Enhancement of the efficacy of histone deacetylase inhibitor-induced gene therapy

Objectives Histone deacetylase inhibitor (HDACI) may alter the status of histone acetylation and activate the silenced gene expressions. The expression of p21WAF1/CIP1 gene could be mostly induced by HDACI to induce cell cycle arrest and inhibit cancer cell proliferation. This study aimed to establish a p21 promoter-driven reporters to evaluate if the HDACIs-induced gene expression (tTKSR39) could be used to enhance the GCV-mediated cytotoxicity in vitro and in vivo.

Methods The p21 promoter-driven triple fusion reporter (which is composed of firefly luciferase, DsRed monomer, truncated HSV-1 thymidine kinase SR39 mutant gene) was constructed and stably transfected into non-small cell lung cancer (NSCLC) cell line H1299 and A549.The well known HDACIs (TSA, SAHA, curcumin or Sulforaphane) were applied to these cells to demonstrate the gene inducibility in vitro and in vivo. The MTT assays were performed to evaluate the cellular viability in the presence of GCV prodrug with or without HDACIs. The nude mice bearing soild tumor xenografts were daily administrated with SAHA (100 mg/kg i.p.) and GCV (20 mg/kg) for 9 days. The therapeutic efficacy was assessed by in vivo bioluminesence imaging and microPET imaging.

Results The p21-driven triple fusion reporter stably expressed cells with HDACIs treatment showed remarkable up-activation of p21 gene expression both in vitro and in vivo. HDACIs may induce significant enhancement of GCV cytotoxicity in these cells. Tumor animal model receiving HDACIs and GCV showed significant tumor growth inhibition.

Conclusions The stably expressed p21-driven triple fusion reporter cells are HDACIs inducible. These clones could be used for new HDACIs drugs screening and other chemical drugs that activate p21. Furthermore, this p21-driven triple fusion reporter construct is useful for suicide gene therapy of cancer by combined HDACIs and GCV prodrug treatment