The lesions and mutations of those parental samples have been previously characterized and reported as part of a larger study by Robertset al(6)

The lesions and mutations of those parental samples have been previously characterized and reported as part of a larger study by Robertset al(6). gene expression profiling. Cellular phosphoprotein analysis demonstrated that JAK-mutated xenografts exhibited heightened activation status of JAK/STAT and MAPK signaling pathways compared with typical B-cell precursor ALL xenografts, which were inhibited by AZD1480 exposure. However , AZD1480 exhibited modest single-agentin vivoefficacy against JAK-mutated xenografts. Combining AZD1480 with selumetinib resulted in profound synergisticin vitrocell killing, although these results were not translatedin vivodespite evidence of target inhibition. Despite validation of target inhibition and the demonstration of profoundin vitrosynergy between AZD1480 and selumetinib, TG6-10-1 it is likely that prolonged target inhibition is required to achievein vivotherapeutic enhancement between JAK and MEK inhibitors in the treatment of JAK-mutated ALL. Keywords: acute lymphoblastic leukemia, xenograft models, JAK/STAT signaling, kinase and phosphatase inhibitors, drug efficacy == Introduction == While the overall cure price for the most common pediatric cancer, acute lymphoblastic leukemia (ALL) now methods 90%, certain high-risk subtypes experience shorter remission duration and a significantly reduced likelihood of survival (1). Recent genome-wide studies have centered on the molecular characterization of those high-risk subtypes, including B-cell precursor ALL (BCP-ALL) harboring mutations in the Janus kinases (JAKs; JAK-mutated ALL) (24). Activating mutations in the pseudokinase or Rabbit polyclonal to TNFRSF10D kinase domains of JAK1, JAK2 or JAK3 were detected in approximately 10% of high-risk pediatric ALL cases, and are frequently accompanied by deletion of theIKZF1gene. These cases also exhibit gene expression signatures similar toBCR-ABL1-positive ALL despite the absence ofBCR-ABL1translocations (24). The presence of JAK mutations in pediatric ALL with this Kinase-like gene expression signature is also significantly associated with large expression of cytokine receptor-like factor 2 (CRLF2) and a dismal outcome (24). JAK mutations and CRLF2 overexpression result in aberrant activation of downstream signaling pathways, including JAK/signal transducer and activator of transcription (STAT), mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) pathways (510). Crosstalk between the JAK/STAT, MAPK and PI3K pathways has also been shown to occur at multiple levels (11). Constitutive activation of the JAK/STAT pathway enhances the MAPK and PI3K signaling pathways, causes cytokine-independent cell survival and proliferation of lymphoid cells (4, 5, 9, 12), and is implicated in the progression of lymphoproliferative diseases such as ALL, as well as other cancers (11, 13, 14). Consequently, they are compelling pathways for the development of targeted therapeutics to improve cancer treatment. Several small molecules with inhibitory activity against JAK members of the family have shown preclinical and clinical activity in the TG6-10-1 treatment of myeloproliferative neoplasms (MPNs), which harbor the JAK2 V617F mutation, as well as other solid TG6-10-1 tumors (1520). Although the JAK2 V617F mutation is different from those that occur in ALL, these mutations occur in the same region of the protein and are functionally analogousin vitro(4, 5). AZD1480 is an ATP-competitive small molecule inhibitor of JAK1 and JAK2 that also shows some selectivity towards JAK3 (20, 21). AZD1480 TG6-10-1 was selected by the Pediatric Preclinical Testing Program (PPTP) for preclinical efficacy testing against a panel of xenografts established in immune-deficient mice that were derived from high-risk pediatric ALL patient subtypes, including all those harboring JAK point mutations, JAK2 fusions, high CRLF2 expression, and a Kinase-like gene expression profile. This rationale was based on the success achieved with imatinib in the treatment ofBCR-ABL1-positive leukemia (22). The JAK1/2 inhibitor ruxolitinib was recently shown to exhibit greaterin vivoefficacy against two Kinase-like pediatric ALL patient-derived xenografts with activation of the JAK/STAT axis (one via aBCR-JAK2translocation) but without CRLF2 overexpression, compared with several xenografts derived from Kinase-like cases harboring JAK point mutations and CRLF2 overexpression. (23). This observation suggests that alternative survival pathways activated by CRLF2 may result in reduced sensitivity of ALL cells with activated JAK/STAT signaling to single-agent JAK inhibitors. Therefore , and since xenografts established from TG6-10-1 JAK-mutated/CRLF2-high ALL biopsies would also be expected to exhibit heightened activation from the MAPK and PI3K/AKT pathways in addition to JAK/STAT (4, 5, 9, 12), we sought to enhance anti-leukemic efficacy by focusing on multiple signaling nodes using the combination of AZD1480 and the MEK inhibitor, selumetinib (AZD6244, ARRY-142886). Selumetinib is a potent small molecule inhibitor of MEK1/2, which blocks ERK1/2 activation (24). Despite strong evidence ofin vitrosynergy between AZD1480 and selumetinib, both drugs exhibited modestin vivosingle agent and combination efficacy. These findings highlight the complexity of translatingin vitrosynergistic drug combinations to thein vivosetting, and suggest that prolonged target inhibition may be required to achievein vivotherapeutic benefit using JAK inhibitors intended for the treatment of pediatric ALL cases harboring JAK point mutations and large CRLF2 expression. == Materials and methods == == Patient and xenograft details == Pretreatment leukemia specimens were obtained from 21.