Orexigen, Takeda in $1 bln deal for obesity drug

* Orexigen to get upfront cash payment of $50 mln
* Deal can pay Orexigen over $1 bln in milestone payments
* Takeda to market obesity drug in U.S., Mexico, Canada
* Cos to share costs of any future product development
* Orexigen shares jump 23 pct (Adds analyst comment, background, updates share price)