Abstract LB-A22: Comparison of the effect of pharmaceutical compounds on tumor cells in 2D and 3D in vitro models using label-free, quantitative 4 dimensional holographic imaging
Authors: Luther Ed , Salzano Giuseppina , Sriraman Shravan K. , Costa Daniel , Torchilin Vladimir P. 
Published: May 2016

Abstract
Introduction
Development of in vitro models for the evaluation of drugs represents a useful approach as in vivo studies may be costly and time consuming. Ideal models should take into account the effects of the cellular microenvironment, which includes the extra-cellular matrix, stroma and neighboring cells.
Phase Holographic Imaging
The Holomonitor®M4 (Phase Holographic Imaging, Lund, Sweden) is an incubator-adapted time-lapse holographic imaging cytometry system that enables quantitative, label-free analysis of living cells. A low-power red laser creates an interference pattern (hologram) which is reconstructed by software into images. Software modules are available for cellular segmentation, calculating quantitative features (optical thickness and volume), and individual cell tracking. Cells were plated in Petri dishes and imaged in 5 minute intervals for 2 to 3 days. The field of view with a 20X objective is 538 μm2 with an effective depth of field in the mm range, allowing monitoring elongated cubes of the tumor microenvironment. We export 2D projections of the holograms into Image J. We then produce 4-dimensional plots of the tumor microenvironment (X and Y position, cell thickness coded as brightness, and time in the Z direction).
2D models of non-motile adherent cells.
When untreated HeLa cells are seeded at low density, colonies manifest as inverted cones increasing in diameter as the cell number increases. Mitotic cells appear as short duration bright spots due to rounding of the cells and increase in optical thickness. Treatment with colchicine at concentrations sufficient to block the completion of mitosis caused the brightness of the tracks is persistent. When treated with doxorubicin (dox) at concentrations sufficient to induce apoptosis, cell tracks briefly become bright, but then decrease in diameter and brightness as the cells gradually disintegrate.
2D models of motile cells.
HT1080 fibroblasts present two distinct morphological types, an amoeboid form that move via extensions of lamellipodia from a leading edge that adhere to a substrate and a mesenchymal form, where small protrusions termed lobopodia propel cells by attaching to ECM components.
In untreated samples, cells are predominately in the amoeboid form, with the cell tracks moving upward. Low concentrations of dox (50nM) abolish cell proliferation, and a shuttling motion is seen, caused by dysfunctional lamellipodia attachment to the substrate prior to eventual cell death.
3D models of motile cells.
We plated HT1080 cells on the dishes, treated them with compounds, and then overlaid the cells with 1 mg/ml collagen type 1.
With 50 nM dox there is a high degree of proliferation and vastly increased planar motion. In videos it can be seen that cells are following pathways created by other cells, consistent with cells burrowing through the ECM.
Conclusion
We developed a novel 4-D holographic imaging method using the Holomonitor HM4 and Image J. Here, we present methods for comparing traditional 2D and 3D in vitro models. Our example of HT1080 cells treated with dox clearly shows the superiority of the 3D model, an important step in developing assays that better emulate multi-dimensional biological processes and offer the possibility of evaluating effects of drugs at lower cost and experimental complexity than those of in vivo assays.
Citation Format: Ed Luther, Giuseppina Salzano, Shravan K. Sriraman, Daniel Costa, Vladimir P. Torchilin. Comparison of the effect of pharmaceutical compounds on tumor cells in 2D and 3D in vitro models using label-free, quantitative 4 dimensional holographic imaging. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-A22.