Yes it's possible but personally I encounter few problems, sometimes it works, sometimes not.
Uncaught TypeError: Cannot read property 'prototype' of undefined
PS : Don't forget to call super methods if you use them.
class A extends Sup.behavior { awake() { Sup.log("Awake from A"); }
}
class B extends A { awake() { super.awake(); Sup.log("Awake from B"); } start() { Sup.log("Start from B"); }
}