The Combination of AZT/Interferon-α Therapy with the HDAC Inhibitor Valproic Acid for the Treatment of Adult T-Cell Leukemia/Lymphoma

Abstract 4877

Adult T-cell leukemia/lymphoma (ATLL) carries a dismal long-term prognosis and is generally chemotherapy resistant. We and other groups have demonstrated that the combination of AZT and interferon (IFN) alpha can effectively suppress ATLL long-term; however, these drugs fail to eradicate malignant ATLL clones as patients ultimately progress. We recently tested our hypothesis that histone deacelytase (HDAC) inhibitors would re-activate latent HTLV-I in ATLL cells harboring intact provirus thus helping to eliminate residual disease after cytoreductive treatment. Histone acetylation can result in HTLV-I promoter activation and viral transcription. We found that HDAC inhibitors, including the inexpensive drug valproic acid (VPA), reactivated HTLV-I expression in ATLL cells and caused apoptosis. Based on these concepts, we recently completed a pilot trial for ATLL using AZT/IFN and adding VPA during the maintenance treatment phase. Thirteen subjects with aggressive acute-type ATLL were enrolled in the study, including 11 treatment-naïve patients. The estimated 12-month overall survival rate was 46%. In 12 evaluable subjects (10 naïve) the complete response (CR) rate was 33% and overall response 42% (5 patients). A total of eight subjects (66%) had a hematologic response, including 5 complete hematologic responses (38%). VPA was added at the beginning of month 3 during AZT/IFN maintenance in 3 subjects. One subject achieved a molecular remission and clearance of ATLL after adding VPA as measured by serial multiplex PCR studies. This subject remains disease-free 2.5 years later. Our findings were surprising, as previous studies performed on long-term responders treated with AZT/IFN alone had not demonstrated any molecular remissions. Our data suggest that VPA could potentially eradicate ATLL clones in vivo. The dual anti-neoplastic and viral inducing roles of HDAC inhibitors can be exploited in the treatment of ATLL. This exciting approach may help advance the cure for this disease. We will present our updated interim clinical trial results at the conference.