Optimization of degrader properties is often a challenge due to their beyond-rule-of-5 nature. Given the paucity of known E3 ligases and the often-limited choice of ligands with varied chemical structures for a given protein target, degrader linkers represent the best position within the chimeric molecules to modify their overall physicochemical properties. In this work, a series of AT7519-based CDK9 degraders was assembled using click chemistry, facilitating the tuning of aqueous solubility and lipophilicity while retaining their linker type and molecular weight. Using chromatographic logD and kinetic solubility experiments, we show that degraders with similar chemical constitution but varied position of the embedded triazole demonstrate different lipophilicity and aqueous solubility properties. Overall, this work highlights the impact of triazole placement on linker composition through application of click chemistry for degrader synthesis and its ability to be used to promote the achievement of favorable physicochemical properties.
Acute myeloid leukemia (AML) is characterized by the uncontrolled expansion of un-differentiated hematopoietic progenitor myeloblasts. AML treatment is very challenging owing to its complex heterogeneity resulting in a dismal 5-year overall survival rate particularly in elderly patients unfit for standard induction chemotherapy. The expansion of AML requires the availability of sufficient nucleotides supporting the anabolic processes required for AML growth thus, targeting nucleotide biosynthesis can halt AML progression. Indeed, targeting dihydroorotate dehydrogenase (DHODH), a critical rate-limiting step in the de novo pyrimidine synthesis pathway not only induced cytotoxicity but has been shown to promote blast differentiation in a HOXA9/MEIS1 over-expressing model. We sought to develop a DHODH inhibitor that had superior properties to those reported for AML therapy. Compound 41 (cmpd 41) demonstrates sub-nanomolar 50% inhibitory concentration for DHODH biochemical activity and potent in vitro activity across several AML cell lines and primary AML cells independent of mutational subtype, including mutated TP53. Cmpd 41 also demonstrated superior in vivo anti-leukemic activity in multiple AML xenograft models as monotherapy and demonstrated synergy with a hypomethylating agent, decitabine in TP53 mutated AML. Given the heterogeneity of AML and frequent emergence of resistant clones, we aimed to investigate ways to enhance response to DHODH inhibitors through combination. After in vitro treatment of AML cell lines and primary patient samples with DHODH inhibitors, we observed an increase in CD38 surface expression suggesting synergy with CD38 targeting monoclonal antibody (mAb) immunotherapies. Indeed, we are the first to report synergy between DHODH inhibitors and anti-CD38 mAb in AML which emphasizes the synergy between this promising novel class of agents with immunotherapies via recruiting innate immunity. Consequently, given the relevance of CD38 mAb therapy to multiple myeloma (MM), we extended these studies to MM and remarkably found that cmpd 41 was highly efficacious as a monotherapy and in combination with CD38 mAb, resulted in complete tumor regression in a subcutaneous MM xenograft model. In summary, we introduce a best in class DHODH inhibitor with a data-driven combination strategy for both AML and MM. Our studies suggest a highly synergistic combination strategy involving immunotherapy for AML and other hematologic malignancies. Citation Format: Ola A. Elgamal, Sandip Vibhute, Sydney Fobare, Abeera Mehmood, Mariah L. Johnson, Jean Truxall, Emily Stahl, Bridget Carmichael, Shelley J. Orwick, Ramasamy Santhanam, Kasey Hill, Susheela Tridandapani, Christopher C. Coss, Alice S. Mims, Karilyn T. Larkin, Mitch A. Phelps, Sharyn D. Baker, Alex Sparreboom, Thomas E. Goodwin, Gerard Hilinski, Chad E. Bennett, Erin Hertlein, John C. Byrd. Introducing a novel DHODH inhibitor with superior in vivo activity as monotherapy or in novel combination regimen with immunotherapy for hematological malignancies [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 1060.
Enhancer of zeste homolog 2 (EZH2) is a part of the polycomb repressive complex and catalyzes the trimethylation of lysine 27 on histone H3 (H3K27me3). EZH2 inhibition has a complex role in the pathogenesis of acute myeloid leukemia (AML), in that it has been shown to be either a tumor suppressor or an oncogene depending on the stage of AML development and the genes that EZH2 is regulating during each stage. Unlike follicular and diffuse large B-cell lymphoma where EZH2 mutations result in gain of function, EZH2 mutations are typically loss of function in myeloid diseases. However, we hypothesized that in AML patients without EZH2 mutations, loss of EZH2 function may produce a phenotype that would allow for therapeutic targeting without influencing normal hematopoiesis. We used EPZ011989 (EPZ), an EZH2 inhibitor tool compound, to inhibit H3K27me3 in our studies. We started by treating the MOLM-13 AML cell line with EPZ and confirmed a decrease in H3K27me3. This reduction in H3K27me3 resulted in a slight decrease in metabolic activity via MTS assays as well as decreased colony formation in methocult. These studies were followed up with EPZ inhibition in primary AML samples in vitro. We found that EZH2 inhibition resulted in decreased self-renewal of primary AML samples but not of CD34+ bone marrow cells from normal donors. Furthermore, we found that after 7-day treatment with EPZ, primary AML samples undergo moderate differentiation as suggested by an increase in CD11b surface expression via flow cytometry. These results are further supported by the morphological changes seen after 14-days of EPZ treatment in vitro. Based on these results, we hypothesize that EZH2 inhibition in primary AML samples promotes the differentiation of AML blasts. Furthermore, our preliminary data suggests that daily treatment with 150 mg/kg of EPZ results in a survival advantage and reduced disease burden in the MOLM-13-luciferase murine xenograft model. Despite loss of function EZH2 mutations portending poor outcomes in myeloid malignancies, we demonstrate that pharmacologic EZH2 inhibition reduces AML blast stemness and promotes differentiation into mature myeloid cells. In contrast, no change in normal CD34+ stem cells occurs with EZH2 inhibition, offering the opportunity to selectively target myeloid leukemia. Citation Format: Sydney Fobare, Ola A. Elgamal, Emily H. Stahl, Abeera Mehmood, Jean Truxall, Mariah L. Johnson, Amina Abdul-Aziz, John C. Byrd, Erin Hertlein. EZH2 inhibition induces blast differentiation in acute myeloid leukemia [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 1824.
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