Benefits of JAK2 Inhibitor Therapy: Why Do They Work in Patients With and Without JAK2 Mutation

Alessandro M. Vannucchi Section of Hematology, University of Florence, Italy

JAK2 V617F is the Commonest Mutation Causing Abnormal JAK/STAT Signaling in MPN

Survival Differentiation Proliferation Oncogenesis Vannucchi et al., CA Cancer J Clin. 2009; 59:171-91

A Myeloproliferative Disorder is Induced by JAK2 V617F in Mice

PV MF Zaleska, Plos One 2006;e18

JH7 JAK2 inhibitors are not specific for the JAK2 V617F mutation Binding to receptors Chaperoning Stabilising at membrane Inhibits basal activity Signaling through P transfer ATP site FERM SH2 PseudoKinase Kinase Kinase site JH6 JH5 JH4 JH3 JH2 JH1 Activation loop V617F

• JAK inhibitors target the ATP binding site of JAK2 at the tyrosine kinase domain and not the pseudokinase domain • Therefore, both mutated and wild-type JAK2 are inhibited by JAK2 inhibitors

V617

James et al. Nature 2005; 434: 1144-8 ; Baxter et al. Lancet 2005; 365: 1054-61; Levine et al. Cancer Cell 2005; 7:387-97; Kralovics et al. NEJM. 2005: 352:1779-90

Inhibition of PV Progenitor Erythroid Differentiation by the JAK2 Inhibitor TG101348

Geron I et al, Cancer Cell, 13; 2008 321 - 330

Effects of Treatment with Ruxolitinib in a JAK2 V617F-Driven Murine Model

Quintás-Cardama et al., Blood 2010;115:3109-3117.

JAK1 and JAK2, or JAK2 Only, Inhibitors

Drug JAK1 Other targets Ruxolitinib/INC424 TG101348/SAR302503 CYT387 CEP-701 AZD1480 SB1518 LY2784544 BMS911543

   none known FLT3, Ret JNK1, CDK2 FLT3, TrkA Aurora A, TrkA, FGFr1 FLT3 na Verstovsek et al. N Engl J Med. 2010; 363:1117-27. Pardanani et al. JCO. 2011; online Jan 10. Pardanani et al. ASH Abstract 2010; Blood 2010; 116:460. Santos et al. Blood. 2010; 115:1131-6.La Fave LM, Trends Pharm Sciences 2012; 33:564-582.

•

Do they work?

•

If yes, Why?

•

Do they work?

•

If yes, Why?

The Effects of Ruxolitinib on Spleen Size is Independent of JAK2 V617F Mutation 22.5

20.0

17.5

15.0

12.5

10.0

7.5

5.0

2.5

0 0 JAK mutation POSITIVE; N = 33 JAK mutation NEGATIVE; N = 6 56 112 168 224 Time on Therapy (days) 280 336

• In the Phase I/II study with TG101348/SAR302503, 8 of 59 pts were JAK2 wild-type • 3 of 4 pts who completed six cycles had >50% reduction of splenomegaly (CI per IWG-MRT) Verstovsek S et al. NEJM 2010; 363:1117-1127; Pardanani A et al, JCO 2011; 29:789-796

Effect of JAK2 V617F Mutation on the Proportion of Patients Obtaining a >35% Spleen reduction *

• No significant difference in response rates was observed between patients with the JAK2V617F mutation compared with those without the mutation, although the trend was towards a greater response rate in JAK2 V617F mutated * By MRI Harrison C et al, ASH 2011; 279

The Effects of Ruxolitinib on Symptomatic Control Is Independent of JAK2 V617F Mutation

Kiladjian JJ et al, ASCO 2012: 451A

The Impact of Ruxolitinib on Survival Is Independent of JAK2 V617F Mutation

Verstovsek S et al. ASH 2011, 378A

•

Do they work?

•

If yes, Why?

Similarly Activated Signaling Pathways in JAK2 V617F Mutated and Wild-type MPN Cells

Anand S et al. Blood 2011;118:1610-1621

Similar Inhibition of Signaling in JAK2 V617F and Wild-type patients with a Selective JAK2 inhibitor

Anand S et al. Blood 2011;118:1610-1621

A Cytokine Storm in PMF Patients

    JAK2 V617F correlated   

Fold-increased over controls

 Tefferi A et al, JCO 2011;29:1356-1363

The Significance of JAK1 and JAK2 Inhibition

Vannucchi AM, N Engl J Med. 2010; 363:1180-2.

Ruxolitinib-Induced Normalisation of Inflammatory Cytokines in Phase I/II Trial

Baseline, Patients with Myelofibrosis vs. Healthy Controls Patients with Myelofibrosis, Day 28 vs. Baseline This effect was observed regardless of JAK2 mutational status or MF subtype

Verstovsek et al. N Engl J Med. 2010; 363:1117-27.

Predicted Effects of JAK1 and JAK2 inhibition

JAK2 inhibitors are not specific for mutated protein

THUS they are effective regardless of the JAK2V617F mutated status

JAK2wt (± JAK1) inhibition affects a variety of cytokine signaling pathways Concurrent Inhibition of JAK2wt might result in anemia and thrombocytopenia Placebo BAT Ruxolitinib 19.2

Anemia 43.2

1.3

Thr’penia 12.9

31 Anemia 42

• A marked reduction of pro-inflammatory cytokines was coincident with improvement in constitutional symptoms

Thr’penia 7 8 % of patients Verstovsek S et al. N Engl J Med. 2010; 363:1117-27; Verstovsek S et al. NEJM 2012; 366:799-807; Harrison C et al. NEJM 2012; 366:787-98

Conclusions

• Abnormal JAK/STAT signaling is a common pathogenetic mechanism in MPN cells independent of the JAK2 mutational status • Current JAK2 inhibitors are not specific for the mutated protein, and target the wild-type JAK2 as well • JAK2 inhibitors are similarly effective in JAK2 mutated and wild type patients • Inhibition of wild-type JAK1 signaling contributes to the clinical efficacy of JAK1/JAK2 inhibitors