Rapamycin

Why is DMSO used as the vehicle in the rapamycin experiments of Gao et al. (2010)?
DMSO is used because rapamycin is soluble in DMSO and methanol.

What is the EC50 of rapamycin in this kind of experiment?
The EC50 of rapamycin varies from cell type to cell type and from experiment to experiment.

Zhu et al. (2009) tell us that rapamycin even smooth muscle cells in veins and arteries have different EC50s.

But Zhu does explain how to calculate the EC50 for any particular experiment:

What is the half-life of rapamycin in culture?
The half-life of rapamycin is 57–63 hours.