Nuclear factor-kappaB pathway as a therapeutic target in head and neck squamous cell carcinoma: pharmaceutical and molecular validation in human cell lines using Velcade and siRNA/NF-kappaB.

Background: Nuclear factor-kappaB (NF-kappaB) is synthesized in the cytoplasm, complexed with its inhibitor, I-kappaB, and NF-kappaB is released in an activated (phosphorylated) form following phosphorylation of I-kappaB and proteasomal degradation of the NF-kappaB.p-kappaB complex. The free p-NF-kappaB can then be translocated to the nucleus where it effects transcriptional activation of genes leading to the synthesis of proteins that are generally pro-growth and anti-apoptosis.

Objective: To gain insight into the role of the NF-kappaB pathway in head and neck squamous cell carcinoma (HNSCC), we selected two HNSCC cell lines, SCC-15 of lingual origin and FaDu of pharyngeal origin, with constitutively activated (phosphorylated) NF-kappaB. We assessed the impact of interrupting the NF-kappaB pathway at the level of proteasomal degradation using Velcade (bortezomib), a proteasome inhibitor, and at the pretranslational level in the synthesis of NF-kappaB using a small interfering RNA (siRNA).

Results: Velcade produced a dose-dependent inhibition of cell growth in both cell lines. At 30 nM, Velcade inhibited cell growth in the SCC-15 cell line by 40%. In both cell lines, Velcade induced nuclear overexpression of p21(WAF1), an inhibitor of G1 cell cycle progression, which appeared to be independent of p53 expression. Addition of siRNA augmented the inhibitory effects of Velcade in FaDu cells; siRNA/NF-kappaB alone led to a 48% decline in basal expression of NF-kappaB protein levels and effected a 25% inhibition of cell growth. In the presence of Velcade (30 nM), siRNA/NF-kappaB increased growth inhibition from 43 to 65%.

Conclusions: The mechanisms involved in growth inhibitory effects of Velcade on HNSCC cell lines include the NF-kappaB pathway, suggesting the possible therapeutic use of Velcade or other NF-kappaB pathway inhibitors (eg, curcumin). The data also suggest that combining siRNA/NF-kappaB with Velcade might achieve greater reduction in the growth of HNSCC in patients with constitutively activated NF-kappaB.