Results of a randomized phase 3 study of oral sapacitabine in elderly patients with newly diagnosed acute myeloid leukemia (SEAMLESS)

BACKGROUND

Acute myeloid leukemia (AML) is fatal in elderly patients who are unfit for standard induction chemotherapy. The objective of this study was to evaluate the survival benefit of administering sapacitabine, an oral nucleoside analogue, in alternating cycles with decitabine, a low-intensity therapy, to elderly patients with newly diagnosed AML.

METHODS

This randomized, open-label, phase 3 study (SEAMLESS) was conducted at 87 sites in 11 countries. Patients aged ≥70 years who were not candidates for or chose not to receive standard induction chemotherapy were randomized 1:1 to arm A (decitabine in alternating cycles with sapacitabine) received 1-hour intravenous infusions of decitabine 20 mg/m² once daily for 5 consecutive days every 8 weeks (first cycle and subsequent odd cycles) and sapacitabine 300 mg twice daily on 3 consecutive days per week for 2 weeks every 8 weeks (second cycle and subsequent even cycles) or to control arm C who received 1-hour infusions of decitabine 20 mg/m² once daily for 5 consecutive days every 4 weeks. Prior hypomethylating agent therapy for preexisting myelodysplastic syndromes or myeloproliferative neoplasms was an exclusion criterion. Randomization was stratified by antecedent myelodysplastic syndromes or myeloproliferative neoplasms, white blood cell count (<10 × 10⁹ /L and ≥10 × 10⁹ /L), and bone marrow blast percentage (≥50% vs <50%). The primary end point was overall survival (OS). Secondary end points were the rates of complete remission (CR), CR with incomplete platelet count recovery, partial remission, hematologic improvement, and stable disease along with the corresponding durations, transfusion requirements, number of hospitalized days, and 1-year survival. The trial is registered at ClinicalTrials.gov (NCT01303796).

RESULTS

Between October 2011 and December 2014, 482 patients were enrolled and randomized to receive decitabine administered in alternating cycles with sapacitabine (study arm, n = 241) or decitabine monotherapy (control arm, n = 241). The median OS was 5.9 months on the study arm versus 5.7 months on the control arm (P = .8902). The CR rate was 16.6% on the study arm and 10.8% on the control arm (P = .1468). In patients with white blood cell counts <10 × 10⁹ /L (n = 321), the median OS was higher on the study arm versus the control arm (8.0 vs 5.8 months; P = .145), as was the CR rate (21.5% vs 8.6%; P = .0017).

CONCLUSIONS

The regimen of decitabine administered in alternating cycles with sapacitabine was active but did not significantly improve OS compared with decitabine monotherapy. Subgroup analyses suggest that patients with baseline white blood cell counts <10 × 10⁹ /L might benefit from decitabine alternating with sapacitabine, with an improved CR rate and the convenience of an oral drug. These findings should be prospectively confirmed.

Phase 1/2 study of DFP-10917 administered by continuous intravenous infusion in patients with recurrent or refractory acute myeloid leukemia

BACKGROUND

DFP-10917, a deoxycytidine nucleoside analogue, has a unique mechanism of action resulting in leukemic cell death when administered for prolonged periods at low doses. The current phase 1/2 study investigated the safety, maximum tolerated dose, and evidence of antileukemic activity for DFP-10917 administered by 7-day or 14-day continuous intravenous infusion in patients with recurrent or refractory acute myeloid leukemia (AML).

METHODS

In the phase 1 dose escalation portion of the study, patients were administered DFP-10917 by 7-day continuous intravenous infusion plus 21-day rest (stage 1) or 14-day continuous intravenous infusion plus 14-day rest (stage 2). The primary objectives of phase 1 were to determine the maximum tolerated dose, the phase 2 dose, and the dose-limiting toxicities (DLTs) of DFP-10917. The primary objectives of phase 2 were to evaluate the overall response rate of DFP-10917 using complete response (CR), CR without platelet recovery (CRp), CR with incomplete blood count recovery (CRi) or partial response.

RESULTS

In stage 1 of phase 1 (4-35 mg/m² /day as a 7-day continuous intravenous infusion), a DLT of grade 3 diarrhea occurred at a dose of 35 mg/m² /day. In stage 2 of phase 1, a dose of 10 mg/m² /day as a 14-day continuous intravenous infusion resulted in DLTs of prolonged hypocellularity, abdominal pain, diarrhea, and vomiting. The dose of 6 mg/m² /day as a 14-day continuous intravenous infusion was found to be well tolerated and was selected for phase 2. Response rates in patients in phase 2 (N = 29) were 20.7% CR, 3.4% CRp, and 24.1% CRi. The overall response rate was 48.3% (95% confidence interval, 29.4%-67.5%).

CONCLUSIONS

DFP-10917 as a 14-day continuous intravenous infusion at a dose of 6 mg/m² /day can be administered safely and appears to be effective in patients with recurrent or refractory AML. A phase 3 investigation comparing DFP-10917 monotherapy versus standard of care in an early recurrent or refractory AML setting is warranted.

Profile of sapacitabine: potential for the treatment of newly diagnosed acute myeloid leukemia in elderly patients

Acute myeloid leukemia (AML) is a hematopoietic stem cell disorder that affects approximately 14,000 persons each year in the US. AML occurs at all ages but the incidence increases with age with the median age at diagnosis being 67 years. Advances in the treatment of AML over the past decades have led to improved survival, albeit mostly in younger patients. The prognosis of older patients with this disease over the same time span has not changed much and remains dismal. This review focuses on the epidemiology and characteristics of AML in elderly patients, the rationale for treating elderly AML patients, and the currently available and potential future treatment options such as sapacitabine. Elderly AML patients treated with intensive chemotherapy have a higher mortality rate, and a lower rate of complete remission and overall survival when compared to the younger population. This is due to both the different biology of the disease and the number of patient-specific factors. However, elderly AML patients treated with aggressive chemotherapy can achieve durable remissions, which offer prolonged survival and improved quality of life. Recent data also indicates that elderly AML patients deemed unfit for intensive chemotherapy benefit from leukemia-specific attenuated dose chemotherapy compared to supportive care alone. This has led to renewed interest to look for anti-leukemic therapies designed specifically for older patients. Sapacitabine, a novel oral nucleoside analog, promises good efficacy, favorable toxicity profile, and ease of administration; all of which makes it very appealing. Results from pre-clinical and clinical studies have been very encouraging and sapacitabine is currently being evaluated in a Phase III study, of which the results are eagerly awaited.

New agents: great expectations not realized

A number of new agents in acute myeloid leukemia (AML) have held much promise in recent years, but most have failed to change the therapeutic landscape. Indeed, with the exception of gemtuzumab ozogamicin (which was subsequently voluntarily withdrawn from the commercial market), no new agent has been approved for acute myeloid leukemia (AML) beyond the 7 + 3 regimen, which was has been in use for over 40 years. This review touches upon the potential reasons for these failures and explores the newer therapeutic approaches being pursued in AML.

Sapacitabine, the prodrug of CNDAC, is a nucleoside analog with a unique action mechanism of inducing DNA strand breaks

Sapacitabine is an orally bioavailable prodrug of the nucleoside analog 2'-C-cyano-2'-deoxy-1-β-D-arabino-pentofuranosylcytosine (CNDAC). Both the prodrug and active metabolite are in clinical trials for hematologic malignancies and/or solid tumors. CNDAC has a unique mechanism of action: after incorporation into DNA, it induces single-strand breaks (SSBs) that are converted into double-strand breaks (DSBs) when cells go through a second S phase. In our previous studies, we demonstrated that CNDAC-induced SSBs can be repaired by the transcription-coupled nucleotide excision repair pathway, whereas lethal DSBs are mainly repaired through homologous recombination. In the current work, we used clonogenic assays to compare the DNA damage repair mechanism of CNDAC with two other deoxycytidine analogs: cytarabine, which is used in hematologic malignacies, and gemcitabine, which shows activity in solid tumors. Deficiency in two Rad51 paralogs, Rad51D and XRCC3, greatly sensitized cells to CNDAC, but not to cytarabine or gemcitabine, indicating that homologous recombination is not a major mechanism for repairing damage caused by the latter two analogs. This study further suggests clinical activity and application of sapacitabine that is distinct from that of cytarabine or gemcitabine.

Sapacitabine for cancer

INTRODUCTION

Sapacitabine is an orally bioavailable nucleoside analog prodrug that is in clinical trials for hematologic malignancies and solid tumors. The active metabolite of sapacitabine, CNDAC (2'-C-cyano-2'-deoxy-1-β-D-arabino-pentofuranosylcytosine), exhibits the unique mechanism of action of causing single-strand breaks (SSBs) after incorporation into DNA, which are converted into double-strand breaks (DSBs) when cells enter a second S-phase. CNDAC-induced DSBs are predominantly repaired through homologous recombination (HR). Cells deficient in HR components are greatly sensitized to CNDAC. Therefore, sapacitabine could be specifically effective against tumors that are deficient in this repair pathway.

AREAS COVERED

This review summarizes results from supporting evidence for the mechanisms of action of sapacitabine, its preclinical activities and the current results of clinical trials in a variety of cancers. The novel action mechanism of sapacitabine is discussed, with a view to validate it as a chemotherapeutic drug targeting malignancies with defects in HR.

EXPERT OPINION

Knowledge of CNDAC mechanism identifies tumors that may be sensitized to sapacitabine, thus enabling a personalized treatment strategy. It also creates the opportunity to overcome resistance to current front-line therapies and identify synergistic interactions with known anticancer drugs. The results of such investigations may provide rationales for the design of sapacitabine-based clinical trials.