CCF642 is a cell-permeable protein disulfide isomerase (PDI) inhibitor that exhibits 100-fold higher potency than PACMA 31 (by di-E-GSSG assay) via an alternative mode of action that most likely involves PDI active-site CGHCK motifs instead of cysteine known to be targeted by PACMA 31. CCF642 displays anti-multiple myeloma (MM) activity both in cultures in vitro (IC50 <1 μM against murine 5TGM1 and nine human MM lines) and in mice in vivo (10 mg/kg, 3X i.p. per wk) without apparent adverse effects to the animals or being cytotoxic to normal bone marrow (NLBM) cells even at concentrations as high as 6.75 μM. Consistent with PDI′s role in ER protein folding process, CCF642 treatment causes acute ER stress accompanied by apoptosis-inducing calcium release in MM cells.
