The Johnstone laboratory fully integrates fundamental cancer and immunological research and pre-clinical development and testing of novel therapeutic regimes, to drive new clinical trials using agents under investigation in our lab.
Major themes include:
- Defining the molecular events underpinning anti-cancer drug action and resistance.
- Dissecting the role of altered epigenetics in tumour onset and progression, and targeting epigenetic enzymes to treat cancer.
- Integrating epigenetic- and immune-based therapeutics to provide more potent and durable therapeutic outcomes.
Investigating the role of CRLF2/JAK2 signalling in high-risk B-cell acute lymphoblastic leukaemia (B-ALL)
Chromosomal translocations leading to overexpression of the cytokine receptor CRLF2 frequently occur in B-cell ALL (B-ALL), and this is closely linked with activating mutations of the kinase JAK2 and adverse prognosis. Overexpressed CRLF2 and mutant JAK2 physically associate, resulting in activation of important oncogenic pathways. To investigate the functional role of CRLF2 and JAK2 mutations during leukaemia initiation, the Johnstone laboratory generated a transgenic model with CRLF2 under the control of the immunoglobulin heavy chain enhancer (Eµ), to enforce lymphoid-specific expression of CRLF2. We transduced Eµ-CRLF2 transgenic stem cells with constructs expressing JAK2WT, JAK2R683G or JAK2P933R, to derive leukaemias that exhibited constitutive JAK-STAT signalling. Our results demonstrate that CRLF2 overexpression and mutant JAK2 cooperate during leukaemia initiation. The overall aim of this research project is to investigate how CRLF2 and JAK2 cooperate in the initiation and progression of B-ALL and to develop novel therapeutic strategies to treat tumours with aberrant CRLF2/JAK2 signalling.
Targeting transcriptional addiction for cancer therapy in mixed lineage leukaemia (MLL)-driven acute myeloid leukaemia (AML)
MYC-translocated lymphomas and mixed lineage leukaemia (MLL)-rearranged acute myeloid leukaemias (AML), both representing poor-risk haemopoietic cancers, are characterised by transcriptional amplification. This “transcriptional addiction” renders these cancers exquisitely sensitive to small molecule inhibitors that target core transcriptional proteins such as BRD4 and CDK9. Our aim is to unravel how transcriptional addiction promotes disease in poor-prognosis leukaemia and lymphoma, and how disruption of oncogenic transcriptional networks with targeted compounds results in anti-tumour effects.
To obtain a comprehensive genome-wide view of chromatin and transcriptional states, novel state-of-the art next-generation sequencing approaches are required. This project will use sequencing technology termed global run-on sequencing (GRO-seq) to enable accurate assessment of RNA polymerase initiation, elongation and termination. This technique will allow us to accurately map the transcriptional landscape in AML and identify the direct effect of transcriptional inhibitors. This will improve our understanding of MLL-driven AML and assist in the identification of novel vulnerabilities in these aggressive cancers, which can be exploited for future anti-cancer therapies.
Exploiting and defining the immune regulatory activities of BET bromodomain inhibitors
Our ability to harness and manipulate the immune system through the use of checkpoint inhibitors and other immune modulators has revolutionised clinical oncology. We have discovered that JQ1, an inhibitor of the BET family of bromodomain-containing epigenetic “readers”, is efficacious in the Eµ-myc model of B-cell lymphoma, and the therapeutic effects of JQ1 were significantly enhanced in an immune-competent setting. We found that JQ1 or BRD4 knockdown caused a rapid reduction in the levels of the checkpoint ligands PDL-1 and PDL-2 on the surface of Eµ-myc lymphomas. Further, combined treatment with JQ1 and anti-PD1 antibody resulted in durable, and often complete, responses in an Eµ-myc lymphoma model.
We hypothesise that the anti-tumour responses to BET inhibitors are a result of direct anti-tumour effects on cell survival/proliferation combined with modulation of the host immune system. We will utilise syngeneic tumour models, small molecule BET inhibitors, immune-regulatory antibodies, sophisticated gene depletion and deletion techniques, and epigenetic characterisation techniques to functionally and mechanistically interrogate the interaction between BET proteins and the immune system.
Targeting epigenetic enzymes in core binding factor AML
Genes encoding core binding factors (CBFs), including AML1/RUNX1 and CBFB, are frequently rearranged in AML. The t(8;21) and inv(16) translocations produce AML1-ETO (A/E) and CBFb-MYH11 (C/M) fusion proteins, and represent class II mutations that cause deregulated haemopoietic stem/progenitor cell (HSPC) self-renewal and differentiation. These cooperate with mutations in class II genes (such as RAS, FLT3 and KIT) that affect HSPC proliferation and survival to drive AML development. Mechanistically, A/E and C/M both recruit histone deacetylases (HDACs) and protein-arginine methyltransferase 1 (PRMT1) to aberrantly repress CBF target genes.
Using an AML model driven by expression of A/E and oncogenic Ras, we recently demonstrated that treatment with the HDAC inhibitor panobinostat caused differentiation of leukaemic blasts and a robust anti-leukaemic response. We will now determine if targeting HDACs in inv(16) AML will also be efficacious and determine the effects of inhibition or genetic depletion of PRMT1 in models of t(8;21) and inv(16) AML. Moreover, we will determine if a therapeutic regimen shown to be effective in AML driven by a particular class II mutation (for example, A/E) is affected by the co-occurrence of class I mutations. Finally, we will concomitantly target proteins and pathways driven by cooperating class I and class II mutations to identify combination therapies most effective for a genetically defined CBF fusion protein-driven AML.
Characteriation of the functional consequence of immunomodulatory drug (IMiD)-mediated BET protein degradation in multiple myeloma
We have made the unprecedented discovery that immunomodulatory drugs (IMiDs) mediate cereblon-directed degradation of BET proteins. For the first time, this mechanistically links the IMiDs with a family of epigenetic readers that modulate pivotal physiological and oncogenic transcriptional networks. Thus we are uniquely poised to dissect the role of BET protein degradation in the previously elusive IMiD mechanism of action. This project will comprehensively evaluate the importance of BET proteins as bona fide cereblon neosubstrates in multiple myeloma, while providing a robust rationale for the translation of IMiD/BET inhibitor combinations to the clinic.
Ghisi M, Kats L, Masson F, Li J, Kratina T, Vidacs E, Gilan O, Doyle MA, Newbold A, Bolden JE, Fairfax KA, de Graaf CA, Firth M, Zuber J, Dickins RA, Corcoran LM, Dawson MA, Belz GT, Johnstone RW (2016). Id2 and E proteins orchestrate the initiation and maintenance of MLL-rearranged acute myeloid leukemia. Cancer Cell. 30(1):59-74
Matthews GM, Mehdipour P, Cluse LA, Falkenberg KJ, Wang E, Roth M, Santoro F, Vidacs E, Stanley K, House CM, Rusche JR, Vakoc CR, Zuber J, Minucci S, Johnstone RW (2015). Functional-genetic dissection of HDAC dependencies in mouse lymphoid and myeloid malignancies. Blood.126(21):2392-403.
Waibel W, Christiansen AJ, Hibbs ML, Shortt J, Jones SA , Simpson I, Light A, O’Donnell K, Morand EF, Tarlinton DM, Johnstone RW*and Hawkins ED* (*Co-senior Authors) (2015). Manipulation of B cell responses with histone deacetylase inhibitors. Nature Communications 27(6): 6838. ( *Co-senior author)
Gregory GP, Hogg SJ, Kats LM, Vidacs E, Baker AJ, Gilan O, Lefebure M, Martin BP, Dawson MA, Johnstone RW*, Shortt J*. (2015). CDK9 inhibition by dinaciclib potently suppresses Mcl-1 to induce durable apoptotic responses in aggressive MYC-driven B-cell lymphoma in vivo. Leukemia. 29(6):1437-41. (*Co-senior Authors)
Bots M, Verbrugge I, Martin BP, Salmon JM, Ghisi M, Baker A, Stanley K, Shortt J, Gert J, Ossenkoppele GI, Zuber Z, Rappapor AR, Atadja P, Lowe SW, and Johnstone RW (2014). Differentiation therapy for the treatment of t(8;21) Acute Myeloid Leukemia using histone deacetylase inhibitors. Blood 123(9):1341-52
Shortt J,Hsu AK, Martin BP, Doggett K, Matthews GM, Doyle MA, Ellul J, Jockel TE, Andrews DM, Hogg SJ, Rietsma A, Faulkner D, Bergsagel PL, Chesi M, Heath, JK, Denny WA, Thompson PE, Neeson PJ, Ritchie DS, McArthur GA, Johnstone RW (2014). The drug vehicle and solvent, N-methylpyrrolidone is an epigenetic immunomodulator and anti-myeloma compound. Cell Reports. 7(4):1009-19.
Waibel M, Solomon VS, Knight DA, Ralli RA, Kim S-K, Banks K-M, Vidacs E, Virely C, Sia KCS, Bracken LS, Collins-Underwood R, Drenberg C, Ramsey LB, Meyer SC, Takiguchi M, Dickins RA, Levine R, Ghysdael J, Dawson MA, Lock RB, Mullighan CG, Johnstone RW (2013). Combined targeting of JAK2 and Bcl-2/Bcl-xL to cure mutant JAK2-driven malignancies and overcome acquired resistance to JAK2 inhibitors. Cell Reports. 5(4):1047-59.