Key Points• RAS pathway mutations are prevalent in relapsed childhood ALL, and KRAS mutations are associated with a poorer overall survival.• RAS pathway mutations confer sensitivity to mitogenactivated protein kinase kinase inhibitors.For most children who relapse with acute lymphoblastic leukemia (ALL), the prognosis is poor, and there is a need for novel therapies to improve outcome. We screened samples from children with B-lineage ALL entered into the ALL-REZ BFM 2002 clinical trial (www. clinicaltrials.gov, #NCT00114348) for somatic mutations activating the Ras pathway (KRAS, NRAS, FLT3, and PTPN11) and showed mutation to be highly prevalent (76 from 206). Clinically, they were associated with high-risk features including early relapse, central nervous system (CNS) involvement, and specifically for NRAS/KRAS mutations, chemoresistance. KRAS mutations were associated with a reduced overall survival. Mutation screening of the matched diagnostic samples found many to be wild type (WT); however, by using more sensitive allelic-specific assays, low-level mutated subpopulations were found in many cases, suggesting that they survived up-front therapy and subsequently emerged at relapse. Preclinical evaluation of the mitogen-activated protein kinase kinase 1/2 inhibitor selumetinib (AZD6244, ARRY-142886) showed significant differential sensitivity in Ras pathway-mutated ALL compared with WT cells both in vitro and in an orthotopic xenograft model engrafted with primary ALL; in the latter, reduced RAS-mutated CNS leukemia. Given these data, clinical evaluation of selumetinib may be warranted for Ras pathway-mutated relapsed ALL. (Blood. 2014;124(23):3420-3430)

Background:Despite intensive research and novel adjuvant therapies, there is currently no cure for metastatic melanoma. The chemokine receptor CXCR4 controls metastasis to sites such as the liver; however, the therapeutic blockade with the existing agents has proven difficult.Methods:AMD11070, a novel orally bioavailable inhibitor of CXCR4, was tested for its ability to inhibit the migration of melanoma cells compared with the commonly described antagonist AMD3100.Results:AMD11070 abrogated melanoma cell migration and was significantly more effective than AMD3100. Importantly for the clinical context, the expression of B-RAF-V600E did not the affect the sensitivity of AMD11070.Conclusion:Liver-resident myofibroblasts excrete CXCL12, which is able to promote the migration of CXCR4-expressing tumour cells from the blood into the liver. Blockade of this axis by AMD11070 thus represents a novel therapeutic strategy for both B-RAF wild-type and mutated melanomas.

For most children who relapse with acute lymphoblastic leukaemia (ALL), the prognosis is poor and there is a need for better prognostic biomarkers and novel therapies to improve outcome. Relapse samples from children with B lineage ALL entered into the ALL-REZ BFM 2002 clinical trial were screened for somatic mutations which activate the RAS pathway using DHPLC and Sanger sequencing. Mutations were found in 78 patients, giving an incidence of 37.9% and were made up of NRAS (n=30), KRAS (n=30), FLT3 (n=10) and PTPN11 (n=9); one patient had both a KRAS and FLT3 mutation. Clinically, mutated cases were associated with early relapse which was particularly significant for NRAS/KRAS mutated patients (p=0.001), with a 5 year probability of event free survival of 46.9% versus 60.1% for wild type (p=0.21). In addition, there was an over representation of NRAS/KRAS mutated patients with CNS involvement, 23.3% compared to 10.3% for the mutation negative group (p=0.014). Mutation screening of the matched diagnostic samples found many to be wild type (26 from 54) but using more sensitive allelic specific assays, low level mutated subpopulations were found in 57% of cases (8 from 14), suggesting these cells survived up front therapy and subsequently emerged at relapse. Assessment of p-ERK levels by western blotting in a large cohort of diagnostic ALL samples confirmed that RAS pathway mutated cases almost always had constitutive activation of the pathway (27 from 32; 84.3%), while relatively few wild type patients were p-ERK positive (9 from 48; 18.7%) (p<0.0001). Using MTS assay, differential sensitivity to the potent MEK1/2 inhibitor, selumetinib (AZD6244, ARRY-142886), was demonstrated in ALL blasts, with GI50 values being significantly lower for p–ERK/mutation positive samples (n=5, mean 250nM, range 18nM-918nM) compared to those that were negative (n=5, mean 68µM, range from 17.8µM-100µM; p=0.0079). This differential sensitivity was mirrored in an orthotopic mouse model using primagrafts derived from primary ALL cells. After intrafemoral injection and leukaemia engraftment, mice were randomised to receive either selumetinib or control vehicle (CV) (25 or 100mg/kg BID) and levels of circulating blasts monitored during treatment by flow cytometry. There was a dramatic reduction in circulating leukaemia cells in mice implanted with the RAS pathway mutant ALL cells (KRAS, G12D and NRAS Q61R) treated with selumetinib, with a mean fold decrease of >8 after 30 drug doses compared to a mean fold increase of >5 for CV. Mice treated with selumetinib and sacrificed at the end of the study showed a significant decrease in spleen size compared to CV treated mice. There was minimal effect of selumetinib in wild type ALLs. Histological analysis of post-mortem brains from mice engrafted with an NRAS mutant primagraft found extensive meningeal leukaemic infiltration in CV-treated, but not selumetinib-treated mice. Pharmacodynamic assessment in spleens of mice engrafted with mutant primagrafts showed absence of p-ERK and increased levels of the apoptotic biomarkers, Bim and cleaved PARP. In summary, we show that RAS pathway mutations are a common genetic abnormality in relapsed ALL and are associated with high risk features and are often relapse-drivers. Targeted MEK inhibition with selumetinib shows excellent activity in RAS mutated ALL both in vitro and in vivo and may offer clinical benefit for a substantial proportion of children with relapsed ALL. Given our findings, clinical trials of selumetinib in RAS pathway positive relapsed patients are warranted. Disclosures: No relevant conflicts of interest to declare.