Nintendo probably owns the rights to them, it looks like the game engine was created by Nintendo and another company put a new front end on it to make it look different.
As far as I know the Giana Sisters are still owned by the developers there.
In 2008, publisher DTP Entertainment and developer Spellbound Interactive, owner of the game IP have announced that a new Giana Sisters game with an extensive graphical update is in development for Nintendo DS and was released in April 2009 in Europe by the developer. [2] There is yet to be an Australian Release Date for the game as well. The game features all-new levels and more gameplay elements, and a recreation of the original game's levels can be unlocked.
From Wikipedia.
