Targetable leukaemia dependency on noncanonical PI3Kγ signalling.

Phosphoinositide-3-kinase-γ (PI3Kγ) is implicated as a target to repolarize tumour-associated macrophages and promote antitumour immune responses in solid cancers1-4. However, cancer cell-intrinsic roles of PI3Kγ are unclear. Here, by integrating unbiased genome-wide CRISPR interference screening with functional analyses across acute leukaemias, we define a selective dependency on the PI3Kγ complex in a high-risk subset that includes myeloid, lymphoid and dendritic lineages. This dependency is characterized by innate inflammatory signalling and activation of phosphoinositide 3-kinase regulatory subunit 5 (PIK3R5), which encodes a regulatory subunit of PI3Kγ5 and stabilizes the active enzymatic complex. We identify p21 (RAC1)-activated kinase 1 (PAK1) as a noncanonical substrate of PI3Kγ that mediates this cell-intrinsic dependency and find that dephosphorylation of PAK1 by PI3Kγ inhibition impairs mitochondrial oxidative phosphorylation. Treatment with the selective PI3Kγ inhibitor eganelisib is effective in leukaemias with activated PIK3R5. In addition, the combination of eganelisib and cytarabine prolongs survival over either agent alone, even in patient-derived leukaemia xenografts with low baseline PIK3R5 expression, as residual leukaemia cells after cytarabine treatment have elevated G protein-coupled purinergic receptor activity and PAK1 phosphorylation. Together, our study reveals a targetable dependency on PI3Kγ-PAK1 signalling that is amenable to near-term evaluation in patients with acute leukaemia.

Improving Unrelated Donor Equity: Assessing Mismatched Donor Opportunities with Real-World Data in a Minority-Predominant Cohort.

Recent advances in graft-versus-host disease (GVHD) prophylaxis including post-transplant cyclophosphamide (PTCy) and abatacept have significantly improved outcomes following HLA-mismatched allogenic hematopoietic stem cell transplantation (allo-HSCT) and have tremendous potential for reducing racial disparities in donor availability. A recent small study employing bone marrow as the source of stem cells showed similar outcomes after 5/8 versus 7/8 matches and is currently being tested in a larger study using peripheral blood stem cells. In this study, we examine real-world alternative donor HSCT options for a minority-predominant cohort in the Bronx, NY, focusing on the availability of lesser-matched (5/8 to 7/8) donors. Records of patients who underwent HLA typing at Montefiore Medical Center (2019 to 2022) were reviewed. The National Marrow Donor Program registry was queried to evaluate the availability of donors with at least 99% likelihood of HLA match at various levels (5/8, 6/8, 7/8, 8/8). Two hundred forty-one patients were included, 70% were non-White. Although the availability of ≥7/8 donors was less common in non-White patients, 100% of patients from each group had at least one or more 5/8 and 6/8 HLA-matched donors and more than 80% of these patients had >100 potential 5/8 and 6/8 HLA-matched donors. There was no statistical difference by race or ethnicity in the mean number of donors at 5/8 and 6/8 HLA-match levels. We demonstrate through real-world data that patients from diverse ethnic and racial backgrounds have access to 5/8 and 6/8 HLA-matched donors for allo-HSCT, potentially eliminating disparities in donor availability and allowing prioritization of other donor selection characteristics such as donor age, sex, ABO, and B leader matching. Further work is needed to study whether the use of mismatched donors offers a more potent graft-versus malignancy effect and optimal GVHD prophylaxis.

Haematopoietic stem cell numbers are not solely determined by niche availability.

Haematopoietic stem cells (HSCs) reside in specialized microenvironments, also referred to as niches, and it has been widely believed that HSC numbers are determined by the niche size alone 1-5 . However, the vast excess of the number of niche cells over that of HSCs raises questions about this model. We initially established a mathematical model of niche availability and occupancy, which predicted that HSC numbers are restricted at both systemic and local levels. To address this question experimentally, we developed a femoral bone transplantation system, enabling us to increase the number of available HSC niches. We found that the addition of niches does not alter total HSC numbers in the body, regardless of whether the endogenous (host) niche is intact or defective, suggesting that HSC numbers are limited at the systemic level. Additionally, HSC numbers in transplanted wild-type femurs did not increase beyond physiological levels when HSCs were mobilized from defective endogenous niches to the periphery, indicating that HSC numbers are also constrained at the local level. Our study demonstrates that HSC numbers are not solely determined by niche availability, thereby rewriting the long-standing model for the regulation of HSC numbers.

Impact of race and ethnicity on early mortality in multiple myeloma: a SEER analysis.

Over the past two decades, there have been significant advances in the treatment of multiple myeloma which has led to an improvement in overall survival (OS) (1,2). However, a notable proportion of patients continue to experience early mortality (EM), defined as two years from the time of diagnosis. This raises the possibility that improvements in myeloma survival have not extended equally to all groups. Using the latest data drawn from the Surveillance Epidemiology and End Results (SEER) database of patients in the United States spanning 2000-2019, we study impact of important sociodemographic factors on EM. Through regression modeling, we demonstrate that patients diagnosed from 2000-2005, of older age, male sex, and of certain racial minority status (non-Hispanic Black and Hispanic) have higher odds of EM. Of these factors, minority status contributed to worse 2-year overall survival as well. We evaluate whether income, as a surrogate to access to care, could potentially explain this finding, but find that race has a distinct relationship with EM that is not modified by income. This is further reinforced by subgroup analysis. After characterizing groups vulnerable to EM, we examine reasons for these disparities and potential avenues to address them.

Unveiling T cell evasion mechanisms to immune checkpoint inhibitors in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a heterogeneous and aggressive hematologic malignancy that is associated with a high relapse rate and poor prognosis. Despite advances in immunotherapies in solid tumors and other hematologic malignancies, AML has been particularly difficult to treat with immunotherapies, as their efficacy is limited by the ability of leukemic cells to evade T cell recognition. In this review, we discuss the common mechanisms of T cell evasion in AML: (1) increased expression of immune checkpoint molecules; (2) downregulation of antigen presentation molecules; (3) induction of T cell exhaustion; and (4) creation of an immunosuppressive environment through the increased frequency of regulatory T cells. We also review the clinical investigation of immune checkpoint inhibitors (ICIs) in AML. We discuss the limitations of ICIs, particularly in the context of T cell evasion mechanisms in AML, and we describe emerging strategies to overcome T cell evasion, including combination therapies. Finally, we provide an outlook on the future directions of immunotherapy research in AML, highlighting the need for a more comprehensive understanding of the complex interplay between AML cells and the immune system.

Acute myeloid leukemias with JAK2/STAT mutations are associated with PD-L1 upregulation.

Even though overexpression of the immune checkpoint protein, programmed cell death ligand-1 (PD-L1), is observed in solid tumors, its expression patterns in acute myeloid leukemia remain understudied. As activation of the JAK/STAT pathway has been shown to enhance PD-L1 expression in preclinical models, we evaluated biopsies from AML patients with activating mutations in JAK2/STATs. PD-L1 expression was significantly upregulated in JAK2/STAT mutant cases when compared to JAK2 wildtype controls as demonstrated by PD-L1 immunohistochemistry staining and quantified using the combined positive score (CPS) system. There is significant overexpression of phosphorylated STAT3 expression in patients with oncogenic JAK2 activation and a positive correlation between p-STAT3 and PD-L1 expression. In conclusion, we demonstrate the CPS scoring system could be applied as a quantitative measure of PD-L1 expression in leukemias and that JAK2/STATs mutant AML can be potential candidates for checkpoint inhibitor trials.

A Metabolically Optimized, Noncytotoxic Low-Dose Weekly Decitabine/Venetoclax in MDS and AML.

PURPOSE: Venetoclax (VEN) added to the hypomethylating agents (HMA) decitabine or azacitidine is the new standard of care for elderly patients with acute myeloid leukemia (AML) and is being evaluated in myelodysplastic syndrome (MDS). Current dosing of HMA/VEN relies on leukemia suppression through cytotoxicity which also impacts normal hematopoiesis. A regimen using once-weekly low-dose decitabine (LDDec) has demonstrated activity in myeloid malignancies. To overcome the severe myelosuppression often seen with HMA/VEN, we evaluated a once-weekly dosing regimen of VEN and LDDec in elderly and/or frail patients who were felt less likely to tolerate severe myelosuppression. PATIENTS AND METHODS: This is a retrospective, single-center analysis of patients with AML, MDS, or chronic myelomonocytic leukemia treated with a once-weekly LDDec/VEN regimen. We also compare this regimen with a cohort treated with standard dosing HMA/VEN. RESULTS: In a retrospective cohort of 39 patients, the overall response rate for patients receiving LDDec/VEN for first-line AML and MDS was 88% and 64%, respectively. In patients with TP53 mutations, the composite complete response rate was 71% and the median overall survival was 10.7 months. When compared with 36 patients receiving standard dose HMA/VEN, the LDDec/VEN patients had a longer time on therapy (175 vs. 78 days; P = 0.014) and a trend toward a higher rate of transfusion independence (47% vs. 26%; P = 0.33). Neutropenic fever occurred in 31% of patients, with a median of one hospitalization at any point during treatment. CONCLUSIONS: This preliminary clinical experience, although retrospective, provides proof-of-activity of noncytotoxic DNA methyltransferase 1-targeting by allowing frequent, sustained drug exposure often not possible with standard HMA/VEN regimens.

Haploinsufficiency of the essential gene Rps12 causes defects in erythropoiesis and hematopoietic stem cell maintenance.

Ribosomal protein (Rp) gene haploinsufficiency can result in Diamond-Blackfan Anemia (DBA), characterized by defective erythropoiesis and skeletal defects. Some mouse Rp mutations recapitulate DBA phenotypes, although others lack erythropoietic or skeletal defects. We generated a conditional knockout mouse to partially delete Rps12. Homozygous Rps12 deletion resulted in embryonic lethality. Mice inheriting the Rps12KO/+ genotype had growth and morphological defects, pancytopenia, and impaired erythropoiesis. A striking reduction in hematopoietic stem cells (HSCs) and progenitors in the bone marrow (BM) was associated with decreased ability to repopulate the blood system after competitive and non-competitive BM transplantation. Rps12KO/+ lost HSC quiescence, experienced ERK and MTOR activation, and increased global translation in HSC and progenitors. Post-natal heterozygous deletion of Rps12 in hematopoietic cells using Tal1-Cre-ERT also resulted in pancytopenia with decreased HSC numbers. However, post-natal Cre-ERT induction led to reduced translation in HSCs and progenitors, suggesting that this is the most direct consequence of Rps12 haploinsufficiency in hematopoietic cells. Thus, RpS12 has a strong requirement in HSC function, in addition to erythropoiesis.

Unraveling the Link between Class 1A PI3-Kinase, Autophagy, and Myelodysplasia.

Myelodysplastic syndrome (MDS) is a clonal malignancy that develops from hematopoietic stem cells (HSCs), but the underlying mechanisms of MDS initiation are not well understood. The phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway is often dysregulated in MDS. To investigate how PI3K inactivation affects HSC function, we generated a mouse model in which three Class IA PI3K genes were deleted in hematopoietic cells. Surprisingly, PI3K deficiency caused cytopenias, reduced survival, and multilineage dysplasia with chromosomal abnormalities, consistent with MDS initiation. PI3K-deficient HSCs had impaired autophagy, and pharmacologic treatment with autophagy-inducing reagents improved HSC differentiation. Furthermore, a similar autophagic degradation defect was observed in MDS patient HSCs. Therefore, our study uncovered a crucial protective role for Class IA PI3K in maintaining autophagic flux in HSCs to preserve the balance between self-renewal and differentiation.

Outcome of Stem Cell Transplantation in HTLV-1-Associated North American Adult T-Cell Leukemia/Lymphoma.

Adult T-cell leukemia/lymphoma (ATLL) remains challenging to treat and has dismal outcome. Allogeneic stem-cell transplantation (allo-SCT) has promising results, but data remain scarce. In this single-center retrospective analysis of 100 patients with ATLL from north America (67 acute, 22 lymphomatous), 17 underwent allo-SCT and 5 autologous SCT (ASCT), with a median follow-up of 65 months. Post-transplant 3-years relapse incidence (RI) and non-relapse mortality (NRM) were 51% and 37%, respectively, and 3-year progression-free survival (PFS) and overall survival (OS) were 31% and 35%, respectively. ASCT 1-year RI was 80% compared to 30% in allo-SCT (p = 0.03). After adjusting for immortal-time bias, allo-SCT had significantly improved OS (HR = 0.4, p = 0.01). In exploratory multivariate analysis, patients achieving first complete response and Karnofsky score ≥ 90 had significantly better outcomes, as did Black patients, compared to Hispanics, who had worse outcome. In transplanted patients, 14 died within 2 years, 4 of which ASCT recipients. Our data are the largest ATLL transplant cohort presented to date outside of Japan and Europe. We show that allo-SCT, but not ASCT, is a valid option in select ATLL patients, and can induce long term survival, with 40% of patients alive after more than 5 years.

PI3-kinase deletion promotes myelodysplasia by dysregulating autophagy in hematopoietic stem cells.

Myelodysplastic syndrome (MDS) is a clonal malignancy arising in hematopoietic stem cells (HSCs). The mechanisms of MDS initiation in HSCs are still poorly understood. The phosphatidylinositol 3-kinase (PI3K)/AKT pathway is frequently activated in acute myeloid leukemia, but in MDS, PI3K/AKT is often down-regulated. To determine whether PI3K down-regulation can perturb HSC function, we generated a triple knockout (TKO) mouse model with Pik3ca, Pik3cb, and Pik3cd deletion in hematopoietic cells. Unexpectedly, PI3K deficiency caused cytopenias, decreased survival, and multilineage dysplasia with chromosomal abnormalities, consistent with MDS initiation. TKO HSCs exhibit impaired autophagy, and pharmacologic autophagy induction improved HSC differentiation. Using intracellular LC3 and P62 flow cytometry and transmission electron microscopy, we also observed abnormal autophagic degradation in patient MDS HSCs. Therefore, we have uncovered an important protective role for PI3K in maintaining autophagic flux in HSCs to preserve the balance between self-renewal and differentiation and to prevent MDS initiation.

Periosteal skeletal stem cells can migrate into the bone marrow and support hematopoiesis after injury.

Functional stromal cells are known to support bone marrow regeneration after chemotherapy or radiation-induced injury to prevent prolonged myelosuppression. However, it is not known how stromal cells within the bone marrow are regenerated after injury. We have utilized a whole bone transplantation model that mimics the initial bone marrow necrosis and fatty infiltration that is seen after bone marrow injury and subsequent recovery. We demonstrate that periosteal skeletal stem cells (P-SSCs) can migrate into the bone marrow and contribute to stromal regeneration and hematopoietic recovery. Once in the bone marrow, P-SSCs are phenotypically and functionally reprogrammed into bone marrow mesenchymal stem cells (BM-MSCs), expressing high levels of hematopoietic stem cell (HSC) niche factors, such as Cxcl12 and Kitl. Additionally, our results further indicate that P-SSCs are more resistant to acute stress than BM-MSCs. Here, we report a new function of P-SSCs, highlighting their major plasticity and the role of the periosteum as a potential source of BM-MSCs following acute bone marrow injury.

Crizotinib Has Preclinical Efficacy in Philadelphia-Negative Myeloproliferative Neoplasms.

PURPOSE: The Philadelphia chromosome-negative myeloproliferative neoplasms (MPN) polycythemia vera, essential thrombocythemia, and primary myelofibrosis are characterized by JAK/STAT pathway activation. JAK inhibitors are approved for MPN treatment, but persistence has been observed, due to JAK/STAT reactivation. EXPERIMENTAL DESIGN: Using MPN patient samples, JAK2-mutated cell lines, and MPN mouse models, we examined both the efficacy and mechanism by which crizotinib, the ALK/MET/RON/ROS1 inhibitor approved for the treatment of non-small cell lung cancer, alters MPN cell proliferation and JAK/STAT activation. RESULTS: We found that crizotinib suppresses proliferation and activation of JAK/STAT signaling, and decreases the disease burden in the JAK2V617F mouse model of MPN. Furthermore, we found that crizotinib could overcome JAK inhibitor persistence to ruxolitinib. Interestingly, phosphorylation of the crizotinib target RON kinase was enhanced in ruxolitinib-persistent cells. We show that phospho-JAK2 and phospho-RON can physically interact to sustain JAK/STAT signaling, and that the combination of crizotinib and ruxolitinib disrupts this interaction. Furthermore, RON knockdown suppresses proliferation and activation of JAK/STAT signaling in JAK2-mutated cells, and RON deletion in a JAK2V617F mouse MPN model decreases the disease burden. We also observed RON hyperactivation in MPN patient cells, suggesting that RON may be an important target of crizotinib in MPN. CONCLUSIONS: In summary, we demonstrate that crizotinib has preclinical efficacy in MPN patient cells, JAK2-mutated cell lines, and a JAK2-mutated mouse model, and that the combination of crizotinib with JAK inhibitors suppresses JAK inhibitor persistence. Our work suggests that crizotinib should be investigated for the treatment of patients with MPN.

A Co-Management Model for Myeloid Malignancies That Evolved during the COVID-19 Pandemic.

INTRODUCTION: Myeloid malignancies are a heterogeneous group of clonal bone marrow disorders that are complex to manage in the community and therefore often referred to subspecialists at tertiary oncology referral centers. Many patients do not live in close proximity to tertiary referral centers and are unable to commute long distances due to age, comorbidities, and frailty. Interventions that minimize the travel time burden without compromising quality of care are an area of unmet need. We describe a cancer care delivery model for patients with myeloid malignancies that is built around telehealth and enables this vulnerable population access to care at an NCI-designated cancer center while receiving majority of their care close to home. METHODS AND MATERIALS: We report on a cohort of patients with myeloid malignancies who were co-managed by a general community oncologist and an academic leukemia subspecialist at Montefiore Einstein Cancer Center in New York. Patients were initially referred to our institute for a second opinion by community practices that are in partnership with Montefiore Health System, and initial visits were in-person or via telehealth. Treatment plans were made after discussion with patient's local community oncologist. Patients then continued to receive majority of their treatment and supportive care including transfusion support with their local oncologist, and follow-up visits were mainly via telehealth with the academic leukemia subspecialist. RESULTS: Our cohort of 12 patients had a median age of 81 years (range, 59-88 years). Patients remained on active treatment for a median time of 357 days (range, 154-557 days). Most of our patients had a performance status of ECOG 2 or higher. Three patients had myelodysplastic syndromes, 7 patients had acute myeloid leukemia, and 2 patients had myelofibrosis. The median number of hospitalizations over the total treatment time period was one. CONCLUSION: We demonstrate a shared academic and community care co-management model for the treatment of myeloid malignancies in elderly, frail patients using telehealth as a backbone with a very low hospitalization rate.

Lenalidomide and Eltrombopag for Treatment of Low- or Intermediate-Risk Myelodysplastic Syndrome: Result of a Phase II Clinical Trial.

PURPOSE: Thrombocytopenia is a serious complication of myelodysplastic syndromes (MDS) associated with an increased bleeding risk and worse prognosis. Eltrombopag (ELT), a thrombopoietin receptor agonist, can increase platelet counts and reverse anti-megakaryopoietic effects of lenalidomide (LEN) in preclinical studies. We hypothesized ELT would reduce the incidence of thrombocytopenia in MDS. PATIENTS AND METHODS: We conducted a Phase II multicenter trial of ELT and LEN in adult patients with low- or intermediate-1-risk MDS with symptomatic or transfusion-dependent anemia or thrombocytopenia (NCT01772420). Thrombocytopenic patients were started on ELT and subsequently treated with LEN after platelets were increased. Patients without thrombocytopenia were started on LEN monotherapy and treated with ELT if they became thrombocytopenic. RESULTS: Fifty-two patients were enrolled; mean age was 71 years (range 34-93). Overall response rate (ORR) in the intention-to-treat population was 35% (18/52). ELT monotherapy led to ORR of 33.3% (7/21), 29% achieving hematologic improvement (HI)-Platelets, and 24% bilineage responses. LEN monotherapy had 38% ORR (6/16) with all responders achieving HI-Erythroid. Fifteen patients received both ELT and LEN with ORR of 33.3%, 20% achieved HI-Erythroid, and 20% HI-Platelets with 13% bilineage responses. Median duration of response was 40 weeks for ELT (range 8-ongoing), 41 weeks (25-ongoing) for LEN, and 88 weeks (8.3-ongoing) for ELT/LEN. Non-hematologic grade 3-4 treatment-related adverse events were infrequent. Among patients on ELT, 2 had major bleeding events, 1 had a reversible increase in peripheral blasts, and 1 developed marrow fibrosis after 6 years on ELT. CONCLUSIONS: ELT and LEN are well tolerated and effective in achieving hematologic improvement in patients with low-/intermediate-risk MDS.

Targetable leukemia dependency on noncanonical PI3Kγ signaling.

Phosphoinositide 3-kinase gamma (PI3Kγ) is implicated as a target to repolarize tumor-associated macrophages and promote anti-tumor immune responses in solid cancers. However, cancer cell-intrinsic roles of PI3Kγ are unclear. Here, by integrating unbiased genome-wide CRISPR interference screening with functional analyses across acute leukemias, we define a selective dependency on the PI3Kγ complex in a high-risk subset that includes myeloid, lymphoid, and dendritic lineages. This dependency is characterized by innate inflammatory signaling and activation of phosphoinositide 3-kinase regulatory subunit 5 ( PIK3R5 ), which encodes a regulatory subunit of PI3Kγ and stabilizes the active enzymatic complex. Mechanistically, we identify p21 (RAC1) activated kinase 1 (PAK1) as a noncanonical substrate of PI3Kγ that mediates this cell-intrinsic dependency independently of Akt kinase. PI3Kγ inhibition dephosphorylates PAK1, activates a transcriptional network of NFκB-related tumor suppressor genes, and impairs mitochondrial oxidative phosphorylation. We find that treatment with the selective PI3Kγ inhibitor eganelisib is effective in leukemias with activated PIK3R5 , either at baseline or by exogenous inflammatory stimulation. Notably, the combination of eganelisib and cytarabine prolongs survival over either agent alone, even in patient-derived leukemia xenografts with low baseline PIK3R5 expression, as residual leukemia cells after cytarabine treatment have elevated G protein-coupled purinergic receptor activity and PAK1 phosphorylation. Taken together, our study reveals a targetable dependency on PI3Kγ/PAK1 signaling that is amenable to near-term evaluation in patients with acute leukemia.