Efficacy of bortezomib in a direct xenograft model of primary effusion lymphoma

Abstract

Primary effusion lymphoma (PEL) is an aggressive B-cell lymphoma most commonly diagnosed in HIV-positive patients and universally associated with Kaposi's sarcoma-associated herpesvirus (KSHV). Chemotherapy treatment of PEL yields only short-term remissions in the vast majority of patients, but efforts to develop superior therapeutic approaches have been impeded by lack of animal models that accurately mimic human disease. To address this issue, we developed a direct xenograft model, UM-PEL-1, by transferring freshly isolated human PEL cells into the peritoneal cavities of NOD/SCID mice without in vitro cell growth to avoid the changes in KSHV gene expression evident in cultured cells. We used this model to show that bortezomib induces PEL remission and extends overall survival of mice bearing lymphomatous effusions. The proapoptotic effects of bortezomib are not mediated by inhibition of the prosurvival NF-κB pathway or by induction of a terminal unfolded protein response. Transcriptome analysis by genomic arrays revealed that bortezomib down-regulated cell-cycle progression, DNA replication, and Myc-target genes. Furthermore, we demonstrate that in vivo treatment with either bortezomib or doxorubicin induces KSHV lytic reactivation. These reactivations were temporally distinct, and this difference may help elucidate the therapeutic window for use of antivirals concurrently with chemotherapy. Our findings show that this direct xenograft model can be used for testing novel PEL therapeutic strategies and also can provide a rational basis for evaluation of bortezomib in clinical trials.Kaposi's sarcoma-associated herpesvirus | Herpesvirus 8

Efficacious proteasome/HDAC inhibitor combination therapy for primary effusion lymphoma

“…Therefore, we analyzed the effect of Btz/SAHA on NF-κB activity in vivo using nuclear extracts from PEL xenografts by EMSA. Contrary to our previous study, in which we observed that Btz had no significant effect on NF-κB activity on UM-PEL-1 cells treated in vitro (14), in this study, we found that Btz induced IκB-α phosphorylation and increased NF-κB (p50/p65) DNA binding at 24 hours as compared with control (Supplemental Figure 5, A and B). Btz-mediated NF-κB activation was further augmented in the presence of SAHA (Supplemental Figure 5, A and B).…”

“…The in vitro antiproliferative and cytotoxic activities of Btz/SAHA in multiple PEL cell lines suggested therapeutic potential in vivo. Therefore, we evaluated the effects of Btz/SAHA in a direct xenograft UM-PEL-1 model, originally established directly from a patient with PEL and continuously propagated in NOD/SCID mice, allowing for the maintenance of the original PEL phenotype (14). Four groups of NOD/SCID mice (n = 5) were inocu-…”

“…Prior studies have demonstrated that Btz-mediated cell killing can occur through the induction of ER stress from the accumulation of nondegraded proteins, leading to the activation of the unfolded protein response (UPR) (17). Our previous study demonstrated that Btz had no significant effect on the UPR in UM-PEL-1c cells in vitro (14). To evaluate the effect of Btz on the UPR in UM-PEL-1 xenografts in vivo, we measured the expression of proteins known to be upregulated by the UPR (CHOP, GRP-78, GRP-94, ATF6, total and phosphorylated eIF2α) by immunoblotting.…”

“…In this model, we demonstrated that the 26S proteasome inhibitor, bortezomib (Btz), induced KSHV lytic gene expression in the primary PEL cells and increased survival of PEL-bearing NOD/SCID mice when compared with doxorubicin treatment (14). Indeed, Btz has emerged as an effective antineoplastic drug in several cancers and has clinical activity in PEL (14)(15)(16).…”

Current status of treatment for primary effusion lymphoma

“…A proteasome inhibitor, bortezomib, is expected to show clinical effects against PEL. Despite the promising results of in vitro experiments and a mouse model (61,62), bortezomib treatment either alone or in combination with chemotherapy showed no clinical improvement (20,63). The optimization of treatment protocol and combination therapy with bortezomib may be needed to show the preferable effects of bortezomib.…”