There's no way for it to happen automagically. Chart labels can't be referenced like you want. Create variable for the expression labels and use the variables as labels and chart title.
Label of Expression1: =vLabel1
Label of Expression2: =vLabel2
Chart title: =vLabel1 & ' - ' vLabel2
Thx for youre reply. Though it will not solve my problem because of two reasons:
1) If I clone the chart, I still need to change the variable names. It is exactly the same amount of work as just retyping the labelnames in the charts title.
2) The chart title of the charts I created before will also change if I adjust the variable names.
Conclusion: I was lazy and wanted to automate too much.