Complex sentence: Increasing the amount of p53, which may initially seem a good way to treat tumors or prevent them from spreading, is in actuality not a usable method of treatment, since it can cause premature aging.
Split into simpler sentences: Increasing the amount of p53, which may seem a solution for treatment of tumors or preventing them from spreading. This, however, is not a usable method of treatment, since it can cause premature aging.