Study Identifies Potential Target for Alternative Therapies in Relapsed, Refractory DLBCL

Relapsed/refractory diffuse large B-cell lymphoma (rrDLBCL) is associated with increased survival signals downstream of ERK, potentially corresponding with mutations in proteins controlling RAS/MEK/ERK signaling, according to new research published in Scientific Reports. The data are the first to implicate a role for RAS guanyl releasing protein 4 (RASGRP4) mutations in B-cell malignancies.

Although DLBCL is the most common non-Hodgkin lymphoma and can be successfully treated with combination immunochemotherapy, little is known regarding rrDLBCL genetics and alternative therapies, authors explained.

Relapse with resistant disease also occurs in approximately 40% of patients, and “all patients with DLBCL currently receive the same treatment, R-CHOP; rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone,” they added. In addition, chemotherapy-resistant disease has a 90% fatality rate in this population.

As the RAS/MEK/ERK pathway is active in other chemotherapy-resistant tumors, researchers set out to determine this pathway’s importance in rrDLBCL.

To carry out the analysis, investigators stained DLBCL patient samples “containing 21 matched diagnostic and relapse biopsies, as well as 13 additional rrDLBCL samples.” Both mutations and phospho-ERK (p-ERK) levels in tumor samples were assessed.

“Unlike other tumor types, rrDLBCL is not mutated in any Ras or Raf family members, despite having increased expression of p-ERK,” authors wrote.

Data showed the following:

• In paired biopsies comparing diagnostic and relapsed specimens, 33% of tumors gained p-ERK expression, suggesting a role in promoting survival.
• Mutations in several Ras-associating proteins, including GTPase-activating proteins, Guanyl exchange factor, and downstream effectors that could account for increased ERK activation, were found.
• In silico modeling indicated an increased interaction between H-Ras and mutant RASGRP4.
• In cell lines, mutant RASGRP4 increased basal p-ERK expression and lead to a growth advantage in colony forming assays when challenged with doxorubicin.

The combination of in vitro and in silico assays revealed RASGRP4 mutations “enhance signaling of the RAS/MEK/ERK pathway, but not p-AKT signaling, and have a survival advantage compared to wild type after exposure to doxorubicin,” researchers said.

Because the study did not show an increased dependance on the MEK/ERK pathway for survival in in vitro analyses when mutant RASGRP4 was expressed, investigators hypothesized that additional RAS-mediated pathways besides p-ERK could be responsible to the resistance phenotype.

Overall, “data suggest that RASGRP4 mutation could provide a survival benefit to generate resistant-subclones. We believe these findings will help to identify suitable alternative MAPK-targeted therapies to R-CHOP in [Germinal center B-cell]-DLBCL,” authors concluded.

Reference

Benoit A, Bou-Petit E, Chou H, et al. Mutated RAS-associating proteins and ERK activation in relapse/refractory diffuse large B cell lymphoma. Sci Rep. Published online January 17, 2022. doi:10.1038/s41598-021-04736-0