Noscapine, a benzylisoquinoline alkaloid, sensitizes leukemic cells to chemotherapeutic agents and cytokines by modulating the NF-kappaB signaling pathway.

Noscapine, a benzylisoquinoline alkaloid derived from opium, was recently reported to exhibit activity against a variety of cancers through a poorly understood mechanism. Because the transcription factor NF-kappaB has been linked with inflammation, survival, proliferation, invasion, and angiogenesis in tumors, we hypothesized that noscapine mediates its effects by modulating the NF-kappaB activation pathway. We found that noscapine potentiates apoptosis induced by cytokines and chemotherapeutic agents in tumor cells. Noscapine alone suppressed proliferation of human leukemia and myeloma cells and downregulated the constitutive expression of cell survival proteins. Noscapine also abrogated the inducible expression of proteins involved in survival, proliferation, invasion, and angiogenesis, all of which are regulated by NF-kappaB. Noscapine suppressed both inducible and constitutive NF-kappaB activation in tumor cells through inhibition of IkappaB kinase, leading to inhibition of phosphorylation and degradation of IkappaBalpha. Noscapine also suppressed phosphorylation and nuclear translocation of p65, leading to inhibition of NF-kappaB reporter activity induced by various components of the NF-kappaB activation pathway. Activity of the NF-kappaB-containing cyclooxygenase-2 promoter was also inhibited by noscapine. Thus, noscapine inhibits the proliferation of leukemia cells and sensitizes them to tumor necrosis factor and chemotherapeutic agents by suppressing the NF-kappaB signaling pathway.