Schlafen 11 further sensitizes BRCA-deficient cells to PARP inhibitors through single-strand DNA gap accumulation behind replication forks

The preferential response to PARP inhibitors (PARPis) in BRCA-deficient and Schlafen 11 (SLFN11)-expressing ovarian cancers has been documented, yet the underlying molecular mechanisms remain unclear. As the accumulation of single-strand DNA (ssDNA) gaps behind replication forks is key for the lethality effect of PARPis, we investigated the combined effects of SLFN11 expression and BRCA deficiency on PARPi sensitivity and ssDNA gap formation in human cancer cells. PARPis increased chromatin-bound RPA2 and ssDNA gaps in SLFN11-expressing cells and even more in cells with BRCA1 or BRCA2 deficiency. SLFN11 was co-localized with chromatin-bound RPA2 under PARPis treatment, with enhanced recruitment in BRCA2-deficient cells. Notably, the chromatin-bound SLFN11 under PARPis did not block replication, contrary to its function under replication stress. SLFN11 recruitment was attenuated by the inactivation of MRE11. Hence, under PARPi treatment, MRE11 expression and BRCA deficiency lead to ssDNA gaps behind replication forks, where SLFN11 binds and increases their accumulation. As ovarian cancer patients who responded (progression-free survival >2 years) to olaparib maintenance therapy had a significantly higher SLFN11-positivity than short-responders (<6 months), our findings provide a mechanistic understanding of the favorable responses to PARPis in SLFN11-expressing and BRCA-deficient tumors. It highlight the clinical implications of SLFN11.

Non-classical Monocytes Enhance the Efficacy of Immune Checkpoint Inhibitors on Colon Cancer in a Syngeneic Mouse Model

BACKGROUND/AIM

The response rate to immune checkpoint inhibitors (ICIs) is approximately 10%-30% and only in a few cancer types. In the present study, we determined whether non-classical monocytes (NCMs) could enhance ICI efficacy in colon cancer using a syngeneic mouse model.

MATERIALS AND METHODS

The MC38 C57BL/6 mouse colon cancer model was used. Cells collected from the bone marrow of C57BL/6 mice were cultured, and NCMs were fractionated by cell sorting and administered via the tail veins to the mice implanted with MC38 cells. The anti-mouse PD-L1 antibody was administered three times, and tumor volume and overall survival were observed.

RESULTS

More tumors were eradicated and more complete response occurred, after cotreatment with ICIs and NCMs than after treatment with ICIs alone. Moreover, no efficacy was observed when NCMs were administered alone.

CONCLUSION

NCMs enhance ICI efficacy. The underlying mechanisms and clinical applications will be studied in the future.

KLC1-ROS1 Fusion Exerts Oncogenic Properties of Glioma Cells via Specific Activation of JAK-STAT Pathway

Here, we investigated the detailed molecular oncogenic mechanisms of a novel receptor tyrosine kinase (RTK) fusion, KLC1-ROS1, with an adapter molecule, KLC1, and an RTK, ROS1, discovered in pediatric glioma, and we explored a novel therapeutic target for glioma that possesses oncogenic RTK fusion. When wild-type ROS1 and KLC1-ROS1 fusions were stably expressed in the human glioma cell lines A172 and U343MG, immunoblotting revealed that KLC1-ROS1 fusion specifically activated the JAK2-STAT3 pathway, a major RTK downstream signaling pathway, when compared with wild-type ROS1. Immunoprecipitation of the fractionated cell lysates revealed a more abundant association of the KLC1-ROS1 fusion with JAK2 than that observed for wild-type ROS1 in the cytosolic fraction. A mutagenesis study of the KLC1-ROS1 fusion protein demonstrated the fundamental roles of both the KLC1 and ROS1 domains in the constitutive activation of KLC1-ROS1 fusion. Additionally, in vitro assays demonstrated that KLC1-ROS1 fusion upregulated cell proliferation, invasion, and chemoresistance when compared to wild-type ROS1. Combination treatment with the chemotherapeutic agent temozolomide and an inhibitor of ROS1, JAK2, or a downstream target of STAT3, demonstrated antitumor effects against KLC1-ROS1 fusion-expressing glioma cells. Our results demonstrate that KLC1-ROS1 fusion exerts oncogenic activity through serum-independent constitutive activation, resulting in specific activation of the JAK-STAT pathway. Our data suggested that molecules other than RTKs may serve as novel therapeutic targets for RTK fusion in gliomas.

Novel quantitative immunohistochemical analysis for evaluating PD-L1 expression with phosphor-integrated dots for predicting the efficacy of patients with cancer treated with immune checkpoint inhibitors

Introduction

Programmed cell death ligand 1 (PD-L1) expression in tumor tissues is measured as a predictor of the therapeutic efficacy of immune checkpoint inhibitors (ICIs) in many cancer types. PD-L1 expression is evaluated by immunohistochemical staining using 3,3´-diaminobenzidine (DAB) chronogenesis (IHC-DAB); however, quantitative and reproducibility issues remain. We focused on a highly sensitive quantitative immunohistochemical method using phosphor-integrated dots (PIDs), which are fluorescent nanoparticles, and evaluated PD-L1 expression between the PID method and conventional DAB method.

Methods

In total, 155 patients with metastatic or recurrent cancer treated with ICIs were enrolled from four university hospitals. Tumor tissue specimens collected before treatment were subjected to immunohistochemical staining with both the PID and conventional DAB methods to evaluate PD-L1 protein expression.

Results

PD-L1 expression assessed using the PID and DAB methods was positively correlated. We quantified PD-L1 expression using the PID method and calculated PD-L1 PID scores. The PID score was significantly higher in the responder group than in the non-responder group. Survival analysis demonstrated that PD-L1 expression evaluated using the IHC-DAB method was not associated with progression-free survival (PFS) or overall survival (OS). Yet, PFS and OS were strikingly prolonged in the high PD-L1 PID score group.

Conclusion

Quantification of PD-L1 expression as a PID score was more effective in predicting the treatment efficacy and prognosis of patients with cancer treated with ICIs. The quantitative evaluation of PD-L1 expression using the PID method is a novel strategy for protein detection. It is highly significant that the PID method was able to identify a group of patients with a favorable prognosis who could not be identified by the conventional DAB method.

Monocyte subsets associated with the efficacy of anti‑PD‑1 antibody monotherapy

Immune checkpoint inhibitors (ICIs) are among the most notable advances in cancer immunotherapy; however, reliable biomarkers for the efficacy of ICIs are yet to be reported. Programmed death (PD)-ligand 1 (L1)-expressing CD14+ monocytes are associated with shorter overall survival (OS) time in patients with cancer treated with anti-PD-1 antibodies. The present study focused on the classification of monocytes into three subsets: Classical, intermediate and non-classical. A total of 44 patients with different types of cancer treated with anti-PD-1 monotherapy (pembrolizumab or nivolumab) were enrolled in the present study. The percentage of each monocyte subset was investigated, and the percentage of cells expressing PD-L1 or PD-1 within each of the three subsets was further analyzed. Higher pretreatment classical monocyte percentages were correlated with shorter OS (r=-0.32; P=0.032), whereas higher non-classical monocyte percentages were correlated with a favorable OS (r=0.39; P=0.0083). PD-L1-expressing classical monocytes accounted for a higher percentage of the total monocytes than non-classical monocytes with PD-L1 expression. In patients with non-small cell lung cancer (NSCLC), a higher percentage of PD-L1-expressing classical monocytes was correlated with shorter OS (r=-0.60; P=0.012), which is similar to the observation for the whole patient cohort. Comparatively, higher percentages of non-classical monocytes expressing PD-L1 were significantly associated with better OS, especially in patients with NSCLC (r=0.60; P=0.010). Moreover, a higher percentage of non-classical monocytes contributed to prolonged progression-free survival in patients with NSCLC (r=0.50; P=0.042), with similar results for PD-L1-expressing non-classical monocytes. The results suggested that the percentage of monocyte subsets in patients with cancer before anti-PD-1 monotherapy may predict the treatment efficacy and prognosis. Furthermore, more classical monocytes and fewer non-classical monocytes, especially those expressing PD-L1, are involved in shortening OS time, which may indicate the poor efficiency of anti-PD-1 treatment approaches.

A protein kinase D inhibitor suppresses AKT on T cells and antagonizes cancer immunotherapy by anti-PD-1

Antibodies that block the interaction between PD-1 and PD-1 ligands (anti-PD-1) are in clinical use for the treatment of cancer, yet their efficacy is limited. Pre-approved therapies that enhance the effect of anti-PD-1 in combination are beneficial. Small-molecule inhibitors that attenuate T cell receptor signaling are reported to prevent T cell exhaustion and induce memory T cells with stem cell potential, resulting in a durable effector T cell response in combination with anti-PD-1. In search of such targets, we focused on protein kinase D (PKD), which is suggested to be suppressive in both tumor growth and TCR signaling. We report that CRT0066101, a PKD inhibitor (PKDi), suppressed the growth of mouse tumors at a sub-micromolar concentration in vitro. Despite its inhibitory effects on tumors, a single treatment of tumor-bearing mice with PKDi did not inhibit, but rather accelerated tumor growth, and reversed the therapeutic effect of anti-PD-1. Mice treated with PKDi showed reduced T cell infiltration and defects in the generation of effector T cells, compared to those treated with anti-PD-1, suggesting that PKDi inhibited ongoing antitumor responses. Mechanistically, PKDi inhibited phosphorylation of AKT, a primary checkpoint that is reactivated by anti-PD-1. In conclusion, PKD is fundamentally required for T cell reactivation by anti-PD-1; therefore, inhibition of PKD is not appropriate for combination therapy with anti-PD-1. On the other hand, a single dose of PKDi was shown to strongly suppress experimental autoimmunity in mice, indicating that PKDi could be useful for the treatment of immune-related adverse events that are frequently reported in anti-PD-1 therapy.

Current-Voltage Characteristics and Solvent Dissociation of Bipolar Membranes in Organic Solvents

In this work, the chronopotentiometric responses, pH changes, and current-voltage (I-V) characteristics of bipolar membrane (BPM)/LiCl-organic solvent systems were measured and compared with those of the BPM/LiCl-water system. Monohydric alcohols, polyhydric alcohols, and amides were used as organic solvents. The chronopotentiograms and pH changes supported that the organic solvents can dissociate into cations and anions at the BPM interface. It is found that amides cannot dissociate easily at the BPM compared with alcohols. The I-V characteristics showed that both the viscosity and acid-base property of organic solvents substantially influences the dissociation behaviors in addition to the autoprotolysis constant and relative permittivity of the solvents.

Regulatory roles of fibronectin and integrin α5 in reorganization of the actin cytoskeleton and completion of adipogenesis

Cellular differentiation is characterized by changes in cell morphology that are largely determined by actin dynamics. We previously showed that depolymerization of the actin cytoskeleton triggers the differentiation of preadipocytes into mature adipocytes as a result of inhibition of the transcriptional coactivator activity of megakaryoblastic leukemia 1 (MKL1). The extracellular matrix (ECM) influences cell morphology via interaction with integrins, and reorganization of the ECM is associated with cell differentiation. Here we show that interaction between actin dynamics and ECM rearrangement plays a key role in adipocyte differentiation. We found that depolymerization of the actin cytoskeleton precedes disruption and degradation of fibrillar fibronectin (FN) structures at the cell surface after the induction of adipogenesis in cultured preadipocytes. A FN matrix suppressed both reorganization of the actin cytoskeleton into the pattern characteristic of adipocytes and terminal adipocyte differentiation, and these inhibitory effects were overcome by knockdown of integrin α5 (ITGα5). Peroxisome proliferator–activated receptor γ was required for down-regulation of FN during adipocyte differentiation, and MKL1 was necessary for the expression of ITGα5. Our findings suggest that cell-autonomous down-regulation of FN-ITGα5 interaction contributes to reorganization of the actin cytoskeleton and completion of adipocyte differentiation.

Isolation and characterization of neural stem/progenitor cells in the subventricular zone of the naked mole-rat brain

Background

The naked mole-rat (NMR) is the longest-lived rodent with a maximum lifespan of more than 37 years and shows a negligible senescence phenotype, suggesting that tissue stem cells of NMRs are highly capable of maintaining homeostasis. However, the properties of NMR tissue stem cells, including neural stem cells (NSCs), are largely unclear.

Methods

Neural stem/progenitor cells (NS/PCs) were isolated from the subventricular zone of the neonate NMR brain (NMR-NS/PCs) and cultured in neurosphere and adherent culture conditions. Expression of NSC markers and markers of neurons, astrocytes, and oligodendrocytes was analyzed by immunocytochemistry. In adherent culture conditions, the proliferation rate and cell cycle of NMR-NS/PCs were assessed and compared with those of NS/PCs from mice (mouse-NS/PCs). The DNA damage response to γ-irradiation was analyzed by immunocytochemistry and reverse transcription-quantitative PCR.

Results

NMR-NS/PCs expressed several NSC markers and differentiated into neurons, astrocytes, and oligodendrocytes. NMR-NS/PCs proliferated markedly slower than mouse-NS/PCs, and a higher percentage of NMR-NS/PCs than mouse-NS/PCs was in G0/G1 phase. Notably, upon γ-irradiation, NMR-NS/PCs exhibited a faster initiation of the DNA damage response and were less prone to dying than mouse-NS/PCs.

Conclusions

NMR-NS/PCs were successfully isolated and cultured. The slow proliferation of NMR-NS/PCs and their resistance to DNA damage may help to prevent stem cell exhaustion in the brain during the long lifespan of NMRs. Our findings provide novel insights into the mechanism underlying delayed aging of NMRs. Further analysis of NMR tissue stem cells may lead to the development of new strategies that can prevent aging in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41232-021-00182-7.

Examination of the acute efficacy and safety about aggressive use of tolvaptan for early rising after admission in super-elder patients with congestive heart failure

Background

From August 2015, for shortening of hospitalization period through efficient medical care in acute phase, we had introduced a unique clinical pathway (PATH) for congestive heart failure (CHF) cases. In PATH, since immediate taking of Tolvaptan, which is an strong oral diuretic and approver for use in the treatment of CHF cases since 2010 in Japan, after admission is specified, early diuresis makes it possible to achieve early rising from bed and streamline each medical care such as oxygen inhalation, continuous infusion, and urethral catheterization. Early rising from bed is particularly important for super-elder CHF patients who merge often frail. On the other hand, for super-elder CHF patients, it is feared that aggressive use of Tolvaptan may frequently cause dehydration, renal damage caused by it, or hypernatremia, which is a peculiar side effect about the drug.

Purpose

In this study, we examined the usefulness and safety of active use of Tolvaptan by introducing PATH in patients with super-elder CHF patients.

Methods

We set up three groups, NE group consist of 37 CHF cases (90 years old or over) who admitted in our hospital before (without) introduction of PATH between April 2014 and July 2015, PE group consist of 130 CHF cases (90 years old or over) and PY group consist of 466 CHF cases (under 90 years old) who ware admitted with introduction of PATH between August 2015 and July 2020. And in each group, we investigated various medical conditions in their acute phase after admission and the incidence of adverse events related to oral administration of tolvaptan, and examined the differences between three groups.

Results

Between NE group and PE group, there were no significant differences in mean age, pre-hospital living status, or clinical status at admission (Figure 1). But due to lean and efficient CHF care, the average length of hospitalization period was significantly shorter in PE group. And, in PE group, each medical care was performed as efficiently as in PY group, but the progression of renal damage or hypernatremia that required unscheduled discontinuation of tolvaptan use occurred more frequently in PE group (Figure 2).

Conclusions

Aggressive Tolvaptan use through our unique clinical pathway for congestive heart failure cases seemed to be useful even in super-elder patients. Although we thought that the safety of active use of tolvaptan for super-elder patients was well tolerated considering the results of this study, the incidence of adverse events such as hypernatremia was clearly higher in super-elder patients than in non-super-elder patients. It seemed that we should pay close attention to the clinical data of super-elder patients after introduction of tolvaptan.

Funding Acknowledgement

Type of funding sources: None. Figure 1Figure 2

Examination about more realistic prognosis evaluation method, how long the patients with congestive heart failure can spend at home

Background

From August 2015, for efficient medical care in congestive heart failure (CHF) cases, we had introduced a unique clinical pathway (PATH) provided the immediate use of Tolvaptan and comprehensive education by multi-disciplinary staff after admission. And by introduction of PATH, we confirmed the shortening effect of hospitalization period with CHF and the suppressive effect of readmission with CHF after discharge. But since almost CHF patients repeat hospitalization and discharge due to change of their medical condition, the investigation for only first readmission rate after discharge is not enough to assess the entire long clinical course of CHF. Recently we found one report about evaluation method for CHF clinical prognosis, how long CHF patients can stay healthy at their own home after discharge within a certain period. This evaluation method is considered to take into account the long clinical course of CHF.

Purpose

We investigated whether the CHF patients introduced PATH on admission could stay longer at their home than CHF patients without PATH.

Methods

Between April 2014 and July 2019, 471 CHF cases, who ware admitted in our hospital at first and could be followed up for at least 1 month after discharge, ware enrolled. We divided them to two groups, PATH- group before introducing PATH (until July 2015, 142 cases), and PATH+ group applied PATH (after August 2015, 329 cases). Between both groups, we investigated the readmission rate (RR) with CHF and the total period (TP) that patients could spend at home within1, 3, 6 and 12month after discharge.

Results

There were no significant differences in mean age, pre-hospital living status, or clinical status at admission between the two groups. On the other hand, due to efficient CHF care, the average length of hospital stay was significantly shorter (figure1). RR within 1, 3, 6 and 12 months after discharge ware all lower in PATH+ group. And TP within 1, 3, 6 and 12 months after discharge ware all longer in PATH+ group (figure2).

Conclusion

By introducing our unique clinical pathway for congestive heart failure cases requiring hospitalization, we could confirm not only the improvement of their conventional clinical prognosis index but also the improvement of their new and more realistic clinical prognosis index after discharge.

Funding Acknowledgement

Type of funding sources: None. Figure 1Figure 2

Our unique clinical pathway for congestive heart failure cases required admission achieved a dramatic reduction of their hospitalization period and a significant reduction of readmission with heart fa

Background

In recent years, the number of elderly congestive heart failure (CHF) cases has been increasing in Japan with the aging of the population. This tendency is particularly remarkable in rural areas where our facilities are located. After admission with CHF, the hospitalization period (PE) was prolonged due to various complications unique to the elderly, and re-exacerbation of CHF occurred shortly after discharge. Approximately 30% of them were readmitted within one year. From August 2015, for shortening of PE and reduction of CHF readmission through the efficiency of CHF treatment and comprehensive patient education, we had introduced a unique clinical pathway (PATH) that provided the immediate use of Tolvaptan and comprehensive education by multi-disciplinary staff after admission.

Purpose

In this study, we verified whether the improvement of clinical prognosis were achieved by introduction of PATH.

Methods

Between April 2014 and July 2019, 635 CHF cases (764 admissions) ware enrolled. We divided them to two groups, N-group before introducing PATH (198 cases, 262 admissions) and P-group applied PATH (437 cases, 502 admission). Between both groups, we compared the various acute care situation, PE and readmission rate with CHF within 1 year after discharge.

Results

There were no differences between P and N-group in mean age, distribution of underlying illness or daily activity level before admission. There ware not also differences about left ventricle function by echocardiography and various blood test data at admission. The enforcement rate of continuous infusion and the rate of urinary catheter placement were significantly lower in the P-group (71 vs 88%; p&lt;0.0001, 52 vs 63%; p&lt;0.01, respectively). And their enforcement duration was significantly shorter in P-group (4.6±5.3 vs 10.5±9.6 days; p&lt;0.0001, 6.3±7.9 vs 12.8±13.1 days; p&lt;0.0001 respectively). The enforcement rate of cardiac rehabilitation was significantly higher in group P (94 vs 84%; p&lt;0.0001), and the starting time of rehabilitation was significantly earlier (2.9±1.5 vs 6.3±4.8th illness day; p&lt;0.0001). As a result, the average HP was significantly shorter in group P (16.5±13.4 vs 28.6±24.1 days, p&lt;0.0001). The readmission rate with CHF within one year after discharge was significantly lower in group P (23 vs 36%; p&lt;0.001).

Conclusion

By the introduction of our original clinical pathway for congestive heart failure, the efficiency of medical care was achieved and the mean hospitalization period was widely shortened. In addition, by the through comprehensive patient education by multi-disciplinary staff involved in the pathway, the self-restraint life style after discharge seemed to be maintained and the readmission with worsening of heart failure was significantly suppressed.

Funding Acknowledgement

Type of funding source: None

The insulin-PI3K-Rac1 axis contributes to terminal adipocyte differentiation through regulation of actin cytoskeleton dynamics

Adipocyte differentiation is accompanied by a pronounced change in the actin cytoskeleton characterized by the reorganization of filamentous (F)-actin stress fibers into cortical F-actin structures. We previously showed that depolymerization of F-actin stress fibers induced by inactivation of RhoA-ROCK (Rho-associated kinase) signaling acts as a trigger for adipocyte differentiation. The relevance and underlying mechanism of the formation of cortical F-actin structures from depolymerized actin during adipocyte differentiation have remained unclear, however. We have now examined the mechanistic relation between actin dynamics and adipogenic induction. Transient exposure to the actin-depolymerizing agent latrunculin A (LatA) supported the formation of adipocyte-associated cortical actin structures and the completion of terminal adipocyte differentiation in the presence of insulin, whereas long-term exposure to LatA prevented such actin reorganization as well as terminal adipogenesis. Moreover, these effects of insulin were prevented by inhibition of phosphatidylinositol 3-kinase (PI3K)-Rac1 signaling and the actin-related protein 2/3 (Arp2/3) complex which is a critical component of the cortical actin networks. Our findings thus suggest that the insulin-PI3K-Rac1 axis leads to the formation of adipocyte-associated cortical actin structures which is essential for the completion of adipocyte differentiation.

P97 Effect of rhythm control therapy for asymptomatic atrial fibrillation

Background/Introduction

Cather ablation (CA) for atrial fibrillation (AF) as rhythm control therapy has widely spread. However, the indication of CA for the patients with asymptomatic AF is controversial (2016 ESC Guidelines for the management of atrial fibrillation developed in collaboration with EACTS). 

Purpose

This study was aimed to examine the effect of CA for asymptomatic AF patients.

Methods

In a total of 522 consecutive patients who were hospitalized for the initial CA for AF, 123 patients (23.6%) who were asymptomatic were retrospectively analyzed. "Asymptomatic AF" was defined when the patients had no complaints during the medical interviews. Quality of life (QOL) was evaluated with the AF QOL Questionnaire score (AFQLQ, invented by the Japanese Society of Electrocardiology) before CA and at 1 year after a single CA.

Results

A total of 79 patients were persistent AF (64.2%). Sinus rhythm maintenance rate at 3 yeas after CA was 57.0% in a single session and 84.8% in multiple sessions. In cardiac echo data at baseline, 3 months, 6 months, and 1 year after CA, left ventricular ejection fraction (LVEF) and left atrium diameter (LAD) were improved in the initial three months after a single CA (LVEF; 62.8 ± 8.0%→64.4 ± 6.5%, p = 0.045, LAD; 39.7 ± 6.1mm→35.3 ± 7.0mm, p = 0.0002). In LA volume measured with CT before and after CA, LA reverse remodeling was observed (102.7 ± 32.3ml→72.4 ± 24.1ml, p&lt;.0001). In AFQLQ2 (severity of symptoms), there was no significant difference (16.3 ± 2.2→15.9 ± 1.7 out of 18, p = 0.69). However, in AFQLQ1 (frequency of symptoms) and AFQLQ3 (limitations of activities and mental anxiety), the score was improved (20.2 ± 4.5→23.4 ± 1.1 out of 24, p&lt;.0001 and 47.6 ± 7.8→51.3 ± 6.1 out of 56, p = 0.0001).  Moreover, in low LVEF patients (LVEF &lt; 50%, n = 8), LVEF was remarkably improved (44.1 ± 4.0%→56.3 ± 10.8%, p = 0.034).

Conclusions

The improvement of LVEF and LA reverse remodeling can be expected at the early stage after CA, because of the reduction of AF burden. Moreover, the further improvement of QOL can be expected after CA, even in the patients with "asymptomatic" AF.

IMP dehydrogenase-2 drives aberrant nucleolar activity and promotes tumorigenesis in glioblastoma

In many cancers, high proliferation rates correlate with elevation of rRNA and tRNA levels, and nucleolar hypertrophy. However, the underlying mechanisms linking increased nucleolar transcription and tumorigenesis are only minimally understood. Here we show that IMP dehydrogenase-2 (IMPDH2), the rate-limiting enzyme for de novo guanine nucleotide biosynthesis, is overexpressed in the highly lethal brain cancer glioblastoma. This leads to increased rRNA and tRNA synthesis, stabilization of the nucleolar GTP-binding protein nucleostemin, and enlarged, malformed nucleoli. Pharmacological or genetic inactivation of IMPDH2 in glioblastoma reverses these effects and inhibits cell proliferation, whereas untransformed glia cells are unaffected by similar IMPDH2 perturbations. Impairment of IMPDH2 activity triggers nucleolar stress and growth arrest of glioblastoma cells even in the absence of functional p53. Our results reveal that upregulation of IMPDH2 is a prerequisite for the occurance of aberrant nucleolar function and increased anabolic processes in glioblastoma, which constitutes a primary event in gliomagenesis.

ROCK Inhibition Induces Terminal Adipocyte Differentiation and Suppresses Tumorigenesis in Chemoresistant Osteosarcoma Cells

Tumors comprise heterogeneous cell types including cancer stem cells (CSC), progenitor cells, and differentiated cells. Chemoresistance is a potential cause of relapse and a key characteristic of CSC, but the development of novel therapeutic approaches for targeting these cells has been limited. We previously established osteosarcoma-initiating (OSi) cells by introducing the gene for c-Myc into bone marrow stromal cells of Ink4a/Arf knockout mice. These OSi cells are composed of two distinct clones: highly tumorigenic cells (AX cells), similar to bipotent committed osteochondral progenitor cells, and tripotent cells of low tumorigenicity (AO cells), similar to mesenchymal stem cells. Here we show that depolymerization of the actin cytoskeleton induces terminal adipocyte differentiation and suppresses tumorigenesis in chemoresistant OSi cells. In contrast to AX cells, AO cells were highly resistant to conventional chemotherapeutic agents such as doxorubicin and were thus identified as chemoresistant cells. Inhibition of Rho-associated coiled-coil containing protein kinase (ROCK) elicited terminal adipocyte differentiation in chemoresistant AO cells through negative regulation of the transcriptional coactivator megakaryoblastic leukemia 1 associated with actin depolymerization. The clinically administered ROCK inhibitor fasudil significantly suppressed growth in vitro and tumorigenicity in vivo of chemoresistant AO cells as well as of OSi cells. Our findings thus suggest a new therapeutic strategy based on the induction of trans-terminal differentiation via modulation of actin cytoskeleton dynamics for therapy-resistant osteosarcoma stem cells. SIGNIFICANCE: These findings suggest that induction of trans-terminal differentiation through regulation of actin dynamics is a potential novel therapeutic approach for targeting chemoresistant stem-like tumor cells.

Abstract LB-334: xCT promotes malignant phenotypes in EGFR-expressing glioma

Malignant glioma such as glioblastoma is a cancer still difficult to treat. System xc(-) is composed of xCT and CD98hc subunits and functions as a plasma membrane antiporter for the uptake of extracellular cystine in exchange for intracellular glutamate, which has been reported to be involved in malignant phenotypes of glioma cells. However, the underlying mechanism of xCT regulation in glioma is not elucidated. Here we show that the epidermal growth factor receptor (EGFR) interacts with xCT and thereby promotes its cell surface expression and function in human glioma cells. EGFR-expressing glioma cells manifested both enhanced antioxidant capacity as a result of increased cystine uptake as well as increased extracellular glutamate which promotes glioma matrix invasion. Imaging mass spectrometry also revealed that brain tumors formed in mice by human glioma cells stably overexpressing EGFR contained higher levels of reduced glutathione compared with those formed by parental cells. Targeted inhibition of xCT suppressed the EGFR-dependent enhancement of antioxidant capacity in glioma cells as well as tumor growth and invasiveness. Our findings propose that xCT is a promising therapeutic target in EGFR-overexpressing malignant glioma.

Citation Format: Kenji Tsuchihashi, Shogo Okazaki, Momoko Yoshikawa, Ryo Seishima, Oltea Sampetrean, Nobuyuki Onishi, Hiroaki Wakimoto, Frank Furnari, Eishi Baba, Koichi Akashi, Hideyuki Saya, Osamu Nagano. xCT promotes malignant phenotypes in EGFR-expressing glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-334. doi:10.1158/1538-7445.AM2017-LB-334

Activation of Transforming Growth Factor Beta 1 Signaling in Gastric Cancer-associated Fibroblasts Increases Their Motility, via Expression of Rhomboid 5 Homolog 2, and Ability to Induce Invasiveness of Gastric Cancer Cells

BACKGROUND & AIMS

Fibroblasts that interact with cancer cells are called cancer-associated fibroblasts (CAFs), which promote progression of different tumor types. We investigated the characteristics and functions of CAFs in diffuse-type gastric cancers (DGCs) by analyzing features of their genome and gene expression patterns.

METHODS

We isolated CAFs and adjacent non-cancer fibroblasts (NFs) from 110 gastric cancer (GC) tissues from patients who underwent gastrectomy in Japan from 2008 through 2016. Cells were identified using specific markers of various cell types by immunoblot and flow cytometry. We selected pairs of CAFs and NFs for whole-exome and RNA sequencing analyses, and compared expression of specific genes using quantitative reverse transcription PCR. Protein levels and phosphorylation were compared by immunoblot and immunofluorescence analyses. Rhomboid 5 homolog 2 (RHBDF2) was overexpressed from a transgene in fibroblasts or knocked down using small interfering RNAs. Motility and invasiveness of isolated fibroblasts and GC cell lines (AGS, KATOIII, MKN45, NUGC3, NUGC4, OCUM-2MD3 and OCUM-12 cell lines) were quantified by real-time imaging analyses. We analyzed 7 independent sets of DNA microarray data from patients with GC and associated expression levels of specific genes with patient survival times. Nude mice were given injections of OCUM-2MD3 in the stomach wall; tumors and metastases were collected and analyzed by immunohistochemistry.

RESULTS

Many of the genes with increased expression in CAFs compared with NFs were associated with transforming growth factor beta 1 (TGFB1) activity. When CAFs were cultured in extracellular matrix, they became more motile than NFs; DGC cells incubated with CAFs were also more motile and invasive in vitro than DGC cells not incubated with CAFs. When injected into nude mice, CAF-incubated DGC cells invaded a greater number of lymphatic vessels than NF-incubated DGC cells. We identified RHBDF2 as a gene overexpressed in CAFs compared with NFs. Knockdown of RHBDF2 in CAFs reduced their elongation and motility in response to TGFB1, whereas overexpression of RHBDF2 in NFs increased their motility in extracellular matrix. RHBDF2 appeared to regulate oncogenic and non-canonical TGFB1 signaling. Knockdown of RHBDF2 in CAFs reduced cleavage of the TGFB receptor 1 (TGFBR1) by ADAM metallopeptidase domain 17 (ADAM17 or TACE) and reduced expression of genes that regulate motility. Incubation of NFs with in interleukin 1 alpha (IL1A), IL1B or tumor necrosis factor, secreted by DGCs, increased fibroblast expression of RHBDF2. Simultaneous high expression of these cytokines in GC samples was associated with shorter survival times of patients.

CONCLUSIONS

In CAFs isolated from human DGCs, we observed increased expression of RHBDF2, which regulates TGFB1 signaling. Expression of RHBDF2 in fibroblasts is induced by inflammatory cytokines (such as IL1A, IL1B, and tumor necrosis factor) secreted by DGCs. RHBDF2 promotes cleavage of TGFBR1 by activating TACE and motility of CAFs in response to TGFB1. These highly motile CAFs induce DGCs to invade extracellular matrix and lymphatic vessels in nude mice.

Simvastatin-Induced Apoptosis in Osteosarcoma Cells: A Key Role of RhoA-AMPK/p38 MAPK Signaling in Antitumor Activity

Osteosarcoma is the most common type of primary bone tumor, novel therapeutic agents for which are urgently needed. To identify such agents, we screened a panel of approved drugs with a mouse model of osteosarcoma. The screen identified simvastatin, which inhibited the proliferation and migration of osteosarcoma cells in vitro Simvastatin also induced apoptosis in osteosarcoma cells in a manner dependent on inhibition of the mevalonate biosynthetic pathway. It also disrupted the function of the small GTPase RhoA and induced activation of AMP-activated protein kinase (AMPK) and p38 MAPK, with AMPK functioning upstream of p38 MAPK. Inhibitors of AMPK or p38 MAPK attenuated the induction of apoptosis by simvastatin, whereas metformin enhanced this effect of simvastatin by further activation of AMPK. Although treatment with simvastatin alone did not inhibit osteosarcoma tumor growth in vivo, its combination with a fat-free diet induced a significant antitumor effect that was enhanced further by metformin administration. Our findings suggest that simvastatin induces apoptosis in osteosarcoma cells via activation of AMPK and p38 MAPK, and that, in combination with other approaches, it holds therapeutic potential for osteosarcoma. Mol Cancer Ther; 16(1); 182-92. ©2016 AACR.