Reactivation of Epstein-Barr virus lytic cycle by histone deacetylase inhibitors

Epstein-Barr virus (EBV) is closely associated with certain lymphoid and epithelial malignancies such as Burkitt lymphoma, nasopharyngeal carcinoma (NPC) and gastric carcinoma (GC). In the tumor cells, the virus persists in a tight latency, expressing a limited number of latent proteins. Reactivation of EBV lytic cycle from latency leads to expression of many more viral lytic proteins which may provide potential therapeutic targets for the EBV-associated cancers. Histone deacetylase (HDAC) inhibitors belong to an emerging class of anti-cancer agents which work through acetylation of different histone and non-histone proteins in cancer cells. Our previous work showed that various pan-HDAC inhibitors, which inhibit eleven HDAC isoforms, can preferentially reactivate EBV lytic cycle in EBV-positive epithelial rather than lymphoid cancers and mediate enhanced killing of EBV-positive NPC and GC cells through augmentation of apoptotic cell death. Recently, we found that a selective class I HDAC inhibitor, romidepsin, can potently induce EBV lytic cycle in NPC and GC cells and confer susceptibility of the induced cells to killing by an anti-viral agent, ganciclovir, in vitro and in vivo. The reactivation of EBV lytic cycle by romidepsin is related to the inhibition of HDAC-1, -2 and -3 isoforms and the activation of PKC-. Interestingly, our current findings suggest that acetylation of non-histone proteins might also play a role in the regulation of EBV lytic cycle upon HDAC inhibition. In this review, we discuss our recent findings on the mechanisms of EBV lytic cycle reactivation and propose possible strategies in using HDAC inhibitors for the treatment of EBV-associated cancers.published_or_final_versio

Induction of MAPK- and ROS-dependent autophagy and apoptosis in gastric carcinoma by combination of romidepsin and bortezomib

Proteasome inhibitors and histone deacetylase (HDAC) inhibitors can synergistically induce apoptotic cell death in certain cancer cell types but their combinatorial effect on the induction of autophagy remains unknown. Here, we investigated the combinatorial effects of a proteasome inhibitor, bortezomib, and an HDAC inhibitor, romidepsin, on the induction of apoptotic and autophagic cell death in gastric carcinoma (GC) cells. Isobologram analysis showed that low nanomolar concentrations of bortezomib/romidepsin could synergistically induce killing of GC cells. The synergistic killing was due to the summative effect of caspase-dependent intrinsic apoptosis and caspase-independent autophagy. The autophagic cell death was dependent on the activation of MAPK family members (ERK1/2 and JNK), and generation of reactive oxygen species (ROS), but was independent of Epstein-Barr virus infection. In vivo, bortezomib/romidepsin also significantly induced apoptosis and autophagy in GC xenografts in nude mice. This is the first report demonstrating the potent effect of combination of HDAC and proteasome inhibitors on the induction of MAPK- and ROS-dependent autophagy in addition to caspase-dependent apoptosis in a cancer type.published_or_final_versio

Malignancies in Chinese patients with neurofibromatosis type 1

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Bortezomib combines with suberoylanilide hydroxamic acid (SAHA) to synergistically induce caspase-dependent apoptosis and blocks SAHA's activation of EBV lytic cycle in nasopharyngeal carcinoma

Poster Session 1 - Vaccines and Anti-Viral Therapeutics: no. 3.13Histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), could induce Epstein-Barr virus (EBV) lytic cycle and apoptosis in EBV-positive nasopharyngeal carcinoma (NPC) cells. In this study, we investigated the effects of combining a proteasome inhibitor, bortezomib, with SAHA in the treatment of NPC cells. Synergistic killing of a panel of EBV-positive NPC cells upon treatment with various combinations of bortezomib (0, 7.5, 15, 30, 60 and 120 nM) and SAHA (0, 0.625, 1.25, 2.5, 5 and 10 uM) was demonstrated by MTT assay and isobologram analysis. The synergistic killing was due to apoptosis as demonstrated by markedly increased sub-G1, annexin V-positive and TUNEL-positive cell populations. Strong proteolytic cleavage of PARP, caspase-3, -7 and -9 and increased reactive oxygen species …postprin

Urate oxidase for the prevention and treatment of tumour lysis syndrome in children with cancer

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Associations between IL12B polymorphisms and tuberculosis in the Hong Kong Chinese population

Background. Interleukin (IL)-12 plays a vital role in regulating cell-mediated immunity against tuberculosis (TB). Methods. To test whether IL12B genetic polymorphisms might contribute to human TB susceptibility, we examined the genotype frequencies of 5 IL12B polymorphisms (at promoter, intron 2, intron 4, exon 5, and 3′ untranslated region [UTR]) in 516 patients with TB and 514 healthy control subjects from the Hong Kong Chinese population. Results. Individuals homozygous for the IL12B intron 2-repeat marker (ATT) 8 had a 2.1-fold increased risk of developing TB (P < .001) (odds ratio, 2.14 [95% confidence interval, 1.45-3.19]). Estimation of the frequencies of multiple-locus haplotypes composed of IL12B promoter, intron 2, intron 4, and 3′ UTR alleles revealed potential risk haplotypes (designated "A" and "K") and protective haplotypes (designated "B") for TB. Furthermore, combining the genotype data of the 4 informative IL12B loci revealed a strong association between a specific genotype pattern, termed "diplotype I" (heterozygous A and K haplotypes), and TB. In contrast, diplotype II (homozygous BB haplotypes) appeared protective against TB. Conclusions. These findings support the association between IL12B intron 2 polymorphism and TB and between specific IL12B haplotypes and TB.published_or_final_versio

Combination of SAHA and bortezomib up-regulates CDKN2A and CDKN1A and induces apoptosis of Epstein-Barr virus-positive Wp-restricted Burkitt lymphoma and lymphoblastoid cell lines

Epstein-Barr virus (EBV) latent proteins exert anti-apoptotic effects on EBV-transformed lymphoid cells by down-regulating BCL2L11 (BIM), CDKN2A (p16(INK4A) ) and CDKN1A (p21(WAF1) ). However, the potential therapeutic effects of targeting these anti-apoptotic mechanisms remain unexplored. Here, we tested both in vitro and in vivo effects of the combination of histone deacetylase (HDAC) and proteasome inhibitors on the apoptosis of six endemic Burkitt lymphoma (BL) lines of different latency patterns (types I and III and Wp-restricted) and three lymphoblastoid cell lines (LCLs). We found that the combination of HDAC and proteasome inhibitors (e.g. SAHA/bortezomib) synergistically induced the killing of Wp-restricted and latency III BL and LCLs but not latency I BL cells. The synergistic killing was due to apoptosis, as evidenced by the high percentage of annexin V positivity and strong cleavage of PARP1 (PARP) and CASP3 (caspase-3). Concomitantly, SAHA/bortezomib up-regulated the expression of CDKN2A and CDKN1A but did not affect the level of BCL2L11 or BHRF1 (viral homologue of BCL2). The apoptotic effects were dependent on reactive oxygen species generation. Furthermore, SAHA/bortezomib suppressed the growth of Wp-restricted BL xenografts in nude mice. This study provides the rationale to test the novel application of SAHA/bortezomib on the treatment of EBV-associated Wp-restricted BL and post-transplant lymphoproliferative disorder.postprin

Identification of Novel Small Organic Compounds with Diverse Structures for the Induction of Epstein-Barr Virus (EBV) Lytic Cycle in EBV-Positive Epithelial Malignancies

Phorbol esters, which are protein kinase C (PKC) activators, and histone deacetylase (HDAC) inhibitors, which cause enhanced acetylation of cellular proteins, are the main classes of chemical inducers of Epstein-Barr virus (EBV) lytic cycle in latently EBV-infected cells acting through the PKC pathway. Chemical inducers which induce EBV lytic cycle through alternative cellular pathways may aid in defining the mechanisms leading to lytic cycle reactivation and improve cells’ responsiveness towards lytic induction. We performed a phenotypic screening on a chemical library of 50,240 novel small organic compounds to identify novel class(es) of strong inducer(s) of EBV lytic cycle in gastric carcinoma (GC) and nasopharyngeal carcinoma (NPC) cells. Five hit compounds were selected after three successive rounds of increasingly stringent screening. All five compounds are structurally diverse from each other and distinct from phorbol esters or HDAC inhibitors. They neither cause hyperacetylation of histone proteins nor significant PKC activation at their working concentrations, suggesting that their biological mode of action are distinct from that of the known chemical inducers. Two of the five compounds with rapid lytic-inducing action were further studied for their mechanisms of induction of EBV lytic cycle. Unlike HDAC inhibitors, lytic induction by both compounds was not inhibited by rottlerin, a specific inhibitor of PKCδ. Interestingly, both compounds could cooperate with HDAC inhibitors to enhance EBV lytic cycle induction in EBV-positive epithelial cancer cells, paving way for the development of strategies to increase cells’ responsiveness towards lytic reactivation. One of the two compounds bears structural resemblance to iron chelators and the other strongly activates the MAPK pathways. These structurally diverse novel organic compounds may represent potential new classes of chemicals that can be used to investigate any alternative mechanism(s) leading to EBV lytic cycle reactivation from latency.published_or_final_versio

Urate oxidase for the prevention and treatment of tumour lysis syndrome in children with cancer

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