Protein Kinase C Delta in Diffuse Large B-Cell Lymphoma Post-Rituximab Era: Potential Prognostic Marker in Germinal Center B-Cell Lymphoma

Abstract

Background: Diffuse Large B-cell lymphoma (DLBCL) is the most common subtype of lymphoma. Acquirement of resistance in DLBCL is a major clinical problem. The identification of biomarkers of clinical behavior may aid in the implementation of novel therapeutic strategies. Protein Kinase C (PKC) delta is a class serine/threonine kinase among the PKC family and contributes to cell proliferation, survival and apoptosis. The role of PKC delta in apoptosis is still controversial. Previously studies reported that overexpressed PKC delta promoted apoptosis. However, recently data showed inhibition of PKC delta blocked proliferation and survival of cancer stem cells in vitro and in vivo . The value of PKC delta expression in lymphoma patients remains unclear. We conducted a retrospective study to investigate the impact of PKC delta expression in DLBCL patients. Methods: Histologically confirmed DLBCL patients (N=98) treated at Fudan University Shanghai Cancer Center with available diagnostic biopsy material were identified. Forty-three patients were treated with CHOP and fifty-nine patients with R+CHOP. PKC delta expression was determined and quantified by immunohistochemistry (IHC) with staining intensity or percentage of positive cells. Tumors were considered positive when at least IRS>9 of tumor cells expressed PKC delta. Kaplan-Meier method was used to calculate progression free survival (PFS) and overall survival (OS) and curves were compared with the long-rank test in both groups. Correlation between the PKC delta expression and clinical variables were tested by Pearson Chi Square test and a two-sided P value of <0.05 was considered to be statistically significant. Additionally, PKC delta was inhibited using a PKC delta inhibitor (Rotterin) in DBCL cell lines. Changes in cell viability following in vitro exposure to rotterin were determined by Presto Blue Assay. Result: In CHOP treatment DLBCL, PKC delta expression was detected in 10/41 (24.4%) DLBCL patients. PKC delta expression was associated with a worse progression free survival (PFS) compared to PKC delta negative patients (50% vs 77%, p=0.036) treated with CHOP. The overall survival (OS) of PKC delta positive patients was also worse compared to the negative group (50% vs. 80%, p=0.023). In rituximab-CHOP (R-CHOP) treated patients, PKC delta was present in 17/57 (29.8%) patients. Surprisingly, no differences between the PKC delta positive group and negative R-CHOP treated groups were observed in terms of PFS or OS. Of interest, a subset analysis of R-CHOP treated DLBCL patients base on the cell of origin (COO) demonstrated that PKC delta expression in germinal center B-cell lymphoma (GCB) DLBCL was associated with an inferior OS outcome. The OS was 67% for GCB-DLBCL expressing PKC delta vs 83% for GCB-DLBCL patients without PKC delta expression (p=0.01). To identify the contribution of PKC delta to the survival of B-cell lymphoma, we performed the in vitro viability assay in different subtype of lymphoma cell lines using Rotterin, a PKC delta inhibitor. We found that in vitro exposure of cell lines to rotterin resulted in cell death in vitro suggesting that PKC delta can serve as a targetable biomarker in DLBCL. Additional pre-clinical studies are underway. Conclusion: This is the first report demonstrating that, PKC delta expression is a negative predictor of clinical outcome. PKC delta is a potential novel target to treat lymphoma and further investigation of PKC delta need to be done in the near future. (Research supported by Shanghai Municipal Commission of Health and Family Planning Project (no.20134030), National Natural Science Foundation of China (no.81670177, no.81001048), Roswell Park Cancer Institute Alliance Grant) [Display omitted] DisclosuresNo relevant conflicts of interest to declare.