Drug Resistance In Myeloid Leukemia Research Articles

Abstract PO-125: Targeting histone methylation to overrule transcriptionally driven drug resistance in myeloid leukemia

Abstract Standard induction chemotherapy, consisting of an anthracycline and cytarabine, has been the first-line therapeutic to treat acute myeloid leukemia (AML). Although this treatment induces complete remissions (CR) in the majority of patients, many face a relapse. Relapse is caused by the survival of chemotherapy-resistant leukemia cells (minimal residual disease, MRD), that may have acquired drug resistance by non-genetic mechanisms. Persistence of MRD is driven by intra-leukemic heterogeneity and plasticity in response to therapy. Leukemia cells within MRD capable of initiating relapse are thought to have stem cell features and are therefore named “leukemic stem cells” (LSCs). In this study, we demonstrated that the anthracycline doxorubicin epigenetically reprograms leukemia cells by inducing tri-methylation of histone 3 lysine 27 (H3K27) and H3K4. Moreover, to understand chemotherapy resistance at the single-cell level and to study intra-leukemia heterogeneity with respect to anthracycline sensitivity, we seeded K562 myeloid leukemia cells in 480 wells, each containing 10.000 cells, and treated the cells with increasing concentrations of doxorubicin. Using this approach, a subpopulation of reversible anthracycline-tolerant cells (ATCs) was identified within the doxorubicin-sensitive leukemia cell population, which lacked upregulation of H3K27me3 or H3K4me3 and exhibited epigenetically regulated expression of stem cell features similar to leukemic stem cells (LSCs). These ATCs have a distinct transcriptional landscape from the leukemia bulk and could be eradicated by the KDM6 inhibitor GSK-J4. In primary human AML, GSK-J4 treatment could eliminate AML blasts and LSCs at diagnosis but importantly it could significantly reduce chemotherapy resistant AML patient cell load (MRD) and survival of LSCs residing within MRD, ex vivo and in vivo. An efficient response to GSK-J4 was associated with upregulation of H3K27 and/or H3K4 methylation, and downregulation of STAT5B. Together, our results reveal plasticity of anthracycline resistance in AML cells and highlight the potential of epigenetic-based therapeutics to target chemotherapy-resistant AML cells. Citation Format: Noortje van Gils, Han J.M.P. Verhagen, Tània Martiáñez, Fedor Denkers, Eline Vermue, Arjo Rutten, Tamás Csikós, Meyrem Çil, Marjon Al, Frank van Gemert, Jeroen J.W.M. Janssen, Gert J. Ossenkoppele, Renee X. Menezes, Linda Smit. Targeting histone methylation to overrule transcriptionally driven drug resistance in myeloid leukemia [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-125.

HnRNP K Contributes to Adriamycin Resistance in Acute Myeloid Leukemia through Regulating Autophagy

To explore the role of heterogeneous nuclear ribonucleoprotein(hnRNP) K regulating autophagy in the drug resistance of acute myeloid leukemia, so as to provide a new molecular marker for treatment of leukemia. The relationship between the expression level of hnRNP K and the drug resistance of myeloid leukemia was verified by fluorescence quantitative PCR; the expression of autophagy related protein LC3I/ II was detected by Western blot after the hnRNP K was modulated by RNA interference technology; the sensitivity of leukemia cells to doxorubicin was analyzed before and after the expression of hnRNP K were modulatd. The expression of hnRNP K and LC3I/II significantly increased in bone marrow nonremission patients and in drug resistant cell line, however, the expression of LC3I/ II decreased when the expression of hnRNP K were reduced, while the sensitivity of cells to adriamycin could be recovered. hnRNP K may be involved in the formation of adriamycin resistance in acute myeloid leukemia by regulating autophagy.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Antagonism of SET Using OP449 Enhances the Efficacy of Tyrosine Kinase Inhibitors and Overcomes Drug Resistance in Myeloid Leukemia

The SET oncoprotein, a potent inhibitor of the protein phosphatase 2A (PP2A), is overexpressed in leukemia. We evaluated the efficacy of SET antagonism in chronic myeloid leukemia (CML) and acute myeloid leukemia (AML) cell lines, a murine leukemia model, and primary patient samples using OP449, a specific, cell-penetrating peptide that antagonizes SET's inhibition of PP2A. In vitro cytotoxicity and specificity of OP449 in CML and AML cell lines and primary samples were measured using proliferation, apoptosis, and clonogenic assays. Efficacy of target inhibition by OP449 was evaluated by immunoblotting and PP2A assay. In vivo antitumor efficacy of OP449 was measured in human HL-60 xenografted murine model. We observed that OP449 inhibited growth of CML cells including those from patients with blastic phase disease and patients harboring highly drug-resistant BCR-ABL1 mutations. Combined treatment with OP449 and ABL1 tyrosine kinase inhibitors was significantly more cytotoxic to K562 cells and primary CD34(+) CML cells. SET protein levels remained unchanged with OP449 treatment, but BCR-ABL1-mediated downstream signaling was significantly inhibited with the degradation of key signaling molecules such as BCR-ABL1, STAT5, and AKT. Similarly, AML cell lines and primary patient samples with various genetic lesions showed inhibition of cell growth after treatment with OP449 alone or in combination with respective kinase inhibitors. Finally, OP449 reduced the tumor burden of mice xenografted with human leukemia cells. We demonstrate a novel therapeutic paradigm of SET antagonism using OP449 in combination with tyrosine kinase inhibitors for the treatment of CML and AML.

EphB4 Expression and Biological Significance in Drug Resistance of Myeloid Leukemia

Abstract 4725Chemotherapy is widely used in treatment of myeloid leukemia, the efficancy of which, however, is often hampered by the development of intrinsic and acquired multidrug resistance(MDR), the exact mechanism of which is still unclear. Overexpression and deregulated activation of protein tyrosine kinase(PTK) are frequently observed in several types of hematologic malignancies, the abnormally signal cascade transducted by which has been demonstrated to play an important role in antiapoptosis, differentiation block, enhancing autonomous proliferation, and also in inducing drug resistance. EphB4 is also a protein tyrosine kinase, a member of the largest family of receptor tyrosine kinase, which has been found with abnormally upregulated expression or activity in many types of cancer especially solid tumor types, such as mammary adenocarcinoma, colon carcinoma, ovarian cancer and prostatic carcinoma. Here the aim of our study was to examine the expression and biological role of EphB4 in drug resistance of myeloid leukemia. Using RT-PCR assay and western blot, we tested the mRNA level in 35 myeloid leukemia patients including 4 cases of acute myeloid leukemia(AML) with primary multiple drug-resistance(MDR), 3 cases of AML which have relapsed, 5 cases of newly diagnosed AML, 5 cases of AML which got (complete remission) CR at the first chemotherapy treatment, 9 cases of chronic myeloid leukemia in chronic phase(CML-CP), and 9 cases of CML in blast crisis(CML-BC). The results showed the EphB4 mRNA level was significantly upregulated in AML bearing relapse(EphB4/β-actin ratio:0.962±0.114) or MDR(EphB4/β-actin ratio: 0.993±0.047) and also in CML-BC(EphB4/β-actin ratio: 1.001±0.060) compared with newly diagnosed AML(EphB4/β-actin ratio: 0.332±0.014), AML with CR(EphB4/β-actin ratio:0.401±0.015) and CML-CP(EphB4/β-actin ratio: 0.432±0.020). Subsequently, we examined both the transcriptional and translational level of EphB4 in several myeloid leukemia cell lines including K562, HL60,U937,KG1α and an adriamycin-resistant cell line—HL60/ADM, and drug-resistant capacity of the five cell lines was also tested by CCK-8 assay. Finally EphB4 protein expression is found to be upregulated at both transcriptional and translational level in K562, KG1αand HL60/ADM, which showed stronger capacity of resistance to gradient concentrations of adriamycin(IC50 of K562:0.451±0.037ug/ml,KG1α:0.217±0.017ug/ml, HL60/ADM: 2.663±0.102ug/ml) compared with that of HL60 and U937(IC50 of HL60:0.040±0.001ug/ml, U937:0.040±0.005ug/ml) in which little or no expression of EphB4 mRNA or protein was observed. And the most noteworthy is that HL60/ADM, which shows the strongest drug resistant capability. also bears the most amount of EphB4 at both transcriptional level (EphB4 /β-actin ratio: 1.002±0.017), and translational level (EphB4 /β-actin ratio: 0.975±0.051). These data supports a role for EphB4 in inducing drug resistance and raise the possibility that therapeutic intervention to EphB4 expression or signaling might inhibit or even reverse drug resistande in meyloid leukemia. Disclosures:No relevant conflicts of interest to declare.

Stem cell factor as a survival and growth factor in human normal and malignant hematopoiesis.

Stem cell factor (SCF) is an essential hematopoietic cytokine that interacts with other cytokines to preserve the viability of hematopoietic stem and progenitor cells, to influence their entry into the cell cycle and to facilitate their proliferation and differentiation. SCF on its own cannot drive noncycling hematopoietic progenitor cells into the cell cycle but does prevent their apoptotic death. SCF when combined with other cytokines increases the cloning efficacy of hematopoietic progenitor cells from all lineages. SCF also stimulates the growth of CD34+ leukemic progenitor cells from most patients with acute myeloid leukemia (AML). The mRNA expression of the SCF receptor c-kit has been shown to be significantly increased in all fresh AML blast cells compared with normal controls (healthy volunteers), in particular CD34+ cells. Two inhibitory cytokines, transforming growth factor-beta and interleukin-4, decreased c-kit expression, whereas tumor necrosis factor-alpha increased c-kit expression, but chemotherapeutic drugs showed no effect on c-kit expression, but chemotherapeutic drugs showed no effect on c-kit expression in AML cells. Apoptosis has been shown to be directly related to a high complete remission rate in AML patients following induction therapy. Since SCF has been shown to stimulate the proliferation of mainly CD34+ AML cells, we have investigated whether the poor response of patients with CD34+ myeloid leukemia cells to chemotherapy could be due to SCF-induced resistance to apoptosis. The effect of SCF on the apoptosis induced by chemotherapeutic drugs commonly used in the treatment of AML - cytarabine, daunorubicin and carboplatin - was examined in human CD34+ myeloid leukemia cells in serum-free cultures. SCF significantly reduced the induced apoptosis by more than 50% in all CD34+ human leukemia cells treated by any of the three chemotherapeutic drugs. Antibodies blocking c-kit reversed the significant inhibitory effect of SCF on chemotherapy-induced apoptosis, confirming the role of SCF in the resistance to chemotherapy-induced apoptosis in CD34+ human leukemia. These results suggest that the poor response of patients with CD34+ leukemia cells could be at least partially due to less chemotherapy-induced apoptosis resulting from protection by SCF as an adjuvant mechanism for drug resistance in myeloid leukemia. We conclude that an antisense strategy to block c-kit expression in AML blast cells may prove valuable for decreasing the chemoresistance of AML patients. The abrogation of leukemic resistance to apoptotic death through anti-SCF/c-pit expression combined with chemotherapy offers potential for designing novel therapeutic approaches for refractory AML patients.