New Way to Measure Cell Survival Developed

MIT biological engineers say they have devised a new toxicity test that can measure chemical effects on cell survival with much greater sensitivity and speed than some of the most popular tests used today.

The traditional test for measuring cell survival, known as the colony formation assay, involves growing cell colonies in tissue culture dishes for two to three weeks after exposing the cells to a chemical compound or another harmful agent such as radiation. A researcher then counts the number of colonies to determine how the treatment affected the cells' survival.

"The counting is really laborious and painfully difficult because you have to constantly make judgement calls as to what is a colony versus debris," explains Bevin Engelward, senior author of the study. "Few people use the colony formation assay anymore because it's difficult, way too slow, and requires huge amounts of cell growth media, so you need a lot of the compound being tested."

In recent years, scientists have begun using other methods that are faster but not as accurate and sensitive as the colony formation assay. These tests do not measure cell growth directly but instead analyze mitochondrial function.

Engelward and colleagues set out to develop a test that could generate results in just a few days while still matching the accuracy and sensitivity of the colony formation assay. The system they invented, which they call the MicroColonyChip, consists of tiny wells on a plate. Treated and untreated cells are placed into these wells and begin to form very small colonies in a grid pattern. Within just a few days, before the colonies become visible to the naked eye, the researchers can use a microscope to image the cells' DNA, which is fluorescently labeled.

The researchers also created a software program that measures the amount of fluorescent DNA in each well and then calculates how much cell growth occurred. By comparing the growth of treated and untreated cells, the researchers can determine the toxicity of whatever compound they are studying.

"We have an automatic scanning system to do the fluorescent imaging, and afterward, the image analysis is completely automated," reports Le Ngo, a former MIT graduate student and postdoc and the lead author of the paper.

The researchers compared their new test to the gold-standard colony formation assay and found that the results were indistinguishable. They were also able to precisely reproduce data on the effects of gamma radiation on human lymphoblastoid cells, collected 20 years ago using the colony formation assay. Using the MicroColonyChip, the researchers obtained their data in three days, instead of three weeks.