Effect of Matrine on Alleviating Retinoic Acid Resisted Acute Promyelocytic Leukemia

Acute promyelocytic leukemia (APL) represents 3.3%-17.4% of acute leukemia in adults. With the application of all-trans retinoic acid (ATRA), more than 85% patient can achieve complete remission, however, high rates of relapse still exist if ATRA is used alone. Primary resistance of ATRA in PML-RARα positive APL is rare during induction therapy but the incidence markedly increases after second relapse and results in poor long time survival of patient. Matrine (MAT) is the effective constituent of Radix Sophorae Flavescentis, a commonly used traditional chinese drug, and has proven ability to inhibit carcinoma cell proliferation and can induce differentiation and apoptosis of K562 cells, however its effect on the differentiation of APL cells, especially on ATRA resistant APL cells is unclear. The aim of our research is to explore the effect of MAT on alleviating retinoic acid resistance in APL cells and address possible mechanisms involved. The characteristics of ATRA sensitive APL cell strain NB4 and resistant APL cell strains NB4-R1 and NB4-R2 were described in our former studies. Dose escalation studies using MAT and ATRA was investigated using methyl thiazolyl tetrazolium (MTT) test. The toxicity of MAT increases with increasing concentration of MAT from 0.001 mmol/L to 10 mmol/L, and the 0.1mmol/L was chosen with its inhibition ratio < 10%. IC50 of ATRA was obtained by drawing the restrain curve; the resistance coefficient (RC) of NB4-R1 and NB4-R2 to ATRA was obtained by the ratios of their IC50 to that of NB4 cell, respectively. And the reversal index (RI) was obtained by the ratios of RC of resistant cell line cells cultured with or without 0.1 mmol/L MAT for 72h. Cell differentiation was evaluated by nitro blue tetrazolium chioride (NBT) test and cell morphology. Differential effects on cell differentiation between MAT combined with 1 umol/L ATRA and controls were observed. For these studies, 1umol/L of ATRA was chosen according to the result of IC50 test, which had low toxicity to resistance cell line cells, with the inhibition ratio < 10%. Apoptosis rate of cells treated with MAT combined with 1 umol/L ATRA was tested by flow cytometry with Annexin V-PI staining. Nested PCR was used for PML/RARa PCR reaction. Our results showed, after treated with ATRA along with 0.1 mmol/L MAT, the resistance factor of NB4-R1 to ATRA decreased markedly (RI=4.96±1.15), but no difference was shown in NB4-R2 cells (RI=0.66±0.17). The positive ratio of NBT and the morphologic changes indicated that the differentiation ability of NB4 and NB4-R1was enhanced significantly with the increasing concentration of MAT combined with 1 umol/L ATRA, which reached the peak at 0.1mmol/L (Figure). The apoptosis ratio (Annexin V-FITC kit) of NB4 and NB4-R1 were also increased with increasing concentration of MAT combined with 1 umol/L ATRA, while no changes were observed using the NB4-R2 cell line. The expression of PML-RARα fusion became weak in NB4 and NB4-R1 cells after treated with 0.1 umol/L ATRA alone, and decreased notably when co-treated with 0.1 mmol/L MAT for 72h in NB4-R1, while the fusion gene expression remained negative in NB4-R2 cells exposed to both drugs. From this study, we conclude that MAT, when used together with ATRA as a low non-toxic dose, can improve the differentiation of NB4 cells and inverse the retinoic acid resistance of NB4-R1 cells, but it has no function on NB4-R2 cells. As the mechanism of ATRA resistance in NB4-R1 and NB4-R2 cells is different, with resistance to the former ascribed to abnormal cyclic adenosine monophosphate (cAMP) mediated pathways, leading to altered differentiation of NB4-R1 which can be corrected when cells are cocultured with cAMP and ATRA, and resistance of NB4-R2 is owing to the variation of PML-RARα, which can only be alleviated in the existence of RXR receptor specific agonist, MAT may play its anti-ATRA resistance role in an ATRA dependent pathway, and lead to the inhibition of the PML-RARα fusion gene. This indicates a possible application of MAT in ATRA resistance therapy. Further research will focus on the mechanism of MAT in the regulation and differentiation as well as apoptosis of APL cells.