Abstract. Signal transducer and activator of transcription (Stat)3, a member of a family of Dna-binding molecules mediating numerous physiological and oncogenic signaling pathways, is a novel target in cancer cells which show high phosphorylation of STAT3. Recently, we identified a novel small-molecule inhibitor of Stat3 dimerization, StX-0119, as a cancer therapeutic. We investigated the mechanisms responsible for the antitumor activity in vitro and in vivo through numerous biochemical and biological assays. Specifically, the effects of StX-0119 on target genes (c-myc, cyclin D1, survivin) and apoptosis induction were analyzed in tumors treated with StX-0119 in vivo. StX-0119 showed strong growth-inhibitory activity against a broad range of hematological cancer cell lines, particularly lymphomas. StX-0119 suppressed the growth of Scc3 cells, a human lymphoma cell line with highly activated Stat3, through apoptosis and down-regulation of Stat3 targets such as c-myc, cyclin D1, survivin and Bcl-xl. notably, tyr-705-phosphorylated Stat3 up-regulation was not significantly suppressed by STX-0119, as opposed to other Stat3 inhibitors. StX-0119 demonstrated potent antitumor effects in vivo in Scc3-bearing nude mice by way of the down-regulation of Stat3 target genes and induction of apoptosis in the tumors. thus, StX-0119 may be a new type of Stat3 inhibitor exhibiting strong antitumor activity. Introductionthe signal transducer and activator of transcription (Stat) protein family is a group of transcription factors that play an important role in relaying signals from growth factors and cytokines (1-3). Stat3 is reported to be involved in oncogenesis by up-regulating the transcription of several genes that control tumor cell survival, resistance to apoptosis, cell cycle progression and angiogenesis. targets of Stat3 include Bcl-2 (4), Bcl-xl (5), c-myc (6), cyclin D1 (7), vascular endothelial growth factor (8) and human telomerase reverse transcriptase (9).Several Stats have been associated with the proliferation and survival of cancer cells; however Stat3 is also widely expressed in normal cells. generally, Stat3 is temporarily activated in a manner strictly regulated by the protein inhibitor of Stats (PiaS), Src homology (SH)2-containing tyrosine phosphatases (SHP1 and SHP2) (10), and suppressor of cytokine signaling/extracellular signal-regulated kinase (SOCS/ERK) (11) to protect cells from excess inflammatory signaling.Moreover, persistent activation of Stat3 occurs in many hematological malignancies (12,13) and solid cancers. constitutive Stat3 activation up-regulates the expression of anti-apoptotic factors including Bcl-xl, Bcl-2 and Mcl-1 and promotes the survival of tumor cells, thus contributing to resistance to faS-or chemotherapy-induced apoptosis (14). Blocking of STAT3 signaling demonstrated significant growth inhibition of cancer cells by down-regulation of the expression of anti-apoptotic genes, leading to apoptosis. the activation of Stat3 occurs when it is phosphorylated at the tyr-705 residue. this...

Although p53 is intact in most cases of retinoblastoma, it is largely inactivated by the ubiqutin-proteasome system through interaction with murine double minute 2 (MDM2) and murine double minute X (MDMX). The present study showed that the histone deacetylase (HDAC) inhibitors valproic acid (VPA) and depsipeptide (FK228) synergistically enhanced ionizing radiation (IR)-induced apoptosis, associated with activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase in Y79 and WER1-Rb1 human retinoblastoma cells. Both VPA and FK228 enhanced IR-induced phosphorylation of histone H2AX on Ser139 preceding apoptosis. Exposure of cells to IR in the presence of VPA or FK228 induced the accumulation of p53 acetylated at Lys382 and phosphorylated at Ser46 through the reduction of binding affinity with MDM2 and MDMX. These results suggest that acetylation of p53 by HDAC inhibitors is a promising new therapeutic target in refractory retinoblastoma.

Abstract. Thymidine phosphorylase (TP) is an enzyme involved in reversible conversion of thymidine to thymine. TP is identical to an angiogenic factor, pletelet-derived endothelial cell growth factor (PD-ECGF) and the expression levels of TP in a variety of malignant tumors were higher than the adjacent non-neoplastic tissues. To investigate the molecular basis for the effect of TP on the metabolic process and the anticancer effect of 5-fluorouracil (5-FU), human gastric carcinoma AZ521 cells and epidermoid carcinoma KB cells were transfected with TP cDNA, and AZ521/TP and KB/ TP were cloned. AZ521/TP and KB/TP cells overexpressed TP and were more sensitive to 5-FU than the counterpart parental cells. TPI, a newly synthesized inhibitor for TP (Ki=2.36x10 -9 M), decreased the sensitivity to 5-FU of the TP expressing cells but not of the parental cells. 5-Formyltetrahydrofolate (leucovorin; LV) stabilized the complex of thymidylate synthase (TS) and 5-fluoro-deoxyuridinemonophosphate (FdUMP), increased the sensitivity to 5-FU of TP expressing AZ521 cells, but not of the parental cells. The levels of FdUMP in TP expressing cells were significantly higher than in parental cells and TPI considerably decreased FdUMP to the level comparable to that in the parental cells. 5-FU increased the expression of early growth response protein-1 (Egr-1) and an angiogenesis inhibitor, thrombospondin-1 (TSP-1), in KB/TP cells but only slightly in KB/CV cells, if any. TPI attenuated the induction of Egr-1 and TSP-1 mRNA by 5-FU, while LV increased the expression of Egr-1 and TSP-1 mRNA in KB/TP cells. These findings demonstrate that the TP has a principal role in the production of FdUMP and the enhanced responses to 5-FU by leucovorin in TP-overexpressing KB and AZ521 cells, and FdUMP but not FUTP is implicated in the induction of Egr-1 and TSP-1 in KB cells. IntroductionThymidine phosphorylase (TP) catalyzes the reversible phosphorolysis of thymidine, deoxyuridine, and their analogues to their respective bases and 2-deoxyribose-1-phosphate (1-3). It also catalyzes deoxyribosyltransfer from one deoxynucleotide to another base, to form a second deoxyuridine (4-6). Recent studies showed that TP is expressed in a wide variety of solid tumors (7-13), but the role of TP in tumor proliferation was unknown. We have found that TP is identical to an angiogenic factor, platelet-derived endothelial cell growth factor (PD-ECGF), and the enzymatic activity of TP is need for the angiogenesis by TP (14-16). TP is also considered to activate some pyrimidine antimetabolites (17-19). 5-Fluorouracil (5-FU) was developed as a potential anti-tumor drug (20), and reportedly activated through three alternative routes. It may be converted to FUMP either directly by orotate phosphoribosyltranferase or by the sequential actions of uridine phosphorylase and uridine kinase. FUMP may be converted to FUDP and then to FUTP, INTERNATIONAL JOURNAL OF ONCOLOGY 36: 1193-1200, 2010 The role of thymidine phosphorylase in the induction of early growth response protein-1...