Efficacious proteasome/HDAC inhibitor combination therapy for primary effusion lymphoma
Shruti Bhatt, … , Izidore S. Lossos, Juan Carlos Ramos
Shruti Bhatt, … , Izidore S. Lossos, Juan Carlos Ramos
Published May 1, 2013
Citation Information: J Clin Invest. 2013;123(6):2616-2628. https://doi.org/10.1172/JCI64503.
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Research Article Oncology

Efficacious proteasome/HDAC inhibitor combination therapy for primary effusion lymphoma

Abstract

Primary effusion lymphoma (PEL) is a rare form of aggressive B cell lymphoma caused by Kaposi’s sarcoma-associated herpesvirus (KSHV). Current chemotherapy approaches result in dismal outcomes, and there is an urgent need for new PEL therapies. Previously, we established, in a direct xenograft model of PEL-bearing immune-compromised mice, that treatment with the proteasome inhibitor, bortezomib (Btz), increased survival relative to that after treatment with doxorubicin. Herein, we demonstrate that the combination of Btz with the histone deacetylase (HDAC) inhibitor suberoylanilidehydroxamic acid (SAHA, also known as vorinostat) potently reactivates KSHV lytic replication and induces PEL cell death, resulting in significantly prolonged survival of PEL-bearing mice. Importantly, Btz blocked KSHV late lytic gene expression, terminally inhibiting the full lytic cascade and production of infectious virus in vivo. Btz treatment led to caspase activation and induced DNA damage, as evidenced by the accumulation of phosphorylated γH2AX and p53. The addition of SAHA to Btz treatment was synergistic, as SAHA induced early acetylation of p53 and reduced interaction with its negative regulator MDM2, augmenting the effects of Btz. The eradication of KSHV-infected PEL cells without increased viremia in mice provides a strong rationale for using the proteasome/HDAC inhibitor combination therapy in PEL.

Authors

Shruti Bhatt, Brittany M. Ashlock, Ngoc L. Toomey, Luis A. Diaz, Enrique A. Mesri, Izidore S. Lossos, Juan Carlos Ramos

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Figure 2

Btz and SAHA synergize to induce KSHV lytic replication, while concurrently inhibiting expression of selective lytic genes in UM-PEL-1c cells.

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Btz and SAHA synergize to induce KSHV lytic replication, while concurren...
UM-PEL-1c cells were treated with 10 nM Btz, 0.5 μM SAHA, or 10 nM Btz/0.5 μM SAHA for 24 hours. (A and C) Total RNA was harvested for qRT-PCR analysis of viral mRNA expression. (B and D) Cells were cytospun and fixed, and immunofluorescence was performed for viral proteins. (A) qRT-PCR analysis reveals that Btz and SAHA induce expression of IE and early lytic viral mRNAs, with the exception of K8, which was inhibited by Btz. (B) The vGPCR protein was immunostained to determine the extent of viral reactivation. Widespread reactivation is seen in the cells treated with the Btz/SAHA combination. (C) K8.1, a late lytic viral gene, was inhibited by Btz at the transcript level. (D) Immunostaining images for K8.1 protein confirm the inhibition of K8.1 expression by Btz. K8.1 expression was normalized to DAPI to account for potential differences in cell number (left). Relative increase in K8.1-positive cells after treatment with SAHA alone and decrease in K8.1-positive cells after adding Btz was observed (right). Results are representative of 3 individual experiments. Error bars represent SEM. Original magnification, ×200 (B); ×100 (D).