ALBERT

Description: BCL-2 inhibition exerts effective pro-apoptotic activities in acute myeloid leukemia (AML) but clinical efficacy as a monotherapy was limited in part due to the treatment-induced MCL-1 increase. Triptolide (TPL) exhibits anti-tumor activities in part by upregulating pro-apoptotic BCL-2 proteins and decreasing MCL-1 expression in various malignant cells. We hypothesized that combined BCL-2 inhibition and TPL exert synergistic anti-leukemia activities and prevent the resistance to BCL-2 inhibition in AML. We here report that TPL combined with BCL-2 inhibitor ABT-199 synergistically induced apoptosis in leukemic cells regardless of p53 status through activating the intrinsic mitochondrial apoptotic pathway in vitro. Although ABT-199 or TPL alone inhibited AML growth in vivo, the combination therapy demonstrated a significantly stronger anti-leukemic effect. Mechanistically, TPL significantly upregulated BH3 only proteins including PUMA, NOXA, BID and BIM and decreased MCL-1 but upregulated BCL-2 expression in both p53 wild type and p53 mutant AML cell lines, while the combination decreased both BCL-2 and MCL-1 and further increased BH3 only BCL-2 proteins. MCL-1 and BCL-2 increases associated with respective ABT-199 and TPL treatment and resistance were also observed in vivo. Significantly downregulating MCL-1 and elevating BH3 only proteins by TPL could not only potentially block MCL-1-mediated resistance but also enhance anti-leukemic efficacy of ABT-199. Conversely, BCL-2 inhibition counteracted the potential resistance of TPL mediated by upregulation of BCL-2. The combination further amplified the effect, which likely contributed to the synthetic lethality. This mutual blockade of potential resistance provides a rational basis for the promising clinical application of TPL and BCL-2 inhibition in AML independent of p53 status. Disclosures Carter: Amgen: Research Funding; AstraZeneca: Research Funding; Ascentage: Research Funding.

Description: Aggressive natural killer cell leukemia (ANKL) is a rare and highly aggressive subtype of mature NK-cell neoplasms. Similar with extranodal NK/T-cell lymphoma, nasal type (ENKL), another subtype of NK-cell neoplasm, ANKL is also an Asian-prevalent and Epstein-Barr virus (EBV)-related neoplasm. In contrast, our knowledge of ANKL, especially about EBV biological behavior in this rare leukemia, lags far behind that of ENKL and other EBV-related hematopoietic malignancies, such as Burkitt lymphoma (BL), Hodgkin lymphoma (HL), and post-transplant lymphoproliferative disorder (PTLD). Dissection of the virus-host crosstalk in ANKL could contribute to better understanding the mechanism and finding out effective therapy for this neoplasm. In the present study, we investigated EBV-associated biological behavior in serial ANKL patients, including the clinical presentation, EBV genomic DNA, EBV antigens expression, cytogenetic-molecular aberrations, and leukemia-associated microenvironment. A total of 28 ANKL patients were collected upon review of the clinical database in Nanfang hospital. Different items of EBV infection evidence consisted of EBV viremia (n=9), EBV genomic DNA (n=20), and EBER/EBNA/LMP1/LMP2A expression (n=23). EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH) was the predominant clinical feature. Bone marrow smear was infiltrated with large granular lymphocyte (LGL) with LMP1/LMP2a-positive bulb, indicating the presence of EBV viral inclusions bodies. Positron emission tomographic (PET)-computed tomographic (CT) scan revealed bone marrow, liver and spleen as the most frequently involved organs, compared with nose and nasopharynx in ENKL. Cytogenetic analysis demonstrated 7q10-32 (n=4) was the “hotspot” of chromosome aberrations in ANKL. PCR analysis with EBNA-2/LMP1 specific primers on reserved DNA samples (n=20) revealed ANKL cells were infected with type-1 EBV strain with wide-type LMP1 (n=20), compared with 30bp-deleted LMP1 gene in ENKL. Integrated mutation analysis (n=20) identified recurrent mutations in Src homology 2 (SH2) domains of STAT5a (n=7) and p16inka (exon 3/4, n=20), but no mutation in SH2 domains of ID2, STAT1, and STAT3. Immunochemical (IHC) analysis on formalin-fixed paraffin-embedded tissues (n=23) revealed latency type-3 EBV expression in ANKL cells, with latency antigens of EBER, EBNA, LMP-1, and LMP-2. Furthermore, LMP-1/LMP-2-positive leukemia/lymphoma-associated macrophages (LAMs, n=23) were enriched in ANKL microenvironment. Notably, EBV-positive LAMs were significantly associated with poor prognosis and disease progression. Univariate analysis revealed significant difference (p

Description: p53, a key regulator of apoptosis, functions primarily upstream in the apoptotic cascade by directly and indirectly modulating Bcl-2 family of proteins. XIAP, a potent antiapoptotic protein, functions primarily downstream by suppressing caspases. Activation of p53 by MDM2 antagonist nutlin3a or inhibition of XIAP by small molecule inhibitors such as phenylurea 1396-11 was found to induce apoptosis in AML cells. Since the functions of XIAP and p53 are mediated and their activities controlled by a network of numerous components, some of which cross-regulate each other, we hypothesized that simultaneous activation of p53 and inhibition of XIAP would be a more effective at activating apoptotic signaling in AML cells. To test this idea, we treated AML cells with nutlin3a and 1396-11 and found that the combination synergistically induced cell death at 24 hours in OCIAML3 cells (combination index CI=0.200±0.047) and Molm13 cells (CI=0.565±0.082), two cell lines harboring wild type p53. Knocking down p53 expression by shRNA blunted the synergistic effect and downregulation of XIAP by antisense oligonucleotide (ASO) enhanced nutlin3a-induced apoptosis in OCI-AML3 cells, suggesting that the synergy was mediated by both p53 activation and XIAP inhibition. The specificity was further supported by data showing that inhibition of MDM2 and XIAP by their respective ASOs induced significantly more cell death than either ASO alone. Although nutlin3a alone induced apoptosis in OCI-AML3 cells, the cell death was not robust and caspase-3 activation was minimal by itself even at 48 hours with 10 μM of nutlin3a. Immunoblot analysis showed increased expression of p53 and its downstream target p21. Of note, because p21 not only induces G1 cell cycle block, it additionally exhibits antiapoptotic activity that diminishes the effects of p53 activation, we also studied effects of these agents on p21 levels. When nutlin3a and 1396–11 were combined, caspase-3 activation was greatly increased and nutlin3a-induced p21 expression was significantly diminished. Moreover, in these experiments, caspase inhibition restored p21 levels and diminished apoptosis enhanced by 1396-11, suggesting that XIAP inhibition-mediated caspase activation eliminates p21, enhancing nutlin3a-induced apoptosis. Furthermore, activation of p53 by nutlin3a increased caspase-6 protein levels and induced mitochondrial release of SMAC, an antagonist of XIAP, suggesting that p53 activation shifts the balance toward apoptosis, promoting the effect of XIAP inhibition. Most importantly, p53 activation and XIAP inhibition greatly enhanced apoptosis in primary blasts from AML patients. Five out of six samples treated showed synergistic killing at 24 hours (CI=0.73±0.13), even when the cells were protected from drug-induced and spontaneous apoptosis by MS-5 stroma cells (CI=0.45±0.06). In conclusion, results demonstrate that simultaneous activation of p53 by antagonizing MDM2 and inhibition of XIAP synergistically activate apoptotic signaling pathways and promote death of AML cells, in part by modulating p21, caspases, and cytosolic SMAC levels. Since both, XIAP and p53, are presently being targeted by ongoing clinical trials in leukemia patients, the combination strategy holds promise for expedited translation into the clinic.

Description: The bone marrow microenvironment (BME) critically supports hematopoietic stem cells and protects leukemia cells from chemotherapy, immune surveillance, and related stresses. A critical component of the BME is the mesenchymal stem cell (MSC). Dan Link’s group demonstrated that MSC are essential for human hematopoiesis, particularly as a source of SDF-1, which regulates homing, proliferation, and differentiation of HSC. Moreover, studies from our group and others have demonstrated that MSC protect leukemia cells from chemotherapy. At present, very little is known about MSC derived from AML patients, and an understanding of the proteomic makeup of these cells in the leukemia microenvironment could help to elucidate mechanisms involved in supporting their pro-tumor function. We used reverse phase protein array analysis (RPPA) to compare the expression of 151 proteins in MSC derived from AML BMs (N = 106) with those from healthy donors (N = 71). The expression of 45 of these proteins was deemed significantly different (p 〈 0.01) between the two sets. AML MSC expressed higher levels of p53 and p21 (CDKN1A), and the expression of the latter was correlated with other proteins within each MSC set. Using beta-galactosidase staining, AML MSC were found to undergo senescence more frequently than normal MSC. Elevated p21 in AML MSC is consistent with this finding. While 15 proteins were positively, and 20 proteins negatively, correlated with p21 expression in normal MSC, there were only three proteins positively, and nine negatively, correlated in AML-derived MSC. In normal MSC, SMAD1 (a key component in MSC growth and differentiation involving multiple receptors like TGF beta and BMP) expression and AKT signaling were low when p21 is expressed. However, in AML MSC this association was not seen, albeit a negative correlation with ITGAL was observed. SMAD1 expression was higher in normal MSC. In normal MSC, the expression of SMAD1 was negatively correlated with PPARG and NPM1, and was positively correlated with the expression of phosphorylated ELK. The opposite relationship was seen in AML MSC (i.e., PPARG and NPM1 exhibited positive correlation with SMAD1 and phosphorylated ELK was negatively correlated with the protein). While the significance of these relationships remains to be determined it is interesting to note that PPARG is a key regulator of adipocyte differentiation in MSC, so perhaps this alteration of SMAD/PPARG in AML MSC could impede their differentiation potential. In an accompanying abstract from our group, we report that AML MSC are primed toward osteoblastic differentiation and do not differentiate into adipocytes (Battula VL et al, ASH 2014). The RPPA data on PPARG is consistent with this finding. SMAD1 also positively regulates miR-21. Since p21 is a miR-21 target, it seems possible that the differences in expression could be attributed to SMAD1 and miR-21 signaling. We analyzed miR-21 expression in normal and AML-derived MSC (N = 10, each) using qRT-PCR and found a statistically significant (p =0.014) increase in its expression in normal MSC relative to their disease counterparts. When anti-miR-21 was transduced into healthy donor MSC, which caused a 3-fold increase in p21 (but no difference in cyclin D1 expression, another miR-21 target whose expression was also increased in AML MSC). AML MSC also exhibited higher protein expression of the B55 alpha subunit (PPP2R2A) of protein phosphatase 2A (PP2A). This expression contrasted interestingly with that of leukemia cells, since we have previously reported low PPP2R2A levels in AML blasts associated with shorter remission durations (Ruvolo et al Leukemia 2011). Furthermore, AKT phosphorylation was negatively correlated with PPP2R2A expression in AML blasts, and normal MSC, but there was no correlation between PPP2R2A and phosphorylated AKT in AML MSC. Also, expression of PPP2R2A was positively correlated with the expression of the survival protein NOL3 (ARC) which may provide new clues to possible survival mechanisms in AML MSC. In summary, these findings represent insights into the proteomic profiling of normal and AML MSC. Results suggest that senescence (via p21), differentiation potential (involving SMAD/PPARG pathway), and survival signaling (including PP2A/AKT) are altered in AML MSC. Studies are underway to determine how these variations in MSC properties impact the AML microenvironment. Disclosures Carter: Tetralogic Pharmaceuticals: Research Funding.

Description: The aberrant function of transcription factors and/or kinase-based signaling pathways that regulate the ability of hematopoietic cells to proliferate, differentiate, and escape apoptosis accounts for the leukemic transformation of myeloid progenitors. Here, we demonstrate that simultaneous retinoid receptor ligation and blockade of the MEK/ERK signaling module, using the small-molecule inhibitor CI-1040, result in a strikingly synergistic induction of apoptosis in both acute myeloid leukemia (AML) and acute promyelocytic leukemia (APL) cells with constitutive ERK activation. This proapoptotic synergism requires functional RAR and RXR retinoid receptors, as demonstrated using RAR- and RXR-selective ligands and RAR-defective cells. In the presence of MEK inhibitors, however, retinoid-induced chromatin remodeling, target-gene transcription, and granulocytic differentiation are strikingly inhibited and apoptosis induction becomes independent of death-inducing ligand/receptor pairs; this suggests that apoptosis induction by combined retinoids and MEK inhibitors is entirely distinct from the classical “postmaturation” apoptosis induced by retinoids alone. Finally, we identify disruption of Bcl-2–dependent mitochondrial homeostasis as a possible point of convergence for the proapoptotic synergism observed with retinoids and MEK inhibitors. Taken together, these results indicate that combined retinoid treatment and MEK blockade exert powerful antileukemic effects and could be developed into a novel therapeutic strategy for both AML and APL.

Description: Survivin, a member of the inhibitors of apoptosis protein family, plays important roles in cell proliferation and survival and is highly expressed in various malignancies, including leukemias. To better understand its role in acute myeloid leukemia (AML), we profiled survivin expression in samples obtained from 511 newly diagnosed AML patients and in CD34+38− AML stem/progenitor cells using a validated reverse-phase protein array; we correlated its levels with clinical outcomes and with levels of other proteins in the same sample set. We found that survivin levels were higher in bone marrow than in paired peripheral blood leukemic cells (n = 140, P = .0001) and that higher survivin levels significantly predicted shorter overall (P = .016) and event-free (P = .023) survival in multivariate Cox model analysis. Importantly, survivin levels were significantly higher in CD34+38− AML stem/progenitor cells than in bulk blasts and total CD34+ AML cells (P 〈 .05). Survivin expression correlated with the expressions of multiple proteins involved with cell proliferation and survival. Particularly, its expression strongly correlated with HIF1α in the stem/progenitor cell compartment. These results suggest that survivin is a prognostic biomarker in AML and that survivin, which is overexpressed in AML stem/progenitor cells, remains a potentially important target for leukemia therapy.

Description: Recent studies suggest that the Bcl-2 and mitogen-activated protein kinase (MAPK) pathways together confer an aggressive, apoptosis-resistant phenotype on acute myelogenous leukemia (AML) cells. In this study, we analyzed the effects of simultaneous inhibition of these 2 pathways. In AML cell lines with constitutively activated MAPK, MAPK kinase (MEK) blockade by PD184352 strikingly potentiated the apoptosis induced by the small-molecule Bcl-2 inhibitor HA14-1 or by Bcl-2 antisense oligonucleotides. Isobologram analysis confirmed the synergistic nature of this interaction. Moreover, MEK blockade overcame Bcl-2 overexpression-mediated resistance to the proapoptotic effects of HA14-1. Most importantly, simultaneous exposure to PD184352 significantly (P = .01) potentiated HA14-1–mediated inhibition of clonogenic growth in all primary AML samples tested. These findings show that the Bcl-2 and MAPK pathways are relevant molecular targets in AML and that their concurrent inhibition could be developed into a new therapeutic strategy for this disease.

Description: Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that regulates cell adhesion, proliferation, stem cell functions, and cell-microenvironment communications. It is activated and/or overexpressed in many malignant cells and promotes tumor progression and metastasis. Several small molecule FAK inhibitors have been developed and some of them have reached clinical trials in solid tumors. High FAK expression was found to be associated with enhanced blast migration, increased cellularity, and poor prognosis in AML, indicating that FAK could be a potential therapeutic target in AML. We showed previously that VS-4718, a potent and selective FAK inhibitor, effectively decreased viable cell number, and also induced cell death in leukemia cell lines with variable potencies in vitro, even in AML cells co-cultured with mesenchymal stromal cells (MSCs) (ASH 2015). To further examine the effect of VS-4718 in vivo, we transplanted Molm14-GFP/Luc cells into NSGS (NOD-SCID IL2Rgnull-3/GM/SF, NSG-SGM3) mice, and treated the mice with VS-4718 (75 mg/kg) twice a day via oral gavage. We found that VS-4718 as a single agent exerted anti-leukemia activity as assessed by in vivo imaging for leukemia burden, human CD45 positivity in mouse peripheral blood, and histological staining of mouse tissues. VS-4718 treated mice survived significantly longer than the untreated controls (medium survival 27 vs 20 days, P = 0.0003). FAK activates multiple signaling pathways and supports tumor cell survival. We found that inhibition of FAK with VS-4718 in Molm14 cells reduced the expression of MCL-1. The BCL-2 antagonist ABT-199 is being tested clinically for the treatment of hematological malignancies. However, as a single agent, ABT-199-treated cells can acquire drug resistance by upregulating MCL-1 and BCL-XL after treatment. We therefore hypothesized that combination of VS-4718 and ABT-199 would be more effective in inducing cell death and reversing the resistance of AML cells exposed to ABT-199 alone. In vitro studies showed that VS-4718 significantly improved the potency of ABT-199 in AML cell lines (ABT-199 EC50 at 24 h: 880.3 nM and 14.5 nM in the presence of 0.4 mM VS-4718, respectively, in Molm14 cells), and the combination of VS-4718 and ABT-199 also synergistically killed primary AML cells even when co-cultured with MSCs in the majority of samples examined, while largely sparing normal BM CD34+ cells. Furthermore, the upregulation of MCL-1 in ABT-199-treated AML cells was antagonized by combining ABT-199 with VS-4718. BCL-XL is known to be regulated by STAT5. The activation of STAT5, which can be regulated by FAK, is considered to be significant in maintaining MCL-1 expression in FLT3-ITD AML cells. We observed that treatment with VS-4718 decreased the level of p-STAT5 as well as MCL-1 and BCL-XL in Molm14 cells harboring FLT3-ITD mutation. These results suggest a novel therapeutic strategy for targeting FAK and BCL-2 family proteins for the treatment of AML. Disclosures Pachter: Verastem, Inc: Employment. Weaver:Verastem, Inc: Employment. Carter:PRISM Pharma/Eisai: Research Funding.