Gossypol acetic acid regulates leukemia stem cells by degrading LRPPRC via inhibiting IL-6/JAK1/STAT3 signaling or resulting mitochondrial dysfunction

BACKGROUND Leukemia stem cells(LSCs)are found to be one of the main factors contributing to poor therapeutic effects in acute myeloid leukemia(AML),as they are protected by the bone marrow microenvironment(BMM)against conventional therapies.Gossypol acetic acid(GAA),which is extracted from the seeds of cotton plants,exerts anti-tumor roles in several types of cancer and has been reported to induce apoptosis of LSCs by inhibiting Bcl2.AIM To investigate the exact roles of GAA in regulating LSCs under different microenvironments and the exact mechanism.METHODS In this study,LSCs were magnetically sorted from AML cell lines and the CD34+CD38-population was obtained.The expression of leucine-rich pentatricopeptide repeat-containing protein(LRPPRC)and forkhead box M1(FOXM1)was evaluated in LSCs,and the effects of GAA on malignancies and mitochondrial RESULTS LRPPRC was found to be upregulated,and GAA inhibited cell proliferation by degrading LRPPRC.GAA induced LRPPRC degradation and inhibited the activation of interleukin 6(IL-6)/janus kinase(JAK)1/signal transducer and activator of transcription(STAT)3 signaling,enhancing chemosensitivity in LSCs against conventional chemotherapies,including L-Asparaginase,Dexamethasone,and cytarabine.GAA was also found to downregulate FOXM1 indirectly by regulating LRPPRC.Furthermore,GAA induced reactive oxygen species accumulation,disturbed mitochondrial homeostasis,and caused mitochondrial dysfunction.By inhibiting IL-6/JAK1/STAT3 signaling via degrading LRPPRC,GAA resulted in the elimination of LSCs.Meanwhile,GAA induced oxidative stress and subsequent cell damage by causing mitochondrial damage.CONCLUSION Taken together,the results indicate that GAA might overcome the BMM protective effect and be considered as a novel and effective combination therapy for AML.

Molecular mechanisms for survival regulation of chronic myeloid leukemia stem cells

Studies on chronic myeloid leukemia(CML)have served as a paradigm for cancer research and therapy.These studies involve the identifi cation of the fi rst cancer-associated chromosomal abnormality and the subsequent development of tyrosine kinase inhibitors(TKIs)that inhibit BCR-ABL kinase activity in CML.It becomes clear that leukemia stem cells(LSCs)in CML which are resistant to TKIs,and eradication of LSCs appears to be extremely difficult.Therefore,one of the major issues in current CML biology is to understand the biology of LSCs and to investigate why LSCs are insensitive to TKI monotherapy for developing curative therapeutic strategies.Studies from our group and others have revealed that CML LSCs form a hierarchy similar to that seen in normal hematopoiesis,in which a rare stem cell population with limitless self-renewal potential gives rise to progenies that lack such potential.LSCs also possess biological features that are different from those of normal hematopoietic stem cells(HSCs)and are critical for their malignant characteristics.In this review,we summarize the latest progress in CML field,and attempt to understand the molecular mechanisms of survival regulation of LSCs.

Molecular mechanisms for stemness maintenance of acute myeloid leukemia stem cells

Human acute myeloid leukemia(AML)is a fatal hematologic malignancy characterized with accumulation of myeloid blasts and differentiation arrest.The development of AML is associated with a serial of genetic and epigenetic alterations mainly occurred in hematopoietic stem and progenitor cells(HSPCs),which change HSPC state at the molecular and cellular levels and transform them into leukemia stem cells(LSCs).LSCs play critical roles in leukemia initiation,progression,and relapse,and need to be eradicated to achieve a cure in clinic.Key to successfully targeting LSCs is to fully understand the unique cellular and molecular mechanisms for maintaining their stemness.Here,we discuss LSCs in AML with a focus on identification of unique biological features of these stem cells to decipher the molecular mechanisms of LSC maintenance.

Signaling pathways governing the behaviors of leukemia stem cells

Leukemia is a malignancy in the blood that develops from the lymphatic system and bone marrow.Although various treatment options have been used for different types of leukemia,understanding the molecular pathways involved in the development and progression of leukemia is necessary.Recent studies showed that leukemia stem cells(LSCs)play essential roles in the pathogenesis of leukemia by targeting several signaling pathways,including Notch,Wnt,Hedgehog,and STAT3.LSCs are highly proliferative cells that stimulate tumor initiation,migration,EMT,and drug resistance.This review summarizes cellular pathways that stimulate and prevent LSCs'self-renewal,metastasis,and tumorigenesis.

HDAC I/IIb selective inhibitor Purinostat Mesylate combined with GLS1 inhibition effectively eliminates CML stem cells

Purinostat Mesylate(PM)is a novel highly selective and active HDAC I/IIb inhibitor,and the injectable formulation of PM(PMF)based on the compound prescription containing cyclodextrin completely can overcome PM’s poor solubility and improves its stability and pharmacokinetic properties.Here,we showed that PM effectively repressed the survival of Ph+leukemia cells and CD34+leukemia cells from CML patients in vitro.In vivo studies demonstrated that PMF significantly prevented BCR-ABL(T315I)induced CML progression by restraining leukemia stem cells(LSCs),which are insensitive to chemotherapy and responsible for CML relapse.Mechanism studies revealed that targeting HDAC I/IIb repressed several important factors for LSCs survival including c-Myc,β-Catenin,E2f,Ezh2,Alox5,and mTOR,as well as interrupted some critical biologic processes.Additionally,PMF increased glutamate metabolism in LSCs by increasing GLS1.The combination of PMF and glutaminase inhibitor BPTES synergistically eradicated LSCs by altering multiple key proteins and signaling pathways which are critical for LSC survival and self-renewal.Overall,our findings represent a new therapeutic strategy for eliminating LSCs by targeting HDAC I/IIb and glutaminolysis,which potentially provides a guidance for PMF clinical trials in the future for TKI resistance CML patients.

CD34^(+)CD38^(-)subpopulation without CD123 and CD44 is responsible for LSC and correlated with imbalance of immune cell subsets in AML

Acute myeloid leukemia(AML)is regarded as a stem cell disease.However,no one unique marker is expressed on leukemia stem cells(LSC)but not on leukemic blasts nor normal hematopoietic stem cells(HSC).CD34^(+)CD38^(-)with or without CD123 or CD44 subpopulations are immunophenotypically defined as putative LSC fractions in AML.Nevertheless,markers that can be effectively and simply held responsible for the intrinsical heterogeneity of LSC is still unclear.In the present study,we examined the frequency of three different LSC subtypes(CD34^(+)CD38^(-),CD34^(+)CD38^(-)CD123^(+),CD34^(+)CD38^(-)CD44^(+))in AML at diagnosis.We then validated their prognostic significance on the relevance of spectral features for diagnostic stratification,immune status,induction therapy response,treatment effect maintenance,and long^(-)term survival.In our findings,high proportions of the above three different LSC subtypes were all significantly characterized with low complete remission(CR)rate,high relapse/refractory rate,poor overall survival(OS),frequent FLT3^(-)ITD mutation,the high level of regulatory T cells(Treg)and monocytic myeloid^(-)derived suppressor cells(M^(-)MDSC).However,there was no significant statistical difference in all kinds of other clinical performance among the three different LSC groups.It was demonstrated that CD34^(+)CD38^(-)subpopulation without CD123 and CD44 might be held responsible for LSC and correlated with an imbalance of immune cell subsets in AML.

Targeting metabolic vulnerabilities to overcome resistance to therapy in acute myeloid leukemia

Malignant hematopoietic cells gain metabolic plasticity, reorganize anabolic mechanisms to improve anabolic output and prevent oxidative damage, and bypass cell cycle checkpoints, eventually outcompeting normal hematopoietic cells. Current therapeutic strategies of acute myeloid leukemia (AML) are based on prognostic stratification that includes mutation profile as the closest surrogate to disease biology. Clinical efficacy of targeted therapies, e.g., agents targeting mutant FMS-like tyrosine kinase 3 (FLT3) and isocitrate dehydrogenase 1 or 2, are mostly limited to the presence of relevant mutations. Recent studies have not only demonstrated that specific mutations in AML create metabolic vulnerabilities but also highlighted the efficacy of targeting metabolic vulnerabilities in combination with inhibitors of these mutations. Therefore, delineating the functional relationships between genetic stratification, metabolic dependencies, and response to specific inhibitors of these vulnerabilities is crucial for identifying more effective therapeutic regimens, understanding resistance mechanisms, and identifying early response markers, ultimately improving the likelihood of cure. In addition, metabolic changes occurring in the tumor microenvironment have also been reported as therapeutic targets. The metabolic profiles of leukemia stem cells (LSCs) differ, and relapsed/refractory LSCs switch to alternative metabolic pathways, fueling oxidative phosphorylation (OXPHOS), rendering them therapeutically resistant. In this review, we discuss the role of cancer metabolic pathways that contribute to the metabolic plasticity of AML and confer resistance to standard therapy;we also highlight the latest promising developments in the field in translating these important findings to the clinic and discuss the tumor microenvironment that supports metabolic plasticity and interplay with AML cells.