JAK2 inhibitors and new therapeutic approaches in PV and ET Francesco Passamonti Division of Hematology University Hospital, Fondazione Macchi Varese, Italy

Current management of PV & ET Treatment objective Preventing thrombotic and bleeding complications and minimizing the risk of transformation to secondary myelofibrosis or leukemia; controlling symptoms Treating complications General basis of treatment PV: phlebotomy to maintain the hematocrit at less than 45% and low-dose aspirin, if not contraindicated ET: low-dose aspirin, if microvascular disturbances and not contraindicated Strict correction of cardiovascular risk factors Cytoreductive therapy with hydroxyurea for: Age > 60 years History of thrombosis Platelet count > 1500 x109/L Poor tolerance of phlebotomies Severe disease-related symptoms Symptomatic or progressive splenomegaly Progressive leukocytosis Barbui et al, J Clin Oncol. 2011 Feb 20;29(6):761-70.

Peg-Interferon in PV (90-135-180 mcg/wk) 37 PV patients untreated or treated for less than 2 years Hematological Complete response at 12 months: 94.6% Still on peg-IFN-α2a alone at 31 months: 78.4% Adverse Events in 89% (grade1, 2) decreasing over time Treatment discontinuation: 35% (24% for toxicity) JAK2 (V617F) allele burden response Complete: 7/29 (24%) Partial: 14/29 (48%) Reduction also in homoz. and 9pLOH Targets JAK2 (V617F) clones without affecting TET2 mutant cells 0 20 40 60 80 100 % V617F 0 6 12 18 24 30 36 Kiladjian et al, Blood. 2008 Oct 15;112(8):3065-72 Kiladjian et al. Leukemia. 2010 Aug;24(8):1519-23 Months

Peg-Interferon in advanced PV 43 patients (median age 53 yrs, 50 months PV-duration) Follow-up: 42 months Overall response rate: 79% Complete hematological response 76% Median time to complete response: 40 days (range, 3 to 1478) Drug-related treatment discontinuation: 20% Molecular response CMR: 18% PMR (> 50%): 35% Quintas Cardama et al, Blood 2013; 122: 893-901.

AOP2014: a new formulation of peg-Interferon for PV Next generation long lasting pegylated-IFN Subcutaneous every 14 days 34 patients (dose finding & extension phases) Median time from PV diagnosis: 24 months 71% ORR in 21 pts at week 28 (33% CR, 38% PR) 91% ORR in 11 pts at week 52 (46% CR, 46% PR) 27 pts (79%) developed drug-related AEs Gisslinger et al., Blood 2012; Abstract 175, ASH 2012

Peg-Interferon–α2a in ET The Nordic Study Group on MPN 42 high-risk patients (21 PV, 21 ET); median follow-up 24 mos Objective: to reduce PLT <400 x109/L or <600 if asymptomatic No thromboembolic or hemorrhagic complications At 6 months: CR=69%; failure rate=31% (13/42), drug-related treatment discontinuation: 14% At 24 months: CR=45% (19/42); failure rate=55% drug-related treatment discontinuation: 38% (16/42) Impairments of QoL (QLQ-C30 ) at 6 months; but at 24 months no change from baseline Samuelsson et al, Cancer 2006 106(11):2397-405.

JAK2 reduction under IFN in ET Danish study on 102 MPN, median follow-up 42 months, (19 ET) Clone reduced in 75% of patients ET patients responding JAK2 V617F reduction % JAK2 V617F Clone increased in 25% of patients, of whom 46% were in complete hematological response Pre-Peg-Interferon Tx Post-Peg- Interferon Tx Larsen et al, Leuk Res 2013 37(9):1041-5.

Studies with Peg-Interferon in PV & ET Randomised Trial of Peg-Interferon Versus Hydroxyurea in PV and ET. Primary Outcome: To compare hematologic response rates in patients randomised to treatment with Peg-Interferon Alpha-2a vs. Hydroxyurea in two strata of patients with high risk PV or high risk ET. Peg-Interferon Salvage Therapy in High Risk PV and ET Primary Outcome: To evaluate the ability of Peg-Interferon Alpha-2a to achieve Complete Response or Partial Response in patients with (1) high risk PV or (2) high risk ET or (3) splanchnic vein thrombosis. ProudPV Trial Phase III study to compare the efficacy and safety of the novel monopegylated interferon alpha 2b AOP2014 versus Hydroxyurea for patients with polycythemia vera.

Anagrelide vs hydroxyurea in ET The PT1 trial 809 ET patients at high risk for vascular events Low-dose aspirin plus either anagrelide or hydroxyurea Primary end point: actuarial risk of arterial and venous thrombosis, serious hemorrhage, or death from thrombotic or hemorrhagic causes Anagrelide was associated with increased rates of arterial thrombosis, serious hemorrhage, and transformation to myelofibrosis, but with a decreased rate of venous thromboembolism Harrison et al, N Engl J Med. 2005 Jul 7;353(1):33-45.

Anagrelide vs hydroxyurea in ET a non inferiority trial, 259 WHO-diagnosed ET at HR No significant differences regarding incidences of major arterial (7 vs 8) and venous (2 vs 6) thrombosis, severe bleeding events (5 vs 2), minor arterial (24 vs 20) and venous (3 vs 3) thrombosis and minor bleeding events (18 vs 15), or rates of discontinuation (adverse events 12 vs 15 or lack of response 5 vs 2). Disease transformation into MF/AML was not reported Gisslinger et al, Blood 2013 121(10):1720-8.

A Phase II study of Ruxolitinib in advanced PV and ET refractory to HU (INCB 18424-256) Inclusion Criteria Refractory or intolerant to HU; contraindication for HU PV: Hct > 45% or 2 phlebotomies in prior 6 months (1 in last 3 months) ET: Platelets > 650 x 109/L Endpoints Response (CR + PR) and safety, PK, PD, symptom assessments 10 mg BID (n=7) 25 mg BID (n=8) 50 mg QD (n=7) 10 mg BID (n=12) PV=34 Part 1 Part 2 10 mg BID (n=8) 25 mg BID (n=8) 50 mg QD (n=8) 25 mg BID (n=15) ET=39 Clinicaltrials.gov number: NCT00726232 Part 1 Part 2

Ruxolitinib in the PV cohort 34 patients with PV enrolled Median age: 58 years Median time from PV diagnosis: 115 months WBC >15 x109/L in 47% PLT > 600 x109/L in 38% Splenomegaly in 74% Median follow-up duration: 3 years 26 remain on study 8 discontinued Progression to MF (n=3) Withdrawal of consent (n=2) Patient decision to conceive Patient complained of shortness of breath Adverse events (n=2) Renal neoplasm Atrial flutter Lack of response (n=1) Verstovsek et al. Cancer. 2013 Oct 30. doi: 10.1002/cncr.28441.

Ruxolitinib in PV: Normalization of WBC and platelet counts WBC count ≤10×109/L Platelet count ≤ 400×109/L Analyses conducted in patients with baseline WBC count >10×109/L (n=25) and patients with baseline platelet count >400×109/L (n=23) ITT analysis: Patients who discontinued are counted as not having response for all study visits that they would have completed up to the date of analysis Verstovsek et al. Cancer. 2013 Oct 30. doi: 10.1002/cncr.28441.

Ruxolitinib in PV: changes in palpable spleen length NOTE: 25 patients had a palpable spleen, but 2 patients did not have a measurement recorded at baseline. Verstovsek et al. Cancer. 2013 Oct 30. doi: 10.1002/cncr.28441.

Reduction in PV-associated symptoms Clinically meaningful improvements in pruritus, night sweats, and bone pain observed within 4 weeks of initiating therapy and sustained through Week 144 ITT analysis: Patients who discontinued are counted as not having response for all study visits that they would have completed up to the date of analysis. Verstovsek et al. Cancer. 2013 Oct 30. doi: 10.1002/cncr.28441.

Patient characteristics – ET (n=39) Age, years 51 Female 64% Months from Diagnosis 88 Refractory to HU 87% No. Prior Therapies 1 (1-3) Hct % 41.0 Platelet count, x109/L 849 (mean 1009) Leukocyte count, x109/L 8.2 Splenomegaly Size, cm (range) 4 (10%) 5 (3-7) JAK2V617F positive 65% JAK2V617F allele burden 16% Verstovsek et al, Blood 2010; Abstract 313.

Platelet count reduction in ET 49% achieved normal platelet counts and 79% achieved <600,000 or a ≥50% reduction as of last follow-up visit 13 of 14 subjects with baseline platelet counts >1,000,000 have achieved a greater than 50% reduction Verstovsek et al, Blood 2010; Abstract 313.

Response rate for Ruxolitinib PV overall response rate (m-ELN): 97% Complete response: 59%, as their best response Partial response: 38%, as their best response ET Overall response rate (mELN): 90% Complete response: 26% CR Partial response: 64% Criteria: CR: Platelet count < 400 x109/L, WBC < 10 x109/L, normal spleen, no disease-related symptoms (pruritus, headache, microvascular disturbances) PR: Platelet count < 600 x109/L OR decrease > 50% from baseline Verstovsek et al. Cancer. 2013 Oct 30. doi: 10.1002/cncr.28441.

Ruxolitinib in PV: Phase 3 Trial The RESPONSE Study (oral) 10 mg bid HU resistance or intolerance (ELN criteria) q3mo phlebotomy requirement Palpable spleen with MRI-confirmed vol. of ≥ 450 cm3 Platelet > 100K N = 100 1o Endpoint Failure Disease Progression Crossover HCT 40–45% inclusive Randomised Best Available Therapy N = 100 Week 32 Week 80 Enrolment completed Special protocol assessment agreement reached with FDA Primary composite endpoint: haematocrit control in the absence of phlebotomy and ≥ 35% reduction in spleen volume at week 32 Secondary endpoints: complete haematological remission at week 32; % of patients who maintain primary endpoint response for ≥ 48 weeks NCT01243944

Response trial Press release Study of ruxolitinib met primary endpoint, improving two key measures of disease control in patients with polycythemia vera Ruxolitinib is the first selective JAK 1/2 inhibitor to demonstrate efficacy in a Phase III trial for treating polycythemia vera

Other phase-III trials with ruxolitinib in PV MAJIC: A randoMised study of best Available therapy versus JAK Inhibition in patients with high risk PVor ET who are resistant to or intolerant of HC RELIEF: Patients who remain symptomatic on HC RESPONSE-II: Per RESPONSE trial, but patients with no palpable spleen

Other investigated drugs Givinostat (29 PV / ET / MF JAK2-pos) 13 PV/ET: 1 CR, 6 PR, 4 NR, 2 off study 16 MF: spleen reduction in 38%; 2 CI and 5 SD Givinostat (2 doses) plus Hydroxyurea (44 PV res. to HD HU) ORR (CR+PR): 55% for givinostat 50 ORR: 50% for givinostat 100 Imetelstat (13 ET, failure or intolerance) ORR: 100% (11/13 CR after a median of 6.1 weeks) Partial molecular response 6/7 patients (85.7%) AE: GI, fatigue, infections (85.7%), neutropenia (78.6%) Vorinostat (19 ET, 44 PV) 81% responded: PR (N=20), CR (N=5), by ELN criteria Discontinuation rate: 52% (drug-related 44%) Rambaldi et al. British Journal of Haematology 2010; 150: 446-455; Finazzi et al. British Journal of Haematol 2013; 161, 688–694; Baerlocher et al. Blood 2012; 120: Abstract 179.; Andersen et al. British Journal of Haematology, 2013, 162, 498–508.

Conclusions Hydroxyurea is a widely used therapy in PV and ET Peg-inteferon is effective on the clinical phenotype and on the clone, but advantage over conventional therapy is still to be demonstrated JAK inhibition with ruxolitinib seems effective in PV and ET and superior to BAT in term of hematocrit control, and spleen size reduction