IDH1 mutations are common in low-grade gliomas and secondary glioblastomas and cause overproduction of (R)-2HG. (R)-2HG modulates the activity of many enzymes, including some that are linked to transformation and some that are probably bystanders. Although prior work on (R)-2HG targets focused on 2OG-dependent dioxygenases, we found that (R)-2HG potently inhibits the 2OG-dependent transaminases BCAT1 and BCAT2, likely as a bystander effect, thereby decreasing glutamate levels and increasing dependence on glutaminase for the biosynthesis of glutamate and one of its products, glutathione. Inhibiting glutaminase specifically sensitized IDH mutant glioma cells to oxidative stress in vitro and to radiation in vitro and in vivo. These findings highlight the complementary roles for BCATs and glutaminase in glutamate biosynthesis, explain the sensitivity of IDH mutant cells to glutaminase inhibitors, and suggest a strategy for maximizing the effectiveness of such inhibitors against IDH mutant gliomas.

A series of three dose escalating studies were conducted to investigate the ability of the 17a-hydroxylase/C 17,20 -lyase inhibitor abiraterone acetate, to cause maximum suppression of testosterone synthesis when delivered to castrate and noncastrate males with prostate cancer. Study A was a single dose study in castrate males. Study B was a single dose study in noncastrate males and study C was a multiple dose study in noncastrate males. The drug was given orally in a once-daily dose and blood samples taken to assess pharmacokinetic (PK) parameters and hormone levels in all patients. The study drug was well tolerated with some variability in PKs. Suppression of testosterone levels to o0.14 nmol l À1 was seen in four out of six castrate males treated with a single dose of 500 mg. At 800 mg given days 1 -12 in noncastrate males, target suppression was achieved in three out of three patients, but a two-to threefold increase of Luteinising Hormone (LH) levels in two out of three patients overcame suppression within 3 days. All patients in the multiple dose study developed an abnormal response to a short Synacthen test by day 11, although baseline cortisol levels remained normal. This is the first report of the use of a specific 17a-hydroxylase/ 17,20 -lyase inhibitor in humans. Repeated treatment of men with intact gonadal function with abiraterone acetate at a dose of 800 mg can successfully suppress testosterone levels to the castrate range. However, this level of suppression may not be sustained in all patients due to compensatory hypersecretion of LH. The enhanced testosterone suppression achieved in castrate men merits further clinical study as a second-line hormonal treatment for prostate cancer. Adrenocortical suppression may necessitate concomitant administration of replacement glucocorticoid.

• ETP-ALL, a high-risk subtype of T-ALL, is characterized by aberrant activation of the JAK/STAT signaling pathway.• The JAK1/2 inhibitor ruxolitinib demonstrates robust activity in patientderived xenograft models of ETP-ALL.Early T-cell precursor (ETP) acute lymphoblastic leukemia (ALL) is a recently described subtype of T-ALL characterized by a unique immunophenotype and genomic profile, as well as a high rate of induction failure. Frequent mutations in cytokine receptor and Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathways led us to hypothesize that ETP-ALL is dependent on JAK/STAT signaling. Here we demonstrate aberrant activation of the JAK/STAT pathway in ETP-ALL blasts relative to non-ETP T-ALL. Moreover, ETP-ALL showed hyperactivation of STAT5 in response to interleukin-7, an effect that was abrogated by the JAK1/2 inhibitor ruxolitinib. In vivo, ruxolitinib displayed activity in 6 of 6 patient-derived murine xenograft models of ETP-ALL, with profound single-agent efficacy in 5 models. Ruxolitinib treatment decreased peripheral blast counts relative to pretreatment levels and compared with control (P < .01) in 5 of 6 ETP-ALL xenografts, with marked reduction in mean splenic blast counts (P < .01) in 6 of 6 samples. Surprisingly, both JAK/STAT pathway activation and ruxolitinib efficacy were independent of the presence of JAK/STAT pathway mutations, raising the possibility that the therapeutic potential of ruxolitinib in ETP-ALL extends beyond those cases with JAK mutations. These findings establish the preclinical in vivo efficacy of ruxolitinib in ETP-ALL, a biologically distinct subtype for which novel therapies are needed. (Blood. 2015;125(11):1759-1767 Introduction Early T-cell precursor (ETP) acute lymphoblastic leukemia (ALL) was first described in 2009 as a subtype of T-ALL with a unique immunophenotype that includes expression of myeloid and early progenitor or stem cell markers in addition to T-cell lineage markers. 1Although overall survival for the majority of T-ALL cases has improved dramatically over the last 50 years, 2 largely due to intensification of chemotherapy regimens, many published studies suggest a large percentage of ETP-ALL cases have dismal outcomes.1,3-7 More recent studies suggest that children with ETP-ALL treated on contemporary protocols that intensify therapy based on minimal residual disease response may not fare as poorly as originally thought. 8,9 ETP-ALL, which represents ;10% to 15% of new T-ALL diagnoses in children 1,4,5 and ;10% to 30% in adults, 3,6 accounts for a disproportionate fraction of T-ALL induction failures (ie, failure to achieve a morphologic remission at the end of the first month of chemotherapy). Novel therapies with alternative mechanistic approaches are urgently needed for chemotherapy-refractory subgroups of ETP-ALL.In addition to an immunophenotype with myeloid/stem cell markers, ETP-ALL cases demonstrate a similar transcriptional and mutational landscape to myeloid leukemias and hematopoietic stem ce...

Key Points• Venetoclax demonstrates potent in vitro and in vivo single-agent activity in MLLrearranged ALL xenografts.• Clinically efficacious BH3-mimetic therapy for other high-risk ALL subtypes is likely to require concurrent BCL-2 and BCL-X L inhibition.The clinical success of the BCL-2-selective BH3-mimetic venetoclax in patients with poor prognosis chronic lymphocytic leukemia (CLL) highlights the potential of targeting the BCL-2-regulated apoptotic pathway in previously untreatable lymphoid malignancies. By selectively inhibiting BCL-2, venetoclax circumvents the dose-limiting, BCL-X L -mediated thrombocytopenia of its less selective predecessor navitoclax, while enhancing efficacy in CLL. We have previously reported the potent sensitivity of many high-risk childhood acute lymphoblastic leukemia (ALL) xenografts to navitoclax. Given the superior tolerability of venetoclax, here we have investigated its efficacy in childhood ALL. We demonstrate that in contrast to the clear dependence of CLL on BCL-2 alone, effective antileukemic activity in the majority of ALL xenografts requires concurrent inhibition of both BCL-2 and BCL-X L . We identify BCL-X L expression as a key predictor of poor response to venetoclax and demonstrate that concurrent inhibition of both BCL-2 and BCL-X L results in synergistic killing in the majority of ALL xenografts. A notable exception is mixed lineage leukemia-rearranged infant ALL, where venetoclax largely recapitulates the activity of navitoclax, identifying this subgroup of patients as potential candidates for clinical trials of venetoclax in childhood ALL. Conversely, our findings provide a clear basis for progressing navitoclax into trials ahead of venetoclax in other subgroups. (Blood. 2016;128(10):1382-1395