If you are using mechanical runners, they need the drawer to be narrower than the opening (usually by 12mm each side) to allow the runner to pass through the opening with the drawer.
If the drawer front is separate from the drawer tray and sits inside the cabinet frame (so the drawer front and frame are flush) then you need to allow for the thickness of the front when choosing the runners.
If the drawer front sits in front of the base unit, making the overall depth of the cabinet + drawer front 470mm, then you should be able to use the 450mm runner.