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Phase I Study of MGCD0103 Given As a Three-Times-Per-Week Oral Dose in Patients With Advanced Solid Tumors

Lillian L. Siu, Roberto Pili, Ignacio Duran, Wells A. Messersmith, Eric X. Chen, Rana Sullivan, Martha MacLean, Serina King, Shirley Brown, Gregory K. Reid, Zuomei Li, Ann M. Kalita, Eric J. Laille, Jeffrey M. Besterman, Robert E. Martell, Michael A. Carducci

From the Princess Margaret Hospital, Toronto; MethylGene Inc, Montreal, Canada; Kimmel Cancer Center at Johns Hopkins, Baltimore, MD; and Pharmion Inc, Boulder, CO

Corresponding author: Lillian L. Siu, MD, FRCPC, Division of Medical Oncology and Hematology, Princess Margaret Hospital, University Health Network, 610 University Ave, Ste 5-718, Toronto, Ontario, M5G 2M9, Canada; e-mail: lillian.siu{at}uhn.on.ca

	ABSTRACT

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Purpose MGCD0103 is a novel isotype-selective inhibitor of human histone deaceylases (HDACs) with the potential to regulate aberrant gene expression and restore normal growth control in malignancies.

Patients and Methods A phase I trial of MGCD0103, given as a three-times-per-week oral dose for 2 of every 3 weeks, was performed in patients with advanced solid tumors. Primary end points were safety, tolerability, pharmacokinetics (PK), pharmacodynamic (PD) assessments of HDAC activity, and histone acetylation status in peripheral WBCs.

Results Six dose levels ranging from 12.5 to 56 mg/m²/d were evaluated in 38 patients over 99 cycles (median, 2; range, 1 to 11). The recommended phase II dose was 45 mg/m²/d. Dose-limiting toxicities consisting of fatigue, nausea, vomiting, anorexia, and dehydration were observed in three (27%) of 11 and two (67%) of three patients treated at the 45 and 56 mg/m²/d dose levels, respectively. Disease stabilization for four or more cycles was observed in five (16%) of 32 patients assessable for efficacy. PK analyses demonstrated interpatient variability which was improved by coadministration with low pH beverages. Elimination half-life ranged from 6.7 to 12.2 hours, and no accumulation was observed with repeated dosing. PD evaluations confirmed inhibition of HDAC activity and induction of acetylation of H3 histones in peripheral WBCs from patients by MGCD0103.

Conclusion At doses evaluated, MGCD0103 appears tolerable and exhibits favorable PK and PD profiles with evidence of target inhibition in surrogate tissues.

	INTRODUCTION

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Histone deacetylation is an important epigenetic event implicated in the development and progression of cancer, by regulating the accessibility of DNA for gene expression and transcription. The basic repeating unit of chromatin is the nucleosome, composed of DNA wrapped around a core of histone proteins.¹ Histones of the nucleosome core can be acetylated and deacetylated depending on the opposing activities of enzyme families, histone deacetylases (HDACs), and histone acetyltransferases. Histone acetyltransferases, as transcription coactivators, catalyze the addition of acetyl groups on the -amino group of lysine residues in the N-terminal tails of core histones. Conversely, HDACs, as transcription corepressors, remove the acetyl groups from the acetylated lysines in histones which results in gene silencing.^2,3 In many cancerous tissues, tumor suppressor genes are silenced through the activity of histone deacetylation. HDAC inhibitors represent a structurally diverse group of molecules whose activity can induce growth arrest, differentiation, apoptosis, and autophagocytic cell death of cancer cells.¹

MGCD0103 is a rationally designed, orally available, isotype-specific, benzamide which inhibits HDAC isoforms 1, 2, 3 (class 1), and 11 (class 4), and avoids the class 2 enzymes. MGCD0103 has demonstrated dose-dependent inhibition of neoplastic growth, using an intermittent dosing schedule, in multiple human tumor xenograft models including colon (HCT116, SW48 and Colo205), non–small-cell lung (A549), prostate (DU145), pancreatic (PANC1), and vulval epidermal (A431) cancer models. Preclinical evaluations in beagle dogs revealed no drug-related changes in cardiovascular parameters, and MGCD0103 did not inhibit the human ether-à-go-go related gene (hERG) flux assay (IC₅₀ [median inhibitory concentration] > 50 µM), suggesting minimal QTc prolongation liability.⁴ Pharmacokinetic (PK) data in animal models showed greater oral bioavailability under fasted conditions, and dose-dependent increases in peak concentrations and plasma exposures.

Based on the relevance of HDACs as cancer therapeutic targets, and the favorable preclinical profile of MGCD0103, a phase I trial was conducted in patients with advanced solid tumors. The primary objective was to determine the safety and tolerability. Secondary objectives included the assessments of PK, pharmacodynamic (PD) changes as measured by whole cell HDAC activity and effects on histone H3 acetylation in blood, and preliminary antitumor efficacy.

	PATIENTS AND METHODS

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Patient Eligibility
Patients were eligible if they had a histologically or cytologically documented advanced solid malignancy, refractory to standard therapy or for which no standard therapy existed. Other key eligibility criteria included: age 18 years; Eastern Cooperative Oncology Group performance status 0 to 2; adequate hematologic, hepatic, and renal functions (WBC count 3 x 10⁹/L, absolute neutrophil count 1.5 x 10⁹/L, platelets 100 x 10⁹/L, bilirubin 1.5 mg/dL, AST/ALT 3 times upper limit of normal or 5 x upper limit of normal if documented liver metastases, creatinine 2.0 mg/dL and calculated creatinine clearance > 50 mL/min, and proteinuria < 2+ or 500 mg protein/24 hours if dipstick 2+); and unlimited prior cytotoxic therapy but there must be a 4-week interval between study treatment and any prior radiotherapy or chemotherapy. Patients with primary brain malignancies or meningeal metastases were excluded but those with stable and treated brain metastases were allowed on study.

The institutional review board of both participating centers approved the study, which was conducted in accordance with federal and institutional guidelines.

Study Design and Patient Evaluation
This was a two-center, single-agent, open-label, phase I study in which MGCD0103 was administered orally with the requirement of fasting for a minimum of 3 hours before and for 0.5 hours after dosing. Study drug was administered on days 1, 3, 5, 8, 10, and 12 every 21 days. The starting dose of 12.5 mg/m²/d was one tenth of the severely toxic dose to 10% of the rats tested in a 28-day toxicity study (125 mg/m²). Dose escalations occurred in increments of approximately 25% to 50% depending on the toxicity encountered, and the following 6 dose levels were evaluated: 12.5, 20, 27, 36, 45, and 56 mg/m²/d. No intrapatient dose escalation was allowed. Dose escalation followed the standard 3 + 3 rule. The recommended phase II dose (RPTD) was defined as the dose level in which one or fewer of six patients developed dose-limiting toxicity (DLT). Approximately half way through the study, the protocol was amended to evaluate the effect of a low pH beverage (such as soda or carbonated soft drinks) on MGCD0103 solubility instead of water.

Toxicity was graded using the National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0. DLTs were defined as adverse events occurring during the first cycle of MGCD0103 administration and fulfilling one of the following criteria: absolute neutrophil count lower than 0.5 x 10⁹/L for 5 days or longer; febrile neutropenia or grade 3 or higher neutropenic infection; platelets lower than 25 x 10⁹/L or thrombocytopenic bleeding; any nonhematologic toxicity grade 3 or higher except nausea, vomiting, or diarrhea associated with suboptimal premedication and/or management; AST/ALT elevations of grade 3 or higher for longer than 7 days; any toxic effect leading to missing two or more doses per cycle; and any toxic effect resulting in the delay of the subsequent cycle by longer than 7 days. Response was assessed using the Response and Evaluation Criteria in Solid Tumors (Appendix A1, online only).⁵

Dose Modification
Patients who experienced any DLT were delayed by 1-week intervals until recovery and then may have continued on study drug with reduction of MGCD0103 dose by one dose level. If no recovery occurred after a delay of 2 weeks from the next scheduled treatment cycle, patients were to discontinue protocol treatment. In addition, patients were required to have absolute neutrophil count 1 x 10⁹/L and platelets 75 x 10⁹/L for dosing on day 8 of each cycle.

Duration of Study Treatment
Patients with objective response or stable disease were allowed to remain on study until disease progression. Otherwise, study treatment continued until disease progression, unacceptable adverse event, patient's decision to withdraw from the study, or changes in the patient's condition including intercurrent illness rendering the continuation of study treatment unacceptable.

Pharmacokinetic Analysis
Blood samples for evaluation of MGCD0103 PK were collected on cycle 1, day 1, and day 12 before dosing and at 0.5, 1, 1.5, 2, 3, 4, 6, 8, and 24 hours postdose, and on cycle 1, day 4 at 24-hour postdose. Whole blood was collected into a 5-mL sodium heparin Vacutainer tube (Becton Dickinson, Franklin Lakes, NJ) and centrifuged at 3,500 rpm for 10 minutes at 4°C. Plasma was aliquoted and stored at –40°C. Samples were analyzed for MGCD0103 concentrations using a validated high performance liquid chromatograph/mass spectrometry method with a quantitation limit of 0.5 ng/mL (Appendix A2, online only).

Pharmacodynamic Analysis
Whole blood samples for PD evaluations were collected in 10-mL sodium heparin Vacutainer tubes before MGCD0103 dosing on days 1, 3, and 8 of cycle 1, as well as on days 1 and 8 of cycles 2 and 4, and at the end of study. Post-treatment samples were collected at 4 and 20 to 24 hours postdose on day 1 and 24 hours postdose on day 10 (designated as day 11 draw) of cycle 1. Blood samples were shipped at room temperature the day of the PD sample draw in order to arrive for processing within 24 hours of collection. Peripheral WBCs were purified from erythrocytes by treatment with EL lysis buffer (Qiagen, Mississauga, Ontario, Canada), washed, resuspended in RPMI-1640 with 10% fetal bovine serum, and aliquoted for PD analysis assays (whole cell HDAC activity and histone H3 acetylation). Details for whole cell enzyme assay, histone and nuclear extract lysate extraction, measurement of histone H3 acetylation by fluorescence-activated cell sorting or by enzyme-linked immunosorbent assay (ELISA), and serum interleukin-6 (IL-6) expression levels by ELISA, are described in online-only Appendix A3.

	RESULTS

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Patient Demographics and Dose Escalation and Recommended Phase II Dose
Thirty-eight patients were enrolled onto this study (Table 1) and completed a total of 99 cycles of MGCD0103 (median, 2; range, 1 to 11). Six dose levels ranging from 12.5 to 56 mg/m²/d were evaluated (Table 2). Some dose levels accrued more than 6 patients, based on the protocol amendment to obtain PK data on MGCD0103 administered with a low-pH beverage. At each of the 20, 27, and 36 mg/m²/d dose levels, dose-limiting grade 3 fatigue was seen in one of six to nine patients. For dose levels 45 and 56 mg/m²/d, DLTs consisting of grade 3 fatigue, nausea, vomiting, anorexia, and dehydration were seen in three (27%) of 11 and two (67%) of three patients, respectively. Asymptomatic grade 3 QTc prolongation was seen in one patient at 45 mg/m²/d, this was unlikely related to study drug as this patient had a borderline pretreatment QTc interval. In addition, asymptomatic and possibly related grade 3 hypophosphatemia was seen in one patient at 45 mg/m²/d, which corrected with phosphate replacement. Based on these findings, the RPTD for MGCD0103 was 45 mg/m²/d when given three times per week for 2 of every 3 weeks.

View this table: [in this window] [in a new window]   Table 3. Adverse Events of Grades 3 and All Cycles, Separated by Dose Levels of MGCD0103

Antitumor Activity
Thirty-two of 38 patients were assessable for response. No objective tumor responses were observed. Five patients (15.6%) with previously progressive colorectal (four cycles), renal cell (four, five, and 11 cycles), and lung (7 cycles) cancers had stable disease for four or more cycles.

Pharmacokinetic Analysis
Based on each patient's body-surface area, the actual dose of MGCD0103 was calculated and then used to determine the amount of water or low pH beverage for coadministration. MGCD0103 was administered with either 100 mL of water with actual doses of 20 to 40 mg of study drug, or 200 mL of water with actual doses of 46 to 66 mg, or 200 mL of low pH beverage with actual doses of 52 to 150 mg. For cycle 1, days 1 and 12, 38, and 14 patients had complete concentration profiles (up to 24 hours), respectively, and these are depicted in Figures A1A and A1B (online only). On both days, for all dose levels, mean maximum concentrations occurred at 0.5 to 1.0 hour postdose, declined biphasically thereafter, and remained detectable at 24 hours.

Mean MGCD0103 PK parameters are presented in Table 4, and individual C_max and AUC_0-24 hour values are plotted in Figures 1A and 1B, respectively. A large interpatient variability was observed, especially in the groups that received the dose with water. Following actual doses ranging from 20 to 66 mg, administered with 100 or 200 mL of water, C_max and AUC_0-24 hour values were not dose-dependent and appeared to remain within the same range of values. However, when administered with 200 mL of a low pH beverage, C_max and AUC_0-24 hours increased proportionately with actual doses between 52 and 150 mg. Median T_max for all groups on both PK days ranged from 0.5 to 1.1 hours, except for the 12.5 mg/m²/d group (3.0 hours). Elimination terminal half-life (t) ranged from 6.7 to 12.2 hours across the entire dose range. No signs of accumulation after multiple dose administration were observed.

View larger version (14K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 1. (A) Individual Cmax values versus dose of MGCD0103. (B) Individual AUC0-24 hours values versus dose of MGCD0103.

View larger version (14K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 2. (A) Histone deacetylase (HDAC) inhibition versus dose and (B) induction of histone H3 acetylation versus dose in peripheral white cells from patients 24-hours post-initial dose of MGCD0103. Correlation of HDAC inhibition (24 hours) versus (C) Cmax and (D) area under the curve (AUC) at day 1 is shown.

	DISCUSSION

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In this patient population, 45 mg/m²/d was the RPTD of MGCD0103 when given on a schedule of three times per week for 2 of every 3 weeks. Subsequent studies of MGCD0103 have used fixed dose dosing, and the RPTD of 45 mg/m²/d would be considered equivalent to 85 to 90 mg of fixed dose. Fatigue was the most common DLT in this study, with other limiting toxicities being nausea, vomiting, anorexia, and dehydration. These toxicities are consistent with class effects observed with other HDAC inhibitors in clinical development.^6-10 The etiology of fatigue induced by HDAC inhibitors is poorly understood. Circulating levels of certain cytokines such as IL-6 have been shown to positively correlate with fatigue in cancer patients.¹¹ In our study, some patients treated at higher doses of MGCD0103 had significant elevations of their IL-6 levels, but no clear correlation with grade 3 fatigue was found. Detailed studies are warranted to further investigate whether serum IL-6 release is related to HDAC inhibition.

Despite the lack of objective tumor responses in this phase I trial, the PK and PD evaluations have demonstrated several favorable pharmacologic properties of MGCD0103. The elimination t of MGCD0103 is about 10 hours at the RPTD of 45 mg/m²/d, which compares positively against the shorter, 1- to 2-hour half-lives of some of the other HDAC inhibitors such as vorinostat and PXD101.^7,12 Furthermore, the PD assays performed in our study revealed that MGCD0103 exerts dose-dependent HDAC inhibitory activity and is able to induce histone acetylation in peripheral WBCs, as a proof of activity on its putative targets using surrogate tissues. Enzyme inhibition readout appeared to be more sensitive than histone acetylation assay to monitor the PD effect, as we did not observe significant induction of histone acetylation at the RPTD. The HDAC enzyme inhibition by MGCD0103 appeared to be sustained, since on day 8 (72 hours after the first three doses) we still observed significant enzyme inhibition at groups treated at RPTD or higher (data not shown). These pharmacologic properties suggest that MGCD0103 may be given with longer rest intervals of up to 72 hours between dosing, such as using a twice-weekly schedule, whereby dose-limiting fatigue may be reduced or ameliorated. In fact, the twice-weekly dosing schedule for MGCD0103 for 3 consecutive weeks, with no recovery period between cycles, has been examined in patients with advanced leukemia or myelodysplastic syndrome, with an RPTD of 66 mg/m²/d.¹³ In addition to laboratory-based PD assays, because HDAC inhibitors may have antiangiogenic properties, vascular functional imaging tools such as dynamic contrast-enhanced magnetic resonance imaging or ultrasound should be considered as noninvasive methods of PD evaluations in future studies.^14-16

The isoform specificity of MGCD0103 has theoretical attributes in comparison to nonspecific HDAC inhibitors. The class I HDAC isoforms (1, 2, 3, and 8) are important in regulating the proliferation and survival of cancer cells. Of all HDAC classes, they are considered by some researchers as having the most clinical relevance in anticancer treatment.^17,18 Experimental evidence illustrating this finding includes the following: HDAC1 knockout in mice resulted in embryonic lethality¹⁹; HDAC2 knockdown by small interfering RNA in HT29 colonic cancer cells resulted in apoptosis²⁰; and small interfering RNA knockdown of HDACs 1 and 3 (class I), but not of HDACs 4 and 7 (class II), inhibited proliferation in HeLa cells.²¹ Currently, HDAC inhibitors appear to have limited clinical activity as monotherapy in solid tumors, and their anticancer activity in epithelial malignancies may be manifested predominantly through combinational evaluations with cytotoxic or other targeted therapeutics. Meanwhile, the promising activity of HDAC inhibitors in some lymphoproliferative malignancies has corroborated the therapeutic value of targeting histone deacetylation.^22,23 The emergence of isoform-specific HDAC inhibitors, such as MGCD0103, may alter the expression of a more focused, disease-related subset of genes with fewer adverse effects, and thereby optimize the therapeutic index of this class of agents. Ongoing clinical trials of MGCD0103 in combination with cytotoxic agents in solid tumors, such as docetaxel and gemcitabine, with demethylating agents such as azacitidine in hematologic malignancies, and as single-agent in lymphoproliferative disorders will provide further insight into the therapeutic benefit of target specificity.

	AUTHORS' DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

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Although all authors completed the disclosure declaration, the following author(s) indicated a financial or other interest that is relevant to the subject matter under consideration in this article. Certain relationships marked with a "U" are those for which no compensation was received; those relationships marked with a "C" were compensated. For a detailed description of the disclosure categories, or for more information about ASCO's conflict of interest policy, please refer to the Author Disclosure Declaration and the Disclosures of Potential Conflicts of Interest section in Information for Contributors.

Employment or Leadership Position: Gregory K. Reid, MethylGene Inc (C); Zuomei Li, MethylGene Inc (C); Ann M. Kalita, MethylGene Inc (C); Eric J. Laille, Pharmion Inc (C); Jeffrey M. Besterman, MethylGene Inc (C); Robert E. Martell, MethylGene Inc (C) Consultant or Advisory Role: Roberto Pili, Pharmion Inc (C); Michael A. Carducci, MethylGene Inc (C), MGI Pharma Inc (C), Merck (C), Abbott Laboratories (C) Stock Ownership: Zuomei Li, MethylGene Inc; Eric J. Laille, Pharmion Inc; Jeffrey M. Besterman, MethylGene Inc Honoraria: None Research Funding: None Expert Testimony: None Other Remuneration: None

	AUTHOR CONTRIBUTIONS

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION AUTHORS' DISCLOSURES OF... AUTHOR CONTRIBUTIONS Appendix REFERENCES

 
Conception and design: Lillian L. Siu, Gregory K. Reid, Zuomei Li, Jeffrey M. Besterman, Robert E. Martell, Michael A. Carducci

Financial support: Gregory K. Reid, Jeffrey M. Besterman, Robert E. Martell

Administrative support: Gregory K. Reid, Jeffrey M. Besterman

Provision of study materials or patients: Lillian L. Siu, Roberto Pili, Ignacio Duran, Wells A. Messersmith, Eric X. Chen, Gregory K. Reid, Jeffrey M. Besterman, Robert E. Martell, Michael A. Carducci

Collection and assembly of data: Roberto Pili, Wells A. Messersmith, Eric X. Chen, Rana Sullivan, Martha MacLean, Serina King, Shirley Brown, Zuomei Li, Ann M. Kalita, Robert E. Martell, Michael A. Carducci

Data analysis and interpretation: Lillian L. Siu, Gregory K. Reid, Zuomei Li, Ann M. Kalita, Eric J. Laille, Robert E. Martell, Michael A. Carducci

Manuscript writing: Lillian L. Siu, Gregory K. Reid, Zuomei Li, Eric J. Laille, Robert E. Martell, Michael A. Carducci

Final approval of manuscript: Lillian L. Siu, Roberto Pili, Ignacio Duran, Wells A. Messersmith, Eric X. Chen, Rana Sullivan, Martha MacLean, Serina King, Shirley Brown, Gregory K. Reid, Zuomei Li, Ann M. Kalita, Eric J. Laille, Jeffrey M. Besterman, Robert E. Martell, Michael A. Carducci

	Appendix

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Appendix A1
Pretreatment evaluations were performed within 14 days of treatment start and included history and physical examination, hematology, biochemistry, urinalysis, and ECG. During the study, hematology and biochemistry evaluations were repeated weekly to twice weekly for the first two cycles. ECGs were done predose on day 1 of cycles one and two, and repeated at 1-hour postdose on day 1 of cycle 1. Baseline radiologic investigations were performed within 28 days of study start, and then repeated every two cycles.

View larger version (48K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig A1. (A) Day 1 mean plasma concentration-time profiles of MGCD0103 on linear (upper panel) and semi-log (lower panel) scales. (B [next page]) Day 12 mean plasma concentration-time profiles of MGCD0103 on linear (upper panel) and semi-log (lower panel) scales. bev, beverage.

Appendix A2
Pharmacokinetic (PK) parameters were derived using noncompartmental methods with WINNonlin (Scientific Consultant, Apex, NC) Professional (Pharsight Corp, Mountain View, CA). The following PK parameters were determined and compared across treatments: peak plasma concentration C_max (ng/mL), time to maximum concentration T_max(hr), area under the plasma-concentration-time curve (AUC_0-24 hours; hr*ng/mL), and plasma half-life t (hr). MGCD0103 plasma concentrations and PK parameters were summarized using descriptive statistics.

Appendix A3
Peripheral white cell isolation. Whole blood was collected in sodium heparin Vacutainer tubes (BD Biosciences, Mississauga, Ontario, Canada) and shipped at room temperature to arrive at the pharmacodynamic laboratory within 24 hours. Buffy coat cells were separated from erythrocytes by centrifugation at 1,850 rpm for 5 minutes, and further purified by treatment with five volumes of EL lysis buffer (Qiagen, Mississauga, Ontario, Canada) for 15 minutes on ice and centrifugation at 1,500 rpm for 10 minutes at 4°C. These peripheral white cells were then washed once with EL buffer and resuspended in RPMI-1640 with 10% fetal bovine serum.

Whole cell histone deaceylases enzyme assay. Isolated peripheral white cells were seeded in 50 µL in 96-well culture plates (Corning Inc, CoStar, Lowell, MA) at a density of 8 x 10⁵ cells. The reaction was initiated by adding 0.3 mmol/L Boc-Lys(-Ac)-AMC (Bachem, Torrance, CA). Cells were incubated with the substrate for 1 hour at 37°C with 5% CO₂. The reaction was then stopped by adding 50 µL of buffer (25 mmol/L Tris-Cl pH 8.0, 137 mmol/L NaCl, 2.7 mmol/L KCl, 1 mmol/L MgCl₂) containing 1 µmol/L TSA (BioMol, Plymouth Meeting, PA), 1:60 diluted Fluor-de-Lys-Developer (BioMol), and 1% NP40 (Sigma-Aldrich Canada, Oakville, Ontario, Canada). The reaction was allowed to develop for 15 minutes at 37°C, and the fluorescent signal was detected by fluorometer (GeminiXS, Molecular Devices, Sunnyvale, CA) at excitation 360 nm, emission 470 nm, and cutoff 435 nm. A standard curve of Boc-Lys-AMC (Bachem) allowed the conversion of fluorescent signal into µM of deacetylated product.

Histone and nuclear lysate extraction. Isolated peripheral white cells were lysed in buffer A (10 mmol/L Tris-HCl pH 8.0, 1.5 mmol/L MgCl₂, 5 mmol/L KCl, 0.5% NP-40, protease inhibitors, and sodium butyrate). After centrifugation at 350 x g for 15 minutes, the nuclear pellet was washed in buffer A. For histone extraction, nuclear pellet was resuspended in cold water. Nonhistone proteins were precipitated with 3.3% H₂SO₄ for 1 hour, then cleared by centrifugation. Acid soluble proteins were recovered by overnight acetone precipitation and resuspended in water. For nuclear lysate extraction, the nuclear pellet was lysed in nuclear lysis buffer (50 mmol/L HEPES pH7.5, 500 mmol/L NaCl, 1% NP-40, 1 mmol/L EDTA, 10% glycerol, protease inhibitors, and sodium butyrate). Samples were sonicated, centrifuged, and the nuclear lysate was collected. Protein concentrations were determined using Bradford protein assay reagent (BioRad, Hercules, CA).

Histone H3 acetylation by fluorescence-activated cell sorting. Isolated peripheral white cells were fixed in paraformaldehyde at room temperature and washed in 1 x phosphate-buffered saline (PBS) before cell membranes were solubilized by incubation in a saponin/1 x PBS solution. Cells were labeled with rabbit antiacetyl-H3 (Upstate, Millipore, Billerica, MA) and with an antirabbit-FITC (Santa Cruz Biotechnology Inc, Santa Cruz, CA) detection antibody. Cells were then washed before analysis by FACScan (BD Biosciences, Mississauga, Ontario, Canada).

Histone H3 acetylation by sandwich enzyme-linked immunosorbent assay. Histone acetylation was analyzed using either purified histones or using nuclear lysate extracts. For sandwich enzyme-linked immunosorbent assay (ELISA), which determines H3Ac and H3 level separately, flat-bottom black plates (VWR International, Mississauga, Ontario, Canada) were coated with anti-histone antibodies (Chemicon) and blocked with 1% BSA + 0.1% TritonX-100 in PBS. For H3Ac ELISA, 2 µg of purified histones or 5 µg of nuclear lysates were incubated in the plate with rabbit antiacetyl-H3 (Upstate); for total H3 ELISA, 0.5 µg of purified histones were mixed with rabbit anti-H3 (Abcam, Cambridge, MA). For both H3Ac and H3, the detection antibody was HRP-coupled goat antirabbit (Sigma). The HRP substrate Amplex-Red (Molecular Probes, Invitrogen, Burlington, Ontario, Canada) was used according to the manufacturer's instructions. H3Ac level from purified histones was normalized to H3 level, while H3Ac level from nuclear lysates was normalized to total protein content.

Serum interleukin-6 expression level. Plasma from patients was separated and frozen until used. Plasma was thawed and centrifuged again at 2,500 rpm for 10 minutes at 10°C. The plasma level of interleukin-6 (IL-6) was determined by ELISA (eBioscience, San Diego, CA), following the manufacturer's protocol. The IL-6 concentration (pg/mL) in the samples was calculated from a standard curve generated by using standard IL-6 also provided in the kit. All the data was calculated and plotted using Excel (Microsoft Corporation, Redmond, WA). The level of IL-6 after treatment was normalized to the baseline level observed before the initiation of the treatment, and expressed as fold induction.

	ACKNOWLEDGMENTS

 
We thank Laura Pearce and Tracy Ann Patterson for project management; Claire Bonfils and Marja Dubay for analysis of histone acetylation; and Christiane Maroun, PhD, for interleukin-6 ELISA analysis.

	NOTES

 
Presented in part at the 42nd Annual Meeting of the American Society of Clinical Oncology, Atlanta, GA, June 2-6, 2006.

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.

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Submitted September 25, 2007; accepted December 21, 2007.

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