PF516 ESTROGEN BETA RECEPTOR: A NEW TARGET FOR DIFFUSE LARGE B‐CELL LYMPHOMA
Authors: M. Langendonk, M. de Jong, B. Reitsma, G. Huls, A. van den Berg, J. Schuringa, L. Visser, T. van Meerten
Journal: HemaSphere (2019)

Background: About 40% of DLBCL patients do not respond to immuno‐chemotherapy and have a poor prognosis, underscoring the need for alternative treatment approaches. Using an unbiased genome‐wide guilt‐by‐association approach we identified the estrogen receptor beta (ERβ) as a possible new target in DLBCL. ERβ can serve as a target for selective ER modulators such as tamoxifen. Tamoxifen is one of the most widely used anticancer drugs, with a history of more than 4 decades of safe clinical use. Aims: To investigate whether ERβ and tamoxifen could serve as a therapeutic target‐drug combination in DLBCL. Methods: Publically available mRNA (Gene expression omnibus) and RNA sequence data (GEPIA) were consulted to study ERβ expression DLBCL and normal B cells. Nanostring was used to establish ERβ mRNA expression in lymphoma cell lines. ERβ and estrogen receptor α (ERα) protein expression were determined using Western Blot (WB) on DLBCL cell lines. Cell viability and apoptosis assays were performed after treatment with tamoxifen, endoxifen, the selective ERβ agonist DPN and the selective ERβ antagonist PHTPP. BH3 profiling was used to study changes in the anti‐apoptotic dependencies for cell lines and patient samples after treatment with tamoxifen. NSG mice were transplanted with DLBCL cell lines and the treatment group was treated with 60‐day release tamoxifen pellets subcutaneously. A nationwide, population based study was consulted to assess DLBCL incidence in patients with breast cancer (BC) treated with or without tamoxifen between 2007 and 2017. Results: ERβ mRNA and RNA seq expression was found to be significantly higher in DLBCL compared to normal B‐cells, and mRNA expression was found to be high in DLBCL compared to other lymphoma cell lines. All DLBCL cell lines expressed ERβ at the protein level, but no ERα. Treatment of DLBCL cell lines with the selective ER modulators tamoxifen and its active metabolite endoxifen dose‐dependently induced apoptosis in all DLBCL cell lines. The selective ERβ antagonist PHTPP also caused cell death, while DPN had no effect. Treatment with tamoxifen induced a BAD‐dependent apoptotic signal and increased anti‐apoptotic dependency for the anti‐apoptotic protein BCL‐2 in both cell lines and patient‐derived DLBCL cells. In our DLBCL mouse model, DLBCL outgrowth was significantly decreased in mice treated with tamoxifen compared to control mice, leading to a significant improved survival (HR 3.9, p = 0.007). To study the clinical relevance of tamoxifen, we investigated the DLBCL incidence in BC patients treated with or without tamoxifen. Of 153,883 patients, 106 patients (0.07%) were diagnosed with both BC and DLBCL. Interestingly, 82 patients (77%) received no tamoxifen treatment, resulting in a relative risk reduction of 38% (p &lt; 0.05) for tamoxifen treated patients. Summary/Conclusion: ERβ is highly expressed in DLBCL. Targeting of ERβ with tamoxifen treatment causes a dose‐dependent decrease in cell viability and induces BAD dependent apoptosis in all DLBCL cell lines. Targeting ERβ with tamoxifen as a treatment for DLBCL, especially considering low costs and limited side effects, would implicate great clinical potential. image