Inhibition of cell growth and nuclear factor-κB activity in pancreatic cancer cell lines by a tylophorine analogue, DCB-3503

A tylophorine analogue, DCB-3503, has been shown to have potent activity against tumor growth in vitro and in vivo, as well as activity in an autoimmune disease model in vivo. This study focuses on investigating the mechanisms responsible for antitumor activity of DCB-3503. The concentrations for inhibiting 50% growth/colony formation ability are 50/162 and 40/149 nmol/L for PANC-1 and HPAC cells, respectively. The growth inhibition effects are associated with DCB-3503-induced reprogramming of tumor cells. DCB-3503 could interfere with cell cycle progression. Several cell cycle regulatory proteins, including cyclin D(1), are down-regulated by DCB-3503. Using several different transcription elements coupled with a reporter gene, it was found that the nuclear factor-kappaB (NF-kappaB) signaling pathway is the most sensitive pathway mediator affected by DCB-3503. The inhibition of NF-kappaB activity is dependent on the down-regulation of nuclear phosphorylated p65, a component of the active form of the NF-kappaB complex. Such a decrease in nuclear phosphorylated p65 can be reversed by a proteosome inhibitor. Furthermore, the activity and protein expression of nuclear IkappaB kinase alpha, which is responsible for p65 phosphorylation, is suppressed and down-regulated in cells treated with DCB-3503. In summary, DCB-3503 could affect cell cycle regulatory proteins and is a potent modulator of NF-kappaB function. It is a potentially useful compound in the management of cancers in which cyclin D1 overexpression and high NF-kappaB activity play a pivotal role.

Induction of thyroid cancer cell apoptosis by a novel nuclear factor kappaB inhibitor, dehydroxymethylepoxyquinomicin

PURPOSE

The objective of the study was to determine the effects of a novel selective nuclear factor kappaB (NF-kappaB) inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), in thyroid carcinoma cells in vitro and in vivo and to additionally elucidate the molecular mechanisms underlying the action of this chemotherapeutic agent.

EXPERIMENTAL DESIGN

In the in vitro experiments, the induction of apoptosis by DHMEQ in various human thyroid carcinoma cell types was determined by flow cytometry analysis of annexin-V binding and the caspase activation by Western blotting. For the in vivo study, female nu/nu mice were xenografted with s.c. FRO thyroid tumors. DHMEQ solution was injected i.p. at a dose of 8 mg/kg/day for two weeks. Tumor dimensions were monitored twice weekly, and apoptosis in tumor specimens was determined by terminal deoxynucleotidyl transferase-mediated nick end labeling staining.

RESULTS

Treatment with DHMEQ substantially inhibited the translocation of p65 and p50 NF-kappaB subunits to the nucleus, the DNA-binding activity of the RelA/p65, NF-kappaB-dependent expression of the inhibitor of apoptosis (IAP)-family proteins, cIAP-1, cIAP-2, and XIAP, and the de novo synthesis of inhibitor of nuclear factor kappaB alpha. At concentration levels ranging from 0.1 to 5 microg/ml, DHMEQ induced a caspase-mediated apoptotic response that could be abrogated by the c-Jun NH(2)-terminal kinase inhibitor SP600125 but not by either mitogen-activated protein/extracellular signal-regulated kinase kinase or p38 inhibitors. In contrast, normal human thyrocytes were resistant to DHMEQ-induced apoptosis. At higher doses of DHMEQ we observed the necrotic-like killing of both normal and malignant thyrocytes, which was resistant to mitogen-activated protein kinase inhibitors. In nude mice DHMEQ substantially inhibited tumor growth without observable side effects, and increased numbers of apoptotic cells were observed in the histologic sections of tumors treated with DHMEQ.

CONCLUSIONS

Our results show the potential usefulness of the novel NF-kappaB inhibitor, DHMEQ, in future therapeutic strategies for the treatment of thyroid cancers that do not respond to conventional approaches.