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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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 7

Btz induces accumulation of viral DNA, with concomitant inhibition of infectious virion production.

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Btz induces accumulation of viral DNA, with concomitant inhibition of in...
(A) Cultured UM-PEL-1c cells were treated for 72 hours with 10 nM Btz, 0.5 μM SAHA, or the 10 nM Btz/0.5 μM SAHA combination. Total intracellular DNA was isolated, and 10 ng was used for qPCR viral load determination. (B and C) Cell-free supernatant from PBS-treated (Control-treated), Btz-treated, SAHA-treated, or Btz/SAHA–treated cells was applied to uninfected HEK293 cells. Forty-eight hours later, the cells were fixed and stained for LANA. For graphing purposes, 1 non-doublet LANA-positive 293 cell was defined as 1 infectious unit. Immunofluorescence of a representative field for each condition is shown. Results are representative of 2 independent experiments. Error bars represent SEM. Original magnification, ×200. (D) Mechanism of action for SAHA, Btz, and the combination. SAHA induces the full KSHV lytic cycle, leading to virus production and apoptosis. Btz also induces the lytic cycle, but it also blocks late lytic gene expression, leading to apoptosis in the absence of virus production. In the combination, SAHA and Btz synergize to induce the lytic cycle; however, the presence of Btz inhibits the completion of the lytic cycle, resulting in massive apoptosis in the absence of virus production.