LRT Compound key using uri-user of request-uri

On acme SBC I need to search in an LRT using a compound key that will have the rn and the usi-user if Request-Uri. If can succesfully  search using the rn and the usi-user or "To" header with ann expresion like:

next-hop        lrt:nameLrt;key=rn,$TO

But I´m no able to do the same with Request_Uri, i.e, I have tried_

next-hop        lrt:nameLrt;key=rn,$Request-Uri

But it doesný work.

any ideas?