Researchers found the TCF4 (E2-2) transcription factor is an oncogene in ABC-like DLBCL, and TCF4 can be targeted via BET inhibition.
The BET protein degrader ARV771 reduced TCF4 expression and exhibited activity against ABC-like DLBCL in vitro and in vivo.
Neeraj Jain, PhD, of the University of Texas MD Anderson Cancer Center in Houston and colleagues reported these findings in.
The researchers performed a genomic analysis of 1,000 DLBCL tumors and discovered that gains of 18q21.2 were the most frequent genetic alteration in ABC-like DLBCL. In analyzing another 249 tumors, the researchers found that TCF4 was the target of the 18q21.2 gains.
Additional experiments with primary DLBCL tumors and DLBCL cell lines indicated that TCF4 regulates IGHM and MYC expression. The researchers also found that the TCF4 gene was “one of the most highly BRD4-loaded genes in DLBCL,” and knocking down BRD4 in DLBCL cell lines reduced TCF4 expression.
These findings prompted the team to test small-molecule BET inhibitors – JQ1 and OTX015 – and a BET protein degrader – ARV771 – in ABC-like DLBCL cell lines with a high TCF4 copy number.
Treatment with JQ1 and OTX015 resulted in upregulation of BRD4, but ARV771 treatment did not. As a result, subsequent experiments were performed with ARV771.
The researchers found that ARV771 induced apoptosis in the cell lines and reduced the expression of TCF4, IgM, and MYC. However, enforced TCF4 expression during ARV771 treatment rescued IgM and MYC expression. This suggests that “reduction of TCF4 is one of the mechanisms by which BET inhibition reduces IgM and MYC expression and induces apoptosis,” according to the researchers.
The team also tested ARV771 in mouse models of ABC-like DLBCL with high TCF4 expression. ARV771 significantly reduced tumor growth and prolonged survival (P less than .05 for both), and there were no signs of toxicity in ARV771-treated mice.
“Our data provide a clear functional rationale for BET inhibition in ABC-like DLBCL,” the researchers wrote. They did note, however, that BCL2 overexpression is associated with resistance to BET inhibitors, and most of the 18q DNA copy number gains the researchers observed in DLBCL encompass TCF4 and BCL2. The team therefore theorized that combining a BET inhibitor with a BCL2 inhibitor could be a promising treatment approach in ABC-like DLBCL and is worthy of further investigation.
This research was supported by the Nebraska Department of Health & Human Services, the Schweitzer Family Fund, the Fred & Pamela Buffet Cancer Center Support Grant, and the MD Anderson Cancer Center NCI CORE Grant. The authors reported having no conflicts of interest related to the study.
SOURCE: Jain N et al. Sci. Transl. Med. 2019 Jun 19..