The Anti-cancer Effect And Mechanism Of H102YK, A Mutant Of Rituximab

Lymphomas are types of cancer derived from lymphocytes, which form part of the immunesystem. About90%of lymphomas are non-Hodgkin lymphomas (NHL), and more than85%of which are derived from B cells. Lymphomas are traditionally treated by combinations ofchemotherapy, radiotherapy, and hematopoietic stem cell transplantation. Antibody-basedtherapies target tumour cells expressing a specific antigen while sparing the majority ofnormal cells leading to a decrease in treatment-associated toxicity， which haverevolutionized the treatment of malignancies, especially NHL, in the last decade.The CD20molecule is an integral membrane protein expressed by B lymphocytes inearly stages of differentiation and by approximately95%B-cell lymphoma cells, and cannot intrigue antigen modulation after binding with CD20mAbs. As a result, it becomes anideal target for the treatment of lymphoma. Rituximab, a monoclonal antibody directedagainst CD20, was the first monoclonal antibody be approved by the US Food and DrugAssociation (FDA) in1997for the treatment of patients with CD20+B cell NHLs.However, it was soon realized that not all patients respond to Rituximab therapy and manypatients with NHL who were previously sensitive to Rituximab become ‘resistant’to repeatRituximab therapy. This led to further attempts to improve the anti-tumor activity ofanti-CD20mAbs.Although there are so many different anti-CD20mAbs, functionally they can be dividedinto just two distinct subtypes, which we term as type I and II. Type I (Rituximab-like)mAbs can induce CD20to redistribute into rafts, whereas type II (Tositumomab-like)mAbs can not. Type I mAbs display a remarkable ability to activate complement and elicitcomplement-dependent cytotoxicity (CDC). Type II mAbs, in marked contrast, arerelatively ineffective in eliciting CDC, but certain mAbs can trigger intracellular signalingin the target cell and directly induce programmed cell death (PCD). Finally, both type I andII mAbs appear to demonstrate efficient antibody-dependent cell-mediated cytotoxicity(ADCC). But a better understanding of CD20mAbs mediated killing mechanisms isessential to develop more effective therapeutic agents.In the previous studies of our laboratory, we modulated the binding property ofRituximab by introducing several point mutations in its complementarity-determiningregions(CDR) by the aid of computational methods. When we introduce a point mutationin the VH102of Rituximab and change the corresponding amino acid from Tyrosine(Y) toLysine(K), we get a Rituximab Variant,which we marked as H102YK. Interestingly we found that although this variant is still a Type I mAb according to its ability to redistributeCD20into lipid raft, was unexpectedly found to have extremely potent apoptosis-inducingactivity. Besides, it can effectively kill Raji cells that are resistant to Rituximab therapy. Inthis research, we studied the in vivo and in vitro anti-tumor effect of H102YK. We havefound that our variant H102YK can effectively prolong the survival time of tumor-bearingmouse compared with Rituximab therapy and combination therapy of Rituximab and11B8.Soon afterwards we revealed the mechanism how it can induce apoptosis. Firstly, themAbs bind to the surface CD20of lymphoma cells, then induce the synthesis of Ceramide,the leakage of lysosomes and the release of Cathepsin B from lysosomes, resulting in theapoptosis of target cells. Our data suggesting that it might be a promising therapeutic agentfor CD20+NHLs.