Phase I trial of panobinostat in children with diffuse intrinsic pontine glioma: A report from the Pediatric Brain Tumor Consortium (PBTC-047).

BACKGROUND: Diffuse intrinsic pontine glioma (DIPG) is a lethal childhood cancer with median survival of less than 1 year. Panobinostat is an oral multihistone deacetylase inhibitor with preclinical activity in DIPG models. Study objectives were to determine safety, tolerability, maximum tolerated dose (MTD), toxicity profile, and pharmacokinetics of panobinostat in children with DIPG. PATIENTS AND METHODS: In stratum 1, panobinostat was administered 3 days per week for 3 weeks on, 1 week off to children with progressive DIPG, with dose escalation following a two-stage continual reassessment method. After this MTD was determined, the study was amended to evaluate the MTD in children with nonprogressive DIPG/Diffuse midline glioma (DMG) (stratum 2) on an alternate schedule, 3 days a week every other week in an effort to escalate the dose. RESULTS: For stratum 1, 19 subjects enrolled with 17/19 evaluable for dose-finding. The MTD was 10 mg/m2/dose. Dose-limiting toxicities included thrombocytopenia and neutropenia. Posterior reversible encephalopathy syndrome was reported in 1 patient. For stratum 2, 34 eligible subjects enrolled with 29/34 evaluable for dose finding. The MTD on this schedule was 22 mg/m2/dose. DLTs included thrombocytopenia, neutropenia, neutropenia with grade 4 thrombocytopenia, prolonged intolerable nausea, and increased ALT. CONCLUSIONS: The MTD of panobinostat is 10 mg/m2/dose administered 3 times per week for 3 weeks on/1 week off in children with progressive DIPG/DMG and 22 mg/m2/dose administered 3 times per week for 1 week on/1 week off when administered in a similar population preprogression. The most common toxicity for both schedules was myelosuppression.

Panobinostat penetrates the blood-brain barrier and achieves effective brain concentrations in a murine model.

PURPOSE: Panobinostat, an orally bioavailable pan-HDAC inhibitor, has demonstrated potent activity in multiple malignancies, including pediatric brain tumors such as DIPG, with increased activity against H3K27M mutant cell lines. Given limited evidence regarding the CNS penetration of panobinostat, we sought to characterize its BBB penetration in a murine model. METHODS: Panobinostat 15 mg/kg was administered IV to 12 CD-1 female mice. At specified time points, mice were euthanized, blood samples were collected, and brains were removed. LC-MS was performed to quantify panobinostat concentrations. Cmax and AUC were estimated and correlated with previously published pharmacokinetic analyses and reports of IC-50 values in DIPG cell lines. RESULTS: Mean panobinostat plasma concentrations (ng/mL) were 27.3 ± 2.5 at 1 h, 7.56 ± 1.8 at 2 h, 1.48 ± 0.56 at 4 h, and 2.33 ± 1.18 at 7 h. Mean panobinostat brain concentrations (ng/g) were 60.5 ± 6.1 at 1 h, 42.9 ± 5.4 at 2 h, 33.2 ± 6.1 at 4 h, and 28.1 ± 4.3 at 7 h. Brain-to-plasma ratio at 1 h was 2.22 and the brain to plasma AUC ratio was 2.63. Based on the published human pharmacokinetic data, the anticipated Cmax in humans is expected to be significantly higher than the IC-50 identified in DIPG models. CONCLUSION: It is expected that panobinostat would be effective in CNS tumors where the IC-50 is in the low nanomolar range. Thus, our data demonstrate panobinostat crosses the BBB and achieves concentrations above the IC-50 for DIPG and other brain tumors and should be explored further for clinical efficacy.

Physiologically-based pharmacokinetic model for alectinib, ruxolitinib, and panobinostat in the presence of cancer, renal impairment, and hepatic impairment.

Renal (RIP) and hepatic (HIP) impairments are prevalent conditions in cancer patients. They can cause changes in gastric emptying time, albumin levels, hematocrit, glomerular filtration rate, hepatic functional volume, blood flow rates, and metabolic activity that can modify drug pharmacokinetics. Performing clinical studies in such populations has ethical and practical issues. Using predictive physiologically-based pharmacokinetic (PBPK) models in the evaluation of the PK of alectinib, ruxolitinib, and panobinostat exposures in the presence of cancer, RIP, and HIP can help in using optimal doses with lower toxicity in these populations. Verified PBPK models were customized under scrutiny to account for the pathophysiological changes induced in these diseases. The PBPK model-predicted plasma exposures in patients with different health conditions within average 2-fold error. The PBPK model predicted an area under the curve ratio (AUCR) of 1, and 1.8, for ruxolitinib and panobinostat, respectively, in the presence of severe RIP. On the other hand, the severe HIP was associated with AUCR of 1.4, 2.9, and 1.8 for alectinib, ruxolitinib, and panobinostat, respectively, in agreement with the observed AUCR. Moreover, the PBPK model predicted that alectinib therapeutic cerebrospinal fluid levels are achieved in patients with non-small cell lung cancer, moderate HIP, and severe HIP at 1-, 1.5-, and 1.8-fold that of healthy subjects. The customized PBPK models showed promising ethical alternatives for simulating clinical studies in patients with cancer, RIP, and HIP. More work is needed to quantify other pathophysiological changes induced by simultaneous affliction by cancer and RIP or HIP.

Phase II, Multicenter, Single-Arm, Open-Label Study to Evaluate the Efficacy and Safety of Panobinostat in Combination with Bortezomib and Dexamethasone in Japanese Patients with Relapsed or Relapsed-and-Refractory Multiple Myeloma.

INTRODUCTION: Panobinostat, bortezomib, and dexamethasone combination therapy demonstrated progression-free survival (PFS) benefit over bortezomib and dexamethasone alone in the PANORAMA-1 study in relapsed/refractory multiple myeloma (MM). Here, we present data from a phase II study (NCT02290431) of this combination in Japanese patients with relapsed or relapsed-and-refractory MM. METHODS: Patients received 3-week cycles of 20-mg oral panobinostat (weeks 1 and 2), 1.3-mg/m2 subcutaneous bortezomib (days 1, 4, 8, and 11), and 20-mg oral dexamethasone (day of and the day following bortezomib administration) for a total of 8 cycles (24 weeks; treatment phase 1). Patients with treatment benefit had an option to enter the extension phase to receive 6-week (42-day) cycles of panobinostat (weeks 1, 2, 4, and 5) plus bortezomib (days 1, 8, 22, and 29) and dexamethasone (day of and the day following bortezomib treatment) for 24 weeks. The primary objective was complete response (CR) + near CR (nCR) rate after treatment phase 1 as per the modified European Society for Blood and Marrow Transplantation criteria. RESULTS: Of the 31 patients, 4 (12.9%) completed the treatment and 27 (87.1%) discontinued; 17 (54.8%) entered the extension phase. In total, 24 patients (77.4%) entered the survival follow-up phase and followed until study closure when the last patient was treated for 1 year after treatment phase 1. The CR + nCR rate was 48.4% (90% CI: 33.6-63.2). The overall response rate (CR + nCR + partial response) was 80.6%. The median PFS, duration of response, time to response, and time to progression were 15.3, 22.7, 1.4, and 15.3 months, respectively. All patients experienced adverse events (AEs), with diarrhea (80.6%), decreased appetite (58.1%), and thrombocytopenia (54.8%) being the most frequent, regardless of relationship to the study treatment. Thrombocytopenia (48.4%), fatigue (25.8%), diarrhea (22.6%), neutrophil count decrease (22.6%), platelet count decrease (22.6%), and lymphocyte count decrease (22.6%) were the most frequent grade 3/4 AEs. CONCLUSION: The study met the primary objective with 48.4% CR + nCR rate. The AEs associated with the combination treatment were safely managed using the existing AE management guidelines, including dose interruption/modification and/or supportive medical intervention. This treatment regimen is an effective option with a favorable benefit/risk profile for Japanese patients with relapsed/refractory MM.

Safety, pharmacokinetics, and pharmacodynamics of panobinostat in children, adolescents, and young adults with relapsed acute myeloid leukemia.

BACKGROUND: Novel therapies are urgently needed for pediatric patients with relapsed acute myeloid leukemia (AML). METHODS: To determine whether the histone deacetylase inhibitor panobinostat could be safely given in combination with intensive chemotherapy, a phase 1 trial was performed in which 17 pediatric patients with relapsed or refractory AML received panobinostat (10, 15, or 20 mg/m2 ) before and in combination with fludarabine and cytarabine. RESULTS: All dose levels were tolerated, with no dose-limiting toxicities observed at any dose level. Pharmacokinetic studies demonstrated that exposure to panobinostat was proportional to the dose given, with no associations between pharmacokinetic parameters and age, weight, or body surface area. Among the 9 patients who had sufficient (>2%) circulating blasts on which histone acetylation studies could be performed, 7 demonstrated at least 1.5-fold increases in acetylation. Although no patients had a decrease in circulating blasts after single-agent panobinostat, 8 of the 17 patients (47%), including 5 of the 6 patients treated at dose level 3, achieved complete remission. Among the 8 complete responders, 6 (75%) attained negative minimal residual disease status. CONCLUSIONS: Panobinostat can be safely administered with chemotherapy and results in increased blast histone acetylation. This suggests that it should be further studied in AML.

Characterizing the pharmacokinetics of panobinostat in a non-human primate model for the treatment of diffuse intrinsic pontine glioma.

PURPOSE: Diffuse intrinsic pontine glioma (DIPG) is one of the deadliest forms of childhood cancers. To date, no effective treatment options have been developed. Recent drug screening studies identified the HDAC inhibitor panobinostat as an active agent against DIPG cells lines and animal models. To guide in the clinical development of panobinostat, we evaluated the CNS pharmacokinetics of panobinostat using CSF as a surrogate to CNS tissue penetration in a pre-clinical nonhuman primate (NHP) model after oral administration. METHODS: Panobinostat was administered orally to NHP (n = 3) at doses 1.0, 1.8, 2.4, and 3.0 mg/kg (human equivalent dose: 20, 36, 48, 60 mg/m2, respectively). The subjects served as their own controls where possible. Serial, paired CSF and plasma samples were collected for 0-48 h. Panobinostat was quantified via a validated uHPLC-MS/MS method. Pharmacokinetic (PK) parameters were calculated using non-compartmental methods. RESULTS: CSF penetration of panobinostat after systemic delivery was low, with levels detectable in only two subjects. CONCLUSION: The CSF penetration of panobinostat was low following oral administration in this pre-clinical NHP model predictive of human PK.

Safety and efficacy of oral panobinostat plus chemotherapy in patients aged 65 years or younger with high-risk acute myeloid leukemia.

The role of histone deacetylase inhibitors in the treatment of acute myeloid leukemia (AML) is not well characterized. The current study evaluated the safety and efficacy of panobinostat in combination with idarubicin and cytarabine in newly diagnosed patients aged ≤65 years with primary or secondary high-risk AML based on cytogenetic classification. Treatment included fixed dose idarubicin (12 mg/m2/d, IV; day 1-3) and cytarabine (100 mg/m2/d, continuous IV infusion; day 1-7) and escalating oral doses of panobinostat at 15 mg, 20 mg, and 25 mg, thrice weekly starting at week 2 of a 28-day cycle. Forty-six patients were enrolled (primary AML [n = 36], secondary AML [n = 10]). The median age was 55 years. The most common all-grade AEs were diarrhea (54.3%), nausea (39.1%), vomiting, and decreased appetite (each, 21.7%), stomatitis (19.6%), and fatigue (17.4%). The overall response rate was 60.9%, 43.5% achieved a complete remission (CR), and 17.4% achieved CR with incomplete count recovery. The event-free survival at 1-year was 78.3%. Panobinostat in combination with idarubicin and cytarabine demonstrated tolerable safety and efficacy in younger patients with high-risk AML. The recommended phase 2 dose of panobinostat in this combination was 20 mg. ClinicalTrials.gov registry no: NCT01242774, and European Trial Registry EudraCT no: 2009-016809-42.

Kinetic Tuning of HDAC Inhibitors Affords Potent Inducers of Progranulin Expression.

Histone deacetylases (HDACs) are enzymes involved in the epigenetic control of gene expression. A handful of HDAC inhibitors have been approved for the treatment of cancer, and HDAC inhibition has also been proposed as a novel therapeutic strategy for neurodegenerative disorders. These disorders include progranulin (PGRN)-deficient forms of frontotemporal dementia caused by mutations in the GRN gene that lead to haploinsufficiency. Hydroxamic-acid-based inhibitors of HDACs 1-3, reported to have fast-on/fast-off binding kinetics, induce increased expression of PGRN in human neuronal models, while the benzamide class of slow-binding HDAC inhibitors does not produce this effect. These observations indicate that the kinetics of HDAC inhibitor binding can be tuned for optimal induction of human PGRN expression in neurons. Here, we further expand on these findings using human cortical-like, glutamatergic neurons. We provide evidence that two prototypical, potent hydroxamic acid HDAC inhibitors that induce PGRN (panobinostat and trichostatin A) exhibit an initial fast-binding step followed by a second, slower step, referred to as mechanism B of slow binding, rather than simpler fast-on/fast-off binding kinetics. In addition, we show that trapoxin A, a macrocyclic, epoxyketone-containing class I HDAC inhibitor, exhibits slow binding with high, picomolar potency and also induces PGRN expression in human neurons. Finally, we demonstrate induction of PGRN expression by fast-on/fast-off, highly potent, macrocyclic HDAC inhibitors with ethyl ketone or ethyl ester Zn2+ binding groups. Taken together, these data expand our understanding of HDAC1-3 inhibitor binding kinetics, and further delineate the specific combinations of structural and kinetic features of HDAC inhibitors that are optimal for upregulating PGRN expression in human neurons and thus may have translational relevance in neurodegenerative disease.

Targeted Lipid Nanoemulsions Encapsulating Epigenetic Drugs Exhibit Selective Cytotoxicity on CDH1-/FOXM1+ Triple Negative Breast Cancer Cells.

The plasticity of cancer epigenetics makes them plausible candidates for therapeutic intervention. We took advantage of elevated expression of lysophosphatidic acid receptor 1 (LPAR1) in triple negative breast cancer (TNBC) tissues to target decitabine (DAC) and panobinostat (PAN) to breast cancer cells. DAC and PAN were shown to reverse abnormal methylation of DNA and altered chromatin structure, respectively, leading to increased expression of tumor suppressor genes and decreased expression of oncogenes. Although DAC and PAN have therapeutic benefits, they are limited by chemical instability and systemic toxicity. Herein, we present LPAR1-targeted, lipid nanoemulsions (LNEs) encapsulating both DAC and PAN. Our results demonstrated that the cell uptake and in vivo biodistribution of LNEs was dependent on LPAR1 expression in TNBCs. DAC/PAN-LNEs were effective in inhibiting the growth of mesenchymal breast cancer cells by restoring CDH1/E-cadherin and suppressing forkhead box M1 (FOXM1) expression. Epithelial breast cancer cells that inherently express low FOXM1 and high CDH1 were unaffected by DAC/PAN-LNEs. Overall, we successfully designed LPAR1-targeted LNEs that selectively act on CDH1(low)/FOXM1(high) TNBC cell lines.

The distribution, clearance, and brainstem toxicity of panobinostat administered by convection-enhanced delivery.

OBJECTIVE The pan-histone deacetylase inhibitor panobinostat has preclinical efficacy against diffuse intrinsic pontine glioma (DIPG), and the oral formulation has entered a Phase I clinical trial. However, panobinostat does not cross the blood-brain barrier in humans. Convection-enhanced delivery (CED) is a novel neurosurgical drug delivery technique that bypasses the blood-brain barrier and is of considerable clinical interest in the treatment of DIPG. METHODS The authors investigated the toxicity, distribution, and clearance of a water-soluble formulation of panobinostat (MTX110) in a small- and large-animal model of CED. Juvenile male Wistar rats (n = 24) received panobinostat administered to the pons by CED at increasing concentrations and findings were compared to those in animals that received vehicle alone (n = 12). Clinical observation continued for 2 weeks. Animals were sacrificed at 72 hours or 2 weeks following treatment, and the brains were subjected to neuropathological analysis. A further 8 animals received panobinostat by CED to the striatum and were sacrificed 0, 2, 6, or 24 hours after infusion, and their brains explanted and snap-frozen. Tissue-drug concentration was determined by liquid chromatography tandem mass spectrometry (LC-MS/MS). Large-animal toxicity was investigated using a clinically relevant MRI-guided translational porcine model of CED in which a drug delivery system designed for humans was used. Panobinostat was administered at 30 µM to the ventral pons of 2 juvenile Large White-Landrace cross pigs. The animals were subjected to clinical and neuropathological analysis, and findings were compared to those obtained in controls after either 1 or 2 weeks. Drug distribution was determined by LC-MS/MS in porcine white and gray matter immediately after CED. RESULTS There were no clinical or neuropathological signs of toxicity up to an infused concentration of 30 µM in both small- and large-animal models. The half-life of panobinostat in rat brain after CED was 2.9 hours, and the drug was observed to be distributed in porcine white and gray matter with a volume infusion/distribution ratio of 2 and 3, respectively. CONCLUSIONS CED of water-soluble panobinostat, up to a concentration of 30 µM, was not toxic and was distributed effectively in normal brain. CED of panobinostat warrants clinical investigation in patients with DIPG.

Clinical Pharmacokinetics and Pharmacodynamics of Panobinostat.

Histone deacetylase (HDAC) inhibitors cause an increase in acetylation that leads to an increase in DNA transcription and accumulation of different proteins, reducing cell proliferation and inducing cell death. Panobinostat is a first-in-line HDAC inhibitor approved for treating multiple myeloma in combination with bortezomib and dexamethasone. It is a pan-deacetylase inhibitor and therefore inhibits not only HDAC but also other deacetylases. The main mechanism of action of panobinostat is to inhibit HDAC, which causes cell cycle arrest and apoptosis, leading to it being an antineoplastic drug. Pooled data of multiple-dose studies show that an oral dose of panobinostat 20 mg resulted in a maximum plasma concentration (C max) of 21.6 ng/mL approximately 1 h after administration, while doses between 10 and 30 mg resulted in dose proportional plasma levels. The absolute bioavailability of panobinostat is 21.4%, and it is moderately bound to plasma proteins. Renal impairment does not influence the intrinsic pharmacokinetics of panobinostat, however hepatic impairment causes an increase in the plasma concentrations of this drug. Therefore, starting treatment at lower doses could be considered in patients with mild to moderate hepatic impairment. Different ethnic backgrounds have an influence on the pharmacokinetics of panobinostat; however, due to major interindividual variability, no dose adjustment is recommended. The area under the concentration-time curve of panobinostat changes significantly under cytochrome P450 (CYP) 3A4 inhibitors, CYP3A4 and CYP2D6 inducers, and P-glycoprotein inhibitors. Panobinostat itself is a CYP2D6 inhibitor, which influences the plasma levels of the CYP2D6 substrate dexamethasone. The main side effects of panobinostat are diarrhea, peripheral neuropathy, asthenia and fatigue; hematologic side effects include neutropenia, thrombocytopenia, and lymphocytopenia.