Conformationally constrained compounds that mimic the secondary structure of reverse-turn regions of biologically active peptides and proteins are disclosed. Such reverse-turn mimetic structures have utility as diagnostic and therapeutic agents for inhibiting or treating disorders modulated by Wnt-signaling pathway, such as cancer, especially colorectal cancer, restenosis associated with angioplasty, polycystic kidney disease, aberrant angiogenesis disease, rheumatoid arthritis disease, tuberous sclerosis complex, Alzheimer's disease, excess hair growth or loss, or ulcerative colitis. In one embodiment, these reverse-term mimetics have a general structure of formula (VI): wherein Ra, Rb, Rc, X1, X2 and X3 are defined as provided herein.