Vitamin E Succinate Induces Remission and Prolongs Survival in a Syngenic Transplant Model of Acute Promyelocytic Leukemia.

Vitamin E Succinate (VES) is a semisinthetic analogue of vitamin E with pro-apoptotic activity against several tumor cell lines and it has reported that the association of VES and other antioxidants with first-line chemotherapy may prolong survival of patients with ovarian carcinoma without significant adverse effects. Recently, we have demonstrated in vitro that VES induces apoptosis in primary cells from patients with Acute Promyelocytic Leukemia (APL) as well as in NB4 cells. In order to test in vivo the efficacy of VES treatment, we used a syngenic transplant model of APL. Leukemic blasts from PML/RARα transgenic mice (TM) were IV injected in non transgenic littermates. Recipients were irradiated with 700 cGy 24h prior to transplant. Massive infiltration of bone marrow (BM), spleen and liver was invariable detected by 21^st Day. Forty-eight mice were randomly assigned to receive daily intraperitoneal (ip) injections of : VES (50UI/g/d) (n=8), Retinoic Acid (RA) (1.5μg/g/d) (n=7), As₂O₃ (2.5μg/g/d) (n=8) or the association VES + RA (n=7) and VES + As₂O₃ (n= 8) at the same doses. Control mice (n=10) were treated with vehicle (DMSO). Treatment was started four days after transplantation and maintained for 21 consecutive days. Survival analysis was based on Kaplan-Meyer estimation and groups were compared by the long-rank test. In any of the five therapeutic arms hematology remission was achieve and survival was significantly longer than in DMSO treated group (P<0.05) (Mean survival time of control: 29.8 days, 95% C.I. = 23.3 – 36.3 days; VES: 66 days, 95%CI = 51.9 – 80.1 days; RA: 60.7 days, 95% CI = 48.1 – 73.2 days; As₂O₃: 69.7 days, 95% CI = 55.4 –84 days; VES+RA: 49.8 days, 95% CI = 29 – 70.5 days; VES+ As₂O₃: 70.3 days, 95% CI = 57 – 83.5 days. Treatment toxicity was evaluated by histopathological analysis of heart, lung, brain, liver and kidney paraffin embedded specimens, and no significant organ damage was detected. In order to determine if the antileukemic effect of VES was due to induction of apoptosis, leukemic cells obtained from spleen were treated in vitro with 10, 20, 40μg/mL of VES or DMSO. After 24h cells were harvested and stained with anti-CD117 and anti-annexin V antibody conjugated with phycoerythrin (PE) or fluorescein isothyocyanate (FITC), and the number of CD117 / Annexin V double positive cells (apoptotic) was determined by flow cytometry (FC). The mean percentage of apoptotic cells in samples treated with 40μg/mL of VES (but not with 10 or 20μg/mL) was significantly higher than in controls (83 ± 8% versus 56 ± 4 %, p< 0.05). Differentiation was evaluated morphologically on Leishman stained cytospin preparations after 72h of in vitro treatment of VES at the same doses above. No significant difference in the number of mature granulocytic cells between treated and control samples was observed. In conclusion, our results demonstrate that treatment with VES alone or in combination with RA or As₂O₃ was well tolerated and extremely effective, and therefore may represent an alternative therapy to relapsed and/or refractory APL cases.