Insights into the cellular pharmacological properties of the BET-inhibitor OTX015/MK-8628 (birabresib), alone and in combination, in leukemia models

Lucile Astorgues-Xerri, Ramiro Vázquez, Elodie Odore, Keyvan Rezai, Carmen Kahatt, Sarah Mackenzie, Mohamed Bekradda, Marie-Magdelaine Coudé, Herve Dombret, Claude Gardin, Francois Lokiec, Eric Raymond, Kay Noel, Esteban Cvitkovic, Patrice Herait, Francesco Bertoni & María E. Riveiro

To cite this article: Lucile Astorgues-Xerri, Ramiro Vázquez, Elodie Odore, Keyvan Rezai, Carmen Kahatt, Sarah Mackenzie, Mohamed Bekradda, Marie-Magdelaine Coudé, Herve Dombret, Claude Gardin, Francois Lokiec, Eric Raymond, Kay Noel, Esteban Cvitkovic, Patrice Herait, Francesco Bertoni & María E. Riveiro (2019): Insights into the cellular pharmacological properties of the BET- inhibitor OTX015/MK-8628 (birabresib), alone and in combination, in leukemia models, Leukemia & Lymphoma, DOI: 10.1080/10428194.2019.1617860
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Insights into the cellular pharmacological properties of the BET-inhibitor OTX015/MK-8628 (birabresib), alone and in combination, in
leukemia models
Lucile Astorgues-Xerriaω, Ramiro V´azquezbω, Elodie Odorec, Keyvan Rezaic, Carmen Kahatta,
Sarah Mackenziea, Mohamed Bekraddaa, Marie-Magdelaine Coude´d, Herve Dombretd, Claude Gardind, Francois Lokiecc, Eric Raymonde, Kay Noelf, Esteban Cvitkovicf, Patrice Heraitf, Francesco Bertonib and Mar´ıa E. Riveiroa
aOncology Therapeutic Development, Clichy, France; bInstitute of Oncology Research, Universit`a della Svizzera Italiana, Bellinzona, Switzerland; cRadioPharmacology Department, Curie Institute–Rene Huguenin Hospital, Saint Cloud, France; dLaboratoire de Transfert des Leuc´emies, Universit´e Paris Diderot, Paris, France; eMedical Oncology Department, CHUV, Lausanne, Switzerland; fOncoethix SA, Lucerne, Switzerland

ARTICLE HISTORY Received 30 January 2019; revised 27 April 2019; accepted 2 May 2019

The bromodomain and extra-C-terminal domain (BET) protein family is a class of epigenetic readers that recog- nize acetyl-lysine residues of histones, and their targeting with small molecules is a novel therapeutic approach [1,2]. OTX015 was the first BET inhibitor to successfully enter into the clinics [3–5], as a result of preclinical anti- tumor activity in a wide range of neoplasms [6–12]. Following our initial report of activity in acute lympho- blastic leukemia (ALL) and acute leukemia (AML) [13], we further studied OTX015 in vitro anti-proliferative activity in 10 leukemia cell lines, including AML (HL60, U937), T-ALL (CCRF-CEM, MOLT-3, Jurkat), chronic myeloid leuke- mia (CML; K562, NALM1) and JAK2-V617F-positive myeloproliferative neoplasms (MPN; SET2, MUTZ8, HEL92.1.7), bearing typical genetic alterations observed in clinics (Supplementary Methods; Table 1). Six cell lines were sensitive at concentrations achievable in plasma of patients with hematologic malignancies treated with OTX015 [14]. The most sensitive cell lines were SET2,
HEL92.1.7, HL60 and U937 (EC50 < 500 nM, Emax > 60%),
while two T-ALL cell types (CCRF-CEM, MOLT-3) and the CML K562 cells appeared resistant (EC50 > 6 mM). OTX015 activity was similar to what was seen with JQ1, and no significant correlations were observed between sensitivity
to BET inhibition and genetic lesions (BCR-ABL1 fusion protein, KRAS, NRAS, TP53, JAK2 V617F or FLT3 mutations). Cell cycle and apoptosis induction were evaluated in a subset of cell lines, including two resistant models

(NALM1, K562) after 48-h treatments with 500 nM OTX015 (Figure 1(A)). The drug mainly exerted cytostatic effects, but also pro-apoptotic based on the cellular context or genetic background, as observed in JAK-mutated cell lines (Figure 1(B)).
To assess whether the resistance was due to a low cel- lular uptake, we analyzed three sensitive (Jurkat, HL60, U937) and two resistant (MOLT-3, K562) leukemic cell lines during 6 h of drug exposure. OTX015 cellular levels
rapidly increased (<5 min) in both sensitive and resistant
cell lines, with a mean concentration of 15 ng/ml/106 cells (3–23 ng/ml/106 cells) after the 6-h incubation (Figure 1(C)), and extracellular levels remained stable dur- ing this period (~200 ng/ml). Thus, OTX015 antiprolifera- tive effects did not appear as related to the dynamics of
absorption. In agreement, OTX015 induced a time- dependent reduction (p < .05) of MYC protein and mRNA expression in sensitive (HL60) and resistant (K562) cells
(Figure S1 (A,B)). The anti-tumor activity of BET inhibitors has been largely attributed to MYC down-regulation. In this case, MYC would not be related to drug sensitivity, but would be a surrogate marker of OTX015 interaction with its targets. This occurred in 4/6 sensitive cell lines after 4 h of exposure and was strongly maintained up to 72 h. On the other hand, in two resistant cell lines (MUTZ8, K562) such modulation was transitory with recovery to baseline levels after 48 h (Figure S1(C)). Similarly, OTX015 significantly down-regulated MTHFD1L

CONTACT Mar´ıa E. Riveiro [email protected] Oncology Therapeutic Development, 100 Rue Martre, 92110 Clichy, France; Francesco Bertoni [email protected] Institute of Oncology Research, via Vincenzo Vela 6, CH-6500 Bellinzona
*These authors contributed equally to this work.
Supplemental data for this article can be accessed here.
© 2019 Informa UK Limited, trading as Taylor & Francis Group


Table 1. The BET inhibitor OTX015 displays antiproliferative effects in a large spectrum of AML, ALL, CML and JAK2-mutated cell lines.
OTX015 JQ1

MPN SET2 120
(90–160) 85 520
(300–910) 88
MPN HEL92.1.7 1900
(800–4400) 77 2800
(1900–4300) 75
AML HL60 285
(204–398) 74 674
(492–950) 78
AML U937 384
(177–831) 60 1222
(541–2764) 67
(150–420) 39 750
(420–1340) 40
ALL-T Jurkat 282
(217–367) 37 967
(601–1557) 37
Ph þ CML NALM1 >6000 – 358
(146–879) 33
ALL-T CCRF-CEM >6000 – >6000 –
ALL-T MOLT-3 >6000 – >6000 –
Ph þ CML K562 >6000 – >6000 –

Tumor type Cell line

EC50 (nM)
(CI95) Emax (%)

EC50 (nM)
(CI95) Emax (%) KRAS NRAS TP53

EC50 and Emax (at 6 mM) for OTX015 and JQ-1 in leukemic cell lines after 72-h-exposure. Results represent the mean with CI95 of at least three independent experiments performed in triplicate. The cell panel was characterized for K-RAS, N-RAS, TP53, JAK2 V617F, NPM1 and FLT3 mutations and BCR-ABL1 fusion proteins. Red indicates mutation, blue is wild-type protein and gray not determined.

and BCL2 in all leukemic cell lines after 4 or 24 h of treat- ment, in a similar manner as MYC, although the effect on BCL2 appeared reversible in three nonresistant cell lines (Figure S2). HEXIM1, SESN3, CDKN1A, HIST1H2BJ,
HIST1H2BK, HIST2H2BE and HIST2H4A were up-regulated in both sensitive and resistant cell lines after 4 h and/or 24 h of exposure. BRD2 mRNA levels were significantly increased (p < .05) in all the leukemic models but one after 24 h of treatment, and changes in BRD3 and BRD4
levels did not differ based on sensitivity (Figure S3).
An important area for further clinical development of BET inhibitors in cancer is the identification of active combination schedules. Thus, we evaluated OTX015 in 48-h combination treatments with chemotherapeutic agents in sensitive (HL60, U937, HEL92.1.7, Jurkat) and resistant (K562, MUTZ8) models (Figure 1(D), Table S1). Synergism, additivity and antagonism were defined according to the Chou–Talalay combination method (Supplementary Methods). Methotrexate and cytarabine were synergistic and additive, respectively, with OTX015 in all the models. Addition of daunorubicin led to syner- gism in the OTX015-resistant K562 and additivity in the remaining cell lines. Dexamethasone exerted synergistic or additive effects in three of four cell lines, whereas everolimus was additive in three models. Concomitant combination of OTX015 with demethylating agent azaciti- dine was additive in the OTX015-sensitive models and synergistic in K562 cells despite a primary resistance to both drugs. Similar results were observed with decita- bine, another hypomethylating agent (data not shown). The addition of the HDAC inhibitor panobinostat was beneficial in three models (synergism in two, additivity in

one). Finally, simultaneous exposure of OTX015 and ruxo- litinib in three JAK2-mutated cell lines was beneficial in two cell lines (synergism in HEL92.1.7, additivity in MUTZ8). Sequential combination of azacitidine (Figure 1(E)) or panobinostat (Figure 1(F)) followed by OTX015 (for 48–48, 72–24 or 72–48 h) generally resulted more efficient than concomitant treatments. Importantly, the
combination of OTX015 (500 nM) with azacitidine (3 mM) induced a significant increase in the subG0/1 fraction, indicative of cell death, with respect control in the
OTX015 sensitive HL60 cells. However, this effect was comparable to azacitidine single agent (Figure 1(G)). In both cases, this correlated with increased cleaved cas- pase-3 (Figure 1(H)).
We then evaluated the downstream effects of OTX015 (500 nM) combined with azacitidine (3 mM) or panobino- stat (20 nM) in sensitive and resistant OTX015 cell lines.
In HL-60 cells, 24 h of OTX015 combined with azacitidine or panobinostat increased apoptosis induction markers such as cleaved caspase-3 and PARP, correlating with increased subG0/G1 after 24 h concomitant exposure with azacitidine. In K562 cells, combination of OTX015 with either drug increased p21 expression, likely related to the cell cycle arrest in G1 observed after 24 h concomi- tant treatment with azacitidine and panobinostat (Figure 1(G)). Furthermore, 24 h OTX015 with azacitidine or pano- binostat synergistically induced C-MYC downregulation in K562 cells (Figure 1(H)).
Epigenetic therapy with BET inhibitors has emerged as a novel approach for cancer treatment, not necessarily via a cytotoxic mechanism but potentially by reprogram- ing the network affecting chromatin structure and


Figure 1. OTX015-mediated effects in leukemia cell models. After a 48-h treatment with 500 nM OTX015, the effects on the cell cycle (A) and apoptosis (B) were evaluated by FACScan and expressed as percentage of cells per cell cycle phase or Annexin V positive, respectively. In A and B, cell lines are ordered according to decreasing OTX015 sensitivity (Emax values), represented by green triangles. (C) OTX015 concentrations in cell supernatants (ng/ml) and pellets (ng/ml/1 106 cells) were determined by UPLC/MS/MS at a range of time points (0–6 h). OTX015 combinations showing additive or synergistic effects after (D) 48 h-con- comitant exposure with various antileukemic agents, and after concomitant or sequential schedules with (E) azacitidine, and (F) panobinostat. Dotted line, CI 1 ± 0.1. Cell lines: (1) HL60; (2) U937; (3) Jurkat; (4) K562; (5) HEL92.1.7; (6) MUTZ8. Metho.: metho- trexate; Dauno.: daunorubicin; Cyt.: cytarabine; Dexa.: dexamethasone; Evero.: everolimus; Aza.: azacitidine; Pano.: panobinostat;
Ruxo.: ruxolitinib. CI values <0.9 indicate synergism, CI values between 0.9 and 1.1 indicate additive effects, and CI values >1.1 indicate antagonism. Evaluation of cell cycle progression (G) and C-MYC, apoptosis and cell cycle related pathway proteins (H)
were evaluated in HL60 and K562 cell lines following single agent, concomitant or sequential combination of 3 mM azacitidine or 20 nM panobinostat followed by 500 nM OTX015 for 24 h per agent. Western blots are representative of at least two independent experiments. In A and G, significant variations in the percentage of OTX015-treated cells in the G1, S and G2/M phases with respect to vehicle-treated controls were determined by a one-way ANOVA test (p < .01) followed by an SNK a posteriori test
(ωp < .05; ωωp < .01). In C, differences in the percentage of Annexin V stained cells between groups were determined by Student
test (ωp < .05; ωωp < .01). In A, C and G, variables were transformed when necessary to obtain homoscedasticity before the
ANOVA test. Each bar and vertical line represents the mean ± SEM. In all cases, n ≤ 3.


transcription. Our work provides novel data on OTX015 as single agent and in combination for different leukemia types and myeloproliferative neoplasms.

LAX, PH, EC and MER performed the conception and design of the research. EO, KR and FL worked on the development of methodology. LAX, EO, KR, FB and MER performed the acquisition of data. KR, FB and MER analyzed the data. RV, FB, CK, MB, ER and MER performed the writing, review and/ or revision of the manuscript. The technical and study super- vision was performed by SM, PH, HD, CG, FL, MB, EC, ER and MER.

Potential conflict of interest: Disclosure forms provided by the authors are available with the full text of this article online at

EC was founder and CSO of Oncoethix SA, and CEO of Oncology Therapeutic Development. PH was founder and CMO of Oncoethix SA. LAX, CK, SM, MB and MER were employees of Oncology Therapeutic Development. HD and FB received research funds from Oncology Therapeutic Development. FB received institutional research funds from Acerta, ADC Therapeutics, Bayer AG, Cellestia, CTI Life Sciences, EMD Serono, Helsinn, ImmunoGen, Menarini Ricerche, NEOMED Therapeutics 1, Oncology Therapeutic Development, PIQUR Therapeutics AG; consultancy fee from Helsinn, Menarini; expert statements provided to HTG; travel grants from Amgen, Astra Zeneca, Jazz Pharmaceuticals, PIQUR Therapeutics.

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