Background: Dihydroorotate dehydrogenase (DHODH), catalyzing the ubiquinone-mediated oxidation of dihydroorotate to orotate, is the rate-limiting enzyme in the de novo synthesis of pyrimidines, and as such may control the rate of cell division. The enzyme is localised on the outer side of the inner mitochondrial membrane, and links both the electron transport chain to pyrimidine production and thus to the maintenance of cell viability. DHODH inhibitors were identified in a myeloid differentiation screen using an ER-HoxA9 GMP cell line, and ASLAN003, a novel small molecule DHODH oral inhibitor, has been found to be a potent inducer of myeloid differentiation in AML cell lines. ASLAN003 also demonstrated the ability to reduce leukemic burden and extend survival in AML xenograft models. ASLAN003 has previously been shown to exhibit a safe and tolerable profile in prior phase I studies in healthy volunteers. Methods: A multicenter, single arm phase IIA study was initiated to evaluate ASLAN003 monotherapy administered as a 28-day cycle in patients with AML who are ineligible for standard therapy. The primary objective is to determine the optimum dose of ASLAN003 in this AML cohort based on efficacy (Overall Complete Remission Rate, % of complete remission [CR] + CR with incomplete hematologic recovery [CRi]), tolerability and safety. The secondary objective is to assess the pharmacokinetics (PK) of ASLAN003 and its metabolites and to further assess the efficacy based on relapse-free survival and clinical benefit rate (CBR, % of partial remission + CR + CRi). Exploratory objectives are to examine the myeloid differentiation effects of ASLAN003 ex vivo and explore possible relationships between the clinical response and molecular profile of leukemic cells. The study contains 3 cohorts for the optimum dose determination (100 mg, 200 mg, and 300 mg once daily [QD], with planned enrollment for 6 patients for each cohort), and an additional expansion cohort with the selected optimum dose (20 patients). Results: Enrollment started in December 2017. As of 12 July 2018, 10 patients were enrolled and treated (6 in the 100 mg QD cohort and 4 in the 200 mg QD cohort). Although the data are immature, two patients to date have exhibited some evidence of clinical activity (one per cohort). A patient in the 100 mg QD cohort, with a baseline peripheral blood blast of 27%, experienced a reduction to 6% on Cycle 3 Day 10 (C3D10), coupled with an upward trend in the percentage of neutrophils (16% at baseline, 64% on C3D10). The patient had underlying chronic lung infection, but also showed suspected symptoms of differentiation syndrome (dyspnea, leukocytosis). After 126 days of ASLAN003 initiation, the patient expired due to AML related clinical deterioration. The second patient in the 200 mg QD cohort experienced a decrease in bone marrow blasts from 26% at baseline, to 12% on C2D1. Concomitantly, there was a slight decrease in peripheral blood blasts with an increase in neutrophil percentages from 7% to 51%. The patient remains on study with further efficacy data awaited. To date, the safety profile is consistent with the previous healthy volunteer studies. Treatment-related adverse events (AEs) are listed in Table 1. The most frequent treatment-related AEs include nausea (n=2, 20%) and leukocytosis (n=2, 20%). Two treatment-related Grade ≥ 3 AEs were observed (Grade 3 anaemia and Grade 3 leukocytosis). The study continues and is currently enrolling to the 200 mg cohort. Conclusion: At the date of submission, this is the first report of clinical activity of a DHODH inhibitor in AML patients. Monotherapy with ASLAN003 was well tolerated and has showed encouraging signs of clinical activity in AML patients. This study is on-going and the optimal dose for AML has not yet been determined. Safety, PK and efficacy data will be updated at the time of presentation. Clinical trial information: NCT03451084 Disclosures Chng: ASLAN Pharmaceuticals: Research Funding. McHale:ASLAN Pharmaceuticals: Employment, Equity Ownership. Hsieh:ASLAN Pharmaceuticals: Employment, Equity Ownership. Shih:ASLAN Pharmaceuticals: Employment; AstraZeneca Taiwan: Employment. McIntyre:ASLAN Pharmaceuticals: Consultancy. Kwek:ASLAN Pharmaceuticals: Employment. Chang:ASLAN Pharmaceuticals: Employment. Lindmark:ASLAN Pharmaceuticals: Employment, Equity Ownership.
Gamma-delta (γδ) T cells represent a special class of unconventional T cells defined by their expression of the somatically rearranged T cell receptor (TCR) γ and δ chains. Unlike TCRαβ, it has been reported that different TCRγδ are also able to bind to their antigens in the context of non-classical MHC-like molecules or totally independent of the MHC complexes. Additionally, a variety of NK receptors are known to be expressed by γδ T cells, conferring their ability to sense alternative classes of cancer-associated antigens in a multimodal manner. Such a diverse mode of antigen recognition possibly endows γδ T cells with a wide spectrum of functional activation program. Our team had previously explored the potential of expanding cord blood (CB) derived γδ T cells (CB-gdT) as well as their corresponding ability to target primary acute myeloid leukemia (AML) cells. Using a feeder cell line-based in vitro expansion protocol, we achieved a clinically relevant scale expansion of γδ T cells over a period of 14 days. These cells exhibit variable degree of potency against a range of human AML cell lines and primary patient samples. In order to dissect the cellular and molecular programs governing the activation, differentiation and functional states of our in vitro expanded CB-gdT, we performed multiplex single cell sequencing analysis using the 10X Genomics Chromium System. After initial quality check and filtering, data from a total of 4,276 cells were retrieved. Among which, we identified 742 unique TCRγδ clonotypes, representing 18.6% of the starting 4,000 FACS purified γδ T cells seeded for expansion. The largest 10% of the clones was found to make up 60.9% of the total retrieved cells, demonstrating a significant extent of clonal focusing in our expansion cultures. Consistent to our FACS analysis, Vδ1 is the predominant TRD chain in the expanded cultures, accounting for 61.2% of all clones. Vγ4 is the most prevalent TRG chain making up to 24.9% of all clones regardless of the paired Vδ subtype. Notably, however, the largest γδ T cell clone did not utilize Vγ4, indicating that Vγ4 clones, although frequent, are not the most proliferative clone. These data are supportive of the adaptive characteristics of CB-gdTs, likely in a TCRγδ dependent manner. Based on uniform manifold approximation and projection for dimension reduction (UMAP), all cells were clustered into 11 subsets. Key cytotoxic genes including GZMB, GZMA and NKG7 were all highly expressed across all clusters, indicating that the expanded cells were indeed functionally cytotoxic. Comparing against multiple curated gene sets, we have identified 3 main subsets of γδ T cells: the Proliferative, Cytotoxic γδ T cells (P-CT), Differentiated Cytotoxic γδ T cells (D-CT) and Late Activated Cytotoxic γδ T cells (LA-CT). P-CT (~46% of all cells) shows an expression profile positively associated with cell proliferation as well as increased cell surface expression of memory T cell markers CD27, CCR7 and CD62L. Similar to cytotoxic genes, genes associated with TCR signaling and interferon response were found to be expressed across all cell clusters, yet with elevated levels in D-CT and LA-CT. Furthermore, cell surface expression of different NK receptors including NKG2D, DNAM1 and NKp30 are more enriched in LA-CT compared to the other 2 subsets, suggesting the acquisition of additional NK receptor related functions in this group of cells. Consistent with the concept of progressive γδ T cell differentiation and activation in culture, we found that in 85 (11.5%) of the γδ T cell clones bearing more than 10 cells each, all clones contain cells distributed across the 3 different γδ T cell subsets. Further analysis did not reveal any relationship between the relative proportion of the subsets within each clone with clone size nor any specific type of delta/gamma chain. Taken together, our high-resolution transcriptome analysis suggests that as CB-gdT expand and differentiate in culture, they are likely to adopt dynamic memory and signal -specific functional programs. More importantly, our data highlights the rich clonal and cellular composition of in vitro expanded CB-gdT. These unique characteristics of our CB-gdT can overcome the challenges of tumor heterogeneity and cell persistence, with the potential of improving outcomes in cell immunotherapy. Disclosures Tan: Tessa Therapeutics Ltd: Current Employment.
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