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

Abstract

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.

Rationale and efficacy of proteasome inhibitor combined with arsenic trioxide in the treatment of acute promyelocytic leukemia

“…8 We had previously reported in an in vitro model that there was evidence of significant de novo micro-environment-mediated drug resistance (EMDR) to ATO. 9 Recently published data indirectly validate our preliminary observation by demonstrating that stromal cell and malignant promyelocyte interaction, mediated by VLA-4 (very late antigen-4) and VCAM-1) vascular cell adhesion molecule-1) interaction, upregulates the nuclear factor (NF)-κB pathway in both the stromal and malignant cell and in turn mediates chemoresistance. 10 …”

“…9 A global gene expression array for differential gene expression in NB4 cells with and without HS-5 cell co-culture was performed. The Gene Set Enrichment Analysis (GSEA) revealed an enrichment of NF-κB pathway in the malignant cell line upon co-culture (Figure 1a and Supplementary Figure S1).…”

Evaluating frequency of PML-RARA mutations and conferring resistance to arsenic trioxide-based therapy in relapsed acute promyelocytic leukemia patients

“…With clonal evolution, other unidentified molecular mechanisms may act in combination with PML mutations to drive the progression and frank relapse. The result of this study is partly supported by the Chendamarai et al report, which found that 4 (15.38 %) of 26 APL cases were observed in the B2 domain of the PML, and at least two patients were not resistant to the ATO-based therapy [17]. However, the study by Chendamarai et al used a single ATO regimen, with majority of patients in the first relapse, which may have potentially contributed to the different final results.…”

“…Recently, missense mutations in the B2 box domain of the PML conferring ATO resistance were reported in the relapsed/refractory patients [13][14][15][16]. However, Chendamarai et al suggested that ATO resistance was probably multifactorial and acquisition mutations of PML are rare [17]. In the current study, PML-RARA screen was performed in a set of APL patients experiencing hematologic or molecular relapse under longitudinal samples, and the association of these mutations with clinical characteristics and treatment response was analyzed.…”

“…A significant relationship was observed between PML mutations and early relapse (P=0.013). Of note, including ATO in the frontline therapy might not induce ATO resistance in APL at initial relapse, although a long-term outcome is less favorable [6,17].…”