2011 – SUBCLONAL MUTATIONS ALTER CORE SIGNALLING NODES AND DRUG RESPONSES IN PAEDIATRIC ACUTE LYMPHOBLASTIC LEUKAEMIA

Aberrant expression of cytokine receptor-like factor 2 (CRLF2) occurs in 5–15% of B-cell acute lymphoblastic leukaemia (B-ALL) and is associated with poor outcomes.

Approximately 50% of CRLF2+ B-ALLs also harbor activating mutations in JAK2. Coexpression of CRLF2 and mutant JAK2 results in constitutive STAT5 activation, and factor-independent transformation of B cell progenitors. The current consensus is that JAK/STAT activation is the hallmark of CRLF2 B-ALL, however JAK2 inhibitors such as Ruxolitinib have shown limited efficacy in this leukemia. We have shown that some CRLF2+ B-ALLs lacking JAK2 mutations instead harbor activating mutations in the RAS-ERK pathway (e.g. KRAS-G12D). Using single-cell sequencing of matched diagnosis and relapse patient samples, we show that in patients with both STAT and ERK activating lesions, these mutations are present in competing clones which fluctuate during disease progression. However, it remains unknown how subclonal mutations alter the signalling properties and drug responses of CRLF2+ leukemias. To investigate this, we established murine models expressing the human CRLF2 receptor complex and common JAK2 and RAS pathway mutations. Using phospho-proteomics, and high throughput drug screening we show for the first time that the combination of CRLF2 with RAS mutations activates distinct signalling networks, compared to CRLF2 combined with mutant JAK2, and that this drives unique drug dependencies that can be therapeutically leveraged. To investigate subclonal dynamics in vivo, we use advanced imaging approaches to visualise how distinct sublones engage bone marrow niche structures during development, and under pressure of chemotherapy. This work reveals novel insights into the importance of subclonal mutations on the biology of CRLF2+ B-ALL.