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Our previous studies have demonstrated that a tylophorine analog DCB-3503 has potent antitumor effect in nude mice bearing HepG2 (a hepatocellular carcinoma cell line) tumor xenografts and inhibitory effect against NF-κB mediated transcription in HepG2 cells (IC50=100 nM). Through collaboration, we observed that DCB-3503 significantly suppressed the development and progression of inflammatory arthritis in mice and almost nearly abrogated inflammatory skin disease in MRL-Faslpr murine lupus model. Consistently DCB-3503 reduced the protein amount of endogenous NF-κB target genes such as TNFα, IL-6, monocyte chemoattractant protein-1 (MCP-1), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) induced by lipopolysaccharide (LPS) treatment in bone marrow-derived dendritic cells. To investigate how DCB-3503 inhibits NF-κB several typical NF-κB related experiments were performed. Our data showed that DCB-3503 has no protective effect against TNFα induced IκBα degradation, no blocking effect against TNFα induced p65 translocation from cytoplasm to nucleus and no inhibitory effect against TNFα induced p65 mediated NF-κB response element binding activity. But strikingly the inhibitory effect of DCB-3503 against NF-κB could be observed within 1 h after 3h pretreatment with TNFα. This revealed that the mechanism of DCB-3503 adopted against NF-κB is a rapid regulatory mechanism. Coincidentally, we observed that DCB-3503 could induce cyclin D1 degradation as early as 30 min in HepG2 cells, and its degradation could be blocked by proteasomal inhibitor PS-341. 30 min treatment of HepG2 cells with DCB-3503 induced cyclin D1 ubiquitination. This cyclin D1 degradation mediated by DCB-3503 was also observed in Huh7, PANC-1 and MCF-7 cells. In addition to degradation of cyclin D1, degradation of cyclin D3, p53, and p21 was observed with 2h DCB-3503 treatment in HepG2 cells, whereas cyclin E showed no change upon DCB-3503 treatment. To correlate the time event of NF-κB inhibition and cyclin D1 degradation mediated by DCB-3503, we propose that DCB-3503 may exert its inhibitory effect of NF-κB through induction of a key p65 interacting protein degradation. Identification of this p65 interacting protein and its degradation is underway. In summary, DCB-3503 has potential for the treatment of cancer and autoimmune disease with a novel mechanism of action. (Y.C.Cheng is supported, in part, by NIH grant no. R01 CA87863.)

[Proc Amer Assoc Cancer Res, Volume 47, 2006]