Investigation into the efficacy of the anti-CD20 monoclonal antibody ofatumumab in chronic lymphocytic leukaemia

Middleton, Odette (2015) Investigation into the efficacy of the anti-CD20 monoclonal antibody ofatumumab in chronic lymphocytic leukaemia. PhD thesis, University of Glasgow.

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Chronic lymphocytic leukaemia (CLL) is the most common leukaemia of the Western world, and unfortunately despite advances in chemotherapeutic agents CLL remains incurable to date. CLL is a highly heterogeneous disease. CLL patients exhibiting progressive disease often become refractory to standard first line therapies, underpinning the need for novel drugs. An emerging field is targeted monoclonal antibody (MAb) development. Rituximab (RTX) a chimeric anti-CD20 MAb is registered as a first line therapy in combination with fludarabine and cyclophosphamide. A next generation type I, human IgG1 anti-CD20 MAb, ofatumumab (OFA), binds to a novel epitope of CD20 resulting in higher potency of complement dependent cytotoxicity (CDC) induction. OFA has recently been given FDA approval for treatment in combination with chlorambucil for previously untreated CLL patients when fludarabine based regimes are not appropriate. OFA is also licensed as a single agent for the treatment of CLL patients refractory to both fludarbine and anti-CD52 MAb alemtuzumab.
This research was conducted to establish what factors within CLL biology may influence RTX or OFA efficacy, in order to highlight the improved activity of OFA in comparison to RTX for the treatment of CLL. The ability of OFA to elicit a CDC response is an important part of its efficacy. Within this study we have demonstrated that OFA activity is limited in the treatment of CLL by several different factors including; complement levels, CD20 expression, microenvironmental stimulation and CLL genetic mutations.
Our study identified that a large proportion, 37.5%, of CLL patients harbour complement deficiencies within their sera, this then led to a significant amount of complement exhaustion with successive OFA treatments, abrogating CDC induction. The detection of excessive complement exhaustion potentially has a clinical impact on the administration of anti-CD20 MAbs.
CD20 expression levels also impact upon CDC induction by OFA, CD20 expression levels display a positive linear correlation with the percentage of CDC induction. Importantly OFA is superior in the induction of CDC in CLL patients with low CD20 expression levels in comparison to RTX. It is well established that CLL patients have lower CD20 expression compared to other B cell malignancies, which is an important factor for anti-CD20 MAb efficacy as CDC induction is critically dependent on the expression levels of the target antigen on the surface of the cell.
Recurrent mutations within NOTCH1 (NOTCH1MUT) have recently been identified as a poor prognostic marker within CLL. Emerging data suggests this mutation confers resistance against anti-CD20 MAbs, possibly through a down-regulation of CD20. We demonstrate that NOTCH1MUT CLL cells do display reduced expression levels of CD20, however this alone did not appear to contribute to all the reduced susceptibility towards anti-CD20 MAb activity. Preliminary gene expression data in combination with Ca2+ flux analysis suggest that NOTCH1MUT CLL cells have deregulated Ca2+ signalling which highlights the role of CD20 as a store-operated Ca2+ channel, and provides another mechanism for their resistance.
Microenvironmental stimulation also impacts upon CLL cell response to RTX and OFA. Mimicking CLL cell interaction with their microenvironmental niche, caused an increase in CDC induction within different CLL cytogenetic subsets, independently to changes in CD20 expression. This is important as the interaction of CLL cells with other components of the microenvironment cause an up-regulation of anti-apoptotic proteins aiding CLL survival and promoting drug resistance.
In conclusion this study highlights the increased efficacy of OFA as a chemotherapeutic agent in the treatment of CLL in comparison to RTX. Collectively these results also demonstrate that a change within the dosing schedule of OFA and complement supplementation using an exogenous source such as fresh frozen plasma could diminish some of the limitations in CDC induction, and potentially lead to enhanced clinical efficacy.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Chronic lymphocytic leukaemia, ofatumumab, rituximab, monoclonal antibody, complement dependent cytotoxicity
Subjects: R Medicine > R Medicine (General)
R Medicine > RC Internal medicine > RC0254 Neoplasms. Tumors. Oncology (including Cancer)
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cancer Sciences > Paul O'Gorman Leukemia Research Centre
Supervisor's Name: Michie, Dr. Alison and Wheadon, Dr. Helen
Date of Award: 2015
Depositing User: Odette Middleton
Unique ID: glathesis:2015-7125
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 04 Mar 2016 13:30
Last Modified: 22 Mar 2016 12:06

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