Drug-tolerant persisters to TRAIL emerge from a dose-dependent surface in a cell-state continuum of sensitivity

Area of Science:

• Cellular biology
• Quantitative biology
• Biophysics

Background:

• Clonal cancer cell populations display heterogeneous responses to cytotoxic drugs, prompting investigation into the underlying mechanisms of drug sensitivity and tolerance.
• Understanding whether this variability stems from discrete cellular phenotypes or a continuum of cell states is crucial for effective cancer therapy.

Purpose of the Study:

• To quantify single-cell caspase-8 activation dynamics following TRAIL treatment.
• To develop and validate an extended mechanistic model of the extrinsic apoptosis pathway, incorporating c-FLIP-mediated control of initiator caspase activation.

Main Methods:

• Single-cell analysis of caspase-8 activation dynamics after TRAIL treatment.
• Development of a mechanistic model for the extrinsic apoptosis pathway with c-FLIP regulation.
• Model fitting to individual cell trajectories across multiple drug doses to infer cell-specific parameters.

Main Results:

• The mechanistic model successfully reproduced the diverse responses of individual cells to TRAIL treatment.
• Inferred cell-specific procaspase-8 and c-FLIP abundances, along with kinetic parameters, were recovered.
• Analysis revealed that drug-sensitive and drug-tolerant outcomes arise from a continuous distribution of cell states, not discrete subpopulations.

Conclusions:

• A single biochemical pathway generates a continuous spectrum of cell states that dictate apoptosis or tolerance upon drug treatment.
• Drug tolerance and fractional killing in clonal populations can be explained by reversible variations within this continuous cell state distribution.
• Modulating cell state distributions relative to a dose-dependent decision surface presents potential strategies to overcome drug persistence.