Preclinical evaluation of the Hsp90 inhibitor SNX-5422 in ibrutinib resistant CLL

B-cell receptor (BCR) antagonists such as the BTK inhibitor ibrutinib have proven to effectively target chronic lymphocytic leukemia (CLL) tumor cells, leading to impressive response rates in these patients. However patients do still relapse on ibrutinib, and the progressive disease is often quite aggressive requiring immediate treatment. Several strategies are being pursued to treat patients who relapse on ibrutinib therapy. As the most common form of relapse is the development of a mutant form of BTK which limits ibrutinib binding, agents which lead to degradation of the BTK protein are a promising strategy. Our study explores the efficacy of the Hsp90 inhibitor, SNX-5422, in CLL. The SNX Hsp90 inhibitor was effective in primary CLL cells, as well as B-cell lines expressing either BTK wild type or C481 mutant BTK, which has been identified as the primary resistance mechanism to ibrutinib in CLL patients. Furthermore the combination of SNX-5422 and ibrutinib provided a remarkable in vivo survival benefit in the Eμ-TCL1 mouse model of CLL compared to the vehicle or single agent groups (51 day median survival in the vehicle and ibrutinib groups versus 100 day median survival in the combination). We report here preclinical data suggesting that the Hsp90 inhibitor SNX-5422, which has been pursued in clinical trials in both solid tumor and hematological malignancies, is a potential therapy for ibrutinib resistant CLL.

Fc-engineered anti-CD33 monoclonal antibody potentiates cytotoxicity of membrane-bound interleukin-21 expanded natural killer cells in acute myeloid leukemia

BACKGROUND

Qualitative and quantitative defects in natural killer (NK) cells have been noted in patients with acute myeloid leukemia (AML), providing rationale for infusion of donor-derived NK cells. We previously showed that decitabine enhances expression of NKG2D ligands in AML with additive cytotoxicity when NK cells and Fc (fragment crystallizable region)-engineered CD33 monoclonal antibody (CD33mAb) was used. We conducted a phase 1 study evaluating decitabine and haploidentical NK cells in relapsed AML. Using patient samples from this study, we evaluated whether ex vivo donor-derived expanded NK cells with or without CD33mAb was effective in decitabine-treated AML.

METHODS

Bone marrow aspirates were collected from patients at pre- and post-NK cell infusion. NK cells from healthy donors were expanded for 14 days using irradiated K562 feeder cells displaying membrane-bound IL-21 (mbIL-21). Patient samples were used to test in vitro activity of mbIL-21 NK cells ± CD33m Ab-dependent cellular cytotoxicity (ADCC) and AML patient derived xenograft (PDX) mice were developed to test in vivo activity.

RESULTS

Upon incubation with primary AML blasts, mbIL-21 NK cells showed variable donor-dependent intra-cellular interferon-γ production, which increased with CD33mAb-coated AML. ADCC assays revealed mbIL-21 NK cells effectively lysed primary AML blasts with higher activity on CD33mAb-coated AML. Importantly, CD33mAb-dependent enhanced cytotoxicity by mbIL-21 NK cells was maintained in AML cells from patients even 24 days post-decitabine treatment. In vivo infusion of mbIL-21 NK cells in AML PDX mice, treated with CD33mAb, reduced the tumor burden.

DISCUSSION

These data show the therapeutic utility of mbIL-21 NK cells that can be further potentiated by addition of CD33mAb in AML.

Preclinical efficacy for a novel tyrosine kinase inhibitor, ArQule 531 against acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is the most common type of adult leukemia. Several studies have demonstrated that oncogenesis in AML is enhanced by kinase signaling pathways such as Src family kinases (SFK) including Src and Lyn, spleen tyrosine kinase (SYK), and bruton's tyrosine kinase (BTK). Recently, the multi-kinase inhibitor ArQule 531 (ARQ 531) has demonstrated potent inhibition of SFK and BTK that translated to improved pre-clinical in vivo activity as compared with the irreversible BTK inhibitor ibrutinib in chronic lymphocytic leukemia (CLL) models. Given the superior activity of ARQ 531 in CLL, and recognition that this molecule has a broad kinase inhibition profile, we pursued its application in pre-clinical models of AML.

METHODS

The potency of ARQ 531 was examined in vitro using FLT3 wild type and mutated (ITD) AML cell lines and primary samples. The modulation of pro-survival kinases following ARQ 531 treatment was determined using AML cell lines. The effect of SYK expression on ARQ 531 potency was evaluated using a SYK overexpressing cell line (Ba/F3 murine cells) constitutively expressing FLT3-ITD. Finally, the in vivo activity of ARQ 531 was evaluated using MOLM-13 disseminated xenograft model.

RESULTS

Our data demonstrate that ARQ 531 treatment has anti-proliferative activity in vitro and impairs colony formation in AML cell lines and primary AML cells independent of the presence of a FLT3 ITD mutation. We demonstrate decreased phosphorylation of oncogenic kinases targeted by ARQ 531, including SFK (Tyr416), BTK, and fms-related tyrosine kinase 3 (FLT3), ultimately leading to changes in down-stream targets including SYK, STAT5a, and ERK1/2. Based upon in vitro drug synergy data, we examined ARQ 531 in the MOLM-13 AML xenograft model alone and in combination with venetoclax. Despite ARQ 531 having a less favorable pharmacokinetics profile in rodents, we demonstrate modest single agent in vivo activity and synergy with venetoclax.

CONCLUSIONS

Our data support consideration of the application of ARQ 531 in combination trials for AML targeting higher drug concentrations in vivo.

Eμ-TCL1xMyc: A Novel Mouse Model for Concurrent CLL and B-Cell Lymphoma

PURPOSE

Aberrant Myc expression is a major factor in the pathogenesis of aggressive lymphoma, and these lymphomas, while clinically heterogeneous, often are resistant to currently available treatments and have poor survival. Myc expression can also be seen in aggressive lymphomas that are observed in the context of CLL, and we sought to develop a mouse model that could be used to study therapeutic strategies for aggressive lymphoma in the context of CLL.

EXPERIMENTAL DESIGN

We crossed the Eμ-TCL1 mouse model with the Eμ-Myc mouse model to investigate the clinical phenotype associated with B-cell-restricted expression of these oncogenes. The resulting malignancy was then extensively characterized, from both a clinical and biologic perspective.

RESULTS

Eμ-TCL1xMyc mice uniformly developed highly aggressive lymphoid disease with histologically, immunophenotypically, and molecularly distinct concurrent CLL and B-cell lymphoma, leading to a significantly reduced lifespan. Injection of cells from diseased Eμ-TCL1xMyc into WT mice established a disease similar to that in the double-transgenic mice. Both Eμ-TCL1xMyc mice and mice with disease after adoptive transfer failed to respond to ibrutinib. Effective and durable disease control was, however, observed by selective inhibition of nuclear export protein exportin-1 (XPO1) using a compound currently in clinical development for relapsed/refractory malignancies, including CLL and lymphoma.

CONCLUSIONS

The Eμ-TCL1xMyc mouse is a new preclinical tool for testing experimental drugs for aggressive B-cell lymphoma, including in the context of CLL.

Abstract 1964: Preclinical efficacy of the HSP90 inhibitor SNX-5422 in targeting C481S mutant BTK and ibrutinib resistant CLL

While chronic lymphocytic leukemia (CLL) is effectively treated by the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib, patients that do relapse on ibrutinib (approximately 19%) have an extremely poor clinical outcome without further intervention. Before clinical diagnosis of relapse, signs of molecular relapse can be identified through deep sequencing for mutations in BTK (C481S) and the immediate downstream BTK target, PLCγ2. The BTK C481S mutation (which reduces ibrutinib binding) can be identified at frequencies as low as 5%, and expansion of this mutant close inevitably leads to clinical relapse. Therefore, identifying methods to target this mutant clone before clinical relapse represents a novel and potentially effective therapeutic strategy.

HSP90 is a chaperone protein responsible for maintaining the stability of a large number of client proteins involved in cancer development. Cancer cells, particularly those reliant on a mutated oncogene, rely heavily on HSP90 for survival, making this an attractive clinical target. Here we have explored the preclinical efficacy of SNX-5422, a chemically unique, orally bioavailable HSP90 inhibitor, in ibrutinib resistant CLL. We determined that SNX-5422 can degrade C481S mutated BTK by utilizing BTK-null B-cell lines over-expressing wildtype or C481S BTK. Whereas ibrutinib reduces BTK activity in only the wildtype BTK transfected cell line, SNX-5422 degrades both wildtype BTK and C481S mutant BTK and impairs downstream signaling. In fact, C481S mutant BTK shows increased degradation compared to wildtype BTK suggesting that the C481S mutant BTK may rely on HSP90 more for stabilization.

We next examined the in vivo efficacy of SNX-5422 in a mouse model of ibrutinib-resistant CLL. Leukemic splenocytes isolated at removal criteria from TCL1 mice continuously treated with ibrutinib were adoptively transferred into syngeneic WT B6 mice. Upon reaching 10% leukemia burden in the peripheral blood, the mice were randomized into 1 of 4 treatment groups: vehicle, SNX-5422 (50 mg/kg MWF), ibrutinib (continuous in drinking water), or SNX-5422 plus ibrutinib (concurrent). Mice treated with the combination of SNX-5422 and ibrutinib exhibit prolonged survival and decreased disease burden in the peripheral blood compared to the vehicle or single agent groups.

In summary, we show that SNX-5422 degrades C481S BTK in vitro and prolongs survival when combined with ibrutinib in vivo. We therefore propose that upon molecular relapse, the use of SNX-5422 may prevent clinical relapse and deepen the response to ibrutinib. A phase 1 study is currently open at Ohio State to investigate whether the addition of SNX-5422 to an established dose of ibrutinib can eliminate the C481S mutant clone and prevent or delay disease progression in subjects with CLL (NCT02914327).

EH and JAW contributed equally as senior authors.

Citation Format: Timothy L. Chen, Bonnie Harrington, Jean Truxall, Ronni Wasmuth, Amy Lehman, Eric Orlemans, John C. Byrd, Jennifer A. Woyach, Erin Hertlein. Preclinical efficacy of the HSP90 inhibitor SNX-5422 in targeting C481S mutant BTK and ibrutinib resistant CLL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1964.

The interleukin-3 receptor CD123 targeted SL-401 mediates potent cytotoxic activity against CD34+CD123+ cells from acute myeloid leukemia/myelodysplastic syndrome patients and healthy donors

Diseases with clonal hematopoiesis such as myelodysplastic syndrome and acute myeloid leukemia have high rates of relapse. Only a small subset of acute myeloid leukemia patients are cured with chemotherapy alone. Relapse in these diseases occurs at least in part due to the failure to eradicate leukemic stem cells or hematopoietic stem cells in myelodysplastic syndrome. CD123, the alpha chain of the interleukin-3 receptor heterodimer, is expressed on the majority of leukemic stem cells and myelodysplastic syndrome hematopoietic stem cells and in 80% of acute myeloid leukemia. Here, we report indiscriminate killing of CD123⁺ normal and acute myeloid leukemia / myelodysplastic syndrome cells by SL-401, a diphtheria toxin interleukin-3 fusion protein. SL-401 induced cytotoxicity of CD123⁺ primary cells/blasts from acute myeloid leukemia and myelodysplastic syndrome patients but not CD123⁻ lymphoid cells. Importantly, SL-401 was highly active even in cells expressing low levels of CD123, with minimal effect on modulation of the CD123 target in acute myeloid leukemia. SL-401 significantly prolonged survival of leukemic mice in acute myeloid leukemia patient-derived xenograft mouse models. In addition to primary samples, studies on normal cord blood and healthy marrow show that SL-401 has activity against normal hematopoietic progenitors. These findings indicate potential use of SL-401 as a “bridge-to-transplant” before allogeneic hematopoietic cell transplantation in acute myeloid leukemia / myelodysplastic syndrome patients.

Oesophagitis caused by Candida kefyr

The unusual case of an oesophagitis caused by Candida kefyr in a patient with squamous cell carcinoma of the oropharynx is reported. The further implementation of C. kefyr in the production of milk products is discussed.

[Pulmonary mucormycosis in an HIV-infected patient]

A 51-year-old man, known to have chronic-aggressive hepatitis B, HIV infection and exertional dyspnoea, was hospitalized because of acute physical deterioration, cough with whitish exudate and dyspnoea at rest. Despite a CD4/CD8 ratio of 0.16 no prophylactic measures against Pneumocystis carinii had been taken. On examination the lungs were unremarkable, but the liver was enlarged and there were petechiae over all parts of the body. Laboratory tests showed impaired liver functions and a rise in lactate dehydrogenase activity (538 U/l). Chest radiogram demonstrated small to very small infiltrates in the lung. As Pneumocystis carinii pneumonia was suspected but bronchoscopy was too risky, he was at first treated with trimethoprim/sulphamethoxazole (four times 320/1600 mg/24 h intravenously). When this failed, he received pentamidine (4 mg/kg, after 4 days 2 mg/kg intravenously), and finally cefotiam (twice 2 g daily), tobramycin (three times 40 mg daily) and corticoids (100 mg). Despite this treatment he died after 10 days from respiratory failure. Autopsy revealed interstitial pneumonia throughout the lung as well as focal mucor infiltrations in the wall of middle-calibre lung veins. Mucor is a ubiquitous, facultatively pathogenic mold fungus.