Question 3 of 6 Intermediate Scenario
How would you distinguish cytostatic from cytotoxic effects in a dose-response experiment?
Short answer
Cytostasis slows or stops net cell accumulation. Cytotoxicity decreases viable cells through cell death. Include a time-zero count and direct death markers alongside endpoint curves.
Why
Treat equally seeded cells with a concentration range and track viable-cell counts from dosing through one or more division cycles. A cytostatic dose produces a flatter growth trajectory than control, while a cytotoxic dose can bring the count below the dosing baseline. Compare growth-rate-normalized GR metrics when untreated cell divisions differ substantially between lines.
Incorporate membrane-impermeant dye uptake or other death indicators to support the mechanism, and confirm that the chosen reporter is not chemically inhibited by the compound. For example, a kinase inhibitor may leave the treated culture at 30,000 cells versus 100,000 controls after three days, yet both began at 20,000. This is not evidence that the compound killed 70% of starting cells.
Some drugs cause delayed death after initial arrest, so use an informative time course. Account for detached cells to avoid losing dead cells during sample preparation.
Common mistakes
- Confusing reduction relative to vehicle control with reduction relative to time-zero viable cells
The interviewer might ask next
What additional data would you collect if the treated count drops only after drug washout?