PS967 PRECLINICAL ACTIVITY OF THE NOVEL ORAL DUAL BET‐CBP/P300 INHIBITORS, NEO1132 AND NEO2734, IN ACUTE MYELOID LEUKEMIA
Authors: Canales T. Martiañez , van Gils N. , Vermue E. , Rutten A. , Denkers F. , van der Deure T. , Giles F. , Smit L. 
Published: June 2019

Background:For decades, combination chemotherapy has been the therapeutic strategy to treat acute myeloid leukemia (AML). Although this treatment induces complete remission in most patients, only 30–40% of patients survive five years after diagnosis. These low cure rates are mainly due to relapse caused by the survival of a small subpopulation of leukemia cells with stem cell features, named “leukemic stem cells” (LSCs). The bromodomain (BRD) extra‐terminal (BET) protein Brd4 is a regulator of c‐Myc and an important therapeutic target in AML. In vivo, inhibition of Brd4 eradicates AML progenitors and reduces AML burden in mice. While treatment with BET inhibitors induces clinical responses in AML, these are usually partial and transient. Cyclic AMP response element‐binding protein (CREB)‐binding protein (CBP) and E1A interacting protein of 300 kDa (EP300 or P300) are homologues BRD‐containing transcriptional co‐activators that regulate transcription through their acetyltransferase activity. We studied NEO2734 and NEO1132, orally‐bioavailable, first‐in‐class dual BET and CBP/P300 inhibitors in preclinical models of AML.Aims:To evaluate the efficiency of NEO2734 and NEO1132 in AML (stem/progenitor) cell elimination.Methods:We studied the effect of treatment with NEO2734, NEO1132 and the CBP/P300 inhibitor tool compound, CPI637, on AML blast differentiation, apoptosis, engraftment potential in a patient‐derived xenograft AML mouse model (NSG mice), and on the clonogenic capacity of long‐ and short‐term surviving AML cells ex vivo and in vivo.Results:To assess the biological activity of NEO2734, we treated a panel of AML cell lines with various concentrations of NEO2734, NEO1132 and CPI637. Nanomolar concentrations of NEO2734 inhibited cell proliferation with IC50 values ranging from 32 nM to 141 nM. Next, we showed that NEO2734 inhibited cell proliferation and induced apoptosis in primary AML CD45dim blasts across a variety of genotypes (example Figure 1a and 1b)(IC50 between 30–100 nM for 5 samples tested). The potency of NEO2734 to inhibit proliferation and to induce apoptosis in AML cell lines and primary AML blasts was higher than that of NEO1132 and much higher than CPI637 (Figure 1a and 1b). Moreover, we observed no increase in the myeloid differentiation marker CD11b in primary AML blasts after NEO2734 treatment.To evaluate whether NEO2734 efficiently reduces human AML burden in the bone marrow in vivo, patient cells were transplanted into mice and the mice were treated with NEO2734 or NEO1132 (10 mg/kg, orally daily 10 times). The percentage of leukemic engraftment was reduced in the treated mice as compared to the controls (Figure 2). NEO2734 treatment inhibited leukemic engraftment more efficiently than NEO1132. Finally, we investigated whether NEO2734 treatment could inhibit clonogenic capacity of leukemic progenitors and long‐term surviving cells from primary AML cases. In all cases studied, a significant reduction in number of colonies after 1 week and 4 weeks of NEO2734 treatment was observed. Importantly, NEO2734 also reduced survival of immunophenotypically defined LSCs, CD34+CD38− cells. The potency of NEO2734 to inhibit LSC and leukemic progenitor survival was higher than that of NEO1132 and much higher than that of CPI637.imageSummary/Conclusion:The dual BET‐CBP/P300 inhibitor NEO2734 efficiently eliminates AML blasts and LSCs/progenitors, suggesting that AML patients should be included in clinical studies of NEO2734.