Is there any postdoc or collaborator from your previous lab that you got along with who could write you a recommendation? Not as good as a letter from the PI obviously, but it can help account for all the time you spend in that lab.
Many of us had been in labs where things just didn't work out for various reasons, but moved on and had great experiences with other mentors. You just have to be honest and self reflective yet diplomatic about why you had to leave. Not everybody works well in overly competitive environments. Great science are done by smaller research groups too.
Research labs can be very hierarchal where undergrads are at the bottom of the ladder, always getting picked on. The clinical world is very hierarchal too. So think of it not as a complete loss but as a learning experience that's better preparing you to work with people.