RAS-protein activation but not mutation status is an outcome predictor and unifying therapeutic target for high-risk acute lymphoblastic leukemia

Abstract

Leukemias are routinely sub-typed for risk/outcome prediction and therapy choice using acquired mutations and chromosomal rearrangements. Down syndrome acute lymphoblastic leukemia (DS‐ALL) is characterized by high frequency of CRLF2‐rearrangements, JAK2‐mutations, or RAS‐pathway mutations. Intriguingly, JAK2 and RAS-mutations are mutually exclusive in leukemic sub‐clones, causing dichotomy in therapeutic target choices. We prove in a cell model that elevated CRLF2 in combination with constitutionally active JAK2 is sufficient to activate wtRAS. On primary clinical DS‐ALL samples, we show that wtRAS-activation is an obligatory consequence of mutated/hyperphosphorylated JAK2. We further prove that CRLF2-ligand TSLP boosts the direct binding of active PTPN11 to wtRAS, providing the molecular mechanism for the wtRAS activation. Pre‐inhibition of RAS or PTPN11, but not of PI3K or JAK‐signaling, prevented TSLP‐induced RAS‐GTP boost. Cytotoxicity assays on primary clinical DS‐ALL samples demonstrated that, regardless of mutation status, high-risk leukemic cells could only be killed using RAS‐inhibitor or PTPN11-inhibitor, but not PI3K/JAK‐inhibitors, suggesting a unified treatment target for up to 80% of DS‐ALL. Importantly, protein activities-based principal-component-analysis multivariate clusters analyzed for independent outcome prediction using Cox proportional-hazards model showed that protein‐activity (but not mutation-status) was independently predictive of outcome, demanding a paradigm-shift in patient‐stratification strategy for precision therapy in high-risk ALL.

Role of thymic stromal lymphopoietin in allergy and beyond

“…Indeed, targeting of JAKs, for example, by proteolysis-targeting chimeras (PROTACs) directed against JAKs, has been shown to be a potent treatment for CRLF2 -rearranged ALL 122 . In Down syndrome-associated ALL, in which there is a high rate of rearrangement of CRLF2 , TSLP increases binding of the tyrosine phosphatase PTPN11 to RAS, resulting in RAS protein activation, which promotes ALL cell growth 123 .…”

Acquired JAK2 mutations confer resistance to JAK inhibitors in cell models of acute lymphoblastic leukemia

“…It is currently unknown whether CRLF2 r/ JAK2 r-mutant ALL preclinical models are susceptible to JAK inhibitor resistance through this same mechanism. However, activation of alternative signaling pathways such as C-MYC and MAPK/ERK have been identified in CRLF2 r/ JAK2 r-mutant ALL 47 , 48 , suggesting that in this setting, JAK inhibitor resistance may develop via upregulation of alternative signaling pathways potentially in preference to acquired mutations within the JAK2 ATP-binding site.…”

Targeting KRAS in Cancer: Promising Therapeutic Strategies

“…Interestingly, a new study revealed that the activation of KRAS wild-type alone is sufficient to induce oncogenic KRAS properties in cases of Down Syndrome (DS)-ALL [17]. Approximately 60% of DS-ALL cases harbor cytokine receptor-like factor 2 (CRLF2) rearrangements, 32% of cases harbor JAK2 mutations and 36% harbor mutations in the RAS-MAPK pathway.…”

“…Both JAK2 and RAS pathway mutations are mutually exclusive. However, high CRLF2 levels and increased activation of JAK2 sufficiently activate wildtype KRAS in 80% of DL-ALL cases, suggesting that therapeutics inhibiting overstimulated KRAS are needed [17].…”