Determination of the absolute chirality of tellurium using resonant diffraction with circularly polarized x-rays

Many proteins, sugars and pharmaceuticals crystallize into two forms that are mirror images of each other (enantiomers) like our right and left hands. Tellurium is one enantiomer having a space group pair, P3(1)21 (right-handed screw) and P3(2)21 (left-handed screw). X-ray diffraction with dispersion correction terms has been playing an important role in determining the handedness of enantiomers for a long time. However, this approach is not applicable for an elemental crystal such as tellurium or selenium. We have demonstrated that positive and negative circularly polarized x-rays at the resonant energy of tellurium can be used to absolutely distinguish right from left tellurium. This method is applicable to chiral motifs that occur in biomolecules, liquid crystals, ferroelectrics and antiferroelectrics, multiferroics, etc.

Anomalous state sandwiched between Fermi liquid and charge ordered Mott-insulating phases of Ti4O7

The Magnéli phase Ti(4)O(7) exhibits two sharp jumps in resistivity with coupled structural transitions as a function of temperature at T(c1) approximately 142 K and T(c2) = 154 K. We have studied electronic structure changes across the two transitions using 7 eV laser, soft x-ray, and hard x-ray (HX) photoemission spectroscopy (PES). Ti 2p-3d resonant PES and HX PES show a clear metallic Fermi edge and mixed valency above T(c2). The low temperature phase below T(c1) shows a clear insulating gap of approximately 100 meV. The intermediate phase between T(c1) and T(c2) indicates a pseudogap coexisting with remnant coherent states. HX PES and complementary calculations have confirmed the coherent screening in the strongly correlated intermediate phase. The results suggest the existence of a highly anomalous state sandwiched between the mixed-valent Fermi liquid and charge ordered Mott-insulating phase in Ti(4)O(7).

Kondo scaling of the pseudogap in CeOs4Sb12 and CeFe4P12

CeOs(4)Sb(12) and CeFe(4)P(12) are classified as Kondo semiconductors, which show coupled changes in electrical transport, thermodynamic and magnetic properties with a low-temperature semiconductor-like electrical resistivity. We have carried out core level and valence band photoemission spectroscopy on single crystal CeOs(4)Sb(12) and CeFe(4)P(12) to study their electronic structure and the evolution of states at the Fermi level as a function of temperature (∼10-300 K). The Ce 3d core level spectra show the presence of f(0), f(1) and f(2) final states with very different relative intensities in the two compounds. Single-impurity Anderson model calculations provide f electron counts of n(f) = 0.97 and 0.86 per Ce atom, suggestive of a low- and high-T(K) (= single ion Kondo temperature) for CeOs(4)Sb(12) and CeFe(4)P(12), respectively. The high-resolution temperature-dependent near-Fermi level spectra show pseudogaps of energy ∼ 50 meV and ∼ 110 meV in the valence band density of states (DOS) of CeOs(4)Sb(12) and CeFe(4)P(12), respectively. The temperature dependence of the DOS at the Fermi level follows the change in effective magnetic moment estimated from magnetic susceptibility for both materials, confirming the Kondo nature of the pseudogap in CeOs(4)Sb(12) and CeFe(4)P(12). A compilation of measured pseudogaps using photoemission and optical spectroscopy identifies the charge gaps Δ(C) for Ce-based Kondo semiconductors and provides a direct relation with T(K) given by Δ(C) ∼ 2k(B)T(K). In conjunction with the known behaviour of the spin gaps Δ(S) ∼ k(B)T(K), the results establish the coupled energy scaling of the spin and charge gaps in Kondo semiconductors.

Out-of-plane nesting driven spin spiral in ultrathin Fe/Cu(001) films

Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane (IP) and out-of-plane (OP) Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films using energy-dependent soft-x-ray momentum-resolved photoemission spectroscopy. We show that the SS originates in nested regions confined to OP FSs, which are drastically modified compared to IP FSs. From precise reciprocal-space maps in successive zones, we obtain the associated real space compressive strain of 1.5+/-0.5% along c axis. An autocorrelation analysis quantifies the incommensurate ordering vector q=(2pi/a)(0,0, approximately 0.86), favoring a SS and consistent with magneto-optic Kerr effect experiments. The results reveal the importance of IP and OP FS mapping for ultrathin films.

Orbital-dependent modifications of electronic structure across the magnetostructural transition in BaFe2As2

Laser angle-resolved photoemission spectroscopy (ARPES) is employed to investigate the temperature (T) dependence of the electronic structure in BaFe2As2 across the magnetostructural transition at T{N} approximately 140 K. A drastic transformation in Fermi surface (FS) shape across T{N} is observed, as expected by first-principles band calculations. Polarization-dependent ARPES and band calculations consistently indicate that the observed FSs at k{z} approximately pi in the low-T antiferromagnetic state are dominated by the Fe3d{zx} orbital, leading to the twofold electronic structure. These results indicate that magnetostructural transition in BaFe2As2 accompanies orbital-dependent modifications in the electronic structure.

The impact of nutritional deficit on mortality of in-patients with pulmonary tuberculosis

SETTING

A metropolitan governmental medical centre, Seoul, Republic of Korea.

OBJECTIVE

To elucidate the impact of the nutritional deficit assessed by the Nutritional Risk Score (NRS) on the outcomes of in-patients with pulmonary tuberculosis (PTB).

DESIGN

All hospitalised patients with microbiologically confirmed PTB were enrolled. A four-point NRS included low body mass index (<18.5 kg/m(2)), hypoalbuminaemia (<30.0 g/l), hypocholesterolaemia (<2.33 mmol/l) and severe lymphocytopaenia (<7 x 10(5) cells/l). The primary outcome was overall in-hospital mortality. The degree of radiographical resolution after anti-tuberculosis treatment was also evaluated.

RESULTS

In a total of 156 patients, the male to female ratio was 1.6:1. The overall mortality was 13.5% and tuberculosis-specific fatality was 3.9%. Predisposing factors and high NRS (> or = 3 points) were independent risk factors for in-hospital death after adjusting for the severity of PTB. High NRS (OR = 16.8, P < 0.001) and predisposing factors (OR = 5.4, P = 0.032) were independent risk factors for 30-day survival. The NRS was not associated with radiographic improvement.

CONCLUSION

Regardless of disease severity, the high NRS was a significant negative predictor among in-patients with PTB; this finding should therefore be considered in the management of PTB despite the current era of effective anti-tuberculosis chemotherapy.

Distinctive Expression of Cancer/Testis-X Antigens in a Subset of ER Negative Breast Carcinomas

Background: Cancer/testis-X antigens are a multigene family that are predominantly expressed in human germ line cells, with little or no expression in somatic adult tissues, but become aberrantly activated in various malignancies. Some such CT-X antigens represent ideal targets for cancer immunotherapy and have already been used in clinical testing. In contrast to melanomas, bladder, lung, ovarian and hepatocellular carcinomas which show higher levels of CT-X antigen expression, the reports in breast cancers have been inconclusive to date and a comprehensive gene expression and clinicopathological analysis has yet to be performed.Material and Methods: Using sequencing data as well as nine publicly available gene expression data sets, we analyzed the expression of Cancer/testis-X antigens in more than 1900 primary breast cancers. Complementary analysis was performed on three tissue microarrays comprising a total of 201 primary breast carcinomas and 53 brain metastases. Clinical information on the ER-, PR-, HER2, Ki67, p53, EGFR and basal markers was available for statistical analysis.Results: A significantly higher expression of Cancer/testis-X antigens was found in ER negative breast carcinomas over different data sets with a concordant gene expression pattern of several Cancer/testis-X antigens. Members of the MAGEA family and NY-ESO-1/CTAG1B were consistently the most prevalent. Immunohistochemical analyses confirmed a significant correlation of MAGEA family and NY-ESO-1/CTAG1B with ER negative (pValue &lt; 0.0001), PR negative (pValue &lt; 0.01) and Ki67 staining (pValue &lt; 0.0001). Many of these tumors were also positive for basal markers.Discussion: Previous studies of Cancer/testis-X antigens in breast have focused on ER positive cancers, in smaller subsets and provided inconclusive results. Using comprehensive gene expression data sets and tissue microarrays, we have demonstrated a significant association of MAGEA family and NY-ESO-1/CTAG1B with ER/PR negative breast cancer. Since these cancers represent a subgroup for which less therapeutic modalities are available, we propose the use of MAGEA and NY-ESO-1/CTAG1B cancer vaccines in the adjuvant setting as an approach to restricting tumor growth and metastases. Clinical trails using MAGEA and NY-ESO-1/CTAG1B are warranted.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3139.

Delivery of NKG2D Ligand Using an Anti-HER2 Antibody-NKG2D Ligand Fusion Protein Results in an Enhanced Innate and Adaptive Anti-Tumor Response

Background: NKG2D ligands activate via the NKG2D receptor expressed on effector cells belonging to both the innate (NK) and adaptive immune systems (CD8+ T cells). Over-expression of NKG2D ligand on the surface of tumor cells leads to tumor regression in several murine models. We reasoned that antibody targeting of NKG2D ligand to tumor cells could also be used to evoke an enhanced anti-tumor immune response.Methods: We fused the murine NKG2D ligand, Rae-1β, to the 3' end of an anti-HER2 IgG3 containing an intact Fc domain (anti-HER2 IgG3-Rae-1β) to target NKG2D ligand to HER2+ breast tumor cells. The cytotoxicity of the fusion proteins was tested in vitro in direct and indirect assays with the murine NK cell line, KY-2. Anti-tumor efficacy was examined in a murine mammary tumor model.Results: Anti-HER2 IgG3-Rae-1β fusion protein bound to both the HER2 antigen, and to NKG2D as determined by flow cytometry. Anti-HER2 IgG3-Rae-1β fusion induced enhanced cytotoxicity of NK effectors against HER2 expressing tumor cells in vitro. EMT6-HER2 bearing BALB/c mice treated with anti-HER2 IgG3-Rae-1β showed markedly decreased tumor growth relative to anti-HER2 IgG3 or PBS injected control mice. Treatment of mice that were implanted on one flank with EMT6 and contralaterally implanted with EMT6-HER2, resulted in prompt regression of EMT6-HER2, and delayed regression of EMT6, suggesting “epitope spreading.” To examine the involvement of NK, CD4, or CD8 cells in the growth inhibition of the Rae-1β fusion protein targeted tumors, we performed lymphocyte subset depletion studies. Mice depleted of either NK cells or CD8+ T cells showed decreased inhibition of tumor growth following treatment with anti-HER2 IgG3-Rae-1β, compared to control mice. These results suggest that NK cells and CD8+ cells play an important role in the anti-tumor activity of anti-HER2 antibody-Rae-1β fusion. Anti-HER2 IgG3-Rae-1β also inhibited growth of EMT6-HER2 in FcγR-/- mice, indicating activity of the fusion in the absence of FcR interaction. No anti-tumor efficacy of anti-HER2 IgG3-Rae-1β was observed in IFNγ-/- mice.To determine if anti-HER2 antibody-Rae-1β fusion led to priming of an adaptive response, twelve mice that had previously rejected EMT6-HER2 tumors following treatment with anti-HER2 IgG3-Rae-1γ, were rechallenged with either EMT6-HER2, or with parental EMT6. Five of six mice rechallenged with EMT6-HER2 and five of six mice rechallenged with EMT6 showed no evidence of tumor growth at day 25, while both EMT6 and EMT6-HER2 grew rapidly in six of six control mice, respectively.Conclusion: Antibody-NKG2D ligand fusion proteins administration leads to an enhanced anti-tumor innate and adaptive immune response. The immune response evoked by targeting of the fusion to HER2, a single surface antigen, encompassed additional non-targeted antigens. Antibody-NKG2D ligand fusion proteins could potentially be used to treat other malignancies by substituting alternate tumor specificities. Murine NKG2D ligand in the antibody fusion molecules could be replaced with human NKG2D ligands for testing in man.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6102.

The inhomogeneous structure of water at ambient conditions

Small-angle X-ray scattering (SAXS) is used to demonstrate the presence of density fluctuations in ambient water on a physical length-scale of approximately 1 nm; this is retained with decreasing temperature while the magnitude is enhanced. In contrast, the magnitude of fluctuations in a normal liquid, such as CCl(4), exhibits no enhancement with decreasing temperature, as is also the case for water from molecular dynamics simulations under ambient conditions. Based on X-ray emission spectroscopy and X-ray Raman scattering data we propose that the density difference contrast in SAXS is due to fluctuations between tetrahedral-like and hydrogen-bond distorted structures related to, respectively, low and high density water. We combine our experimental observations to propose a model of water as a temperature-dependent, fluctuating equilibrium between the two types of local structures driven by incommensurate requirements for minimizing enthalpy (strong near-tetrahedral hydrogen-bonds) and maximizing entropy (nondirectional H-bonds and disorder). The present results provide experimental evidence that the extreme differences anticipated in the hydrogen-bonding environment in the deeply supercooled regime surprisingly remain in bulk water even at conditions ranging from ambient up to close to the boiling point.

Doxorubicin-induced platelet cytotoxicity: a new contributory factor for doxorubicin-mediated thrombocytopenia

BACKGROUND

Doxorubicin (DOX) is a widely used anticancer drug for solid tumors and hematologic malignancy, but its active use is hampered by serious adverse effects, including thrombocytopenia. Although bone marrow toxicity of DOX has been suggested to be the sole mechanism underlying the reduced platelet counts, the direct effects of DOX on platelets have never been examined.

OBJECTIVE

Here, we investigated the DOX-induced platelet cytotoxicity and its underlying mechanism in an effort to elucidate the contribution of platelet cytotoxicity to DOX-induced thrombocytopenia.

RESULTS

In freshly isolated human platelets, DOX induced platelet cytotoxicity in a time-dependent and concentration-dependent manner. Reactive oxygen species (ROS) generation, decreased glutathione levels and subsequent protein thiol depletion were shown to underlie the DOX-induced platelet cytotoxicity. Conspicuously, DOX-treated platelets displayed apoptotic features such as caspase-3 activation, reduced mitochondrial transmembrane potential, and phosphatidylserine exposure. Decreased glutathiolation of procaspase-3 was shown to be a link between protein thiol depletion and caspase-3 activation. It is of note that DOX-mediated platelet cytotoxicity was significantly enhanced by shear stress, a common complicating factor in cancer patients. These in vitro results were further confirmed by an in vivo animal model, where administration of DOX induced a platelet count decrease, ROS generation, caspase-3 activation, protein thiol depletion, and damaged platelet integrity.

CONCLUSION

We demonstrated that DOX can directly induce platelet cytotoxicity through ROS generation, decreased glutathione levels, and protein thiol depletion. We believe that this study provides important evidence for the role of DOX-induced platelet cytotoxicity in the development of thrombocytopenia in DOX-treated patients.

Spectroscopic evidence for competing reconstructions in polar multilayers LaAlO3/LaVO3/LaAlO3

We have studied the valence redistribution of V in LaAlO(3)/LaVO(3)/LaAlO(3) trilayers, which are composed of only polar layers grown on SrTiO3 (001) substrates, by core-level photoemission spectroscopy. We have found that the V valence is intermediate between V3+ and V4+ for thin LaAlO3 cap layers, decreases with increasing cap-layer thickness, and finally recovers the bulk value of V3+ at approximately 10 unit-cell thickness. In order to interpret these results, we propose that the atomic reconstruction of the polar LaAlO3 surface competes with the purely electronic V valence change so that the polar catastrophe is avoided at the cost of minimum energy.

A new HLA-B*51 variant, B*5158, identified by sequence-based typing in a Korean individual

A novel human leukocyte antigen (HLA)-B*51 allele, officially named HLA-B*5158, was identified in the cord blood from Korean. HLA-B*5158 allele shows single nucleotide difference from B*510101 in exon 2 at nucleotide position 214 (C/T), resulting in an amino acid substitution, Trp48Arg.

A multicenter phase II study to evaluate efficacy and safety of gefitinib as the first-line treatment for Korean patients (pts) with advanced pulmonary adenocarcinoma harboring EGFR mutations

8066

Background: This study (D7913L00056) was designed to prospectively evaluate the efficacy and safety of first-line gefitinib treatment in pts with advanced pulmonary adenocarcinoma harboring EGFR mutations and to explore the molecular factors affecting the efficacy of gefitinib. Methods: Chemo-naïve pts with advanced (stage IIIB/IV/recurrent disease) pulmonary adenocarcinoma underwent direct DNA sequencing of tumor EGFR exons 18, 19 and 21. Pts with EGFR mutations received gefitinib 250 mg/d until disease progression or unacceptable toxicity. The primary end-point was objective response rate (ORR). The protocol planned to accrue 45 pts with EGFR mutations in a single stage. Results: Out of 147 screened pts, 45 pts (31%) had EGFR mutations and received gefitinib. The most common EGFR mutations were in-frame exon 19 deletions (del 19, 29 pts, 64%) and L858R point mutations in exon 21 (L858R, 15 pts, 33%). One patient had atypical mutation of L861Q in exon 21. The ORR by RECIST was 53.3% (95% CI, 38.8 to 67.9) and disease control rate (DCR) including stable disease was 86.7%. Progression free survival (PFS) at 12 months (mo) was 74.6% (95% CI, 58.8 to 85.1). Median PFS was not reached after median 10.1 mo follow-up. Treatment was well tolerated. Six pts experienced grade 3 toxicities including rash, pruritis, and anorexia. No grade 4 toxicities were reported. Subgroup analysis according to the EGFR mutation subtypes was carried out. The ORR and DCR were higher in pts with del 19 than those with L858R (62.1% vs 33.3%; P=0.0705 and 96.6% vs 66.7%; P=0.0062, respectively). All 4 pts with progressive disease had an L858R mutation. No secondary resistant mutations such as T790M were found in those pts. In addition, PFS at 12 mo was significantly better in pts with del 19 than those with L858R (63.2% vs 23.8%, P=0.0034). Conclusions: Gefitinib as the first-line treatment for Korean pts with advanced pulmonary adenocarcinoma harboring EGFR mutations was very effective and well tolerated. Subgroup analysis suggests that the benefit from gefitinib treatment was more prominent in pts with the del 19 mutation.

[Table: see text]

Prognostic significance of serum vascular endothelial growth factor per platelet count in gastric cancer patients

e22031

Background: Recent studies have shown that VEGF expression not in tissues but in serum sample is correlated with tumor vascularity, and high serum VEGF levels could predict poor prognosis in cancer patients. However there are limited data regarding the clinical and prognostic significance of serum VEGF levels per platelet count in advanced gastric cancer. In this study, we conducted a study to evaluate the prognostic implication of serum VEGF per platelet count in patients with advanced gastric cancer. Methods: 111 patients with histologically confirmed gastric cancer, 10 patients with early gastric cancer were included and control serum samples were acquired from 10 healthy volunteers. The levels of VEGF were measured using human VEGF quantitative enzyme-linked immunosorbent assay (ELISA). Survival curves were calculated using the Kaplan-Meier method and survival comparisons were made by the log rank test in metastatic gastric cancer. The Cox proportional hazards regression model was utilized for multivariate analyses after univariate analysis defined relevant prognostic variables. Results: A trend toward a significant positive correlation between serum VEGF and platelet counts was observed in patients of AGC (r = 0.477, P = 0.000) and there was a significant correlation between serum VEGF levels and differentiation of tumor (p = 0.014), stage (p = 0.036). The overall survival (log rank, p =0.0432) and the progression free survival (median 4.5 vs. 8.9 months; log rank, p =0.0116) were significantly shorter in patients with high VEGF per platelet count (≥1.626 pg/106). In the multivarivate analysis, performance status (P=0.025), the presence of peritoneal carcinomatosis (P=0.006), serum VEGF per platelet (P=0.005) were found to be significantly associated with poor progression free survival. Conclusions: This study demonstrated that serum VEGF per platelet count are correlated with poor overall survival and progression free survival in patients with advanced gastric cancer. Therefore measurement of serum VEGF per platelet might be useful markers for predicting disease progression and prognosis of advanced gastric cancer.

No significant financial relationships to disclose.

Clinical outcome of sequential chemotherapy in metastatic and/or recurrent gastric cancer

e15521

Background: Little is known about data on subsequent chemotherapy (CTx) following 1st-line CTx in stage IV gastric cancer. The purpose of this study was to analyze the natural history of stage IV gastric cancer with sequential CTx Methods: A total of 532 patients (pts) with unresectable gastric adenocarcinoma were studied. They were managed with a strategy of maximal administration of CTx only if pts’ general conditions were allowed. Response evaluation was performed by RECIST every 2 cycles. Response of unmeasurable lesions was dichotomized only into stable disease or progressive disease. Results: When pts were divided into CTx group (460 of 532, 87%) and best supportive care group (BSC; 72 of 532, 13%) resulting from poor performance/pt's refusal/comorbidity (31/23/18), the former had younger age (p = 0.046), better performance (p < 0.001), and less advanced metastatic sites (p = 0.001) than the latter. Median overall survivals from diagnosis of unresectable cancer were 12.0/13.3/2.5 months for overall/CTx/BSC, respectively. 87%/47%/23% of the whole pts received 1st/2nd/3rd-line CTx, respectively. Median number of regimens delivered was 2. Maximally 5th-line CTx was given to 15 pts (3%). Response and disease control rates were 21.7%/12.5%/11.8% and 79.4%/56.3%/49.4% for 1st/2nd/3rd lines, respectively. Median progression-free and overall survivals from CTx were 5.5/3.4/2.5 months and 12.1/7.9/5.5 months for 1st/2nd/3rd lines, respectively. The most common cause of discontinuation of CTx was disease progression (68%/74%/70%) followed by pt's refusal (22%/13%/12%) for 1st/2nd/3rd lines, respectively. Prognosticators were performance status, histology, metastatic site, and CTx before 1st or 2nd line. Conclusions: When pts with unresectable gastric cancer were managed with a strategy of maximal administration of CTx, a considerable number of pts could receive 2nd or 3rd line CTx, showing modest activity. Performance status and metastatic site were consistent prognosticators even if lines changed. Our data on the natural history of stage IV gastric cancer with sequential CTx may suggest that clinical trials can be performed in a 2nd or 3rd line setting as well.

No significant financial relationships to disclose.

Comparison of long-term outcome between doublet versus triplet neoadjuvant chemotherapy in nonmetastatic osteosarcoma of extremity

10542

Background: Multimodal approach had improved outcomes of non-metastatic osteosarcoma. This study was to compare outcomes between doublet (AP; doxorubicin and cisplatin) and triplet (IAP; AP and ifosfamide) neoadjuvant chemotherapy for non-meteastatic osteosarcoma of extremity in a single institute. Methods: A total of 124 osteosarcoma patients were enrolled. In AP group, doublet regimen was given to 77 patients from 1991 to 1999, who received intra-arterial cisplatin(120mg/m2) at day 1 and intravenous doxorubicin (25mg/m2) for 3 days. In IAP group, triplet regimen was given to 49 patients from 2000 to 2007, who received ifosfamide additionally at a dose of 2.5g/m2/day for 3 days. After completion of 3 cycles of chemotherapy, patients underwent limb-salvage surgery. We assessed tumor response according to pathologic tumor necrosis, and treated further adjuvant chemotherapy. In AP group, responder received 3 more cycles of AP, while non-responders received 6 cycles of ifosfamide-contaning regimens. In IAP group, all patients had 3 more cycles of IAP chemotherapy. Results: The median follow-up duration was 5.2 years (0.4–16.7). The most frequent site and histology were distal femur and osteoblastic type. Overall pathologic response was more than 90% tumor necrosis in 74.8% of patients. Total necrosis of tumor was also found in 46 patients (37.4%). There was no difference between two groups in pathologic response (76.3% vs. 72.3%; p=0.62) or other clinico-pathologic parameters. Tumor recurrence was occurred in 31.5% of patients with the most common site of lung (84.6%). There was no difference between two groups in recurrence (p=0.17) or lung metastasis (p=0.53). There were no statistical differences in disease free survival (p=0.75) and overall survival (p=0.07) between two groups. In toxicity profiles, there were more hematologic toxicity in IAP group (febrile neutropenia,p<0.001; thrombocytopenia,p<0.05), while there were no statistical differences in treatment related death. Conclusions: The addition of ifosfamide to doxorubicin and cisplatin in neoadjuvant chemotherapy did not show improved outcomes in this study. Further trials are required to elucidate optimal neoadjuvant chemotherapy and effective salvage regimens.

No significant financial relationships to disclose.

Strong mass renormalization at a local momentum space in multiorbital Ca1.8Sr0.2RuO4

We have studied the mass renormalization in Ca2-xSrxRuO4 (x=0.2) using high-resolution angle-resolved photoemission spectroscopy. We observed precise band dispersions near the Fermi level (E_{F}) and the corresponding Fermi surfaces. A characteristic flat band with approximately 4 meV dispersion accompanying sharp quasiparticle (QP) peaks shows up in a limited momentum region around (pi, 0). The QP peak rapidly evolves below the crossover temperature T;{*} approximately 20 K, which agrees well with the mass enhancement behavior indicated by thermal, magnetic, and transport properties. We discuss the origin of the mass renormalization in relation to the local flat band at (pi, 0) possibly derived from the gamma (d_{xy}) band.