Abstract 2782: Neuroendocrine tumor spheroid growth and drug response assessment using optical metabolic imaging
Authors: Gillette Amani , Babiarz Christopher , Pasch Cheri , Deming Dustin , Skala Melissa 
Published: September 2020

Gastroenteropancreatic neuroendocrine tumors (GEP-NET) are the second most common form of gastrointestinal cancer, and account for roughly 60% of all neuroendocrine tumors. Unfortunately, no animal models or cell lines exist that reflect the in vivo characteristics of human GEP-NETs. Specifically, human GEP-NETs have low proliferation rates that animal models and cell lines fail to capture. Therefore, drug testing for GEP-NETs often begins in patients without rigorous pre-clinical validation. There is a need to predict the most effective treatments prior to clinical trials for GEP-NET patients, to increase treatment efficacy and reduce toxicities.

Here we show that a three-dimensional spheroid model of primary GEP-NET patient tumors is representative of the original patient tumors including histological features and markers of proliferation (Ki67). Furthermore, this study uses the spheroid model to test a novel drug combination on GEP-NET spheroids, specifically ABT263, a Bcl-2 family inhibitor, and everolimus, a standard GEP-NET treatment that inhibits mTOR. Previous studies have shown that ABT263 induces apoptosis in cancer cells when used in combination with everolimus, making this a promising drug combination for GEP-NET patients. Treatment response to ABT263, everolimus, and the combination, was tested in three-dimensional spheroids derived from seven primary GEP-NET patients, using two-photon optical metabolic imaging (OMI). OMI captures the fluorescence lifetime (τm) and intensity of metabolic cofactors NAD(P)H and FAD. These metrics can be combined into a single number, the OMI index, which was developed to separate responsive and non-responsive cells. The OMI index is the linear combination of the norm-centered redox ratio (NAD(P)H intensity / FAD intensity) + NAD(P)H τm - FAD τm. The OMI index also provides single cell response information from intact spheroids, so that heterogeneity in response can be quantified. Altogether, two-photon OMI in primary patient GEP-NET spheroids provides a novel tool to measure metabolic response to drug treatment.

At 72 hours post-treatment, all patients except two showed a decrease in OMI index, corresponding with a response, to the combination treatment. Heterogeneous response was resolved with two distinct subpopulations of cell metabolism in one of the nonresponsive patients. No changes in spheroid diameter were observed with any treatment, due to the slow growth rate of the GEP-NET tumors and spheroids, further highlighting a need for molecular measures of drug response in these samples. We have shown that representative GEP-NET models can be generated in patient-derived tumor spheroids. Additionally, ABT263 plus everolimus is a promising combination treatment for GEP-NETs. Overall, this work shows that patient-derived tumor spheroids can be established from GEP-NETs, and that OMI provides single-cell metabolic measurements of drug response to guide drug development for patients.

Citation Format: Amani Gillette, Christopher Babiarz, Cheri Pasch, Dustin Deming, Melissa Skala. Neuroendocrine tumor spheroid growth and drug response assessment using optical metabolic imaging [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2782.