The mTOR complex 2 (mTORC2) containing mTOR and rictor is thought to be rapamycin insensitive and was recently shown to regulate the prosurvival kinase AKT by phosphorylation on Ser473. We investigated the molecular effects of mTOR inhibition by the rapamycin derivatives ( IntroductionThe mammalian target of rapamycin (mTOR) pathway regulates cell growth, proliferation, and survival. 1 mTOR, the central component of this pathway, partitions between 2 scaffold proteins, raptor and rictor. Upon activation, the rapamycin-sensitive raptor/mTOR protein complex (mTORC1) increases mRNA translation via activation of p70S6-kinase and inhibition of eIF4E-binding protein 4EPB1. 2 The rictor/mTOR protein complex (mTORC2) was discovered only recently, is thought to be rapamycin insensitive, and phosphorylates AKT in the hydrophobic Ser473 site. It is therefore essential for AKT activity. 3 Despite activity in model systems, the clinical antitumor activity of rapamycin derivatives in patients has been modest, 1,4 and only a fraction of patients responds (reviewed in Thomas 5 ). This has been attributed to the unanticipated ability of rapamycin to increase AKT activity via release of feedback inhibition of growth signaling pathways, both in cell systems and in tumor biopsies from patients. 6 However, in certain cell types, prolonged inhibition of mTOR by rapamycin may impair mTORC2 assembly and hence AKT activation. 7 In this study, we investigated the molecular consequences of mTOR inhibition in leukemic cells, both in vitro and in a clinical trial in vivo. Our results demonstrate that rapamycin derivatives suppress assembly of mTORC2, resulting in marked inhibition of AKT signaling. We propose that rapamycin-induced functional blockade of AKT in leukemic cells may define a subset of hematologic malignancies that is likely to respond favorably to mTOR inhibition, and that inhibition of AKT signaling may serve as a valuable biomarker of mTOR inhibition in vivo. Materials and methodsAcute myeloid leukemia (AML) cell lines were cultured under standard conditions 8 with rapamycin derivatives CCI-779 and RAD001. Bone marrow or peripheral blood samples for the in vitro studies were obtained from patients with newly diagnosed or recurrent acute myeloid leukemia (AML) after informed consent. Peripheral blood samples were obtained from relapsed or refractory patients with hematologic malignancies treated with CCI-779 (temsirolimus; Wyeth Pharmaceuticals, Pearl River, NY) or RAD001 (everolimus; Novartis Pharmaceuticals, East Hanover, NJ) 9 after obtaining written informed consent. Approval was obtained from the M. D. Anderson Cancer Center institutional review board for these studies. Clinical characteristics of patients are summarized in Table S1 (available on the Blood website; see the Supplemental Materials link at the top of the online article). Expression of total and phosphorylated AKT (Ser473), p70S6K (Thr389), 4EBP1 (Thr70), FoxO1 (Ser256), and PTEN was detected by Western blot analysis as previously reported. 7 mTOR was immun...

Purpose: Everolimus (RAD001, Novartis), an oral derivative of rapamycin, inhibits the mammalian target of rapamycin (mTOR), which regulates many aspects of cell growth and division.

Purpose Previous studies suggest a potential therapeutic role for mTOR inhibition in lymphoid malignancies. This single-center phase I/II study was designed to test the safety and efficacy of the mTOR inhibitor everolimus in combination with HyperCVAD chemotherapy in relapsed/refractory acute lymphoblastic leukemia. Experimental Design Twenty-four patients were treated; 15 received everolimus 5 mg/day and 9 received 10 mg/day with HyperCVAD. Results The median age of patients was 25 years (range, 11-64) and median number of prior treatments was 2 (range, 1-7). Grade 3 mucositis was the dose-limiting toxicity and the maximum tolerated everolimus dose was 5 mg/day. Responses included complete remission (CR) in 6 patients (25%), CR without platelet recovery (CRp) in 1 (4%), and CR without recovery of counts (CRi) in 1 (4%), for an overall response rate of 33%. Additionally, partial response (PR) was noted in 2 patients (8%). Seven of 11 patients treated in first salvage achieved CR/CRp (64%). The median OS was 29 weeks for patients in first salvage versus 15 weeks for patients in second salvage and beyond (P≤0.001). A response was noted in 5 of 10 (50%) heavily pretreated T-ALL patients (median of 4 prior salvage regimens). Everolimus significantly inhibited phosphorylation of S6RP, but this did not correlate with response. No significant decreases in p4EBP1 and pAkt levels were noted. Responders had higher everolimus dose-adjusted area under the curve (P=0.025) and lower clearance (P=0.025) than non-responders. Conclusions The combination of HyperCVAD and everolimus is well tolerated and moderately effective in relapsed ALL, specifically T-ALL.

7500 Background: Mutations in the isocitrate dehydrogenase-1 gene ( IDH1) result in myeloid differentiation arrest and accumulation of the oncometabolite 2-hydroxyglutarate (2-HG), promoting leukemogenesis. We report a primary safety and efficacy analysis of the IDH1 inhibitor ivosidenib (IVO; 500 mg PO daily D15-continous) combined with venetoclax (VEN; D1-14 per 28-day cycle), with and without azacitidine (AZA; 75mg/m2 D1-7). Methods: Eligible patients age ≥18 with IDH1 mutated myeloid malignancies (high-risk MDS and AML) enrolled into one of three successive cohorts (Cohort 1: IVO+VEN 400 mg, Cohort 2: IVO+VEN 800 mg, Cohort 3: IVO+VEN 400 mg+AZA). Primary endpoints include safety and tolerability and overall response rate (ORR) by revised IWG criteria. Key secondary endpoints include survival endpoints and PK correlates. Results: 19 patients (median age 68) enrolled, 17 with AML: 9 relapsed/refractory AML (R/R; median 1 prior line of therapy), 5 treatment naïve AML, and 3 HMA-failure MDS with secondary AML. Two patients had high-risk MDS. ELN risk was favorable, intermediate, and adverse risk in 37%, 15%, and 47%. Co-mutations included NPM1 (37%), chromatin-spliceosome (32%), methylation (16%), and RAS pathway (21%). Adverse events of special interest included IDH differentiation syndrome (n=4, grade > 3 in 1) and tumor lysis syndrome (TLS; n=2), including one grade 3 TLS event in a NPM1+ patient (successfully managed without hemodialysis). In evaluable patients (n=18), composite complete remission (CRc: CR+CRi+CRh) rates were 78% overall (treatment naive: 100%, R/R: 75%), and 67%, 100%, and 67% by cohort (median time to best response: 2 months). 7 (50%) patients achieving CRc were also MRD negative by flow cytometry. 1 patient had HI without CR/CRi and 1 had a MLFS. 9 (50%) patients remain on study, 3 (17%) proceeded to SCT in CR, 2 were non-responders, and 5 (22%) experienced progressive disease following CRc occurring after a median of 3 months. After a median follow up of 3.5 months, median OS was not reached in treatment naïve patients, and 9.7 months in R/R patients. Conclusions: IVO+VEN +AZA therapy is well tolerated and highly effective for patients with IDH1 mutated AML. Follow up and accrual is ongoing to better define duration and biomarkers of response. Clinical trial information: NCT03471260 . [Table: see text]

Phosphatidylinositol-3-kinase (PI3K) signaling plays a crucial role in oncogene-mediated tumor growth and proliferation. Buparlisib (BKM120) is an oral pan-class I PI3K inhibitor. This phase I study was conducted to determine the dose limiting toxicity (DLT) and maximum tolerated dose (MTD) of BKM120 in patients (pts) with relapsed/refractory acute leukemias. Fourteen pts (12 acute myeloid leukemia, 1 acute lymphoblastic leukemia, and 1 mixed phenotype leukemia) were enrolled. Twelve pts received BKM-120 80 mg/day and two 100 mg/day. The MTD was 80 mg/day. Of the 14 patients treated, the best response was stable disease in one patient that lasted 82 days. The median survival for all patients was 75 days (range 10–568). Three patients with a 3q26 chromosome abnormality had a significantly improved median survival of 360 days (range 278–568) as compared to a median survival of 57 days (range, 10–125) among the 11 other patients. The most frequent drug-related toxicities included confusion, mucositis, dysphagia, and fatigue. Western blot profiling revealed a decrease in p-pS6K/total pS6K in 5/7 (71%) available patient samples with a mean quantitative inhibition of 65% (range, 32–100%) and a decrease in p-FOXO3/total FOXO3 in 4/6 (67%) samples with a mean quantitative inhibition of 93% (range, 89–100%). BKM120 administered at 80 mg/day showed modest efficacy and was tolerable in advanced acute leukemias.