5,6-Dichloro-ribifuranosylbenzimidazole- and apigenin-induced sensitization of colon cancer cells to TNF-α-mediated apoptosis

Abstract

Tumor necrosis factor-alpha (TNF-alpha) is a multifunctional cytokine involved in the expression of many genes integral to the inflammatory response. In addition, it activates both apoptotic and survival pathways, the latter being mediated through the activation of the transcription factor nuclear factor-kappaB (NF-kappaB). Protein kinase CK2, a serine-threonine kinase that is universally upregulated in human malignancies, may be involved at multiple levels in this process. However, its role in mediating a survival response within colon cancer cells remains incompletely understood. Here we report that inhibition of CK2 in HCT-116 and HT-29 cells with the use of two specific CK2 inhibitors, 5,6-dichloro-ribifuranosylbenzimidazole (DRB) and apigenin, effected a synergistic reduction in cell survival when used in conjunction with TNF-alpha. Furthermore, there was a demonstrable synergistic reduction in colony formation in soft agar with the use of the same combinations. Western blot analysis showed that poly-ADP ribose polymerase and procaspase-3 cleavage complemented the fluorescence-activated cell sorter analysis findings of significantly increased subdiploid DNA-containing cell populations using these conditions. Remarkably, these events occurred in the absence of any reduction in the expression of the Bcl-2 family members Bcl-2, Mcl-1, and Bcl-xL or any change in the proapoptotic molecules Bad or Bax. One-hybrid NF-kappaB promoter assays utilizing a Gal4-p65 transactivation domain construct revealed that the TNF-induced transactivation was inhibited by both DRB and apigenin. This was associated with a concomitant reduction in the expression of a recognized anti-apoptotic NF-kappaB target, manganese superoxide dismutase, demonstrated by Q-PCR. Our findings indicate a potentially novel strategy for the treatment of colon cancer, one that targets CK2 simultaneous with TNF-alpha administration.

Phosphorylation of RanGAP1 Stabilizes Its Interaction with Ran and RanBP1

“…2A, both drugs inhibited the RanGAP1 phosphorylation in vivo in a dose-dependent manner. As reported previously, higher concentrations of DRB were required to achieve a similar degree of inhibition (Farah et al, 2003). As exemplified in Fig.…”

“…To confirm this hypothesis experimentally, the phosphorylation was analyzed in the presence of the known CK2 inhibitors, apigenin (Song et al, 2000; 2003; Farah et al, 2003) and DRB (Zandomeni et al, 1986;Farah et al, 2003) in the culture medium. For the cultured cell lines, apigenin was used in the range of 40 to 150 mM, at which concentrations approximately 50% of the CK2 activity was reported to be inhibited (Song et al, 2003;Song et al, 2000).…”

Luteolin sensitizes tumor necrosis factor-α-induced apoptosis in human tumor cells

“…Different cell types used in those studies may explain the different responses to the same stimulus. Some other flavonoids such as apigenin and flavopiridol have also been found to suppress TNFastimulated NF-kB transcriptional activity without affecting IkBa degradation in some human colorectal cancer non-small-cell lung carcinoma cells (Farah et al, 2003;Kim et al, 2003a).…”

Apigenin and cancer chemoprevention: Progress, potential and promise (Review)

“…These results suggest that there is a p53-independent pathway for apigenin in p53-mutant cell lines, which induces p21/WAF1 expression and growth-inhibition. Farah et al (92) reported on 5, 6-dichloro-ribifurano-sylbenzimidazole (DRB)-and apigenin-induced sensitization of colon cancer cells to TNF·-mediated apoptosis. Inhibition of CK2 in HCT-116 and HT-29 cells with the use of two specific CK2 inhibitors, DRB and apigenin, affected a synergistic reduction in cell survival when used in conjunction with TNF·.…”