The problem is, you don't seem to know exactly how the drug approval process works. You use words like "proof of concept" that don't make sense from the context. It doesn't make sense to answer it in detail now, I'll just say one thing: Without successful preclinical studies, you cannot test on people! Preclinical studies are used to examine the properties of the active ingredient in order to ensure that it can be used safely in humans. Animal experiments, for example, are a prerequisite. In addition, various laboratory tests are used to examine the physical and chemical properties of the new drug. By carrying out special experiments, it is possible to estimate what influence the drug has on the human body and what side effects may occur.
By the way, you never know whether a drug will work in humans until you conduct clinical studies. That's the point. Incidentally, most drugs fail in the phase 2 study.