Decitabine in patients with myelodysplastic syndromes: A multi‐center, open‐label, dose comparison trial

Abstract Background The hypomethylating agent decitabine is the standard therapy for intermediate or high risk myelodysplastic syndrome (MDS). Methods In this trial, 191 adult patients with intermediate/high risk MDS (IPSS score ≥ 0.5) randomly received decitabine using a standard regimen (20 mg/m2/day for 5 consecutive days; n = 94) or an extended regimen with lower daily dose (12 mg/m2/day for 8 consecutive days; n = 97) every 4 weeks, for a total of 4 cycles. Results The median follow‐up was 14 months (range 2–36). The primary end point of overall response rate in the intent‐to‐treat analysis was 41.5% and 38.1% in the standard and extended dosing arms, respectively (p = 0.660). Complete remission and marrow complete remission also did not differ between the two arms. Cytopenia was the most frequent adverse event (76.4%). The median duration of neutropenia per cycle did not differ between the two arms during the first two cycles, but significantly shorter in the extended dosing arm in the third cycle (8.5 vs. 15.5 days, p = 0.049) and in the fourth cycle (8 vs. 14 days, p = 0.294). Conclusion The 5‐day 20‐mg/m2/day and 8‐day 12‐mg/m2/day decitabine regimens have similar efficacy and safety in patients with intermediate or high risk MDS.


| INTRODUCTION
Myelodysplastic syndrome (MDS) is a heterogeneous group of acquired clonal hematopoietic progenitor cell diseases characterized by ineffective hematopoiesis, cytopenia, and leukemic transformation. 1,2 Epigenetic changes, most notably aberrant DNA hypermethylation, are implicated in the pathogenesis and leukemic transformation of MDS. 3,4 The DNA hypomethylating agent decitabine is the standard therapy for higher risk MDS patients, 5,6 but the dosing regimen has been evolving, with a general trend for shorter courses but increasing dosage in each course. [7][8][9][10][11][12][13] Decitabine was launched in China in 2009 without clinical trials. A subsequent phase 3b trial in 135 Chinese patients with de novo or secondary MDS showed 29.4% overall response rate (ORR) for 3-h infusion at 15 mg/m 2 every 8 h for 3 consecutive days/cycle/6 weeks and 25.5% ORR for 1-h infusion at 20 mg/m 2 once daily on days 1-5/cycle/4 weeks. 10 A recent retrospective study of 13 Chinese patients with de novo MDS showed 69.2% ORR with intravenous decitabine at 6 mg/m 2 per day for 7 days, repeated every 4 weeks. 14 Up to date, there has been no clinical trials of decitabine in Chinese patients with intermediate-or high-risk de novo MDS. We conducted a multicenter, open-label, dose comparison trial to compare the efficacy and safety of two decitabine dosing regimens (20 mg/m 2 /day for 5 consecutive days vs. 12 mg/m 2 /day for 8 consecutive days, every 4 weeks) in Chinese patients with intermediate-or high-risk de novo MDS.
Trial protocol adhered to the SPIRIT statement 15 and was approved by the ethics committees of all participating institutions (Appendix A). Written informed consent was obtained before enrollment. The trial is registered with Clini calTr ials.gov (NCT02013102) and was conducted in accordance with the Declaration of Helsinki.

| Intervention
Patients were randomized at a 1:1 ratio to receive intravenous decitabine at 20 mg/m 2 /day for 5 days (standard dosing arm) or at 12 mg/m 2 /day for 8 days (extended dosing arm) every 4 weeks for a total of four cycles. Treatment was discontinued upon disease progression, severe infection, major bleeding, or severe myelosuppression. All patients received best supportive care.

| Efficacy evaluation
The primary endpoint of ORR, as defined by the modified International Working Group 2006 (IWG 2006) criteria, 16 was compared in both the intent-to-treat (ITT) and per-protocol population. ORR included complete response (CR), marrow CR (mCR), and partial response (PR). Secondary efficacy endpoints, including CR, mCR, PR, hematologic improvement (HI), cytogenetic response, and transfusion requirements, were analyzed in the per-protocol population. Routine blood examination was performed every week. Bone marrow (BM) was examined every two cycles. Both overall survival Tianjin Municipal Natural Science Foundation, Grant/Award Number: 16JCZDJC35300, 18JCYBJC27200 and 18JCYBJC91700; Tianjin Science and Technology Plan Project, Grant/Award Number: 16ZXMJSY00180 remission and marrow complete remission also did not differ between the two arms. Cytopenia was the most frequent adverse event (76.4%). The median duration of neutropenia per cycle did not differ between the two arms during the first two cycles, but significantly shorter in the extended dosing arm in the third cycle (8.5 vs. 15.5 days, p = 0.049) and in the fourth cycle (8 vs. 14 days, p = 0.294).

Conclusion:
The 5-day 20-mg/m 2 /day and 8-day 12-mg/m 2 /day decitabine regimens have similar efficacy and safety in patients with intermediate or high risk MDS.

K E Y W O R D S
complete remission, decitabine, hypomethylating agent, myelodysplastic syndromes, overall survival (OS) and progression-free survival (PFS) were calculated from the day when therapy was initiated.

| Safety evaluation
Safety was evaluated in all patients who received at least one dose of the investigational drug using the CTCAE version 4.0, and coded to a preferred term using the Medical Dictionary for Regulatory Activities (MedDRA). Severe adverse events (SAEs) were defined as any AE that resulted in death, was life-threatening, required hospitalization, prolonged hospitalization, caused significant or persistent disability or incapacity, or birth defects. All patients were followed until recovery from any treatment-emergent AEs (TEAEs).

| Statistical analysis
Statistical analyses were conducted using SAS 9.4. Continuous variables were compared with Student's t-test or Wilcoxon signed sum test. Categorical variables were analyzed with χ 2 test or Fisher's exact test, as appropriate. Changes from baseline were compared using analyses of variance (ANOVA) or rank-sum test. The ITT population included all patients who received at least one dose of the study drug and had a baseline assessment and at least one post-baseline assessment. The per-protocol population included patients who completed at least two treatment cycles as planned and underwent efficacy evaluation. p ≤ 0.05 (two-sided) was considered statistically significant and 95% confidence interval (CI) was used to describe the results.

| Demographic and baseline characteristics
The study flowchart is shown in Figure 1. Demographic and baseline characteristics of the patients are provided in Table 1
Subgroup analysis stratified by age (cutoff at 65 years) failed to show significant difference in the ORR between the two arms in either subgroup (Table 3). Subgroup analyses based on risk or WHO classification subtype also failed to show significant difference in the ORR between the two arms.

| DISCUSSION
The trial showed similar efficacy measures (including ORR, CR, mCR, and PFS) and safety profiles in the two arms, suggesting that either the 5-day 20-mg/m 2 /day or 8-day 12-mg/m 2 /day decitabine regimen is appropriate for use in Chinese patients with intermediate-or high-risk MDS. There seemed to be marginal benefit in the duration of neutropenia with the extended dosing regimen. Decitabine produces distinct effects at different dosages: it inhibits cell proliferation by irreversibly blocking DNA synthesis at high doses and blocks hypermethylation and consequently re-expression of tumor suppressor genes at low doses. 17,18 Low dose decitabine (15 mg/m 2 , IV, over 3 h, every 8 h, 3 d, repeated every 6 weeks) was initially recommended for MDS, but was discontinued due to severe hematologic and nonhematologic toxicities. In a meta-analysis of 1378 patients (15 studies), 100 mg/m 2 / course decitabine regimen had higher CR rate than the 135 mg/m 2 /course regimen, and higher ORR than the 60-75 mg/m 2 /course regimen. 19 Currently, the recommended standard protocol in MDS patients is 20 mg/m 2 /day for 5 consecutive days, every 4 weeks. Several previous studies showed approximately 50% ORR, with low treatmentemergent mortality. [20][21][22][23] In this trial, the median duration of neutropenia was shorter in the extended dosing arm in the third cycle (8.5 vs. 15.5 days) and in the fourth cycle (8 vs. 14 days), but not in the first two cycles. Such a potential benefit with the 8-day 12-mg/m 2 /day regimen requires verification in future studies. In a previous retrospective analysis, 24 patients with dose modifications had a significantly higher ORR versus those without, suggesting better treatment effects with extended period of decitabine exposure.
The median age of MDS at the diagnosis is about 70 years, and many patients have comorbid conditions that could influence treatment decisions and prognosis. In this trial, the ORR was 78.6% and 68.8% in the two arms in patients >65 years of age versus 58.3% and 54.2% in younger patients, indicating that decitabine is more effective and safer in elderly Chinese patients.
About 70% of the patients in this trial had higher risk MDS, for which hypomethylating agents are the best option. Kantarjian et al. compared low intensity decitabine therapy with intensive chemotherapy in patients with higher risk MDS and found significant survival advantage with decitabine. 25 In a phase 3 study by the EORTC Leukemia Cooperative Group and German MDS Study Group, decitabine prolonged PFS in high-risk MDS patients with complex karyotypes harboring two or more autosomal monosomies. 26 Another clinical trial showed that, in comparison to traditional chemotherapy, decitabine followed by low-dose idarubicin plus cytarabine could reduce the rate of leukemic transformation in highrisk myeloid neoplasms. 27 Consistent with previous data, 8 the median PFS for the entire patient cohort in the current study was 12 months, and 22 patients progressed to AML during the 14-month follow-up. Of note, decitabine resistance has been associated with more enriched somatic mutations, including mutations in TP53, GATA2, KRAS, RUNX1, STAG2, ASXL1, ZRSR2, and TET2. [28][29][30][31] Treatment options for such conditions include intensive chemotherapy (mainly based on anthracycline-cytarabine combinations), allogeneic stem cell transplantation and targeted therapies (such as venetoclax, IDH1 or IDH2 inhibitors). 32 Novel treatments under development include telomerase inhibitors and CTLA-4 inhibitors. [33][34][35][36][37] With the progress of detection technology and indepth study of pathogenesis, the treatment of MDS has made great progress. For the low-risk group MDS, EPO, Eltrombopag, lenalidomide, Luspatercept, and iron removal treatment showed some efficacy. For the high-risk group MDS, HMA treatment is one of the current standard treatments, but there are still unmet medical needs. Some new targeted drugs have been used for the treatment of high-risk MDS, such as IDH1 inhibitor, 38 Bcl2 inhibitor, 39 XPO1 inhibitor, 40 anti-CD47 antibody, 41 anti-PD-1antibody, 42 et al., combined with azacytidine have shown good efficacy. Hematopoietic stem cell transplantation is the only curable method, while it still faces some problems, such as the selection of donors, the necessity of HMA bridging, the improvement of pretreatment scheme, the chimerism rate and implantation and MRD detection in the process of transplantation, and the "preemptive" treatment to prevent recurrence.
The rate of hematologic TEAEs in our study was practically identical in the two arms: 77.66% in the standard dosing arm and 75.26% in the extended dosing arm. Consistent with previous trials 43,44 and metaanalyses, 45,46 the rate of grade 3/4 hematologic TEAEs were generally comparable between the two arms, but the median duration of neutropenia per cycle seemed to be shorter in the extended dosing arm in the third and fourth cycles.
This study has several limitations. First, 53 patients (19 and 34 in the two arms, respectively) did not complete four cycles of treatment as initially planned. Second, treatment after four cycles was not uniform, and could introduce bias to OS data. Future studies with larger sample size, longer follow-up, and more meticulous data collection are needed. In adult Chinese patients with intermediate-or high-risk MDS, decitabine is equally effective when given on an 8-day 12-mg/m 2 /day versus 5-day 20-mg/m 2 / day decitabine regimen, with generally comparable safety profile.