Karp, Judith E.

To improve the outcome of relapsed/refractory acute myeloid leukemia (AML), a randomized phase II trial of three novel regimens was conducted. Ninety patients were enrolled and were in first relapse or were refractory to induction/re‐induction chemotherapy. They were randomized to the following regimens: carboplatin‐topotecan (CT), each by continuous infusion for 5 days; alvocidib (formerly flavopiridol), cytarabine, and mitoxantrone (FLAM) in a timed sequential regimen; or sirolimus combined with mitoxantrone, etoposide, and cytarabine (S‐MEC). The primary objective was attainment of a complete remission (CR). A Simon two‐stage design was used for each of the three arms. The median age of the patients in the FLAM arm was older at 62 years compared with 55 years for the CT arm and the S‐MEC arm. The overall response was 14% in the CT arm (5/35, 90% CI 7%‐35%), 28% in the FLAM arm (10/36, 90% CI, 16%‐43%), and 16% in the S‐MEC arm (3/19, 90% CI, 4%‐36%). There were nine treatment‐related deaths, seven of which occurred in the FLAM arm with four of these in elderly patients. We conclude that the FLAM regimen had an encouraging response rate and should be considered for further clinical development but should be used with caution in elderly patients.

Abstract Current understanding suggests that malignant stem and progenitor cells must be reduced or eliminated for prolonged remissions in myeloid neoplasms such as acute myelogenous leukemia (AML) or myelodysplastic syndrome (MDS). Multicolor flow cytometry has been widely used to distinguish stem and myeloid progenitor cells from other populations in normal and malignant bone marrow. In this study, we present a method for assessing drug sensitivity in MDS and AML patient hematopoietic stem and myeloid progenitor cell populations ex vivo using the investigational Nedd8-activating enzyme inhibitor MLN4924 and standard-of-care agent cytarabine as examples. Utilizing a multicolor flow cytometry antibody panel for identification of hematopoietic stem cells, multipotent progenitors, common myeloid progenitors, granulocyte-monocyte progenitors, and megakaryocyte-erythroid progenitors present in mononuclear cell fractions isolated from bone marrow aspirates, we compare stem and progenitor cell counts after treatment for 24 hours with drug versus diluent. We demonstrate that MLN4924 exerts a cytotoxic effect on MDS and AML stem and progenitor cell populations, whereas cytarabine has more limited effects. Further application of this method for evaluating drug effects on these populations ex vivo and in vivo may inform rational design and selection of therapies in the clinical setting.

Abstract Purpose: The PARP inhibitor veliparib delays DNA repair and potentiates cytotoxicity of multiple classes of chemotherapy drugs, including topoisomerase I inhibitors and platinating agents. This study evaluated veliparib incorporation into leukemia induction therapy using a previously described topotecan/carboplatin backbone. Experimental Design: Employing a 3+3 trial design, we administered escalating doses of veliparib combined with topotecan + carboplatin in relapsed or refractory acute leukemias, aggressive myeloproliferative neoplasms (MPN), and chronic myelomonocytic leukemia (CMML). Results: A total of 99 patients received veliparib 10–100 mg orally twice daily on days 1–8, 1–14, or 1–21 along with continuous infusion topotecan 1.0–1.2 mg/m2/d + carboplatin 120–150 mg/m2/d on days 3–7. The MTD was veliparib 80 mg twice daily for up to 21 days with topotecan 1.2 mg/m2/d + carboplatin 150 mg/m2/d. Mucositis was dose limiting and correlated with high veliparib concentrations. The response rate was 33% overall (33/99: 14 CR, 11 CRi, 8 PR) but was 64% (14/22) for patients with antecedent or associated aggressive MPNs or CMML. Leukemias with baseline DNA repair defects, as evidenced by impaired DNA damage–induced FANCD2 monoubiquitination, had improved survival [HR = 0.56 (95% confidence interval, 0.27–0.92)]. A single 80-mg dose of veliparib, as well as veliparib in combination with topotecan + carboplatin, induced DNA damage as manifested by histone H2AX phosphorylation in CD34+ leukemia cells, with greater phosphorylation in cells from responders. Conclusions: The veliparib/topotecan/carboplatin combination warrants further investigation, particularly in patients with aggressive MPNs, CMML, and MPN- or CMML-related acute leukemias. Clin Cancer Res; 23(4); 899–907. ©2016 AACR.

Abstract Purpose: In preclinical studies, the PARP inhibitor veliparib enhanced the antileukemic action of temozolomide through potentiation of DNA damage. Accordingly, we conducted a phase 1 study of temozolomide with escalating doses of veliparib in patients with relapsed, refractory acute myeloid leukemia (AML) or AML arising from aggressive myeloid malignancies. Experimental Design: Patients received veliparib [20–200 mg once a day on day 1 and twice daily on days 4–12 in cycle 1 (days 1–8 in cycle ≥2)] and temozolomide [150–200 mg/m2 daily on days 3–9 in cycle 1 (days 1–5 in cycle ≥2)] every 28 to 56 days. Veliparib pharmacokinetics and pharmacodynamics [ability to inhibit poly(ADP-ribose) polymer (PAR) formation and induce H2AX phosphorylation] were assessed. Pretreatment levels of MGMT and PARP1 protein, methylation of the MGMT promoter, and integrity of the Fanconi anemia pathway were also examined. Results: Forty-eight patients were treated at seven dose levels. Dose-limiting toxicities were oral mucositis and esophagitis lasting >7 days. The MTD was veliparib 150 mg twice daily with temozolomide 200 mg/m2 daily. The complete response (CR) rate was 17% (8/48 patients). Veliparib exposure as well as inhibition of PAR polymer formation increased dose proportionately. A veliparib-induced increase in H2AX phosphorylation in CD34+ cells was observed in responders. Three of 4 patients with MGMT promoter methylation achieved CR. Conclusions: Veliparib plus temozolomide is well tolerated, with activity in advanced AML. Further evaluation of this regimen and of treatment-induced phosphorylation of H2AX and MGMT methylation as potential response predictors appears warranted. Clin Cancer Res; 23(3); 697–706. ©2016 AACR.

Abstract Purpose: DNA repair defects have been previously reported in myeloproliferative neoplasms (MPN). Inhibitors of PARP have shown activity in solid tumors with defects in homologous recombination (HR). This study was performed to assess MPN sensitivity to PARP inhibitors ex vivo. Experimental Design: HR pathway integrity in circulating myeloid cells was evaluated by assessing the formation of RAD51 foci after treatment with ionizing radiation or PARP inhibitors. Sensitivity of MPN erythroid and myeloid progenitors to PARP inhibitors was evaluated using colony formation assays. Results: Six of 14 MPN primary samples had reduced formation of RAD51 foci after exposure to ionizing radiation, suggesting impaired HR. This phenotype was not associated with a specific MPN subtype, JAK2 mutation status, or karyotype. MPN samples showed increased sensitivity to the PARP inhibitors veliparib and olaparib compared with normal myeloid progenitors. This hypersensitivity, which was most pronounced in samples deficient in DNA damage–induced RAD51 foci, was observed predominantly in samples from patients with diagnoses of chronic myelogenous leukemia, chronic myelomonocytic leukemia, or unspecified myelodysplastic/MPN overlap syndromes. Conclusions: Like other neoplasms with HR defects, MPNs exhibit PARP inhibitor hypersensitivity compared with normal marrow. These results suggest that further preclinical and possibly clinical study of PARP inhibitors in MPNs is warranted. Clin Cancer Res; 22(15); 3894–902. ©2016 AACR.

Key Points Agents that inhibit both complexes containing the mammalian target of rapamycin are particularly toxic to acute lymphocytic leukemia cells. This killing reflects engagement of a 4EBP1/c-MYC/PUMA axis downstream of mTORC1 and an NF-κB/EGR1/BIM axis downstream of mTORC2.

Abstract Background: Cytarabine and an anthracycline, the mainstay of AML therapy, affords a five-year survival below 30%. Accordingly, there is a continuing need for improved AML therapies. CPX-351 encapsulates within liposomes a fixed 5:1 molar ratio of cytarabine and daunorubicin that is synergistic (in vitro) and markedly improved in anti-leukemic activity (in vivo). Promising evidence of improved remission and survival rates with CPX-351 compared to standard of care treatments has also been observed clinically and a pivotal Phase 3 trial is currently ongoing. Because Chk1 inhibition has been shown to enhance the actions of both cytarabine and anthracyclines, there has been interest in assessing the effect of CPX-351 when combined with Chk1 inhibitors. Here we describe the evaluation of CPX-351 alone and in combination with the Chk1 inhibitors MK-8776 and LY2603618 in AML cell lines and in clinical AML samples ex vivo. Methods: Effects of CPX-351 on Chk1 phosphorylation and cell cycle distribution in the human AML lines U937 and HL-60 were analyzed by immunoblotting and flow cytometry. Effects of Chk1 inhibitors on CPX-351-induced apoptosis were assessed by flow cytometry after propidium iodide staining (DNA cleavage), Hoechst staining (nuclear fragmentation) and colony formation in soft agar (long-term survival). Effects CPX-351 ± MK-8776 on clinical AML samples were assayed using clonogenic assays. Results: Treatment of U937 cells with CPX-351 resulted in phosphorylation of Chk1 on Ser317 and Ser296 (sites of ATR-mediated phosphorylation and autophosphorylation, respectively) as well as S phase slowing consistent with Chk1 activation. Co-treatment of AML cell lines with Chk1 inhibitors + CPX-351 resulted in increased apoptotic morphological changes and DNA fragmentation as well as diminished clonogenic survival compared to CPX-351 alone. The CPX-351/MK-8776 combination displayed enhanced antiproliferative effects against some clinical AML isolates ex vivo compared to CPX-351 alone, with additional assays ongoing. Conclusions: Collectively, these results show that Chk1 inhibition enhances the cytotoxicity of CPX-351 in AML cell lines and some clinical AML samples, offering the possibility that CPX-351 may be well suited for combining with such molecularly targeted agents. Citation Format: Nicole D. Vincelette, Larry M. Karnitz, Judith E. Karp, Douglas B. Smith, Allan D. Hess, Lawrence D. Mayer, Scott H. Kaufmann. CPX-351 (cytarabine:daunorubicin liposome for injection) anti-leukemia activity is potentiated by Chk1 inhibition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3479. doi:10.1158/1538-7445.AM2015-3479

Key Points BCL2 mutations in FL correlate with activation-induced cytidine deaminase expression and frequently alter the amino acid sequence of the protein. Mutations in the BCL2 coding sequence at diagnosis are associated with shortened time to transformation and earlier death due to lymphoma.

ABSTRACTThe bone marrow provides a protective environment for acute myeloid leukemia (AML) cells that often allows leukemic stem cells to survive standard chemotherapeutic regimens. Targeting these leukemic stem cells within the bone marrow is critical for preventing relapse. We recently demonstrated that SDF‐1, a chemokine abundant in the bone marrow, induces apoptosis in AML cell lines and in patient samples expressing high levels of its receptor, CXCR4. Here we show that a subset of osteoblast lineage cells within the bone marrow can protect AML cells from undergoing apoptosis in response to the SDF‐1 naturally present in that location. In co‐culture systems, osteoblasts at various stages of differentiation protected AML cell lines and patient isolates from SDF‐1‐induced apoptosis. The differentiation of the osteoblast cell lines, MC3T3 and W‐20‐17, mediated this protection via a cell contact‐independent mechanism. In contrast, bone marrow‐derived mesenchymal cells, the precursors of osteoblasts, induced apoptosis in AML cells via a CXCR4‐dependent mechanism and failed to protect AML cells from exogenously added SDF‐1. These results indicate that osteoblasts in the process of differentiation potently inhibit the SDF‐1‐driven apoptotic pathway of CXCR4‐expressing AML cells residing in the bone marrow. Drugs targeting this protective mechanism could potentially provide a new approach to treating AML by enhancing the SDF‐1‐induced apoptosis of AML cells residing within the bone marrow microenvironment. J. Cell. Biochem. 115: 1128–1137, 2014. © 2013 Wiley Periodicals, Inc.