Session: 625. Lymphoma: Pre-Clinical—Chemotherapy and Biologic Agents: Poster I
Hematology Disease Topics & Pathways:
Leukemia, ALL, apoptosis, Diseases, Lymphoma (any), Non-Biological, cell division, Therapies, chemotherapy, Non-Hodgkin Lymphoma, Biological Processes, DNA damage, DNA repair, T-Cell Lymphoma, Xenograft models, Lymphoid Malignancies, Study Population, pharmacology
Methods: The in vitro anti-tumor activity of selective CTPS1 inhibition was investigated in a 2D monolayer assay in a panel of 200 cancer cell lines. Cell viability was measured with the Cell Titer-Blue Cell Viability Assay after 4 days incubation. Human PBMCs were isolated and T-cells were activated with anti CD3/CD28 antibodies to assess effects of CTPS1 inhibition on intracellular nucleotide levels which were quantified using Liquid Chromatography Mass Spectrometry (LC-MS). Jurkat T-ALL cells and WI38 embryonic fibroblasts were used to assess apoptosis which was quantified using the Caspase-Glo 3/7 Assay. Murine xenograft studies were conducted in NOD.SCID mice implanted with T-ALL cell lines to assess anti-tumor effects of CTPS1 inhibitors.
Results: The panel of cancer cell lines consisted of 56 derived from hematological cancers and 141 derived from solid tumors. STP938, a potent and selective inhibitor of CTPS1 specifically blocked cell proliferation of the hematological cancers. 43 (77%) of the hematological cell lines had an IC50 <100nM whereas only 15% of the solid tumor derived cell lines were affected by the CTPS1 inhibitor. The T-cell derived cell lines were extremely sensitive with many IC50 <10nM. Profiling of intracellular nucleotide levels using activated human T-cells exposed to increasing concentrations of STP938 demonstrated the selective depletion of CTP but not ATP or GTP (see Figure). Jurkat T-ALL cells and WI38 fibroblasts were evaluated for markers of apoptosis in the presence of increasing concentrations of STP938. The Jurkat T-ALL cells exhibited a dose dependent increase in caspase 3/7 levels indicative of apoptosis. The WI38-fibroblast cells were unaffected. Murine xenograft studies using NHL T lymphoma and leukemia cell lines were conducted with oral dosing of CTPS1 inhibitor starting at the time of tumor cell inoculation or once tumors were established. In all cases, in a dose-dependent manner, CTPS1 inhibitors reduced or ablated tumor growth meeting NCI criteria for efficacy.
Conclusions: Our preliminary results indicate that inhibition of CTPS1 enables cell specific inhibition of de novo pyrimidine nucleotide synthesis with a particular sensitivity displayed by cell lines derived from hematological malignancies. This disruption of de novo nucleotide synthesis by CTPS1 inhibition selectively induces apoptosis in lymphocyte cells but not in other cell types that are able to rely upon CTPS2 for their CTP synthesis. Orally bioavailable small molecule inhibitors of CTPS1 exert an anti-tumor effect in vivo in murine xenograft models and thus inhibition of CTPS1 represents a novel targeted approach to treat hematological malignancies.
Disclosures: Parker: Step Pharma: Current Employment.
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