lometrexol (T-64)

By combining in-cell stable isotope incorporation assay with quantitative metabolomics we show: cellular uptake of external purines and their internal generation are equivalent; an upregulation in lysosome biogenesis that functions in response to purine deficiency caused by methotrexate (MTX) and lometrexol (LTX) treatment. This leads to increased RNA digestion as visualized by a newly developed intracellular RNA-FRET oligo assay. Interestingly, downregulation of lysosomal RNase activity through knockdown of RNAseT2 increased RNA accumulation and a compensating increase in DNPB.

These findings establish purine metabolic enzyme inhibition as a viable therapeutic strategy to induce differentiation and attenuate tumor progression in high-risk MYCN-amplified NBs.

Our findings suggest that HB patients harboring activated β-catenin mutations and consequent DNPS upregulation, may be treated efficaciously with DNPS enzyme inhibitors like lometrexol. These novel findings bear major therapeutic implications for targeted precision medicine of HB.

Similar scaffold commercial drugs leucal (LEU), epirubicin (EPI), and lometrexol also displayed strong binding to the active site of MTHFD2...The interaction of breast cancer serum with high expression of MTHFD2 also showed an increase in binding of epirubicin in the presence of leucovorin...Further experimental studies are required to establish the potential mode of inhibition of the novel small ligands. Future in vivo trials may validate the effectiveness of the combinatorial therapy.

Finally, we demonstrated that tumors with MLL3 and/or MLL4 mutations were highly sensitive to lometrexol in vivo, both in culture and in animal models of cancer. Our results depicted a targetable metabolic dependency arising from epigenetic factor deficiency, providing molecular insight to inform therapy for cancers with epigenetic alterations secondary to MLL3/4 COMPASS dysfunction.

Moreover, the GART inhibitor lometrexol (LMX) and drugs approved for clinical treatment of primary and metastatic BC (4OH-tamoxifen and the CDK4/CDK6 inhibitors) exert synergic antiproliferative effects in BC cells. In conclusion, GART inhibition by LMX or other inhibitors of the de novo purine biosynthetic pathway could be a novel effective strategy for the treatment of primary and metastatic BCs.