Abstract 3957: Receptor Activator of NF-κB (RANK) confers resistance to chemotherapy in AML and associates with dismal disease course

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults. Untreated, AML leads to death within months after first symptoms. Combinatorial chemotherapy, mostly using a pyrimidine analog together with an anthracycline, made this previously incurable disease medicable, and response to remission-inducing chemotherapy strongly correlates with patient outcome. Despite advances in treatment over the recent years, AML still has a poor prognosis with an average 5-year survival rate of 30%. A better understanding of the molecular mechanisms predicting and affecting treatment efficacy is key to improve disease control and outcome. Here we studied the expression, prognostic relevance and functional role of the tumor necrosis factor receptor (TNFR) family member Receptor Activator of Nuclear Factor (NF)-κB (RANK) in AML. We conducted an experimental ex vivo study using leukemic cells of 54 AML patients. Substantial surface expression of RANK was detected on the primary AML cells in 35% of the analyzed patients. We further found that RANK signaling induced the release of the cytokines IL-6, IL-8, TNF and IL-10 acting as growth and survival factors for the leukemic cells and mediated resistance of AML cells to treatment with doxorubicin and cytarabine, the most commonly used cytostatic compounds in AML treatment. In line, prevalence of RANK expression on leukemic cells correlated with dismal disease course of patients as revealed by reduced overall survival. Together, our results show that RANK plays a yet unrecognized role in AML pathophysiology and resistance to treatment. Moreover, the association of RANK expression with adverse disease course identifies RANK as potential “functional” prognostic marker and putative target for therapeutic intervention to improve treatment response of AML patients.

Citation Format: Kim L. Clar, Lisa M. Weber, Bastian J. Schmied, Jonas S. Heitmann, Maddalena Marconato, Claudia Tandler, Pascal Schneider, Helmut R. Salih. Receptor Activator of NF-κB (RANK) confers resistance to chemotherapy in AML and associates with dismal disease course [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 3957.

Abstract 2860: A CD135 immunocytokine with target cell-restricted IL-15 activity for treatment of AML

After diagnosis, a primary goal of treatment in acute myeloid leukemia (AML) is to achieve a morphological complete remission (CR) by induction chemotherapy. However, about half of the patients in CR show remaining minimal residual disease (MRD), which constitutes the basis for relapse. With the aim to eradicate MRD and thus improve long-term survival in AML, we recently conducted a phase I trial evaluating safety/tolerability and preliminary efficacy of an Fc-optimized antibody targeting CD135/FLT3 (FLYSYN, NCT02789254) to induce NK cell anti-leukemia reactivity. This trial enrolling AML patients in CR with detectable MRD revealed that FLYSYN is safe and well tolerated, with about 45% of patients achieving a molecular response after treatment with the target dose (Heitmann et al., Blood 2020). Besides by reinforcing the ADCC-inducing capability of antibodies, NK cell immunity can be further increased by cytokines like IL-15, and multiple efforts presently aim to exploit the latter cytokine for cancer treatment. However, clinical efficacy of IL-15 so far is limited as systemic application causes substantial side effects due to unspecific immune activation (Conlon et al, JCO 2015). To overcome this limitation, we aimed to develop an immunocytokine consisting of our Fc-optimized CD135 mAb fused to IL-15. However, the activity of the cytokine moiety within classical ICs does not depend on antigen binding, and thus application of clinically effective doses is still prevented by toxicity due to unspecific immune activation. To overcome this problem, we took advantage of the unique mechanism of action of IL-15, which stimulates IL-15Rβ/γ on cytotoxic lymphocytes as membrane-bound complex with IL-15Rα on monocytes and DCs (trans-presentation) and generated an IL-15 mutant with abolished IL-15Rα binding. The latter allows to substitute physiological trans-presentation by binding of the construct to the target antigen, thereby limiting side effects. Functional analysis using primary AML cells as targets revealed that our modified immunocytokine (MIC135) induced target-restricted NK cell anti-leukemia reactivity in a profoundly greater extent than the Fc-optimized FLYSYN antibody. Notably, in stark contrast to FLYSYN, MIC135 induced prominent NK cell proliferation, and target cell killing upon treatment with MIC135 was likewise clearly superior. Analyses regarding off-target toxicity confirmed the target-antigen restricted efficacy of MIC135 compared to anti-CD135 immunocytokine with wildtype IL-15 (IC135). Furthermore, our MIC135 did not induce unwanted effects against healthy FLT3 expressing cells. Taken together, MIC135 induces NK cell reactivity against leukemia cells in a highly target cell-restricted manner and displays higher efficacy than Fc-optimized antibodies, thus constituting a promising treatment option for AML.

Citation Format: Martina S. Lutz, Bastian J. Schmied, Fabian Riegg, Latifa Zekri, Jonas S. Heitmann, Melanie Maerklin, Martin Pfluegler, Gundram Jung, Helmut R. Salih. A CD135 immunocytokine with target cell-restricted IL-15 activity for treatment of AML [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 2860.

Receptor Activator of NF-κB (RANK) Confers Resistance to Chemotherapy in AML and Associates with Dismal Disease Course

Simple Summary

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults. Despite the emergence of new therapeutic agents in recent years, curation remains challenging, and new and better treatment options are needed. In the present study, we investigated the expression, prognostic significance, and functional role of the Receptor Activator of Nuclear Factor-κB (RANK) in AML. We found that RANK is expressed on leukemic cells in a substantial proportion of AML patients and is associated with a dismal disease course. We further demonstrated that signaling via RANK induces release of factors that favor AML cell survival and confers resistance to chemotherapeutics in AML treatment. Together, our findings identify RANK as novel prognostic marker and putative candidate for therapeutic intervention in AML to enhance response to treatment.

Abstract

Although treatment options of acute myeloid leukemia (AML) have improved over the recent years, prognosis remains poor. Better understanding of the molecular mechanisms influencing and predicting treatment efficacy may improve disease control and outcome. Here we studied the expression, prognostic relevance and functional role of the tumor necrosis factor receptor (TNFR) family member Receptor Activator of Nuclear Factor (NF)-κB (RANK) in AML. We conducted an experimental ex vivo study using leukemic cells of 54 AML patients. Substantial surface expression of RANK was detected on primary AML cells in 35% of the analyzed patients. We further found that RANK signaling induced the release of cytokines acting as growth and survival factors for the leukemic cells and mediated resistance of AML cells to treatment with doxorubicin and cytarabine, the most commonly used cytostatic compounds in AML treatment. In line, RANK expression correlated with a dismal disease course as revealed by reduced overall survival. Together, our results show that RANK plays a yet unrecognized role in AML pathophysiology and resistance to treatment, and identify RANK as “functional” prognostic marker in AML. Therapeutic modulation of RANK holds promise to improve treatment response in AML patients.

Induction of NK Cell Reactivity against B-Cell Acute Lymphoblastic Leukemia by an Fc-Optimized FLT3 Antibody

Antibody-dependent cellular cytotoxicity (ADCC) is a major mechanism by which antitumor antibodies mediate therapeutic efficacy. At present, we evaluate an Fc-optimized (amino acid substitutions S239D/I332E) FLT3 antibody termed 4G8-SDIEM (FLYSYN) in patients with acute myeloid leukemia (NCT02789254). Here we studied the possibility to induce NK cell ADCC against B-cell acute lymphoblastic leukemia (B-ALL) by Fc-optimized FLT3 antibody treatment. Flow cytometric analysis confirmed that FLT3 is widely expressed on B-ALL cell lines and leukemic cells of B-ALL patients. FLT3 expression did not correlate with that of CD20, which is targeted by Rituximab, a therapeutic monoclonal antibody (mAb) employed in B-ALL treatment regimens. Our FLT3 mAb with enhanced affinity to the Fc receptor CD16a termed 4G8-SDIE potently induced NK cell reactivity against FLT3-transfectants, the B-ALL cell line SEM and primary leukemic cells of adult B-ALL patients in a target-antigen dependent manner as revealed by analyses of NK cell activation and degranulation. This was mirrored by potent 4G8-SDIE mediated NK cell ADCC in experiments with FLT3-transfectants, the cell line SEM and primary cells as target cells. Taken together, the findings presented in this study provide evidence that 4G8-SDIE may be a promising agent for the treatment of B-ALL, particularly in CD20-negative cases.

An Fc-Optimized CD133 Antibody for Induction of Natural Killer Cell Reactivity against Colorectal Cancer

The introduction of monoclonal antibodies (mAbs) has largely improved treatment options for cancer patients. The ability of antitumor mAbs to elicit antibody-dependent cellular cytotoxicity (ADCC) contributes to a large extent to their therapeutic efficacy. Many efforts accordingly aim to improve this important function by engineering mAbs with Fc parts that display enhanced affinity to the Fc receptor CD16 expressed, e.g., on natural killer (NK) cells. Here we characterized the CD133 mAb 293C3-SDIE that contains an engineered Fc part modified by the amino acid exchanges S239D/I332E—that reportedly increase the affinity to CD16—with regard to its ability to induce NK reactivity against colorectal cancer (CRC). 293C3-SDIE was found to be a stable protein with favorable binding characteristics achieving saturating binding to CRC cells at concentrations of approximately 1 µg/mL. While not directly affecting CRC cell growth and viability, 293C3-SDIE potently induced NK cell activation, degranulation, secretion of Interferon-γ, as well as ADCC resulting in potent lysis of CRC cell lines. Based on the preclinical characterization presented in this study and the available data indicating that CD133 is broadly expressed in CRC and represents a negative prognostic marker, we conclude that 293C3-SDIE constitutes a promising therapeutic agent for the treatment of CRC and thus warrants clinical evaluation.

The novel deubiquitinase inhibitor b-AP15 induces direct and NK cell-mediated antitumor effects in human mantle cell lymphoma

The first therapeutic proteasome inhibitor bortezomib has clinical efficacy in mantle cell lymphoma (MCL) which resulted in its incorporation in treatment algorithms for this disease. Impairment of proteasomal function by bortezomib is mediated via inhibition of the 20S core particle. However, proteasome function can also be modified by targeting upstream components of the ubiquitin-proteasome system. Recently, b-AP15 has been identified as a small molecule achieving proteasome inhibition by targeting the deubiquitinase (DUB) activity of the 19S regulatory subunit and was found to inhibit cancer cell growth in preclinical analyses. In the present study, both direct antitumor effects and the possibility to induce natural killer group 2 member D ligands (NKG2DL) to reinforce NK cell immunity with b-AP15 were investigated to provide a rational basis for clinical evaluation of this novel DUB inhibitor in MCL. Treatment with b-AP15 resulted in reduced viability as well as induction of apoptosis in a time- and dose-dependent manner, which could be attributed to caspase activation in MCL cells. In addition, treatment with b-AP15 differentially induced NKG2DL expression and subsequent NK cell lysis of MCL cells. These results indicate that the DUB inhibitor b-AP15 displays substantial antitumor activity in human MCL and suggest that b-AP15 might be a novel therapeutic option in the treatment of MCL that warrants clinical investigation.

Prognostic relevance of HER2/neu in acute lymphoblastic leukemia and induction of NK cell reactivity against primary ALL blasts by trastuzumab

The epidermal growth factor receptor HER2/neu is expressed on various cancers and represents a negative prognostic marker, but is also a target for the therapeutic monoclonal antibody Trastuzumab. In about 30% of cases, HER2/neu is expressed on acute lymphoblastic leukemia (ALL) cells and was proposed to be associated with a deleterious prognosis. Here we evaluated clinical data from 65 ALL patients (HER2/neu+, n = 17; HER2/neu-, n = 48) with a median follow-up of 19.4 months (range 0.6-176.5 months) and observed no association of HER2/neu expression with response to chemotherapy, disease free or overall survival. In vitro, treatment of primary ALL cells (CD20+HER2/neu+, CD20+HER2/neu- and CD20-HER2/neu-) with Rituximab and Trastuzumab led to activation of NK cells in strict dependence of the expression of the respective antigen. NK reactivity was more pronounced with Rituximab as compared to Trastuzumab, and combined application could lead to additive effects in cases where both antigens were expressed. Besides providing evidence that HER2/neu expression is no risk factor in ALL patients, our data demonstrates that HER2/neu can be a promising target for Trastuzumab therapy in the subset of ALL patients with the potential to improve disease outcome.