Abstract 1022: Characterization of lurbinectedin as a single agent and in combinations with DNA damage response inhibitor for the treatment and bio-marker discovery of SCLC

AbstractAberrant and exclusive expression of chromatin regulators in retinoblastoma (RB) in contrast to terminally differentiated normal retina presents a unique opportunity of selective targeting for RB. However, precise roles of these chromatin regulators in RB development and their potential as therapeutic targets have not been defined thoroughly. Here, we report that targeting of disruptor of telomeric silencing 1-like (DOT1L), a histone H3K79 methyltransferase, sensitizes RB cells to chemotherapeutic drugs by impairing the DNA damage response and thereby potentiating apoptosis while it is largely inefficacious as a single-agent therapy. Moreover, we identified high mobility group AT-hook 2 (HMGA2) as a novel DOT1L target gene in RB cells and found that its aberrant expression is dependent on DOT1L. As HMGA2 depletion reduced CHK1 phosphorylation during DNA damage response and augmented the drug sensitivity in RB cells, our results suggested that DOT1L targeting has a dual role in chemosensitization of RB cells by directly interfering with the immediate involvement of DOT1L in early DNA damage response upon genotoxic insults and also by downregulating the expression of HMGA2 as a rather late effect of DOT1L inhibition. Furthermore, we provide the first preclinical evidence demonstrating that combined therapy with a DOT1L inhibitor significantly improves the therapeutic efficacy of etoposide in murine orthotopic xenografts of RB by rendering the response to etoposide more potent and stable. Taken together, these results support the therapeutic benefits of DOT1L targeting in combination with other chemotherapeutic agents in RB, with mechanistic insights into how DOT1L targeting can improve the current chemotherapy in an RB cell-selective manner.

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Combination of the Histone Deacetylase Inhibitor Vorinostat and Dasatinib Increases Apoptosis in Bcr-abl+ Cells and Reverses Changes Associated with CML Progression.

Blood ◽

10.1182/blood.v108.11.2165.2165 ◽

2006 ◽

Vol 108 (11) ◽

pp. 2165-2165

Author(s):

Leo Kretzner ◽

Anna Scuto ◽

Agnes Juhasz ◽

Richard Jove ◽

Yun Yen ◽

...

Keyword(s):

Dna Damage ◽

Histone Deacetylase ◽

Dna Damage Response ◽

Histone Deacetylase Inhibitors ◽

Fusion Gene ◽

Single Agent ◽

Chronic Phase ◽

Myelogenous Leukemia ◽

Advanced Phase ◽

Damage Response

Abstract Chronic myelogenous leukemia (CML) is associated with the bcr-abl fusion gene product, a constitutively active non-receptor tyrosine kinase driving cell division. The potent bcr-abl kinase inhibitor, dasatinib, is now FDA approved for imatinib-refractory patients, being active in most cases other than those with the T315I mutation. However, accelerated phase CML is typified by further genetic changes, including the suppression of various DNA damage response and apoptosis related proteins (Radich, et al PNAS 2006). Thus a novel approach which may reverse these changes, might provide better treatment of accelerated phase CML. A new class of agents targeting epigenetic processes, the histone deacetylase inhibitors (HDACi), is believed to act upon chromatin allowing re-expression of tumor suppressor genes believed to be closed off to transcription by the tumor in its effort to grow in an uncontrolled manner. We reasoned that adding an HDACi to dasatinib treatment of CML cells could promote re-expression of genes responding to genetic instability in these cells. To test this hypothesis we tested dasatinib (D) and the HDACi Vorinistat (V, suberoylanilide hydroxamic acid, SAHA) alone and in combination, using K562 cells. Apoptosis was measured by Annexin V staining after 48 hours. Apoptosis results: 1uM Vorinostat: 10%; 2 uM V: 16%. Dasatinib 0.5 nM: 28%, 1 nM D: 44% In combination, 1uM V + 0.5 nM D: 41%, 1 uM V + 1nM D: 64%, 2 uM V + 0.5 nM D: 65%, 2 uM V + 1 nM D: 67%, suggesting significant increase in apoptosis for the combination over either single agent treatment alone. We therefore began surveying panels of DNA damage- and apoptosis-related genes by means of RT-PCR. Studying the combination of 2 uM V + 1 nM D, we found increased expression of several proteins, including GADD45G and FANCG, both DNA damage response proteins suppressed in the progression to accelerated phase CML. Other proapoptotic proteins were increased such as MAP2K6, SEMA4A, BIK, and TNF superfamily members 7 and 25. This data suggests that the changes associated with progression from chronic phase to accelerated and blast crisis CML may be epigenetic in nature, and that these changes may be reversed by the combination of vorinostat and dasatinib. A clinical trial of dasatanib and vorinostat in advanced phase CML would be of value.

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