[Analysis of the types and functions of CD34+ cells in full-thickness skin defect wounds of normal mice and diabetic mice by single-cell RNA sequencing]

Objective: To analyze the types and functions of CD34+ cells in full-thickness skin defect wounds of normal mice and diabetic mice by single-cell RNA sequencing. Methods: This study was an experimental study. The CD34+ cell lineage tracing mouse was produced, and the visualization of CD34+ cells under the fluorescent condition was realized. Six male CD34+ cell lineage tracing mice aged 7-8 weeks (designated as diabetic group) were intraperitoneally injected with streptozotocin to establish a diabetic model, and full-thickness skin defect wounds were prepared on their backs when they reached 13 weeks old. Another 6 male CD34+ cell lineage tracing mice aged 13 weeks (designated as control group) were also subjected to full-thickness skin defect wounds on their backs. On post-injury day (PID) 4, wound tissue was collected from 3 mice in control group and 2 mice in diabetic group, and digested to prepare single-cell suspensions. CD34+ cells were screened using fluorescence-activated cell sorting, followed by single-cell RNA sequencing. The Seurat 4.0.2 program in the R programming language was utilized for dimensionality reduction, visualization, and cell clustering analysis of CD34+ cell types, and to screen and annotate the marker genes for each CD34+ cell subpopulation. Kyoto encyclopedia of genes and genomes (KEGG) and gene ontology (GO) enrichment analysis was performed to analyze the differentially expressed genes (DEGs) of CD34+ fibroblasts (Fbs), smooth muscle cells (SMCs), keratinocytes (KCs), and chondrocyte-like cells (CLCs) in the wound tissue of two groups of mice for exploring cellular functions. Results: On PID 4, CD34+ cells in the wound tissue of both groups of mice were consisted of 7 cell types, specifically endothelial cells, Fbs, KCs, macrophages, T cells, SMCs, and CLCs. Among these, Fbs were further classified into 5 subpopulations. Compared with those in control group, the proportions of CD34+ endothelial cells, Fbs subpopulation 1, Fbs subpopulation 4, KCs, and CLCs in the wound tissue of mice were increased in diabetic group, while the proportions of CD34+ Fbs subpopulation 2, Fbs subpopulation 3, and SMCs were decreased. The marker genes for annotating CD34+ CLCs, endothelial cells, Fbs subpopulation 1, Fbs subpopulation 2, Fbs subpopulation 3, Fbs subpopulation 4, Fbs subpopulation 5, KCs, macrophages, SMCs, and T cells were respectively metastasis-associated lung adenocarcinoma transcript 1, fatty acid binding protein 4, Gremlin 1, complement component 4B, H19 imprinted maternally expressed transcript, Dickkopf Wnt signaling pathway inhibitor 2, fibromodulin, keratin 5, CD74 molecule, regulator of G protein signaling 5, and inducible T-cell co-stimulator molecule. KEGG and GO enrichment analysis revealed that, compared with those in control group, DEGs with significant differential expression (SDE) in CD34+ Fbs from the wound tissue of mice in diabetic group on PID 4 were significantly enriched in terms related to inflammatory response, extracellular matrix (ECM) organization, regulation of cell proliferation, and aging (with Pvalues all <0.05), DEGs with SDE in CD34+ SMCs were significantly enriched in terms related to cell migration, apoptotic process, positive regulation of transcription, and phagosome (with P values all <0.05), DEGs with SDE in CD34+ KCs were significantly enriched in terms related to mitochondrial function, transcription, and neurodegenerative diseases (with P values all <0.05), and DEGs with SDE in CD34+ CLCs were significantly enriched in terms related to rhythm regulation, ECM, and viral infection (with P values all <0.05). Conclusions: CD34+ cells display high heterogeneity in the healing process of full-thickness skin defect wounds in both normal mice and diabetic mice. The significantly enriched functions of DEGs with SDE in CD34+ cell subpopulations in the wound tissue of the two mouse groups are closely related to the wound healing process.

Gene expression of non-homologous end-joining pathways in the prognosis of ovarian cancer

Ovarian cancer is the deadliest gynecologic malignancy in women, with a 46% five-year overall survival rate. The objective of the study was to investigate the effects of non-homologous end-joining (NHEJ) genes on clinical outcomes of ovarian cancer patients. To determine if these genes act as prognostic biomarkers of mortality and disease progression, the expression profiles of 48 NHEJ-associated genes were analyzed using an array of statistical and machine learning techniques: logistic regression models, decision trees, naive-Bayes, two sample t-tests, support vector machines, hierarchical clustering, principal component analysis, and neural networks. In this process, the correlation of genes with patient survival and disease progression and recurrence was noted. Also, multiple features from the gene set were found to have significant predictive capabilities. APTX, BRCA1, PAXX, LIG1, and TP53 were identified as most important out of all the candidate genes for predicting clinical outcomes of ovarian cancer patients.

Transforming Growth Factor Beta and Epithelial to Mesenchymal Transition Alter Homologous Recombination Repair Gene Expression and Sensitize BRCA Wild-Type Ovarian Cancer Cells to Olaparib

Epithelial ovarian cancer (EOC) remains the most lethal gynecologic malignancy, largely due to metastasis and drug resistant recurrences. Fifteen percent of ovarian tumors carry mutations in BRCA1 or BRCA2, rendering them vulnerable to treatment with PARP inhibitors such as olaparib. Recent studies have shown that TGFβ can induce "BRCAness" in BRCA wild-type cancer cells. Given that TGFβ is a known driver of epithelial to mesenchymal transition (EMT), and the connection between EMT and metastatic spread in EOC and other cancers, we asked if TGFβ and EMT alter the susceptibility of EOC to PARP inhibition. Epithelial EOC cells were transiently treated with soluble TGFβ, and their clonogenic potential, expression, and function of EMT and DNA repair genes, and response to PARP inhibitors compared with untreated controls. A second epithelial cell line was compared to its mesenchymal derivative for EMT and DNA repair gene expression and drug responses. We found that TGFβ and EMT resulted in the downregulation of genes responsible for homologous recombination (HR) and sensitized cells to olaparib. HR efficiency was reduced in a dose-dependent manner. Furthermore, mesenchymal cells displayed sensitivity to olaparib, cisplatin, and the DNA-PK inhibitor Nu-7441. Therefore, the treatment of disseminated, mesenchymal tumors may represent an opportunity to expand the clinical utility of PARP inhibitors and similar agents.

Clinical efficacy of targeted therapy, immunotherapy combined with hepatic artery infusion chemotherapy (FOLFOX), and lipiodol embolization in the treatment of unresectable hepatocarcinoma

To evaluate the clinical efficacy of targeted therapy and immunotherapy combined with hepatic arterial infusion chemotherapy (HAIC) of FOLFOX and lipiodol embolization in the treatment of unresectable hepatocellular carcinoma. Patients included in the study were those who received targeted therapy and immunotherapy combined with HAIC of FOLFOX and lipiodol embolization in Zhongshan People's Hospital from December 2020 to June 2021 for unresectable hepatocellular carcinoma. Evaluation indicators included objective response rate (ORR), median progression-free survival (mPFS), median duration of response (mDOR), 1-year overall survival rate (OS), surgical conversion rate, and adverse events. Treatment response was assessed using Response Evaluation Criteria in Solid Tumors (mRECIST and RECIST v1.1). A total of 35 patients were included in this study, 30 of whom completed treatment evaluation. According to mRECIST evaluation criteria, the objective response rate (ORR) was 83.3% (25/30); the complete response (CR) was 60% (18/30); the partial response (PR) was 23.3% (7/30), and stable disease (SD) was 16.7% (5/30). The mDOR was 10.3 months (95% Cl: 8.27-NE), and the mPFS was 13.2 months (95% CI: 10.3-NE); the surgical conversion rate was 30.0% (9/30). The 1-year OS was 96.7%. There were no serious surgical complications and grade 4 or 5 adverse events of targeted therapy, immunotherapy and HAIC. Some patients had grade 3 adverse reactions in gastrointestinal toxicity or hepatotoxicity, and the adverse reactions were improved after corresponding symptomatic treatment. We concluded that HAIC of FOLFOX and lipiodol embolization combined with targeted therapy and immunotherapy had a significant curative effect in the treatment of unresectable hepatocellular carcinoma, with no serious adverse reactions and a high rate of surgical conversion rate.

In silico screening identifies a novel small molecule inhibitor that counteracts PARP inhibitor resistance in ovarian cancer

Poly ADP-ribose polymerase (PARP) inhibitors are promising targeted therapy for epithelial ovarian cancer (EOC) with BRCA mutations or defective homologous recombination (HR) repair. However, reversion of BRCA mutation and restoration of HR repair in EOC lead to PARP inhibitor resistance and reduced clinical efficacy of PARP inhibitors. We have previously shown that triapine, a small molecule inhibitor of ribonucleotide reductase (RNR), impaired HR repair and sensitized HR repair-proficient EOC to PARP inhibitors. In this study, we performed in silico screening of small molecule libraries to identify novel compounds that bind to the triapine-binding pocket on the R2 subunit of RNR and inhibit RNR in EOC cells. Following experimental validation of selected top-ranking in silico hits for inhibition of dNTP and DNA synthesis, we identified, DB4, a putative RNR pocket-binding inhibitor markedly abrogated HR repair and sensitized BRCA-wild-type EOC cells to the PARP inhibitor olaparib. Furthermore, we demonstrated that the combination of DB4 and olaparib deterred the progression of BRCA-wild type EOC xenografts and significantly prolonged the survival time of tumor-bearing mice. Herein we report the discovery of a putative small molecule inhibitor of RNR and HR repair for combination with PARP inhibitors to treat PARP inhibitor-resistant and HR repair-proficient EOC.

Flow Cytometric Analyses of p53-Mediated Cell Cycle Arrest and Apoptosis in Cancer Cells

Phenotypic analysis of the effects of a gene of interest may be limited because stable expression of some genes leads to adverse consequences in cell survival, such as disturbance of cell cycle progression, senescence, autophagy, and programmed cell death. One of the best examples is tumor suppressor p53. p53 functions as a tumor suppressor by inducing cell cycle arrest and apoptosis in response to genotoxic and environmental insults. The choice and timing of either pathways induced by p53 depend on cellular context, cell types, and the degree of cellular/genomic damage (For review, see (Chen J, Cold Spring Harb Perspect Med 6:a026104, 2016)). The uncertainty makes the studies on the long-term effects of p53 in cells challenging. This chapter describes a method of flow cytometric analysis of ectopic expression of p53 to better quantify cell cycle distribution and apoptosis in cells treated with DNA damaging agents. The method can be easily adapted to other genes of interest to study their contributions to the fate of variety of cell types in response to endogenous or exogenous stresses.

[Comparison of the curative effect of transjugular intrahepatic portosystemic shunt with expanded polytetrafluoroethylene-covered stent and drug combined with gastroscopy as the secondary prevention of esophageal -gastric variceal bleeding in portal hypertension]

Objective: To compare the clinical efficacy of transjugular intrahepatic portosystemic shunt (TIPS) with expanded polytetrafluoroethylene (ePTFE)-covered stent and drug combined with gastroscopy as the secondary prevention of esophageal-gastric variceal bleeding in portal hypertension. Methods: Patients with esophageal-gastric variceal bleeding who received TIPS treatment (ePTFE covered stent) or gastroscopy for the first time as the secondary prevention for portal hypertension at Nanfang Hospital of Southern Medical University through March to July 2017 were selected. One year after the operation, liver function changes, ascites remission rates, incidence of hepatic encephalopathy, re-bleeding rate, average hospitalization frequency and expenses, survival time, as well as the TIPS patency conditions were analyzed in the two groups of patients. 2 test, Kaplan-Meier method and Mann-Whitney U test were used to analyze the data. Results: There were 74 and 66 cases in the TIPS and the drug combined gastroscopy group and the follow-up duration (14.57 ± 0.79) was 12-16 months. One year after surgery, the remission rate of ascites in the TIPS group was higher 57.1% (32/56) than that of the drug combined gastroscopy group (0), and the difference was statistically significant (χ(2) = 2 = 36.73, P < 0.01). The cumulative incidence of hepatic encephalopathy at 1, 3, 6, and 12 months after surgery in the TIPS group was 32.4% (24/74), 37.8% (28/74), 40.5% (30/74), and 40.5% (30/74), respectively. The cumulative incidence of hepatic encephalopathy in the drug combined gastroscopy group was 3.0% (2/66), 3.0% (2/66), 3.0% (2/66), and 6.1% (4/66), respectively. Kaplan-Meier analysis showed that the cumulative incidence of hepatic encephalopathy in the TIPS group was higher than that of the drug combined gastroscopy group (χ(2) = 11.29, P < 0.01). The incidence of severe hepatic encephalopathy ( grade III to IV) at 1, 3, 6, and 12 months after surgery in the TIPS group was 2.7% (2/74), 0, 0, and 0, respectively. The incidence of severe hepatic encephalopathy in drug combined gastroscopy group was 0, and there was no statistically significant difference in development of hepatic encephalopathy between the two groups (P > 0.05). The re-bleeding rates of TIPS group and drug combined gastroscopy group were 0 and 27.3% (18/66), respectively, and the difference was statistically significant (χ(2) = 22.42, P < 0.01). There was no death reported during the follow-up period between both groups. The hospitalization frequency times (1.45 ± 0.80) in TIPS group was lower than that of the drug combined gastroscopy group times (3.24 ± 1.80), and the difference was statistically significant (U = -4.52, P < 0.01). Conclusion: In the prevention of esophageal-gastric variceal bleeding, TIPS (ePTFE-covered stent) treatment has the advantages of reducing re-bleeding rate, high ascites remission rate and hospitalizations frequency. In addition, patients treated with TIPS have a higher incidence of hepatic encephalopathy than that of drugs combined with gastroscopy. However, TIPS did not exacerbate the incidence of hepatic encephalopathy, and there was no significant difference in the 1-year survival rate after TIPS and drugs combined with gastroscopy treatment.

[Therapeutic effect of low-temperature radiofrequency coblation on early-stage laryngeal cancer]

Objective: To evaluate the safety,efficacy and prognosis of low-temperature plasma radiofrequency coblation for early-stage laryngeal cancer(Tis, T1 and T2). Method: A retrospective analysis of 202 patients with early-stage laryngeal cancer who underwent the low-temperature radiofrequency coblation surgery, including 34 cases of Tis(16.83%), 49 cases of stage T1aN0M0(24.26%), 50 cases of stage T1bN0M0(24.75%) and 69 cases of stage T2N0M0(34.16%). Surgical patients were followed up closely for 6 to 60 months, with a median follow-up of 29 months. Result: Of the 202 patients,165(81.68%) had no recurrence and achieved good surgical results. None of them suffered severe complications such as post-operative hemorrhage and asphyxia. 37 cases(18.32%) had recurrence, including 1 case(0.50%) in stage Tis, 7 cases(3.47%) in stage T1a,7 cases(3.47%) in stage T1b, and 22 cases(10.89%) in stage T2. Thirteen patients who had recurrence underwent total laryngectomy(5 of which had a recurrence of T3 and 8 of which progressed to T4), including 1 in the stage T1a,2 in the stage T1b, and 10 in the stage T2. Vertical hemilaryngectomy were performed in 4 cases, 3 cases of stage T1a and 1 case of stage T2; 5 cases underwent plasma radiofrequency coblation again, including 3 cases of stage T1b and 2 cases of stage T2,no recurrence was found in all the patients; 1 patient had no obvious recurrence in the larynx but had cervical lymph node metastasis, radical neck dissection was performed; 1 patient with stage T2 recurrence was treated with a tracheotomy to relieve laryngeal obstruction without further treatment;3 cases showed improvement by radiotherapy and chemotherapy treatment after recurrence; 9 death cases,5 patients died after radiotherapy and chemotherapy, and 4 patients stopped getting treatment after recurrence.Conclusion: Low-temperature radiofrequency coblation surgery for patients with early-stage laryngeal cancer has great advantages in the preservation of laryngeal function and reduction of surgical trauma after surgery compared with traditional surgical method, and can obtain satisfactory results, but the selection of surgical indications for some patients with clinical stage T2 is still need to be carefully considered..

Combination of triapine, olaparib, and cediranib suppresses progression of BRCA-wild type and PARP inhibitor-resistant epithelial ovarian cancer

PARP inhibitors target BRCA mutations and defective homologous recombination repair (HRR) for the treatment of epithelial ovarian cancer (EOC). However, the treatment of HRR-proficient EOC with PARP inhibitors remains challenging. The objective of this study was to determine whether the combination of triapine (ribonucleotide reductase inhibitor), cediranib (vascular endothelial growth factor receptor tyrosine kinase inhibitor), and the PARP inhibitor olaparib synergized against BRCA wild-type and HRR-proficient EOC in xenograft mouse models. In addition, the mechanisms by which cediranib augmented the efficacy of triapine and olaparib were investigated. BRCA-wild type and PARP inhibitor-resistant EOC cell lines were implanted subcutaneously (s.c.) into nude mice or injected intraperitoneally (i.p.) into SCID-Beige mice. Mice were then treated i.p. with olaparib, cediranib, triapine, various double and triple combinations. The volume of s.c tumor in nude mice and the abdominal circumference of SCID-Beige mice were measured to evaluate the effectiveness of the treatment to delay tumor growth and prolong the survival time of mice. In both xenograft mouse models, the combination of triapine, olaparib and cediranib resulted in marked suppression of BRCA-wild type EOC growth and significant prolongation of the survival time of mice, with efficacy greater than any double combinations and single drugs. Furthermore, we identified that cediranib abrogated pro-survival and anti-apoptotic AKT signaling, thereby enhancing the efficacy of triapine and olaparib against BRCA-wild type EOC cells. Taken together, our results demonstrate a proof-of-principle approach and the combination regiment holds promise in treating BRCA-wild type and PARP inhibitor-resistant EOC.

Targeting Cyclin-Dependent Kinases for Treatment of Gynecologic Cancers

Ovarian, uterine/endometrial, and cervical cancers are major gynecologic malignancies estimated to cause nearly 30,000 deaths in 2018 in US. Defective cell cycle regulation is the hallmark of cancers underpinning the development and progression of the disease. Normal cell cycle is driven by the coordinated and sequential rise and fall of cyclin-dependent kinases (CDK) activity. The transition of cell cycle phases is governed by the respective checkpoints that prevent the entry into the next phase until cellular or genetic defects are repaired. Checkpoint activation is achieved by p53- and ATM/ATR-mediated inactivation of CDKs in response to DNA damage. Therefore, an aberrant increase in CDK activity and/or defects in checkpoint activation lead to unrestricted cell cycle phase transition and uncontrolled proliferation that give rise to cancers and perpetuate malignant progression. Given that CDK activity is also required for homologous recombination (HR) repair, pharmacological inhibition of CDKs can be exploited as a synthetic lethal approach to augment the therapeutic efficacy of PARP inhibitors and other DNA damaging modalities for the treatment of gynecologic cancers. Here, we overview the basic of cell cycle and discuss the mechanistic studies that establish the intimate link between CDKs and HR repair. In addition, we present the perspective of preclinical and clinical development in small molecule inhibitors of CDKs and CDK-associated protein targets, as well as their potential use in combination with hormonal therapy, PARP inhibitors, chemotherapy, and radiation to improve treatment outcomes.

Abstract 850: The Pi3K/Akt pathway mediates epithelial-mesenchymal transition (EMT) and malignant progression in BRCA-defective epithelial ovarian cancer

Objectives: Despite improvement in therapy, the majority of patients with ovarian cancer relapses and eventually succumbs to the disease. Therefore, there is an urgent need for further understanding the development and progression of ovarian cancer. It is well established that the phosphatidylinositol 3-kinase (Pi3k/Akt) pathway is activated in 70% of ovarian cancers. We have previously shown that in AKT activity is up regulated in BRCA1 and BRCA-2 deficient cancer. Epithelial-mesenchymal transition (EMT), a process by which cells acquire motility and lose their intercellular adhesions, plays an important role in normal development. Cancer cells have been shown to exhibit similar EMT-like process during invasion and metastasis. Recently, the activation of the Pi3k/Akt pathway is emerging as a central feature of EMT. This study aims to investigate whether activation of the Pi3k/Akt pathway is necessary for promoting EMT and malignant progression in BRCA-defective ovarian cancer.

Methods: BRCA2-mutated PEO1 and BRCA2-wild type PEO4 epithelial ovarian cancer cell lines were derived from the same patient at first and second relapse, respectively, following platinum-based chemotherapy. Non-targeted siRNA control (NTC) and BRCA1-knockdown (BRCA1-kd) SKOV3 cell lines were previously established in our laboratory. Western blot analysis and luciferase reporter assay were performed to determine EMT markers (snail, slug, fibronectin) in BRCA defective ovarian cancer cells. Scratch wound assays were conducted to determine the ability of cells to migrate. Clonogenic and apoptosis assays were carried out to determine cell survival in response to various concentrations of carboplatin and olaparib with or without MK-2206, a small molecule inhibitor of AKT.

Results: PEO1 cells exhibited an increase in mesenchymal markers Snail and fibronectin, whereas PEO4 cells exhibited an increase in the epithelial marker E-cadherin. PEO1 cells also exhibited an increase in cell migration compared with PEO4 cells. In the luciferase reporter assay, BRCA2- mutated PEO1 and BRCA-1 Kd SKOV3 cells exhibited lower levels of the epithelial maker, E-cadherin compared to their BRCA-wild type counterparts, PEO4 and SKOV3 NTC, respectively. Treatment with MK-2206 caused increased susceptibility of BRCA1-kd SKOV3 cells to olaparib compared with BRCA1-wild type SKOV3-NTC cells.

Conclusions: BRCA2-mutated PEO1cells manifested an increase in mesenchymal markers and invasive phenotypes. BRCA1-Kd SKOV3 cells manifested a decrease in the epithelial trait, E-cadherin activity. In addition, AKT inhibition heightened susceptibility of BRCA-1Kd SKOV3 cells to DNA damaging agents such as olaparib. These findings suggest that BRCA-defective cells rely on the induction of EMT via activation of AKT to survive DNA damage and develop therapeutic resistance during malignant progression.

Citation Format: Mehida Alexandre, Z Ping Lin, Elena S. Ratner. The Pi3K/Akt pathway mediates epithelial-mesenchymal transition (EMT) and malignant progression in BRCA-defective epithelial ovarian cancer [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 850. doi:10.1158/1538-7445.AM2017-850

MK-2206 sensitizes BRCA-deficient epithelial ovarian adenocarcinoma to cisplatin and olaparib

BACKGROUND

Platinum resistance is a major obstacle in the treatment of epithelial ovarian cancer (EOC). Activation of the AKT pathway promotes platinum resistance while inhibition of AKT sensitizes chemoresistant cells. Patients with BRCA mutant EOC, and thus a defect in the homologous recombination (HR) repair pathway, demonstrate greater clinical response to platinum and olaparib therapy than patients with BRCA wild-type EOC. MK-2206, an allosteric inhibitor of AKT phosphorylation, sensitizes a variety of cell types to various anticancer agents and is currently undergoing phase II trials as monotherapy for platinum-resistant ovarian, fallopian tube, and peritoneal cancer. This study examines the differential effects of AKT inhibition with cisplatin and olaparib therapy in BRCA1/2-deficient versus wild-type EOC.

METHODS

PEO1, a chemosensitive BRCA2-mutant serous ovarian adenocarcinoma, and PEO4, a reverted BRCA2-proficient line from the same patient after the development of chemotherapeutic resistance, were primarily used for the study. In PEO1, MK-2206 demonstrated moderate to strong synergism with cisplatin and olaparib at all doses, while demonstrating antagonism at all doses in PEO4.

RESULTS

Baseline phospho-AKT activity in untreated cells was upregulated in both BRCA1- and 2-deficient cell lines. MK-2206 prevented cisplatin- and olaparib-induced AKT activation in the BRCA2-deficient PEO1 cells. We propose that BRCA-deficient EOC cells upregulate baseline AKT activity to enhance survival in the absence of HR. Higher AKT activity is also required to withstand cytotoxic agent-induced DNA damage, leading to strong synergism between MK-2206 and cisplatin or olaparib therapy in BRCA-deficient cells.

CONCLUSIONS

MK-2206 shows promise as a chemosensitization agent in BRCA-deficient EOC and merits clinical investigation in this patient population.

Triapine potentiates platinum-based combination therapy by disruption of homologous recombination repair

Background:

Platinum resistance may be attributable to inherent or acquired proficiency in homologous recombination repair (HRR) in epithelial ovarian cancer (EOC). The objective of this study was to evaluate the efficacy of the small molecule inhibitor triapine to disrupt HRR and sensitise BRCA wild-type EOC cells to platinum-based combination therapy in vitro and in vivo.

Methods:

The sensitivity of BRCA wild-type cancer cells to olaparib, cisplatin, carboplatin, doxorubicin, or etoposide in combination with triapine was evaluated by clonogenic survival assays. The effects of triapine on HRR activity in cells were measured with a DR-GFP reporter assay. The ability of triapine to enhance the effects of the carboplatin-doxil combination on EOC tumour growth delay was determined using a xenograft tumour mouse model.

Results:

Platinum resistance is associated with wild-type BRCA status. Triapine inhibits HRR activity and enhances the sensitivity of BRCA wild-type cancer cells to cisplatin, olaparib, and doxorubicin. However, sequential combination of triapine and cisplatin is necessary to achieve synergism. Moreover, triapine potentiates platinum-based combination therapy against BRCA wild-type EOC cells and produces significant delay of EOC tumour growth.

Conclusions:

Triapine promises to augment the clinical efficacy of platinum-based combination regimens for treatment of platinum-resistant EOC with wild-type BRCA and proficient HRR activity.

Cataloging antineoplastic agents according to their effectiveness against platinum-resistant and platinum-sensitive ovarian carcinoma cell lines

Although epithelial ovarian cancers (EOCs) are initially treated with platinum-based chemotherapy, EOCs vary in platinum responsiveness. Cataloging antineoplastic agents according to their effectiveness against platinum-resistant and platinum-sensitive EOC cell lines is valuable for development of therapeutic strategies to avoid platinum inefficacy and to exploit platinum sensitivity. TOV-21G devoid of FANCF expression, OV-90 and SKOV-3 were employed as examples of platinum-sensitive, platinum-intermediate and platinum-resistant cell lines, respectively. Antineoplastic agents examined included mitomycin C, doxorubicin, etoposide, gemcitabine, chlorambucil, paclitaxel, triapine and X-rays. Their effectiveness against cell lines was analyzed by clonogenic assays. Cytotoxic profiles of mitomycin C and carboplatin were similar, with mitomycin C exhibiting greater potency and selectivity against TOV-21G than carboplatin. Cytotoxic profiles of doxorubicin, etoposide and X-rays overlapped with that of carboplatin, while OV-90 overexpressing Rad51 was more resistant to chlorambucil than SKOV-3. The efficacy of paclitaxel and triapine was independent of platinum sensitivity or resistance. Consistent with these cytotoxic profiles, cisplatin/mitomycin C, triapine, and paclitaxel differed in the capacity to induce phosphorylation of H2AX, and produced unique inhibitory patterns of DNA/RNA syntheses in HL-60 human leukemia cells. Paclitaxel and triapine in combination produced additive antitumor effects in M109 murine lung carcinoma. In conclusion, mitomycin C is potentially more effective against Fanconi anemia pathway-deficient EOCs than carboplatin. Doxorubicin and etoposide, because of their overlapping cytotoxic properties with carboplatin, are unlikely to be efficacious against platinum-refractory EOCs. Paclitaxel and triapine are effective regardless of platinum sensitivity status, and promising in combination for both platinum-sensitive and platinum-refractory EOCs.

Droplet optofluidic imaging for λ-bacteriophage detection via co-culture with host cell Escherichia coli

Bacteriophages are considered as attractive indicators for determining drinking water quality since its concentration is strongly correlated with virus concentrations in water samples. Previously, bacteriophage detection was based on a plague assay that required a complicated labelling technique and a time-consuming culture assay. Here, for the first time, a label-free bacteriophage detection is reported by using droplet optofluidic imaging, which uses host-cell-containing microdroplets as reaction carriers for bacteriophage infection due to a higher contact ratio. The optofluidic imaging is based on the effective refractive index changes in the microdroplet correlated with the growth rate of the infected host cells, which is highly sensitive, i.e. can detect one E. coli cell. The droplet optofluidic system is not only used in drinking water quality monitoring, but also has high potential applications for pathogenic bacteria detection in clinical diagnosis and food industry.

Distinct mechanisms of cell-kill by triapine and its terminally dimethylated derivative Dp44mT due to a loss or gain of activity of their copper(II) complexes

Triapine, currently being evaluated as an antitumor agent in phase II clinical trials, and its terminally dimethylated derivative Dp44mT share the α-pyridyl thiosemicarbazone backbone that functions as ligands for transition metal ions. Yet, Dp44mT is approximately 100-fold more potent than triapine in cytotoxicity assays. The aims of this study were to elucidate the mechanisms underlying their potency disparity and to determine their kinetics of cell-kill in culture to aid in the formulation of their clinical dosing schedules. The addition of Cu(2+) inactivated triapine in a 1:1 stoichiometric fashion, while it potentiated the cytotoxicity of Dp44mT. Clonogenic assays after finite-time drug-exposure revealed that triapine produced cell-kill in two phases, one completed within 20 min that caused limited cell-kill, and the other occurring after 16 h of exposure that produced extensive cell-kill. The ribonucleotide reductase inhibitor triapine at 0.4 μM caused immediate complete arrest of DNA synthesis, whereas Dp44mT at this concentration did not appreciably inhibit DNA synthesis. The inhibition of DNA synthesis by triapine was reversible upon its removal from the medium. Cell death after 16 h exposure to triapine paralleled the appearance of phospho-(γ)H2AX, a marker of DNA double-strand breaks induced by collapse of DNA replication forks after prolonged replication arrest. In contrast to triapine, Dp44mT produced robust cell-kill within 1h in a concentration-dependent manner. The short-term action of both agents was prevented by thiols, indicative of the involvement of reactive oxygen species. The time dependency in the production of cell-kill by triapine should be considered in treatment regimens.

Triapine disrupts CtIP-mediated homologous recombination repair and sensitizes ovarian cancer cells to PARP and topoisomerase inhibitors

PARP inhibitors exploit synthetic lethality to target epithelial ovarian cancer (EOC) with hereditary BRCA mutations and defects in homologous recombination repair (HRR). However, such an approach is limited to a small subset of EOC patients and compromised by restored HRR due to secondary mutations in BRCA genes. Here, it was demonstrated that triapine, a small-molecule inhibitor of ribonucleotide reductase, enhances the sensitivity of BRCA wild-type EOC cells to the PARP inhibitor olaparib and the topoisomerase II inhibitor etoposide. Triapine abolishes olaparib-induced BRCA1 and Rad51 foci, and disrupts the BRCA1 interaction with the Mre11-Rad50-Nbs1 (MRN) complex in BRCA1 wild-type EOC cells. It has been shown that phosphorylation of CtIP (RBBP8) is required for the interaction with BRCA1 and with MRN to promote DNA double-strand break (DSB) resection during S and G(2) phases of the cell cycle. Mechanistic studies within reveal that triapine inhibits cyclin-dependent kinase (CDK) activity and blocks olaparib-induced CtIP phosphorylation through Chk1 activation. Furthermore, triapine abrogates etoposide-induced CtIP phosphorylation and DSB resection as evidenced by marked attenuation of RPA32 phosphorylation. Concurrently, triapine obliterates etoposide-induced BRCA1 foci and sensitizes BRCA1 wild-type EOC cells to etoposide. Using a GFP-based HRR assay, it was determined that triapine suppresses HRR activity induced by an I-SceI-generated DSB. These results suggest that triapine augments the sensitivity of BRCA wild-type EOC cells to drug-induced DSBs by disrupting CtIP-mediated HRR.

IMPLICATIONS

These findings provide a strong rationale for combining triapine with PARP or topoisomerase inhibitors to target HRR-proficient EOC cells.

Abstract 4490: Triapine sensitizes chemoresistant ovarian cancer cells to platinum therapy

Objectives:

Epithelial ovarian cancer (EOC) is the second most common female pelvic reproductive organ cancer in the United States, and carries the highest mortality in this category in the Western world. The progression free survival and overall survival depend greatly on tumor sensitivity to a platinum chemotherapy. Once platinum resistance is encountered, response rates of only 6-30% are achieved. Triapine, a novel small-molecule drug developed in our laboratory, potently inhibits the activity of ribonucleotide reductase involved in the key step of DNA synthesis and replication. Given that triapine caused profound disruption of dNTP levels and S phase progression, we examined the effects of triapine on the repair of replication-associated DSBs and on the sensitivity of platinum resistant EOC to DNA damaging and platinum therapy.

Methods:

Cell sensitivity to varying ratios of treating drug combinations (triapine/6-thio-guanine alone, triapine/6-thioguanine with cisplatin, carboplatin, doxorubicin, or paclitaxel) was carried out by clonogenic survival assays using multiple EOC cells lines (A2780, CP70, CAOV-3, IGROV-1, BG-1, PEO1, PEO4, SKOV-3). Colonies were stained and counted to determine % survival. DNA replication was determined by EdU incorporation into DNA using flow cytometry and confocal microscopy.

Results:

Treatment with triapine leads to synergistic sensitization of BRCA wild-type EOC cells to platinum drugs. The degree of sensitization by triapine is more pronounced toward the lower concentrations of platinum drugs, at which DNA replication is still ongoing. Platinum drugs induce DNA double strand breaks (DSBs) and Rad51 foci in BRCA wild type EOC cells. Triapine attenuates formation of Rad51 foci, a marker of DSB repair, in these cells. For EOC cells that are highly platinum resistant, combination of triapine and 6-thioguanine is required to achieve significant sensitization to platinum drugs.

Conclusions:

Platinum drugs induce replication-associated DSBs and Rad51-dependent repair in BRCA wild-type EOC cells. Triapine inhibits Rad51-dependent repair of DSBs and therefore sensitizes BRCA wild-type EOC cells to platinum drugs. The mechanism by which 6-thioguanine enhances the effects of triapine is currently being investigated. Our findings indicate for the first time that triapine and 6-thioguanine can be used in combination with platinum agents to target BRCA wild-type and platinum-resistant EOC.

Citation Format: Elena S. Ratner, Margaret Whicker, Z. Ping Lin, Alan C. Sartorelli. Triapine sensitizes chemoresistant ovarian cancer cells to platinum therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4490. doi:10.1158/1538-7445.AM2013-4490

Abstract 3277: Pifithrin-α and veliparib synergize in the sensitization of p53 wild-type ovarian cells to cisplatin therapy

Objectives. Veliparib (ABT), a PARP1/2 inhibitor, has been studied in ovarian adenocarcinoma treatment, particularly in conjunction with platinum therapy, and sensitizes cells to cisplatin (Cis). Pifithrin-α (PFT), a transcriptional inhibitor of p53, sensitizes p53 wild-type ovarian cancer cells to antimicrotubule agent-induced apoptosis. No studies have evaluated the interaction of PFT with platinum drugs or PARP inhibitors. We evaluated the potential synergistic interactions between PFT and ABT/Cis in p53 intact ovarian cancer cells.

Methods. We conducted clonogenic assays using BG-1, a human ovarian adenocarcinoma cell line with WT p53 activity. Cells were seeded in 6-well plates and, after 24 hours, treated with combinations of 5μM PFT and multiple doses of ABT and Cis. After 8 days, colony counts were obtained with automated GelDoc software. To identify synergistic interactions, Combination Indices (CI) were calculated with Calcusyn software.

Results. At the lowest dose of Cis (0.625μM), relative cell survival is 60.4% with Cis-PFT, 64.9% with Cis-ABT, and 24.5% with Cis-ABT-PFT. At the highest dose (10μM), relative cell survival is 34.3% with Cis-PFT, 5.25% with Cis-ABT, and 0.85% with Cis-ABT-PFT. At low concentrations of Cis, Cis-PFT showed mild to moderate antagonism. At Cis concentrations &gt;2.5μM, moderate synergism developed. At all concentrations, PFT-ABT showed moderate to strong antagonism. Cis-ABT-PFT showed moderate to strong synergism at all concentrations.

Conclusions. PFT sensitizes BG-1 cells to Cis in a dose dependent pattern, improving synergism at increasing doses of both Cis and PFT. In contrast, PFT shows marked antagonism to the cytotoxic effects of ABT, independent of ABT dose. The combination of ABT+PFT shows strong, dose-independent synergism in the sensitization of BG-1 cells to Cis and significantly reduces relative survival, suggesting the potential for improved tumor control at reduced doses of cisplatin in p53 WT ovarian cancer.

Pifithrin-α and veliparib synergize in the sensitization of BG-1 cells to cisplatin therapy Cis (μM) ABT (μM) PFT (μM) CI Synergy Cisplatin + Pifithrin-α 0.625 − 5 1.729 −−− 1.25 − 5 1.342 −− 2.5 − 5 0.865 + 5 − 5 0.469 +++ 10 − 5 0.390 +++ Veliparib + Pifithrin-α − 0.625 5 1.803 −−− − 1.25 5 3.325 −−−− − 2.5 5 1.647 −−− − 5 5 2.657 −−− − 10 5 1.503 −−− Cisplatin + Veliparib 0.625 1.25 − 0.566 +++ 1.25 2.5 − 0.794 ++ 2.5 5 − 0.863 + 5 10 − 0.656 +++ 10 20 − 0.823 ++ Cisplatin + Veliparib + Pifithrin-α 0.625 1.25 5 0.293 ++++ 1.25 2.5 5 0.418 +++ 2.5 5 5 0.392 +++ 5 10 5 0.291 ++++ 10 20 5 0.262 ++++ Synergism: CI&lt;1, “+” Antagonism: CI&gt;1, “−”

Citation Format: Margaret Whicker, Brian Liang, Z. Ping Lin, Alan Sartorelli, Elena Ratner. Pifithrin-α and veliparib synergize in the sensitization of p53 wild-type ovarian cells to cisplatin therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3277. doi:10.1158/1538-7445.AM2013-3277

Bisoprolol improved endothelial function and myocardium survival of hypertension with stable angina: a randomized double-blinded trial

AIM

This study was designed to determine the effect of bisoprolol on endothelial function of brachial artery and the myocardium survival in hypertensive patients with stable angina.

PATIENTS AND METHODS

222 subjects with hypertension who had received coronary angiography examination were involved in the study, 162 in bisoprolol therapy group (96 men, 59%) and 60 in non-bisoprolol group (39 men, 65%). In accordance with results of angiography (coronary stenosis ≥ 50%), the patients in bisoprolol group were divided into three sub-groups: (1) single-vessel coronary disease group (n=42); (2) double-vessel coronary disease group (n=44); (3) multi-vessel coronary disease group (n=39) and hypertension-only group (n=37). All the subjects were treated with conventional drugs plus bisoprolol and followed up for 12 months. Parameters of clinical features, echocardiography, radionuclide ventriculographic and laboratory findings were measured and analyzed.

RESULTS

After 12 months bisoprolol treatment, the flow-mediated vasodilatation (FMD) and 99Tcm-sestamibi (99Tcm-MIBI) uptake fraction which reflects the survival of myocardium were improved markedly in bisoprolol group (all p < 0.05). Interestingly, a more significant improvement in FMD and 99Tcm-MIBI uptake fraction were observed in severe coronary disease sub-groups (double-vessel group and multi-vessel group) when compared with single-vessel sub-group (p < 0.05).

CONCLUSIONS

Hypertensive subjects with stable angina might get benefit from the treatment of bisoprolol in improving endothelial function and the survival of myocardium.

Abstract 2743: Triapine sensitizes ovarian cancer cells to platinum drugs and PARP inhibitors

Triapine (3-aminopyridine-2-carboxaldehyde thiosemicarbazone) is a ribonucleotide reductase (RNR) inhibitor that is 1000-times more potent than clinically-used hydroxyurea. Consisting primarily of R2 and R1 subunits during the S phase of the cell cycle, RNR catalyzes the rate-limiting step in the production of deoxyribonucleotides (dNTPs) required for DNA synthesis. Triapine chelates iron to form the triapine-Fe complex that quenches the tyrosyl radical at the R2 subunit and leads to enzymatic inactivation. In recent phase I and II trials, treatment of locally advanced cervical cancer with triapine in combination with cisplatin and radiation was well tolerated and produced high durable complete clinical responses in patients. This promising combination therapy may be attributable to the inhibitory effects of triapine on the repair of cisplatin- and radiation-induced DNA damage. However, the exact DNA repair mechanisms modulated by triapine remain poorly understood. In this study, we demonstrate that treatment of ovarian cancer cells with triapine prompts rapid and prolonged depletion of dATP/dNTP pools, which in turn leads to formation of DNA double strand breaks (DSBs) and inhibition of DNA synthesis in S and G2/M phases of the cell cycle. Furthermore, we show that treatment with triapine results in enhanced sensitization of BRCA-proficient (wild-type) ovarian cancer cells to platinum drugs (cisplatin and carboplatin) and the PARP inhibitor olaparib. Both platinum drugs and PARP inhibitors indirectly cause DSBs which require BRCA1- and BRCA2-dependent homologous recombination (HR) to repair. Collectively, these results suggest that triapine acts to abrogate replicative DNA synthesis and post-replication repair, thereby deterring HR repair of DSBs caused by platinum drugs and other DNA damaging modalities. While 70% of ovarian cancer patients initially respond to platinum-based chemotherapy, the majority of these patients will develop recurrent cancer resistant to the platinum drugs. Emergence of platinum-resistant cancer populations may be associated with increasing proficiency of cancer cells to employ HR to repair DNA damage. Given that, our findings provide the rationale for the use of triapine to enhance the efficacy of platinum-based chemotherapy and PARP inhibitors, and potentially eradicate platinum-resistant ovarian cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2743. doi:1538-7445.AM2012-2743

Reduced level of ribonucleotide reductase R2 subunits increases dependence on homologous recombination repair of cisplatin-induced DNA damage

Ribonucleotide reductase (RNR) catalyzes the rate-limiting step in the production of deoxyribonucleoside triphosphates (dNTPs) required for replicative and repair DNA synthesis. Mammalian RNR is a heteromeric enzyme consisting primarily of R1 and R2 subunits during the S phase of the cell cycle. We have shown previously that the presence of excess R2 subunits protects p53-deficient human colon cancer cells from cisplatin-induced DNA damage and replication stress. However, the mode of DNA repair influenced by changes in the level of the R2 subunit remained to be defined. In the present study, we demonstrated that depletion of BRCA1, an important factor of homologous recombination repair (HRR), preferentially sensitized stable R2-knockdown p53(-/-) HCT116 cells to the cytotoxicity of cisplatin and γ-H2AX induction. In accord with this finding, these R2-knockdown cells exhibited increased dependence on HRR, as evidenced by elevated levels of cisplatin-induced Rad51 foci and sister chromatid exchange frequency. Furthermore, stable knockdown of the R2 subunit also led to decreased cisplatin-induced gap-filling synthesis in nucleotide excision repair (NER) and a reduced dATP level in the G(2)/M phase of the cell cycle. These results suggest that an increased level of the R2 subunit extends the availability of dATP in the G(2)/M phase to promote the repair of NER-mediated single-strand gaps that are otherwise converted into double-strand breaks in the subsequent S phase. We propose that HRR becomes important for recovery from cisplatin-DNA lesions when the postexcision process of NER is restrained by reduced levels of the R2 subunit and dATP in p53-deficient cancer cells.

Disruption of cAMP and prostaglandin E2 transport by multidrug resistance protein 4 deficiency alters cAMP-mediated signaling and nociceptive response

Multidrug resistance protein 4 (MRP4; ABCC4) is a member of the MRP/ATP-binding cassette family serving as a transmembrane transporter involved in energy-dependent efflux of anticancer/antiviral nucleotide agents and of physiological substrates, including cyclic nucleotides and prostaglandins (PGs). Phenotypic consequences of mrp4 deficiency were investigated using mrp4-knockout mice and derived immortalized mouse embryonic fibroblast (MEF) cells. Mrp4 deficiency caused decreased extracellular and increased intracellular levels of cAMP in MEF cells under normal and forskolin-stimulated conditions. Mrp4 deficiency and RNA interference-mediated mrp4 knockdown led to a pronounced reduction in extracellular PGE(2) but with no accumulation of intracellular PGE(2) in MEF cells. This result was consistent with attenuated cAMP-dependent protein kinase activity and reduced cyclooxygenase-2 (Cox-2) expression in mrp4-deficient MEF cells, suggesting that PG synthesis is restrained along with a lack of PG transport caused by mrp4 deficiency. Mice lacking mrp4 exhibited no outward phenotypes but had a decrease in plasma PGE metabolites and an increase in inflammatory pain threshold compared with wild-type mice. Collectively, these findings imply that mrp4 mediates the efflux of PGE(2) and concomitantly modulates cAMP mediated signaling for balanced PG synthesis in MEF cells. Abrogation of mrp4 affects the regulation of peripheral PG levels and consequently alters inflammatory nociceptive responses in vivo.

Ataxia-telangiectasia mutated kinase regulates ribonucleotide reductase and mitochondrial homeostasis

Ataxia-telangiectasia mutated (ATM) kinase orchestrates nuclear DNA damage responses but is proposed to be involved in other important and clinically relevant functions. Here, we provide evidence for what we believe are 2 novel and intertwined roles for ATM: the regulation of ribonucleotide reductase (RR), the rate-limiting enzyme in the de novo synthesis of deoxyribonucleoside triphosphates, and control of mitochondrial homeostasis. Ataxia-telangiectasia (A-T) patient fibroblasts, wild-type fibroblasts treated with the ATM inhibitor KU-55933, and cells in which RR is inhibited pharmacologically or by RNA interference (RNAi) each lead to mitochondrial DNA (mtDNA) depletion under normal growth conditions. Disruption of ATM signaling in primary A-T fibroblasts also leads to global dysregulation of the R1, R2, and p53R2 subunits of RR, abrogation of RR-dependent upregulation of mtDNA in response to ionizing radiation, high mitochondrial transcription factor A (mtTFA)/mtDNA ratios, and increased resistance to inhibitors of mitochondrial respiration and translation. Finally, there are reduced expression of the R1 subunit of RR and tissue-specific alterations of mtDNA copy number in ATM null mouse tissues, the latter being recapitulated in tissues from human A-T patients. Based on these results, we propose that disruption of RR and mitochondrial homeostasis contributes to the complex pathology of A-T and that RR genes are candidate disease loci in mtDNA-depletion syndromes.

Excess ribonucleotide reductase R2 subunits coordinate the S phase checkpoint to facilitate DNA damage repair and recovery from replication stress

Ribonucleotide reductase (RNR), which consists of R1 and R2 subunits, catalyzes a key step of deoxyribonucleoside triphosphate (dNTP) synthesis for DNA replication and repair. The R2 subunit is controlled in a cell cycle-specific manner for timely DNA synthesis and is negatively regulated by p53 in response to DNA damage. Herein we demonstrate that the presence of excess R2 subunits in p53(-/-) HCT-116 human colon cancer cells protects against DNA damage and replication stress. siRNA-mediated stable knockdown (>80%) of excess R2 subunits has no effect on proliferative growth but results in enhanced accumulation of gamma-H2Ax and delayed recovery from DNA lesions inflicted by exposure to cisplatin and Triapine. This accentuated induction of gamma-H2Ax in R2-knockdown cells is attributed to reduced ability to repair damaged DNA and overcome replication blockage. The lack of excess R2 subunits consequently augments chk1 activation and cdc25A degradation, causing impeded cell progression through the S phase and enhanced apoptosis in response to DNA damage and replication stress. In contrast, the level of R1 subunits appears to be limiting, since depletion of the R1 subunit directly activates the S phase checkpoint due to replication stress associated with impaired RNR activity. These findings suggest that excess R2 subunits facilitate DNA damage repair and recovery from replication stress through coordination with the S phase checkpoint in the absence of functional p53. Thus, the level of the R2 subunit constitutes an important determinant of the chemosensitivity of cancer cells and serves as a potential target for enhancement of DNA-damage based therapy.

Age-related differences in vincristine toxicity and biodistribution in wild-type and transporter-deficient mice

The impact of mouse multidrug resistance genes mdrla/b and mrpl on age-related differences in the toxicity and biodistribution of vincristine (VCR) was evaluated in wild-type, mrpl(-/-), mdrla/b(-/-), and combined mdrla/b(-/-), mrpl(-/-) weanling and adult mice given a single IP dose of VCR ranging from 0.0625 to 6 mg/kg. Weanling mice of all four genotypes were more sensitive than adult animals as determined by survival rate, average time of death, and pathologic findings. Wild-type animals were the least sensitive and combined mdrla/b(-/-), mrpl(-/-) mice the most sensitive to VCR toxicity. Mdrla/b(-/-) and mrpl(-/-) genotypes exhibited intermediate sensitivities, with mdrla/b(-/-) mice being more sensitive than mrpl(-/-) animals to the vinca alkaloid. Administration of [3H]VCR to wild-type and mdrla/b(-/-), mrpl(-/-) animals revealed relatively greater accumulation of radioactive VCR equivalents in weanlings over adults in several tissues, with weanling mdrla/b(-/-), mrpl(-/-) lung and heart exhibiting the greatest enhanced accumulation of 26- and 15-fold over adults, respectively. A similar cardiopulmonary differential accumulation of VCR was not observed in wild-type weanlings to adults. Semiquantitative RT-PCR expression analyses of ABC transporter genes in weanling and adult tissues of wild-type and combined mdrla/b(-/-), mrpl(-/-) mice did not reveal major age-related differences in these ABC transporters that would explain the relatively greater toxicity observed in weanling mice. However, the greater cardiopulmonary accumulation of VCR equivalents seen in the combined mdrla/b(-/-), mrpl(-/-) weanlings over that of adults underscores the potential for unique organ and age-related toxicities of this agent in the setting of transporter deficiency.

Resistance to purine and pyrimidine nucleoside and nucleobase analogs by the human MDR1 transfected murine leukemia cell line L1210/VMDRC.06

Overexpression of human MDR1 P-glycoprotein [Pgp] is associated with cellular resistance to bulky amphipathic drugs, such as taxol, anthracyclines, vinca alkaloids, and epipodophyllotoxins by actively effluxing drugs from cells. We have found that human MDR1 transfected murine L1210/VMDRC.06 leukemia cells exhibit relatively large amounts of Pgp and high levels of resistance to 6-mercaptopurine [6-MP] and other purine and pyrimidine nucleobase and nucleoside analogs. L1210/VMDRC.06 cells accumulated 6-MP as the nucleotide in vitro at only about one-third of that formed by parental L1210 cells in normal medium; however, under conditions of ATP-depletion, the amount of 6-MP nucleotide formed was essentially the same in both cell lines. The findings support active efflux of 6-MP in L1210 cells, suggesting involvement of Pgp in 6-MP resistance even though it is generally believed that Pgp does not transport such agents. The resistance pattern observed in L1210/VMDRC.06 cells was not duplicated in P388/VMDRC.04 leukemia cells transfected with the same MDR1 cDNA, even though a similar amount of Pgp was present in both cell lines. Immunofluorescent staining of surface membrane Pgp showed that L1210/VMDRC.06 cells contained at least three-fold more surface Pgp than P388/VMDRC.04, implying that P388/VMDRC.04 cells are unable to actively efflux 6-MP and other antimetabolites as effectively as L1210/VMDRC.06, because of significantly lower membrane Pgp. The findings suggest that the exceedingly large concentration of overexpressed Pgp in the surface membrane of L1210/MDRC.06 cells is responsible for resistance to 6-MP and other purine and pyrimidine analogs, even though these agents usually are not considered to be substrates for Pgp.

Stable suppression of the R2 subunit of ribonucleotide reductase by R2-targeted short interference RNA sensitizes p53(-/-) HCT-116 colon cancer cells to DNA-damaging agents and ribonucleotide reductase inhibitors

Ribonucleotide reductase catalyzes the production of deoxyribonucleoside diphosphates, the precursors of deoxyribonucleoside triphosphates for DNA synthesis. Mammalian ribonucleotide reductase (RNR) is a tetramer consisting of two non-identical homodimers, R1 and either R2 or p53R2, which are considered to be involved in DNA replication and repair, respectively. We have demonstrated that DNA damage by doxorubicin and cisplatin caused a steady elevation of the R2 protein in p53(-/-) HCT-116 human colon carcinoma cells but induced degradation of the protein in p53(+/+) cells. To evaluate the involvement of R2 in response to DNA damage, p53(-/-) HCT-116 cells were stably transfected with an expression vector transcribing short hairpin/short interference RNA directed against R2 mRNA. Stably transfected clones exhibited a pronounced reduction of the R2 protein with no change in the cellular growth rate. Furthermore, short interference RNA-mediated reduction of the R2 protein caused a marked increase in sensitivity to the DNA-damaging agent cisplatin as well as to the RNR inhibitors Triapine and hydroxyurea. Ectopic expression of p53R2 partially reversed the cytotoxicity of cisplatin but not that of RNR inhibitors to R2 knockdown cells. The increase in sensitivity to cisplatin and RNR inhibitors was correlated with the suppression of dATP and dGTP levels caused by stable expression of R2-targeted short interference RNA. These results indicated that DNA damage resulted in elevated levels of the R2 protein and dNTPs and, consequently, enhanced the survival of p53(-/-) HCT-116 cells. The findings provide evidence that R2-RNR can be employed to supply dNTPs for the repair of DNA damage in cells with an impaired p53-dependent induction of p53R2.

Comparative study of the importance of multidrug resistance-associated protein 1 and P-glycoprotein to drug sensitivity in immortalized mouse embryonic fibroblasts

Multidrug resistance-associated protein 1 and P-glycoprotein are major ATP-binding cassette transporters that function as efflux pumps and confer resistance to a variety of structurally unrelated anticancer agents. To evaluate the comparative importance of these transporters with respect to anticancer agents, we established and characterized SV40-immortalized [mrp1(-/-)] (KO), [mdr1a/1b(-/-)] (DKO), and combined [mrp1 (-/-), mdr1a/1b(-/-)] (TKO) deficient fibroblast lines derived from primary embryonic fibroblasts of knockout mice. Western blot analyses demonstrated that KO and DKO fibroblasts exhibited similar levels of P-glycoprotein and mrp1, respectively, to that of wild-type (WT) fibroblasts. In addition, semiquantitative reverse transcription-PCR measurements of other multidrug resistance-associated protein (mrp) family members demonstrated that TKO fibroblasts displayed expression profiles of mrps 2-7 comparable to that of WT fibroblasts. These results indicate that loss of mrp1, P-glycoprotein, or both transporters does not cause overt compensatory changes in the expression of the other determined transporters. Using cell viability and calcein accumulation assays, we demonstrated that KO and DKO fibroblasts exhibited a low to moderate increase in sensitivity to vincristine and etoposide and in calcein accumulation compared to WT fibroblasts, whereas TKO fibroblasts displayed a markedly enhanced sensitivity to these agents and further elevated calcein accumulation. Furthermore, verapamil, an inhibitor of both mrp1 and P-glycoprotein, significantly sensitized WT fibroblasts to both vincristine and etoposide while having no effect on the sensitivity of TKO cells to these agents. Collectively, these findings indicate that mrp1 and P-glycoprotein are major determinants of drug sensitivity in immortalized mouse embryonic fibroblasts. They also suggest the existence of a compensatory mechanism by which the loss of one transporter can be functionally offset by the other in the transport of common drug substrates.

Prostaglandin A1 inhibits stress-induced NF-kappaB activation and reverses resistance to topoisomerase II inhibitors

Stress conditions associated with solid tumors lead to the formation of heterogeneous tumor cell subpopulations and insensitivity to cancer chemotherapeutics. In this report, we show that EMT6 mouse mammary tumor cells treated with the chemical stress, brefeldin A (BFA), or the physiological stress, hypoxia, develop resistance to the topoisomerase II (topoII) inhibitors teniposide and etoposide. BFA and hypoxia treatment did not alter intracellular drug concentrations, topoll protein levels, or inhibit topoII activity. BFA and hypoxia did cause the activation of the nuclear transcription factor NF-kappaB. We demonstrate that pretreatment with the synthetic cyclopentenone prostaglandin A1 (PGA1) inhibits stress-induced NF-kappaB activation and reverses BFA- and hypoxia-induced resistance. The reversal of BFA-induced resistance can occur when PGA1 is administered either before or several hours after the induction of stress. Taken together, these data support the involvement of NF-kappaB in stress-induced drug resistance, show that pharmacologic inhibitors of NF-kappaB can disrupt the biological consequences of stress, and imply that inhibitors of NF-kappaB may be useful agents to enhance the clinical efficacy of topoII-directed chemotherapeutics.

Reversal of physiological stress-induced resistance to topoisomerase II inhibitors using an inducible phosphorylation site-deficient mutant of I kappa B alpha

Physiological stress conditions associated with the tumor microenvironment play a role in resistance to anticancer therapy. In this study, treatment of EMT6 mouse mammary tumor cells with hypoxia or the chemical stress agents brefeldin A (BFA) or okadaic acid (OA) causes the development of resistance to the topoisomerase II inhibitor etoposide. The mechanism of physiological stress-induced drug resistance may involve the activation of stress-responsive proteins and transcription factors. Our previous work shows that treatment with BFA or OA causes activation of the nuclear transcription factor NF-kappa B. Pretreatment with the proteasome inhibitor carbobenzyoxyl-leucinyl-leucinyl-leucinal inhibits stress-induced NF-kappa B activation and reverses BFA-induced drug resistance. To test whether NF-kappa B specifically mediates stress-induced drug resistance, an inducible phosphorylation site-deficient mutant of I kappa B alpha (I kappa B alpha M, S32/36A) was introduced into EMT6 cells. In this study, we show that I kappa B alpha M expression inhibits stress-induced NF-kappa B activation and prevents BFA-, hypoxia-, and OA-induced resistance to etoposide. These results indicate that NF-kappa B activation mediates both chemical and physiological drug resistance to etoposide. Furthermore, they imply that coadministration of agents that inhibit NF-kappa B may enhance the efficacy of topoisomerase II inhibitors in clinical cancer chemotherapy.

The pharmacological phenotype of combined multidrug-resistance mdr1a/1b- and mrp1-deficient mice

Two major classes of plasma membrane proteins that actively extrude a wide range of structurally diverse hydrophobic amphipathic antineoplastic agents from cells, with different mechanisms of action, lead to multidrug resistance. To study the importance of these ATP-binding cassette transporters to the toxicity of cancer chemotherapy agents, we have used mice genetically deficient in both the mdr1a and mdr1b genes [mdr1a/1b(-/-) mice], the mrp1 gene [mrp1(-/-) mice], and the combined genes mdr1a/1b and mrp1 [mdr1a/1b(-/-), mrp1(-/-) mice] and embryonic fibroblasts derived from wild-type mice and from the three gene knockout animals. The consequences of export pump deficiencies were evaluated primarily using vincristine and etoposide. Mice deficient in the three genes, mdr1a/1b and mrp1, exhibited a 128-fold increase in toxicity to vincristine and a 3-5-fold increase in toxicity to etoposide; increased toxicity to embryonic fibroblast cells from triple knockout mice also occurred with vincristine and etoposide. Vincristine, which normally does not express toxicity to the bone marrow and to the gastrointestinal mucosa when used at therapeutic doses, caused extensive damage to these tissues in mdr1a/1b(-/-), mrp1(-/-) mice. The findings indicate that the P-glycoprotein and mrpl are compensatory transporters for vincristine and etoposide in the bone marrow and the gastrointestinal mucosa and emphasize the potential for increased toxicities by the combined inhibition of these efflux pumps.

Quenching and enhancement of aroyl luminescence in excited nitrogen

This study investigates both decreases and increases of aromatic carbonyl phosphorescence in excited nitrogen, i.e., in a gas-chromatographic device called the aroyl luminescence detector (ALD). The ALD responds, with nigh specificity, to subpicogram amounts of strongly phosphorescing aroyls. Aroyl response may, however, be quenched by coeluting peaks or gaseous impurities. This deleterious effect has been investigated with O2, H2, CH4, and C3H8 as model quenchers. Aroyl phosphorescence is more severely quenched than the nitrogen background, i.e., the so-called second-positive system, N2 (C 3 pi u)-->N2 (B 3 pi g). Oxygen, while being the strongest among the tested quenchers of aroyl phosphorescence, is the weakest quencher of nitrogen emission. The efficiency of various quenchers is similar for aroyl compounds of similar structure. It differs, however--though not by more than a factor of 2--among aroyls of different chemical types. In contrast to these intensity-reducing effects, aroyl phosphorescence is significantly enhanced by the addition of argon to (the carrier and excitation gas) nitrogen. It is proposed that the reaction sequence Ar*(3P0,2) + N2-->N2(C)*-->N2(B)* + hv-->N2(A)* + hv results in an increased yield of the metastable N2(A 3 sigma u+) state (this state being considered responsible for the n-->pi* excitation of aroyl compounds via an efficient triplet-triplet energy-transfer process).

Triplet-state energies and substituent effects of excited aroyl compounds in the gas phase

Triplet-state energy values obtained from the gas phase are still scarce. In this study, the triplet-state energies of 58 aroyl compounds, introduced as gas chromatographic peaks at atmospheric pressure and typically 473 K, have been determined from the 0-0 bands of their n --> pi* type phosphorescence spectra in excited nitrogen. Correlations of those gas-phase triplet-state energies with Hammett constants could be observed for substituted acetophenones, benzaldehydes and benzophenones.

Gas chromatographic determination of primary alcohols as their formylbenzoic esters by gas-phase luminescence detection

A new and convenient method is described for the derivatization of primary alcohols with p-formylbenzoyl chloride, and the sensitive photometric detection of the resulting formylbenzoic ester derivatives based on their gas-phase luminescence in excited nitrogen. The coupling reaction proceeds rapidly and quantitatively, and the formylbenzoic esters show good GC properties. The minimum detectable amounts of the derivatized alcohols, at a signal three-times the peak-to-peak noise, lie between 10 and 100 pg per injection, and their linear ranges cover approximately three-orders of magnitude.

Prevention of brefeldin A-induced resistance to teniposide by the proteasome inhibitor MG-132: involvement of NF-kappaB activation in drug resistance

Brefeldin A, an agent that disrupts protein transport from the endoplasmic reticulum to the Golgi, induces the expression of GRP78 and the activation of nuclear factor (NF)-kappaB in cells. Treatment of cells with brefeldin A causes the development of resistance to topoisomerase II-directed agents, such as etoposide and doxorubicin. In this study, we show that treatment of EMT6 mouse mammary tumor cells with brefeldin A strongly induces GRP78 mRNA (8.5-fold) and resistance to teniposide (VM26). Treatment with okadaic acid causes a minor increase in GRP78 mRNA (2.1-fold) yet still induces resistance to VM26 as effectively as brefeldin A. In contrast, cells treated with castanospermine show a moderate increase in GRP78 mRNA (3.9-fold) but no resistance to VM26. These data imply that GRP78 induction does not mediate the development of drug resistance. An alternative mechanism of drug resistance may involve activation of the transcription factor, NF-kappaB, and we show that both brefeldin A and okadaic acid activate NF-kappaB in EMT6 cells. Furthermore, we demonstrate that treatment with the proteasome inhibitor MG-132 blocks the activation of NF-kappaB and prevents the development of resistance to VM26 induced by brefeldin A. Collectively, these results suggest that the resistance to VM26 in EMT6 cells treated with brefeldin A is mediated by the activation of NF-kappaB rather than the induction of GRP78. Our results also suggest that inhibition of NF-kappaB activation in tumor cells may increase the efficacy of topoisomerase II-directed agents in chemotherapy.

Hormonal regulation of glutamine metabolism by OK cells

The precise mechanism(s) of action of PTH, insulin or glucagon in the regulation of renal glutamine and ammonia metabolism is unknown. Our aim was to delineate the effects and the site(s) of action of these hormones on renal glutamine metabolism. Experiments were carried out using OK cells as a model system. Cell cultures were incubated for three hours in a bicarbonate buffer of pH 7.4 supplemented with either 1 mM [2-15N] or [5-15N] glutamine and 10(-7) M PTH, insulin or glucagon. Comparative studies were performed at pH 6.8, 7.4 or 7.6 without hormone. PTH and acute acidosis significantly stimulated glutamine metabolism via both the phosphate-dependent glutaminase (PDG) and glutamate dehydrogenase (GLDH) pathways. The opposite was observed at pH 7.6. Insulin augmented flux via PDG with little effect on the GLDH pathway. Glucagon had insignificant effects on either PDG or GLDH pathways. Intracellular [15N] glutamate formed from [2-15N] glutamine was removed partially by transamination to alanine, aspartate and serine and partially by translocation to an extracellular compartment. Acidosis, PTH and insulin enhanced the formation of [15N] alanine with little effect on [15N] aspartate. PTH, insulin and glucagon significantly stimulated the production of [15N]serine, whereas acidosis had little effect. The translocation of intracellular glutamate was significantly increased by acidosis, PTH and insulin and decreased by acute alkalosis. The data indicate that: (a) PTH mimicks the effect of acute acidosis on renal glutamine metabolism, that is, augmented glutamine metabolism through both PDG and GLDH pathways and stimulated the output of intracellular glutamate. This effect might be mediated via decreased activity of the Na(+)-H+ exchanger associated with cellular acidification and/or through a second messenger; (b) insulin, but not glucagon, increased glutamine uptake and metabolism, and simultaneously enhanced output of intracellular glutamate sufficiently to stimulate the PDG pathway; and (c) overall, glucagon had little effect on glutamine metabolism by OK cells compared with either PTH or insulin.

Interrelationships of leucine and glutamate metabolism in cultured astrocytes

The aim was to study the extent to which leucine furnishes alpha-NH2 groups for glutamate synthesis via branched-chain amino acid aminotransferase. The transfer of N from leucine to glutamate was determined by incubating astrocytes in a medium containing [15N]leucine and 15 unlabeled amino acids; isotopic abundance was measured with gas chromatography-mass spectrometry. The ratio of labeling in both [15N]glutamate/[15N]leucine and [2-15N]glutamine/[15N]leucine suggested that at least one-fifth of all glutamate N had been derived from leucine nitrogen. At the same time, enrichment in [15N]leucine declined, reflecting dilution of the 15N label by the unlabeled amino acids that were in the medium. Isotopic abundance in [15N]isoleucine increased very quickly, suggesting the rapidity of transamination between these amino acids. The appearance of 15N in valine was more gradual. Measurement of branched-chain amino acid transaminase showed that the reaction from leucine to glutamate was approximately six times more active than from glutamate to leucine (8.72 vs. 1.46 nmol/min/mg of protein). However, when the medium was supplemented with alpha-ketoisocaproate (1 mM), the ketoacid of leucine, the reaction readily ran in the "reverse" direction and intraastrocytic [glutamate] was reduced by approximately 50% in only 5 min. Extracellular concentrations of alpha-ketoisocaproate as low as 0.05 mM significantly lowered intracellular [glutamate]. The relative efficiency of branched-chain amino acid transamination was studied by incubating astrocytes with 15 unlabeled amino acids (0.1 mM each) and [15N]glutamate. After 45 min, the most highly labeled amino acid was [15N]alanine, which was closely followed by [15N]leucine and [15N]isoleucine. Relatively little 15N was detected in any other amino acids, except for [15N]serine. The transamination of leucine was approximately 17 times greater than the rate of [1-14C]leucine oxidation. These data indicate that leucine is a major source of glutamate nitrogen. Conversely, reamination of alpha-ketoisocaproate, the ketoacid of leucine, affords a mechanism for the temporary "buffering" of intracellular glutamate.

Brain glutamate metabolism: neuronal-astroglial relationships

The concentration of glutamate in the brain extracellular fluid must be kept low (approximately 3 microM) in order to maximize the signal-to-noise ratio upon the release of glutamate from neurons. In addition, the nerve endings require a supply of glutamate precursors that will not cause depolarization. The major precursor to neuronal glutamate is glutamine, which is synthesized in astrocytes and converted to glutamate in neurons. However, glutamine is not the sole source. Alanine also might serve as a precursor to glutamate via transamination, although this reaction is relatively inactive in synaptosomes. Finally, the branched-chain amino acids, and in particular leucine, appear to be very important precursors to glutamate and glutamine in astrocytes. By providing alpha-NH2 groups for the synthesis of glutamine, leucine also abets the uptake into brain of neutral amino acids, which are transported in exchange for brain glutamine. In addition, the branched-chain ketoacids are readily reaminated to the cognate amino acids, in the process consuming glutamate. Intraneuronal consumption of glutamate via ketoacid reamination might serve to buffer internal [glutamate] and to modulate the releasable pool.

Glutamate dehydrogenase reaction as a source of glutamic acid in synaptosomes

The role of the glutamate dehydrogenase reaction as a pathway of glutamate synthesis was studied by incubating synaptosomes with 5 mM 15NH4Cl and then utilizing gas chromatography-mass spectrometry to measure isotopic enrichment in glutamate and aspartate. The rate of formation of [15N]glutamate and [15N]aspartate from 5 mM 15NH4Cl was approximately 0.2 nmol/min/mg of protein, a value much less than flux through glutaminase (4.8 nmol/min/mg of protein) but greater than flux through glutamine synthetase (0.045 nmol/min/mg of protein). Addition of 1 mM 2-oxoglutarate to the medium did not affect the rate of [15N]glutamate formation. O2 consumption and lactate formation were increased in the presence of 5 mM NH3, whereas the intrasynaptosomal concentrations of glutamate and aspartate were unaffected. Treatment of synaptosomes with veratridine stimulated reductive amination of 2-oxoglutarate during the early time points. The production of ([15N]glutamate + [15N]aspartate) was enhanced about twofold in the presence of 5 mM beta-(+/-)-2-aminobicyclo [2.2.1]heptane-2-carboxylic acid, a known effector of glutamate dehydrogenase. Supplementation of the incubation medium with a mixture of unlabelled amino acids at concentrations similar to those present in the extracellular fluid of the brain had little effect on the intrasynaptosomal [glutamate] and [aspartate]. However, the enrichment in these amino acids was consistently greater in the presence of supplementary amino acids, which appeared to stimulate modestly the reductive amination of 2-oxoglutarate. It is concluded: (a) compared with the phosphate-dependent glutaminase reaction, reductive amination is a relatively minor pathway of synaptosomal glutamate synthesis in both the basal state and during depolarization; (b) NH3 toxicity, at least in synaptosomes, is not referable to energy failure caused by a depletion of 2-oxoglutarate in the glutamate dehydrogenase reaction; and (c) transamination is not a major mechanism of glutamate nitrogen production in nerve endings.

Glutathione turnover in cultured astrocytes: studies with [15N]glutamate

The incorporation of [15N]glutamic acid into glutathione was studied in primary cultures of astrocytes. Turnover of the intracellular glutathione pool was rapid, attaining a steady state value of 30.0 atom% excess in 180 min. The intracellular glutathione concentration was high (20-40 nmol/mg protein) and the tripeptide was released rapidly into the incubation medium. Although labeling of glutathione (atom% excess) with [15N]glutamate occurred rapidly, little accumulation of 15N in glutathione was noted during the incubation compared with 15N in aspartate, glutamine, and alanine. Glutathione turnover was stimulated by incubating the astrocytes with diethylmaleate, an electrophile that caused a partial depletion of the glutathione pool(s). Diethylmaleate treatment also was associated with significant reductions of intraastrocytic glutamate, glycine, and cysteine, i.e., the constituents of glutathione. Glutathione synthesis could be stimulated by supplementing the steady-state incubation medium with 0.05 mM L-cysteine, such treatment again partially depleting intraastrocytic glutamate and causing significant reductions of 15N labeling of both alanine and glutamine, suggesting that glutamate had been diverted from the synthesis of these amino acids and toward the formation of glutathione. The current study underscores both the intensity of glutathione turnover in astrocytes and the relationship of this turnover to the metabolism of glutamate and other amino acids.