Comparison of Newly Diagnosed and Relapsed Patients with Acute Promyelocytic Leukemia Treated with Arsenic Trioxide: Insight into Mechanisms of Resistance

There is limited data on the clinical, cellular and molecular changes in relapsed acute promyeloytic leukemia (RAPL) in comparison with newly diagnosed cases (NAPL). We undertook a prospective study to compare NAPL and RAPL patients treated with arsenic trioxide (ATO) based regimens. 98 NAPL and 28 RAPL were enrolled in this study. RAPL patients had a significantly lower WBC count and higher platelet count at diagnosis. IC bleeds was significantly lower in RAPL cases (P=0.022). The ability of malignant promyelocytes to concentrate ATO intracellularly and their in-vitro IC50 to ATO was not significantly different between the two groups. Targeted NGS revealed PML B2 domain mutations in 4 (15.38%) of the RAPL subset and none were associated with secondary resistance to ATO. A microarray GEP revealed 1744 genes were 2 fold and above differentially expressed between the two groups. The most prominent differentially regulated pathways were cell adhesion (n=92), cell survival (n=50), immune regulation (n=74) and stem cell regulation (n=51). Consistent with the GEP data, immunophenotyping revealed significantly increased CD34 expression (P=0.001) in RAPL cases and there was in-vitro evidence of significant microenvironment mediated innate resistance (EM-DR) to ATO. Resistance and relapse following treatment with ATO is probably multi-factorial, mutations in PML B2 domain while seen only in RAPL may not be the major clinically relevant cause of subsequent relapses. In RAPL additional factors such as expansion of the leukemia initiating compartment along with EM-DR may contribute significantly to relapse following treatment with ATO based regimens.相较于初诊急性早幼粒细胞白血病（newly diagnosed acute promyelocytic leukemia, NAPL）患者，复发性急性早幼粒细胞白血病（relapsed acute promyelocytic leukemia, RAPL）的临床、细胞及分子层面变化相关数据较为匮乏。本研究开展一项前瞻性队列研究，对比接受三氧化二砷（arsenic trioxide, ATO）为基础方案治疗的NAPL与RAPL患者，共纳入98例NAPL患者及28例RAPL患者。初诊时，RAPL患者的白细胞计数显著低于NAPL患者，而血小板计数更高；RAPL组的颅内出血发生率显著更低（P=0.022）。两组恶性早幼粒细胞的细胞内ATO富集能力以及体外ATO半数抑制浓度（IC50）均无显著差异。靶向高通量测序（next-generation sequencing, NGS）结果显示，28例RAPL患者中有4例（15.38%）携带PML B2结构域突变，且该突变未与ATO继发耐药存在关联。基因表达谱芯片（gene expression profiling, GEP）分析显示，两组间共有1744个基因的表达差异达到2倍及以上。差异表达最为显著的通路包括细胞黏附通路（n=92）、细胞存活通路（n=50）、免疫调控通路（n=74）以及干细胞调控通路（n=51）。与GEP结果一致，免疫表型分析显示RAPL患者的CD34表达水平显著升高（P=0.001）；体外实验证实存在显著的微环境介导的ATO天然耐药（EM-DR）现象。ATO治疗后出现的耐药与复发可能为多因素共同作用的结果：仅在RAPL患者中检出的PML B2结构域突变，或许并非临床相关的后续复发主要诱因。在RAPL患者中，白血病起始细胞群扩增联合微环境介导的天然耐药等额外因素，可能对ATO为基础方案治疗后的复发起到显著推动作用。