Combined effect of all-trans retinoic acid and arsenic trioxide in acute promyelocytic leukemia cells in vitro and in vivo

Abstract

All-trans retinoic acid (tRA) and arsenic trioxide (As 2 O 3 ) induce non-cross-resistant complete clinical remission in patients with acute promyelocytic leukemia with t(15;17) translocation and target PML-RAR␣, the leukemogenic protein, by different pathways suggesting a possible therapeutic synergism. To evaluate this possibility, this study examined the effect of As 2 O 3 on tRA-induced differentiation and, conversely, the effect of tRA on As 2 O 3 -induced apoptosis. As 2 O 3 at subapoptotic concentrations (0.5 M) decreased tRA-induced differentiation in NB4 cells but synergized with atRA to induce differentiation in tRA-resistant NB4 subclones MR-2 and R4 cells as measured by nitroblue tetrazolium reduction and tRA-inducible genes (TTGII, RAR␤, RIG-E). tRA cleaved PML-RAR␣ into distinct fragments in NB4 but not in tRAresistant MR-2 or R4 cells, whereas As 2 O 3 completely degraded PML-RAR␣ in all 3 cell lines. As 2 O 3 -induced apoptosis was decreased by tRA pretreatment of NB4 cells but not of R4 cells and was associated with a strong induction of Bfl-1/A1 expression, a Bcl-2 protein family member. Severe combined immunodeficient mice bearing NB4 cells showed an additive survival effect after sequential treatment, but a toxic effect was observed after simultaneous treatment with tRA and As 2 O 3 . These data suggest that combined As 2 O 3 and tRA treatment may be more effective than single agents in tRAresistant patients. Although in vitro data do not always translate to in vivo response, toxicity and potential drug antagonism may be diminished by decreasing the concentration of As 2 O 3 when given at the same time with therapeutic levels of tRA. IntroductionAcute promyelocytic leukemia (APL) is a specific type of acute myeloid leukemia characterized by the t(15;17) translocation that fuses the PML gene on chromosome 15 to the retinoic acid receptor ␣ (RAR␣) gene on chromosome 17 to form the fusion gene and leukemogenic protein PML-RAR␣. 1,2 The specific sensitivity of APL cells to all-trans retinoic acid (tRA)-induced differentiation has been exploited to achieve a 90% remission rate with a projected 60% to 70% cure of patients with APL when combined with chemotherapy. [3][4][5][6][7] However, the disease may relapse with resistance to further tRA and chemotherapy treatment. 8 The recent discovery that treatment with As 2 O 3 induces durable remission in APL patients in relapse after tRA or chemotherapy has provided a novel therapy for APL patients. 9-11 However, the reported chronic toxicities and carcinogenicity of As 2 O 3 has hampered its acceptance as a first-choice drug, 12 even though limited side effects were found in relapsed APL patients successfully treated with As 2 O 3 . 10,11 Consideration of the facts that the toxicity of As 2 O 3 is dose dependent and reversible and that small amounts of As 2 O 3 have been used in traditional Chinese medicine suggests that it may be possible to use As 2 O 3 as a first-choice drug if low concentrations prove effective.Arsenic trioxide induces both apoptos...

Retinoid X Receptor Agonists Increase Bcl2a1 Expression and Decrease Apoptosis of Naive T Lymphocytes

“…Previous studies have found that all-trans-retinoic acid increases Bcl2a1 mRNA levels and decreases apoptosis in the NB4 and PBL985 acute promyelocytic leukemia cell lines (55)(56)(57)(58). In a more recent study with PBL985 cells, 9-cis-retinoic acid increased Bcl2a1 expression but the RXR-selective agonist SR11237 did not (59).…”

Role of the pro-survival molecule Bfl-1 in melanoma

“…In addition to NFB, other transcription factors have been implicated in the transcriptional regulation of Bfl-1. These include all-trans retinoic acids in leukemia cells 401 , retinoic X receptor agonists in naïve T lymphocytes 402 , and the transcription factors WT-1 403 and PU.1 404 . On the other hand, Bfl-1 transcription has also been observed to be blocked by the transcription factor Blimp-1 in plasma cells 405 .…”

How to manage acute promyelocytic leukemia

“…29,58 Second, combination of the two agents allows a significantly prolonged survival or even disease eradication in APL animals. 63,64 Third, the two compounds target PML --RARa and modulate key networks involved in apoptosis/ differentiation via distinct but related pathways. 24,65,66 Mechanistically, the combined use of ATO with ATRA has brought about a conceptual revolution of synergistic targeting of leukemia and thus impacts the conventional chemotherapy-based treatment.…”