A protein-bound polysaccharide, PSK, enhances tumor suppression induced by docetaxel in a gastric cancer xenograft model.

BACKGROUND: We have reported previously that docetaxel (TXT) induces apoptosis and nuclear factor-kappaB (NF-kappaB) activation, and that blockade of NF-kappaB activation augments TXT-induced apoptosis in human gastric cancer cells. In addition, we have also shown that a protein-bound polysaccharide PSK enhances TXT-induced apoptosis through NF-kappaB inhibition in human pancreatic cancer cells. Based on these observations, in the present study the possibility that PSK could enhance TXT-mediated tumor suppression was examined in vivo and in vitro. MATERIALS AND METHODS: A gastric cancer xenograft model was used to examine the enhanced TXT-mediated tumor suppression by PSK in vivo. The effects of PSK on proliferation and apoptosis induced by TXT in gastric cancer cells were evaluated in vitro using a human gastric cancer cell line, MK-1. The effect of PSK on increased TXT-induced invasion was also measured. RESULTS: PSK enhanced TXT-mediated tumor suppression in vivo. Immunohistochemical analyses of the tumors revealed that TXT increased NF-kappaB activation in the tumors and this was suppressed by PSK. In the ex vivo experimental system, PSK enhanced the growth inhibition and apoptosis induced by TXT in the MK-1 cells and reduced the increased invasive ability induced by TXT. CONCLUSION: PSK enhanced TXT-induced tumor suppression in a gastric cancer xenograft model.

IkappaBalpha independent induction of NF-kappaB and its inhibition by DHMEQ in Hodgkin/Reed-Sternberg cells.

Constitutive nuclear factor kappaB (NF-kappaB) activation characterizes Hodgkin/Reed-Sternberg (H-RS) cells. Blocking constitutive NF-kappaB has been shown to be a potential strategy to treat Hodgkin lymphoma (HL). Here, for the first time we show that although constitutive NF-kappaB level of H-RS cell lines is very high, topoisomerase inhibitors further enhance NF-kappaB activation through IkappaB kinase activation in not only H-RS cell lines with wild-type IkappaBalpha, but also in those with IkappaBalpha mutations and lacking wild-type IkappaBalpha. Thus, both constitutive and inducible NF-kappaB are potential targets to treat HL. We also present the data that indicate the involvement of IkappaBbeta in NF-kappaB induction by topoisomerase inhibitors. A new NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ) inhibited constitutive NF-kappaB activity and induced apoptosis of H-RS cell lines. DHMEQ also inhibited the growth of H-RS cells without significant systemic toxicity in a NOD/SCID/gammac(null) (NOG) mice model. DHMEQ and topoisomerase inhibitors revealed enhancement of apoptosis of H-RS cells by blocking inducible NF-kappaB. Results of this study suggest that both constitutive and inducible NF-kappaB are molecular targets of DHMEQ in the treatment of HL. The results also indicate that IkappaBbeta is involved in NF-kappaB activation in H-RS cells and IkappaBbeta substitutes for IkappaBalpha in H-RS cells lacking wild-type IkappaBalpha.

Serum level of soluble CD30 correlates with the aggressiveness of adult T-cell leukemia/lymphoma.

Adult T-cell leukemia/lymphoma (ATL) is a highly aggressive disease with poor prognosis. CD30(+) cells are frequently observed in lymph node cells and peripheral blood mononuclear cells of ATL patients. In order to elicit the role of CD30(+) cells in ATL development, we investigated expression of the membrane type of CD30 (mCD30) and the soluble form of CD30 (sCD30) on ATL cells. Both mCD30 and sCD30 are expressed on various numbers of ATL cells in vivo as well as cell lines such as MT-2, L540 and Karpas 299. The level of serum sCD30 in each clinical stage showed an elevated level in patients with acute type (mean +/- standard error; 545.2 +/- 18.6 U/mL) rather than with lymphoma type ATL (327.62 +/- 94.85 U/mL). In four patients whose sera were stored and examined longitudinally, the levels decreased following the response to chemotherapy but not in patients with chemotherapy resistance. Thus, our results imply that sCD30 levels may be another useful marker for the activity and aggressiveness of ATL.

Dual targeting of transformed and untransformed HTLV-1-infected T cells by DHMEQ, a potent and selective inhibitor of NF-kappaB, as a strategy for chemoprevention and therapy of adult T-cell leukemia.

Human T-cell leukemia virus type I (HTLV-1) causes adult T-cell leukemia (ATL), a fatal T-cell leukemia resistant to chemotherapy, after more than 50 years of clinical latency from transmission through breast-feeding. Polyclonal expansion of virus-infected T cells predisposes them to transformation. Constitutive activation of nuclear factor-kappaB (NF-kappaB) in the leukemic cells is essential for their growth and survival. Blocking NF-kappaB has been shown to be a potential strategy to treat ATL. We tested this approach using a novel NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), and also examined its application to chemoprevention by selective purging of the HTLV-1-infected cells. DHMEQ inhibited NF-kappaB activation in primary ATL cells and cell lines derived from them and induced apoptotic cell death. NF-kappaB inhibition down-regulated expression of genes involved in antiapoptosis or cell-cycle progression. DHMEQ protected severe combined immunodeficiency (SCID) mice inoculated with HTLV-1-transformed cells from death. In addition, DHMEQ selectively targeted HTLV-1-infected cells in the peripheral blood of virus carriers in vitro, resulting in a decreased number of infected cells. We conclude that NF-kappaB is a potential molecular target for treatment and prevention of ATL. As a potent NF-kappaB inhibitor, DHMEQ is a promising compound allowing the translation of this strategy into clinical medicine.

Integration of human T-cell leukemia virus type 1 in genes of leukemia cells of patients with adult T-cell leukemia.

Adult T-cell leukemia (ATL) occurs after a long latent period of persistent infection by human T-cell leukemia virus type 1 (HTLV-1). However, the mechanism of oncogenesis by HTLV-1 remains to be clarified. It was reported that the incidence curve of ATL versus age was consistent with a multistage carcinogenesis model. Although HTLV-1 is an oncogenic retrovirus, a mechanism of carcinogenesis in ATL by insertional mutagenesis as one step during multistage carcinogenesis has not been considered thus far, because the exact integration sites on the chromosome have not been analyzed. Here we determined the precise HTLV-1 integration sites on the human chromosome, by taking advantage of the recently available human genome database. We isolated 25 integration sites of HTLV-1 from 23 cases of ATL. Interestingly, 13 (52%) of the integration sites were within genes, a rate significantly higher than that expected in the case of random integration (P = 0.043, chi(2) test). These results suggest that preferential integration into genes at the first infection is a characteristic of HTLV-1. However considering that some of the genes are related to the regulation of cell growth, the integration of HTLV-1 into or near growth-related genes might contribute to the clonal selection of HTLV-1-infected cells during multistage carcinogenesis of ATL.

Cell-free human T-cell leukemia virus type 1 binds to, and efficiently enters mouse cells.

Human T-cell leukemia virus type 1 (HTLV-1) is an etiologic agent of adult T-cell leukemia / lymphoma and other HTLV-1-associated diseases. However, the interaction between HTLV-1 and T cells in the pathogenesis of these diseases is poorly understood. Mouse cells have been reported to be resistant to cell-free HTLV-1 infection. However, we recently reported that HTLV-1 DNA could be observed 24 h after cell-free HTLV-1 infection of mouse cell lines. To understand HTLV-1 replication in these cells in detail, we concentrated the virus produced from c77 feline kidney cell line and established an efficient infection system. The amounts of adsorption of HTLV-1 are larger in mouse T cell lines, EL4 and RLm1, than those in human T cell lines, Molt4 and HUT78, and are similar to that in human kidney cell line, 293T. Unexpectedly, however, the amounts of entry of HTLV-1 are about 10-fold larger in the two mouse cell lines than those in the three human cell lines employed. Moreover, viral DNA was detectable from 1 h in EL4 and RLm1 cells, but only from 2 - 3 h in 293T, Molt4 and HUT78 cells. However, the amount of viral DNA in EL4 cells became smaller than that in Molt4 cells. HTLV-1 expression could be detected until day 1 - 2 in RLm1 and EL4 cells, and until day 4 in Molt4 cells. Our results suggest that mouse cell experiments would give useful information to dissect the early steps of cell-free HTLV-1 infection.