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Keywords:

  • myelofibrosis;
  • histone deacetylase inhibitor;
  • panobinostat;
  • epigenetics;
  • phase I

Summary

  1. Top of page
  2. Summary
  3. Patients and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Funding
  8. Authorship contributions
  9. Conflict of interest
  10. References
  11. Supporting Information

Panobinostat (LBH589), a novel histone deacetylase inhibitor (HDACi), was evaluated in a phase I study of patients with primary myelofibrosis (PMF) and post-essential thrombocythaemia/polycythaemia vera-related myelofibrosis (Post-ET/PV MF). Eighteen patients (PMF 56%; Post-PV MF 28%; Post-ET MF 17%) were treated in three cohorts at oral doses of (i) 20, (ii) 30, and (iii) 25 mg three times weekly consecutively. Reversible thrombocytopenia was the dose-limiting toxicity. Five patients (two in Dose Cohort 1, one in Dose Cohort 2 and two in Dose Cohort 3) received six or more cycles and were evaluable for response assessment. After the sixth cycle, three of these five patients achieved clinical improvement (CI) with 100% reduction in palpable splenomegaly from baseline, and two patients experienced stable disease. Panobinostat therapy was also associated with improvement in the degree of anaemia in two of the five patients. Of the three patients who achieved CI after six cycles, one patient achieved a near complete remission after 15 cycles of treatment and another patient had resolution of marrow fibrosis after 16 cycles. We conclude that panobinostat is a well-tolerated, clinically active treatment for MF patients, regardless of JAK2 V617F status, and most effective when given at low doses over long periods of time.

Myelofibrosis (MF) is a clonal haematological malignancy with an estimated median survival of approximately 4–6 years for which haematopoietic stem cell transplantation is the only curative therapy (Cervantes et al, 2012). Ruxolitinib (Jakafi®, Incyte Corporation, Wilmington, DE, USA) is a first-in-class Federal Drug Administration (FDA)-approved tyrosine kinase inhibitor for the treatment of MF (Harrison et al, 2012; Verstovsek et al, 2012). Other Janus kinase (JAK) inhibitors are currently being evaluated, but none of these agents uniformly result in correction of cytopenias or in reduction in the JAK2 V617F allele burden (Verstovsek, 2011).

Panobinostat (Novartis Pharmaceuticals, East Hanover, NJ, USA) is a novel cinnamic hydroxamic potent pan-histone deacetylase inhibitor (HDACi) that specifically enhances acetylation of histone H3, H4 and heat shock protein 90 (HSP90; Glaser, 2007). Panobinostat has been reported to have clinical activity in limited samples of patients with MF (Spencer et al, 2007). Therefore, we conducted a phase I study of panobinostat in patients with MF.

Patients and methods

  1. Top of page
  2. Summary
  3. Patients and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Funding
  8. Authorship contributions
  9. Conflict of interest
  10. References
  11. Supporting Information

Study design and treatment

This open label, investigator-initiated, phase I dose escalation study was approved by the Mount Sinai School of Medicine Program for the Protection for Human Subjects (PPHS) and informed written consent was obtained in accordance with the Declaration of Helsinki. The principal investigator held the Investigational New Drug (IND) approval for this study and Novartis provided financial support and study medication. This trial was registered at www.ClinicalTrials.gov (identification number: NCT01298934).

The drug was provided in 5 mg and 20 mg pink/orange gelatin capsules. Patients were instructed to take the study drug at the same time of the day on Monday, Wednesday and Friday of each week. The initial starting dose was 20 mg based on a prior Novartis-sponsored study of oral panobinostat in a broad spectrum of haematological malignancies (Spencer et al, 2007). Panobinostat doses were altered through three levels in a standard 3 + 3 dose escalation scheme. A cycle was defined as 28 days and a total of six cycles comprised the core study period. Patients were enrolled in cohorts of three and the dose was escalated by 10 mg increments in subsequent cohorts if the appropriate dose escalation rules were met. At the discretion of the principal investigator, a dose of 5 mg below the dose-limiting toxicity (DLT) was also explored.

Supportive care and red blood cell transfusions, but not platelet transfusions were permitted throughout the study period and other chemotherapeutic or investigational agents were not allowed. The maximum tolerated dose (MTD) was defined as the dose at which fewer than two of six patients experienced a DLT. The recommend phase II dose (RPTD) was defined as the dose level below the MTD. Patients who did not experience a DLT within the first cycle (28 days of treatment) remained on study drug for six cycles and were assessed for efficacy. Patients who achieved stable disease, clinical improvement (CI), partial response (PR) or complete response (CR) according to International Working Group for Myelofibrosis Research and Treatment (IWG-MRT) criteria were allowed to receive the drug indefinitely, until disease progression (Tefferi et al, 2006), or the occurrence of serious adverse event (SAE).

Adverse events (AEs) were assessed by National Cancer Institute (NCI, Bethesda, MD) Common Toxicity Criteria for Adverse Events (CTCAE) version 3.0 (http://ctep.cancer.gov/protocolDevelopment/electronic_applications/docs/ctcaev3.pdf) and labelled a DLT during the first 28 d on study if the event was unrelated to disease progression, inter-current illness, or concomitant medications. Haematological DLT was defined as a platelet count <50 × 109/l for seven consecutive days for those patients starting the trial with a baseline platelet count >100 × 109/l and >50% reduction in the platelet count for those patients starting with a baseline count of <100 × 109/l. An absolute neutrophil count (ANC) <0·5 × 109/l for 7 d or neutropenic fever (>38·5°C) with an ANC <1·0 × 109/l also constituted a DLT. Anaemia was not considered a DLT and patients were transfused to maintain a haemoglobin >80 g/l. Dose modifications were allowed after the first cycle and study drug was restarted at a 5 mg dose reduction after the AE resolved to ≤CTCAE grade 1. Study drug was withheld for thrombocytopenia and restarted at a 5 mg dose reduction once the platelet count ≥50 × 109/l. Only two dose reductions were allowed for both haematological and non-haematological AEs.

Patient selection and eligibility criteria

Patients aged 18 years or older were eligible for enrolment in this protocol. Newly diagnosed PMF patients, as defined by the World Health Organization (WHO) revised diagnostic criteria (Tefferi et al, 2007), or patients with a diagnosis of post-ET/PV MF as reported by Barosi et al (2008) with intermediate or high risk disease as defined by the Lille prognostic scoring system (Dupriez et al, 1996) were eligible. Previously treated MF patients with disease that was refractory or intolerant to prior therapy, or relapsed were also eligible. Patients were required to have an Eastern Cooperative Oncology Group (ECOG) performance status of two or less.

Objectives and endpoints

The primary objective of this phase I study was to identify the DLT, MTD and RPTD, as well as treatment related AEs beyond the first 28 d of therapy. Secondary objectives included clinical response assessment by IWG-MRT response criteria, and evaluation of effects on biomarkers as measured by histone acetylation status, JAK2 V617F allele burden, and karyotypic abnormalities.

Response assessment

Response was assessed at day 28 of cycle six by the clinical, haematological and pathological criteria of the IWG-MRT for standardization of response assessment in clinical trials (Tefferi et al, 2006). Patients who obtained at least stable disease by cycle 6 day 28 remained on study indefinitely or until disease progression occurred, and were re-assessed for response when deemed clinically appropriate by the investigators.

Statistical design and analysis

Patient characteristics were summarized using frequencies and percentages for categorical variables and statistics, such as means, standard deviations, medians and ranges for continuous variables. Response rate was reported with an exact 95% confidence interval.

Results

  1. Top of page
  2. Summary
  3. Patients and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Funding
  8. Authorship contributions
  9. Conflict of interest
  10. References
  11. Supporting Information

Patient characteristics

Twenty patients were enrolled between November 2008 and March 2010. Two patients were screen failures and are not further analysed. Patient characteristics are summarized by dose cohort in Table 1. Eighteen patients were evaluable for DLT. Thirteen of the patients (72%) had received prior MF-directed therapy including hydroxycarbamide, interferon α, and thalidomide. Twelve (67%) were JAK2 V617F-positive with a median allele burden of 63% (range 10–100%). Eleven (61%) had a normal karyotype at baseline, while the remaining seven (39%) patients had a variety of cytogenetic abnormalities including 20q-, trisomy 8, trisomy 9, trisomy 10, and a jumping 1q chromosomal abnormality (Najfeld et al, 2010).

Table 1. Baseline characteristics of phase I patients by dose administered (N = 18)
 All (N = 18)Dose 20 mg (N = 6)Dose 30 mg (N = 6)Dose 25 mg (N = 6)
  1. MF, myelofibrosis; PMF, primary myelofibrosis; PPV, post-polycythaemia vera; PET, post-essential thrombocythaemia, SD, standard deviation.

Age at Treatment in years [mean (SD)]64·5 (9·0)64·7 (10·9)69·0 (9·0)59·8 (5·1)
Sex
Female10 (56%)3 (50%)4 (67%)3 (50%)
Male8 (44%)3 (50%)2 (33%)3 (50%)
Lille risk score
I7 (39%)2 (33%)2 (33%)3 (50%)
II11 (61%)4 (67%)4 (67%)3 (50%)
MF subtype
PMF10 (56%)4 (67%)4 (67%)2 (33%)
PPV MF5 (28%)2 (33%)03 (50%)
PET MF3 (17%)02 (33%)1 (17%)
JAK2 V617F positive patients – %12 (67%)4 (67%)5 (83%)3 (50%)
Cytogenetic abnormalities – %7 (39%)3 (50%)3 (50%)1 (17%)
Time to treatment, months – mean (SD)23·7 (31·4)32·0 (44·9)21·7 (30·8)17·5 (15·8)
Previous MF directed therapy – %13 (72%)3 (50%)5 (83%) 5 (83%)
History of any previous transfusions – %11 (61%)3 (50%)4 (67%)4 (67%)
White blood cell count, × 109/l – mean (SD)13·3 (12·0)11·0 (11·4)13·5 (15·9)15·5 (9·8)
Haemoglobin, g/l – mean (SD)93 (21)86 (16)100 (32)95 (08)
Platelet count, × 109/l – mean (SD)232·5 (167·2)289·3 (263·4)137·0 (70·2)271·2 (64·0)
Palpable splenomegaly baseline – % of patients16 (89%)6 (100%)5 (83%)5 (83%)
Palpable splenomegaly, cm – mean (SD) N = 1615·4 (7·1)14·8 (7·6)15·4 (6·6)16·2 (8·3)

Panobinostat dose escalation and toxicities

Dose escalation

The starting cohort of six patients received a dose of 20 mg PO TIW weekly and one patient experienced a DLT due to thrombocytopenia. The second cohort of six patients received 30 mg PO TIW weekly and included two patients with a DLT of thrombocytopenia. For the third cohort, an intermediate dose of 25 mg PO TIW was selected by the investigators; none of the six patients in this cohort experienced a DLT. This dose was selected as the RPTD. The median number of completed cycles of therapy (range) was 3·5 (0–39), 0·5 (0–6), and 1·5 (0–30) for the 20, 30, and 25 mg cohorts, respectively.

Haematological toxicity

Table 2 lists the laboratory abnormalities that were thought to be at least possibly attributed to the drug at any point on study. Reversible thrombocytopenia was the DLT at the 20 mg (n = 1) and 30 mg (n = 2) dose. Thrombocytopenia was seen as early as day 8 and in each case the platelet count returned to baseline within 7–10 d after withdrawal of panobinostat. Life threatening bleeding was not observed. No clinical or laboratory characteristics of the patients who experienced thrombocytopenia as a DLT could be identified, including baseline platelet count. Two additional patients experienced thrombocytopenia that required dose reduction of panobinostat after cycle 1. Currently two patients are still actively receiving study drug at cycle 30 (Dose Cohort 3) and 39 (Dose Cohort 1). The first of these two patients had their dose reduced from 25 to 15 mg due to thrombocytopenia and has maintained a stable platelet count of approximately 200 × 109/l for over 1 year. Anaemia was the most frequently observed haematological AE, occurring in 50% (nine out of 18) of patients (grade 3/4 in 7 patients, 39%). Grade 3/4 neutropenia was observed in 17% (three out of 18) of patients but there were no instances of febrile neutropenia.

Table 2. Adverse events possibly related to panobinostat therapy at any time on study
Laboratory eventPatients with AE's of any gradePatients with maximum grade 3 or 4Patients with maximum grade 3 or 4 AE by dose level
20 mg30 mg25 mg
Anaemia (low haemoglobin)9 (50%)7 (39%)5 (83%)1 (17%)2 (33%)
Thrombocytopenia (low platelets)8 (44%)6 (33%)1 (17%)4 (67%)1 (17%)
Neutropenia3 (17%)3 (17%)1 (17%)1 (17%)1 (17%)
Creatinine (high)2 (11%)0000
Bilirubin1 (6%)0000
Clinical eventPatients with AE's of any gradePatients with maximum grade 3 or 4Patients with maximum grade 3 or 4 AE by dose level
Dose 1Dose 2Dose 3
  1. Only adverse events (AEs) that were at least possibly related to study treatment are listed. All AEs regardless of grade and attribution are listed by patient in Appendix S1.

Diarrhoea16 (89%)0000
Nausea7 (39%)0000
Fatigue6 (33%)0000
Musculoskeletal pain6 (33%)0000
Dyspepsia4 (22%)0000
Weight loss3 (16%)0000
Abdominal Pain3 (16%)0000
Emesis2 (11%)0000
Constipation2 (11%)0000
Neuropathy2 (11%)0000
Anorexia2 (11%)0000
Non-haematological toxicity

Table 2 also presents the list of the non-haematological toxicities that were at least possibly attributed to the study drug at any point on study. Panobinostat was well tolerated, and no grade 3/4 clinical AEs were noted. Diarrhoea was the most common AE (16 out of 18, 89%) and was grade 1 in all but one case, which was grade 2, and predictably occurred the day following administration of panobinostat. None of the patients discontinued study drug due to diarrhoea which was easily managed with loperamide. Fatigue was reported in 33% (six out of 18) of patients and was the most difficult clinical AE to gauge for study drug attribution. None of the patients developed clinically significant bleeding attributable to the study drug. Musculoskeletal AEs included bone pain, joint pain, and muscle cramps and was reported in 33% (six out of 18) of patients. Other reported clinical AEs at least possibly related to panobinostat were dyspepsia, abdominal pain, neuropathy, constipation, weight loss, emesis, and nausea (grade 1/2). Appendix S1 lists all AEs by maximum grade experienced by each patient regardless of attribution at any point in the trial.

Clinical activity

Splenomegaly

Of the 18 patients that received study drug, 13 patients (72%) received more than 4 weeks of therapy and 11 of these 13 had palpable splenomegaly at baseline [mean ± standard deviation (SD) = 15·4 ± 7·5 cm]. Table 3 shows the median percentage change in spleen size from baseline to best response by dose level. Five patients received six or more cycles of treatment. At the end of cycle six, four of these five patients who had baseline splenomegaly were evaluable for response, with one patient achieving a 44% reduction and three achieving 100% reduction in palpable splenomegaly. Spleen volume measurements by ultrasound were completed in four patients after two and six cycles of continuous therapy with panobinostat and showed a 27% and 47% mean reduction in spleen volume, respectively. Patients did not experience an immediate rebound in spleen size after discontinuation of panobinostat and in some cases the spleen remained reduced in size by palpation up to 6 weeks after drug discontinuation (data not shown).

Table 3. Percent change in spleen size from baseline to best response by dose level (N = 11)a
Panobinostat dose, mgNo. of patientsMedian % change in spleen size
  1. a

    Includes all patients with palpable splenomegaly at baseline with at least 1 full cycle of treatment.

205−37·5% (−17·7 to 100%)
302−18·4% (−11·8 to 25%)
254−38·8% (−25·9 to 100%)
Symptoms

Patients reported resolution of constitutional symptoms (weight loss, fevers, night sweats) as well as improvements in early satiety, abdominal bloating/discomfort, bone pain, fatigue and energy level. For many patients, improvement in these symptoms was most appreciable after several months and was not always associated with reduction in spleen size (data not shown).

Clinical responses according to IWG-MRT criteria

Five patients were evaluable at the end of cycle six and are described in Table 4. Responders included patients that were male and female, JAK2 V617F-positive and-negative, previously treated and treatment naïve, as well as transfusion-dependent and -independent. Four patients received panobinostat for at least 12 months and two of these four patients are currently on study for over 24 months with durable responses as judged by improvement in anaemia (CI = 2) and elimination of palpable splenomegaly (CI = 2). After six cycles, the response rate for all patients who received at least one full cycle of treatment is 38% (five of 12, 95% confidence interval: 14%, 68%).

Table 4. Characteristics of 5 MF patients evaluable for response after 6 cycles on panobinostat
 Individual Patients
Patient 4Patient 7Patient 11Patient 15aPatient 18
  1. MF, myelofibrosis; PMF, primary myelofibrosis; PPV, post-polycythaemia vera; PET, post-essential thrombocythaemia; ECOG PS, Eastern Cooperative Oncology Group performance score; WT, wild type; ESA, erythropoietin stimulating agent; IFN, interferon α; thal, thalidomide; pred, prednisolone; HC, hydroxycarbamide; ANA, anagrelide; LBH589, Panobinostat; IWG-MRT, International Working Group for Myelofibrosis Research and Treatment; CI, clinical improvement; CR, complete remission.

  2. a

    Patient had documented partial response at cycle 12 and near complete remission at cycle 16 that was reconfirmed at cycle 24 at a reduced dose of 15 mg.

  3. b

    Defined by a history of at least two units of red blood cell transfusions in the last month for a haemoglobin level of <85 g/l that was not associated with clinically overt bleeding.

Age, years7252745566
SexFemaleFemaleMaleFemaleFemale
MF subtypePMFPMFPMFPET MFPPV MF
ECOG PS10111
JAK2 status (% burden)JAK2 V617F (45)JAK2 WTJAK2 V617F (10)JAK2 WTJAK2 V617F (50)
Karyotype46,XX46,XX46,XY46,XX46, XX
Prior treatmentESA, IFN, ThalNoneThalESA, predHC, ANA
Palpable spleen length at baseline, cm750916
Palpable spleen length after 6 cycles, cm00009
% Reduction in spleen length after six cycles100%100%0100%44%
Transfusion dependence at baselinebYesYesYesYesYes
Platelet count at baseline, ×109/l7932080195187
LBH589 Dose PO TIW20 mg20 mg30/25 mg25/20/15 mg25/20/25 mg
Number of cycles of therapy completed243963016
Response by IWG-MRT at end of 6 cyclesCI-spleen CI-anaemiaCI-spleenStable diseaseCI-spleen CI-anaemiaStable disease
Best response by IWG-MRT >6 cyclesCI-spleen CI-anaemiaCI-spleenStable diseaseNear CRStable disease

Two patients (Patients 7 and 15) were noted to have complete resolution of palpable splenomegaly, normalization of blood counts and disappearance of leucoerythroblastosis after cycle 6 d 28. Patient 7 had resolution of baseline splenomegaly by cycle five and maintained a mean haemoglobin of 100 g/l after 34 cycles. Patient 15 had resolution of palpable splenomegaly by cycle three and had an increase in baseline haemoglobin from 88 to 133 g/l by cycle 12. Patient 4 started on study requiring weekly transfusions to maintain a mean haemoglobin of 65 g/l. After six cycles she had resolution of palpable splenomegaly, improvement in global weakness and fatigue, and her transfusion requirement frequency decreased to every 3–4 weeks with a mean haemoglobin of 80 g/l.

Bone marrow histopathological changes associated with panobinostat therapy

Bone marrow evaluations after six cycles of treatment were performed on five subjects and did not demonstrate any appreciable changes in cellularity, cellular morphology, and grade of fibrosis at that time point. Patient 15 underwent bone marrow evaluation after cycles 16 and 30, which showed sustained dramatic reversal of the histopathological abnormalities (Fig 1). Patient 7 also had a significant reduction in marrow reticulin/collagen fibrosis, from grade 4 to grade 1, after 24 cycles of therapy (Fig 2).

image

Figure 1. Bone marrow histopathological assessment of a single patient after 16 cycles of Panobinostat. Pretreatment biopsy (A) Haematoxylin and Eosin (H&E) stain, ×100; (B) H&E stain, ×400; (C) reticulin stain, ×100; (D) trichrome stain, ×100) shows hypocellular marrow with decreases in myeloid and erythroid lineages. Megakaryocytes are increased and seen in compact clusters, and include markedly pleomorphic, hyperlobated forms. There is a diffuse network of coarse reticulin fibres, with areas of collagen deposition, as well as osteosclerosis. Post-treatment biopsy (E) H&E stain, ×100; (F) H&E stain, ×400; (G) reticulin stain, ×100; (H) trichrome stain, ×100 shows hypercellular marrow with increases in all haematopoietic lineages. Megakaryocytes show mild pleomorphism. There is partial resolution of fibrosis, with only moderately increased reticulin fibres, and minimal collagen deposition.

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image

Figure 2. Bone marrow histopathological assessment of a single patient after 16 cycles of Panobinostat (A, B), Bone marrow biopsy prior to therapy, Haematoxylin and Eosin (H&E) stain (A) Reticulin stain (B) (×400 magnification). Megakaryocytes are increased and include pleomorphic hyperlobated and hypolobated forms. There is diffuse reticulin fibrosis with abundant coarse fibres (grade 3–4, Bauermeister scale). (C, D), Bone marrow biopsy subsequent to therapy, H&E stain (C) Reticulin stain (D) (×400 magnification). Reticulin fibres are minimally increased (grade 1, Bauermeister scale). Pleomorphic megakaryocytes remain present.

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Pharmacodynamics and biomarkers

The effects of panobinostat on H3/H4 acetylation in CD34+ cells were assessed (Fig 3). The CD34+ cells could be divided into two subpopulations based on the degree of histone acetylation (AcH3lo and AcH3hi; AcH4lo and AcH4hi respectively). There was significant up-regulation of histone acetylation (H3 and H4) from baseline by cycle 1 day 15 in patients analysed. CD34+ AcH3hi cells increased from 11·4 ± 6·0% at baseline to 48·2 ± 9·4% at cycle 1 day 15, and CD34+ AcH4hi cells increased from 3·0 ± 2·6% to 17·0 ± 5·6% (Fig 3).

image

Figure 3. Enhanced histone acetylation of H3/H4 in CD34+ MF cells from patients treated with Panobinostat at varying doses. (A) Flow cytometric analysis shows the histone acetylation H3 (Acety-H3, AcH3) status of PMF CD34+ cells at baseline and cycle 1 d 15. The histogram represents the mean percent change and standard deviation (SD) of CD34+ AcH3hi cells (n = 4). (B) Flow cytometric analysis shows the histone acetylation H4 status of PMF CD34+ cells at baseline and cycle 1, day 15. The histogram represents the mean percent change and SD of CD34+ AcH4hi cells (n = 4). Statistical significance was determined using Student's paired-samples t-test.

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Quantitation of the JAK2 V617F allele burden was assessed in four JAK2 V617F-positive patients. One patient achieved a 25% reduction in JAK2 V617F allele burden with panobinostat therapy at cycle 3. Due to the small numbers of JAK2 V617F-positive MF patients evaluable for molecular response at cycle 3 day 1, statistical analysis was not possible.

There were no noted cytogenetic responses in the patients that were treated with panobinostat during the phase I study. The five patients evaluable for clinical response at cycle 6 day 28 (Table 4) had normal karyotypes at baseline and did not acquire new abnormalities while being treated.

Discussion

  1. Top of page
  2. Summary
  3. Patients and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Funding
  8. Authorship contributions
  9. Conflict of interest
  10. References
  11. Supporting Information

At an RPTD of 25 mg three times a week, panobinostat was well tolerated and reversible thrombocytopenia was the noted DLT in patients with MF. Panobinostat was effective in improving MF-related symptoms in the majority of patients treated for longer than a month. Significant reduction in splenomegaly was observed at the end of six cycles. Objective responses in anaemia occurred in three patients treated after at least six cycles. Two patients were noted to have a significant and reproducible reduction in marrow fibrosis after a minimum of 12 cycles of therapy. Importantly, a near CR was obtained in a single patient after >12 cycles of therapy at a reduced dose of 15 mg PO TIW. This is consistent with a concept of prolonged therapy with chromatin-modifying agents to achieve a meaningful haematopathological response (Silverman et al, 2008). Treatment of MF with single agent oral panobinostat appears to require a minimum of 12 cycles in order to achieve improvement in blood counts and possibly longer to achieve reversal of bone marrow histopathological abnormalities. Due to the limited number of patients treated in this study, we were not able to determine the effects of this drug on the JAK2 V617F allele burden or its ability to eliminate cytogenetic abnormalities.

The rationale for the use of HDACi for the treatment of MF patients is based on preclinical studies. In vitro studies exposing the HEL cell line and primary JAK2 V617F-positive cells from PV and ET patients to givinostat have shown selective reduction in the mutant JAK2 clone with preservation of JAK2 wild type expressing cells (Atadja, 2009). PMF is characterized by an increased proportion of circulating peripheral blood CD34+ haematopoietic stem cells and our group has previously shown that ex vivo exposure of PMF CD34+ cells to sequential DNA methyltransferase (DNMT) inhibitor and HDACi leads to dramatic reduction in the burden of malignant progenitor cells as detected by a reduction in JAK2 V617F allele burden (Shi et al, 2007).

Currently, the results of three other clinical trials of HDACi therapy in MF patients have been reported (De Angelo et al, 2010; Rambaldi et al, 2010; Quintas-Cardama et al, 2012). Panobinostat, at starting doses of 40 mg three times weekly, was evaluated in a separate phase II study demonstrating clinical activity in some patients at the expense of increased toxicity (De Angelo et al, 2010). A phase II study of givinostat in JAK2 V617F-positve MPN patients included three major responses in the 16 treated MF patients (Rambaldi et al, 2010). A recent report of a phase II trial of pracinostat in MF patients has demonstrated modest activity in terms of reduction in splenomegaly and improvement in anaemia (Quintas-Cardama et al, 2012).

Treatment of MF patients with panobinostat is associated with acceptable haematological and non- haematological toxicity and can result in clinical improvement in patients with advanced MF. Prolonged administration of low doses of panobinostat to patients with MF has the potential to ameliorate MF-related symptoms, eliminate the leucoerythroblastic blood picture, improve anaemia, reverse bone marrow pathological features and reduce bone marrow fibrosis. Based on these observations, panobinostat appears to be a promising new agent for the treatment of patients with both JAK2 V617F-positive and -negative MF, which merits further evaluation in a phase II trial.

Acknowledgements

  1. Top of page
  2. Summary
  3. Patients and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Funding
  8. Authorship contributions
  9. Conflict of interest
  10. References
  11. Supporting Information

The authors would like to thank Steven Fruchtman, Carole Paley, Michael Ondovik, and Jessica Rine for their helpful discussions.

Authorship contributions

  1. Top of page
  2. Summary
  3. Patients and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Funding
  8. Authorship contributions
  9. Conflict of interest
  10. References
  11. Supporting Information

JM designed the trial, conducted the research, wrote the manuscript, ML performed the biomarker studies and created figures, TL acquired and analysed data, BP evaluated the bone marrow pathology and created the figure, JDG collaborated in the study design, analysis of the data, and preparation of the manuscript. TH collaborated in the analysis of the data. VN performed cytogenetic analysis, and RH designed the trial and assisted in writing the manuscript.

References

  1. Top of page
  2. Summary
  3. Patients and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Funding
  8. Authorship contributions
  9. Conflict of interest
  10. References
  11. Supporting Information
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Supporting Information

  1. Top of page
  2. Summary
  3. Patients and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. Funding
  8. Authorship contributions
  9. Conflict of interest
  10. References
  11. Supporting Information
FilenameFormatSizeDescription
bjh12220-sup-0001-AppendixS1.docxWord document15KAppendix S1. All Adverse Events with maximum grade by patient regardless of attribution.

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