Phase I study of the novel Cdc2/CDK1 and AKT inhibitor terameprocol in patients with advanced leukemias.

PURPOSE: Inhibiting survivin and Cdc2 (CDK1) has preclinical anti-leukemic activity. Terameprocol is a small molecule survivin and Cdc2/CDK1 inhibitor that was studied in a Phase I dose-escalation trial. PATIENTS AND METHODS: Sixteen patients with advanced acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) were enrolled and 15 treated with Terameprocol in three dose cohorts intravenously three times per week for 2 weeks every 21 days. RESULTS: Patients had AML (n = 11), chronic myelogeneous leukemia in blast phase (CML-BP, n = 2) and one each T-cell acute lymphoblastic leukemia (T-ALL) and MDS. Four, five and six patients were treated at the 1000, 1500 and 2200 mg Terameprocol dose cohorts respectively. Common related treatment emergent adverse events (TEAE) were grade 1 or 2 headache, transaminitis and pruritus, with one grade 4 serious AE (SAE) of pneumonia. No dose limiting toxicity (DLT) was observed, however, due to other observed grade 3 TEAE the recommended phase 2 dose (RP2D) was determined at 1500 mg 3×/week for 2 weeks of a 21-day cycle. Partial remission and transfusion independence in a CML-BP patient (1500 mg cohort) and hematological improvement in erythroid (HI-E) and platelet lineage (HI-P) in an AML patient were observed. Five AML patients had stable disease greater/equal to 2 months. Pharmacodynamic studies showed a reduction of CDK1 and phospho-AKT protein expression. CONCLUSION: Terameprocol can be safely administered to advanced leukemia patients, sufficient drug exposure was obtained and clinical activity and biomarker modulation were observed.

BCL-2 family proteins as 5-Azacytidine-sensitizing targets and determinants of response in myeloid malignancies.

Synergistic molecular vulnerabilities enhancing hypomethylating agents in myeloid malignancies have remained elusive. RNA-interference drug modifier screens identified antiapoptotic BCL-2 family members as potent 5-Azacytidine-sensitizing targets. In further dissecting BCL-XL, BCL-2 and MCL-1 contribution to 5-Azacytidine activity, siRNA silencing of BCL-XL and MCL-1, but not BCL-2, exhibited variable synergy with 5-Azacytidine in vitro. The BCL-XL, BCL-2 and BCL-w inhibitor ABT-737 sensitized most cell lines more potently compared with the selective BCL-2 inhibitor ABT-199, which synergized with 5-Azacytidine mostly at higher doses. Ex vivo, ABT-737 enhanced 5-Azacytidine activity across primary AML, MDS and MPN specimens. Protein levels of BCL-XL, BCL-2 and MCL-1 in 577 AML patient samples showed overlapping expression across AML FAB subtypes and heterogeneous expression within subtypes, further supporting a concept of dual/multiple BCL-2 family member targeting consistent with RNAi and pharmacologic results. Consequently, silencing of MCL-1 and BCL-XL increased the activity of ABT-199. Functional interrogation of BCL-2 family proteins by BH3 profiling performed on patient samples significantly discriminated clinical response versus resistance to 5-Azacytidine-based therapies. On the basis of these results, we propose a clinical trial of navitoclax (clinical-grade ABT-737) combined with 5-Azacytidine in myeloid malignancies, as well as to prospectively validate BH3 profiling in predicting 5-Azacytidine response.

Optimization of regulated LTR-mediated expression.

Retroviral vectors are ideally suited to the study of gene function, allowing efficient, stable expression. Many biological systems (e.g., cell cycle, apoptosis) require the use of regulated expression systems. We therefore developed a regulated retroviral vector system, TRA99, based on a tetracycline transactivator-dependent LTR, where the MMLV enhancer was replaced with a tetracycline-response element. Using fluorescence-activated flow cytometric analysis of a destabilized green fluorescent protein to monitor expression levels, we optimized the minimal promoter configuration with respect to both activated and repressed transcription. The TRA99 vectors demonstrate regulated expression with activated levels comparable to those of standard retroviral vectors and repressed levels indistinguishable from background. This was achieved without using an internal promoter cassette, thus retaining the cis-packaging elements requisite for helper-mediated transfer.

Purification and biologic characterization of plasma-derived megakaryocyte growth and development factor.

The isolation and cloning of the ligand for the cytokine receptor, Mpl, have been recently described. In this report we present details of the purification of this novel cytokine (megakaryocyte growth and development factor [MGDF]) from aplastic canine plasma. Two forms of canine MGDF, with apparent molecular weights of 25 kD and 31 kD and sharing a common N-terminal amino acid sequence, were isolated. The sole contaminant detected in purified 25-kD or 31-kD MGDF was canine Ig. Canine MGDF is characterized as a human megakaryocyte colony-stimulating factor that acts synergistically with human recombinant stem cell factor but not interleukin-3. MGDF also appears to be physiologically regulated in response to platelet demand. In canine and murine models, serum levels of MGDF activity peak during the thrombocytopenic periods after irradiation, 5-fluorouracil, or antiplatelet antisera injections. These data indicate that the megakaryocyte-stimulating activity that accumulates in plasma in response to platelet losses is a novel cytokine that functions through an interaction with the Mpl cytokine receptor.

The induction of growth factor-independence in murine myelocytes by oncogenes results in monoclonal cell lines and is correlated with cell crisis and karyotypic instability.

Infection of established (IL-3)-dependent hematopoietic cell lines with Abelson murine leukemia virus (A-MLV) abrogates their requirement for IL-3 and leads to non-autocrine growth factor-independent cells. We were interested to determine whether A-MLV can induce IL-3 independence also in non-established cells. To obtain long-term cultures of diploid myelocytes, splenic hematopoietic cells were first infected with MMCV, a murine retrovirus carrying the avian v-myc oncogene. These cultures were superinfected with A-MLV. In three independent experiments, the first growth factor-independent cells appeared between 18 and 43 days after superinfection with A-MLV and represented .02-1% of the population. Furthermore, the cultures that became growth factor-independent were monoclonal for integration of the v-abl gene. These results indicate that the acquisition of growth factor-independence after superinfection of v-myc-expressing cells with A-MLV is a rare event. The low frequency of growth factor-independent cells was not due to a low percentage of infected cells, since 15-25% of the cells were infected with A-MLV after 7 days. The first appearance of growth factor-independent cells coincided with crisis in the cultures, as indicated by a high incidence of cell death and a reduced overall growth rate of the cell populations. These growth factor-independent cells exhibited variable karyotypes, including many that were near-triploid to near-tetraploid. In summary, growth factor-independence induced by super-infection with A-MLV, like that induced by double-infection with v-myc- and v-H-ras-containing viruses, is associated with unstable karyotypes. The growth factor-independent cells show variable ploidy characteristic of cells which survived crisis.

Autocrine growth and progression of murine X-ray-induced T cell lymphomas.

Primary tumors of X-ray-induced murine T cell lymphomas comprise autocrine, growth factor-dependent cells. We have grown cell lines from primary X-ray-induced thymic lymphomas (PXTLs) under conditions which minimize the progression of the cells from factor dependence to factor independence. All (22) PXTL lines grown secrete a growth factor which supports their own growth and which we will call lymphoma growth factor LGF. LGF-dependent cells are non-tumorigenic or poorly tumorigenic, do not clone in soft agar, have no detectable rearrangements in the c-myc or Pim-1 region and possess near diploid or pseudodiploid karyotypes without evidence for trisomy of chromosomes nos. 15 or 17. PXTL-secreted LGF has no interleukin 1, 2, or 3 activity nor do LGF-secreting cells synthesize detectable IL-1, -2, or -3 mRNA. LGF contains no detectable interferon or GM-CSF activity in specific bioassays. Purified EGF, TGF beta, and interleukin preparations are inactive on LGF-dependent PXTL cells. Thus LGF appears to be a new growth factor that is required for the proliferation of non-progressed T lymphoma cells. Upon progression PXTL cells become growth factor independent, are highly tumorigenic in vivo, clone in soft agar, and assume a near triploid karyotype containing numerous chromosomal aberrations. Thus in X-ray-induced lymphomagenesis an autocrine, LGF-dependent phase precedes the progressed phase characterized by rearrangements in the myc and/or Pim-1 regions as well as by many chromosomal aberrations visible in the karyotype.