Yoshinari Shinsato

Ribonucleotide reductase is an effective target to overcome gemcitabine resistance in gemcitabine-resistant pancreatic cancer cells with dual resistant factors.

Gemcitabine is widely used for pancreatic, lung, and bladder cancer. However, drug resistance against gemcitabine is a large obstacle to effective chemotherapy. Nucleoside transporters, nucleoside and nucleotide metabolic enzymes, and efflux transporters have been reported to be involved in gemcitabine resistance. Although most of the resistant factors are supposed to be related to each other, it is unclear how one factor can affect the other one. In this study, we established gemcitabine-resistant pancreatic cancer cell lines. Gemcitabine resistance in these cells is caused by two major processes: a decrease in gemcitabine uptake and overexpression of ribonucleotide reductase large subunit (RRM1). Knockdown of RRM1, but not the overexpression of concentrative nucleoside transporter 1 (CNT1), could completely overcome the gemcitabine resistance. RRM1 knockdown in gemcitabine-resistant cells could increase the intracellular accumulation of gemcitabine by increasing the nucleoside transporter expression. Furthermore, a synergistic effect was observed between hydroxyurea, a ribonucleotide reductase (RR) inhibitor, and gemcitabine on the gemcitabine-resistant cells. Here we indicate that RR is one of the most promising targets to overcome gemcitabine resistance in gemcitabine-resistant cells with dual resistant factors.

Primary malignant melanoma in the pineal region treated without chemotherapy.

Background: Primary pineal malignant melanomas are uncommon intracranial tumor. Here we discuss and review a case of primary pineal malignant melanoma over its feature of imaging studies, pathological findings, and management. Case Description: A 49-year-old woman receiving renal dialysis underwent computed tomography due to a 4-month history of tinnitus and hearing disturbance. A high-density 35-mm diameter tumor was detected in the pineal region; there was obstructive hydrocephalus. The tumor was heterogeneously hyperintense on T1-weighted magnetic resonance images, iso- and low-mixed intense on T2-weighted images with hemorrhagic components, and very low-intense on T2* images. A tumor was subtotally removed via the occipital transtentorial approach. Histologically, it consisted of densely proliferated spindle-shaped or polygonal cells with rich cytoplasmic melanin. The neoplastic cells manifested cellular pleomorphism, nuclear atypia, and mitosis (3/10 high-power fields) and were immunopositive for HMB45, Melan-A, and S100 protein. The MIB-1 index was 17.4%. Whole-body 18-fluoro-deoxyglucose positron emission tomography did not demonstrate any sites with hyper uptake. Examination of the skin and mucosa identified no lesions suggestive of melanoma. She underwent treatment with the whole brain and extended local boost irradiation. Chemotherapy was not delivered due to renal failure. Follow-up imaging studies showed no recurrence or distant lesions 56 weeks after surgery. Conclusion: We report a rare case of primary pineal malignant melanoma with prolonged survival of more than 56 weeks after subtotal tumor resection followed by whole-brain and extended local irradiation without chemotherapy. Radiotherapy without chemotherapy might be sufficient for the treatment of this tumor.

Filamin C promotes lymphatic invasion and lymphatic metastasis and increases cell motility by regulating Rho GTPase in esophageal squamous cell carcinoma

To establish treatments to improve the prognosis of cancer patients, it is necessary to find new targets to control metastasis. We found that expression of FilaminC (FLNC), a member of the actin binding and cross-linking filamin protein family is correlated with lymphatic invasion and lymphatic metastasis in esophageal squamous cell carcinoma (ESCC) by increasing cell motility through activation of Rho GTPase. Immunohistochemistry analysis showed that FLNC expression in ESCC is associated with lymphatic invasion, metastasis, and prognosis. FLNC knockdown in esophageal cancer cell lines decreased cell migration in wound healing and transwell migration assays, and invasion in transwell migration assays. Furthermore, FLNC knockdown reduced the amount of activated Rac-1 (GTP-Rac1) and activated Cdc42 (GTP-Cdc42). Our results suggest that FLNC expression is a useful biomarker of ESCC metastatic tendency and that inhibiting FLNC function may be useful to control the metastasis of ESCC.

Thymidine phosphorylase in cancer aggressiveness and chemoresistance

&NA; Thymidine phosphorylase (TP) is a rate‐limiting enzyme in thymidine catabolism. TP has several important roles in biological and pharmacological mechanisms; importantly TP acts as an angiogenic factor and one of metabolic enzymes of fluoro‐pyrimidine anticancer agents and modifies inflammation. Improving our understanding of the characteristics and functions of TP has led to the development of novel TP‐based anticancer therapies. We recently reported that TP‐dependent thymidine catabolism contributes to tumour survival in low nutrient conditions and the pathway from thymidine to the glycolysis cascade is affected in the context of physiological and metabolic conditions. In this review, we describe recent advancement in our understanding of TP, with a focus on cancer cell biology and the pharmacology of pyrimidine analogue anticancer agents. This review provides comprehensive understanding of the molecular mechanism of TP function in cancer. Graphical abstract Figure. No caption available.

ATP7B expression confers multidrug resistance through drug sequestration.

We previously reported that ATP7B is involved in cisplatin resistance and ATP7A confers multidrug resistance (MDR) in cancer cells. In this study, we show that ATP7B expressing cells also are resistant to doxorubicin, SN-38, etoposide, and paclitaxel as well as cisplatin. In ATP7B expressing cells, doxorubicin relocated from the nuclei to the late-endosome at 4 hours after doxorubicin exposure. EGFP-ATP7B mainly colocalized with doxorubicin. ATP7B has six metal binding sites (MBSs) in the N-terminal cytoplasmic region. To investigate the role of the MBSs of ATP7B in doxorubicin resistance, we used three mutant ATP7B (Cu0, Cu6 and M6C/S) expressing cells. Cu0 has no MBSs, Cu6 has only the sixth MBS and M6C/S carries CXXC to SXXS mutation in the sixth MBS. Cu6 expressing cells were less resistance to the anticancer agents than wild type ATP7B expressing cells, and had doxorubicin sequestration in the late-endosome. Cu0- and M6C/S-expressing cells were sensitive to doxorubicin. In these cells, doxorubicin did not relocalize to the late-endosome. EGFP-M6C/S mainly localized to the trans-Golgi network (TGN) even in the presence of copper. Thus the cysteine residues in the sixth MBS of ATP7B are essential for MDR phenotype. Finally, we found that ammonium chloride and tamoxifen suppressed late endosomal sequestration of doxorubicin, thereby attenuating drug resistance. These results suggest that the sequestration depends on the acidity of the vesicles partly. We here demonstrate that ATP7B confers MDR by facilitating nuclear drug efflux and late endosomal drug sequestration.

Molecular basis for the regulation of hypoxia-inducible factor-1α levels by 2-deoxy-D-ribose

The angiogenic factor, platelet-derived endothelial cell growth factor/thymidine phosphorylase (PD-ECGF/TP), stimulates the chemotaxis of endothelial cells and confers resistance to apoptosis induced by hypoxia. 2-Deoxy-D-ribose, a degradation product of thymidine generated by TP enzymatic activity, inhibits the upregulation of hypoxia-inducible factor (HIF) 1α, BNIP3 and caspase-3 induced by hypoxia. In the present study, we investigated the molecular basis for the suppressive effect of 2-deoxy-D-ribose on the upregulation of HIF-1α. 2-Deoxy-D-ribose enhanced the interaction of HIF-1α and the von Hippel-Lindau (VHL) protein under hypoxic conditions. It did not affect the expression of HIF-1α, prolyl hydroxylase (PHD)1/2/3 and VHL mRNA under normoxic or hypoxic conditions, but enhanced the interaction of HIF-1α and PHD2 under hypoxic conditions. 2-Deoxy-D-ribose also increased the amount of hydroxy-HIF-1α in the presence of the proteasome inhibitor MG-132. The expression levels of TP are elevated in many types of malignant solid tumors and, thus, 2-deoxy-D-ribose generated by TP in these tumors may play an important role in tumor progression by preventing hypoxia-induced apoptosis.

Thymidine catabolism promotes NADPH oxidase-derived reactive oxygen species (ROS) signalling in KB and yumoto cells

Thymidine phosphorylase (TP) is a rate-limiting enzyme in the thymidine catabolic pathway. TP is identical to platelet-derived endothelial cell growth factor and contributes to tumour angiogenesis. TP induces the generation of reactive oxygen species (ROS) and enhances the expression of oxidative stress-responsive genes, such as interleukin (IL)-8. However, the mechanism underlying ROS induction by TP remains unclear. In the present study, we demonstrated that TP promotes NADPH oxidase-derived ROS signalling in cancer cells. NADPH oxidase inhibition using apocynin or small interfering RNAs (siRNAs) abrogated the induction of IL-8 and ROS in TP-expressing cancer cells. Meanwhile, thymidine catabolism induced by TP increased the levels of NADPH and intermediates of the pentose phosphate pathway (PPP). Both siRNA knockdown of glucose 6-phosphate dehydrogenase (G6PD), a rate-limiting enzyme in PPP, and a G6PD inhibitor, dihydroepiandrosterone, reduced TP-induced ROS production. siRNA downregulation of 2-deoxy-D-ribose 5-phosphate (DR5P) aldolase, which is needed for DR5P to enter glycolysis, also suppressed the induction of NADPH and IL-8 in TP-expressing cells. These results suggested that TP-mediated thymidine catabolism increases the intracellular NADPH level via the PPP, which enhances the production of ROS by NADPH oxidase and activates its downstream signalling.

ATP7B expression in human glioblastoma is related to temozolomide resistance

Glioblastoma multiforme (GBM) is one of the most aggressive types of brain malignancy, with resistance to chemotherapy being a primary treatment obstacle. ATPase copper transporting β (ATP7B) is involved in multidrug resistance; however, its expression in GBM remains to be evaluated. In the present study, GBM specimens from 79 patients who underwent gross total tumor removal followed by concomitant temozolomide (TMZ) chemotherapy and radiotherapy were assessed immunohistochemically. The association between the overall survival times of patients and the expression of ATP7B in neoplastic cells was evaluated. In 12/79 tumors (15.2%) >10% of neoplastic cells were immunohistochemically-positive for ATP7B, and categorized as high-ATP7B GBM. In the remaining 67 tumors (84.8%) the rate of ATP7B-positive cells was <10% and recorded as low-ATP7B GBM. The median overall survival times of patients with high- and low-ATP7B GBM were 14.6, and 24.7 months, respectively. High expression of ATP7B was identified to be associated with shorter overall survival times (hazard ratio, 0.452; 95% confidence interval, 0.206–0.994; P=0.048). Of the 79 patients, 12 underwent a second operation due to recurrence. These tissue samples were also subjected to immunohistochemical study. The ATP7B positivity rate of tumor cells obtained during the second surgery was significantly higher compared with that in the first surgery (9.17±2.56 vs. 2.75±0.55%; P=0.008). In addition, two ATP7B-transfected GBM cell lines were identified to be significantly resistant (3.8- and 1.7-fold, respectively) to TMZ compared with the control cell line. The findings of the present study suggest that ATP7B influences GBM resistance to TMZ.

Abstract 5420: Ribosomal protein-p53-MDM2 signaling by nucleolar stress response and drug discovery

Ribosomal biogenesis is a major energy consuming cellular step, and tightly regulated by the demand of protein synthesis associated with cell growth and proliferation. Thus, defects that impair ribosomal biogenesis cause nucleolar stress response. This response initiates a cascade mediated by ribosomal proteins (RPs), particularly RPL5, RPL11, RPL23, and RPS7. These RPs are usually located in the nucleolus but are rapidly released into the nucleoplasm upon nucleolar stress, activating the tumor suppressor MDM2-p53 pathway. Thus, nucleolar stress response is considered as a quality control surveillance mechanism that regulates balance between proper protein synthesis and cell cycle progression for tumor suppression. However, it is unknown whether there are direct connections between p53-activating RP genes and cancer development in vivo, and whether this stress response might be target for cancer therapy. We identified nucleolar protein PICT1 as a novel key regulator of nucleolar stress response. To clarify PICT1 function, we generated PICT1-deficient mice and ES cells and carried out extensive analyses. Our results show that even without DNA damage, PICT1 loss results in p53-dependent growth arrest in vitro and in vivo. We further show that PICT1 binds to RPL11, and that RPL11 is released from nucleoli in the absence of PICT1. In PICT1-deficient cells, increased binding of RPL11 to MDM2 blocks MDM2-mediated ubiquitination of p53, leading to p53 accumulation and repression of cell proliferation. Human colon and esophageal cancer patients with low PICT1 expression have better prognoses. Similarly, when shRNA is used to deplete PICT1 in various tumor cell lines with intact p53 signaling, the cells slow in growth and accumulate p53. These data suggest that PICT1 is a novel key regulator of the MDM2-p53 pathway on nucleolar stress response and promotes tumor progression by retaining RPL11 in the nucleolus. Thus, the nucleolar stress response PICT1 regulates could play a definitive role in tumor suppression and, chemicals which induce nucleolar stress response might be lead to new cancer therapeutics. Therefore, we next constructed a reporter system to visualize and quantitate nucleolar stress response. We found that this reporter system allowed quantitative measurement depend on strength and duration of this stress. As this reporter system showed excellent accuracy, we next screened 400 inhibitors, 1,300 approved drug, and hundreds of natural products from marine species. We found hit compounds including RNA synthesis inhibitor Doxorubicin and Aclarubicin, and also positive control compound, ActinomycinD. In addition, inhibitors of CDK and HDAC were included here. Thus, the nucleolar stress reporter system may reveal unexpected physiological functions of the nucleolar stress response, such as mitotic progression and epigenetics regulation, and identify novel cancer therapeutics, especially for individuals with intact-p53 signaling. Citation Format: Kohichi Kawahara, Takuto Kawahata, Fumito Horikuchi, Yohei Kamijo, Masatatsu Yamamoto, Yoshinari Shinsato, Kentaro Minami, Kazunari Arima, Toshiyuki Hamada, Tatsuhiko Furukawa. Ribosomal protein-p53-MDM2 signaling by nucleolar stress response and drug discovery. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5420. doi:10.1158/1538-7445.AM2015-5420