Philadelphia, PA, October 19, 2017—Researchers have developed a patient-derived xenograft model of pancreatic neuroendocrine tumors (PNETs) that has been proven to be a valid PNET model and is hoped to become an important addition to the PNET research armamentarium, according to study results presented here at the North American Neuroendocrine Tumors Society (NANETS) 2017 Symposium.
"There is currently no good, patient-derived xenograft model for PNETs, so there was a need for this kind of model,” began Chester Chamberlain, MD, faculty member, University of California San Francisco, CA.
“This is a very important model because, unlike models that are in more commonly used and that are available, this [model] actually has the most relevant biology for these kinds of tumors. These are the kinds of [models] that we like to study, that have been shown, most recently, to be the most effective in terms of predicting response in patients and response to therapies. But there hasn’t been one for this type of tumor; they’re particularly difficult to grow, they’re very slow growing. So this is the first model to be developed of this type, and we are very excited to have that,” he added.
Dr. Chamberlain and colleagues developed their model using PNET tissue samples taken from a patient with PNET liver metastases. The patient was producing insulin and underwent surgery for refractory hypoglycemia. Researchers then implanted the PNET samples subcutaneously into nude mice, and stained them with H&E or antibodies for immunofluourescent analysis.
Using real-time TaqMan RT-PCT, researchers assayed for the expression of developmental transcription factor that were specifically expressed in NETs. They used a radiolabeled somatostatin analog 68Ga-DOTATOC to conduct PET-CT of treated NETS in vivo.
The mice implanted with PNET xenografts were treated with everolimus. Dr. Chamberlain and colleagues then performed whole-exome PNET sequencing with Illumina HiSEQ2500 (Illumina), which they analyzed with the Bina-Roche genomic analysis platform.
Dr. Chamberlain and fellow researchers found that the HNV xenografts maintained a well-differentiated NET morphology (Ki67 index 6%-8%, G2), chromogranin A, and serotonin and insulin expression. They also maintained a neuroendocrine-specific gene expression signature with serial passage.
mTOR pathway activity was detected in HNV via Western blot. mTOR was inhibited by everolimus, and HNV growth completely stopped. Upon 68Ga-DOTATATE PET-CT, HNV was clearly detected, which may suggest that it expresses somatostatin receptors.
Researchers conducted whole-exome sequencing of HNV to establish a mutational landscape, and on preliminary analysis, found that the HNV contained many mutations in established pancreatic NET-associated genes, including MEN1, BRCA2, PTEN, and SETD2.
They also found phosphorylation of S6 ribosomal protein after evaluating phosphorylated receptor tyrosine kinases and signaling nodes using the PathSCan RTK Signaling Antibody Array Kit. This finding indicates mTOR pathway activation.
“The patient-derived xenograft model for pancreatic NETs is here. It’s here, it’s available, and it works. In particular, not only do we have it now, but we’ve already tested it with two different types of drugs, one FDA-approved, and shown that we get a response. Not only that, but we also get acquired resistance for a drug. And we were able to use the model to identify an investigational drug that can overcome that resistance based on our model. This is new. It’s available. We have it. Talk to us,” concluded Dr. Chamberlain.