SHP1 loss augments DLBCL cellular response to ibrutinib: a candidate predictive biomarker

SHP1, a tyrosine phosphatase, negatively regulates B-cell receptor (BCR) signaling. Ibrutinib selectively inhibits BTK and has been approved for the treatment of several types of B-cell lymphomas, but not yet in diffuse large B-cell lymphoma (DLBCL). A phase 3 clinical trial of ibrutinib–containing regimen has been completed to evaluate its activity in subtypes or subsets of DLBCL patients. Although the subtype of activated B-cell like (ABC) DLBCL is characterized by chronic active BCR signaling, only a fraction of ABC-DLBCL patients seem to benefit from ibrutinib-containing regimen. New alternative predictive biomarkers are needed to identify patients who better respond. We investigated if SHP1 plays a role in defining the level of the BCR activity and impacts the response to ibrutinib. A meta-analysis revealed that lack of SHP1 protein expression as well as SHP1 promoter hypermethylation is strongly associated with NHL including DLBCL. On a tissue microarray of 95 DLBCL samples, no substantial difference in SHP1 expression was found between the GCB and non-GCB subtypes of DLBCL. However, we identified a strong reverse correlation between SHP1 expression and promoter methylation suggesting that promoter hypermethylation is responsible for SHP1 loss. SHP1 knockout in BCR-dependent GCB and ABC cell lines increased BCR signaling activities and sensitize lymphoma cells to the action of ibrutinib. Rescue of SHP1 in the knockout clones, on the other hand, restored BCR signaling and ibrutinib resistance. Further, pharmacological inhibition of SHP1 in both cell lines and patient-derived primary cells demonstrate that SHP1 inhibition synergized with ibrutinib in suppressing tumor cell growth. Thus, SHP1 loss may serve as an alternative biomarker to cell-of-origin to identify patients who potentially benefit from ibrutinib treatment. Our results further suggest that reducing SHP1 pharmacologically may represent a new strategy to augment tumor response to BCR-directed therapies.