Zidovudine Blocks NF-κB activity in Vivo in Adult T-Cell Leukemia

Abstract

Adult T-cell leukemia (ATL) is a lymphoid malignancy caused by the human T-cell leukemia virus type I (HTLV-I), which carries a poor prognosis. A hallmark of ATL is the high constitutive expression of NF-κB, which predominantly exerts an anti-apoptotic effect contributing to chemotherapy resistance. Many of the elegant studies about the pathogenesis of ATL have focused on Tax, a viral transactivator of NF-κB, using HTLV-I expressing cell lines and mouse models, however in primary tumors the virus remains latent and Tax is not detected. We and other investigators have demonstrated the clinical efficacy of Zidovudine (AZT) and interferon-alpha (IFNα) combination therapy in both chronic and acute ATL subtypes with some patients achieving clinical remission or stable disease for many years while on maintenance therapy. The exact mechanisms of these antiviral drugs in ATL remain unclear. In a recent analysis of primary ATL tumors, we implicated the expression of both c-Rel and the NF-κB target gene product IRF-4/MUM-1 in AZT/IFN resistant disease. We have recently opened to accrual a Phase II clinical trial titled Prospective Study of the Molecular Characteristics of Sensitive and Resistant Disease in Patients with HTLV-I Associated Adult T Cell Leukemia Treated with Zidovudine Plus Interferon alpha-2b, which includes the novel use of pegylated interferon-alpha and valproic acid (as HDAC inhibitor) in the maintenance phase as an attempt to eradicate residual ATL clones, which usually occurs after AZT and IFNα therapy even after longterm remission. Our goals are also to study the anti-tumor mechanisms of these drugs in ATL, and define molecular criteria for response. As part of the correlative studies in our Phase II trial, we have analyzed leukemic ATL cells collected from patients during the first 48 hours of treatment (AZT given alone prior to IFN) and found in vivo stabilization of IκB (the repressor protein of NF-κB) by Western Blot in patients responding to the treatment, suggesting a role for this antiviral drug in blocking NF-κB activity as previously hypothesized in our laboratory. We also examined the expression of NF-κB related genes using a custom designed gene expression array by a novel technology (NanoString Inc.) of selected NF-κB target genes and found downregulation of most these genes in vivo by AZT alone. So far, all ATL tumors analyzed exhibited high expression of many NF-κB target genes, and over forty of these are differentially overexpressed in ATL specimens as compared to normal CD4+ T-cells. Some the differentially expressed genes include those encoding NF-κB/Rel, interferon regulatory factor (IRF), and bcl-2 related proteins. A comprehensive analysis of over forty ATL tumors, including specimens collected in both Miami and Brazil, is ongoing and expected to be completed soon. Baseline tumor characteristics and prognostic variables of previously collected tumors, as well interim results of our clinical and molecular studies will be reported.