Enzyme Inhibitors: Using in vivo in yeast
This is usually the way this kind of inhibitors are used. There needs to be a way that they come into the cells (if they stay in solution and cannot reach their target they will be useless), but then they inhibit their targets.

What usually needs to be done is to determine which concentrations are needed in the cell culture (or the medium) to be effective for the inhibition but not to harm the cells. Therefore I usually use different concentrations of the inhibitor in culture and then measure the outcome.

To find the right concentrations, see if there are some recommendations from the manufacturers. Otherwise you will probably have to dig through Pubmed to find some starting point.