Acquired Resistance to EZH2 Inhibitor GSK343 Promotes the Differentiation of Human DLBCL Cell Lines toward an ABC-Like Phenotype

Chemical biology and pharmacology of histone lysine methylation inhibitors

Histone lysine methylation is a post-translational modification that plays a key role in the epigenetic regulation of a broad spectrum of biological processes. Moreover, the dysregulation of histone lysine methyltransferases (KMTs) has been implicated in the pathogenesis of several diseases particularly cancer. Due to their pathobiological importance, KMTs have garnered immense attention over the last decade as attractive therapeutic targets. These endeavors have culminated in tens of chemical probes that have been used to interrogate many aspects of histone lysine methylation. Besides, over a dozen inhibitors have been advanced to clinical trials, including the EZH2 inhibitor tazemetostat approved for the treatment of follicular lymphoma and advanced epithelioid sarcoma. In this Review, we highlight the chemical biology and pharmacology of KMT inhibitors and targeted protein degraders focusing on the clinical development of EZH1/2, DOT1L, Menin-MLL, and WDR5-MLL inhibitors. We also briefly discuss the pharmacologic targeting of other KMTs.

H3K27m3 overexpression as a new, BCL2 independent diagnostic tool in follicular and cutaneous follicle center lymphomas

Approximately 15% of follicular lymphomas (FL) lack overexpression of BCL2 and the underlying translocation t(14;18). These cases can be diagnostically challenging, especially regarding follicular hyperplasia (FH). In a subset of FL, mutations in genes encoding for epigenetic modifiers, such as the histone-lysine N-methyltransferase EZH2 (enhancer of zeste homolog 2), were found, which might be used diagnostically. These molecular alterations can lead to an increased tri-methylation of histone H3 at position lysine 27 (H3K27m3) that, in turn, can be visualized immunohistochemically. The aim of this study was to analyze the expression of H3K27m3 in FL, primary cutaneous follicle center lymphomas (PCFCL), and pediatric-type FL (PTFL) in order to investigate its value in the differential diagnosis to FH and other B cell lymphomas and to correlate it to BCL2 expression and the presence of t(14;18). Additionally, the mutational profile of selected cases was considered to address H3K27m3’s potential use as a surrogate parameter for mutations in genes encoding for epigenetic modifiers. Eighty-nine percent of FL and 100% of PCFCL cases overexpressed H3K27m3, independently of BCL2, EZH2, and the presence of mutations. In contrast, 95% of FH and 100% of PTFL cases lacked H3K27m3 overexpression. Other B cell lymphomas considered for differential diagnosis also showed overexpression of H3K27m3 in the majority of cases. In summary, overexpression of H3K27m3 can serve as a new, BCL2 independent marker in the differential diagnosis of FL and PCFCL, but not PTFL, to FH, while being not of help in the differential diagnosis of FL to other B cell lymphomas.