Russell T. Burke

CX-4945, a selective inhibitor of casein kinase-2 (CK2), exhibits anti-tumor activity in hematologic malignancies including enhanced activity in chronic lymphocytic leukemia when combined with fludarabine and inhibitors of the B-cell receptor pathway

CX-4945, a selective inhibitor of casein kinase-2 (CK2), exhibits anti-tumor activity in hematologic malignancies including enhanced activity in chronic lymphocytic leukemia when combined with fludarabine and inhibitors of the B-cell receptor pathway

The Selective Syk Inhibitor P505-15 (PRT062607) Inhibits B Cell Signaling and Function In Vitro and In Vivo and Augments the Activity of Fludarabine in Chronic Lymphocytic Leukemia

B-cell receptor (BCR) associated kinases including spleen tyrosine kinase (SYK) contribute to the pathogenesis of B-cell malignancies. SYK is persistently phosphorylated in a subset of non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL), and SYK inhibition results in abrogation of downstream kinase activity and apoptosis. P505-15 (also known as PRT062607) is a novel, highly selective, and orally bioavailable small molecule SYK inhibitor (SYK IC50 = 1 nM) with anti-SYK activity that is at least 80-fold greater than its affinity for other kinases. We evaluated the preclinical characteristics of P505-15 in models of NHL and CLL. P505-15 successfully inhibited SYK-mediated B-cell receptor signaling and decreased cell viability in NHL and CLL. Oral dosing in mice prevented BCR-mediated splenomegaly and significantly inhibited NHL tumor growth in a xenograft model. In addition, combination treatment of primary CLL cells with P505-15 plus fludarabine produced synergistic enhancement of activity at nanomolar concentrations. Our findings support the ongoing development of P505-15 as a therapeutic agent for B-cell malignancies. A dose finding study in healthy volunteers has been completed.

YM155 potently kills acute lymphoblastic leukemia cells through activation of the DNA damage pathway

BackgroundNovel-targeted therapies are in rapid development for the treatment of acute lymphoblastic leukemia (ALL) to overcome resistance and decrease toxicity. Survivin, a member of the inhibitor of apoptosis gene family and chromosome passenger complex, is critical in a variety of human cancers, including ALL. A well-established suppressor of survivin has been the small molecule, YM155. Reports are identifying other mechanisms of action for YM155. Therefore, we sought to investigate the mode of action and role of YM155 for therapeutic use in the context of ALL.MethodsPrimary ALL samples and ALL cell lines were interrogated with YM155 to identify drug sensitivity. Ph+ALL harboring the BCR-ABL1 oncogene were tested for any interaction with YM155 and the multi-kinase inhibitor dasatinib. Representative ALL cell lines were tested to identify the response to YM155 using standard biochemical assays as well as RNA expression and phosphorylation arrays.ResultsALL samples exhibited significant sensitivity to YM155, and an additive response was observed with dasatinib in the setting of Ph+ALL. ALL cells were more sensitive to YM155 during S phase during DNA replication. YM155 activates the DNA damage pathway leading to phosphorylation of Chk2 and H2AX. Interestingly, screening of primary patient samples identified unique and exquisite YM155 sensitivity in some but not all ALL specimens.ConclusionThese results are the first to have screened a large number of primary patient leukemic samples to identify individual variations of response to YM155. Our studies further support that YM155 in ALL induces DNA damage leading to S phase arrest. Finally, only subsets of ALL have exquisite sensitivity to YM155 presumably through both suppression of survivin expression and activation of the DNA damage pathway underscoring its potential for therapeutic development.

Longitudinal tracking of single live cancer cells to understand cell cycle effects of the nuclear export inhibitor, selinexor

Longitudinal tracking is a powerful approach to understand the biology of single cells. In cancer therapy, outcome is determined at the molecular and cellular scale, yet relationships between cellular response and cell fate are often unknown. The selective inhibitor of nuclear export, selinexor, is in development for the treatment of various cancers. Selinexor covalently binds exportin-1, causing nuclear sequestration of cargo proteins, including key regulators of the cell cycle and apoptosis. The cell cycle effects of selinexor and the relationships between cell cycle effects and cell fates, has not been described for individual cells. Using fluorescent cell cycle indicators we report the majority of cell death after selinexor treatment occurs from a protracted G1-phase and early S-phase. G1- or early S-phase treated cells show the strongest response and either die or arrest, while those treated in late S- or G2-phase progress to mitosis and divide. Importantly, the progeny of cell divisions also die or arrest, mostly in the next G1-phase. Cells that survive selinexor are negative for multiple proliferation biomarkers, indicating a penetrant, arrested state. Selinexor acts quickly, shows strong cell cycle selectivity, and is highly effective at arresting cell growth and inducing death in cancer-derived cells.

Inhibition of exportin-1 function results in rapid cell cycle-associated DNA damage in cancer cells

Selective inhibitors of nuclear export (SINE) are small molecules in development as anti-cancer agents. The first-in-class SINE, selinexor, is in clinical trials for blood and solid cancers. Selinexor forms a covalent bond with exportin-1 at cysteine-528, and blocks its ability to export cargos. Previous work has shown strong cell cycle effects and drug-induced cell death across many different cancer-derived cell lines. Here, we report strong cell cycle-associated DNA double-stranded break formation upon the treatment of cancer cells with SINE. In multiple cell models, selinexor treatment results in the formation of clustered DNA damage foci in 30-40% of cells within 8 hours that is dependent upon cysteine-528. DNA damage strongly correlates with G1/S-phase and decreased DNA replication. Live cell microscopy reveals an association between DNA damage and cell fate. Cells that form damage in G1-phase more often die or arrest, while those damaged in S/G2-phase frequently progress to cell division. Up to half of all treated cells form damage foci, and most cells that die after being damaged, were damaged in G1-phase. By comparison, non-transformed cell lines show strong cell cycle effects but little DNA damage and less death than cancer cells. Significant drug combination effects occur when selinexor is paired with different classes of agents that either cause DNA damage or that diminish DNA damage repair. These data present a novel effect of exportin-1 inhibition and provide a strong rationale for multiple combination treatments of selinexor with agents that are currently in use for the treatment of different solid cancers.

Functional genomic landscape of acute myeloid leukaemia.

The implementation of targeted therapies for acute myeloid leukaemia (AML) has been challenging because of the complex mutational patterns within and across patients as well as a dearth of pharmacologic agents for most mutational events. Here we report initial findings from the Beat AML programme on a cohort of 672 tumour specimens collected from 562 patients. We assessed these specimens using whole-exome sequencing, RNA sequencing and analyses of ex vivo drug sensitivity. Our data reveal mutational events that have not previously been detected in AML. We show that the response to drugs is associated with mutational status, including instances of drug sensitivity that are specific to combinatorial mutational events. Integration with RNA sequencing also revealed gene expression signatures, which predict a role for specific gene networks in the drug response. Collectively, we have generated a dataset—accessible through the Beat AML data viewer (Vizome)—that can be leveraged to address clinical, genomic, transcriptomic and functional analyses of the biology of AML.Analyses of samples from patients with acute myeloid leukaemia reveal that drug response is associated with mutational status and gene expression; the generated dataset provides a basis for future clinical and functional studies of this disease.

Loss of p53 expression in cancer cells alters cell cycle response after inhibition of exportin-1 but does not prevent cell death

ABSTRACT The tumor suppressor protein p53 is central to the cellular stress response and may be a predictive biomarker for cancer treatments. Upon stress, wildtype p53 accumulates in the nucleus where it enforces cellular responses, including cell cycle arrest and cell death. p53 is so dominant in its effects, that p53 enforcement – or – restoration therapy is being studied for anti-cancer therapy. Two mechanistically distinct small molecules that act via p53 are the selective inhibitor of nuclear export, selinexor, and MDM2 inhibitor, nutlin-3a. Here, individual cells are studied to define cell cycle response signatures, which captures the variability of responses and includes the impact of loss of p53 expression on cell fates. The individual responses are then used to build the population level response. Matched cell lines with and without p53 expression indicate that while loss-of-function results in altered cell cycle signatures to selinexor treatment, it does not diminish overall cell loss. On the contrary, response to single-agent nutlin-3a shows a strong p53-dependence. Upon treatment with both selinexor and nutlin-3a there are combination effects in at least some cell lines – even when p53 is absent. Collectively, the findings indicate that p53 does act downstream of selinexor and nutlin-3a, and that p53 expression is dispensable for selinexor to cause cell death, but nutlin-3a response is more p53-dependent. Thus, TP53 disruption and lack of expression may not predict poor cell response to selinexor, and selinexor’s mechanism of action potentially provides for strong efficacy regardless of p53 function.

Through the Looking Glass: Time-lapse Microscopy and Longitudinal Tracking of Single Cells to Study Anti-cancer Therapeutics

The response of single cells to anti-cancer drugs contributes significantly in determining the population response, and therefore is a major contributing factor in the overall outcome. Immunoblotting, flow cytometry and fixed cell experiments are often used to study how cells respond to anti-cancer drugs. These methods are important, but they have several shortcomings. Variability in drug responses between cancer and normal cells, and between cells of different cancer origin, and transient and rare responses are difficult to understand using population averaging assays and without being able to directly track and analyze them longitudinally. The microscope is particularly well suited to image live cells. Advancements in technology enable us to routinely image cells at a resolution that enables not only cell tracking, but also the observation of a variety of cellular responses. We describe an approach in detail that allows for the continuous time-lapse imaging of cells during the drug response for essentially as long as desired, typically up to 96 hr. Using variations of the approach, cells can be monitored for weeks. With the employment of genetically encoded fluorescent biosensors numerous processes, pathways and responses can be followed. We show examples that include tracking and quantification of cell growth and cell cycle progression, chromosome dynamics, DNA damage, and cell death. We also discuss variations of the technique and its flexibility, and highlight some common pitfalls.

Abstract 4645: Cell cycle specific effects and associated DNA damage of selective inhibitors of nuclear export (SINE)

Nuclear export of proteins is fundamental for cell growth and function. Selinexor is a SINE compound that is in clinical development for the treatment of different cancers. Selinexor forms a slowly reversible covalent bond to Exportin-1 (XPO1), preventing its association with protein cargos, thereby resulting in their nuclear retention. XPO1 cargos include the majority of tumor suppressor proteins (TSP) and cell cycle regulators such as p53, p21 and p27 that have key roles in cancer progression and drug response. It is unclear how selinexor affects cell cycle progression in individual cells and the subsequent stress and fate of those cells. To elucidate selinexor action, we developed cell lines that stably express fluorescent ubiquitin cell cycle reporters (FUCCI), and followed individual cells longitudinally using continuous time-lapse microscopy for 72 hours. We report that in fibrosarcoma-derived HT-1080 cells that express wildtype p53 and p21, 18% of the initial cell population became arrested with >90% in G1- or S-phase and 40% died with 64% from G1- or early S-phase after a cell cycle delay or arrest. We also found that 42% of cells divided, but the progeny died or arrested in G1- or S-phase of the next cell cycle - often after cell cycle arrest or slowed cell cycle progression. Using FUCCI, we tracked the response of cells treated acutely in specific cell cycle stages. Cells treated in G1-phase most often arrested or died in G1- or S-phase, whereas cells treated in G2-phase usually progressed to cell division. As FUCCI revealed S-phase progression defects and associated cell death, we further characterized this phenotype. Using nucleotide incorporation with fluorescent detection, we observed that as early as 2 hours after selinexor treatment only a subset of cells is undergoing DNA replication. Cells that were able to replicate their DNA are doing that inefficiently as both the rate and maximal levels of nucleotide incorporation are significantly reduced. S-phase arrest and progression defects may manifest as DNA double-strand breaks. We find a strong association between S-phase status and DNA damage. In some cells, the damage occurs within hours of selinexor treatment and appears as a striking cluster of foci. At 8 hours, nearly 35-45% of cells contain DNA damage clusters. Importantly, the damage clusters sometimes repair as determined by fixed cell time-course analysis and live-cell microscopy. We are exploring the nature of these DNA damage structures and the mechanisms of their formation and repair. In summary, selinexor is fast acting, shows cell cycle selectivity, results in DNA damage and is highly effective at arresting cell growth and inducing apoptosis in tumor cells. These data suggest that selinexor may exert anti-cancer effects even on slow growing tumors where the bulk of the cell mass presents a G1-like state and that it likely combines well with other cell cycle targeted therapeutics. Citation Format: Russell T. Burke, Joshua Marcus, John DeSisto, Yosef Landesman, James D. Orth. Cell cycle specific effects and associated DNA damage of selective inhibitors of nuclear export (SINE). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4645.