How would you test whether a signaling inhibitor affects its intended pathway?

Why

Choose an established substrate, receptor state or phosphorylation event close to the intended target, then test doses and time points around a defined stimulus. For example, a MEK inhibitor may reduce phospho-ERK rapidly while total ERK remains stable. Use vehicle, pathway-positive and assay-negative controls, and monitor viable cell numbers.

Stronger causal support comes from a structurally distinct inhibitor or genetic perturbation and, if feasible, rescue with a resistant target allele. Check feedback loops and compensatory phosphorylation rather than assuming every downstream readout changes monotonically. A cytotoxic concentration can non-specifically suppress many signaling proteins.

Analyze the proximal effect at concentrations that do not broadly damage cells, and keep a record of confluence and serum-starvation conditions because both change basal signaling. The final claim should match the evidence: target engagement, pathway modulation or phenotypic efficacy are separate layers.