Mdm2/p53 levels in bone marrow mesenchymal stromal cells is essential for maintaining the hematopoietic niche in response to DNA damage

Mesenchymal stromal cells (MSCs) are a key component of the bone marrow (BM) niche, providing essential support required for maintenance of hematopoietic stem cells. To advance our understanding of physiological functions of p53 and Mdm2 in BM-MSCs, we developed traceable conditional mouse models targeting Mdm2 and/or Trp53 in vivo . We demonstrate that Mdm2 is essential for the emergence, maintenance and hematopoietic support of BM-MSCs. Mdm2 haploinsufficiency in BM-MSCs resulted in genotoxic stress-associated thrombocytopenia, suggesting a functional role for Mdm2 in hematopoiesis. In a syngeneic mouse model of acute myeloid leukemia (AML), Trp53 deletion in BM-MSCs improved survival, and protected BM against hematopoietic toxicity from a murine Mdm2i, DS-5272. The transcriptional changes were associated with dysregulation of glycolysis, gluconeogenesis, and Hif-1α in BM-MSCs. Our results reveal a physiologic function of Mdm2 in BM-MSC, identify a previously unknown role of p53 pathway in BM-MSC-mediated support in AML and expand our understanding of the mechanism of hematopoietic toxicity of MDM2is.

The multi-kinase inhibitor CG-806 exerts anti-cancer activity against acute myeloid leukemia by co-targeting FLT3, BTK, and Aurora kinases

Background

Despite the development of several FLT3 inhibitors that have improved outcomes in patients with FLT3-mutant acute myeloid leukemias (AML), drug resistance is frequently observed, which may be associated with the activation of additional pro-survival pathways such as those regulated by BTK, aurora kinases, and potentially others in addition to acquired tyrosine kinase domains (TKD) mutations of FLT3 gene. FLT3may not always be a driver mutation.

Objective

To evaluate the anti-leukemia efficacy of the novel multi-kinase inhibitor CG-806, which targets FLT3 and other kinases, in order to circumvent drug resistance and target FLT3 wild-type (WT) cells.

Methods

The anti-leukemia activity of CG-806 was investigated by measuring apoptosis induction and analyzing cell cycle with flow cytometry in vitro, and its anti-leukemia.

Results

CG-806 demonstrated superior anti-leukemia efficacy compared to commercially available FLT3 inhibitors, both in vitro and in vivo, regardless of FLT3 mutational status. The mechanism of action of CG-806 may involve its broad inhibitory profile of FLT3, BTK, and aurora kinases. InFLT3 mutant cells, CG-806 induced G1 phase blockage, while in FLT3WT cells, it resulted in G2/M arrest. Targeting FLT3 and Bcl-2 and/or Mcl-1 simultaneously resulted in a synergistic pro-apoptotic effect in FLT3mutant leukemia cells.

Conclusion

The results of this study suggest that CG-806 is a promising multi-kinase inhibitor with anti-leukemia efficacy, regardless of FLT3 mutational status. A phase 1 clinical trial of CG-806 for the treatment of AML has been initiated (NCT04477291).

Clinical and molecular profiling of AML patients with chromosome 7 or 7q deletions in the context of TP53 alterations and venetoclax treatment

Deletions in chromosome 7 (del(7)) or its long arm (del(7q)) constitute the most common adverse cytogenetic events in acute myeloid leukemia (AML). We retrospectively analyzed 243 treatment-naive patients with AML and del(7) (168/243; 69%) or del(7q) (75/243; 31%) who did not receive any myeloid-directed therapy prior to AML diagnosis. This is the largest comprehensive clinical and molecular analysis of AML patients with del(7) and del(7q). Our results show that relapse-free survival was significantly longer for AML patients with del(7q) compared to del(7), but the overall survival and remission duration were similar. TP53 mutations and del5/5q were the most frequent co-occurring mutations and cytogenetic abnormalities, and conferred worse outcomes in del(7) and del(7q) patients. Venetoclax-based treatments were associated with worse outcomes in TP53 mutated AML patients with del(7) or del(7q), as well as del(7) with TP53 wildtype status, requiring further investigation.

Phase II Study of Venetoclax Added to Cladribine Plus Low-Dose Cytarabine Alternating With 5-Azacitidine in Older Patients With Newly Diagnosed Acute Myeloid Leukemia

PURPOSE

The combination of venetoclax and 5-azacitidine (5-AZA) for older or unfit patients with acute myeloid leukemia (AML) improves remission rates and survival compared with 5-AZA alone. We hypothesized that the addition of venetoclax to cladribine (CLAD)/low-dose araC (low-dose cytarabine [LDAC]) alternating with 5-AZA backbone may further improve outcomes for older patients with newly diagnosed AML.

METHODS

This is a phase II study investigating the combination of venetoclax and CLAD/LDAC alternating with venetoclax and 5-AZA in older (≥ 60 years) or unfit patients with newly diagnosed AML. The primary objective was composite complete response (CR) rate (CR plus CR with incomplete blood count recovery); secondary end points were overall survival, disease-free survival (DFS), overall response rate, and toxicity.

RESULTS

A total of 60 patients were treated; median age was 68 years (range, 57-84 years). By European LeukemiaNet, 23%, 33%, and 43% were favorable, intermediate, and adverse risk, respectively. Fifty-six of 60 evaluable patients responded (composite CR: 93%) and 84% were negative for measurable residual disease. There was one death (2%) within 4 weeks. With a median follow-up of 22.1 months, the median overall survival and DFS have not yet been reached. The most frequent grade 3/4 nonhematologic adverse events were febrile neutropenia (n = 33) and pneumonia (n = 14). One patient developed grade 4 tumor lysis syndrome.

CONCLUSION

Venetoclax and CLAD/LDAC alternating with venetoclax and 5-AZA is an effective regimen among older or unfit patients with newly diagnosed AML. The rates of overall survival and DFS are encouraging. Further study of this non-anthracycline-containing backbone in younger patients, unfit for intensive chemotherapy, as well as comparisons to standard frontline therapies is warranted.

Concomitant targeting of FLT3 and BTK overcomes FLT3 inhibitor resistance in acute myeloid leukemia through inhibition of autophagy

Strategies to overcome resistance to FMS-like tyrosine kinase 3 (FLT3)-targeted therapy in acute myeloid leukemia (AML) are urgently needed. We identify autophagy as one of the resistance mechanisms, induced by hypoxia and the bone marrow (BM) microenvironment via Bruton's tyrosine kinase (BTK) activation. Suppressing autophagy/BTK sensitized FLT3-mutated AML to FLT3 inhibitor-induced apoptosis. Further, co-targeting FLT3/BTK/Aurora kinases (AURKs) with a novel multi-kinase inhibitor CG-806 (luxeptinib) induced profound apoptosis induction in FLT3-mutated AML by co-suppressing FLT3/BTK, antagonizing autophagy, and causing leukemia cell death in FLT3 wild-type AML by AURK-mediated G2/M arrest and polyploidy, in addition to FLT3 inhibition. Thus, CG-806 exerted profound anti-leukemia activity against AMLs regardless of FLT3 mutation status. CG-806 further significantly reduced AML burden and extended survival in an in vivo PDX leukemia murine model of FLT3 inhibitorresistant FLT3-ITD/TKD double mutant primary AML. Taken together, CG-806 exerts a unique mechanistic action and pre-clinical activity, suggesting further development in FLT3 wild-type and mutant AML.

Azacitidine plus venetoclax in patients with high-risk myelodysplastic syndromes or chronic myelomonocytic leukaemia: phase 1 results of a single-centre, dose-escalation, dose-expansion, phase 1-2 study

BACKGROUND

Therapies beyond hypomethylating agents such as azacitidine are needed in high-risk myelodysplastic syndromes. Venetoclax is an orally bioavailable small molecule BCL-2 inhibitor that is synergistic with hypomethylating agents. We therefore aimed to evaluate the safety, tolerability, and preliminary activity of azacitidine combined with venetoclax for treatment-naive and relapsed or refractory high-risk myelodysplastic syndromes or chronic myelomonocytic leukaemia.

METHODS

We did a single centre, dose-escalation, dose-expansion, phase 1-2 trial at the University of Texas MD Anderson Cancer Center (Houston, TX, USA). This Article details the phase 1 results. We enrolled patients (≥18 years) with treatment-naive or relapsed or refractory high-risk myelodysplastic syndromes or chronic myelomonocytic leukaemia and bone marrow blasts of more than 5%. No specific Eastern Cooperative Oncology Group status restriction was used. Patients were treated with intravenous or subcutaneous azacitidine (75 mg/m²) for 5 days and oral venetoclax (100-400 mg) for 7-14 days. The primary outcome was safety and tolerability as well as determination of the maximum tolerated dose and recommended phase 2 dose of the azacitidine and venetoclax combination using a 3 + 3 study design. All patients who received one dose of study drug were included in the analyses. This study is registered with ClinicalTrials.gov, number NCT04160052. The phase 2 dose-expansion part of the trial is ongoing.

FINDINGS

Between Nov 12, 2019, and Dec 17, 2021, a total of 23 patients were enrolled in the phase 1 portion of this study (17 [74%] hypomethylating agent naive and six [26%] post-hypomethylating agent failure). 18 (78%) patients were male and five (22%) were female; 21 (91%) were white and two (9%) were Asian. Median follow-up was 13·2 months (IQR 6·8-18·3). The maximum tolerated dose was not reached and the recommended phase 2 dose was established as azacitidine 75 mg/m² for 5 days plus venetoclax 400 mg for 14 days. The most common grade 3-4 treatment-emergent adverse events were neutropenia (nine [39%] of 23), thrombocytopenia (nine [39%]), lung infection (seven [30%]), and febrile neutropenia (four [17%]). Three deaths due to sepsis, which were not deemed treatment-related, occurred on the study drugs. The overall response rate was 87% (95% CI 66-97; 20 of 23 patients).

INTERPRETATION

Azacitidine with venetoclax is safe and shows encouraging activity in patients with high-risk myelodysplastic syndromes or chronic myelomonocytic leukaemia.

FUNDING

MD Anderson Cancer Center.

A phase two study of high dose blinatumomab in Richter's syndrome

Richter's Syndrome (RS) is an aggressive transformation of CLL, usually clonally-related diffuse large B-cell lymphoma (DLBCL), characterized by frequent TP53 mutations, intrinsic chemoresistance and poor survival. TP53-independent treatments are needed. We conducted a single center, phase 2, investigator-initiated study of high dose blinatumomab (maximum 112 mcg/d after initial, weekly dose escalation), NCT03121534, given for an 8-week induction and 4-week consolidation cycle. Responses were assessed by Lugano 2014 criteria. Serial multi-parameter flow cytometry from blood was performed to identify patient-specific biomarkers for response. Nine patients were treated. Patients had received a median of 4 and 2 prior therapies for CLL and RS, respectively. Five of 9 had del(17p) and 100% had complex karyotype. Four patients had reduction in nodal disease, including one durable complete response lasting >1 y. Treatment was well tolerated, with no grade >3 cytokine release syndrome and 1 case of grade 3, reversible neurotoxicity. Immunophenotyping demonstrated the majority of patients expressed multiple immune checkpoints, especially PD1, TIM3 and TIGIT. The patient who achieved CR had the lowest levels of immune checkpoint expression. Simultaneous targeting with immune checkpoint blockade, especially PD1 inhibition, which has already demonstrated single-agent efficacy in RS, could achieve synergistic killing and enhance outcomes.

Abstract 5337: Tolinapant (ASTX660) enhances the anti-leukemic activity of Venetoclax and Dexamethasone in T cell acute lymphoblastic leukemia (T-ALL)

Background: Inhibitors of apoptosis proteins (IAPs) are overexpressed in ALL leading to resistance to apoptosis and chemo-resistance. Tolinapant, a non-peptidomimetic antagonist of the cellular and X-linked inhibitors of apoptosis (cIAP1/2 and XIAP) being evaluated in Phase 1/2 clinical trial [NCT02503423] showed single-agent activity in T-cell lymphoma. Objectives: Herein, we analyzed the preclinical activity of tolinapant in combination with ABT199 and Dexamethasone (DEX) in T-ALL (in vitro and ex-vivo patient derived xenografts (PDX).

Results: Using a panel of 8 T-ALL cell lines we analyzed the single agent activity of tolinapant. Loucy and SUP-T11 were most sensitive (IC50 = 190-309 nM). CCRF-CEM and ALL-SIL showed moderate sensitivity (IC50 = 10-18 µM) while Jurkat, MOLT16, MOLT4 and PF382 were resistant. Western blotting (WB) showed decreased levels of cIAP1and cIAP2 with no change in XIAP in response to tolinapant as a single agent. We next investigated the efficacy of tolinapant with Bcl2 inhibitor ABT199. The combination of ABT199 and ASTX660 was synergistic in Loucy cell line with combination index (CI) of 0.14. Cell death was increased to 64±3% in combination v/s 27±0.9% in ABT199. WB showed decreased cIAP2 and increased levels of cleaved caspase 7 and cleaved caspase 9 in combination compared to single agents, suggesting increased apoptosis. Treatment of PDX-derived cells with tolinapant and ABT199 was more effective than monotherapy in inducing apoptosis in CD45+ bulk (46±0.7% to 63±6%, p<0.0001) and leukemia initiating cells (LICs, CD45+ CD7+ CD19- CD34+) (39±3% to 54±8%, p=0.003). Next, we checked the effect of combination of DEX with tolinapant in T-ALL cell lines. CCRF-CEM cell line is from a relapsed patient and is resistant to DEX. The combination was synergistic with CI of 0.26 and cell death of 50±4% compared to 20±3% by DEX. A triple combination of DEX, ABT199 and tolinapant increased apoptotic response to 82.9±1%, compared to DEX+ABT199 dual combination where apoptosis was induced to 52.4±2%. Strong synergy in terms of both cytoreduction as well as apoptosis induction was observed in SUP-T11 cells. Tolinapant sensitized SUP-T11 cells to DEX with ED50 value of 542 nM in combination compared to ~2 µM with DEX treatment. Simultaneous analysis of cell proliferation, stress response and DNA damage using single-cell proteomics analysis showed downregulation of proliferation (Ki-67), stress response (ATF4, LC3B) and increased levels of cleaved PARP, cleaved caspase 3 suggesting increased apoptosis in combination of tolinapant with DEX. Treatment of PDX-derived cells with tolinapant enhanced the cytotoxic effect of DEX in CD45+ bulk (58±2% to 71±0.1%, p<0.0001) and LICs (62±2% to 78±0.9%, p<0.0001).

Conclusion: Tolinapant synergizes with the anti-leukemic activity of ABT199 and DEX, establishing a therapeutic rationale for IAP antagonist in T-ALL.

Citation Format: Priyanka Sharma, Sujan Piya, Huaxian Ma, Natalia Baran, Muharrem Muftuoglu, Mahesh Basyal, Vivian Ruvolo, George Ward, Tomoko Smyth, Martin J. Sims, Michael Andreeff, Gautam Borthakur. Tolinapant (ASTX660) enhances the anti-leukemic activity of Venetoclax and Dexamethasone in T cell acute lymphoblastic leukemia (T-ALL) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5337.

Abstract 5479: Discovery and evaluation of GT19630, a c-Myc/GSPT1 cereblon E3 ligase modulator (CELMoD), for targeting Myc-driven blood cancers and small cell lung cancers (SCLC)

c-Myc is an oncogenic transcriptional factor driving tumor initiation, progression and poor prognosis in 80% of all tumor types, especially in B-cell malignancies and small cell lung cancer (SCLC) with Myc genomic alterations. Myc dysregulation have been directly linked to the poor clinical outcome in these cancers. Therefore, it is highly warranted to discover and develop novel Myc therapeutical agents for targeting Myc driven cancers. Here we described GT19630, a GSPT1/Myc CELMoD. GT19630 was discovered through an SAR effort for c-Myc degrader by using c-Myc ELISA and Western blot assays in c-Myc driven HL60 AML cells. GT19630 selectively degraded c-Myc proteins in HL60 cells (IC50=1.5 nM) as compared to growth-factor regulated c-Myc erythroid progenitor cells (TF-1 cells) with IC50=52.5 nM. GT19630 also selectively inhibited HL60 cell proliferation (IC50= 0.33 nM), as compared to its IC50 (26.2 nM) in GM-CSF-TF-1 proliferation, as well as in bone marrow colony-forming cell assays (myeloid=40.2 nM), suggesting>100X selectivity for HL60 cells over normal blood cells. Through the SAR for Myc degrader, GT19630 has been evolved as a leading molecule sharing chemical properties to CELMoDs. Therefore, this compound was further evaluated by proteomics and western blot, GT19630 was confirmed to selective degradation of CELMoD targets, GSPT1/GSPT2 (translation termination factor G1 to S phase transition proteins 1 and 2) with IC90<1 nM and CK1 alpha (IC90<10 nM), but not IKZF1/Ikaros. In silico modeling of GT19630 was performed in the DDB1−CRBN−CC-885−GSPT1 complex and confirmed the docking similarity with CELMoDs. Further, GT19630 inhibited the cell proliferation with IC50<10 nM in 74% B-cell malignant cell lines (20/27) bearing deregulated c-Myc and in 79% of SCLC cell lines (4/19) carrying deregulated Myc (c-Myc, N-Myc or L-Myc) tested. Moreover, GT19630 completely degraded Myc proteins in AML, lymphoma and multiple myeloma (c-Myc) and SCLC (c-Myc and N-Myc) xenograft tumors at the lowest dose of 1.0 mg/kg and induced complete tumor regression (lowest dose=0.3 mg/kg) tested. Furthermore, this compound eradicated lymphoma cells in Daudi-induced liquid lymphoma mouse models. In addition, GT19630, as a potent GSPT1/Myc CELMoD, demonstrated an even-driven pharmacology in vivo and induced complete tumor regression with a dosing regimen of 3 day on/7 day off. Remarkably, GT19630 selectively degraded Myc proteins in HL60 and DMS114 SCLC xenograft tumors as compared to a much less potency at degrading c-Myc in rat spleen. Finally, GT19630 demonstrated favorable PK and safety profiles (an 8-fold safety therapeutic windows) with no effect on myeloid lineages in rats at the dose of 6 mg/kg for 14 days, indicating GT19630 lacks myelosuppression as reported for other CELMoDs. Currently, GT19630 has been advanced into IND enabling stage.

Citation Format: Liandong Ma, Youzhi Tong, Zhaohui Yang, Qianxiang Zhou, Hongha Yan, Ru Xu, Jie Chen, Jie Pan, Huiyuan Wang, Jiangwei Li, Dong Chen, Xiang Cai, Jie Qu, Yini Wang, Jun Qin, Yuki Nishida, Michael Andreeff, Qilnli Guo, Yuki Nishida, Michael Andreeff. Discovery and evaluation of GT19630, a c-Myc/GSPT1 cereblon E3 ligase modulator (CELMoD), for targeting Myc-driven blood cancers and small cell lung cancers (SCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5479.

Quizartinib (QUIZ) with decitabine (DAC) and venetoclax (VEN) is active in patients (pts) with FLT3-ITD mutated acute myeloid leukemia (AML): A phase I/II clinical trial

7036

Background: QUIZ, a potent 2nd generation FLT3 inhibitor (FLT3i) demonstrated synergy with VEN in AML cell lines and PDX models (Mali Haematologica 2020). We evaluated the safety and efficacy of DAC + VEN + QUIZ triplet in patients with newly diagnosed (ineligible for intensive induction chemotherapy) or relapsed/refractory (R/R; up to 5 prior chemotherapies) FLT3 ITD mutated AML. Methods: All pts received 10 days of DAC (20 mg/m2) in Cycle 1. Pts underwent day 14 bone marrow (BM) biopsy, and VEN (400 mg/day starting from day1) was put on hold in pts with BM blasts ≤ 5% or aplasia. Those with day14 BM blast >5% continued VEN for 21 days during cycle 1. In subsequent cycles, DAC was reduced to 5 days. QUIZ (30 or 40 mg/day) was administered daily continuously. Results: Overall, 28 pts were enrolled and evaluable at the time of this report. Of the 23 pts with R/R AML (median 3 [range 1-5] prior therapies, 78% with ≥1 prior FLT3i including prior gilteritinib (GILT) in 70%, and 39% had a prior ASCT), 78% achieved CRc (3 CR, 15 CRi) with 6/16 and 5/18 responders FLT3-PCR and multicolor flow cytometry (MFC) negative, respectively. Pts with RAS/MAPK mutations had the lowest response rates (Table). Interestingly, no emergent TKD mutations were noted at relapse after the triplet but 3/8 evaluable pts had emergent RAS/MAPK mutations. 60-day mortality rate was 5%. Of 5 patients with newly diagnosed AML (median age 69), all achieved CRc (2 CR, 3 CRi) with 4/5 and 2/4 responders FLT3-PCR and MFC negative, respectively. 60-day mortality was 0. 2 pts developed hematologic DLT with 40 mg/day QUIZ dose (grade 4 neutropenia with a <5% cellular BM lasting ≥42 days). Hence, QUIZ 30 mg/day dose was determined as RP2D for the triplet. Grade 3/4 non-hematologic toxicities included lung infections (42%) and neutropenic fever (30%). No QTcF prolongations >480 msec were noted. With a median follow-up (f/u) of 13 months, the median OS was 7.6 months in R/R cohort (1-year OS of 30%). 8/18 responding R/R pts (including 5/8 prior GILT exposed pts) underwent ASCT with a median OS of 19 vs 8 months in those who underwent ASCT versus not (p=0.26). Of the 5 frontline responding pts median OS was 14.5 months, 2 were alive in CR, 1 died in CR1 post-ASCT, 2 died due to relapsed disease at the last f/u. Conclusions: DAC + VEN + QUIZ is active in R/R FLT3-ITD mutated AML pts, with CRc rates of 78% and the median OS of 7.6 months. Interestingly, RAS/MAPK mutations but not emergent TKD mutations were associated with primary and secondary resistance to the triplet. Accrual continues, and updated clinical, NGS, and mass cytometry (CyTOF) data will be presented. Clinical trial information: NCT03661307. [Table: see text]

Acute myeloid leukemia with KMT2Ar and association with risk of bleeding and early mortality

7026

Background: Acute myeloid leukemia (AML) with rearrangement of KMT2A is characterized by chemotherapy resistance and high rates of relapse. However, additional causes of treatment failure or early mortality have not been well-defined in this entity. Methods: In a retrospective analysis, we compared causes and rates of early mortality following induction treatment between a cohort of adults with KMT2Ar AML (N=172) and an age-matched cohort of patients (pts) with normal karyotype (NK) AML (N=522). Results: The 30 and 60-day (60d) mortality in pts with KMT2Ar AML were significantly higher compared to those with NK AML, with rates of 10% (17/172 pts) and 15% (26/172 pts) in KMT2Ar AML vs 4% (20/522 pts) and 7% (38/522 pts) in NK AML, respectively ( P=0.004). Among those who died within 60d, the most common contributing cause in KMT2Ar was respiratory failure without a clear infectious etiology in 38% (10/26 pts) vs 11% (4/38 pts) in NK AML ( P=0.01). We found 42% (11/26 pts) with KMT2Ar AML who died within 60d were either diagnosed with or had high clinical suspicion for diffuse alveolar hemorrhage (DAH) that warranted empiric therapy vs 18% (7/38 pts) with NK AML ( P=0.05). Given the high occurrence of DAH in KMT2Ar AML, we set out to quantify bleeding events and recorded major and minor bleeds as defined by the International Society of Thrombosis and Haemostasis. We found 65% (17/26 pts) with KMT2Ar AML had at least one bleeding event vs 32% (12/38 pts) with NK AML ( P=0.01). There was a significantly higher frequent occurrence of major bleeds (rate ratio=6.22; P=0.005) and total bleeding events (rate ratio=4.5; P=0.001) in KMT2Ar AML vs NK AML. KMT2Ar was associated with disseminated intravascular coagulopathy (DIC), as 93% of evaluable pts (14/15 pts) vs 54% (7/13 pts) in NK AML had overt DIC before death. Longitudinal trajectories of DIC parameters of pts who died within 60d showed significantly higher prothrombin time levels ( P=0.008) in KMT2Ar. In a multivariate analysis, KMT2Ar and a monocytic phenotypic were the only independent predictors of any bleeding event in pts who died within 60d (OR 3.5, 95% CI 1.4-10.4, P=0.03; OR 3.2, 95% CI 1.1-9.4, P=0.04). Conclusions: KMT2Ar AML is associated with higher early mortality and an increased risk of bleeding and coagulopathy compared with NK AML. Early recognition and aggressive management of DIC and coagulopathy are important considerations that could mitigate the risk of death during induction treatment.[Table: see text]

Inhibition of mitochondrial complex I reverses NOTCH1-driven metabolic reprogramming in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is commonly driven by activating mutations in NOTCH1 that facilitate glutamine oxidation. Here we identify oxidative phosphorylation (OxPhos) as a critical pathway for leukemia cell survival and demonstrate a direct relationship between NOTCH1, elevated OxPhos gene expression, and acquired chemoresistance in pre-leukemic and leukemic models. Disrupting OxPhos with IACS-010759, an inhibitor of mitochondrial complex I, causes potent growth inhibition through induction of metabolic shut-down and redox imbalance in NOTCH1-mutated and less so in NOTCH1-wt T-ALL cells. Mechanistically, inhibition of OxPhos induces a metabolic reprogramming into glutaminolysis. We show that pharmacological blockade of OxPhos combined with inducible knock-down of glutaminase, the key glutamine enzyme, confers synthetic lethality in mice harboring NOTCH1-mutated T-ALL. We leverage on this synthetic lethal interaction to demonstrate that IACS-010759 in combination with chemotherapy containing L-asparaginase, an enzyme that uncovers the glutamine dependency of leukemic cells, causes reduced glutaminolysis and profound tumor reduction in pre-clinical models of human T-ALL. In summary, this metabolic dependency of T-ALL on OxPhos provides a rational therapeutic target.

Venetoclax combined with FLAG-IDA induction and consolidation in newly diagnosed acute myeloid leukemia

Multi-agent induction chemotherapy (IC) improves response rates in younger patients with acute myeloid leukemia (AML); however, relapse remains the principal cause of treatment failure. Improved induction regimens are needed. A prospective single-center phase Ib/II study evaluating fludarabine, cytarabine, G-CSF, and idarubicin combined with venetoclax (FLAG-IDA + VEN) in patients with newly diagnosed (ND) or relapsed/refractory AML. The primary efficacy endpoint was assessment of overall activity (overall response rate [ORR]: complete remission [CR] + CR with partial hematologic recovery [CRh] + CR with incomplete hematologic recovery [CRi] + morphologic leukemia free state + partial response). Secondary objectives included additional assessments of efficacy, overall survival (OS), and event-free survival (EFS). Results of the expanded ND cohort with additional follow-up are reported. Forty-five patients (median age: 44 years [range 20-65]) enrolled. ORR was 98% (N = 44/45; 95% credible interval 89.9%-99.7%). Eighty-nine percent (N = 40/45) of patients attained a composite CR (CRc + CRh + CRi) including 93% (N = 37/40) who were measurable residual disease (MRD) negative. Twenty-seven (60%) patients transitioned to allogeneic stem cell transplant (alloHSCT). Common non-hematologic adverse events included febrile neutropenia (44%; N = 20), pneumonia (22%, N = 10), bacteremia (18%, N = 8), and skin/soft tissue infections (44%, N = 20). After a median follow-up of 20 months, median EFS and OS were not reached. Estimated 24-month EFS and OS were 64% and 76%, respectively. FLAG-IDA + VEN is an active regimen in ND-AML capable of producing high MRD-negative remission rates and enabling transition to alloHSCT when appropriate in most patients. Toxicities were as expected with IC and were manageable. Estimated 24-month survival appears favorable compared to historical IC benchmarks.

Transgenic Expression of IL15 Retains CD123-Redirected T Cells in a Less Differentiated State Resulting in Improved Anti-AML Activity in Autologous AML PDX Models

Immunotherapy with T-cells expressing bispecific T-cell engagers (ENG T-cells) is a promising approach to improve the outcomes for patients with recurrent/refractory acute myeloid leukemia (AML). However, similar to T-cells expressing chimeric antigen receptors (CARs), their antitumor activity is limited in the setting of chronic antigen stimulation. We therefore set out to explore whether transgenic expression of IL15 improves the effector function of ENG T-cells targeting CD123-positive AML. T-cells expressing CD123-specific ENG (CD123-ENG) ± IL15 were generated by retroviral transduction from peripheral blood T cells from healthy donors or patients with AML. In this study, we characterized in detail the phenotype and effector functions of ENG T-cell populations in vitro and in vivo. IL15-expressing CD123-ENG (CD123-ENG.IL15) T-cells retained their antigen-specificity and effector function in the setting of chronic antigen exposure for more 30 days of coculture with AML blasts in contrast to CD123-ENG T-cells, whose effector function rapidly eroded. Furthermore, CD123-ENG.IL15 T-cells remained in a less differentiated state as judged by a high frequency of naïve/memory stem T-cell-like cells (CD45RA+CCR7+/CD45RO−CD62L+ cells) without evidence of T-cell exhaustion. Single cell cytokine profiling using IsoPlexis revealed enhanced T-cell polyfunctionality of CD123-ENG.IL15 T-cells as judged by effector cytokine production, including, granzyme B, IFN-γ, MIP-1α, perforin, TNF-α, and TNF-β. In vivo, CD123-ENG.IL15 T-cells exhibited superior antigen-specific anti-AML activity and T-cell persistence in both peripheral blood and tissues (BM, spleens, and livers), resulting in a significant survival advantage in one AML xenograft model and two autologous AML PDX models. In conclusion, we demonstrate here that the expansion, persistence, and anti-AML activity of CD123-ENG T-cells can be significantly improved by transgenic expression of IL15, which promotes a naïve/TSCM-like phenotype. However, we also highlight that targeting a single tumor antigen (CD123) can lead to immune escape, reinforcing the need to develop approaches to target multiple antigens. Likewise, our study demonstrates that it is feasible to evaluate autologous T cells in AML PDX models, which will be critical for future preclinical evaluations of next generation AML-redirected T-cell therapies.

Hypomethylating agent and venetoclax with FLT3 inhibitor "triplet" therapy in older/unfit patients with FLT3 mutated AML

In older/unfit newly diagnosed patients with FLT3 mutated acute myeloid leukemia (AML), lower intensity chemotherapy (LIC) in combination with either a FLT3 inhibitor or with venetoclax results in poor overall survival (median 8 to 12.5 months). We performed a retrospective analysis of 87 newly diagnosed FLT3 mutated AML patients treated on triplet (LIC + FLT3 inhibitor + Venetoclax, [N = 27]) and doublet (LIC + FLT3 inhibitor, [N = 60]) regimens at our institution. Data were collected from prospective clinical trials in 75% (N = 65) and 25% (N = 22) who received the same treatment regimens outside of a clinical trial. Triplet therapy was associated with significantly higher rates of complete remission (CR) (67% versus 32%, P = 0.002), CR/CRi (93% versus 70%, P = 0.02), FLT3-PCR negativity (96% versus 54%, P < 0.01), and flow-cytometry negativity (83% versus 38%, P < 0.01) than doublets. At the end of the first cycle, the median time to ANC > 0.5 (40 versus 21 days, P = 0.15) and platelet > 50 K (29 versus 25 days, P = 0.6) among responders was numerically longer with triplets, but 60-day mortality was similar (7% v 10%). With a median follow-up of 24 months (median 12 months for triplet arm, and 63 months for doublet arm), patients receiving a triplet regimen had a longer median overall survival (not reached versus 9.5 months, P < 0.01). LIC combined with FLT3 inhibitor and venetoclax (triplet) may be an effective frontline regimen for older/unfit FLT3 mutated AML that should be further validated prospectively.

A multi-arm phase Ib/II study designed for rapid, parallel evaluation of novel immunotherapy combinations in relapsed/refractory acute myeloid leukemia

We conducted a phase Ib/II multi-arm, parallel cohort study to simultaneously evaluate various immunotherapeutic agents and combinations in relapsed/refractory acute myeloid leukemia (AML). Overall, 50 patients were enrolled into one of 6 arms: (A) single agent PF-04518600 (OX40 agonist monoclonal antibody), (B) azacitidine + venetoclax + gemtuzumab ozogamicin (GO), (C) azacitidine + avelumab (anti-PD-L1 monoclonal antibody) + GO, (D) azacitidine + venetoclax + avelumab, (E) azacitidine + avelumab + PF-04518600, and (F) glasdegib + GO. Among all regimens evaluated, azacitidine + venetoclax + GO appeared most promising. In this arm, the CR/CRi rates among venetoclax-naïve and prior venetoclax-exposed patients were 50% and 22%, respectively, and the 1-year OS rate was 31%. This study shows the feasibility of a conducting a multi-arm trial to efficiently and simultaneously evaluate novel therapies in AML, a needed strategy in light of the plethora of emerging therapies. This trial was registered at www.clinicaltrials.gov as NCT03390296.

Maximal activation of apoptosis signaling by co-targeting anti-apoptotic proteins in BH3 mimetic-resistant AML and AML stem cells

MCL-1 is known to play a major role in resistance to BCL-2 inhibition, but the contribution of other BCL-2 family proteins has not been fully explored. We here demonstrate ineffectiveness of MCL-1 inhibitor AMG176 in venetoclax-resistant, and conversely, of venetoclax in AMG176-resistant AML. Like cells with acquired resistance to venetoclax, cells with acquired resistance to AMG176 express increased MCL-1. Both cells with acquired resistance to venetoclax and to AMG176 express increased levels of BCL-2 and BCL-2A1, decreased BAX, and/or altered levels of other BCL-2 proteins. Co-targeting BCL-2 and MCL-1 was highly synergistic in AML cell lines with intrinsic or acquired resistance to BH3 mimetics or engineered to genetically-overexpress BCL-2 or BCL-2A1 or downregulate BAX. The combination effectively eliminated primary AML blasts and stem/progenitor cells resistant to or relapsed after venetoclax-based therapy irrespective of mutations and cytogenetic abnormalities. Venetoclax and AMG176 combination markedly suppressed anti-apoptotic BCL-2 proteins and AML stem/progenitor cells and dramatically extended mouse survival (median 336 vs control 126 d, P&lt;0.0001) in a PDX model developed from a venetoclax/hypomethylating agent therapy-resistant AML patient. However, decreased BAX levels in the bone marrow residual leukemia cells after 4-wk combination treatment may represent a resistance mechanism that contributed to their survival. Enhanced anti-leukemia activity was also observed in a PDX model of monocytic AML, known to be resistant to venetoclax therapy. Our results support co-dependence on multiple anti-apoptotic BCL-2 proteins and suppression of BAX as mechanisms of AML resistance to individual BH3 mimetics. Co-targeting of MCL-1 and BCL-2 eliminates otherwise apoptosis-resistant cells.

Metabolic stress induces GD2+ cancer stem cell-like phenotype in triple-negative breast cancer

BACKGROUND

Metabolic stress resulting from nutrient deficiency is one of the hallmarks of a growing tumour. Here, we tested the hypothesis that metabolic stress induces breast cancer stem-like cell (BCSC) phenotype in triple-negative breast cancer (TNBC).

METHODS

Flow cytometry for GD2 expression, mass spectrometry and Ingenuity Pathway Analysis for metabolomics, bioinformatics, in vitro tumorigenesis and in vivo models were used.

RESULTS

Serum/glucose deprivation not only increased stress markers but also enhanced GD2⁺ BCSC phenotype and function in TNBC cells. Global metabolomics profiling identified upregulation of glutathione biosynthesis in GD2^high cells, suggesting a role of glutamine in the BCSC phenotype. Cueing from the upregulation of the glutamine transporters in primary breast tumours, inhibition of glutamine uptake using small-molecule inhibitor V9302 reduced GD2⁺ cells by 70-80% and BCSC characteristics in TNBC cells. Mechanistic studies revealed inhibition of the mTOR pathway and induction of ferroptosis by V9302 in TNBC cells. Finally, inhibition of glutamine uptake significantly reduced in vivo tumour growth in a TNBC patient-derived xenograft model using NSG (non-obese diabetic/severe combined immunodeficiency with a complete null allele of the IL-2 receptor common gamma chain) mice.

CONCLUSION

Here, we show metabolic stress results in GD2⁺ BCSC phenotype in TNBC and glutamine contributes to GD2⁺ phenotype, and targeting the glutamine transporters could complement conventional chemotherapy in TNBC.

In-depth analysis of SARS-CoV-2-specific T cells reveals diverse differentiation hierarchies in vaccinated individuals

SARS-CoV-2 vaccines pose as the most effective approach for mitigating the COVID-19 pandemic. High-degree efficacy of SARS-CoV-2 vaccines in clinical trials indicates that vaccination invariably induces an adaptive immune response. However, the emergence of breakthrough infections in vaccinated individuals suggests that the breadth and magnitude of vaccine-induced adaptive immune response may vary. We assessed vaccine-induced SARS-CoV-2 T cell response in 21 vaccinated individuals and found that SARS-CoV-2–specific T cells, which were mainly CD4⁺ T cells, were invariably detected in all individuals but the response was varied. We then investigated differentiation states and cytokine profiles to identify immune features associated with superior recall function and longevity. We identified SARS-CoV-2–specific CD4⁺ T cells were polyfunctional and produced high levels of IL-2, which could be associated with superior longevity. Based on the breadth and magnitude of vaccine-induced SARS-CoV-2 response, we identified 2 distinct response groups: individuals with high abundance versus low abundance of SARS-CoV-2–specific T cells. The fractions of TNF-α– and IL-2–producing SARS-CoV-2 T cells were the main determinants distinguishing high versus low responders. Last, we identified that the majority of vaccine-induced SARS-CoV-2 T cells were reactive against non-mutated regions of mutant S-protein, suggesting that vaccine-induced SARS-CoV-2 T cells could provide continued protection against emerging variants of concern.

Activation of RAS/MAPK pathway confers MCL-1 mediated acquired resistance to BCL-2 inhibitor venetoclax in acute myeloid leukemia

Despite high initial response rates, acute myeloid leukemia (AML) treated with the BCL-2-selective inhibitor venetoclax (VEN) alone or in combinations commonly acquires resistance. We performed gene/protein expression, metabolomic and methylation analyses of isogenic AML cell lines sensitive or resistant to VEN, and identified the activation of RAS/MAPK pathway, leading to increased stability and higher levels of MCL-1 protein, as a major acquired mechanism of VEN resistance. MCL-1 sustained survival and maintained mitochondrial respiration in VEN-RE cells, which had impaired electron transport chain (ETC) complex II activity, and MCL-1 silencing or pharmacologic inhibition restored VEN sensitivity. In support of the importance of RAS/MAPK activation, we found by single-cell DNA sequencing rapid clonal selection of RAS-mutated clones in AML patients treated with VEN-containing regimens. In summary, these findings establish RAS/MAPK/MCL-1 and mitochondrial fitness as key survival mechanisms of VEN-RE AML and provide the rationale for combinatorial strategies effectively targeting these pathways.

Targeting the NOTCH1-MYC-CD44 axis in leukemia-initiating cells in T-ALL

The NOTCH1-MYC-CD44 axis integrates cell-intrinsic and extrinsic signaling to ensure the persistence of leukemia-initiating cells (LICs) in T-cell acute lymphoblastic leukemia (T-ALL) but a common pathway to target this circuit is poorly defined. Bromodomain-containing protein 4 (BRD4) is implicated to have a role in the transcriptional regulation of oncogenes MYC and targets downstream of NOTCH1, and here we demonstrate its role in transcriptional regulation of CD44. Hence, targeting BRD4 will dismantle the NOTCH1-MYC-CD44 axis. As a proof of concept, degrading BRD4 with proteolysis targeting chimera (PROTAC) ARV-825, prolonged the survival of mice in Notch1 mutated patient-derived xenograft (PDX) and genetic models (ΔPTEN) of T-ALL. Single-cell proteomics analysis from the PDX model, demonstrated quantitative reduction of LICs (CD34+ CD7+ CD19−) and downregulation of the NOTCH1-MYC-CD44 axis, along with cell cycle, apoptosis and PI3K/Akt pathways. Moreover, secondary transplantation from PDX and ΔPTEN models of T-ALL, confirmed delayed leukemia development and extended survival of mice engrafted with T-ALL from ARV-825 treated mice, providing functional confirmation of depletion of LICs. Hence, BRD4 degradation is a promising LIC-targeting therapy for T-ALL.

Inhibition of BCL2A1 by STAT5 inactivation overcomes resistance to targeted therapies of FLT3-ITD/D835 mutant AML

•

BCL2A1 is upregulated and exerts a pro-survival function in FLT3-ITD/D835 AML cells.

•

Upregulation of BCL2A1 attenuates sensitivity to quizartinib in FLT3-ITD/D835 cells.

•

Gilteritinib decreases BCL2A1 through inactivation of STAT5 in FLT3-ITD/D835 cells.

•

Gilteritinib/Venetoclax has a synergistic anti-tumor activity in FLT3-ITD/D835 cells.

Tyrosine kinase inhibitors (TKIs) are established drugs in the therapy of FLT3-ITD mutated acute myeloid leukemia (AML). However, acquired mutations, such as D835 in the tyrosine kinase domain (FLT3-ITD/D835), can induce resistance to TKIs. A cap analysis gene expression (CAGE) technology revealed that the gene expression of BCL2A1 transcription start sites was increased in primary AML cells bearing FLT3-ITD/D835 compared to FLT3-ITD. Overexpression of BCL2A1 attenuated the sensitivity to quizartinib, a type II TKI, and venetoclax, a selective BCL2 inhibitor, in AML cell lines. However, a type I TKI, gilteritinib, inhibited the expression of BCL2A1 through inactivation of STAT5 and alleviated TKI resistance of FLT3-ITD/D835. The combination of gilteritinib and venetoclax showed synergistic effects in the FLT3-ITD/D835 positive AML cells. The promoter region of BCL2A1 contains a BRD4 binding site. Thus, the blockade of BRD4 with a BET inhibitor (CPI-0610) downregulated BCL2A1 in FLT3-mutated AML cells and extended profound suppression of FLT3-ITD/D835 mutant cells. Therefore, we propose that BCL2A1 has the potential to be a novel therapeutic target in treating FLT3-ITD/D835 mutated AML.