Thread by @rosslevinemd

Part 2 of the GOLDI-lox preprint set, led by @andrewdunbar_md and @bowman_rl. Q: If you had a system which can test oncogenic dependency in context of co-mutant disease alleles, what question would you ask? For us, it was simple; JAK2V617F! #mpnsm
biorxiv.org/content/10.110…

The role of JAK2V617F in MPN pathogenesis has long been demonstrated, and expression of JAK2V617F induces MPN in vivo as shown by many groups including @mullallylab, Tony Green, Radek Skoda, and Jean-Luc Villeval.

The role of JAK2V617F in MPN pathogenesis has long been demonstrated, and expression of JAK2V617F induces MPN in vivo as shown by many groups including @mullallylab, Tony Green, Radek Skoda, and Jean-Luc Villeval.

Moreover, work by @scienceadvocacy, Tony Green and colleagues suggested that antecedent TET2 mutations might render JAK2-mutant cells less responsive to JAK inhibitors.

However, we remain “believers” that JAK2 represents the best therapeutic target in MPN, and have used genetic and pharmacologic (tool type II inhibitors) to suggest that MPN cells remain JAK2 dependent. But we could never prove this for JAK2V617F in vivo.

Enter JAK2V617F GOLDI-Lox: We developed a reversible JAK2V617F model with Dre->Cre functionality, such that the Cre sites which delete/reverse JAK2V617F are only available after Dre recombination induces mutant expression.

Andy/Bobby showed that Dre mRNA expression in JAK2V617F-GL cells induces same MPN as observed with Cre-lox models, with PV->fibrosis. JAK2V617F activation with Dre followed by Cre-mediated mutant deletion-> blood counts, spleen weights and fibrosis rapidly normalize

Most importantly, mutant clone fitness (in comp transplants) was abrogated by JAK2V617F reversal, all the way to mutant stem cells! In a “bake-off” against ruxolitinib->JAK2V617F mutant allele reversal showed dramatically increased efficacy compared to current JAK inhibitors

The problem is the drug, not the target!

They then used the JAK2V617F-GL system to perform transcriptional/epigenetic profiling of JAK2V617F mutant HSPCs. Key targets/pathways reversibly activated by JAK2V617F in vivo matched up beautifully with the human sc study by @danlandau! So cool!

biorxiv.org/content/10.110…

They then asked if co-occurring mutations alter JAK2V617F dependency in vivo. HSPCs with Tet2 loss followed by JAK2V617F activation had increased self-renewal and enhanced myeloproliferation in vivo->BUT REMAIN JAK2 DEPENDENT!

These studies suggest that the most pressing need for MPN patients is better JAK2 inhibitors, whether they more potently target mutant + wt JAK2 or can target JAK2V617F specifically.

This work shows how a reversible mutant allele expressed from the endogenous locus can address critical questions related to oncogenic dependency. And this can be applied to lots of different mutant/malignant contexts! Stay tuned…

Thanks again to @theNCI @MSKCancerCenter @DamonRunyon for supporting this work, and for our collaborators in the @landau_lab and the MPN-RC led by Ron Hoffman!