Abstract LB-248: Protein arginine methyltransferase 5 (PRMT5) inhibition as a therapeutic strategy in B-cell lymphoma

PRMT5 is responsible for symmetric dimethylation of arginine residues in glycine and arginine rich (GAR) motifs on a variety of cytosolic and nuclear proteins including histones, spliceosome components, regulators of translation, transcription factors, kinases and others. PRMT5 driven methylation of some of these proteins has been implicated in tumorigenesis. For example, PRMT5 deposits repressive marks on histones and silences a subset of tumor suppressor genes, such as RB and ST7. PRMT5 methylation of non-histone substrates (such as E2F1 and p53) also contributes to cancer cell growth and death. PRMT5 driven methylation of spliceosome subunits and components of translational machinery has been well described but its connection to PRMT5's role in cancer has not been established. We have identified first-in-class small molecules that are highly potent, selective, reversible inhibitors of PRMT5. Cellular mechanistic studies revealed that PRMT5 inhibition decreases symmetric arginine dimethylation on a variety of cellular proteins including spliceosome components, histones and transcription factors. PRMT5 inhibition leads to gene expression and splicing changes ultimately resulting in the induction of p53 in lymphoma cell lines. In addition to impacting the p53 pathway, PRMT5 inhibition leads to attenuation of the expression of cell cycle related genes, genes involved in ribosome and spliceosome homeostasis, as well as genes important for cellular metabolism. PRMT5 inhibitor attenuates proliferation and induces cell death in a subset of mantle cell and diffuse large B-cell lymphoma cell lines and inhibits tumor growth in xenograft models of mantle cell lymphoma. These data underline the potential of PRMT5 inhibitors as a therapeutic strategy in mantle cell and diffuse large B-cell lymphoma.

Citation Format: Olena Barbash, Sarah Gerhart, David Soong, Christine Thompson, Rocio Montes de Oca, Ping Zhang, Charles McHugh, Kristy Kuplast, Christina Majer, Richard Chesworth, Jesse Smith, Robert Copeland, Elayne Penebre, Kenneth Duncan, Neil Johnson, Chris Carpenter, Ryan Kruger. Protein arginine methyltransferase 5 (PRMT5) inhibition as a therapeutic strategy in B-cell lymphoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-248. doi:10.1158/1538-7445.AM2015-LB-248

T-type calcium channel blockers that attenuate thalamic burst firing and suppress absence seizures

Absence seizures are a common seizure type in children with genetic generalized epilepsy and are characterized by a temporary loss of awareness, arrest of physical activity, and accompanying spike-and-wave discharges on an electroencephalogram. They arise from abnormal, hypersynchronous neuronal firing in brain thalamocortical circuits. Currently available therapeutic agents are only partially effective and act on multiple molecular targets, including γ-aminobutyric acid (GABA) transaminase, sodium channels, and calcium (Ca(2+)) channels. We sought to develop high-affinity T-type specific Ca(2+) channel antagonists and to assess their efficacy against absence seizures in the Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model. Using a rational drug design strategy that used knowledge from a previous N-type Ca(2+) channel pharmacophore and a high-throughput fluorometric Ca(2+) influx assay, we identified the T-type Ca(2+) channel blockers Z941 and Z944 as candidate agents and showed in thalamic slices that they attenuated burst firing of thalamic reticular nucleus neurons in GAERS. Upon administration to GAERS animals, Z941 and Z944 potently suppressed absence seizures by 85 to 90% via a mechanism distinct from the effects of ethosuximide and valproate, two first-line clinical drugs for absence seizures. The ability of the T-type Ca(2+) channel antagonists to inhibit absence seizures and to reduce the duration and cycle frequency of spike-and-wave discharges suggests that these agents have a unique mechanism of action on pathological thalamocortical oscillatory activity distinct from current drugs used in clinical practice.