The Berlin local district Pankow like other regional names ending with -ow was derived from a Slavic name of this region. Still today variants of the Sorbian language are spoken in eastern parts of Germany but Sorbian is not a German dialect. The ending "-w" is not pronounced in Sorbian.
These names are not derived from Old Prussian even though we do find many Sorbian loanwords in Old Prussian likely due to the geographic proximity.