A Phase I, First-in-Human Study of GSK2849330, an Anti-HER3 Monoclonal Antibody, in HER3-Expressing Solid Tumors.

BACKGROUND: GSK2849330, an anti-HER3 monoclonal antibody that blocks HER3/Neuregulin 1 (NRG1) signaling in cancer cells, is engineered for enhanced antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. This phase I, first-in-human, open-label study assessed the safety, pharmacokinetics (PK), pharmacodynamics, and preliminary activity of GSK2849330 in patients with HER3-expressing advanced solid tumors. PATIENTS AND METHODS: Patients with various tumor types were prospectively selected for HER3 expression by immunohistochemistry; a subset was also screened for NRG1 mRNA expression. In the dose-escalation phase, patients received GSK2849330 1.4-30 mg/kg every 2 weeks, or 3 mg/kg or 30 mg/kg weekly, intravenously (IV). In the dose-expansion phase, patients received 30 mg/kg GSK2849330 IV weekly. RESULTS: Twenty-nine patients with HER3-expressing cancers, of whom two expressed NRG1, received GSK2849330 (dose escalation: n = 18, dose expansion: n = 11). GSK2849330 was well tolerated. No dose-limiting toxicities were observed. The highest dose, of 30 mg/kg weekly, expected to provide full target engagement, was selected for dose expansion. Treatment-emergent adverse events (AEs) were mostly grade 1 or 2. The most common AEs were diarrhea (66%), fatigue (62%), and decreased appetite (31%). Dose-proportional plasma exposures were achieved, with evidence of HER3 inhibition in paired tissue biopsies. Of 29 patients, only 1 confirmed partial response, lasting 19 months, was noted in a patient with CD74-NRG1-rearranged non-small cell lung cancer (NSCLC). CONCLUSION: GSK2849330 demonstrated a favorable safety profile, dose-proportional PK, and evidence of target engagement, but limited antitumor activity in HER3-expressing cancers. The exceptional response seen in a patient with CD74-NRG1-rearranged NSCLC suggests further exploration in NRG1-fusion-positive cancers. IMPLICATIONS FOR PRACTICE: This first-in-human study confirms that GSK2849330 is well tolerated. Importantly, across a variety of HER3-expressing advanced tumors, prospective selection by HER3/NRG1 expression alone was insufficient to identify patients who could benefit from treatment with this antibody-dependent cell-mediated cytotoxicity- and complement-dependent cytotoxicity-enhanced anti-HER3 antibody. The only confirmed durable response achieved was in a patient with CD74-NRG1-rearranged lung cancer. This highlights the potential utility of screening for NRG1 fusions prospectively across tumor types to enrich potential responders to anti-HER3 agents in ongoing trials.

Safety, Pharmacokinetics, and Pharmacodynamics of the TLR4 Agonist GSK1795091 in Healthy Individuals: Results from a Randomized, Double-blind, Placebo-controlled, Ascending Dose Study.

PURPOSE: Interest in Toll-like receptor (TLR) agonists for cancer treatment has been renewed after promising preliminary clinical data in combination with checkpoint inhibitors. This first-in-human study assessed the safety, tolerability, and pharmacokinetic (PK) and pharmacodynamic (PD) properties of intravenous GSK1795091, a synthetic TLR4 agonist, in healthy volunteers as a precursor to evaluation in patients with cancer. METHODS: Healthy participants were randomized (1:3; double-blinded manner) to receive placebo or a single intravenous injection of GSK1795091 at doses of 7-100 ng. The primary objective was to evaluate the safety and tolerability of GSK1795091; secondary and exploratory objectives were to characterize GSK1795091 PK and PD properties. FINDINGS: Forty participants received study treatment (10 received placebo and 30 received GSK1795091). Overall, 3 of the 10 participants (30%) who received placebo and 16 of the 30 (53%) who received GSK1795091 experienced ≥1 adverse event (AE). The most common AEs were influenza-like illness, headache, back pain, and increased body temperature. One participant experienced late-occurring AEs (alanine aminotransferase and aspartate aminotransferase increases), considered possibly related to GSK1795091. No serious AEs were reported. GSK1795091 PK properties were characterized by dose proportional increase in exposure. Transient and dose-dependent changes in induced cytokine and chemokine concentrations and immune cell counts were observed 1-4 h after GSK1795091 administration and returned to baseline within 24 h. IMPLICATIONS: Intravenously administered GSK1795091 was acceptably tolerated in healthy volunteers, had favorable PK properties, and stimulated immune cell changes in a dose-dependent manner, providing evidence of target engagement and downstream pharmacology. These results supported the design and initiation of a repeat-dose study of intravenous GSK1795091 in combination with other immunotherapies in patients with advanced cancer. ClinicalTrials.gov identifier: NCT02798978.

Four-factor prothrombin complex concentrate versus plasma for rapid vitamin K antagonist reversal in patients needing urgent surgical or invasive interventions: a phase 3b, open-label, non-inferiority, randomised trial.

BACKGROUND: Rapid reversal of vitamin K antagonist (VKA)-induced anticoagulation is often necessary for patients needing urgent surgical or invasive procedures. The optimum means of VKA reversal has not been established in comparative clinical trials. We compared the efficacy and safety of four-factor prothrombin complex concentrate (4F-PCC) with that of plasma in VKA-treated patients needing urgent surgical or invasive procedures. METHODS: In a multicentre, open-label, phase 3b randomised trial we enrolled patients aged 18 years or older needing rapid VKA reversal before an urgent surgical or invasive procedure. We randomly assigned patients in a 1:1 ratio to receive vitamin K concomitant with a single dose of either 4F-PCC (Beriplex/Kcentra/Confidex; CSL Behring, Marburg, Germany) or plasma, with dosing based on international normalised ratio (INR) and weight. The primary endpoint was effective haemostasis, and the co-primary endpoint was rapid INR reduction (≤1·3 at 0·5 h after infusion end). The analyses were intended to evaluate, in a hierarchical fashion, first non-inferiority (lower limit 95% CI greater than -10% for group difference) for both endpoints, then superiority (lower limit 95% CI >0%) if non-inferiority was achieved. Adverse events and serious adverse events were reported to days 10 and 45, respectively. This trial is registered at ClinicalTrials.gov, number NCT00803101. FINDINGS: 181 patients were randomised (4F-PCC n=90; plasma n=91). The intention-to-treat efficacy population comprised 168 patients (4F-PCC, n=87; plasma, n=81). Effective haemostasis was achieved in 78 (90%) patients in the 4F-PCC group compared with 61 (75%) patients in the plasma group, demonstrating both non-inferiority and superiority of 4F-PCC over plasma (difference 14·3%, 95% CI 2·8-25·8). Rapid INR reduction was achieved in 48 (55%) patients in the 4F-PCC group compared with eight (10%) patients in the plasma group, demonstrating both non-inferiority and superiority of 4F-PCC over plasma (difference 45·3%, 95% CI 31·9-56·4). The safety profile of 4F-PCC was generally similar to that of plasma; 49 (56%) patients receiving 4F-PCC had adverse events compared with 53 (60%) patients receiving plasma. Adverse events of interest were thromboembolic adverse events (six [7%] patients receiving 4F-PCC vs seven [8%] patients receiving plasma), fluid overload or similar cardiac events (three [3%] patients vs 11 [13%] patients), and late bleeding events (three [3%] patients vs four [5%] patients). INTERPRETATION: 4F-PCC is non-inferior and superior to plasma for rapid INR reversal and effective haemostasis in patients needing VKA reversal for urgent surgical or invasive procedures. FUNDING: CSL Behring.

A double-blind, randomized, multiple-dose, parallel-group study to characterize the occurrence of diarrhea following two different dosing regimens of neratinib, an irreversible pan-ErbB receptor tyrosine kinase inhibitor.

PURPOSE: Neratinib, a potent, low-molecular-weight, orally administered, irreversible, pan-ErbB receptor tyrosine kinase inhibitor has antitumor activity in ErbB2 + breast cancer. The objective of this study was to characterize the onset, severity, and duration of diarrhea after administration of neratinib 240 mg once daily (QD) and 120 mg twice daily (BID) for ≤14 days in healthy subjects. METHODS: A randomized, double-blind, parallel-group, inpatient study was conducted in 50 subjects given oral neratinib either 240 mg QD or 120 mg BID with food for ≤14 days. The primary endpoint was the proportion of subjects with diarrhea of at least moderate severity (grade 2; 5-7 loose stools/day). In subjects with grade 2 diarrhea, fecal analytes were determined. Pharmacokinetic profiles were characterized for neratinib on Days 1 and 7. RESULTS: No severe (grade 3) diarrhea was reported. By Day 4, all subjects had grade 1 diarrhea. Grade 2 diarrhea occurred in 11/22 evaluable subjects (50 % [90 % confidence interval (CI): 28-72 %]) in the QD group and 17/23 evaluable subjects (74 % [90 % CI: 52-90 %]) in the BID group (P = 0.130). In fecal analyses, 18 % tested positive for hemoglobin and 46 % revealed fecal lactoferrin. Specimen pH was neutral to slightly alkaline. In pharmacokinetic analyses, Day 1 peak plasma concentration and Day 7 steady-state exposure were higher with the QD regimen than the BID regimen. In an exploratory analysis, ABCG2 genotype showed no correlation with severity or onset of diarrhea. CONCLUSIONS: Incidences and onsets of at least grade 1 and at least grade 2 diarrhea were not improved on BID dosing compared with QD dosing.

A single-dose placebo- and moxifloxacin-controlled study of the effects of temsirolimus on cardiac repolarization in healthy adults.

PURPOSE: Temsirolimus, a selective inhibitor of mammalian target of rapamycin, is an approved treatment for patients with advanced renal cell carcinoma (RCC). This study assessed the effect of intravenous (i.v.) temsirolimus 25 mg, the recommended dose for patients with RCC, on the corrected QT (QTc) interval. METHODS: This 3-period crossover study enrolled healthy subjects. In periods 1 and 2, subjects received i.v. placebo either alone or with open-label oral moxifloxacin. In period 3, subjects received a single dose of temsirolimus 25 mg. The primary statistical objective was to estimate the effect of temsirolimus compared with placebo on change from time-matched baseline QTc at the end of infusion (0.5 h). Assay sensitivity was evaluated by the effect of moxifloxacin on change from time-matched baseline QTc compared with placebo. RESULTS: In total, 58 subjects were enrolled. Temsirolimus had no effect on QTc interval in the primary analysis. At 11 of 12 secondary time points, the upper bound for the temsirolimus QTc 90% confidence intervals for the time-matched change from baseline difference from placebo was <10 ms, with no evidence of QTc trends or relationship to concentrations of temsirolimus or its major metabolite, sirolimus. Moxifloxacin, the positive control, produced a significant increase in the QTc interval compared with placebo 0.5-4 h post-dose (P < 0.0001). No subject had a QTc interval exceeding 450 ms or a change from baseline of >30 ms. CONCLUSIONS: Therapeutic exposure to temsirolimus is not associated with clinically significant changes in QTc intervals in healthy adults.

A phase I ascending single-dose study of the safety, tolerability, and pharmacokinetics of bosutinib (SKI-606) in healthy adult subjects.

PURPOSE: Bosutinib (SKI-606), a dual Src/Abl tyrosine kinase inhibitor, is in clinical development for the treatment of patients with chronic myelogenous leukemia (CML). To support clinical development, we conducted a dose-escalation and food-effect evaluation of safety, tolerability, and pharmacokinetics (PK) of bosutinib in healthy adults. METHODS: This was a randomized, double-blind, placebo-controlled, single-ascending dose, sequential-group study of oral bosutinib. Subjects randomly received bosutinib 200, 400, 600, and 800 mg with food; 200 and 400 mg without food; or placebo. Plasma concentrations were determined by a liquid chromatography-tandem mass spectrometry assay. Non-compartmental PK analyses were performed, and power models assessed dose linearity. RESULTS: Of 55 enrolled subjects, 33 (81%) subjects had adverse events (AEs) after receiving bosutinib. Common AEs included diarrhea (39%), nausea (29%), and headache (22%). Bosutinib 200-600 mg with food was safe and well tolerated. Bosutinib exposures (C (max) and AUC) were linear and dose proportional from 200 to 800 mg with food. Absorption was relatively slow; median time to C (max) was 6 h. Apparent volume of distribution (V (z)/F) was 131-214 L/kg, mean apparent clearance (CL/F) was 2.25-3.81 L/h/kg, and mean terminal elimination half-life (t (1/2)) was 32-39 h. Preliminary food effect assessment showed that exposure to bosutinib increased by ~2.52-fold (P = 0.002) for C (max) and ~2.28-fold (P = 0.002) for AUC when 200 mg bosutinib was administered with food compared with administration under fasting conditions; administration of 400 mg bosutinib with food increased AUC by ~1.5-fold (P = 0.037). Approximately 1% of administered dose was excreted in urine. CONCLUSIONS: Bosutinib 200-600 mg with food was safe and well tolerated. Under fed conditions, bosutinib exposures were linear and dose proportional, and C (max) increased by ~1.5-fold. The t (1/2) supported a once-daily dosing regimen.

A randomized, crossover, placebo- and moxifloxacin-controlled study to evaluate the effects of bosutinib (SKI-606), a dual Src/Abl tyrosine kinase inhibitor, on cardiac repolarization in healthy adult subjects.

Effects of therapeutic and supratherapeutic concentrations of bosutinib, a dual Src/Abl tyrosine kinase inhibitor, on the corrected QT interval (QTc) in 60 healthy adults were assessed, according to ICH-E14 guidelines, in this 2-part, randomized, single-dose, double-blind, crossover, placebo- and open-label moxifloxacin-controlled study. Subjects received placebo, moxifloxacin and bosutinib 500 mg with food (therapeutic) in Part 1. In Part 2, subjects received placebo and bosutinib 500 mg plus ketoconazole (supratherapeutic). ANOVA compared baseline-adjusted QTc for bosutinib with placebo; and bosutinib plus ketoconazole with placebo plus ketoconazole. Primary endpoint was population-specific QT correction (QTcN). Secondary endpoints were Bazett QT correction (QTcB), Fridericia's formula QT correction (QTcF) and individual QT correction (QTcI). Upper bounds for 90% confidence intervals were <10 msec for the mean change in QTcN from placebo at all postdose time points, suggesting that mean therapeutic exposures (C(max) , 114 ng/mL; AUC, 2,330 ng · h/mL) and mean supratherapeutic exposures (C(max) , 326 ng/mL; AUC, 15,200 ng · h/mL) were not associated with QTc changes. Similar results were obtained for QTcB, QTcF and QTcI. No clinically relevant pharmacokinetic/pharmacodynamic relationship was observed between bosutinib concentrations and QTc. No subjects had QTcB, QTcF, QTcI or QTcN >450 msec or change from baseline >30 msec. In summary, therapeutic and supratherapeutic bosutinib exposures are not associated with QTc prolongation in healthy adults.

Pharmacokinetics of oral neratinib during co-administration of ketoconazole in healthy subjects.

AIM: The primary objective was to evaluate the pharmacokinetics of a single dose of neratinib, a potent, low-molecular-weight, orally administered, irreversible pan-ErbB (ErbB-1, -2, -4) receptor tyrosine kinase inhibitor, during co-administration with ketoconazole, a potent CYP3A4 inhibitor. METHODS: This was an open-label, randomized, two-period, crossover study. Fasting healthy adults received a single oral dose of neratinib 240 mg alone and with multiple oral doses of ketoconazole 400 mg. Blood samples were collected up to 72 h after each neratinib dose. Plasma concentration data were analyzed using a noncompartmental method. The least square geometric mean ratios [90% confidence interval (CI)] of C(max) (neratinib+ketoconazole): C(max) (neratinib alone), and AUC(neratinib+ketoconazole): AUC(neratinib alone) were assessed. RESULTS: Twenty-four subjects were enrolled. Compared with neratinib administered alone, co-administration of ketoconazole increased neratinib C(max) by 3.2-fold (90% CI: 2.4, 4.3) and AUC by 4.8-fold (3.6, 6.5). Median t(max) was 6.0 h with both regimens. Ketoconazole decreased mean apparent oral clearance of neratinib from 346 lh(-1) to 87.1 lh(-1) and increased mean elimination half-life from 11.7 h to 18.0 h. The incidence of adverse events was comparable between the two regimens (50% neratinib alone, 65% co-administration with ketoconazole). CONCLUSION: Co-administration of neratinib with ketoconazole, a potent CYP3A inhibitor, increased neratinib C(max) by 3.2-fold and AUC by 4.8-fold compared with administration of neratinib alone. These results indicate that neratinib is a substrate of CYP3A and is susceptible to interaction with potent CYP3A inhibitors and, thus, dose adjustments may be needed if neratinib is administered with such compounds.

Effect of ketoconazole on the pharmacokinetics of oral bosutinib in healthy subjects.

Bosutinib (SKI-606), a dual inhibitor of Src and Abl tyrosine kinases, is being developed for the treatment of chronic myelogenous leukemia. The effect of coadministration of ketoconazole on the pharmacokinetic (PK) profile of bosutinib was evaluated in an open-label, randomized, 2-period, crossover study. Healthy subjects (fasting) received a single dose of oral bosutinib 100 mg alone and with multiple once-daily doses of oral ketoconazole 400 mg. PK sampling occurred through 96 hours. The least square geometric mean treatment ratios (90% confidence interval [CI]) of C(max(bosutinib+ketoconazole))/C(max(bosutinib alone)), AUC(T(bosutinib+ketoconazole))/AUC(T(bosutinib alone)), and AUC((bosutinib+ketoconazole))/AUC((bosutinib alone)) were assessed. Compared with bosutinib administered alone, coadministration with ketoconazole increased bosutinib C(max) 5.2-fold, AUC(T) 7.6-fold, and AUC 8.6-fold. Ketoconazole coadministration decreased the mean apparent clearance of bosutinib approximately 9-fold and increased the mean (SD) terminal half-life from 46.2 (16.4) hours to 69.0 (29.1) hours. The incidence of adverse events (AEs) was comparable between the 2 treatments. The most common AEs were headache, nausea, and increased blood creatinine. No safety-related discontinuations or serious AEs occurred. These PK results indicate that bosutinib is susceptible to interaction with potent CYP3A4 inhibitors.

A single-dose, crossover, placebo- and moxifloxacin-controlled study to assess the effects of neratinib (HKI-272) on cardiac repolarization in healthy adult subjects.

PURPOSE: Neratinib is an orally administered, small-molecule, irreversible pan-ErbB inhibitor in development for the treatment of ErbB2-positive breast cancer. This study assessed the effects of therapeutic and supratherapeutic neratinib concentrations on cardiac repolarization, in accordance with current regulatory guidance. EXPERIMENTAL DESIGN: This was a two-part study in healthy subjects. In part 1, subjects were randomized to receive placebo, 400 mg moxifloxacin, or 240 mg neratinib (therapeutic dose) following a high-fat meal. In part 2, after a washout period, subjects received placebo plus 400 mg ketoconazole or 240 mg neratinib plus ketoconazole (supratherapeutic dose). ANOVA was used to compare the baseline-adjusted QTc interval for neratinib with that of placebo (reference), and for neratinib plus ketoconazole with that of placebo plus ketoconazole (reference). Pharmacokinetic/pharmacodynamic analyses and categorical summaries of interval data were done. Assay sensitivity was evaluated by the effect of moxifloxacin on QTc compared with placebo. RESULTS: Sixty healthy subjects were enrolled in this study. The upper bounds of the 90% confidence interval for baseline-adjusted QTcN (population-specific corrected QT) were 450 milliseconds or change from baseline >30 milliseconds. Moxifloxacin produced a significant increase in QTcN compared with placebo (P < 0.05). CONCLUSIONS: Therapeutic and supratherapeutic plasma concentrations of neratinib do not prolong the QTc interval in healthy subjects.

Intravenous temsirolimus in cancer patients: clinical pharmacology and dosing considerations.

Temsirolimus, a highly specific inhibitor of mammalian target of rapamycin (mTOR), is a novel anticancer targeted therapy with a new mechanism of action. The prototype mTOR inhibitor, oral rapamycin, is poorly soluble and undergoes extensive first-pass metabolism, leading to low and potentially variable absorption and exposure. For some tumors, maximizing the bioavailability and dose intensity via intravenous (IV) administration may provide optimal clinical benefit. Temsirolimus is an ester analog of rapamycin that retains its potent intrinsic mTOR inhibitory activity while exhibiting better solubility for IV formulation. In the treatment of advanced renal cell carcinoma, temsirolimus is administered as a 30- to 60-minute IV infusion once weekly at a flat dose of 25 mg. This dosage results in high peak temsirolimus concentrations and limited immunosuppressive activity. Because temsirolimus is active and well tolerated, different dosages and schedules are being explored for other solid and hematologic malignancies, including mantle cell lymphoma. Temsirolimus exhibits a high volume of distribution that, together with IV administration, leads to extensive distribution into peripheral tissues. In addition, significant and protracted exposures are attained with sirolimus (rapamycin), the major equipotent metabolite of temsirolimus. Whereas temsirolimus and sirolimus are both metabolized by cytochrome P450 (CYP) 3A4, drug interaction studies with agents that induce or inhibit CYP3A4 activity indicate that exposure to the sirolimus metabolite is somewhat sensitive to pharmacokinetic (PK) drug interaction. Therefore, temsirolimus dose adjustments are warranted if coadministration cannot be avoided. Despite its complexity, the PK profile of IV temsirolimus is well characterized in cancer patients and provides a strong basis for its future study as a monotherapy or in combination with other anticancer agents.

Disposition of desipramine, a sensitive cytochrome P450 2D6 substrate, when coadministered with intravenous temsirolimus.

PURPOSE: Intravenous (i.v.) temsirolimus, a novel inhibitor of mammalian target of rapamycin (mTOR), is approved for treatment of renal cell carcinoma. In vitro studies with pooled human liver microsomes showed that temsirolimus and its principal metabolite, sirolimus, inhibit the CYP2D6 isozyme (K(i) = 1.5 and 5 microM, respectively), indicating potential for pharmacokinetic interaction with agents that are substrates of CYP2D6. METHODS: This 2-period study in healthy subjects investigated the pharmacokinetics of a single oral 50-mg dose of the CYP2D6 substrate desipramine, first without and subsequently with a single coadministered i.v. 25-mg dose of temsirolimus. RESULTS: The study population consisted of 25 males and 1 female; 10 were black, 12 were white, and 4 were of other races. Plasma and whole blood samples were available from all 26 subjects in period 1 following oral desipramine and from 23 subjects in period 2 following oral desipramine and i.v. temsirolimus coadministration. The 90% confidence intervals for least squares geometric mean ratios of desipramine and 2-hydroxy-desipramine C(max), AUC(T), and AUC were within 80-125%, indicating that parameter differences did not manifest into clinically relevant exposure changes. A single i.v. 25-mg dose of temsirolimus, alone or with desipramine, was well tolerated in healthy subjects. CONCLUSIONS: A single i.v. 25-mg dose of temsirolimus did not alter disposition of desipramine. Temsirolimus i.v. 25 mg may be safely administered with agents metabolized through the CYP2D6 pathway, but vigilance for drug interaction is warranted in patients with advanced malignancies.

Pharmacokinetic profile of temsirolimus with concomitant administration of cytochrome p450-inducing medications.

Temsirolimus is a novel inhibitor of the mammalian target of rapamycin, with antitumor activity in advanced tumors. Because temsirolimus and its metabolite, sirolimus, are cytochrome P450 (CYP) 3A4/5 substrates, the potential exists for interaction with drugs that induce CYP3A activity, including enzyme inducers and rifampin. Cancer patients received once-weekly intravenous (IV) 220 mg/m(2) temsirolimus with or without enzyme inducers. Coadministration with enzyme inducers decreased temsirolimus maximum plasma concentration (C(max)) by 36% and increased volume of distribution by 99%. Sirolimus C(max) and area under the concentration-time curve (AUC) were decreased by 67% and 43%, respectively. In healthy adult subjects, coadministration of 25-mg intravenous temsirolimus with rifampin had no significant effect on temsirolimus C(max) and AUC but decreased sirolimus C(max) and AUC by 65% and 56%, respectively. Rifampin decreased AUC(sum) by 41%. Temsirolimus was well tolerated in both studies. If concomitant agents with CYP3A induction potential are used, higher temsirolimus doses may be needed to achieve adequate tumor tissue drug levels.

HDAC4: a corepressor controlling bone development.

RUNX2 is a transcription factor with a well-characterized role in bone development. In this issue of Cell, Vega and colleagues (Vega et al., 2004) show that HDAC4 interacts with RUNX2 and impacts upon chondrocyte hypertrophy and bone formation.

ETO interacting proteins.

The 8;21 translocation produces a fusion between the ETO gene and that encoding the myeloid transcription factor AML1. The AML1-ETO fusion substitutes the majority of the ETO protein for the coregulator recruitment domains of AML1. Biochemical analyses of ETO have led to the identification of numerous interacting proteins including many corepressors. Importantly, the proteins interacting with ETO are different from those of wild-type AML1, suggesting that altered coregulator recruitment underlies the oncogenic properties of AML1-ETO. The list of corepressors capable of binding ETO includes histone deacetylases (HDACs) and components of distinct HDAC core complexes. These investigations have provided mechanistic insight into corepressor recruitment by ETO and clues to the leukemogenic activity of AML1-ETO.

A chromatin immunoprecipitation screen reveals protein kinase Cbeta as a direct RUNX1 target gene.

RUNX1 (also known as AML1) is a DNA-binding transcription factor that functions as a tumor suppressor and developmental determinant in hematopoietic cells. Target promoters have been identified primarily through the use of differential expression strategies and candidate gene approaches but not biochemical screens. Using a chromatin immunoprecipitation screen, we identified protein kinase Cbeta as a direct RUNX1 target gene and demonstrate that endogenous RUNX1 binds the chromatinized protein kinase Cbeta promoter of U937 cells. A phylogenetically conserved RUNX1-binding site within the PKCbeta promoter binds RUNX1 in electrophoretic mobility shift analyses and confers RUNX1 responsiveness on a heterologous promoter. Changes in RUNX1 activity affect endogenous protein kinase Cbeta expression, and a dominant-negative form of RUNX1 protects U937 cells from apoptotic stimuli previously shown to be dependent on protein kinase Cbeta. This protection can be reversed by the ectopic expression of protein kinase Cbeta. Together these findings demonstrate that protein kinase Cbeta is a direct, downstream target of RUNX1 and links RUNX1 to a myeloid apoptotic pathway.

Cooperative function of Aml1-ETO corepressor recruitment domains in the expansion of primary bone marrow cells.

AML1-ETO is an oncoprotein that can promote self-renewal of primary hematopoietic cells by opposing the activity of AML1. Two domains, Nervy-homology(NH) 2 and NH4, have been implicated in the recruitment of corepressors by AML1-ETO, but the relative roles of NH2 and NH4 vary in different cell lines and have not been examined in nonimmortalized cells. Here, we have used a series of differentiation, proliferation, and self-renewal assays in an effort to determine the roles of the NH domains using progenitor-enriched primary bone marrow cells. In these assays, deletion of NH2 or NH4, individually, has a minimal effect on AML1-ETO function, and the mutants retain the ability to promote long-term expansion of cells. In contrast, the double deletion of NH2 and NH4 eliminates the activity of the fusion protein. Thus, the double deletion of NH2 and NH4 produces a functional deficit greater than the sum of the individual deletions. These findings suggest that the NH2 and NH4 domains function cooperatively in the corepressor environment of primary bone marrow cells.