Caffeic acid phenyl ester in propolis is a strong inhibitor of matrix metalloproteinase-9 and invasion inhibitor: isolation and identification. - Jin,U.H.; Chung,T.W.; Kang,S.K.; Suh,S.J.; Kim,J.K.; Chung,K.H.; Gu,Y.H.; Suzuki,I.; Kim,C.H. (Clin Chim Acta, 2005)