June 2009

Research Corner

An ESUN Resource

Combining PCI-24781, a Novel Histone Deacetylase Inhibitor, with Chemotherapy for the Treatment of Soft Tissue Sarcoma

Histone deactylase inhibitors (HDACi) are a promising new class of anticancer therapeutics.  However, little is known about HDACi activity in soft tissue sarcomas (STS). The investigators of this study investigated the novel HDACi PCI-24781, alone/in combination with conventional chemotherapy, to determine its potential anti-STS–related effects and the underlying mechanisms involved.  Immunoblotting was used to evaluate the effects of PCI-24781 on histone and nonhistone protein acetylation and expression of potential downstream targets. Cell culture–based assays were utilized to assess the effects of PCI-24781 on STS cell growth, cell cycle progression, apoptosis, and chemosensitivity. Quantitative reverse transcription-PCR, chromatin immunoprecipitation, and reporter assays helped elucidate molecular mechanisms resulting in PCI-24781–induced Rad51 repression. The effect of PCI-24781, alone or with chemotherapy, on tumor and metastatic growth was tested in vivo using human STS xenograft models.  The results were as follows: PCI-24781 exhibited significant anti-STS proliferative activity in vitro, inducing S phase depletion, G2/M cell cycle arrest, and increasing apoptosis. Superior effects were seen when combined with chemotherapy. A PCI-24781–induced reduction in Rad51, a major mediator of DNA double-strand break homologous recombination repair, was shown and may be a mechanism underlying PCI-24781 chemosensitization. The investigators showed that PCI-24781 transcriptionally represses Rad51 through an E2F binding-site on the Rad51 proximal promoter. Although single-agent PCI-24781 had modest effects on STS growth and metastasis, marked inhibition was observed when combined with chemotherapy. The investigators conclude: In light of these findings, this novel molecular-based combination may be applicable to multiple STS histologic subtypes, and potentially merits rigorous evaluation in human STS clinical trials.

 

Prognostic Significance of Tumor Response at the End of Therapy in Group III Rhabdomyosarcoma: A Report From the Children's Oncology Group

Some patients with rhabdomyosarcoma (RMS) achieve less than a complete response (CR) despite receiving all planned therapy. The investigators of this study assessed the impact of best response at the completion of all therapy on patient outcome. They studied 419 clinical group III participants who completed all protocol therapy without developing progressive disease for Intergroup Rhabdomyosarcoma Study (IRS) IV. Response (complete resolution [CR], partial response [PR; 50% decrease], or no response [NR; < 50% decrease and < 25% increase]) was determined by radiographic measurement and categorized by the best response. The results were as follows: At the end of therapy, 341 participants (81%) achieved a best response of CR and 78 (19%) had a best response of PR/NR. Five-year failure-free survival was similar for participants achieving CR (80%) and PR/NR (78%). After adjustment for age, nodal status, primary site, and histology, there was no significant indication of lower risk of failure (hazard ratio [HR], 0.77; 95% CI, 0.46 to 1.27; P = .3) nor death (HR, 0.63; 95% CI, 0.36 to 1.09; P = .1) for CR versus PR/NR participants. Seventeen participants with a best response of PR/NR had surgical procedures; eight (50%) of 16 with available pathology reports had residual viable tumor and only three achieved a complete resection. Resection of residual masses was not associated with improved outcome. The investigators conclude: CR status at the end of protocol therapy in clinical group III participants was not associated with a reduction of disease recurrence and death. Aggressive alternative therapy may not be warranted for RMS patients with a residual mass at the end of planned therapy.

 

Molecular classification of solid tumours: towards pathway-driven therapeutics

The last decade has witnessed unprecedented developments in the genetic and epigenetic analyses of solid tumors. Transcriptional and DNA copy-number studies have improved understanding and classification of solid tumors and highlighted the patterns of genomic aberrations associated with outcome. The identification of altered transcriptional and translational silencing by microRNAs and epigenetic modification by methylation in tumors has showed a layer of additional intricacy to the regulation of gene expression in different tumor types. The advent of massive parallel sequencing has allowed whole cancer genomes to be sequenced with extraordinary speed and accuracy providing insight into the complexity of gene mutations present in solid tumors. Functional genomic studies using RNA interference-screening tools promises to improve the classification of solid tumors by probing the relevance of each gene to tumor phenotype. In this review article, the authors discuss how these studies have contributed to solid tumor classification and why such studies are central to the future of oncology. They suggest that these developments are gradually leading to a change in emphasis of early clinical trials to a therapeutic model guided by the molecular classification of tumors. The investigation of drug efficacy later in development is beginning to rely on patient selection defined by predictive molecular criteria that complement solid tumor classification based on anatomic site.

 

A high proportion of bone marrow T cells with regulatory phenotype (CD4+CD25hiFoxP3+) in Ewing sarcoma patients is associated with metastatic disease

Immunosuppressive CD4+CD25hiFoxP3+ T cells (Treg cells) have been found at increased densities within the tumor microenvironment in many malignancies and interfere with protective antitumor immune responses. Osseous Ewing sarcomas (ESs) are thought to derive from a bone marrow (BM) mesenchymal cell of origin, and microscopic marrow involvement defines a subpopulation of patients at a high risk of relapse. The investigators of this study hypothesized that BM-resident T cells may contribute to a permissive milieu for immune escape of ESs. Using 6-color-flow cytometry, they investigated the pattern of immune cell subset distribution including NK cells,  T cells, central and effector memory CD8+ and CD4+ T cells as well as T cells with regulatory phenotype (Treg cells) in BM obtained at diagnosis from 45 primary or relapsed ES patients treated within standardized protocols. Although patients at relapse had an inverted CD4:CD8 T-cell ratio, neither CD8+ effector/memory T-cell subsets nor Treg cells significantly differed from patients at diagnosis. No significant associations of innate and effector/memory T-cell subpopulations with known risk factors were found, including age, gender, tumor site, primary metastases and histological tumor response. By contrast, Treg cells were found at significantly higher frequencies in patients with primary metastatic disease compared with localized ESs (5.0 vs. 3.3%, p = 0.01). Thus, the investigators believe increased BM Treg cells in patients with metastasized ES may reflect an immune escape mechanism that contributes to the development of metastatic disease. Immunotherapeutic strategies will have to adequately consider the regulatory milieu within areas of Ewing tumor-immune interactions.

 

Trabectedin in myxoid liposarcomas (MLS): a long-term analysis of a single-institution series

Trabectedin has been approved in Europe as second-line therapy for advanced soft tissue sarcomas. A previous analysis showed that myxoid liposarcomas (MLS) are particularly sensitive to the drug. This study reports on the long-term efficacy of trabectedin in a subgroup of that series. Since September 2002, 32 advanced pretreated MLS patients received trabectedin at the study’s center. Data were reviewed focusing on their long-term outcome. The results were as follows: Trabectedin was given as a 24-h continuous infusion every 21 days. A total of 376 and a median of 12 courses per patient (range 2–26; interquartiles range (IQR) 8–15) were delivered. Response rate per RECIST was 50% [95% confidence interval (CI) 32% to 68%], median progression-free survival (PFS) was 17 months (95% CI 13.5–30.1) and median overall survival is still not reached. In 10 patients, therapy was stopped in the absence of any evident disease, mostly after complete surgery of residual lesions. In these 10 patients, at a median follow-up of 25 months, PFS was 28.1 months (95% CI 25.6–36.4) from treatment start. The investigators conclude: These data indicate that the high response rate of MLS to trabectedin translates into prolonged PFS. Surgery of residual metastatic disease is already used quite extensively in metastatic MLS. Trabectedin may give further significance to this kind of surgery.

 

Targeting the mTOR Signaling Network for Cancer Therapy

The serine-threonine kinase mammalian target of rapamycin (mTOR) plays a major role in the regulation of protein translation, cell growth, and metabolism. Alterations of the mTOR signaling pathway are common in cancer, and thus mTOR is being actively pursued as a therapeutic target. Rapamycin and its analogs (rapalogs) have proven effective as anticancer agents in a broad range of preclinical models. Clinical trials using rapalogs have demonstrated important clinical benefits in several cancer types; however, objective response rates achieved with single-agent therapy have been modest. Rapalogs may be more effective in combination with other anticancer agents, including chemotherapy and targeted therapies. It is increasingly apparent that the mTOR signaling network is quite complex, and rapamycin treatment leads to different signaling responses in different cell types. A better understanding of mTOR signaling, the mechanism of action of rapamycin, and the identification of biomarkers of response will lead to more optimal targeting of this pathway for cancer therapy.

 

Optimizing the Treatment of Gastrointestinal Stromal Tumors: The Roles of Tumor Genotyping, Imatinib Blood-level Testing, and New Therapeutic Strategies

Gastrointestinal stromal tumors (GISTs) are the most common soft tissue sarcoma of the gastrointestinal tract. Formerly untreatable, except by surgery, the management of these tumors has been revolutionized by the use of small molecule kinase inhibitors that target the underlying pathogenetic mutant kinases found in the vast majority of cases. Recent studies have suggested that future improvements in therapy may be possible using improved diagnostic testing strategies (tumor mutation testing, imatinib blood-level testing) and development of new drugs that target aberrant signal transduction in GIST cells. In this review article, the authors discuss how the treatment of patients with GIST might be further optimized.

 

The prognostic value of DNA ploidy in a total population of uterine sarcomas

The diagnosis of uterine sarcoma is associated with poor outcome for the patient and there is a need for reliable prognostic markers. Most previous studies on the prognostic value of DNA ploidy include few uterine sarcomas and report conflicting results. The investigators of this study examined the prognostic value of DNA ploidy and its association with clinicopathological parameters and crude survival in a total population of 354 sarcoma. The results were as follows: In univariate analyses, they observed significantly better crude survival for endometrial stromal sarcomas (ESS) and adenosarcoma (AS) patients with diploid as compared with nondiploid tumors, but not for patients with leiomyosarcomas (LMS). In Cox multivariate analyses, DNA ploidy was the only significant predictor of survival for patients with AS. In LMS, mitotic index (MI), tumor size, tumor extent and tumor margins, whereas for ESS, MI, tumor extent and tumor necrosis obtained independent significance of survival. DNA ploidy was a significant predictor of survival for LMS patients in Cox regression analyses when excluding MI. The investigators conclude: DNA ploidy might be useful as a prognostic marker in patients with LMS and AS.

 

Gamma Knife Radiosurgery as a Therapeutic Strategy for Intracranial Sarcomatous Metastases

The purpose of this study was to determine the indication and outcomes for Gamma Knife stereotactic radiosurgery (GKSRS) in the care of patients with intracranial sarcomatous metastases. Data from 21 patients who underwent radiosurgery for 60 sarcomatous intracranial metastases (54 parenchymal and 6 dural-based) were studied. Nine patients had radiosurgery for solitary tumors and 12 for multiple tumors. The primary pathology was metastatic leiomyosarcoma (4 patients), osteosarcoma (3 patients), soft-tissue sarcoma (5 patients), chondrosarcoma (2 patients), alveolar soft part sarcoma (2 patients), and rhabdomyosarcoma, Ewing's sarcoma, liposarcoma, neurofibrosarcoma, and synovial sarcoma (1 patient each). Twenty patients received multimodality management for their primary tumor, and 1 patient had no evidence of systemic disease. The mean tumor volume was 6.2 cm(3) (range, 0.07-40.9 cm(3)), and a median margin dose of 16 Gy was administered. Three patients had progressive intracranial disease despite fractionated whole-brain radiotherapy before SRS. The results were as follows: A local tumor control rate of 88% was achieved (including patients receiving boost, up-front, and salvage SRS). New remote brain metastases developed in 7 patients (33%). The median survival after diagnosis of intracranial metastasis was 16 months, and the 1-year survival rate was 61%. The investigators conclude: Gamma Knife radiosurgery was a well-tolerated and initially effective therapy in the management of patients with sarcomatous intracranial metastases. However, many patients, including those who also received fractionated whole-brain radiotherapy, developed progressive new brain disease.

 

Ewing Sarcoma Fusion Protein EWSR1/FLI1 Interacts with EWSR1 Leading to Mitotic Defects in Zebrafish Embryos and Human Cell Lines

The mechanism whereby the fusion of EWSR1 with the ETS transcription factor FLI1 contributes to malignant transformation in Ewing sarcoma remains unclear. The investigators of this study show that injection of human or zebrafish EWSR1/FLI1 mRNA into developing zebrafish embryos leads to mitotic defects with multipolar and disorganized mitotic spindles. Expression of human EWSR1/FLI1 in HeLa cells also results in mitotic defects, along with mislocalization of Aurora kinase B, a key regulator of mitotic progression. Because these mitotic abnormalities mimic those observed with the knockdown of EWSR1 in zebrafish embryos and HeLa cells, they investigated whether EWSR1/FLI1 interacts with EWSR1 and interferes with its function. EWSR1 coimmunoprecipitates with EWSR1/FLI1, and overexpression of EWSR1 rescues the mitotic defects in EWSR1/FLI1-transfected HeLa cells. This interaction between EWSR1/FLI1 and EWSR1 in Ewing sarcoma may induce mitotic defects leading to genomic instability and subsequent malignant transformation.

 

Therapeutic Guidelines for the Treatment of Bone Metastasis: A Report from the American College of Radiology Appropriateness Criteria Expert Panel on Radiation Oncology

Bone metastases remain a therapeutic challenge because of the diversity of the problems they cause, the relative paucity of data regarding their treatment, and the necessity for management by a multidisciplinary palliative care team. The American College of Radiology convened an Appropriateness Criteria Expert Panel on Radiation Oncology for the treatment of bone metastasis to create representative clinical case scenarios and then rank the appropriate use of treatment modalities as well as the most reasonable radiotherapy dose schema and treatment planning methods. This report presents both the resulting Appropriateness Criteria and the rationale for making these decisions. The treatment recommendations are placed within the larger framework of the role of radiation in palliative care by discussing the efficiency of palliative radiotherapy schedules, cost effectiveness issues, and the need for additional research regarding the proper multidisciplinary care of patients with symptomatic bone metastasis.

 

Expression of insulin-like growth factor 2 in mesenchymal neoplasms

This article discusses the link between the insulin-like growth factor (IGF) and tumor formation and growth.  While the number of specimens studied has been low, there is evidence of "high expression of IGF2, encoding the activating ligand for this system, in gastrointestinal stromal tumors (GISTs) and in synovial sarcomas."     The authors refer to known reports of GIST patients suffering from hypoglycemia, as a result of raised IGF2.  Clinical trials are now underway, using drugs that target the "signaling system" of IGF.  The authors state their purpose as "to survey IGF2 expression at the protein level on a broad number of mesenchymal tumors representing all major diagnostic classes."

The researchers examined tissue microarrays from 1288 cases, using antibody-based staining methods.  From this they found data regarding 51 categories for diagnosing tumors of bone and soft-tissue.  The samples were assessed for "membranous and/or cytoplasmic IFG2 immunoreactivity."  The study reports that high expression of IGF2 was found in "solitary fibrous tumors".  High expressions were also found in:

This knowledge opens another pathway for researchers to investigate as they work towards a therapy directed towards the IGF signaling pathways.  On a sobering note, the authors point out that "Of the 445 GIST cases with clinical information, those with high expression of IGF2 had a significantly worse outcome than those with low or no expression." 

V6N3 ESUN Copyright © 2009 Liddy Shriver Sarcoma Initiative.