Lymphoma Translational Research

Introduction – According to recently published cancer statistics, in 2007 approximately 63,190 new cases of non-Hodgkin’s lymphoma will be diagnosed and 18,860 lymphoma patients will die from their disease despite currently available treatment. The incidence of lymphoma has been steadily increasing over the last two decades and is now consider the second most rapidly increasing cause of cancer related death in the United States of America.

Non-Hodgkin’s lymphoma is the fifth most common cause of cancer and the sixth most common cause of cancer related death in this country. The treatment of B-cell lymphomas continues to be challenging despite current available therapies. The early use of rituximab as a single agent or in combination with various systemic chemotherapy regimens (i.e. CVP, CHOP) have resulted in improved response rates, duration of remission and improved survival in patients with FCL or diffuse large B-cell lymphomas (DLBCL).

Two recently published retrospective analysis suggest that the use of various monoclonal antibodies (mAbs) targeting CD20 (rituximab) in combination with systemic polychemotherapy improves the overall survival in patients with FCL when compared to chemotherapy alone. Stronger evidence is available for lymphoma patients with aggressive histology. While a significant number of patients benefit from rituximab-based therapies, several patients fail to respond or relapse after initial remission as a result of intrinsic or acquired resistance.

In an attempt to contribute scientifically to our knowledge of B-cell NHL we developed a translation research program aimed to:

1) optimize rituximab activity,
2) develop novel additional biologically based-therapies,
3) identify patients at higher risk to fail rituximab therapies, and
4) define the resistance mechanisms developed by lymphoma cells in an attempt to evade rituximab-based killing.

Several biological effects have been postulated as rituximab’s primary mechanism of anti-tumor activity, including: antibody-dependent cellular cytotoxicity (ADCC), complement-mediated cytotoxicity (CMC), and induction of apoptosis/anti-proliferation. Our group of investigators is the first to formally study mechanisms of resistance to rituximab in lymphoma models. During the last four years our laboratory has continue to work in understanding the mechanisms responsible for rituximab resistance.

To this end, we developed several rituximab-resistant cell lines (RRCL) derived from four rituximab-sensitive parental B-cell lymphoma cell lines (Raji, Ramos, SU-DHL-4 and RL cells). Despite that each of the resistant cell lines displays appreciable surface CD20 expression, several abnormalities at both the genetic and protein levels have been demonstrated.

They include:
a) reduced CD20 mRNA expression,
b)reduced CD20 surface protein and total protein, and
c) altered CD20 protein structure in the rituximab-resistant cell lines.

In addition, multiple genes that may contribute to the resistant phenotype have been identified to be upregulated in the rituximab-resistant cell lines. These include components of the ubiquitin-proteasome pathway (e.g. E1 ubiquitin activating enzyme). Proteasome inhibition synergizes with rituximab in an in vivo murine tumor model, implicating further the proteasome as a potential modulator of rituximab resistance. We also evaluated the use of novel target specific molecules, such as thalidomide analogs (CC5013, CC4047), anti-sense oligonucleotides targeting Bcl-2 (G3139) or survivin or new compounds such as monophosphoril lipid A for the treatment of lymphoma.

We were able to demonstrate that the use of thalidomide analogs are effective as single agents against several lymphoma cell lines and that can enhance the anti-tumor activity of rituximab using murine models. Similarly, we were able to demonstrate that using anti-sense oligonucleotides targeting Bcl-2 renders lymphoma cells more susceptible to the biological effects of rituximab in vitro and in vivo.

We completed or currently conducting several projects focusing on strategies that will enhance rituximab’s biological activity. Some of these strategies included the use of rituximab in combination with other monoclonal antibodies (anti-CD22, HLL1, HLL2, alemtuzumab, anti-HLA class II, anti-TRAIL receptor, anti-CD80 and fully humanized anti-CD20 antibodies); immunotoxins (CMC-544); or the administration of cytokines to stimulate the recruitment of immune effector cells in response to monoclonal antibodies therapy (i.e. GM-CSF or G-CSF).

A major area of research is the study of intracellular signals that result in apoptosis of lymphoma cells following binding of rituximab to the CD20 antigen. To this end are studying the effects of targeting the Bcl-2 family protein using BH-3 mimetics (ABT-737 and GX15-070).

Our Lymphoma Translational Research Program has developed numerous scientific collaborations with research at various Institutions such as the Garden State Cancer Center, Fox Chase Cancer Center, University of Calgary, New York University, Dana Farber Cancer Institute, University of Rochester, and the National Institutes of Health. In addition, we have collaborated with numerous pharmaceutical and biotechnology companies (i.e. Amgen Inc., Genentech Inc., BiogenIDEC Pharm., Berlex Inc., Genta Inc., Celgene Inc., Chiron Inc., Protein Design Lab. Inc., Abott Inc., GEMINEX Inc.,) in the testing and evaluation of novel target-specific molecules.

Current Research

Ongoing studies are aimed to better understand the mechanisms responsible for rituximab resistance. Our goals are to determine pathways involved in the development of rituximab resistance to determine if share pathways of resistance do exist with other biological agents (i.e. monoclonal antibodies) or chemotherapy agents. Specifically we are studying:
1. Deregulation of apoptotic-antiapoptotic proteins in rituximab resistant cells.
2. The role of CD20 regulation in resistance to rituximab.
3. Define the molecular basis responsible for the biological anti-tumor activity of rituximab and other monoclonal antibodies targeting antigens present in lymphomas
4. Develop therapeutic strategies that will enhance the anti-tumor activity of rituximab against B-cell lymphomas using pre-clinical models that will direct the design of future clinical trials.
5. Design novel therapeutic approaches to overcome rituximab resistance.
6. The efficacy of combination of rituximab with other chemotherapeutic agents in anti-tumor activity.