Comparison of Superior-Level Facet Joint Violations Between Robot-Assisted Percutaneous Pedicle Screw Placement and Conventional Open Fluoroscopic-Guided Pedicle Screw Placement

Objective

To compare the superior‐level facet joint violations (FJV) between robot‐assisted (RA) percutaneous pedicle screw placement and conventional open fluoroscopic‐guided (FG) pedicle screw placement in a prospective cohort study.

Methods

This was a prospective cohort study without randomization. One‐hundred patients scheduled to undergo RA (n = 50) or FG (n = 50) transforaminal lumbar interbody fusion were included from February 2016 to May 2018. The grade of FJV, the distance between pedicle screws and the corresponding proximal facet joint, and intra‐pedicle accuracy of the top screw were evaluated based on postoperative CT scan. Patient demographics, perioperative outcomes, and radiation exposure were recorded and compared. Perioperative outcomes include surgical time, intraoperative blood loss, postoperative length of stay, conversion, and revision surgeries.

Results

Of the 100 screws in the RA group, 4 violated the proximal facet joint, while 26 of 100 in the FG group had FJV (P = 0.000). In the RA group, 3 and 1 screws were classified as grade 1 and 2, respectively. Of the 26 FJV screws in the FG group, 17 screws were scored as grade 1, 6 screws were grade 2, and 3 screws were grade 3. Significantly more severe FJV were noted in the FG group than in the RA group (P = 0.000). There was a statistically significant difference between RA and FG for overall violation grade (0.05 vs 0.38, P = 0.000). The average distance of pedicle screws from facet joints in the RA group (4.16 ± 2.60 mm) was larger than that in the FG group (1.92 ± 1.55 mm; P = 0.000). For intra‐pedicle accuracy, the rate of perfect screw position was greater in the RA group than in the FG group (85% vs 71%; P = 0.017). No statistically significant difference was found between the clinically acceptable screws between groups (P = 0.279). The radiation dose was higher in the FG group (30.3 ± 11.3 vs 65.3 ± 28.3 μSv; P = 0.000). The operative time in the RA group was significantly longer (184.7 ± 54.3 vs 117.8 ± 36.9 min; P = 0.000).

Conclusions

Compared to the open FG technique, minimally invasive RA spine surgery was associated with fewer proximal facet joint violations, larger facet to screw distance, and higher intra‐pedicle accuracy.

Rate and Risk Factors of Superior Facet Joint Violation during Cortical Bone Trajectory Screw Placement: A Comparison of Robot-Assisted Approach with a Conventional Technique

Objective

To compare the incidence and risk factors of superior facet joint violation (FJV) during cortical bone trajectory screw placement in robot‐assisted approach versus conventional technique.

Methods

A retrospective study, including 69 patients having cortical bone trajectory (CBT) screw instrumentation for symptomatic degenerated diseases or trauma, was conducted between June 2015 to January 2019. All patients underwent CBT surgery performed by the same team of experienced surgeons. Patients were randomly divided into two groups: a conventional group (CG, 46 cases) and a robot group (RG, 23 cases). The surgical robotic system was used for screw instrumentation in the robot group and the traditional screw instrumentation with fluoroscopic guidance was used in the conventional group. Cortical screws followed a medio‐to‐lateral path in the transverse plane and a caudal‐to‐cephalad path in the sagittal plane. Preoperative and postoperative computed tomography (CT) scans were obtained to determine the degree and incidence of FJV. The violation status of facet joint was evaluated according to the modified classification: grade 0, no violation; grade 1, screw shaft, screw head or rod within 1 mm of or abutting the facet joint, but did not enter the articular facet joint; grade 2, screw shaft, screw head or rod clearly in the facet joint. The following factors that may contribute to the occurrence of FJV were analyzed: age, sex, body mass index (BMI), proximal fusion level, fusion length, the side of screw, preoperative vertebral slip, superior facet angle, and degenerative scoliosis. The chi‐squared test and Student's t‐test were used for analysis of the variables for significance (P < 0.05).

Results

FJV occurred in 41.3% of patients in CG and 17.3% of patients in RG. A chi‐squared analysis revealed a significantly lower rate of FJV for RG compared with CG (P = 0.04). In the CG, 17 of the 109 cephalad screws were grade 1 (15.6%), and five were grade 2 (4.6%). In the RG, three of the 46 cephalad screws were grade 1 (6.5%), and three were grade 2 (6.5%). There was a statistically significant difference in the incidence of FJV between the left and right screw with fluoroscopy‐assisted CBT screw instrumentation (P < 0.05). A significant correlation between scoliosis with the FJV was found in CG (P < 0.05) and in RG (P < 0.05). With regard to superior facet angle, a measurement ≥45° was a significant risk factor of FJV in CG (P < 0.05) and in RG (P < 0.05).

Conclusions

A robot‐assisted approach could reduce the incidence of FJV compared with the conventional approach in CBT technique.

6-Phosphofructo-2-Kinase/Fructose-2,6-Biphosphatase-2 Regulates TP53-Dependent Paclitaxel Sensitivity in Ovarian and Breast Cancers

PURPOSE

Paclitaxel is an integral component of primary therapy for breast and epithelial ovarian cancers, but less than half of these cancers respond to the drug. Enhancing the response to primary therapy with paclitaxel could improve outcomes for women with both diseases.Experimental Design: Twelve kinases that regulate metabolism were depleted in multiple ovarian and breast cancer cell lines to determine whether they regulate sensitivity to paclitaxel in Sulforhodamine B assays. The effects of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 2 (PFKFB2) depletion on cell metabolomics, extracellular acidification rate, nicotinamide adenine dinucleotide phosphate, reactive oxygen species (ROS), and apoptosis were studied in multiple ovarian and breast cancer cell lines. Four breast and ovarian human xenografts and a breast cancer patient-derived xenograft (PDX) were used to examine the knockdown effect of PFKFB2 on tumor cell growth in vivo.

RESULTS

Knockdown of PFKFB2 inhibited clonogenic growth and enhanced paclitaxel sensitivity in ovarian and breast cancer cell lines with wild-type TP53 (wtTP53). Silencing PFKFB2 significantly inhibited tumor growth and enhanced paclitaxel sensitivity in four xenografts derived from two ovarian and two breast cancer cell lines, and prolonged survival in a triple-negative breast cancer PDX. Transfection of siPFKFB2 increased the glycolysis rate, but decreased the flow of intermediates through the pentose-phosphate pathway in cancer cells with wtTP53, decreasing NADPH. ROS accumulated after PFKFB2 knockdown, which stimulated Jun N-terminal kinase and p53 phosphorylation, and induced apoptosis that depended upon upregulation of p21 and Puma.

CONCLUSIONS

PFKFB2 is a novel target whose inhibition can enhance the effect of paclitaxel-based primary chemotherapy upon ovarian and breast cancers retaining wtTP53.

Comparison of the One-Time Accuracy of Simulated Freehand and Navigation Simulated Pedicle Screw Insertion

OBJECTIVE

To compare one-time accuracy rate between simulated freehand (SFH) and navigation simulated (NS) pedicle screw insertion, assuming no second chance to correct screws.

METHODS

A simulated, comparative, cross-sectional study was conducted on 69 patients undergoing lumbar spine surgery. An intraoperative registration system captured the planned point of entry and trajectory of pedicle screws for both SFH under direct visualization and NS under navigation-aided visualization. Pedicle screw insertion was simulated for each captured image (370 screws) using Surgimap. Rajasekaran's method helped evaluate the point of entry accuracy and trajectory.

RESULTS

Accuracy rate was better for the NS method (97.8%) than for the SFH method (63.8%). Of 370 screws in the SFH group, 134 penetrated the cortex, with 31 resulting in >4 mm penetration. Of 370 screws in the NS group, 8 penetrated the cortex, <4 mm penetration. Of 134 misplaced screws in the SFH group, 64 were due to error in the point of entry, 63 were due to error in the trajectory angle, and 7 were due to both errors. Of 8 errors in the NS group, 7 were due to the point of entry.

CONCLUSIONS

Intraoperative navigation had significantly better one-time accuracy of pedicle screw insertion than freehand insertion and should be used to avoid injury to the pedicle and surrounding tissue from screw reinsertion.

Computer-assisted, minimally invasive transforaminal lumbar interbody fusion: One surgeon's learning curve A STROBE-compliant article

Minimally invasive (MI) transforaminal lumbar interbody fusion (TLIF) is a challenging technique with a long learning curve. We combined computer-assisted navigation and MI TLIF (CAMISS TLIF) to treat lumbar degenerative disease. This study aimed to evaluate the learning curve associated with computer-assisted navigation MI spine surgery (CAMISS) and TLIF for the surgical treatment of lumbar degenerative disease. Seventy four consecutive patients with lumbar degenerative disease underwent CAMISS TLIF between March 2011 and May 2015; all surgeries were performed by a single surgeon. According to the plateau of the asymptote, the initial 25 patients constituted the early group and the remaining patients comprised the latter group. The clinical evaluation data included operative times, anesthesia times, intraoperative blood losses, days until ambulation, postoperative hospital stays, visual analog scale (VAS) leg and back pain scores, Oswestry disability index (ODI) values, Macnab outcome scale scores, complications, radiological outcomes, and rates of conversion to open surgery. The complexity of the cases increased over the series, but the complication rate decreased (12.00%-6.12%). There were significant differences between the early and late groups with respect to the average surgical times and durations of anesthesia, but no differences in intraoperative blood losses, days until ambulation, postoperative hospital stays, complication rate, VAS, ODI, Macnab outcome scale scores, or solid fusion rates. There was no need for conversion to open procedures in either group. Our study showed that a plateau asymptote for CAMISS TLIF was reached after 25 operations. The later patients experienced shorter operative times and anesthesia durations.

Abstract 3564: Silencing pfkfb2 enhances paclitaxel sensitivity by modulating metabolism of p53 wt ovarian and breast cancer cells and xenografts

Breast cancer is the most common cause and epithelial ovarian cancer the fourth most common cause of cancer death among women in the developed world. While breast cancer can be cured in 70% of cases, only 30% of ovarian cancer patients remain free from disease long term. Paclitaxel is an integral component of primary therapy for both forms of cancer, but less than half of breast and ovarian cancers respond to the drug. Enhancing the response to primary therapy with paclitaxel could improve outcomes for women with both diseases. In recent years several kinases have been identified that regulate the sensitivity of cancer cells to paclitaxel by inhibiting centrosome splitting or enhancing microtubule stability. Much less attention has been given to kinases that affect paclitaxel sensitivity by modulating cancer cell metabolism.

We previously performed siRNA kinome-screens to identify molecular targets whose decreased expression overcomes paclitaxel resistance and increases paclitaxel sensitivity in ovarian cancer cells. We showed that 20% of the potential kinase targets whose knockdown modulates paclitaxel sensitivity participate in glucose and energy metabolism. Among these, a leading candidate was 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 2 (PFKFB2), an isoform of the glycolytic enzyme phosphofructokinase (PFK2). PFKFB2 is overexpressed in a fraction of ovarian and breast cancers.

Knockdown of PFKFB2 inhibited clonogenic growth of ovarian and breast cancer cell lines and enhanced paclitaxel sensitivity in the cell lines with wt TP53. Liposome encapsulated PFKFB2 siRNA significantly inhibited tumor growth and enhanced sensitivity to paclitaxel in xenografts derived from ovarian cancer cell lines. Knockdown of PFKFB2 increased glycolysis, decreasing the flow of glycolytic intermediates to the pentose-phosphate pathway with reduced G6PD activity in wt TP53 cancer cell lines. With decreased NADPH, ROS accumulated after PFKFB2 knockdown, stimulating phosphorylation of JNK, inducing G1 cell cycle arrest, and initiating apoptosis dependent upon upregulation of p21Cip1 and Puma which are downstream targets of TP53. Our studies have shown for the first time that PFKFB2, a glycolytic enzyme, drives tumor cell growth and regulates paclitaxel sensitivity by inducing apoptosis and G1 cell cycle arrest. These findings highlight a remarkable degree of coordination between cancer metabolism with cell proliferation and chemo-sensitivity, which may provide a novel target in patients with ovarian cancers and breast cancers where TP53 function remains intact.

Citation Format: Hailing Yang, Shu Zhang, Weiqun Mao, Ahmed A. Ahmed, Nicholas B. Jennings, Cristian Rodriguez-Aguayo, Gabriel Lopez-Berestein, Anil K. Sood, Xiao-Feng Le, Zhen Lu, Robert C. Bast. Silencing pfkfb2 enhances paclitaxel sensitivity by modulating metabolism of p53 wt ovarian and breast cancer cells and xenografts [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 3564. doi:10.1158/1538-7445.AM2017-3564

Jab1/Csn5-Thioredoxin Signaling in Relapsed Acute Monocytic Leukemia under Oxidative Stress

Purpose: High levels of ROS and ineffective antioxidant systems contribute to oxidative stress, which affects the function of hematopoietic cells in acute myeloid leukemia (AML); however, the mechanisms by which ROS lead to malignant transformation in relapsed AML-M5 are not completely understood. We hypothesized that alterations in intracellular ROS would trigger AML-M5 relapse by activating the intrinsic pathway.Experimental Design: We studied ROS levels and conducted c-Jun activation domain-binding protein-1 (JAB1/COPS5) and thioredoxin (TRX) gene expression analyses with blood samples obtained from 60 matched AML-M5 patients at diagnosis and relapse and conducted mechanism studies of Jab1's regulation of Trx in leukemia cell lines.Results: Our data showed that increased production of ROS and a low capacity of antioxidant enzymes were characteristics of AML-M5, both at diagnosis and at relapse. Consistently, increased gene expression levels of TRX and JAB1/COPS5 were associated with low overall survival rates in patients with AML-M5. In addition, stimulating AML-M5 cells with low concentrations of hydrogen peroxide led to increased Jab1 and Trx expression. Consistently, transfection of ectopic Jab1 into leukemia cells increased Trx expression, whereas silencing of Jab1 in leukemia cells reduced Trx expression. Mechanistically, Jab1 interacted with Trx and stabilized Trx protein. Moreover, Jab1 transcriptionally regulated Trx. Furthermore, depletion of Jab1 inhibited leukemia cell growth both in vitro and in vivoConclusions: We identified a novel Jab1-Trx axis that is a key cellular process in the pathobiologic characteristics of AML-M5. Targeting the ROS/Jab1/Trx pathway could be beneficial in the treatment of AML-M5. Clin Cancer Res; 23(15); 4450-61. ©2017 AACR.

CDK5 Regulates Paclitaxel Sensitivity in Ovarian Cancer Cells by Modulating AKT Activation, p21Cip1- and p27Kip1-Mediated G1 Cell Cycle Arrest and Apoptosis

Cyclin-dependent kinase 5 (CDK5) is a cytoplasmic serine/ threonine kinase. Knockdown of CDK5 enhances paclitaxel sensitivity in human ovarian cancer cells. This study explores the mechanisms by which CDK5 regulates paclitaxel sensitivity in human ovarian cancers. Multiple ovarian cancer cell lines and xenografts were treated with CDK5 small interfering RNA (siRNA) with or without paclitaxel to examine the effect on cancer cell viability, cell cycle arrest and tumor growth. CDK5 protein was measured by immunohistochemical staining of an ovarian cancer tissue microarray to correlate CDK5 expression with overall patient survival. Knockdown of CDK5 with siRNAs inhibits activation of AKT which significantly correlates with decreased cell growth and enhanced paclitaxel sensitivity in ovarian cancer cell lines. In addition, CDK5 knockdown alone and in combination with paclitaxel induced G1 cell cycle arrest and caspase 3 dependent apoptotic cell death associated with post-translational upregulation and nuclear translocation of TP53 and p27^Kip1 as well as TP53-dependent transcriptional induction of p21^Cip1 in wild type TP53 cancer cells. Treatment of HEYA8 and A2780 wild type TP53 xenografts in nu/nu mice with CDK5 siRNA and paclitaxel produced significantly greater growth inhibition than either treatment alone. Increased expression of CDK5 in human ovarian cancers correlates inversely with overall survival. CDK5 modulates paclitaxel sensitivity by regulating AKT activation, the cell cycle and caspase-dependent apoptosis. CDK5 inhibition can potentiate paclitaxel activity in human ovarian cancer cells.

Clinically relevant microRNAs in ovarian cancer

microRNAs (miRNAs/miRs) belong to a class of small noncoding RNAs that can negatively regulate messenger RNA (mRNA) expression of target genes. miRNAs are involved in multiple aspects of ovarian cancer cell dysfunction and the phenotype of ovarian cancer cells can be modified by targeting miRNA expression. miRNA profiling has detected a number of candidate miRNAs with the potential to regulate many important biologic functions in ovarian cancer, but their role still needs to be clarified, given the remarkable heterogeneity among ovarian cancers and the context-dependent role of miRNAs. This review summarizes the data collected from The Cancer Genome Atlas (TCGA) and several other genome-wide projects to identify dysregulated miRNAs in ovarian cancers. Copy number variations (CNVs), epigenetic alterations, and oncogenic mutations are also discussed that affect miRNA levels in ovarian disease. Emphasis is given to the role of particular miRNAs in altering expression of genes in human ovarian cancers with the potential to provide diagnostic, prognostic, and therapeutic targets. Particular attention has been given to TP53, BRCA1/2, CA125 (MUC16), HE4 (WFDC2), and imprinted genes such as ARHI (DIRAS3). A better understanding of the abnormalities in miRNA expression and downstream transcriptional and biologic consequences will provide leads for more effective biomarkers and translational approaches in the management of ovarian cancer.

Abstract 5433: Knockdown of the glycolytic enzyme PFKFB2 induces growth inhibition and enhances paclitaxel sensitivity in ovarian cancer cells

Knockdown of certain glycolytic enzymes can affect ovarian cancer cell growth and enhance sensitivity to paclitaxel. 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-2 (PFKFB-2) is the cardiac isoform of the most important glycolytic regulator, phosphofructokinase-2, From the TCGA database of &gt;300 ovarian cancers, the PFKFB2 gene ranked in the top 33% of overexpressed genes and in the top 19% of genes with copy number gain. We found that PFKFB2 mRNA was upregulated in 10 of 12 ovarian cancer cell lines when expression of the gene was compared to that in normal ovarian epithelial cells in culture. Knockdown of PFKFB2 with siRNA markedly inhibited cell proliferation and increased paclitaxel sensitivity in p53 wild type ovarian cancer cell lines as demonstrated in short-term cytotoxicity and long-term clonogenic assays. Liposome encapsulated PFKFB2 siRNA significantly inhibited growth (P&lt;0.05) of human ovarian cancer xenografts in two ovarian cancer models (Hey A8 and A2780); even greater growth inhibition was observed when PFKFB2 siRNA treatment was combined with paclitaxel. Cell growth inhibition in cell culture was linked to G1 arrest and to a modest increase in apoptosis. Induction of p21Cip1 and p27Kip1 protein by PFKFB2 knockdown contributed to the G1 arrest, since silencing p21Cip1 and p27Kip1 dramatically reduced PFKFB2 knockdown-induced G1 arrest. PFKFB2 knockdown also modulated the expression of CDK2 and the phosphorylation of p27Kip1. Induction of p53 protein contributed to both PFKFB2 knockdown-induced G1 arrest and to apoptosis, since silencing p53 markedly alleviated PFKFB2 knockdown-induced G1 arrest and apoptosis. PFKFB2 knockdown inhibited expression of the ABC transporter family members ABCC4 and ABCG2 at the level of transcription, possibly contributing to enhanced paclitaxel retention and increased cytotoxicity after PFKFB2 knockdown. Taken together, these results suggest that PFKFB2 protein may regulate cell growth and sensitivity to paclitaxel by multiple mechanisms, particularly in p53 wild type ovarian cancers. As methods to deliver siRNA evolve in the clinic, PFKFB2 may provide a novel target for enhancing sensitivity to paclitaxel-based chemotherapy in patients with low grade serous ovarian cancer where p53 function remains intact.

Citation Format: Shu Zhang, Weiqun Mao, Anil K. Sood, Nicholas B. Jennings, Cristian Rodriguez-Aguayo, Gabriel Lopez-Berestein, Zong-Fang Li, Robert C. Bast, Xiao-Feng Le. Knockdown of the glycolytic enzyme PFKFB2 induces growth inhibition and enhances paclitaxel sensitivity in ovarian cancer cells. [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 5433. doi:10.1158/1538-7445.AM2013-5433

Abstract 3055: miR-495 functions as a novel regulator of the estrogen and progesterone receptorsin human breast cancers

The estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2, also known as ErbB-2 or c-neu) are the major biomarkers that define the classification and treatment options for patients with breast cancers. ER and PR positive breast cancers are more likely to respond to hormonal therapy. HER2 positive breast cancers are more likely to respond to trastuzumab targeted therapy. On the other end, triple negative breast cancers (TNBC) which lack ER and PR and do not overexpress HER2 do not respond well to hormonal therapy or HER2 targeted therapy and are associated with poor prognosis. Once patients with TNBC develop chemoresistance or relapse, there is no additional treatment option available. The key for developing novel therapeutics in TNBC is to elucidate the exact mechanisms by which these receptors undergo silencing, especially ER and PR. MicroRNAs (miRNAs), a class of small noncoding RNAs, have been shown to be important gene regulators in all biological processes including breast carcinogenesis and progression. Through an in silico analysis of the latest miRNAs database with four different miRNA algorithms, we have identified 11 putative miRNAs that target all 3′-untranslated regions (3’-UTRs) of the ER, PR and HER2 genes. miR-495 was one of the putative miRNAs that has been verified to be a significant regulator of ER and PR. Ectopic expression of miR-495 mimics in BT474 and MDA-MB-361 breast cancer cells greatly reduced ER and PR protein expression, but not HER2 expression. Enforced expression of a miR-495 inhibitor or antigomiR-495 in MDA-MB-361 breast cancer cells significantly elevated ER and PR expression. More importantly, miR-495 markedly inhibited the luciferase activities of both ER and PR reporters that contained the wild-type 3’-UTRs of ER and PR. miR-495 could not, however, affect the luciferase activities of the mutant ER and PR reporters that had been deleted the seed sequences in the 3’-UTRs of ER and PR, indicating that ER and PR are direct downstream targets of miR-495. miR-495 expression in primary breast cancers was assessed by in situ hybridization on a tissue microarray that containing 97 cases of randomly selected breast cancers. miR-495 levels were upregulated in thirteen breast cancers (13.4%). Among these 13 cases, 6 were TNBCs (46.2%), 2 were ER/PR low expressing breast cancers and 1 was ER/PR negative HER2 positive breast cancer. Therefore, miR-495 is a novel negative regulator of ER and PR and is upregulated in primary TNBC. Selective inhibition of miR-495 expression in TNBC with miR-495 inhibitors or antigomiR-495 may restore ER and PR expression.

Citation Format: Xiao-Feng Le, Hui Ling, Maggie Mao, Xinna Zhang, Shu Zhang, George A. Calin, Yun Wu, Robert C. Bast. miR-495 functions as a novel regulator of the estrogen and progesterone receptorsin human breast cancers. [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 3055. doi:10.1158/1538-7445.AM2013-3055

Paradoxical impact of two folate receptors, FRα and RFC, in ovarian cancer: effect on cell proliferation, invasion and clinical outcome

Despite being an essential vitamin, folate has been implicated to enhance tumor growth, as evidenced by reports on overexpression of folate receptor alpha (FRα) in carcinomas. The role of another folate transporter, reduced folate carrier (RFC), is largely unknown. This study investigated the roles of folate, FRα and RFC in ovarian cancers. We demonstrated FRα mRNA and protein overexpression and reduced RFC expression in association with FRα gene amplification and RFC promoter hypermethylation, respectively. FRα overexpression was associated with tumor progression while RFC expression incurred a favorable clinical outcome. Such reciprocal expression pattern was also observed in ovarian cancer cell lines. Folate was shown to promote cancer cell proliferation, migration and invasion in vitro, and down-regulate E-cadherin expression. This effect was blocked after either stable knockdown of FRα or ectopic overexpression of RFC. This hitherto unreported phenomenon suggests that, RFC can serve as a balancing partner of FRα and confer a protective effect in patients with high FRα-expressing ovarian carcinomas, as evidenced by their prolonged overall and disease-free survivals. In conclusion, we report on the paradoxical impact of FRα (putative oncogenic) and RFC (putative tumor suppressive) in human malignancies. FRα and RFC may potentially be explored as therapeutic target or prognostic marker respectively. We recommend caution and additional research on folate supplements in cancer patients.

Modulation of MicroRNA-194 and cell migration by HER2-targeting trastuzumab in breast cancer

Trastuzumab, a humanized monoclonal antibody directed against the extracellular domain of the HER2 oncoprotein, can effectively target HER2-positive breast cancer through several mechanisms. Although the effects of trastuzumab on cancer cell proliferation, angiogenesis and apoptosis have been investigated in depth, the effect of trastuzumab on microRNA (miRNA) has not been extensively studied. We have performed miRNA microarray profiling before and after trastuzumab treatment in SKBr3 and BT474 human breast cancer cells that overexpress HER2. We found that trastuzumab treatment of SKBr3 cells significantly decreased five miRNAs and increased three others, whereas treatment of BT474 cells significantly decreased two miRNAs and increased nine. The only change in miRNA expression observed in both cell lines following trastuzumab treatment was upregulation of miRNA-194 (miR-194) that was further validated in vitro and in vivo. Forced expression of miR-194 in breast cancer cells that overexpress HER2 produced no effect on apoptosis, modest inhibition of proliferation, significant inhibition of cell migration/invasion in vitro and significant inhibition of xenograft growth in vivo. Conversely, knockdown of miR-194 promoted cell migration. Increased miR-194 expression markedly reduced levels of the cytoskeletal protein talin2 and specifically inhibited luciferase reporter activity of a talin2 wild-type 3'-untranslated region, but not that of a mutant reporter, indicating that talin2 is a direct downstream target of miR-194. Trastuzumab treatment inhibited breast cancer cell migration and reduced talin2 expression in vitro and in vivo. Knockdown of talin2 inhibited cell migration/invasion. Knockdown of trastuzumab-induced miR-194 expression with a miR-194 inhibitor compromised trastuzumab-inhibited cell migration in HER2-overexpressing breast cancer cells. Consequently, trastuzumab treatment upregulates miR-194 expression and may exert its cell migration-inhibitory effect through miR-194-mediated downregulation of cytoskeleton protein talin2 in HER2-overexpressing human breast cancer cells.

Preferential inhibition of hepatocellular carcinoma by the flavonoid Baicalein through blocking MEK-ERK signaling

Baicalein is a purified flavonoid extracted from the roots of Scutellaria baicalensis or Scutellaria radix. Although previous studies have suggested that Baicalein possesses an in vitro anti-hepatocellular carcinoma activity, its in vivo effects and mechanisms of action are still not completely understood. In this study, Baicalein at concentrations of 40-120 µM exhibited significant cytotoxicity to three hepatocellular carcinoma (HCC) cell lines but marginal cytotoxicity to a normal liver cell line in vitro. Compared to a standard chemotherapy drug, 5-fluorouracil (5-FU), Baicalein had greater effect on HCC cells but less toxicity on normal liver cells. Treatment with Baicalein dramatically reduced mitochondrial transmembrane potential, and activated caspase-9 and caspase-3. Blockade of Baicalein-induced apoptosis with a pan-caspase inhibitor partially attenuated Baicalein-induced growth inhibition in HCC. Baicalein treatment significantly inhibited tumor growth of HCC xenografts in mice. Induction of apoptosis was demonstrated in Baicalein-treated xenograft tumors by the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Furthermore, Baicalein treatment dramatically decreased the levels of phosphorylation of MEK1, ERK1/2 and Bad in vitro and in vivo. Overexpression of human MEK1 partially blocked Baicalein-induced growth inhibition. Consequently, these findings suggest that Baicalein preferentially inhibits HCC tumor growth through inhibition of MEK-ERK signaling and by inducing intrinsic apoptosis.

Abstract 3057: CDK5 modulates the cell cycle, apoptosis and paclitaxel sensitivity in human ovarian cancer cells with wild-type p53 function

Cyclin-dependent kinase 5 (CDK5) is a ubiquitously expressed serine/threonine kinase that was initially identified in bovine brain extracts and plays an important role in normal neuron development and neurodegenerative diseases. This molecule has recently been shown to possess many cellular functions in non-neuronal tissues as well. Using a kinome siRNA screen, we identified CDK5 as a kinase that modulates paclitaxel sensitivity in human ovarian cancer cells. The aim of this report is to identify mechanisms by which CDK5 regulates paclitaxel sensitivity in human ovarian cancer cells. Despite nucleotide sequence homology with human CDK1, a role of CDK5 in regulating the cell cycle remains unclear. Here we demonstrate dual roles of CDK5 in regulating the cell cycle and apoptosis. We have found that knockdown of CDK5 with multiple siRNAs markedly inhibits cell proliferation and increases paclitaxel sensitivity in several p53 wild type ovarian cancer cell lines using assays for cell viability and clonogenic growth. CDK5 knockdown with or without paclitaxel treatment induces G1 arrest of the cell cycle and apoptotic cell death linked to a significant induction of p53, p21Cip1 and p27Kip1 proteins. Induction of G1 arrest following CDK5 knockdown depends on induction of p21Cip1 and p27Kip1, since silencing p21Cip1 and/or p27Kip1 dramatically reduces CDK5 knockdown-induced G1 arrest. A CDK5 knockdown-induced increase of p53 expression contributes both to CDK5 knockdown-induced G1 arrest and to apoptosis, as silencing p53 markedly diminishes CDK5 knockdown-induced G1 arrest and apoptosis. As expected, a CDK5 knockdown-induced increase in p21Cip1 expression depends on p53-mediated transcriptional activation demonstrated by QRT-PCR and reporter luciferase assays. CDK5 knockdown activates caspase-3 and a pan-caspase inhibitor completely blocks CDK5 knockdown-induced apoptosis. Significant Inhibition of Bcl-2 expression is found in CDK5 knockdown-induced apoptosis and additional inhibition of Bcl-2 expression is found with combined CDK5 and paclitaxel treatment. Taken together, these data suggest that CDK5 can modulate paclitaxel sensitivity through regulating both the cell cycle and apoptosis. CDK5 inhibition can potentiate paclitaxel activity in human ovarian cancer cells with wild-type p53 function, providing a novel approach for enhancing the efficacies of paclitaxel-based regimens for low grade ovarian cancer in the clinic.

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 3057. doi:1538-7445.AM2012-3057

Abstract 1912: Jab1/Csn5 as a novel driver for therapeutic resistance in HER2-positive breast cancer

Her2-positive (Her2+) breast cancer has the second worst prognosis of the five subtypes of breast cancer. The most successful targeted therapy for Her2+ breast cancer to date is trastuzumab (Herceptin)-based. However, the median duration of response to trastuzumab is shorter than 1 year, and about 75% of patients who initially responsed, has experienced resistance to the therapy after a year. Thus, better treatment strategies for Her2+ subtype are urgently needed. We and other researchers previously demonstrated that c-Jun activation domain-binding protein 1 (Jab1) negatively regulates p27, mediates p27 nuclear-to-cytoplasmic export and degradation and contributes to the loss of p27 that is seen in &gt;50% of breast tumors and that correlates with poor clinical outcome in breast cancer cells. Thus, implicates the potential role of Jab1 in interfering with trastuzumab. We identified Jab1/Csn5 as a novel oncogene. Jab1 is amplified and overexpressed in elevated in 50% of primary and 90% of metastatic breast tumors, but is low or absent in normal adult breast tissue. In addition, high Jab1 expression is associated with short progression-free survival durations in breast cancer patients. Our preliminary data showed that inactivation of Jab1/Csn5 in trastuzumab-resistant breast cancer cells sensitized the cells to trastuzumab in a dose- and time-dependent manners. However, the ways in which Jab1 expression is up-regulated in Her2+ breast cancer cells and how this up-regulation drives trastuzumab resistance remain largely unclear. In this study, we will seek to analyze the cross-talk between Src/Stat3 or Akt signaling and Jab1 activation in breast carcinoma. We have found that Stat3 is a novel positive regulator of Jab1 expression in breast cancer cells and that Jab1 overexpression driven by the Src/Stat3 pathway compensates for trastuzumab's inhibition of Her2 signaling in Her2+ breast cancer cells. This suggests that activated Stat3, by up-regulating Jab1 expression, inhibits trastuzumab-induced cell-cycle arrest. In general, our proposed study elucidates Jab1 as a novel contributor to trastuzumab resistance and determine its potential as a prognostic and predictive marker as well as an important therapeutic target. The successful completion of our study would benefit breast cancer patients in three ways. 1) Because Jab1 is rarely expressed in mammary epithelial cells, targeting Jab1 would be less toxic to normal epithelial cells, compared to other agents. 2) Combining Jab1 with trastuzumab would interfere with both Src/Stat3 and Akt pathway. This would significantly benefit patients with Her2+ breast cancer refractory to this therapy due to PTEN loss or activating mutant Stat3. 3) Because Jab1 expression is higher in trastuzumab-resistant cells than in trastuzumab-sensitive cells, Jab1 could be used as a marker of tumor response to trastuzumab.

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 1912. doi:1538-7445.AM2012-1912

Plasma microRNA 210 levels correlate with sensitivity to trastuzumab and tumor presence in breast cancer patients

BACKGROUND

Trastuzumab is part of the standard treatment for patients with human epidermal growth factor receptor 2 (HER-2)-positive breast cancer, but not all patients respond to trastuzumab. Altered microRNA (miR) expression levels in cancer cells have been correlated with prognosis and response to chemotherapy. The authors of this report hypothesized that altered miR expression levels in plasma are associated with sensitivity to trastuzumab in patients with HER-2 positive breast cancer.

METHODS

Quantitative reverse transcriptase-polymerase chain reaction was used to analyze plasma samples, including samples from patients with breast cancer who were enrolled in a clinical trial of neoadjuvant trastuzumab-based chemotherapy. Expression levels of miR-210, miR-21, miR-29a, and miR-126 were analyzed according to the type of response (pathologic complete response [n = 18] vs residual disease [n = 11]). MicroRNA expression levels also were compared in trastuzumab-sensitive and trastuzumab-resistant breast cancer cells derived from BT474 cells and in an independent set of preoperative plasma samples (n = 39) and postoperative plasma samples (n = 30) from 43 breast cancer patients who did not receive any treatment.

RESULTS

At baseline before patients received neoadjuvant chemotherapy combined with trastuzumab, circulating miR-210 levels were significantly higher in those who had residual disease than in those who achieved a pathologic complete response (P = .0359). The mean expression ratio for miR-210 was significantly higher in trastuzumab-resistant BT474 cells, and miR-210 expression was significantly higher before surgery than after surgery (P = .0297) and in patients whose cancer metastasized to the lymph nodes (P = .0030).

CONCLUSIONS

Circulating miR-210 levels were associated with trastuzumab sensitivity, tumor presence, and lymph node metastases. These results suggest that plasma miR-210 may be used to predict and perhaps monitor response to therapies that contain trastuzumab.

iASPP and chemoresistance in ovarian cancers: effects on paclitaxel-mediated mitotic catastrophe

PURPOSE

iASPP is a specific regulator of p53-mediated apoptosis. Herein, we provided the first report on the expression profile of iASPP in ovarian epithelial tumor and its effect on paclitaxel chemosensitivity.

EXPERIMENTAL DESIGN

Expression and amplification status of iASPP was examined in 203 clinical samples and 17 cell lines using immunohistochemistry, quantitative real-time PCR, and immunoblotting, and correlated with clinicopathologic parameters. Changes in proliferation, mitotic catastrophe, apoptosis, and underlying mechanism in ovarian cancer cells of different p53 status following paclitaxel exposure were also analyzed.

RESULTS

The protein and mRNA expression of iASPP was found to be significantly increased in ovarian cancer samples and cell lines. High iASPP expression was significantly associated with clear cell carcinoma subtype (P = 0.003), carboplatin and paclitaxel chemoresistance (P = 0.04), shorter overall (P = 0.003), and disease-free (P = 0.001) survival. Multivariate analysis confirmed iASPP expression as an independent prognostic factor. Increased iASPP mRNA expression was significantly correlated with gene amplification (P = 0.023). iASPP overexpression in ovarian cancer cells conferred resistance to paclitaxel by reducing mitotic catastrophe in a p53-independent manner via activation of separase, whereas knockdown of iASPP enhanced paclitaxel-mediated mitotic catastrophe through inactivating separase. Both securin and cyclin B1/CDK1 complex were involved in regulating separase by iASPP. Conversely, overexpressed iASPP inhibited apoptosis in a p53-dependent mode.

CONCLUSIONS

Our data show an association of iASPP overexpression with gene amplification in ovarian cancer and suggest a role of iASPP in poor patient outcome and chemoresistance, through blocking mitotic catastrophe. iASPP should be explored further as a potential prognostic marker and target for chemotherapy.

Src family kinases and paclitaxel sensitivity

Src-family Kinases (SFKs) participate in the regulation of proliferation, differentiation, apoptosis, autophagy, adhesion, migration, invasion and angiogenesis in normal and cancer cells. Abnormal expression of SFKs has been documented in cancers that arise in breast, colon, ovary, melanocyte, gastric mucosa, head and neck, pancreas, lung, and brain. Targeting SFKs in cancer cells has been shown to be a promising therapeutic strategy in solid tumors, particularly in ovarian, colon and breast cancers. Paclitaxel is one of most widely used chemotherapeutic agents for the management of ovarian, breast, lung and head/neck cancers. As a microtubule-stabilizing agent, paclitaxel possesses both mitosis-dependent and mitosis-independent activities against cancer cells. A variety of mechanisms such as deregulation of P-glycoprotein, alteration of tubulin isotypes, alteration of microtubule-regulatory proteins, deregulation of apoptotic signaling pathways, mutation of tubulins and overexpression of copper transporters have been implicated in the development of primary or secondary resistance to paclitaxel. By affecting cancer cell survival, proliferation, autophagy, microtubule stability, motility, and/or angiogenesis, SFKs interact with mechanisms that regulate paclitaxel sensitivity. Inhibition of SFKs can potentiate the anti-tumor activity of paclitaxel by enhancing apoptosis, autophagy and microtubule stability. Based on pre-clinical observations, administration of SFK inhibitors in combination with paclitaxel could improve treatment for ovarian, breast, lung and head/neck cancers. Identification and validation of predictive biomarkers could also permit personalization of the therapy.

The role of p27(Kip1) in dasatinib-enhanced paclitaxel cytotoxicity in human ovarian cancer cells

BACKGROUND

Less than 50% of ovarian cancers respond to paclitaxel. Effective strategies are needed to enhance paclitaxel sensitivity.

METHODS

A library of silencing RNAs (siRNAs) was used to identify kinases that regulate paclitaxel sensitivity in human ovarian cancer SKOv3 cells. The effect of dasatinib, an inhibitor of Src and Abl kinases, on paclitaxel sensitivity was measured in ovarian cancer cells and HEY xenografts. The roles of p27(Kip1), Bcl-2, and Cdk1 in apoptosis induced by dasatinib and paclitaxel were assessed using a terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, siRNA knockdown of gene expression, transfection with Bcl-2 and Cdk1 expression vectors, and flow cytometry. All statistical tests were two-sided.

RESULTS

Src family and Abl kinases were identified as modulators of paclitaxel sensitivity in SKOv3 cells. The siRNA knockdown of Src, Fyn, or Abl1 enhanced paclitaxel-mediated growth inhibition in ovarian cancer cells compared with a control siRNA. HEY cells treated with dasatinib plus paclitaxel formed fewer colonies than did cells treated with either agent alone. Treatment of HEY xenograft-bearing mice with dasatinib plus paclitaxel inhibited tumor growth more than treatment with either agent alone (average tumor volume per mouse, dasatinib + paclitaxel vs paclitaxel: 0.28 vs. 0.81 cm3, difference = 0.53 cm3, 95% confidence interval [CI] = 0.44 to 0.62 cm3, P = .014); dasatinib + paclitaxel vs. dasatinib: 0.28 vs. 0.55 cm3, difference = 0.27 cm3, 95% CI = 0.21 to 0.33 cm3, P = .035). Combined treatment induced more TUNEL-positive apoptotic cells than did either agent alone. The siRNA knockdown of p27(Kip1) decreased dasatinib- and paclitaxel-induced apoptosis compared with a negative control siRNA (sub-G1 fraction, control siRNA vs. p27(Kip1) siRNA: 42.5% vs. 20.1%, difference = 22.4%, 95% CI = 20.1% to 24.7%, P = .017). Studies with forced expression and siRNA knockdown of Bcl-2 and Cdk1 suggest that dasatinib-mediated induction of p27(Kip1) enhanced paclitaxel-induced apoptosis by negatively regulating Bcl-2 and Cdk1 expression.

CONCLUSION

Inhibition of Src family and Abl kinases with either siRNAs or dasatinib enhances paclitaxel sensitivity of ovarian cancer cells through p27(Kip1)-mediated suppression of Bcl-2 and Cdk1 expression.

Modulating microtubule stability enhances the cytotoxic response of cancer cells to Paclitaxel

The extracellular matrix protein TGFBI enhances the cytotoxic response of cancer cells to paclitaxel by affecting integrin signals that stabilize microtubules. Extending the implications of this knowledge, we tested the more general hypothesis that cancer cell signals which increase microtubule stability before exposure to paclitaxel may increase its ability to stabilize microtubules and thereby enhance its cytotoxicity. Toward this end, we carried out an siRNA screen to evaluate how genetic depletion affected microtubule stabilization, cell viability, and apoptosis. High content microscopic analysis was carried out in the absence or presence of paclitaxel. Kinase knockdowns that stabilized microtubules strongly enhanced the effects of paclitaxel treatment. Conversely, kinase knockdowns that enhanced paclitaxel-mediated cytotoxicity sensitized cells to microtubule stabilization by paclitaxel. The siRNA screen identified several genes that have not been linked previously to microtubule regulation or paclitaxel response. Gene shaving and Bayesian resampling used to classify these genes suggested three pathways of paclitaxel-induced cell death related to apoptosis and microtubule stability, apoptosis alone, or neither process. Our results offer a functional classification of the genetic basis for paclitaxel sensitivity and they support the hypothesis that stabilizing microtubules prior to therapy could enhance antitumor responses to paclitaxel treatment.

Stat3 and CCAAT/enhancer binding protein beta (C/EBP-beta) regulate Jab1/CSN5 expression in mammary carcinoma cells

Introduction

The c-Jun coactivator, Jun activation-domain binding protein 1 (Jab1) also known as the fifth component of the COP9 signalosome complex (CSN5), is a novel candidate oncogene whose aberrant expression contributes to the progression of breast carcinoma and other human cancers. The mechanism of Jab1 gene expression and its deregulation in cancer cells remains to be identified. We therefore investigated the transcriptional regulatory mechanisms of Jab1 expression in human breast carcinoma cells.

Methods

To identify potential regulators of Jab1 transcription, we cloned the 5' upstream region of the human Jab1 gene and mapped its transcriptional start site. We identified binding sequences for the CCAAT/enhancer binding protein (C/EBP) and GATA, as well as a signal transducer and activator of transcription-3 (Stat3) consensus sequence overlapping the C/EBP site, using 5'- deletion analysis and a gene reporter assay. Mutational analysis of these binding sites was performed to confirm their roles in promoting Jab1 transcription in breast cancer cells. We further confirmed these binding sites using electrophoretic mobility shift assays (EMSAs) and chromatin immunoprecipitation (ChIP) assays. We also analyzed whether the siRNA-mediated inactivation of Stat3 and Src could reduce Jab1-promoter activity and whether interleukine-6 (IL-6) could mediate increased Jab1 expression through Stat3 signaling.

Results

We identified binding sequences for C/EBP, GATA, as well as a Stat3 consensus sequence overlapping the C/EBP site in the promoter region of Jab1. C/EBP-beta2 is a potential transcriptional activator of Jab1 and mutation of the C/EBP/Stat3 binding site significantly reduced Jab1-promoter activity. In addition, inhibiting Stat3 significantly reduced Jab1-promoter activation. EMSA and ChIP assays confirmed that C/EBP, GATA1 and Stat3 bind to Jab1 promoter in breast carcinoma cells. We also found that Src, an activator of Stat3, is involved in Jab1-promoter activation. siRNA knockdown of Src reduced the Jab1-promoter activity, similar to the results seen when Stat3 was inhibited in breast carcinoma cells. Interestingly, reactivation of Stat3 in normal mammary epithelial cells (MCF-10A, MCF-10F) is sufficient to reactivate Jab1 expression. Treatment with the cytokine IL-6 resulted in increased Jab1 expression that was blocked by inhibition of Stat3.

Conclusions

These findings reveal a novel mechanism of Jab1 gene regulation and provide functional and mechanistic links between the Src/Stat3 and IL-6/Stat3 signaling axes that are involved in the activation of Jab1 transcription and regulation of this novel oncogenic protein.

Abstract 4000: Trastuzumab targeting of HER2 upregulates miRNA-194 and downregulates profilin 2 and DNMT3A in HER2 positive breast cancer

Trastuzumab, a humanized monoclonal antibody directed against the extracellular domain of oncoprotein HER2, is widely used in standard therapy for women with HER2-positive breast cancer. Although the effects of trastuzumab on cancer cell proliferation, angiogenesis, and apoptosis have been intensively investigated, the effect of trastuzumab on microRNA (miRNA) is unknown. Since miRNA provides a novel layer of gene regulation and may play role in trastuzumab action, we have consequently performed miRNA microarray profiling before and after trastuzumab treatment in both SKBr3 and BT474 breast cancer cells that overexpress HER2. Trastuzumab significantly decreased five human miRNAs and increased three others in SKBr3 cells, whereas in BT474 cells it significantly decreased two miRNAs and increased ten. The only miRNA that shared the same change in both cell lines was miRNA-194 (miR194), which was upregulated following trastuzumab treatment. Upregulation of miR194 by trastuzumab was further validated in vitro and in vivo by quantitative reverse transcription PCR (QRT-PCR) or Northern blotting. miR194 expression in 92 cases of breast cancer and 21 normal breast tissues (all were FFPE samples) was examined by QRT-PCR. miR194 levels were significantly higher in breast cancer samples versus normal tissues (p=0.0003), in estrogen-positive breast cancer samples (p=0.002), and in HER2-negative breast cancer samples (p=0.032). Importantly, expression of precursor miR194 specifically downregulated the protein levels of DNA methytransferase DNMT3A and actin cytoskeleton organizer profilin 2. miR-194 specifically inhibited the luciferase activity of wild type DNMT3A 3’-UTR construct, but not that of mutant vector, indicating that DNMT3A is a direct downstream target of miR-194. Both trastuzumab treatment and overexpression of miR-194 inhibited cell motility of breast cancer cells, which may result from the inhibition of DNMT3A and profilin 2. In summary, trastuzumab treatment upregulates miR194 expression and may exert its therapeutic effects through downregulation of miR194-downstream targets DNMT3A and profilin 2 in HER2-positive breast cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4000. doi:10.1158/1538-7445.AM2011-4000

A genistein derivative, ITB-301, induces microtubule depolymerization and mitotic arrest in multidrug-resistant ovarian cancer

Purpose

To investigate the mechanistic basis of the anti-tumor effect of the compound ITB-301.

Methods

Chemical modifications of genistein have been introduced to improve its solubility and efficacy. The anti-tumor effects were tested in ovarian cancer cells using proliferation assays, cell cycle analysis, immunofluorescence, and microscopy.

Results

In this work, we show that a unique glycoside of genistein, ITB-301, inhibits the proliferation of SKOv3 ovarian cancer cells. We found that the 50% growth inhibitory concentration of ITB-301 in SKOv3 cells was 0.5 μM. Similar results were obtained in breast cancer, ovarian cancer, and acute myelogenous leukemia cell lines. ITB-301 induced significant time- and dose-dependent microtubule depolymerization. This depolymerization resulted in mitotic arrest and inhibited proliferation in all ovarian cancer cell lines examined including SKOv3, ES2, HeyA8, and HeyA8-MDR cells. The cytotoxic effect of ITB-301 was dependent on its induction of mitotic arrest as siRNA-mediated depletion of BUBR1 significantly reduced the cytotoxic effects of ITB-301, even at a concentration of 10 μM. Importantly, efflux-mediated drug resistance did not alter the cytotoxic effect of ITB-301 in two independent cancer cell models of drug resistance.

Conclusion

These results identify ITB-301 as a novel anti-tubulin agent that could be used in cancers that are multidrug resistant. We propose a structural model for the binding of ITB-301 to α- and β-tubulin dimers on the basis of molecular docking simulations. This model provides a rationale for future work aimed at designing of more potent analogs.

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-011-1575-2) contains supplementary material, which is available to authorized users.

Overexpression of proto-oncogene FBI-1 activates membrane type 1-matrix metalloproteinase in association with adverse outcome in ovarian cancers

Background

FBI-1 (factor that binds to the inducer of short transcripts of human immunodeficiency virus-1) is a member of the POK (POZ and Kruppel) family of transcription factors and play important roles in cellular differentiation and oncogenesis. Recent evidence suggests that FBI-1 is expressed at high levels in a subset of human lymphomas and some epithelial solid tumors. However, the function of FBI-1 in human ovarian cancers remains elusive.

Results

In this study, we investigated the role of FBI-1 in human ovarian cancers, in particularly, its function in cancer cell invasion via modulating membrane type 1-matrix metalloproteinase (MT1-MMP). Significantly higher FBI-1 protein and mRNA expression levels were demonstrated in ovarian cancers samples and cell lines compared with borderline tumors and benign cystadenomas. Increased FBI-1 mRNA expression was correlated significantly with gene amplification (P = 0.037). Moreover, higher FBI-1 expression was found in metastatic foci (P = 0.036) and malignant ascites (P = 0.021), and was significantly associated with advanced stage (P = 0.012), shorter overall survival (P = 0.032) and disease-free survival (P = 0.016). In vitro, overexpressed FBI-1 significantly enhanced cell migration and invasion both in OVCA 420 and SKOV-3 ovarian carcinoma cells, irrespective of p53 status, accompanied with elevated expression of MT1-MMP, but not MMP-2 or TIMP-2. Moreover, knockdown of MT1-MMP abolished FBI-1-mediated cell migration and invasion. Conversely, stable knockdown of FBI-1 remarkably reduced the motility of these cells with decreased expression of MT1-MMP. Promoter assay and chromatin immunoprecipitation study indicated that FBI-1 could directly interact with the promoter spanning ~600bp of the 5'-flanking sequence of MT1-MMP and enhanced its expression in a dose-dependent manner. Furthermore, stable knockdown and ectopic expression of FBI-1 decreased and increased cell proliferation respectively in OVCA 420, but not in the p53 null SKOV-3 cells.

Conclusions

Our results suggested an important role of FBI-1 in ovarian cancer cell proliferation, cell mobility, and invasiveness, and that FBI-1 can be a potential target of chemotherapy.

Dasatinib induces autophagic cell death in human ovarian cancer

BACKGROUND

Dasatinib, an inhibitor of Src/Abl family kinases, can inhibit tumor growth of several solid tumors. However, the effect and mechanism of action of dasatinib in human ovarian cancer cells remains unknown.

METHODS

Dasatinib-induced autophagy was determined by acridine orange staining, punctate localization of GFP-LC3, LC3 protein blotting, and electron microscopy. Significance of beclin 1, AKT, and Bcl-2 in dasatinib-induced autophagy and growth inhibition was assayed by small interfering RNA (siRNA) silencing and/or overexpression of the gene of interest.

RESULTS

Dasatinib inhibited cell growth by inducing little apoptosis, but substantial autophagy in SKOv3 and HEY ovarian cancer cells. In vivo studies showed dasatinib inhibited tumor growth and induced both autophagy and apoptosis in a HEY xenograft model. Knockdown of beclin 1 and Atg12 expression with their respective siRNAs diminished dasatinib-induced autophagy, whereas knockdown of p27Kip1 with specific siRNAs did not. Small hairpin RNA knockdown of beclin 1 expression reduced dasatinib-induced autophagy and growth inhibition. Dasatinib reduced the phosphorylation of AKT, mTOR, p70S6K, and S6 kinase expression. Constitutive expression of AKT1 and AKT2 inhibited dasatinib-induced autophagy in both HEY and SKOv3 cells. Dasatinib also reduced Bcl-2 expression and activity. Overexpression of Bcl-2 partially prevented dasatinib-induced autophagy.

CONCLUSIONS

Dasatinib induces autophagic cell death in ovarian cancer that partially depends on beclin 1, AKT, and Bcl-2. These results may have implications for clinical use of dasatinib.

SIK2 is a centrosome kinase required for bipolar mitotic spindle formation that provides a potential target for therapy in ovarian cancer

Regulators of mitosis have been successfully targeted to enhance response to taxane chemotherapy. Here, we show that the salt inducible kinase 2 (SIK2) localizes at the centrosome, plays a key role in the initiation of mitosis, and regulates the localization of the centrosome linker protein, C-Nap1, through S2392 phosphorylation. Interference with the known SIK2 inhibitor PKA induced SIK2-dependent centrosome splitting in interphase while SIK2 depletion blocked centrosome separation in mitosis, sensitizing ovarian cancers to paclitaxel in culture and in xenografts. Depletion of SIK2 also delayed G1/S transition and reduced AKT phosphorylation. Higher expression of SIK2 significantly correlated with poor survival in patients with high-grade serous ovarian cancers. We believe these data identify SIK2 as a plausible target for therapy in ovarian cancers.

A novel compound modified from tanshinone inhibits tumor growth in vivo via activation of the intrinsic apoptotic pathway

A novel compound, acetyltanshinone IIA (ATA) was obtained from chemical modifications of tanshinone TIIA (TIIA) isolated from a medicinal plant, Salvia miltiorrhiza. ATA exhibited increased water solubility and stronger apoptotic activity on multiple cancer cell lines than TIIA. ATA displayed a higher growth inhibition ability on breast cancer especially HER2 positive cells than normal cells and it inhibited xenografted tumor growth in mice. Mechanistic studies showed that ATA could induce significant reactive oxygen species (ROS) generation, Bax translocation to mitochondria, resulting in mitochondria damage, cytochrome c release, caspase-3 activation and apoptotic cell death. ATA-mediated ROS production and its downstream apoptotic events could be blocked by an antioxidant agent, propyl gallate, indicating the prominent role of ROS in ATA-induced apoptosis. Overexpression of Bcl-2 protein reduced ATA-induced cell death. In conclusion, ATA is a novel anticancer agent with potent in vitro and in vivo anticancer ability. ROS-mediated Bax activation should be the mechanism by which ATA induces apoptosis and inhibits tumor growth.

Abstract 2051: DNA (cytosine-5-)-methyltransferases 3A (DNMT3A) is a direct target of miR-194 in breast cancer

microRNAs (miRNAs) are small non-coding RNAs of 19-25 nucleotides in length that can modulate gene expression that regulate biological and malignant processes. DNA methylation is catalyzed primarily by three DNMTs - DNMT1, DNMT3A, and DNMT3B and contributes to cancer initiation and progression. While DNMT3A protein overexpression has been detected in colon, lung, skin and testis cancers, its expression in breast cancer has not been previously reported. Targets and function for miR-194 have not been well defined. In this study, we investigated the expression of miR-194, DNMT3A, and the possible role of miR-194 in regulating DNMT3A in breast cancer cells. Expression of miR-194 precursor in breast cancer cell lines specifically downregulated DNMT3A mRNA and protein levels. miR-194 specifically inhibited the luciferase activity of wild type DNMT3A 3’-UTR construct, but not that of mutant vector, indicating that DNMT3A is a direct downstream target of miR-194. Furthermore, miR-194 expression appeared to correlate inversely with DNMT3A mRNA or protein expression in breast cancer cell lines and patient samples. An increase in miR-194 expression stimulated tumor suppressors cyclin G2, p27Kip1 and ADAM23 expression, which can be regulated by DNA methylation. Overexpression of miR-194 inhibited cell motility of breast cancer cells without alteration of the cell cycle distribution. Most DNMT3A protein localized in the nucleus, but a small fraction of DNMT3A protein was found in the cytoplasm. The prognostic value of miR-194 and DNMT3A in breast cancer is being studied using a breast cancer tissue array, quantitative real time PCR and immunohistochemical staining. In summary, this report demonstrates DNMT3A as a direct target of miR-194 in breast cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2051.

Abstract 1585: Loss of CDK5 sensitizes ovarian cancer cells to paclitaxel by enhancing intracellular retention

In order to improve the efficacy of paclitaxel in treatment of ovarian cancer, we have performed a kinome siRNA library screen to identify kinases that regulate paclitaxel sensitivity. CDK5 was one of kinase targets that could modulate paclitaxel sensitivity in SKOv3 cells. Unlike typical cyclin dependent kinases, CDK5 does not have a clearly defined role in the regulation of the cell cycle. CDK5 is required for the regulation of neuronal synaptic vesicular transport in the brain through phosphorylation of Munc 18, a key regulator of vesicular exocytosis. In this report, we aimed to explore the mechanisms by which CDK5 potentiate paclitaxel activity. We found that eighteen ovarian cancer cell lines expressed variable CDK5 levels measured by quantitative real time PCR and Western blotting. Basal levels of CDK5 in ovarian cancer cell lines appeared not to correlate with paclitaxel sensitivity. We used immunoprecipitation of CDK5 and in vitro kinase assays using 32P-ATP and observed that paclitaxel treatment of SKOv3 cells resulted in a profound (&gt;20 fold) increase in CDK5 activity. Selective depletion of CDK5 using 4 individual siRNAs in SKOv3, TOV112 and DOV13 ovarian cancer cells lines resulted in a significant increase in paclitaxel-induced cytotoxicity as measured by cell viability assays. In addition, loss of CDK5 resulted in a significant increase in paclitaxel-mediated induction of caspase 3/7 activation in the ovarian cancer cell lines SKOv3, ES2, OVAR429 and DOV13. Remarkably, the magnitude of sensitization was directly proportional (p&lt;0.001) to the dose of paclitaxel used. Knockdown of CDK5 did not enhance microtubule stabilization or increase paclitaxel-induced mitotic arrest. Instead, CDK5 depletion in SKOv3 cells resulted in a significant (p&lt;0.001) increase in retention of fluorescent-tagged paclitaxel. This effect was similar to but independent from the effect of inhibition of trans-membrane pumps using verapamil, suggesting that the two mechanisms act in parallel. Indeed, knockdown of CDK5 in combination with verapamil resulted in greater intracellular retention of paclitaxel in SKOv3 cells. Consequently, we conclude that depletion of CDK5 results in decreased paclitaxel exocytosis leading to increased cytotoxicity to ovarian cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1585.

MEKK3 expression correlates with nuclear factor kappa B activity and with expression of antiapoptotic genes in serous ovarian carcinoma

BACKGROUND

Constitutively activated nuclear factor kappa B (NFkappaB) contributes to the development of cancer by regulating the expression of genes involved in cell survival, metastasis, and angiogenesis. The authors have demonstrated that MEKK3 plays a critical role in cytokine-mediated NFkappaB activation, and that stable expression of MEKK3 in cultured cells leads to increased NFkappaB activity.

METHODS

MEKK3 expression in ovarian cancer cells or tumors was assessed by Western blotting and real-time polymerase chain reaction. NFkappaB activities were analyzed by electrophoretic mobility shift assay and luciferase reporter assays. Western blot analysis for the survival factors were also performed and correlated with MEKK3 and NFkappaB activities. Cell survival assays were used to determine the sensitivity of ovarian cancer cells to various chemotherapeutic agents.

RESULTS

The authors found that 63% of the ovarian cancers had higher MEKK3 expression than the normal ovarian epithelial cells. Ovarian cancers with high MEKK3 showed correspondingly high IkappaB kinase and NFkappaB activity. Moreover, MEKK3 coimmunoprecipitated with Akt and cooperated with Akt to synergistically activate NFkappaB. Consistent with increased MEKK3 and NFkappaB activity in ovarian cancers, Bcl-2, Bcl-xL, survivin, and X-linked inhibitor of apoptosis levels were increased, which correlated with increased resistance to chemotherapeutic agents. Knockdown of MEKK3 with small interfering RNA significantly increased cancer cell sensitivity to paclitaxel.

CONCLUSIONS

MEKK3 may be aberrantly expressed in ovarian cancers and plays an important role in tumors with constitutively activated NFkappaB.

Specific blockade of VEGF and HER2 pathways results in greater growth inhibition of breast cancer xenografts that overexpress HER2

We have previously reported that breast cancer cells which overexpress HER2 produce higher levels of VEGF than cells with low levels of HER2. This study tested the hypothesis that dual targeting of the VEGF (with VEGF-Trap) and HER2 (with trastuzumab) pathways would result in greater growth inhibition of HER2-overexpressing breast cancer xenografts than either agent alone. In this study we found that human and murine endothelial cells expressed high levels of VEGF receptors (VEGFR1, VEGFR2, & VEGFR3). VEGF-Trap decreased levels of secreted VEGF derived from both human and murine cells and effectively blocked VEGF-induced tyrosine phosphorylation of VEGFR2. VEGF-Trap as a single treatment inhibited tumor microvessel density (MVD), tumor vasculature, cell proliferation and tumor growth of BT474 xenografts in a dose-dependent manner from 2.5 mg/kg to 25 mg/kg. VEGF-Trap decreased levels of both human VEGF and PlGF protein in vivo. Trastuzumab as a single agent effectively inhibited BT474 tumor growth in a dose-dependent manner, associated with a decrease in human VEGF, tumor MVD and tumor cell proliferation. Treatment with a combination of VEGF-Trap (2.5-10 mg/kg) and trastuzumab (1 mg/kg) produced significantly greater inhibition of BT474 tumor growth than either individual agent, associated with greater inhibition of tumor MVD and tumor cell proliferation. Thus, VEGF-Trap in combination with trastuzumab produces superior growth inhibition of tumor xenografts which overexpress HER2, which may result from inhibition of both tumor angiogenesis and proliferation. Similar mechanisms may contribute to the clinical anti-tumor activity of trastuzumab in combination with inhibitors of VEGF signaling pathway in women with breast cancers which overexpress HER2.

Role of PELP1/MNAR signaling in ovarian tumorigenesis

Emerging evidence suggests that nuclear receptor (NR) coregulators have potential to act as master genes and their deregulation can promote oncogenesis. Proline-, glutamic acid-, and leucine-rich protein-1 (PELP1/MNAR) is a novel NR coregulator. Its expression is deregulated in hormone-driven cancers. However, the role of PELP1/MNAR in ovarian cancer progression remains unknown. Analysis of serial analysis of gene expression data suggested deregulation of PELP1/MNAR expression in ovarian tumors. Western analysis of PELP1/MNAR in normal and serous ovarian tumor tissues showed 3- to 4-fold higher PELP1/MNAR expression in serous tumors compared with normal ovarian tissues. To examine the significance of PELP1/MNAR in ovarian cancer progression, we have generated model cells that overexpress PELP1/MNAR and ovarian cancer cells in which PELP1/MNAR expression is down-regulated by stable expression of PELP1/MNAR-specific shRNA. Down-regulation of PELP1/MNAR in cancerous ovarian model cells (OVCAR3) resulted in reduced proliferation, affected the magnitude of c-Src and protein kinase B (AKT) signaling, and reduced tumorigenic potential of ovarian cancer cells in a nude mouse model. PELP1/MNAR overexpression in nontumorigenic immortalized surface epithelial cells (IOSE cells) promoted constitutive activation of c-Src and AKT signaling pathways and promoted anchorage-independent growth. Immunohistochemical studies using human ovarian cancer tissue arrays (n = 123) showed that PELP1/MNAR is 2- to 3-fold overexpressed in 60% of ovarian tumors, and PELP1/MNAR deregulation occurs in all different types of ovarian cancer. Collectively, these results suggest that PELP1/MNAR signaling plays a role in ovarian cancer cell proliferation and survival, and that its expression is deregulated in ovarian carcinomas.

Roles of human epidermal growth factor receptor 2, c-jun NH2-terminal kinase, phosphoinositide 3-kinase, and p70 S6 kinase pathways in regulation of cyclin G2 expression in human breast cancer cells

The CCNG2 gene that encodes the unconventional cyclin G2 was one of the few genes up-regulated on anti-human epidermal growth factor receptor 2 (HER2) antibody-mediated inhibition of HER2 signaling. The purpose of this study was to explore how HER2 signaling modulates cyclin G2 expression and the effect of elevated cyclin G2 on breast cancer cell growth. Treatment of breast cancer cells that overexpress HER2 (BT474, SKBr3, and MDAMB453) with the anti-HER2 antibody trastuzumab or its precursor 4D5 markedly up-regulated cyclin G2 mRNA in vitro and in vivo, as shown by real-time PCR. Immunoblot and immunofluorescence analysis with specific antibodies against cyclin G2 showed that anti-HER2 antibody significantly increased cyclin G2 protein expression and translocated the protein to the nucleus. Trastuzumab was not able to induce cyclin G2 expression in cells weakly expressing HER2 (MCF7) or in cells that had developed resistance to trastuzumab. Enforced expression of HER2 in T47D and MDAMB435 breast cancer cells reduced cyclin G2 levels. Collectively, these data suggest that HER2-mediated signaling negatively regulates cyclin G2 expression. Inhibition of phosphoinositide 3-kinase (LY294002), c-jun NH(2)-terminal kinase (SP600125), and mammalian target of rapamycin (mTOR)/p70 S6 kinase (p70S6K; rapamycin) increased cyclin G2 expression. In contrast, treatment with inhibitors of p38 mitogen-activated protein kinase (SB203580), mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1/2 (U0126), or phospholipase Cgamma (U73122) did not affect cyclin G2 expression. Anti-HER2 antibody in combination with LY294002, rapamycin, or SP600125 induced greater cyclin G2 expression than either agent alone. Ectopic expression of cyclin G2 inhibited cyclin-dependent kinase 2 activity, Rb phosphorylation, cell cycle progression, and cellular proliferation without affecting p27(Kip1) expression. Thus, cyclin G2 expression is modulated by HER2 signaling through multiple pathways including phosphoinositide 3-kinase, c-jun NH(2)-terminal kinase, and mTOR signaling. The negative effects of cyclin G2 on cell cycle and cell proliferation, which occur without altering p27(Kip1) levels, may contribute to the ability of trastuzumab to inhibit breast cancer cell growth.

Anti-HER2 antibody trastuzumab inhibits CDK2-mediated NPAT and histone H4 expression via the PI3K pathway

The anti-HER2 antibody trastuzumab (Herceptin) has been used to treat patients with breast cancers that overexpress HER2. We have demonstrated that p27(Kip1) upregulation is one of the key events that cause G(1) arrest upon trastuzumab treatment. Here, we have examined the effect of trastuzumab on expression of CDK2, Rb, E2F, NPAT and histone H4 in breast cancer cells that overexpress HER2. Trastuzumab treatment dramatically inhibited the kinase activity and expression of CDK2, whereas the kinase activity and expression of CDK4 were not affected. Unlike the p27(Kip1) upregulation that occurs primarily through post-translational mechanisms, CDK2 was downregulated primarily at a transcriptional level as shown by Northern blotting and real-time RT-PCR analyses. With a decrease in CDK2 activity, trastuzumab decreased the kinase activity of cyclin E but had little effect on cyclin E protein level. Overexpression of wild-type cyclin E or its lower molecular weight forms did not influence the response to trastuzumab. Levels and activities of CDK6, cyclin A, and cyclin D1 were all suppressed by trastuzumab. As a result, trastuzumab inhibited Rb phosphorylation that associates with CDK2, cyclin E, CDK6, cyclin A, or cyclin D1. As predicted from these changes, trastuzumab decreased the DNA-binding activity of E2F, decreased the level of NPAT protein, and decreased the level of histone H4 mRNA. Blockade of the PI3K pathway with LY294002 produced similar effects to trastuzumab treatment on expression of each of these genes. Taken together, treatment of breast cancer cells that overexpress HER2 with the anti-HER2 antibody trastuzumab inhibits CDK2, Rb phosphorylation, E2F activity, NPAT, and histone H4 via PI3K signaling that are needed for both DNA and histone synthesis during progression from G(1) phase to S phase of the cell cycle.

HER2-targeting antibodies modulate the cyclin-dependent kinase inhibitor p27Kip1 via multiple signaling pathways

Anti-HER2 antibody trastuzumab is emerging as a frontline therapy for patients with metastatic breast cancers that overexpress HER2. Understanding the molecular mechanisms by which the antibody inhibits tumor growth should permit the design of even more effective trastuzumab-based protocols. Several groups including our own have demonstrated that induction of cyclin-dependent kinase (CDK) inhibitor p27Kip1 protein is one of the key mechanisms of action of HER2-targeting antibodies. In this review, we discuss currently available data regarding the multiple signaling targets and pathways by which HER2-targeting antibodies upregulate p27Kip1 protein in breast cancer cells that overexpress HER2. Anti-HER2 antibodies inhibit HER2-mediated signaling in cancer cells, ultimately upregulating the levels and activity of p27Kip1 protein. At least six signaling targets and pathways are modulated by trastuzumab. By inhibiting CDK2 and decreasing Thr187 phosphorylation of p27Kip1, trastuzumab abrogates targeting of SCF-ubiquitin E3 ligase and minimizes proteasome degradation of p27Kip1. By inhibiting AKT and human kinase interacting stathmin (hKIS), trastuzumab blocks Thr157-, Thr198- and Ser10-induced p27Kip1 translocation from the nucleus to the cytosol, which increases the inhibitory effect of p27Kip1. By inhibiting Jun activation domain-binding protein 1 (Jab1) trastuzumab increases nuclear retention of p27Kip1. By inhibiting cyclin D and c-Myc, trastuzumab releases the sequestrated p27bKip1 protein from cyclin D-CDK4/6 complexes and increase the effect of p27Kip1 on CDK2-cyclin E complexes. By stimulating minibrain related kinase (MIRK), trastuzumab stabilizes p27Kip1 in the nucleus, which increases inhibitory action of p27Kip1 on CDK2. The targets and pathways affected by trastuzumab work in concert to maximize the expression and inhibitory effect of p27Kip1, which leads to cell cycle G1 arrest and growth inhibition.

Genes affecting the cell cycle, growth, maintenance, and drug sensitivity are preferentially regulated by anti-HER2 antibody through phosphatidylinositol 3-kinase-AKT signaling

The molecular mechanisms by which the anti-HER2 antibodies trastuzumab and its murine equivalent 4D5 inhibit tumor growth and potentiate chemotherapy are not fully understood. Inhibition of signaling through the phosphatidylinositol 3-kinase (PI3K)-AKT pathway may be particularly important. Treatment of breast cancer cells that overexpress HER2 with trastuzumab inhibited HER2-HER3 association, decreased PDK1 activity, reduced Thr-308 and Ser-473 phosphorylation of AKT, and reduced AKT enzymatic activity. To place the role of PI3K-AKT in perspective, gene expression was studied by using Affymetrix microarrays and real time reverse transcription-PCR. Sixteen genes were consistently down-regulated 2.0-4.9-fold in two antibody-treated breast cancer cell lines. Fourteen of the 16 genes were involved in three major functional areas as follows: 7 in cell cycle regulation, particularly of the G(2)-M; 5 in DNA repair/replication; and 2 in modifying chromatin structure. Of the 16 antibody-regulated genes, 64% had roles in cell growth/maintenance and 52% contributed to the cell cycle. Direct inhibition of PI3K with an inhibitor markedly reduced expression of 14 genes that were also affected by the antibody. Constitutive activation of AKT1 blocked the effect of the anti-HER2 antibody on cell cycle arrest and on eight differentially expressed genes. The antibody enhanced docetaxel-induced growth inhibition but did not increase the fraction of apoptotic cells induced with docetaxel alone. In contrast, the antibody plus docetaxel markedly down-regulated two genes, HEC and DEEPEST, required for passage through G(2)-M. Thus, anti-HER2 antibody preferentially affects genes contributing to cell cycle progression and cell growth/maintenance, in part through the PI3K-AKT signaling. Transcriptional regulation by anti-HER2 antibody through PI3K-AKT pathway may potentiate the growth inhibitory activity of docetaxel by affecting cell cycle progression.

The role of cyclin-dependent kinase inhibitor p27Kip1 in anti-HER2 antibody-induced G1 cell cycle arrest and tumor growth inhibition

Cyclin-dependent kinase (CDK) inhibitor p27Kip1 binds to the cyclin E.CDK2 complex and plays a major role in controlling cell cycle and cell growth. Our group and others have reported that anti-HER2 monoclonal antibodies exert inhibitory effects on HER2-overexpressing breast cancers through G1 cell cycle arrest associated with induction of p27Kip1 and reduction of CDK2. The role of p27Kip1 in anti-HER2 antibody-induced cell cycle arrest and growth inhibition is, however, still uncertain. Here we have provided several lines of evidence supporting a critical role for p27Kip1 in the anti-HER2 antibody-induced G1 cell cycle arrest and tumor growth inhibition. Induction of p27Kip1 and G1 growth arrest by anti-HER2 antibody, murine 4D5, or humanized trastuzumab (Herceptin) are concentration-dependent, time-dependent, irreversible, and long-lasting. The magnitude of G1 cell cycle arrest induced by trastuzumab or 4D5 is well correlated with the level of p27Kip1 protein induced. Up-regulation of p27Kip1 and G1 growth arrest could no longer be removed with as little as 14 h of treatment with trastuzumab. Anti-HER2 antibody-induced p27Kip1 protein, G1 arrest, and growth inhibition persist at least 5 days after a single treatment. The magnitude of growth inhibition of breast cancer cells induced by anti-HER2 antibody closely parallels the level of p27Kip1 induced. Induced expression of exogenous p27Kip1 results in a p27Kip1 level-dependent G1 cell cycle arrest and growth inhibition similar to that obtained with anti-HER2 antibodies. Reducing p27Kip1 expression using p27Kip1 small interfering RNA blocks anti-HER2 antibody-induced p27Kip1 up-regulation and G1 arrest. Treatment with anti-HER2 antibody significantly increases the half-life of p27Kip1 protein. Inhibition of ubiquitin-proteasome pathway, but not inhibition of calpain and caspase activities, up-regulates p27Kip1 protein to a degree comparable with that obtained with anti-HER2 antibodies. We have further demonstrated that anti-HER2 antibody significantly decreases threonine phosphorylation of p27Kip1 protein at position 187 (Thr-187) and increases serine phosphorylation of p27Kip1 protein at position 10 (Ser-10). Expression of S10A and T187A mutant p27Kip1 protein increases the fraction of cells in G1 and reduces a further antibody-induced G1 arrest. Consequently, p27Kip1 plays an important role in the anti-HER2 antibody-induced G1 cell cycle arrest and tumor growth inhibition through post-translational regulation. Regulation of the phosphorylation of p27Kip1 protein is one of the post-translational mechanisms by which anti-HER2 antibody upregulates the protein.

Paclitaxel induces inactivation of p70 S6 kinase and phosphorylation of Thr421 and Ser424 via multiple signaling pathways in mitosis

The 70 kDa ribosomal S6 kinase (p70S6K) is important for cell growth and survival. Activation of p70S6K requires sequential phosphorylation of multiple serine and threonine sites often triggered by growth factors and hormones. Here, we report that paclitaxel, a microtubule-damaging agent, induces phosphorylation of p70S6K at threonine 421 and serine 424 (T421/S424) in a concentration- and time-dependent manner in multiple breast and ovarian cancer cell lines demonstrated by a T421/S424 phospho-p70S6K antibody. Phosphoamino-acid analysis and Western blot analysis by serine-/threonine-specific antibodies further confirms that both serine and threonine residues are phosphorylated in p70S6K following treatment with paclitaxel. Paclitaxel-induced p70S6K(T421/S424) phosphorylation requires both de novo RNA and protein synthesis via multiple signaling pathways including ERK1/2 MAP kinase, JNK, PKC, Ca(++), PI3K, and mammalian target of rapamycin (mTOR). Despite phosphorylation of p70S6K(T421/S424), paclitaxel inactivates this kinase in a concentration- and time-dependent manner as illustrated by in vitro kinase assay. Inhibitors of mTOR, PI3K, and Ca(++) impair p70S6K activity, whereas inhibitors of JNK and PKC stimulate p70S6K activity. Inhibition of PKC and JNK prevents paclitaxel-induced p70S6K inactivation. Moreover, the paclitaxel-induced phosphorylation and low activity of p70S6K mainly occurs during mitosis. In summary, paclitaxel is able to induce p70S6K(T421/S424) phosphorylation and decrease its activity in mitotic cells via multiple signaling pathways. Our data suggest that paclitaxel-induced p70S6K(T421/S424) phosphorylation and kinase inactivation are differentially regulated. Our data also indicate that paclitaxel may exert its antitumor effect, at least in part, via inhibition of p70S6K.

Reexpression of the tumor suppressor gene ARHI induces apoptosis in ovarian and breast cancer cells through a caspase-independent calpain-dependent pathway

ARHI, an imprinted putative tumor suppressor gene, encodes a M(r) 26,000 GTP-binding protein that is 60% homologous to ras and rap but has a dramatically different function. ARHI expression is down-regulated in a majority of breast and ovarian cancers. Using a dual adenovirus system, we have reexpressed ARHI in ovarian cancer and breast cancer cells that have lost ARHI expression. Reexpression of ARHI inhibited growth, decreased invasiveness, and induced apoptosis. At 5 days after infection with ARHI adenovirus, 30-45% of MDA-MB-231 breast cancer cells and 5-11% of SKOv3 ovarian cancer cells were apoptotic as judged by a terminal deoxynucleotidyl transferase-mediated nick end labeling assay and by Annexin V staining with flow cytometric analysis. Although poly(ADP-ribose) polymerase could be detected immunohistochemically in the nuclei of apoptotic cells, no activation of the effector caspases (caspase 3, 6, 7, or 12) or the initiator caspases (caspase 8 or 9) could be detected in cell lysates using Western blotting. When gene expression was analyzed on a custom cDNA array that contained 2304 known genes, infection with ARHI adenovirus up-regulated 15 genes relative to control cells infected with LacZ adenovirus. The greatest degree of mRNA up-regulation was observed in a Homo sapiens calpain-like protease. On Western blot analysis, calpain protein was increased 2-3-fold at 3-5 days after infection with ARHI adenovirus. No increase in calpain protein was observed after LacZ adenovirus infection. Calpain cleavage could be detected after ARHI reexpression, and inhibitors of calpain, but not inhibitors of caspase, partially prevented ARHI-induced apoptosis. Consequently, reexpression of ARHI in breast and ovarian cancer cells appears to induce apoptosis through a caspase-independent, calpain-dependent mechanism.

Heregulin-induced apoptosis is mediated by down-regulation of Bcl-2 and activation of caspase-7 and is potentiated by impairment of protein kinase C alpha activity

Heregulins are a group of growth factors that play diverse and critical roles in the signaling network of the human epidermal growth factor receptor (HER or EGFR) superfamily. Our earlier studies have shown that recombinant heregulinbeta1 (HRG) induces apoptosis in SKBr3 breast cancer cells that overexpress HER2. Here we report molecular mechanisms of HRG-induced apoptosis. HRG treatment of SKBr3 cells for 72 h decreased the level of Bcl-2 protein. HRG treatment led to degradation of poly (ADP-ribose) polymerase (PARP) and activated both caspase-9 and caspase-7. No significant activation of caspase-3, -6, or -8 was detected. Expression of exogenous caspase-7 by adenovirus-caspase-7 (Ad-casp-7) in SKBr3 cells resulted in apoptosis, which mimicked the effect of HRG treatment. Expression of exogenous caspase-7 had no impact on Bcl-2 expression, but promoted PARP degradation. Two highly selective inhibitors of protein kinase C (PKC), GF109203X (GF) and Ro318425 (Ro), significantly enhanced HRG-induced apoptosis as determined by flow cytometric analysis and DNA fragmentation assay. Accordingly, the PKC inhibitor GF further decreased the level of Bcl-2 protein and further degraded PARP in HRG-treated cells. Assay of PKC activity indicated that HRG activated PKC in SKBr3 cells, predominantly affecting the PKCalpha isoform. To confirm which PKC isoform(s) mediated potentiation of HRG-induced apoptosis, the profile of PKC isoforms was measured in SKBr3 cells. Five PKC isoforms, PKCalpha, PKCiota, PKCzeta, PKClambda, and PKCdelta as well as their receptors (RACK1) were expressed in this cell line. Treatment with PKC inhibitors GF and Ro decreased protein levels of both PKCalpha and PKCdelta at 24 h. PKCalpha levels were still depressed at 72 h. GF and Ro had little effect on the expression of other PKC isoforms. An inhibitor of classical PKC isoforms (Go6976) enhanced HRG-induced apoptosis, whereas the PKCdelta selective inhibitor rottlerin did not. As PKCalpha was the only classical isoform expressed in SKBr3 cells, the effect of Go6976 on HRG-induced apoptosis largely related to inhibition of PKCalpha. Constitutive expression of wild-type PKCalpha attenuated the apoptosis produced by HRG and GF. Consequently, HRG-induced apoptosis in SKBr3 cells appeared to involve down-regulation of Bcl-2 protein, activation of caspase-9 and caspase-7, and degradation of PARP. Inhibition of PKC function enhanced HRG-induced apoptosis, leading to synergistic down-regulation of Bcl-2 expression. Impairment of the PKCalpha isoform alone was sufficient to potentiate HRG-induced apoptosis.

Differential signaling by an anti-p185(HER2) antibody and heregulin

To understand the molecular mechanisms by which anti-p185HER2 antibody and the ligand heregulin inhibit tumor growth, we have investigated several signaling proteins and pathways. We report here that anti-p185HER2 monoclonal antibody ID5 induced tyrosine phosphorylation of HER2 in SKBr3 breast cancer cells that overexpress p185HER2. Heregulin beta1 induced phosphorylation of both HER3 and HER2. ID5 produced a greater association of phospholipase C (PLC)-gamma1 with HER2 than did heregulin. Concordantly, ID5, but not heregulin, increased PLC-gamma1 activity. However, the G1 cell cycle arrest and induction of p27Kip1 produced by ID5 were not affected by the inhibition of PLC-gamma. ID5 preferentially induced binding of the Mr 46,000 isoform of SHC to HER2, whereas heregulin preferentially induced binding of the Mr 52,00 isoform of SHC to HER3. Heregulin, but not ID5, induced the p85 subunit of phosphatidylinositol 3'-kinase (PI3-K) to interact with HER3. Heregulin induced sustained activation of P13-K signaling, whereas ID5 had only a transient effect. Heregulin, but not ID5, activated the c-Jun-NH2-terminal kinase cascade. Pretreatment of SKBr3 cells with ID5 decreased heregulin-induced association of HER2 with HER3 as well as the activation of c-Jun-NH2-terminal kinase and PI3-K activities. Inhibition of the mitogen-activated protein kinase pathway in SKBr3 cells did not affect heregulin-induced G2-M-phase arrest, apoptosis, and differentiation. Heregulin-induced apoptosis could be blocked by inhibition of p70s6k, but not by inhibition of PI3-K. Heregulin-induced differentiation could be eliminated by inhibition of PI3-K. We conclude that ID5 and heregulin signal via different pathways, although both agents can inhibit the clonogenic growth of cells that overexpress HER2.

Anti-HER2 antibody and heregulin suppress growth of HER2-overexpressing human breast cancer cells through different mechanisms

Previous reports have shown that certain anti-HER2 antibodies and heregulin can inhibit clonogenic growth of breast and ovarian cancers that overexpress HER2. Anti-HER2 antibodies bind to HER2 directly, whereas heregulin does not bind to HER2 alone, but rather interacts with HER2 through the formation of heterodimers with HER3 or HER4. The purpose of the present study was to elucidate the mechanisms by which anti-HER2 antibody and heregulin inhibit tumor growth. The anti-HER2 monoclonal antibody (mAb) ID5 was found to block G1-S progression of the cell cycle, whereas heregulin inhibited passage through G2-M. Compatible with the effects on the cell cycle, treatment with mAb ID5 decreased levels of cyclin-dependent kinase (CDK) 2, cyclin E, and CDK6 proteins and reduced cyclin E-CDK2-associated kinase activity; mAb HD5-treated cells had increased p27Kip1 expression and an increased association of p27Kip1 with CDK2. In contrast, treatment with heregulin increased protein levels of CDK2, CDK6, CDC2, and cyclin B1. More Retinoblastoma protein was found in the hypophosphorylated state in the cells treated with mAb ID5, whereas more retinoblastoma protein was in the hyperphosphorylated state in heregulin-treated cells. Heregulin was able to induce cell differentiation as assessed by Oil Red O staining and apoptosis as assessed by sub-G1 peak on flow cytometry and the presence of DNA fragmentation in ApopTag histochemistry staining. Neither differentiation nor apoptosis was observed in the cells treated with mAb ID5. We conclude that anti-HER-2 mAb ID5 and heregulin exert growth inhibition through different mechanisms. In mammary cells overexpressing HER2, anti-HER2 mAb ID5 induces G1 arrest, whereas heregulin induces G2-M arrest, cell differentiation, and apoptosis.

The outcome of heregulin-induced activation of ovarian cancer cells depends on the relative levels of HER-2 and HER-3 expression

Members of the epidermal growth factor receptor family of tyrosine kinases, including epidermal growth factor receptor, c-erbB-2 (HER-2), c-erbB-3 (HER-3), and c-erbB-4 (HER-4), can be coexpressed at different levels in nonhematopoietic tissues. Amplification and overexpression of HER-2 is found in approximately one-third of cancers that arise in the breast and ovary. In our previous studies, heregulin (HRG) and anti-HER-2 antibodies inhibited proliferation, increased invasiveness, and enhanced tyrosine autophosphorylation of SKBr3 breast cancer cells that overexpressed HER-2. In the present report, the effects of HRG and anti-HER-2 antibody have been compared in six ovarian cancer cell lines. HRG inhibited anchorage-independent growth of SKOv3 cells that overexpressed HER-2 (10(5) receptors/cell) but stimulated the growth of OVCA420, OVCA429, OVCA432, OVCA433, and OVCAR-3 cells that expressed lower levels of the receptor (10(4) receptors/cell). Thus, cell lines with a high level of HER-2 relative to HER-3 or HER-4 were growth inhibited, whereas cell lines with lower levels of HER-2 were growth stimulated by HRG. Stimulation or inhibition of clonogenic growth did not correlate with endogenous expression of HRG or with the impact of exogenous HRG on phosphorylation of HER-2, HER-3, or HER-4. Anti-HER-2 antibodies inhibited the growth of SKOv3 cells but failed to affect the growth of the other cell lines. In OVCAR-3 cells that had been transfected with HER-2 cDNA to increase expression to 10(5) receptors/cell, HRG inhibited rather than stimulated growth. Conversely, when HER-2 expression by SKOv3 cells was downregulated by transfection of the viral E1A gene, HRG stimulated rather than inhibited growth. To evaluate the relative importance of HER-3 and HER-4, NIH 3T3 cells were cotransfected with HER-2 and HER-3 or with HER-2 and HER-4. HRG inhibited the growth of cells with a high ratio of HER-2:HER-3, whereas HRG stimulated the growth of cells with low levels of the two receptors. In cells that express only HER-2 and HER-4, HRG stimulated the growth of cells that expressed HER-4 independent of HER-2 levels. Anti-HER-2 antibodies inhibited the growth of transfectants with high levels of HER-2 expression independent of HER-3 or HER-4 expression. In ovarian cancer cells that express all three receptors, the relative levels of HER-2 and HER-3 appear to determine the response to HRG. Taken together, these studies support the concept that the level of HER-2 expression can modulate response to HRG, determining whether the response is stimulatory or inhibitory. In contrast, agonistic antibodies that bind to HER-2 alone inhibit anchorage-independent growth but fail to mimic HRG's ability to stimulate growth of cells with low HER-2: HER-3 ratios.

Regulation of AML2/CBFA3 in hematopoietic cells through the retinoic acid receptor alpha-dependent signaling pathway

AML2 is a member of the acute myelogenous leukemia, AML family of transcription factors. The biologic functions of AML1 and AML3 have been well characterized; however, the functional role of AML2 remains unknown. In this study, we found that AML2 protein expressed predominantly in cells of hematopoietic origin is a nuclear serine phosphoprotein associated with the nuclear matrix, and its expression is not cell cycle-related. In HL-60 cells AML2 expression can be induced by all three natural retinoids, all-trans-retinoic acid (RA), 13-cis-RA, and 9-cis-RA in a dose-dependent manner. A synthetic retinoic acid derivative, 4HPR, which neither activates RA receptor (RAR) alpha nor retinoic X receptor alpha was unable to induce the expression of AML2. A RAR-selective activator, TTNPB, induced AML2 expression similar to RA. Our study further showed that AGN193109, a potent RARalpha antagonist, suppressed AML2 expression induced by RA and that a retinoic X receptor pan agonist AGN194204 had no effect on its expression. Taken together, these studies conclusively demonstrated that the expression of AML2 in HL-60 cells is regulated through the RARalpha-specific signaling pathway. Our study further showed that after all-trans-retinoic acid priming, AML2 expression could be augmented by vitamin D(3). Based on these studies we hypothesize that AML2 expression is normally regulated by retinoid/vitamin D nuclear receptors mainly through the RARalpha-dependent signaling pathway and that it may play a role in hematopoietic cell differentiation.

Recombinant PML adenovirus suppresses growth and tumorigenicity of human breast cancer cells by inducing G1 cell cycle arrest and apoptosis

Our previous studies demonstrated that the promyelocytic leukemia gene, PML which involved in the 15;17 translocation in acute promyelocytic leukemia (APL) is a growth and transformation suppressor. In this study, recombinant PML adenovirus, Ad-PML was constructed and used to infect human breast cancer cells in vitro and in vivo, the anti-oncogenic function of PML and its mechanism of growth suppressing effect in breast cancer cells were examined. We showed that Ad-PML effectively infected the MCF-7 and SK-BR-3 cells. A high level of PML protein was expressed within 24 h post-infection and a detectable level remained at day 16. Ad-PML significantly suppressed the growth rate, clonogenicity, and tumorigenicity of breast cancer cells. Intratumoral injections of MCF-7-induced tumors by high titer Ad-PML suppressed tumor growth in nude mice by about 80%. The injection sites expressed high level of PML and associated with a massive apoptotic cell death. To elucidate the molecular mechanism of PML's growth suppressing function, we examined the effect of Ad-PML on cell cycle distribution in MCF-7 and SK-BR-3 cells. We found that Ad-PML infection caused a cell cycle arrest at the G1 phase. We further showed that G1 arrest of MCF-7 cells is associated with a significant decrease in cyclin D1 and CDK2. An increased expression of p53, p21 and cyclin E was found. The Rb protein became predominantly hypophosphorylated 48 h post-infection. These findings indicate that PML exerts its growth suppressing effects by modulating several key G1 regulatory proteins. Our study provides important insight into the mechanism of tumor suppressing function of PML and suggests a potential application of Ad-PML in human cancer gene therapy.

Characterization of the ETO and AML1-ETO proteins involved in 8;21 translocation in acute myelogenous leukemia

The AML1 and ETO genes are disrupted by the nonrandom chromosomal translocation t(8;21) in acute myelogenous leukemia (AML). While the AML1 gene encodes a transcription factor indispensable for definitive hematopoiesis, the biological function of ETO is unknown. To understand the role of ETO and AML1-ETO in the pathogenesis of AML, the full length cDNAs of ETO and AML1-ETO were cloned and antibodies against AML1 and ETO proteins have been developed in our laboratory. Western blot analysis showed that ETO and AML1-ETO were identified as 70 kDa and 94 kDa proteins, respectively, and that both proteins, like AML1, were associated with the nuclear matrix. To examine whether the t(8;21)-positive AMLs expressed a 94-kDa AML1-ETO, protein fractions isolated from leukemia blasts of 10 patients with t(8;21)-positive AML and the Kasumi-1 cells were analyzed by Western blotting. The 94 kDa AML1-ETO fusion protein was detected in all samples. However, this fusion protein was not detectable in all 40 patients with t(8;21)-negative AMLs. The biological significance of AML1-ETO was examined in K562 cells, which stably overexpress AML1-ETO. We found that AML1-ETO blocked the erythroid differentiation of K562 cells induced by low doses of Ara-C. Thus, t(8;21)-positive AMLs appear to overexpress the AML1-ETO fusion protein, which may be responsible for differentiation block and leukemogenesis in AML.

Stable overexpression of PML alters regulation of cell cycle progression in HeLa cells

Our previous studies demonstrated that PML is a growth suppressor that suppresses oncogenic transformation of NIH/3T3 cells and rat embryo fibroblasts. PML is a nuclear matrix-associated phosphoprotein whose expression is regulated during the cell cycle. Disruption of PML function by t(15;17) in acute promyelocytic leukemia (APL) plays a critical role in leukemogenesis. To further study the role of PML in the control of cell growth, we have stably overexpressed PML protein in the HeLa cell line. This overexpression of PML significantly reduced the growth rate of HeLa cells and suppressed anchorage-independent growth in soft agar. We consequently investigated several parameters correlated with cell growth and cell cycle progression. We found that, in comparison with the parental HeLa cells, HeLa/PML stable clones showed proportionally more cells in G1 phase, fewer cells in S phase and about the same number in G2/M phase. The HeLa/PML clones showed a significantly longer doubling time as a result of a lengthening of the G1 phase. No effect on apoptosis was found in HeLa cells overexpressing PML. This observation indicates that PML suppresses cell growth by increasing cell cycle duration as a result of G1 elongation. To further understand the mechanism of the effect of PML on HeLa cells, expression of cell cycle-related proteins in HeLa/PML and parental HeLa cells was analyzed. We found that Rb phosphorylation was significantly reduced in PML stable clones. Expression of cyclin E, Cdk2 and p27 proteins was also significantly reduced. These studies indicate that PML affects cell cycle progression by mediating expression of several key proteins that normally control cell cycle progression. These results further extend our current understanding of PML function in human cells and its important role in cell cycle regulation.