Abstract 1301: Real-time single-cell drug response assay in metastatic breast cancer cell lines using quantitative phase imaging
Authors: Moustafa Tarek E. , Polanco Edward R. , Butterfield Andrew , Scherer Sandra D. , Welm Bryan E. , Bernard Philip S. , Zangle Thomas A. 
Published: July 2021

Abstract
Introduction: The ability for oncologists to predict a cancer's response to therapy is limited to a few biomarkers used for histologic diagnosis and targeted therapy. Often, in advanced and metastatic disease these biomarkers provide no alternative options for next step systemic treatments. There is a need in oncology for functional assays that can determine a tumor's response to a drug, regardless of its tissue of origin, previous treatments, or mutation status. Quantitative phase imaging (QPI) can measure changes in single cell mass in response to drug treatment in vitro and ex vivo. This platform offers advantages over other functional/metabolic assays in that it monitors changes in real-time and on a single cell basis, revealing heterogeneity in drug response.
Methods: Here, we describe the validation of QPI for the measurement of breast cancer cell response to therapy versus CellTiterGlo (CTG), an endpoint ATP assay. We ran a series of 3-day drug response assays using QPI alongside CTG. We used a 96 well plate with a 6-point dose response between 1.6 nM and 20 μM for multiple cell lines spanning a range of receptor statuses (MCF7, MDA-MB-231, BT-474) with two controls in triplicate. We analyzed single-cell data to measure the heterogeneity of response and assessed how cell-to-cell heterogeneity is affected by dose. Our response data were fitted to a four-parameter Hill equation to compute the IC50 and depth of response.
Results: We found that QPI can determine IC50s for effective treatments as validated by concordance to CTG. As measured by QPI, doxorubicin has a substantial depth of response, indicating cytotoxic effects. Doxorubicin data also show a tighter range of growth rates at high concentration than control, which implies low heterogeneity of response. As expected, ER positive MCF7 cells responded to hydroxy-tamoxifen. This response shows a similar reduction in heterogeneity to doxorubicin but with a reduced depth of response indicating a cytostatic effect. MDA-MB-231 response to palbociclib exhibits a wide range of growth rates, indicating an increase in heterogeneity as measured by QPI. Fluorouracil response shows no significant difference in heterogeneity from control.
Conclusion: In summary, QPI is a useful tool for functional assays that can capture IC50, depth of response, and single-cell heterogeneity of response. In particular, this additional information about single-cell behavior and heterogeneity cannot be measured using a typical endpoint assay. Future work is needed to prove the clinical utility of functional assays from QPI.
Citation Format: Tarek E. Moustafa, Edward R. Polanco, Andrew Butterfield, Sandra D. Scherer, Bryan E. Welm, Philip S. Bernard, Thomas A. Zangle. Real-time single-cell drug response assay in metastatic breast cancer cell lines using quantitative phase imaging [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1301.