyme B PET uptake ended up responding to the therapy and their tumors subsequently disappeared, whereas those with low uptake had their tumors continue to grow.
We were very excited about this and so we expanded our collaboration with co-authors Keith Flaherty and Genevieve Boland to get patient samples from patients who were on checkpoint inhibitor therapy to see if the same pattern held true in humans. When we looked at the human melanoma tumor samples we saw the same pattern, high secreted granzyme levels in responders and much lower levels in non-responders.
Dr. Richard Leigh[/caption]
Dr. Richard Leigh MD
Neuro Vascular Brain Imaging Unit
National Institute of Neurological Disorders and Stroke
National Institutes of Health, Bethesda, MD
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: Patients who suffer an ischemic stroke have limited treatment options. One of the reasons for this is that our treatments can sometimes make the stroke worse by transforming the ischemic stroke into a hemorrhagic stroke. In our study we identified a new piece of information that we can extract from the patient’s MRI scan that informs us on the risk of having a hemorrhage.
Dr. Mathias Buttmann[/caption]
PD Dr. Mathias Buttmann
Senior Consultant Neurologist and Head of the Multiple Sclerosis Outpatient Clinic
University of Wuerzburg
Wuerzburg, Germany
MedicalResearch.com: What is the background for this study? What are the main findings?
Dr. Buttmann: The synthetic anthracenedione mitoxantrone is approved for disease-modifying treatment of patients with aggressive forms of relapsing or secondary progressive multiple sclerosis (MS). It has been known for years that this DNA-intercalating agent increases the risk of acute myeloid leukemia. We performed a retrospective cohort study to investigate whether mitoxantrone also increases the risk for other types of malignancies. We included all 677 mitoxantrone-treated multiple sclerosis patients who were seen at our large German academic MS centre between 1994 and 2007 and collected follow-up information on the occurrence of malignancies, death and causes of death as of 2011. Follow-up was complete in 676 patients. The median age at mitoxantrone initiation was 41 years and the median follow-up duration was 8.7 years. We identified 37 patients with a malignancy after mitoxantrone initiation, among them 4 cases of acute myeloic leukemia and 7 cases of colorectal cancer.
Compared to the general population matched for sex, age and year of occurrence, we calculated an 1.5-fold increased incidence of any type of malignancy, a tenfold increased incidence of acute myeloic leukemia and a threefold increased incidence of colorectal cancer, while the incidence of other types of malignancies was not increased. Higher age at mitoxantrone initiation but neither higher cumulative mitoxantrone dose nor treatment with other immuosuppressive agents was identified as a malignancy risk factor. Fifty-five patients had died, among them 12 from a malignancy. Our study confirmed previous reports on an increased incidence of acute myeloic leukemia after mitoxantrone treatment and newly described an association between mitoxantrone therapy and an increased incidence of colorectal cancer.
