I don't believe it can be done using the Chart title option, but here is a work-around I've used. Instead of using the Chart Title option, insert a textbox from the drawing tool bar. Assign a name to the cell you want to reference such as "reference". Then, selected the textbox and then click in the formula bar. Enter =reference. This will link the textbox to the reference cell and will update the title whenever the reference changes. One point, this does not seem to work with charts based on Pivot tables. The textbox does not refresh automatically. With these you have to reselect the textbox and re-enter the =reference in the formula bar each time.
it works perfectly, thanks Lenze
This will work with Chart Titles as well...
Just select the Chart Title, activate the formula
bar and click on the cell containing the text
that you'd like to use as a title.