An Open-Label, Multicenter, Single-Arm, Phase I Dose Escalation Study of OP-2100, an Orally Bioavailable Prodrug of Decitabine, for Patients with Relapsed or Refractory Higher-Risk Myelodysplastic Syndromes and Chronic Myelomonocytic Leukemia

CONCLUSIONS

Hypomethylating agents (HMA) are commonly used to treat high-risk myelodysplastic syndromes (MDS) and chronic myelomonocytic leukemia (CMML).Decitabine (DEC), one of the HMAs, is S phase-specifically incorporated into DNA to exert its effect, and sustained plasma concentration may increase its efficacy (Saunthararajah et al. J Clin Invest. 2015). Therefore, we developed OP-2100, an orally bioavailable prodrug of DEC. It showed equal efficacy to conventional HMAs in various blood cancer mouse models and exhibited a favorable safety profile in healthy mice (Watanabe et al. Blood. 2020; Ureshino et al. Mol Cancer Ther. 2021). In addition, it exhibited a sustained-release pharmacokinetic (PK) profile when orally administered to monkeys. In a phase I study, OP-2100 monotherapy showed the expected PK profile on patients with relapsed or refractory higher-risk MDS and CMML, and we reported the preliminary result.

We designed a single-arm, multicenter phase I study for Japanese patients with MDS or CMML with intermediate-risk, high-risk, or very high-risk by Revised International Prognostic Scoring System (IPSS-R) and relapsed, refractory, or intolerant to standard therapy. The primary objective was to determine the maximum tolerated dose following the incidence of dose-limiting toxicity (DLT) in the first cycle, whereas the secondary objectives were to evaluate the safety, PK, and efficacy. Treatment-emergent adverse events (TEAEs) and response to therapy were assessed per NCI CTCAE v5.0 and IWG 2018 response criteria, respectively. Oral administration of OP-2100 as a single agent was continued for the patients daily on days 1-5 of each 28-day cycle until meeting discontinuation criteria, including disease progression. The dose level was defined as 30, 50, 80, and 120 mg/day. The initial dose of 50 mg/day was determined based on the highest non-severely toxic dose of OP-2100 in monkeys and the PK of DACOGEN TM in humans. This study was implemented in the 3+3 design according to DLT incidence. The plasma concentration of DEC and OP-2100 was measured on days 1 and 5. Furthermore, the LINE-1 methylation, a common HMA pharmacodynamics marker, was measured. This study is registered in the Japan Registry for Clinical Trials (jRCT2071220035).

In total 3 patients with a history of azacitidine treatment for MDS were registered in the 50-mg initial cohort. These patients had been categorized as intermediate to high-risk in the IPSS-R, respectively. Table 1 shows patient characteristics. Out of 3, 2 patients did not experience DLT, while the 3rd one suffered from Grade 4 neutropenia, which was confirmed as DLT. As of April 30, the most common TEAEs were cytopenia of leukopenia, neutropenia, and thrombocytopenia, all of which were Grade 3 or 4. Other adverse events of Grade 3 or 4 include anemia, lymphopenia, COVID-19, and fall. In terms of efficacy, 2 patients had stable disease, while one had progressive, according to the IWG2018 response criteria. However, the 2 patients with stable disease still received administration up to 9 and 5 cycles, respectively (Figure 1). The PK profile of DEC after OP-2100 administration indicated sustained release, with an area under the curve (AUC) similar to that of DACOGEN TM (5-day regimen, 1-h continuous intravenous administration at 20 mg/m 2) and C max approximately 1/5. The LINE-1 methylation exhibited the similar behavior as conventional HMAs.

The PK profile of DEC released from the prodrug after 50 mg of OP-2100 oral administration in 3 patients showed a similar AUC to that of the 5-day regimen of DACOGEN TM, and then C max showed a low with sustained plasma concentration. Among the 3 patients, OP-2100 could be administered for at least 5 cycles in 2 patients. To determine maximum tolerated dose, enrollment for this study is ongoing.