Cell-based screening of extracts of natural sources to search for inhibitors of the ubiquitin-proteasome system and identification of proteasome inhibitors from the fungus Remotididymella sp.

The ubiquitin-proteasome system (UPS) regulates selective protein degradation to maintain protein homeostasis. Small molecules that inhibit the UPS-dependent protein degradation are promising anti-tumor agents. We report a cell-based luminescent assay using HeLa cells expressing luciferase-fused oxygen-dependent destruction domain (ODD) of hypoxia-inducible factor 1 α (HIF-1 α). ODD is degraded by the UPS and this assay system can aid in the identification of natural products that inhibit either process of the UPS, including ubiquitination/deubiquitination and proteasomal degradation. This reporter assay can exclude the influences of coloring or fluorescent compounds in extracts, thereby leading to effective high-throughput processing. The screening of 15,025 extracts of natural sources identified the culture extract of the fungus Remotididymella sp. (18F02908). Bioassay-guided isolation yielded two new polyketides, mellains A (1) and B (2), together with leptosphaerodione (3) and its acetone adduct 4. Compound 1 was revealed to have an unprecedented benzo[g]isoquinoline-8,10-dione skeleton. Evaluation of the biological activities demonstrated that these polyketides inhibit the proteasomal proteolysis. This is the first report of the identification of proteasome inhibitors from natural sources using a cell-based reporter assay targeting UPS inhibitors.

Potent reactive oxygen species-JNK-p38 activation by sodium salicylate potentiates death of primary effusion lymphoma cells.

BACKGROUND: Primary effusion lymphoma (PEL) is a rare but aggressive form of non-Hodgkin's B-cell lymphoma in immunodeficient patients. Resistance to conventional chemotherapeutic regimens is common in PEL and contributes to a very poor prognosis; hence, novel potent anti-PEL agents are required. Anticancer effects of non-steroidal anti-inflammatory drugs (NSAIDs) are well-established in epithelial cancer but are unclear in hematological malignancies. Therefore, the anticancer activities of selected NSAIDs, sodium salicylate (NaS), on PEL cell lines are of interest. MATERIALS AND METHODS: Anti-proliferation of NaS on PEL cell lines was shown by MTT. Apoptosis induction and caspase activations were determined by flow cytometry analysis. ROS production was accessed by DCFH-DA. Western blot was performed to determine molecular mechanisms. RESULTS: NaS effectively inhibited cell proliferation of all PEL cell lines. Caspase-dependent apoptosis was demonstrated and simultaneous induction of reactive oxygen species production and c-Jun N-terminal kinases (JNK)-p38 activation was observed prior to apoptosis induction, and these might be responsible for NaS-induced apoptosis. CONCLUSION: Significant anticancer effects of NaS on PEL cell lines were found. A novel role of NaS for PEL treatment is suggested.

Diethyldithiocarbamate suppresses an NF-kappaB dependent metastatic pathway in cholangiocarcinoma cells.

Cholangiocarcinoma (CCA) is a tumor of biliary ducts, which has a high mortality rate and dismal prognosis. Constitutively activation of the transcription factor nuclear factor kappa-B (NF-κB) has been previously demonstrated in CCA. It is therefore a potential target for CCA treatment. Effects of diethyldithiocarbamate (DDTC) on NF-κB-dependent apoptosis induction in cancer have been reported; however, anti-metastasis has never been addressed. Therefore, here the focus was on DDTC effects on CCA migration and adhesion. Anti-proliferation, anti-migration and anti-adhesion activities were determined in CCA cell lines, along with p65 protein levels and function. NF-κB target gene expression was determined by quantitative RT-PCR. DDTC inhibited CCA cell proliferation. Suppression of migration and adhesion were observed prior to anti-CCA proliferation. These effects were related to decreased p65, reduction in NF-κB DNA binding, and impaired activity. Moreover, suppression of ICAM-1 expression supported NF-kB-dependent anti-metastatic effects of DDTC. Taken together, DDTC suppression of CCA migration and adhesion through inhibition of NF-κB signaling pathway is suggested from the current study. This might be a promising treatment choice against CCA metastasis.

Potent antitumor activity of zoledronic acid-induced Vγ9Vδ2 T cells against primary effusion lymphoma.

Primary effusion lymphoma (PEL) is a subtype of aggressive and resistant non-Hodgkin lymphoma that occurs predominantly in patients with advanced AIDS. In this study, we examined the antitumor activity of zoledronic acid (Zol)-induced Vγ9Vδ2 T cells against PEL cells in vitro and in vivo. Vγ9Vδ2 T cells recognized endogenous mevalonate metabolites and MICA/B of PEL cell lines, inducing cytotoxicity via granule exocytosis and TRAIL-mediated pathway. Vγ9Vδ2 T cells suppressed the development of PEL cells and existed in a PEL xenograft mouse model. These results show that immunotherapy with Zol-induced Vγ9Vδ2 T cells could demonstrate an efficient strategy for PEL.