Amir Goldkorn

Circulating Tumor Cell Counts Are Prognostic of Overall Survival in SWOG S0421: A Phase III Trial of Docetaxel With or Without Atrasentan for Metastatic Castration-Resistant Prostate Cancer

PURPOSE Circulating tumor cell (CTC) enumeration has not been prospectively validated in standard first-line docetaxel treatment for metastatic castration-resistant prostate cancer. We assessed the prognostic value of CTCs for overall survival (OS) and disease response in S0421, a phase III trial of docetaxel plus prednisone with or without atrasentan. PATIENTS AND METHODS CTCs were enumerated at baseline (day 0) and before cycle two (day 21) using CellSearch. Baseline counts and changes in counts from day 0 to 21 were evaluated for association with OS, prostate-specific antigen (PSA), and RECIST response using Cox regression as well as receiver operator characteristic (ROC) curves, integrated discrimination improvement (IDI) analysis, and regression trees. RESULTS Median day-0 CTC count was five cells per 7.5 mL, and CTCs < versus ≥ five per 7.5 mL were significantly associated with baseline PSA, bone pain, liver disease, hemoglobin, alkaline phosphatase, and subsequent PSA and RECIST response. Median OS was 26 months for < five versus 13 months for ≥ five CTCs per 7.5 mL at day 0 (hazard ratio [HR], 2.74 [adjusting for covariates]). ROC curves had higher areas under the curve for day-0 CTCs than for PSA, and IDI analysis showed that adding day-0 CTCs to baseline PSA and other covariates increased predictive accuracy for survival by 8% to 10%. Regression trees yielded new prognostic subgroups, and rising CTC count from day 0 to 21 was associated with shorter OS (HR, 2.55). CONCLUSION These data validate the prognostic utility of CTC enumeration in a large docetaxel-based prospective cohort. Baseline CTC counts were prognostic, and rising CTCs at 3 weeks heralded significantly worse OS, potentially serving as an early metric to help redirect and optimize therapy in this clinical setting.

Exosome-Mediated Transfer of microRNAs Within the Tumor Microenvironment and Neuroblastoma Resistance to Chemotherapy

BACKGROUND How exosomic microRNAs (miRNAs) contribute to the development of drug resistance in the context of the tumor microenvironment has not been previously described in neuroblastoma (NBL). METHODS Coculture experiments were performed to assess exosomic transfer of miR-21 from NBL cells to human monocytes and miR-155 from human monocytes to NBL cells. Luciferase reporter assays were performed to assess miR-155 targeting of TERF1 in NBL cells. Tumor growth was measured in NBL xenografts treated with Cisplatin and peritumoral exosomic miR-155 (n = 6 mice per group) CD163, miR-155, and TERF1 levels were assessed in 20 NBL primary tissues by Human Exon Arrays and quantitative real-time polymerase chain reaction. Students t test was used to evaluate the differences between treatment groups. All statistical tests were two-sided. RESULTS miR-21 mean fold change (f.c.) was 12.08±0.30 (P < .001) in human monocytes treated with NBL derived exosomes for 48 hours, and miR-155 mean f.c. was 4.51±0.25 (P < .001) in NBL cells cocultured with human monocytes for 48 hours. TERF1 mean luciferase activity in miR-155 transfected NBL cells normalized to scrambled was 0.36 ± 0.05 (P <.001). Mean tumor volumes in Dotap-miR-155 compared with Dotap-scrambled were 322.80±120mm(3) and 76.00±39.3mm(3), P = .002 at day 24, respectively. Patients with high CD163 infiltrating NBLs had statistically significantly higher intratumoral levels of miR-155 (P = .04) and lower levels of TERF1 mRNA (P = .02). CONCLUSIONS These data indicate a unique role of exosomic miR-21 and miR-155 in the cross-talk between NBL cells and human monocytes in the resistance to chemotherapy, through a novel exosomic miR-21/TLR8-NF-кB/exosomic miR-155/TERF1 signaling pathway.

Docetaxel and atrasentan versus docetaxel and placebo for men with advanced castration-resistant prostate cancer (SWOG S0421): A randomised phase 3 trial

BACKGROUND The endothelin pathway has a role in bone metastases, which are characteristic of advanced prostate cancer. Atrasentan, an endothelin receptor antagonist, has shown activity in prostate cancer. We therefore assessed its effect on survival in patients with castration-resistant prostate cancer with bone metastases. METHODS In a double-blind phase 3 trial, men with metastatic castration-resistant prostate cancer, stratified for progression type (prostate-specific antigen or radiological), baseline pain, extraskeletal metastases, and bisphosphonate use, were randomly assigned in a 1:1 ratio to docetaxel (75 mg/m(2) every 21 days, intravenously) with atrasentan (10 mg/day, orally) or placebo for up to 12 cycles and treated until disease progression or unacceptable toxicity. Patients who did not progress on treatment were permitted to continue atrasentan or placebo for up to 52 weeks. Coprimary endpoints were progression-free survival (PFS) and overall survival. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00134056. FINDINGS 498 patients were randomly assigned to the atrasentan group and 496 to the placebo group. The trial was halted early for futility in April, 2011, after a planned interim analysis. Median PFS was 9·2 months (95% CI 8·5-9·9) in the atrasentan group and 9·1 months (8·4-10·2) in the placebo group (hazard ratio 1·02, 0·89-1·16; p=0·81). Median overall survival was 17·8 months (16·4-19·8) in the atrasentan group versus 17·6 months (16·4-20·1) in the placebo group (1·04, 0·90-1·19; p=0·64). 278 (57%) of 492 patients in the atrasentan group had grade 3 and greater toxicity compared with 294 (60%) of 486 in the placebo group (p=0·22). Three deaths in the atrasentan group and seven in the placebo group were judged to be possibly or probably due to protocol treatment. INTERPRETATION Atrasentan, when added to docetaxel, does not improve overall survival or PFS in men with castration-resistant prostate cancer and bone metastases; therefore, single-agent docetaxel should remain as one of the standard treatments. FUNDED National Cancer Institute, Sanofi-Aventis, and Abbott Laboratories.

Cancer Cells Cyclically Lose and Regain Drug-Resistant Highly Tumorigenic Features Characteristic of a Cancer Stem-like Phenotype

Drug resistance and brisk tumor initiation have traditionally been viewed as preexisting phenotypes present in small subpopulations of neoplastic cells sometimes termed cancer stem cells. However, recent work in cancer cell lines has shown that drug-resistant tumor-initiating features can emerge de novo within fractionated subpopulations of cells initially lacking these phenotypes. In the present study, we asked whether such phenotypic plasticity exists broadly in unperturbed cancer cell lines and tumor xenografts growing spontaneously without interventions such as drug selection or fractionation into subpopulations used in prior studies. To address this question, we used side population (SP) analysis combined with fluorescence labeling to identify a drug-resistant highly tumorigenic subpopulation and to track and analyze its interaction with the larger phenotypically negative population over time. Remarkably, we observed that SP size fluctuated in a cyclical manner: first contracting via differentiation into the non-SP (NSP) and then reexpanding via simultaneous direct conversion of numerous NSP cells back to the SP phenotype both in culture and in tumor xenografts. These findings show for the first time that adaptive, cancer-promoting traits such as drug resistance and brisk tumor initiation arise not only as solitary events under selective pressures but also as highly orchestrated transitions occurring concurrently in large numbers of cells even without specifically induced drug selection, ectopic gene expression, or fractionation into subpopulations. This high level of coordinated phenotypic plasticity bears consideration when using cancer cell lines as experimental models and may have significant implications for therapeutic efforts targeting cancer stem cells, which are marked by a drug-resistant tumor-initiating phenotype. Mol Cancer Ther; 10(6); 938–48. ©2011 AACR.

Assembly of mutant-template telomerase RNA into catalytically active telomerase ribonucleoprotein that can act on telomeres is required for apoptosis and cell cycle arrest in human cancer cells.

The telomerase ribonucleoprotein is a promising target for cancer therapy, as it is highly active in many human malignancies. A novel telomerase targeting approach combines short interfering RNA (siRNA) knockdown of endogenous human telomerase RNA (hTer) with expression of a mutant-template hTer (MT-hTer). Such combination MT-hTer/siRNA constructs induce a rapid DNA damage response, telomere uncapping, and inhibition of cell proliferation in a variety of human cancer cell lines. We tested which functional aspects of the protein catalytic component of telomerase [human telomerase reverse transcriptase (hTERT)] are required for these effects using human LOX melanoma cells overexpressing various hTERTs of known properties. Within 3 days of MT-hTer/siRNA introduction, both growth inhibition and DNA damage responses were significantly higher in the setting of wild-type hTERT versus catalytically dead hTERT or mutant hTERT that is catalytically competent but unable to act on telomeres. These effects were not attenuated by siRNA-induced knockdown of the telomeric protein human Rap1 and were additive with knockdown of the telomere-binding protein TRF2. Hence, the effects of MT-hTer/siRNA require a telomerase that is both catalytically competent to polymerize DNA and able to act on telomeres in cells.

Cancer cells acquire a drug resistant, highly tumorigenic, cancer stem-like phenotype through modulation of the PI3K/Akt/β-catenin/CBP pathway

Cancer initiation and progression have been attributed to newly discovered subpopulations of self‐renewing, highly tumorigenic, drug‐resistant tumor cells termed cancer stem cells. Recently, we and others reported a new phenotypic plasticity wherein highly tumorigenic, drug‐resistant cell populations could arise not only from pre‐existing cancer stem‐like populations but also from cancer cells lacking these properties. In the current study, we hypothesized that this newfound phenotypic plasticity may be mediated by PI3K/Akt and Wnt/β‐catenin signaling, pathways previously implicated in carcinogenesis, pluripotency and drug resistance. Using GFP expression, Hoechst dye exclusion and fluorescence activated cell sorting (FACS) of cancer cell lines, we identified and tracked cancer stem‐like side populations (SP) of cancer cells characterized by high tumorigenicity and drug resistance. We found that pharmacological inhibition or genetic depletion of PI3K and AKT markedly reduced the spontaneous conversion of nonside population (NSP) cells into cancer stem‐like SP cells, whereas PI3K/Akt activation conversely enhanced NSP to SP conversion. PI3K/AKT signaling was mediated through downstream phosphorylation of GSK3β, which led to activation and accumulation of β‐catenin. Accordingly, pharmacological or genetic perturbation of GSK3β or β‐catenin dramatically impacted conversion of NSP to SP. Further downstream, β‐catenins effects on NSP‐SP equilibrium were dependent upon its interaction with CBP, a KAT3 family coactivator. These studies provide a mechanistic model wherein PI3K/Akt/β‐catenin/CBP signaling mediates phenotypic plasticity in and out of a drug‐resistant, highly tumorigenic state. Therefore, targeting this pathway has unique potential for overcoming the therapy resistance and disease progression attributed to the cancer stem‐like phenotype.

Perillyl Alcohol for the Treatment of Temozolomide-Resistant Gliomas

Perillyl alcohol (POH) is a monoterpene that has been used orally for the treatment of systemic cancer. However, when used orally significant gastrointestinal side effects and lack of overall efficacy were documented. Recently, in a phase II trial in Brazil for the treatment of temozolomide (TMZ)-resistant malignant gliomas, POH was well tolerated when administered intranasally. The present study explores the effects and mechanisms of POH on TMZ-sensitive and TMZ-resistant glioma cells. In vitro studies showed that POH was cytotoxic to TMZ-resistant as well as TMZ-sensitive glioma cells, and this effect was independent of O6-methylguanine-DNA methyltransferase expression. POH induced cytotoxicity, in part, through the endoplasmic reticulum (ER) stress pathway as shown by the increased expression of glucose-regulated protein-78 (GRP78), activating transcription factor 3, and C/EBP-homologous protein. In addition, POH impeded survival pathways, such as mTOR and Ras. As well, POH reduced the invasive capacity of sensitive and resistant glioma cells. POH alone and/or in combination with other ER stress–inducing cytotoxic drugs (i.e., 2, 5-dimethyl-celecoxib, nelfinavir) further induced apoptosis in TMZ-sensitive and TMZ-resistant glioma cells. To show whether intranasal delivery of POH was effective for the treatment of TMZ-resistant gliomas, animals bearing intracranial tumors were given POH intranasally. Animals treated through intranasal administration of POH exhibited a decrease in tumor growth and an increase in survival. Our data show that POH is an effective anti-glioma cytotoxic agent for TMZ-resistant gliomas when administered intranasally. Mol Cancer Ther; 11(11); 2462–72. ©2012 AACR.

Circulating tumor cells in prostate cancer.

Circulating tumor cells (CTCs) can provide a non-invasive, repeatable snapshot of an individual patient’s tumor. In prostate cancer, CTC enumeration has been extensively studied and validated as a prognostic tool and has received FDA clearance for use in monitoring advanced disease. More recently, CTC analysis has been shifting from enumeration to more sophisticated molecular characterization of captured cells, which serve as a “liquid biopsy” of the tumor, reflecting molecular changes in an individual’s malignancy over time. Here we will review the main CTC studies in advanced and localized prostate cancer, highlighting the important gains as well as the challenges posed by various approaches, and their implications for advancing prostate cancer management.

Circulating tumor cell telomerase activity as a prognostic marker for overall survival in SWOG 0421: A phase III metastatic castration resistant prostate cancer trial

Circulating tumor cells (CTC) are promising biomarkers in metastatic castration resistant prostate cancer (mCRPC), and telomerase activity (TA) is a recognized cancer marker. Therefore, we hypothesized that CTC TA may be prognostic of overall survival (OS) in mCRPC. To test this, we used a novel Parylene‐C slot microfilter to measure live CTC TA in S0421, a phase III SWOG‐led therapeutic trial. Blood samples underwent CTC capture and TA measurement by microfilter, as well as parallel enumeration by CellSearch (Janssen/J&J). Cox regression was used to assess baseline (pre‐treatment) TA versus OS, and recursive partitioning was used to explore potential prognostic subgroups and to generate Kaplan‐Meier (KM) OS curves. Samples were obtained from 263 patients and generated 215 TA measures. In patients with baseline CTC count ≥5 (47% of patients), higher CTC TA was associated with hazard ratio 1.14 (p = 0.001) for OS after adjusting for other clinical covariates including CTC counts and serum PSA at study entry. Recursive partitioning identified new candidate risk groups with KM OS curve separation based on CTC counts and TA. Notably, in men with an intermediate range baseline CTC count (6–54 CTCs/7.5 ml), low versus high CTC TA was associated with median survival of 19 versus 12 months, respectively (p = 0.009). Baseline telomerase activity from CTCs live‐captured on a new slot microfilter is the first CTC‐derived candidate biomarker prognostic of OS in a large patient subgroup in a prospective clinical trial. CTC telomerase activity thus merits further study and validation as a step towards molecular CTC‐based precision cancer management.

Prostate tumor cells with cancer progenitor properties have high telomerase activity and are rapidly killed by telomerase interference

Cancer progenitor cells (CPCs) have been postulated to promote treatment resistance and disease progression in prostate and other malignancies. We investigated whether the enzyme telomerase, which is active in cancer cells and in normal stem cells, plays an important role in CPC which can be exploited to neutralize these cells.