The mTOR inhibitor, everolimus (RAD001), overcomes resistance to imatinib in quiescent Ph-positive acute lymphoblastic leukemia cells

Obesity and Leukemia: Biological Mechanisms, Perspectives, and Challenges

PURPOSE OF REVIEW

To examine the epidemiological data on obesity and leukemia; evaluate the effect of obesity on leukemia outcomes in childhood acute lymphoblastic leukemia (ALL) survivors; assess the potential mechanisms through which obesity may increase the risk of leukemia; and provide the effects of obesity management on leukemia. Preventive (diet, physical exercise, obesity pharmacotherapy, bariatric surgery) measures, repurposing drugs, candidate therapeutic agents targeting oncogenic pathways of obesity and insulin resistance in leukemia as well as challenges of the COVID-19 pandemic are also discussed.

RECENT FINDINGS

Obesity has been implicated in the development of 13 cancers, such as breast, endometrial, colon, renal, esophageal cancers, and multiple myeloma. Leukemia is estimated to account for approximately 2.5% and 3.1% of all new cancer incidence and mortality, respectively, while it represents the most frequent cancer in children younger than 5 years. Current evidence indicates that obesity may have an impact on the risk of leukemia. Increased birthweight may be associated with the development of childhood leukemia. Obesity is also associated with worse outcomes and increased mortality in leukemic patients. However, there are several limitations and challenges in meta-analyses and epidemiological studies. In addition, weight gain may occur in a substantial number of childhood ALL survivors while the majority of studies have documented an increased risk of relapse and mortality among patients with childhood ALL and obesity. The main pathophysiological pathways linking obesity to leukemia include bone marrow adipose tissue; hormones such as insulin and the insulin-like growth factor system as well as sex hormones; pro-inflammatory cytokines, such as IL-6 and TNF-α; adipocytokines, such as adiponectin, leptin, resistin, and visfatin; dyslipidemia and lipid signaling; chronic low-grade inflammation and oxidative stress; and other emerging mechanisms. Obesity represents a risk factor for leukemia, being among the only known risk factors that could be prevented or modified through weight loss, healthy diet, and physical exercise. Pharmacological interventions, repurposing drugs used for cardiometabolic comorbidities, and bariatric surgery may be recommended for leukemia and obesity-related cancer prevention.

New biomarkers and therapeutic strategies in acute lymphoblastic leukemias: Recent advances

Acute lymphoblastic leukemia (ALL) represents a heterogeneous group of hematologic malignancies, and it is normally characterized by an aberrant proliferation of immature lymphoid cells. Moreover, dysregulation of multiple signaling pathways that normally regulate cellular transcription, growth, translation, and proliferation is frequently encountered in this malignancy. ALL is the most frequent tumor in childhood, and adult ALL patients still correlate with poor survival. This review focuses on modern therapies in ALL that move beyond standard chemotherapy, with a particular emphasis on immunotherapeutic approaches as new treatment strategies. Bi-specific T-cell Engagers (BiTE) antibodies, the chimeric antigen receptor (CAR)-T cells, or CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats [CRISPR]-associated nuclease 9) represent other new innovative approaches for this disease. Target and tailored therapy could make the difference in previously untreatable cases, i.e., precision and personalized medicine. Clinical trials will help to select the most efficient novel therapies in ALL management and to integrate them with existing treatments to achieve durable cures.

Targeting mTOR in Acute Lymphoblastic Leukemia

Acute Lymphoblastic Leukemia (ALL) is an aggressive hematologic disorder and constitutes approximately 25% of cancer diagnoses among children and teenagers. Pediatric patients have a favourable prognosis, with 5-years overall survival rates near 90%, while adult ALL still correlates with poorer survival. However, during the past few decades, the therapeutic outcome of adult ALL was significantly ameliorated, mainly due to intensive pediatric-based protocols of chemotherapy. Mammalian (or mechanistic) target of rapamycin (mTOR) is a conserved serine/threonine kinase belonging to the phosphatidylinositol 3-kinase (PI3K)-related kinase family (PIKK) and resides in two distinct signalling complexes named mTORC1, involved in mRNA translation and protein synthesis and mTORC2 that controls cell survival and migration. Moreover, both complexes are remarkably involved in metabolism regulation. Growing evidence reports that mTOR dysregulation is related to metastatic potential, cell proliferation and angiogenesis and given that PI3K/Akt/mTOR network activation is often associated with poor prognosis and chemoresistance in ALL, there is a constant need to discover novel inhibitors for ALL treatment. Here, the current knowledge of mTOR signalling and the development of anti-mTOR compounds are documented, reporting the most relevant results from both preclinical and clinical studies in ALL that have contributed significantly into their efficacy or failure.

Tyrosine kinase inhibitor-induced defects in DNA repair sensitize FLT3(ITD)-positive leukemia cells to PARP1 inhibitors

Mutations in FMS-like tyrosine kinase 3 (FLT3), such as internal tandem duplications (ITDs), can be found in up to 23% of patients with acute myeloid leukemia (AML) and confer a poor prognosis. Current treatment options for FLT3(ITD)-positive AMLs include genotoxic therapy and FLT3 inhibitors (FLT3i's), which are rarely curative. PARP1 inhibitors (PARP1i's) have been successfully applied to induce synthetic lethality in tumors harboring BRCA1/2 mutations and displaying homologous recombination (HR) deficiency. We show here that inhibition of FLT3(ITD) activity by the FLT3i AC220 caused downregulation of DNA repair proteins BRCA1, BRCA2, PALB2, RAD51, and LIG4, resulting in inhibition of 2 major DNA double-strand break (DSB) repair pathways, HR, and nonhomologous end-joining. PARP1i, olaparib, and BMN673 caused accumulation of lethal DSBs and cell death in AC220-treated FLT3(ITD)-positive leukemia cells, thus mimicking synthetic lethality. Moreover, the combination of FLT3i and PARP1i eliminated FLT3(ITD)-positive quiescent and proliferating leukemia stem cells, as well as leukemic progenitors, from human and mouse leukemia samples. Notably, the combination of AC220 and BMN673 significantly delayed disease onset and effectively reduced leukemia-initiating cells in an FLT3(ITD)-positive primary AML xenograft mouse model. In conclusion, we postulate that FLT3i-induced deficiencies in DSB repair pathways sensitize FLT3(ITD)-positive AML cells to synthetic lethality triggered by PARP1i's. Therefore, FLT3(ITD) could be used as a precision medicine marker for identifying AML patients that may benefit from a therapeutic regimen combining FLT3 and PARP1i's.

Targeting the phosphatidylinositol 3-kinase/Akt/mechanistic target of rapamycin signaling pathway in B-lineage acute lymphoblastic leukemia: An update

Despite considerable progress in treatment protocols, B-lineage acute lymphoblastic leukemia (B-ALL) displays a poor prognosis in about 15-20% of pediatric cases and about 60% of adult patients. In addition, life-long irreversible late effects from chemo- and radiation therapy, including secondary malignancies, are a growing problem for leukemia survivors. Targeted therapy holds promising perspectives for cancer treatment as it may be more effective and have fewer side effects than conventional therapies. The phosphatidylinositol 3-phosphate kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) signaling pathway is a key regulatory cascade which controls proliferation, survival and drug-resistance of cancer cells, and it is frequently upregulated in the different subtypes of B-ALL, where it plays important roles in the pathophysiology, maintenance and progression of the disease. Moreover, activation of this signaling cascade portends a poorer prognosis in both pediatric and adult B-ALL patients. Promising preclinical data on PI3K/Akt/mTOR inhibitors have documented their anticancer activity in B-ALL and some of these novel drugs have entered clinical trials as they could lead to a longer event-free survival and reduce therapy-associated toxicity for patients with B-ALL. This review highlights the current status of PI3K/Akt/mTOR inhibitors in B-ALL, with an emphasis on emerging evidence of the superior efficacy of synergistic combinations involving the use of traditional chemotherapeutics or other novel, targeted agents.

Non ABL-directed inhibitors as alternative treatment strategies for chronic myeloid leukemia

The introduction of ABL Tyrosine Kinase Inhibitors (TKIs) has significantly improved the outcome of Chronic Myeloid Leukemia (CML) patients that, in large part, achieve satisfactory hematological, cytogenetic and molecular remissions. However, approximately 15-20% fail to obtain optimal responses according to the current European Leukemia Network recommendation because of drug intolerance or resistance.Moreover, a plethora of evidence suggests that Leukemic Stem Cells (LSCs) show BCR-ABL1-independent survival. Hence, they are unresponsive to TKIs, leading to disease relapse if pharmacological treatment is discontinued.All together, these biological events generate a subpopulation of CML patients in need of alternative therapeutic strategies to overcome TKI resistance or to eradicate LSCs in order to allow cure of the disease.In this review we update the role of "non ABL-directed inhibitors" targeting signaling pathways downstream of the BCR-ABL1 oncoprotein and describe immunological approaches activating specific T cell responses against CML cells.

The photosensitizer verteporfin has light-independent anti-leukemic activity for Ph-positive acute lymphoblastic leukemia and synergistically works with dasatinib

Cell lines have been used for drug discovery as useful models of cancers; however, they do not recapitulate cancers faithfully, particularly from the viewpoints of microenvironmental independence. Patient-derived xenografts (PDX) are established by the transfer of primary tumor cells directly from patients into immunodeficient mice and can provide primary-like tumor cells of the amount needed at the desired time. We developed a high-throughput drug screening system using PDX cells and performed drug screening using the PDX cells of Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ ALL). We established four Ph⁺ ALL PDX mice and performed high-throughput screening of 3440 compounds using leukemia cells from the PDX mice (PDX-cell screening). The profiles of drugs selected by PDX-cell screening were markedly different from those by screening using the Ph⁺ ALL cell line. We found that verteporfin, an FDA-approved drug, exhibited strong PDX cell-specific cytotoxicity. In the validation assay, its GI₅₀ was 228 nM, 395 nM, and 538 nM in three PDX cells and 3.93 μM, 2.11 μM, and 5.61 μM in three cell lines. Although verteporfin is a photosensitizer activated by photoirradiation, its cytotoxic effects were mediated by the light-independent production of reactive oxygen species; therefore, its anti-leukemic effects were also exerted in vivo without photoirradiation. Furthermore, it exhibited synergistic effects with dasatinib, an ABL kinase inhibitor. These results indicated the potential of verteporfin as a new anti-leukemic reagent.

Small-molecule Hedgehog inhibitor attenuates the leukemia-initiation potential of acute myeloid leukemia cells

Aberrant activation of the Hedgehog signaling pathway has been implicated in the maintenance of leukemia stem cell populations in several model systems. PF‐04449913 (PF‐913) is a selective, small‐molecule inhibitor of Smoothened, a membrane protein that regulates the Hedgehog pathway. However, details of the proof‐of‐concept and mechanism of action of PF‐913 following administration to patients with acute myeloid leukemia (AML) are unclear. This study examined the role of the Hedgehog signaling pathway in AML cells, and evaluated the in vitro and in vivo effects of the Smoothened inhibitor PF‐913. In primary AML cells, activation of the Hedgehog signaling pathway was more pronounced in CD34⁺ cells than CD34⁻ cells. In vitro treatment with PF‐913 induced a decrease in the quiescent cell population accompanied by minimal cell death. In vivo treatment with PF‐913 attenuated the leukemia‐initiation potential of AML cells in a serial transplantation mouse model, while limiting reduction of tumor burden in a primary xenotransplant system. Comprehensive gene set enrichment analysis revealed that PF‐913 modulated self‐renewal signatures and cell cycle progression. Furthermore, PF‐913 sensitized AML cells to cytosine arabinoside, and abrogated resistance to cytosine arabinoside in AML cells cocultured with HS‐5 stromal cells. These findings imply that pharmacologic inhibition of Hedgehog signaling attenuates the leukemia‐initiation potential, and also enhanced AML therapy by sensitizing dormant leukemia stem cells to chemotherapy and overcoming resistance in the bone marrow microenvironment.

Murine models of acute leukemia: important tools in current pediatric leukemia research

Leukemia remains the most common diagnosis in pediatric oncology and, despite dramatic progress in upfront therapy, is also the most common cause of cancer-related death in children. Much of the initial improvement in outcomes for acute lymphoblastic leukemia (ALL) was due to identification of cytotoxic agents that are active against leukemia followed by the recognition that combination of these cytotoxic agents and prolonged therapy are essential for cure. Recent data demonstrating lack of progress in patients for whom standard chemotherapy fails suggests that the ability to improve outcome for these children will not be dramatically impacted through more intensive or newer cytotoxic agents. Thus, much of the recent research focus has been in the area of improving our understanding of the genetics and the biology of leukemia. Although in vitro studies remain critical, given the complexity of a living system and the increasing recognition of the contribution of leukemia extrinsic factors such as the bone marrow microenvironment, in vivo models have provided important insights. The murine systems that are used can be broadly categorized into syngeneic models in which a murine leukemia can be studied in immunologically intact hosts and xenograft models where human leukemias are studied in highly immunocompromised murine hosts. Both of these systems have limitations such that neither can be used exclusively to study all aspects of leukemia biology and therapeutics for humans. This review will describe the various ALL model systems that have been developed as well as discuss the advantages and disadvantages inherent to these systems that make each particularly suitable for specific types of studies.

Mammalian target of rapamycin inhibitor rapamycin enhances anti-leukemia effect of imatinib on Ph+ acute lymphoblastic leukemia cells

BCR-ABL fusion gene typically causes a type of acute lymphoblastic leukemia (ALL), known as Ph+ ALL. Although imatinib (IM) treatment induced high rates of complete response (CR), serious acute and late complications are frequent, whereas more vexatiously resistance to chemotherapy and clinical relapse develops. Therefore, the efficacy of treatment in Ph+ ALL is still to be determined. In this study, we focused our attention on the potential benefit of rapamycin (RAPA), an mammalian target of rapamycin (mTOR) inhibitor, in combination with IM on a Ph+ ALL cell line SUP-B15 and a primary Ph+ ALL sample in vitro. Analysis of cell proliferation showed that RAPA (50 nm) plus IM exerted good synergistic effect on Ph+ ALL cells. Notably, we found that IM treatment induced the abnormal activation of the components of mTOR signaling pathway and p-BCR-ABL, whereas RAPA potently eliminated this deleterious side effect induced by IM and might overcome the resistance to IM. The synergistic effect was also associated with the increase in autophagy, which seemed to have an opposite role with apoptosis in Ph+ ALL cells, and cell cycle arrest in G1 phase. Altogether, our results suggested that IM in combination with RAPA was more effective for Ph+ ALL cells than IM alone.