In quadrilateral $PROQ$, $m(\widehat{PRO})=m(\widehat{PQO})=90^{\circ}\Right arrow PROQ$ is inscribable.
In quadrilateral $POQB$, $m(\widehat{PQO})=m(\widehat{PBO})=90^{\circ}\Right arrow POQB$ is inscribable.
The two quadrilaterals have in common the points $P,O,Q$, so all the five points are cyclic.