Epichaperome inhibition targets TP53-mutant AML and AML stem/progenitor cells

TP 53-mutant acute myeloid leukemia (AML) remains the ultimate therapeutic challenge. Epichaperomes, formed in malignant cells, consist of heat shock protein 90 (HSP90) and associated proteins that support the maturation, activity, and stability of oncogenic kinases and transcription factors including mutant p53. High-throughput drug screening identified HSP90 inhibitors as top hits in isogenic TP53-wild-type (WT) and -mutant AML cells. We detected epichaperomes in AML cells and stem/progenitor cells with TP53 mutations but not in healthy bone marrow (BM) cells. Hence, we investigated the therapeutic potential of specifically targeting epichaperomes with PU-H71 in TP53-mutant AML based on its preferred binding to HSP90 within epichaperomes. PU-H71 effectively suppressed cell intrinsic stress responses and killed AML cells, primarily by inducing apoptosis; targeted TP53-mutant stem/progenitor cells; and prolonged survival of TP53-mutant AML xenograft and patient-derived xenograft models, but it had minimal effects on healthy human BM CD34+ cells or on murine hematopoiesis. PU-H71 decreased MCL-1 and multiple signal proteins, increased proapoptotic Bcl-2-like protein 11 levels, and synergized with BCL-2 inhibitor venetoclax in TP53-mutant AML. Notably, PU-H71 effectively killed TP53-WT and -mutant cells in isogenic TP53-WT/TP53-R248W Molm13 cell mixtures, whereas MDM2 or BCL-2 inhibition only reduced TP53-WT but favored the outgrowth of TP53-mutant cells. Venetoclax enhanced the killing of both TP53-WT and -mutant cells by PU-H71 in a xenograft model. Our data suggest that epichaperome function is essential for TP53-mutant AML growth and survival and that its inhibition targets mutant AML and stem/progenitor cells, enhances venetoclax activity, and prevents the outgrowth of venetoclax-resistant TP53-mutant AML clones. These concepts warrant clinical evaluation.

A phase 1/2 study of azacitidine, venetoclax and pevonedistat in newly diagnosed secondary AML and in MDS or CMML after failure of hypomethylating agents

BACKGROUND

Pevonedistat is a first-in-class, small molecular inhibitor of NEDD8-activating enzyme that has clinical activity in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). Preclinical data suggest synergy of pevonedistat with azacitidine and venetoclax.

METHODS

This single-center, phase 1/2 study evaluated the combination of azacitidine, venetoclax and pevonedistat in older adults with newly diagnosed secondary AML or with MDS or chronic myelomonocytic leukemia (CMML) after failure of hypomethylating agents. Patients received azacitidine 75 mg/m2 IV on days 1-7, venetoclax at maximum dose of 200-400 mg orally on days 1-21 (AML cohort) or days 1-14 (MDS/CMML cohort) and pevonedistat 20 mg/m2 IV on days 1, 3 and 5 for up to 24 cycles. The primary endpoints for the phase 2 portion of the study were the CR/CRi rate in the AML cohort and the overall response rate (CR + mCR + PR + HI) in the MDS/CMML cohort.

FINDINGS

Forty patients were enrolled (32 with AML and 8 with MDS/CMML). In the AML cohort, the median age was 74 years (range 61-86 years), and 27 patients (84%) had at least one adverse risk cyto-molecular feature, including 15 (47%) with a TP53 mutation or MECOM rearrangement; seventeen patients (53%) had received prior therapy for a preceding myeloid disorder. The CR/CRi rate was 66% (CR 50%; CRi 16%), and the median overall survival (OS) was 8.1 months. In the MDS/CMML cohort, 7 patients (87%) were high or very high risk by the IPSS-R. The overall response rate was 75% (CR 13%; mCR with or without HI 50%; HI 13%). The most common grade 3-4 adverse events were infection in 16 patients (35%), febrile neutropenia in 10 patients (25%) and hypophosphatemia in 9 patients (23%). In an exploratory analysis, early upregulation of NOXA expression was observed, with subsequent decrease in MCL-1 and FLIP, findings consistent with preclinical mechanistic studies of pevonedistat. Upregulation of CD36 was observed, which may have contributed to therapeutic resistance.

CONCLUSIONS

The triplet combination of azacitidine, venetoclax and pevonedistat shows encouraging activity in this very poor-risk population of patients with AML, MDS or CMML. Trial registration ClinicalTrials.gov (NCT03862157).

A Phase I study of Milademetan (DS3032b) in combination with low dose cytarabine with or without venetoclax in acute myeloid leukemia: Clinical safety, efficacy, and correlative analysis

In TP53 wild-type acute myeloid leukemia (AML), inhibition of MDM2 can enhance p53 protein expression and potentiate leukemic cell apoptosis. MDM2 inhibitor (MDM2i) monotherapy in AML has shown modest responses in clinical trials but combining options of MDM2i with other potent AML-directed agents like cytarabine and venetoclax could improve its efficacy. We conducted a phase I clinical trial (NCT03634228) to study the safety and efficacy of milademetan (an MDM2i) with low-dose cytarabine (LDAC)±venetoclax in adult patients with relapsed refractory (R/R) or newly diagnosed (ND; unfit) TP53 wild-type AML and performed comprehensive CyTOF analyses to interrogate multiple signaling pathways, the p53-MDM2 axis and the interplay between pro/anti-apoptotic molecules to identify factors that determine response and resistance to therapy. Sixteen patients (14 R/R, 2 N/D treated secondary AML) at a median age of 70 years (range, 23-80 years) were treated in this trial. Two patients (13%) achieved an overall response (complete remission with incomplete hematological recovery). Median cycles on trial were 1 (range 1-7) and at a median follow-up of 11 months, no patients remained on active therapy. Gastrointestinal toxicity was significant and dose-limiting (50% of patients ≥ grade 3). Single-cell proteomic analysis of the leukemia compartment revealed therapy-induced proteomic alterations and potential mechanisms of adaptive response to the MDM2i combination. The response was associated with immune cell abundance and induced the proteomic profiles of leukemia cells to disrupt survival pathways and significantly reduced MCL1 and YTHDF2 to potentiate leukemic cell death. The combination of milademetan, LDAC±venetoclax led to only modest responses with recognizable gastrointestinal toxicity. Treatment-induced reduction of MCL1 and YTHDF2 in an immune-rich milieu correlate with treatment response.

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).

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.

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.

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.

Abstract 6038: Combined targeting of E-selectin/CXCR4 and FLT3 by GMI-1359 and sorafenib effectively reduces leukemia cell burden and protects normal hematopoiesis in a patient-derived AML xenograft model

Acute myelogenous leukemia (AML) is characterized by an accumulation of abnormal white blood cells. Internal tandem duplications in the Fms-like tyrosine kinase 3 (FLT3-ITD) account for 30% of adult AML cases and confer poor prognosis (Kottaridis et al., 2003; Thiede et al., 2002). FLT3 inhibitors like sorafenib efficiently eliminate leukemia blast in the peripheral blood (PB), but frequently not in the bone marrow (BM) (Zhang et al., 2008). This suggests a protective effect of the BM on leukemic stem cells, which is mediated by E-selectin and CXCL12 expression in endothelial cells (ECs) and mesenchymal stem cells (MSCs) in the BM vascular and endosteal niches (Horacek et al., 2013; Peled and Tavor, 2013). Our previous study demonstrated that targeting E-selectin/CXCR4 with the dual E-selectin/CXCR4 antagonist GMI-1359 markedly reduced leukemia cell adhesion to ECs and MSCs and eliminated the BM-mediated protection of leukemic cells during FLT3-targeted therapy in vitro, and effectively reduced leukemia cell in the BM in vivo (Zhang et al., 2016). Further, GMI-1359 combined with cytarabine/daunorubicin provided a profound survival benefit in FLT3-mutated leukemia cell MV4-11-bearing mice (Zhang et al., 2015). In the preset study, we compared expression levels of E-selectin ligands and CXCR4 in FLT3 inhibitor-sensitive Ba/F3-FLT3-ITD cells and their inhibitor-resistant counterparts Ba/F3-FLT3-ITD+D835Y and Ba/F3-FLT3-ITD+F691L. The resistant cells expressed 1.7 to ~5.6-fold higher E-selectin ligand and 10-fold higher CXCR4 levels. In addition, BM-mimetic hypoxia culture profoundly upregulated P-selectin glycoprotein ligand-1 (PSGL-1) and CXCR4 levels on leukemia cells. PSGL-1 is also a high-efficiency ligand for E-selectin. We then evaluated anti-leukemia effects of co-targeting E-selectin/CXCR4 and FLT3 with GMI-1359 and sorafenib in a patient-derived AML xenograft model (harboring FLT3-ITD and WT1 mutations). Leukemia cell engraftment was evaluated using FACS and immunohistochemistry by hCD45 staining. We observed that GMI-1359 efficiently mobilized leukemic cells into PB and in combination with sorafenib enhanced the anti-leukemia activity and significantly reduced leukemia cell infiltration by 92%, 82%, 69% and 45% in liver, lung, spleen and BM, respectively, as compared with vehicle-treated mice (p < 0.05). The GMI-1359/sorafenib combination improved mouse survival (median survival were 109, 87, 126 and 138.5 days for the vehicle, GMI-1359, sorafenib and combination groups, respectively). Importantly, we observed that the combination protected normal hematopoiesis by increasing the number of BM megakaryocytes, myelocytes, and erythrocytes. The underlying mechanism(s) for this effect is under investigation. Our findings suggest that co-targeting E-selectin/CXCR4/FLT3 exerts remarkable protection of normal hematopoiesis in addition to more efficiently reducing leukemia cells.

Citation Format: Weiguo Zhang, Kyung Hee Chang, Mahesh Basyal, Yannan Jia, Lauren Ostermann, William E. Fogler, John L. Magnani, Michael Andreeff. Combined targeting of E-selectin/CXCR4 and FLT3 by GMI-1359 and sorafenib effectively reduces leukemia cell burden and protects normal hematopoiesis in a patient-derived AML xenograft model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6038.