Targeting the PI3K/AKT/Survivin Pathway with Ritonavir In Therapy-Resistant Mantle Cell Lymphoma

Abstract 2855

Mantle cell lymphoma (MCL) is an aggressive B cell lymphoma accounting for about 6% of non-Hodgkin's lymphoma cases in the US. While multiple therapy regimens are available to treat MCL, patients ultimately relapse within 3–4 years from therapy-resistant MCL, making MCL carry the worst prognosis of all non-Hodgkin's B cell lymphomas. To improve therapies for patients with MCL, we must understand the biological causes for relapse and therapy-resistance in MCL and develop mechanisms to target the unique properties in relapsing MCL. Recently, we have isolated and produced therapy-resistant MCL cell lines by inoculating NOD-SCID mice with a human MCL cell line, Granta-519 (GP), and subsequently treating with CHOP chemotherapy regimen plus bortezomib. When mice relapsed following therapy, tumor cells were isolated from the kidneys and livers, and cultured to produce stable cell lines, named GRK and GRL, respectively. GRK and GRL cells exhibited increased proliferative and therapy-resistant properties in vitro, and GRL showed increased aggressiveness in vivo also, as compared with GP. Using quantitative PCR (qRT-PCR) to assess the activation of pathways relating to lymphoma progression, the PI3K/Akt/survivin pathway was found to be differentially activated in GRL and GRK compared to GP, including a 6.5 fold increase in survivin in GRL. Therefore, we inhibited survivin in GRL using the FDA-approved protease inhibitor ritonavir (Abbott Laboratories), as recent studies suggest this compound is able to downregulate survivin in lymphoblastoid B cells (Dewan, et al. Int J Cancer 2009; 124[3]: 622–629). When GRL cells were incubated with ritonavir plus vincristine or doxorubicin, MTT assays showed significant inhibition of cell proliferation/survival (p < 0.05) compared to the effects of ritonavir alone. Also, flow cytometric analysis of Annexin V demonstrated dose-dependent induction of apoptosis upon ritonavir treatment in GRL. In addition, qRT-PCR analysis demonstrated a decrease in mRNA expression of the pro-survival genes cyclin D2, Rel A, survivin, and BCL2 in GP and GRL cells after ritonavir treatment. Together, these studies demonstrate the potentials of utilizing ritonavir in a combined treatment regimen designed to target therapy-resistant MCL. As ritonavir is already an FDA-approved drug, these studies hold promise for expediting future in vivo and clinical studies that may eliminate therapy-resistant cells responsible for relapse in MCL patients.(This research was supported by the Lymphoma Research Foundation, New York, NY).