Modeling mantle cell

PITTSBURGH—An article published recently in Experimental Biology and Medicine describes a new drug discovery model for mantle cell lymphoma, a deadly subtype of non-Hodgkin’s lymphoma. The study, led by Dr. Kathryn Whitehead in the Department of Biomedical Engineering and Chemical Engineering at Carnegie Mellon University, reports the development of a drug-resistant cell line that recapitulates the chemoresistance typically observed in patients.

Mantle cell lymphoma is an aggressive subtype of non-Hodgkin’s lymphoma that kills tens of thousands of people annually. Mantle cell lymphoma is considered incurable, even though new treatments have yielded promising results. The combination chemotherapy regimen CHOP (cyclophosphamide, doxorubicin hydrochloride [hydroxydaunorubicin], vincristine sulfate [Oncovin], and prednisone) has a high response rate in patients. But the cancer becomes resistant to treatment over time, and the duration of the response is often less than three years.

The development of effective treatments for patients with advanced disease is hampered by the lack of conventional cell culture and preclinical models of mantle cell lymphoma that mimic the chemoresistance seen in patients. The lack of chemoresistant models has also limited the understanding of the mechanisms used by cells to acquire resistance.

“A significant challenge in cancer therapy today is a lack of models that are representative of true human disease,” Whitehead said. “We are pleased to have developed a mantle cell lymphoma cell culture model that recapitulates typical levels of chemoresistance in patients.”

In this study, Whitehead and colleagues describe the generation of a chemoresistant mantle cell lymphoma cell line that mimics the low-level resistance observed in patients.

“One of the first obstacles in studying CHOP in vitro was activating the prodrugs prednisone and cyclophosphamide, which require hepatic enzymes to be converted to cytotoxic metabolites,” notes the article. “In the case of prednisone, we simply used its active form, prednisolone, in the CHOP mixture. In the case of cyclophosphamide, however, the direct use of its active forms 4-hydroxycyclophosphamide and phophoramide mustard are not viable options due to their low biological stability in vitro. As such, we took the approach of activating cyclophosphamide in vitro by mimicking hepatic activity using an S9 mix which contains the cytochrome P450 enzymes as well as the co-factors necessary for proper enzymatic activity.”

“Our primary objective was to develop an in vitro mantle cell lymphoma model that displayed resistance to conventional CHOP therapy ... we chose to develop a clinically relevant model to mimic the conditions of resistance in patients as closely as possible. To develop this drug-resistant cell line, it was important to first analyze the response of parental cells to CHOP to determine a suitable starting concentration,” the article continues. “Although these cells exhibited a strongly resistant phenotype, the main disadvantage of a clinically relevant model is their instability. This means that they require regular dosing of CHOP in order to maintain their resistance.”

JeKO-1 cells treated with increasing concentrations of the chemotherapy cocktail CHOP developed tolerance to CHOP treatment and exhibited rapid proliferation when exposed to therapeutic levels of CHOP. These cells also exhibited increased expression of three oncogenes implicated in the development of mantle cell lymphoma—Cyclin D1, Mcl-1 and Bcl-1.

“While the overexpression of cyclin D1 is a hallmark of mantle cell lymphoma, increased expression of the antiapoptotic proteins Mcl-1 and Bcl-2 is also involved in resistance to cell death. Here we showed that all three of these genes are overexpressed in resistant cells, suggesting a potential mechanistic factor in drug resistance,” states the article.

“This model should be extremely valuable in identifying therapeutics that can overcome the issue of drug resistance,” noted Dr. Steven R. Goodman, editor-in-chief of Experimental Biology & Medicine.