The HDAC Inhibitor FK228 Enhances Adenoviral Transgene Expression by a Transduction-Independent Mechanism but Does Not Increase Adenovirus Replication

• The histone deacetylase inhibitor FK228 has previously been shown to enhance adenoviral transgene expression when cells are pre-incubated with the drug. Upregulation of the coxsackie adenovirus receptor (CAR) has been proposed as the main mechanism. In the present study, we found that the highest increase in transgene expression was achieved when non-toxic concentrations of FK228 were added immediately after transduction demonstrating that the main effect by which FK228 enhances transgene expression is transduction independent. FK228 had positive effects both on Ad5 and Ad5/f35 vectors with a variety of transgenes and promoters, indicating that FK228 works mainly by increasing transgene expression at the transcriptional level. In some cases, the effects were dramatic, as demonstrated by an increase in CD40L expression by FK228 from 0.3% to 62% when the murine prostate cancer cell line TRAMP-C2, was transduced with Ad[CD40L]. One unexpected finding was that the transgene expression of an adenoviral vector with the prostate-specific PPT promoter decreased in the human prostate cancer cell line LNCaP when FK228 was administered. This is probably a consequence of phenotypic alteration of LNCaP towards a neuroendocrine phenotype after FK228 treatment. The observations in this study indicate that FK228 enhances adenoviral therapy by a transduction-independent mechanism. Furthermore, since histone deacetylase inhibitors may alter the phenotype of cells, it is important to keep in mind that the activity and specificity of tissue- and tumor-specific promoters may also be affected.

Nyckelord

FK228

depsipeptide

HDAC inhibitor

adenovirus

CD40 ligand

prostate-specific promoter

MEDICINE

MEDICIN

Medicin

Medicine

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