A teaser trailer was shown at Comic-Con and Duncan Jones announced he'll start production on the movie early next year. Here's a description of the teaser from io9:
The footage showcased an alien-looking landscape full of rocky outcroppings, where a sweaty unshaven figure in armor is drinking water from a leather pouch. There's a cage with rocks in it, a squeaking noise, green lightning in the sky. The man tosses the water pouch on the ground, and draws his sword with a loud ringing sound. He takes a shield from an armored skeleton, and bangs his sword against it.
And then you see the massive arm of a... creature... heading towards him. We glimpse the green skin and some of the armor, and then finally we get an extreme closeup of the orc as it raises its axe and brings it down onto the man's head.