What to Know About CRISPR Screens and Bulk Spheroid Production

2D cancer models — the classic cells in a dish — and animal models of cancer have long histories, but both have limitations in terms of their relevance to human cancer and their ability to replicate all the features of diseases.

Fortunately, new technologies are enabling a better way. Cancer spheroids are an up-and-coming group of models with increasing uses in research, including CRISPR screens. The combination of CRISPR screening and innovative bulk spheroid production techniques holds great promise for cancer research.

Scalable Cancer-Spheroid Models Can Lead to New Breakthroughs

Both spheroids and organoids are 3D culture models. Spheroids are aggregated masses of cells without polarity and usually with only one cell type. Organoids are often polarized, may contain a hollow lumen, and may contain a more complex mixture of cell types. These model systems allow researchers to study cancer and other diseases in a more physiologically relevant setting while lessening the reliance on model animals such as mice, whose biology has important differences from human biology.

While simpler to make than organoids, cancer spheroids can capture several aspects of tumor biology that 2D cultures don't replicate. For example, cells on the surface of a spheroid experience different microenvironments than those on the interior, effectively modeling the gradients of oxygen, drug, and nutrient availability in a real tumor. Cells in spheroids experience a closer match to the biophysical environment in a tumor since multiple aspects of cell-cell interactions and signaling differ in 2D versus 3D. Spheroids can also provide a better model for the gene expression and metabolic profile of in vivo tumors.

Bulk spheroid production can be a limiting factor in experiments, especially because uniformity is needed. However, recent technological developments allow researchers to grow spheroids reliably and with straightforward procedures.

Genome-Wide CRISPR Screens Are Exploring Cancer Biology

Since CRISPR-Cas9 systems were first used for gene editing in 2012, CRISPR has revolutionized many areas of life science research by offering scientists greater ability and flexibility in manipulating genomes. CRISPR-Cas9 allows researchers to functionally knock out genes, while variations of CRISPR techniques enable manipulations like gain-of-function, up-regulation, or down-regulation of gene expression.

Researchers are combining CRISPR editing and spheroid cultures to perform genome-wide screens in cancer cells. This combination offers cancer researchers the chance to undertake a genome-scale investigation of the effects of gene knockouts or gene modulation on the 3D growth of cells in a more physiologically relevant model system, allowing the discovery of new cancer drivers that may not have a detectable effect in 2D cultures.

A research group at Stanford performed genome-wide CRISPR screens on lung adenocarcinoma cells grown in both 2D monolayers and 3D spheroids. They found that compared to 2D screening, the 3D spheroid screen turned up many more growth-promoting genes that are often mutated in cancers. The team used the spheroid screen to identify the gene CPD as a 3D cancer driver and as a potential drug target and prognostic marker.

Other teams have used CRISPR screens on spheroids to investigate the biology of lung, prostate, and other cancers.

Considering Bulk Spheroid Production for Screens

For CRISPR screens, laboratories need to produce high-quality cancer spheroids at a large scale and with uniformity and predictability. Recent developments in laboratory technology are making it easier to generate high-quality spheroids and allowing more labs to invest in this type of research.

Researchers have developed several methods for growing spheroids. Flasks with ultra-low attachment surfaces, spinner flasks, and bioreactors promote spheroid formation by forcing cells to grow in suspension. However, with these methods, it can be challenging to control the spheroids' size and attain uniformity. Wells with ultra-low attachment coatings allow researchers to control spheroid size but generate only a single spheroid per well, which can make scaling difficult.

Multi-well microcavity plates like Corning® Elplasia® plates allow up to thousands of spheroids per well. They can increase the signal and the number of imaging data points per well while allowing researchers to control the spheroids' size and composition by changing the initial seeding density. Microcavity plates can make spheroid screening possible for more labs without needing specialized equipment.

New Products Aid Bulk Spheroid Production

In addition to Elplasia® plates, Corning offers other microcavity products for bulk spheroid production, including Elplasia® flasks and the forthcoming Elplasia® open well plates.

Elplasia® microcavity plates come in formats similar to a six-to-384 well microplate, produce between 79 and 2,885 spheroids per well, and are compatible with brightfield and fluorescence microscopy to facilitate imaging directly in the plate. If you're considering these products for your laboratory, free samples of Elplasia® plates can be requested. Simply fill out a short form and a Corning representative will reach out to arrange a shipment.

As labs continue to work toward the fight against cancer, more developments and breakthroughs in this area are sure to occur. Visit Corning's website to learn more about spheroid applications and technology, or get in touch with an expert today.