All signs are pointing toward its continued success.When it comes to pre-revenue biotechs, it's often a struggle to build an investment thesis beyond "if the medicine works, the stock will go up." And while that proposition is certainly true with Viking Therapeutics, (VKTX 4.52%) there's more than one reason for why the stock is worth buying.In fact, there are at least four arguments supporting an investment, so let's take a look at each.1. It's racing closer to generating revenue for the first timeViking i ...