DNA methylation inhibition in myeloma: Experience from a phase 1b study of low-dose continuous azacitidine in combination with lenalidomide and low-dose dexamethasone in relapsed or refractory multiple myeloma.

The DNA methyltransferase inhibitor azacytidine (aza) may reactivate pathways associated with plasma cell differentiation, cell cycle control, apoptosis, and immune recognition and thereby restore sensitivity to lenalidomide (len) and dexamethasone (dex) in relapsed and/or refractory multiple myeloma (RRMM). We aimed to develop an aza regimen that reaches epigenetically active levels 8 times in 28 days with less bone marrow toxicity than the myeloid malignancy standard of 7 consecutive doses to enable safe combination with len. Aza was escalated from 30 mg/m2 once a week up to a predefined maximum of 50 mg/m2 twice a week in combination with GFR-adjusted len (≥ 60 mL/min: 25 mg, 3059 mL/min: 10 mg) day 1 to 21 every 28 days and dex 40 mg once a week followed by a limited expansion study to a total N of 23 at the highest tolerated dose. Fifty-one patients (pts) with RRMM were screened, 42 were treated and 41 were evaluable for response based on at least 1 response assessment or progression after treatment start. The median number of prior lines of therapy was 5 (1-11) and 81% (34) were refractory to len and/or pomalidomide (pom). Two DLTs occurred in different cohorts, 1 neutropenic fever in 1/6 pts on the aza 40 mg/m2 twice a week GFR ≥ 60 mL/min cohort and 1 GGT elevation in 1/6 pts on the aza 50 mg/m2 GFR 30-59 mL/min cohort. An MTD was not reached and aza 50 mg/m2 SC twice a week was chosen for the expansion study. At least possibly related Grade 3/4 AEs occurred in 28 pts (67%) with the following in > 1 pt: neutropenia (N = 16, 38%), anemia (N = 6, 14%), lymphopenia (N = 5, 12%), thrombocytopenia (N = 4, 10%), leukopenia (N = 4, 10%), febrile neutropenia (N = 4, 10%), fatigue (N = 3, 7%), fever (N = 2, 5%), and infection (N = 2, 5%). At a median follow up time for alive pts of 60.2 months (range: 36.1-82.5 months), the overall response rate (≥ partial response) and clinical benefit response rate (≥ minor response) was 22 and 32%, respectively, with 4 very good partial responses (10%), 5 partial responses (12%), and 4 minor responses (10%). The median PFS was 3.1 months (95% confidence interval [CI]: 2.1-5.1 months), median TTP 2.7 months (95% CI: 2.1-7.5 months), and median OS 18.6 months (95% CI: 12.9-33.0 months). Achieving at least minor response and reaching TTP > 6 months was associated with approximately 35% lower median plasma levels of the enzyme that inactivates aza, plasma cytidine deaminase (CDA, P< .0001). Two of the len refractory pts achieved longer disease control than with any prior regimen and 1 responded immediately after progression on len, bortezomib, and prednisone. Analyses of the methylation state of over 480,000 CpG sites in purified myeloma cells at screening were possible in 11 pts and on day 28 in 8 of them. As in other studies, the majority of differentially methylated CpGs compared to normal plasma cells were hypomethylated in myeloma. Treatment decreased the number of CpGs that were differentially methylated in normal plasma cells by > 0.5% in 6 and by > 5% in 3 of the 8 pts, most pronounced in 2 pts with clinically convincing aza contribution who achieved a reduction in overall differentially methylated CpGs by 23 and 68%, respectively, associated with increased expression of immunoglobulin genes. The study demonstrated tolerability of twice a week SC aza at 50 mg/m2 with len and dex in RRMM and suggested aza may help overcome the len/pom refractory state, possibly by activating differentiation pathways. Relatively low response rates and association of clinical benefit with low plasma levels of the aza inactivating enzyme CDA suggest the aza regimen will need to be optimized further and pt selection may be required to maximize benefit.

A pilot clinical trial of oral tetrahydrouridine/decitabine for noncytotoxic epigenetic therapy of chemoresistant lymphoid malignancies.

One mechanism by which lymphoid malignancies resist standard apoptosis-intending (cytotoxic) treatments is genetic attenuation of the p53/p16-CDKN2A apoptosis axis. Depletion of the epigenetic protein DNA methyltransferase 1 (DNMT1) using the deoxycytidine analog decitabine is a validated approach to cytoreduce malignancy independent of p53/p16. In vivo decitabine activity, however, is restricted by rapid catabolism by cytidine deaminase (CDA). We, therefore, combined decitabine with the CDA-inhibitor tetrahydrouridine and conducted a pilot clinical trial in patients with relapsed lymphoid malignancies: the doses of tetrahydrouridine/decitabine used (∼10/0.2 mg/kg orally (PO) 2×/week) were selected for the molecular pharmacodynamic objective of non-cytotoxic, S-phase dependent, DNMT1-depletion, guided by previous Phase 1 studies. Patients with relapsed/refractory B- or T-cell malignancies (n = 7) were treated for up to 18 weeks. Neutropenia without concurrent thrombocytopenia is an expected toxicity of DNMT1-depletion and occurred in all patients (Grade 3/4). Subjective and objective clinical improvements occurred in 4 of 7 patients, but these responses were lost upon treatment interruptions and reductions to manage neutropenia. We thus performed parallel experiments in a preclinical in vivo model of lymphoma to identify regimen refinements that might sustain DNMT1-targeting in malignant cells but limit neutropenia. We found that timed-alternation of decitabine with the related molecule 5-azacytidine, and combination with inhibitors of CDA and de novo pyrimidine synthesis could leverage feedback responses of pyrimidine metabolism to substantially increase lymphoma cytoreduction but with less neutropenia. In sum, regimen innovations beyond incorporation of a CDA-inhibitor are needed to sustain decitabine DNMT1-targeting and efficacy against chemo-resistant lymphoid malignancy. Such potential solutions were explored in preclinical in vivo studies.

A pilot clinical trial of the cytidine deaminase inhibitor tetrahydrouridine combined with decitabine to target DNMT1 in advanced, chemorefractory pancreatic cancer.

DNA methyltransferase 1 (DNMT1) is scientifically validated as a molecular target to treat chemo-resistant pancreatic ductal adenocarcinoma (PDAC). Results of clinical studies of the pyrimidine nucleoside analog decitabine to target DNMT1 in PDAC have, however, disappointed. One reason is high expression in PDAC of the enzyme cytidine deaminase (CDA), which catabolizes decitabine within minutes. We therefore added tetrahydrouridine (THU) to inhibit CDA with decitabine. In this pilot clinical trial, patients with advanced chemorefractory PDAC ingested oral THU ~10 mg/kg/day combined with oral decitabine ~0.2 mg/kg/day, for 5 consecutive days, then 2X/week. We treated 13 patients with extensively metastatic chemo-resistant PDAC, including 8 patients (62%) with ascites: all had received ≥ 1 prior therapies including gemcitabine/nab-paclitaxel in 9 (69%) and FOLFIRINOX in 12 (92%). Median time on THU/decitabine treatment was 35 days (range 4-63). The most frequent treatment-attributable adverse event was anemia (n=5). No deaths were attributed to THU/decitabine. Five patients had clinical progressive disease (PD) prior to week 8. Eight patients had week 8 evaluation scans: 1 had stable disease and 7 PD. Median overall survival was 3.1 months. Decitabine systemic exposure is expected to decrease neutrophil counts; however, neutropenia was unexpectedly mild. To identify reasons for limited systemic decitabine effect, we measured plasma CDA enzyme activity in PDAC patients, and found a > 10-fold increase in those with metastatic vs resectable PDAC. We concluded that CDA activity is increased not just locally but also systemically in metastatic PDAC, suggesting a need for even higher CDA-inhibitor doses than used here.

Oral tetrahydrouridine and decitabine for non-cytotoxic epigenetic gene regulation in sickle cell disease: A randomized phase 1 study.

BACKGROUND: Sickle cell disease (SCD), a congenital hemolytic anemia that exacts terrible global morbidity and mortality, is driven by polymerization of mutated sickle hemoglobin (HbS) in red blood cells (RBCs). Fetal hemoglobin (HbF) interferes with this polymerization, but HbF is epigenetically silenced from infancy onward by DNA methyltransferase 1 (DNMT1). METHODS AND FINDINGS: To pharmacologically re-induce HbF by DNMT1 inhibition, this first-in-human clinical trial (NCT01685515) combined 2 small molecules-decitabine to deplete DNMT1 and tetrahydrouridine (THU) to inhibit cytidine deaminase (CDA), the enzyme that otherwise rapidly deaminates/inactivates decitabine, severely limiting its half-life, tissue distribution, and oral bioavailability. Oral decitabine doses, administered after oral THU 10 mg/kg, were escalated from a very low starting level (0.01, 0.02, 0.04, 0.08, or 0.16 mg/kg) to identify minimal doses active in depleting DNMT1 without cytotoxicity. Patients were SCD adults at risk of early death despite standard-of-care, randomized 3:2 to THU-decitabine versus placebo in 5 cohorts of 5 patients treated 2X/week for 8 weeks, with 4 weeks of follow-up. The primary endpoint was ≥ grade 3 non-hematologic toxicity. This endpoint was not triggered, and adverse events (AEs) were not significantly different in THU-decitabine-versus placebo-treated patients. At the decitabine 0.16 mg/kg dose, plasma concentrations peaked at approximately 50 nM (Cmax) and remained elevated for several hours. This dose decreased DNMT1 protein in peripheral blood mononuclear cells by >75% and repetitive element CpG methylation by approximately 10%, and increased HbF by 4%-9% (P < 0.001), doubling fetal hemoglobin-enriched red blood cells (F-cells) up to approximately 80% of total RBCs. Total hemoglobin increased by 1.2-1.9 g/dL (P = 0.01) as reticulocytes simultaneously decreased; that is, better quality and efficiency of HbF-enriched erythropoiesis elevated hemoglobin using fewer reticulocytes. Also indicating better RBC quality, biomarkers of hemolysis, thrombophilia, and inflammation (LDH, bilirubin, D-dimer, C-reactive protein [CRP]) improved. As expected with non-cytotoxic DNMT1-depletion, platelets increased and neutrophils concurrently decreased, but not to an extent requiring treatment holds. As an early phase study, limitations include small patient numbers at each dose level and narrow capacity to evaluate clinical benefits. CONCLUSION: Administration of oral THU-decitabine to patients with SCD was safe in this study and, by targeting DNMT1, upregulated HbF in RBCs. Further studies should investigate clinical benefits and potential harms not identified to date. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01685515.