Clinical activity, pharmacokinetics, and pharmacodynamics of oral hypomethylating agents for myelodysplastic syndromes/neoplasms and acute myeloid leukemia: A multidisciplinary review

OBJECTIVE

To review the pharmacokinetic (PK)-pharmacodynamic (PD) profiles, disease setting, dosing, and safety of oral and parenteral hypomethylating agents (HMAs) for the treatment of myelodysplastic syndromes/neoplasms (MDS) and acute myeloid leukemia (AML), and to provide a multidisciplinary perspective on treatment selection and educational needs relating to HMA use.

DATA SOURCES

Clinical and real-world data for parenteral decitabine and azacitidine and two oral HMAs: decitabine-cedazuridine (DEC-C) for MDS and azacitidine (CC-486) for AML maintenance therapy.

DATA SUMMARY

Differences in the PK-PD profiles of oral and parenteral HMA formulations have implications for their potential toxicities and planned use. Oral DEC-C (decitabine 35 mg and cedazuridine 100 mg) has demonstrated equivalent systemic area under the concentration-time curve (AUC) exposure to a 5-day regimen of intravenous (IV) decitabine 20 mg/m2 and showed no significant difference in PD. The AUC equivalence of oral DEC-C and IV decitabine means that these regimens can be treated interchangeably (but must not be substituted within a cycle). Oral azacitidine has a distinct PK-PD profile versus IV or subcutaneous azacitidine, and the formulations are not bioequivalent or interchangeable owing to differences in plasma time-course kinetics and exposures. Clinical trials are ongoing to evaluate oral HMA combinations and novel oral HMAs, such as NTX-301 and ASTX030.

CONCLUSIONS

Treatment with oral HMAs has the potential to improve quality of life, treatment adherence, and disease outcomes versus parenteral HMAs. Better education of multidisciplinary teams on the factors affecting HMA treatment selection may help to improve treatment outcomes in patients with MDS or AML.

Oral hypomethylating agents: beyond convenience in MDS

Oral hypomethylating agents (HMAs) represent a substantial potential boon for patients with myelodysplastic syndrome (MDS) who have previously required between 5 and 7 visits per month to an infusion clinic to receive therapy. For patients who respond to treatment, ongoing monthly maintenance visits represent a considerable burden to quality of life, and for those who are early in therapy, these sequential visits may tax transportation and financial resources that would be optimally distributed over the treatment cycle to facilitate transfusion support. The availability of oral HMAs may support the optimal application of these agents by contributing to adherence and lessening the burden of therapy, potentially encouraging patients to stay on longer-term treatment. Distinct pharmacokinetic profiles for the recently approved oral HMAs (oral azacitidine and decitabine-cedazuridine) result in differential toxicity profiles and have prompted their clinical trial development in lower- and higher-risk MDS, respectively.

Mass balance and metabolite profiling of 14C-guadecitabine in patients with advanced cancer

Purpose The objective of this mass balance trial was to determine the excretory pathways and metabolic profile of the novel anticancer agent guadecitabine in humans after administration of a 14C-radiolabeled dose of guadecitabine. Experimental design Included patients received at least one cycle of 45 mg/m2 guadecitabine subcutaneously as once-daily doses on Days 1 to 5 of a 28-day cycle, of which the 5th (last) dose in the first cycle was spiked with 14C-radiolabeled guadecitabine. Using different mass spectrometric techniques in combination with off-line liquid scintillation counting, the exposure and excretion of 14C-guadecitabine and metabolites in the systemic circulation, excreta, and intracellular target site were established. Results Five patients were enrolled in the mass balance trial. 14C-guadecitabine radioactivity was rapidly and almost exclusively excreted in urine, with an average amount of radioactivity recovered of 90.2%. After uptake in the systemic circulation, guadecitabine was converted into ß-decitabine (active anomer), and from ß-decitabine into the presumably inactive metabolites M1-M5. All identified metabolites in plasma and urine were ß-decitabine related products, suggesting almost complete conversion via cleavage of the phosphodiester bond between ß-decitabine and deoxyguanosine prior to further elimination. ß-decitabine enters the intracellular activation pathway, leading to detectable ß-decitabine-triphosphate and DNA incorporated ß-decitabine levels in peripheral blood mononuclear cells, providing confirmation that the drug reaches its DNA target site. Conclusion The metabolic and excretory pathways of guadecitabine and its metabolites were successfully characterized after subcutaneous guadecitabine administration in cancer patients. These data support the clinical evaluation of safety and efficacy of the subcutaneous guadecitabine drug product.

A Phase I Trial of a Guadecitabine (SGI-110) and Irinotecan in Metastatic Colorectal Cancer Patients Previously Exposed to Irinotecan

PURPOSE

Chemotherapeutic resistance eventually develops in all patients with metastatic colorectal cancer (mCRC). Gene silencing through promoter demethylation is one potential reversible mechanism of resistance with administration of hypomethylating agents. We evaluated the safety and tolerability of guadecitabine and irinotecan in patients with mCRC previously treated with irinotecan.

PATIENTS AND METHODS

In this 3+3 dose-escalation study, patients with mCRC previously exposed to irinotecan received guadecitabine days 1 to 5 of a 28-day cycle and irinotecan 125 mg/m2 days 8 and 15 [dose level (DL) 1, guadecitabine 45 mg/m2; DL -1: guadecitabine 30 mg/m2; DL -1G: guadecitabine 30 mg/m2 with growth factor support (GFS); DL 1G: guadecitabine 45 mg/m2 with GFS].

RESULTS

Twenty-two patients were treated across four DLs. Dose-limiting toxicities were neutropenic fever (DL 1 and -1G), biliary drain infection (DL -1), colonic obstruction (DL -1), and severe dehydration (DL 1G). Most common toxicities were neutropenia (82% any grade, 77% Grade 3/4), neutropenic fever (23%), leukopenia (73% any grade, 50% Grade 3/4), and injection site reactions (64% total, 0% Grade 3/4). Patients received a median of 4.5 cycles of treatment; 12/17 evaluable patients had stable disease as best response, with one having initial disease progression but subsequently durable partial response. Circulating tumor DNA showed decrease in global demethylation by LINE-1 after treatment.

CONCLUSIONS

We report the first study of chemo-priming with epigenetic therapy in gastrointestinal cancers. Guadecitabine 45 mg/m2 and irinotecan 125 mg/m2 with GFS was safe and tolerable in patients with mCRC, with early indication of benefit. These data have provided the basis for an ongoing phase II randomized, multicenter trial.

Oral Azacitidine (CC-486) for the Treatment of Myelodysplastic Syndromes and Acute Myeloid Leukemia

The myelodysplastic syndromes (MDS) comprise a heterogeneous group of clonal myeloid malignancies characterized by multilineage cytopenias, recurrent cytogenetic abnormalities, and risk of progression to acute myeloid leukemia (AML). AML, which can occur de novo as well as secondary to MDS, is characterized by malignant clones of myeloid lineage in the bone marrow and peripheral blood, with dissemination into tissues. The cytidine nucleoside analog and epigenetic modifier azacitidine is approved in the U.S. for the treatment of all French-American-British subtypes of MDS and in many countries for the treatment of AML with 20%-30% blasts and multilineage dysplasia according to the World Health Organization classification. Benefits of azacitidine treatment of patients with AML with >30% blasts have also been shown in a recent phase III trial. Oral administration of azacitidine may enhance patient convenience, eliminate injection-site reactions, allow for alternative dosing and scheduling, and enable long-term treatment. Phase I studies with oral azacitidine (CC-486) have shown biological activity, clinical responses, and tolerability in patients with MDS and AML. Extended dosing schedules of oral azacitidine (for 14 or 21 days of 28-day cycles) are currently under investigation as frontline therapy in patients with lower risk MDS, as maintenance therapy for patients with AML not eligible for stem cell transplant, and as maintenance therapy for patients with MDS or AML following stem cell transplant. This review presents clinical data supporting the use of injectable azacitidine in MDS and AML and examines the rationale for and results of the clinical development of oral azacitidine.

Pharmacokinetics and Pharmacodynamics with Extended Dosing of CC-486 in Patients with Hematologic Malignancies

CC-486 (oral azacitidine) is an epigenetic modifier in development for patients with myelodysplastic syndromes and acute myeloid leukemia. In part 1 of this two-part study, a 7-day CC-486 dosing schedule showed clinical activity, was generally well tolerated, and reduced DNA methylation. Extending dosing of CC-486 beyond 7 days would increase duration of azacitidine exposure. We hypothesized that extended dosing would therefore provide more sustained epigenetic activity. Reported here are the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of CC-486 extended dosing schedules in patients with myelodysplastic syndromes (MDS), chronic myelomonocytic leukemia (CMML) or acute myeloid leukemia (AML) from part 2 of this study. PK and/or PD data were available for 59 patients who were sequentially assigned to 1 of 4 extended CC-486 dosing schedules: 300mg once-daily or 200mg twice-daily for 14 or 21 days per 28-day cycle. Both 300mg once-daily schedules and the 200mg twice-daily 21-day schedule significantly (all P < .05) reduced global DNA methylation in whole blood at all measured time points (days 15, 22, and 28 of the treatment cycle), with sustained hypomethylation at cycle end compared with baseline. CC-486 exposures and reduced DNA methylation were significantly correlated. Patients who had a hematologic response had significantly greater methylation reductions than non-responding patients. These data demonstrate that extended dosing of CC-486 sustains epigenetic effects through the treatment cycle.

Phase 1 dose escalation trial of ilorasertib, a dual Aurora/VEGF receptor kinase inhibitor, in patients with hematologic malignancies

BACKGROUND

Ilorasertib (ABT-348) is a novel inhibitor of Aurora kinase, vascular endothelial growth factor (VEGF) and platelet-derived growth factor receptors, and the Src families of tyrosine kinases. Ilorasertib alone or in combination with azacitidine demonstrated activity in preclinical models in various hematological malignancies, indicating that pan-Aurora kinase and multiple kinase inhibition may have preferential antileukemic activity. This phase 1 trial determined the safety, pharmacokinetics, and preliminary antitumor activity of ilorasertib alone or combined with azacitidine in advanced hematologic malignancies.

PATIENTS AND METHODS

Fifty-two patients (median age, 67 years; 35 % with >4 prior regimens) with acute myelogenous leukaemia (AML; n = 38), myelodysplastic syndrome (n = 12), or chronic myelomonocytic leukaemia (n = 2) received 3 or 6 doses of ilorasertib per 28-day cycle and were assigned to arm A (once-weekly oral), B (twice-weekly oral), C (once-weekly oral plus azacitidine), or D (once-weekly intravenous) treatment.

RESULTS

Maximum tolerated doses were not determined; the recommended phase 2 oral monotherapy doses were 540 mg once weekly and 480 mg twice weekly. The most common grade 3/4 adverse events were hypertension (28.8 %), hypokalemia (15.4 %), anemia (13.5 %), and hypophosphatemia (11.5 %). Oral ilorasertib pharmacokinetics appeared dose proportional, with a 15-hour half-life and no interaction with azacitidine. Ilorasertib inhibited biomarkers for Aurora kinase and VEGF receptors, and demonstrated clinical responses in 3 AML patients.

CONCLUSIONS

Ilorasertib exhibited acceptable safety and pharmacokinetics at or below the recommended phase 2 dose, displayed evidence of dual Aurora kinase and VEGF receptor kinase inhibition, and activity in AML.

A phase I trial of two sequence-specific schedules of decitabine and vorinostat in patients with acute myeloid leukemia

This phase I trial evaluated two schedules of escalating vorinostat in combination with decitabine every 28 days: (i) sequential or (ii) concurrent. There were three dose-limiting toxicities: grade 3 fatigue and generalized muscle weakness on the sequential schedule (n = 1) and grade 3 fatigue on the concurrent schedule (n = 2). The maximum tolerated dose was not reached on both planned schedules. The overall response rate (ORR) was 23% (three complete response [CR], two CR with incomplete incomplete blood count recovery [CRi], one partial response [PR] and two morphological leukemic free state [MLFS]). The ORR for all and previously untreated patients in the sequential arm was 13% (one CRi; one MLFS) and 0% compared to 30% (three CR; one CRi; one PR; one MLFS) and 36% in the concurrent arm (p = 0.26 for both), respectively. Decitabine plus vorinostat was safe and has clinical activity in patients with previously untreated acute myeloid leukemia. Responses appear higher with the concurrent dose schedule. Cumulative toxicities may limit long-term usage on the current dose/schedules.

A phase I study in patients with solid or hematologic malignancies of the dose proportionality of subcutaneous Azacitidine and its pharmacokinetics in patients with severe renal impairment

STUDY OBJECTIVE

To assess the dose proportionality of azacitidine pharmacokinetics (PK) after single subcutaneous (SC) doses of 25-100 mg/m2, and determine the effect of renal impairment on PK after single and multiple 75 mg/m2 SC azacitidine doses.

DESIGN

Multicenter, phase I, open-label, parallel group study.

SETTING

Community clinics and major academic centers.

PATIENTS

Twenty-seven patients with solid or hematologic malignancies.

INTERVENTIONS

Part 1 evaluated azacitidine dose proportionality in patients with normal renal function randomized to single 25, 50, 75, or 100 mg/m2 SC doses. The 75 mg/m2 dosing group received 4 additional days of SC azacitidine. In Part 2, patients with severe renal impairment (creatinine clearance < 30 ml/min/1.73 m2 Cockcroft-Gault adjusted) received azacitidine 75 mg/m2 for 5 consecutive days.

MEASUREMENTS AND MAIN RESULTS

PK parameters were determined using noncompartmental methods. In patients with normal renal function (n=21), azacitidine area under the plasma-time curve (AUC0-∞) and maximum observed plasma concentration (Cmax) were dose proportional within the 25-100 mg/m2 range. Concentration versus time profiles after single and multiple azacitidine 75 mg/m2 doses were similar in shape for patients with normal (n=6) or impaired renal function (n=6), with higher mean concentrations in the latter group. Higher mean exposures (AUC0-∞ and Cmax) in renally impaired patients were observed; however, individual exposure values were, with few exceptions, within the same range in both groups. No drug accumulation after multiple doses was observed in either group. Terminal half-life and time to maximum plasma concentration were comparable between groups. Azacitidine tolerability was similar in patients with normal or impaired renal function.

CONCLUSION

Azacitidine is dose proportional over the 25-100 mg/m2 dosing range. Overall, renal impairment had no important effect on azacitidine PK. Therefore, no initial azacitidine dose adjustment in patients with renal impairment is required.

Demethylation of DNA by decitabine in cancer chemotherapy

Genes involved in all aspects of tumor development and growth can become aberrantly methylated in tumor cells, including genes involved in apoptosis and cell cycle regulation. Decitabine, 2'-deoxy-5-azacytidine, can inhibit DNA methyltransferases and reverse epigenetic silencing of aberrantly methylated genes. Nucleoside DNA methyltransferase inhibitors, such as decitabine, have been reported to have antitumor activity, especially against hematologic malignancies. Such demethylating agents have been proposed to reactivate tumor suppressor genes aberrantly methylated in tumor cells, leading to inhibition of tumor growth. An important consequence of this is that, unlike conventional cytotoxic agents, it may be best to use such drugs at concentrations lower than the maximum tolerated dose and in a manner dependent on their demethylating activity. Furthermore, synergistic activity with other types of investigational epigenetic therapies and existing chemotherapies opens the possibility of rational combinations and scheduling of these agents based on their biologic activity.

Development of a supercritical fluid chromatography-tandem mass spectrometry method for the determination of azacitidine in rat plasma and its application to a bioavailability study

Azacitidine is widely used for the treatment of myelodysplastic syndromes (MDS) and acute myelogenous leukaemia (AML). The analysis of azacitidine in biological samples is subject to interference by endogenous compounds. Previously reported high-performance liquid chromatography/tandem mass spectrometric (HPLC-MS/MS) bioanalytical assays for azacitidine suffer from expensive sample preparation procedures or from long separation times to achieve the required selectivity. Herein, supercritical fluid chromatography with tandem mass spectrometry (SFC-MS/MS) was explored as a more promising technique for the selective analysis of structure-like or chiral drugs in biological matrices. In this study, a simple, rapid and specific SFC/MS/MS analytical method was developed for the determination of azacitidine levels in rat plasma. Azacitidine was completely separated from the endogenous compounds on an ACQUITY UPLC™ BEH C₁₈ column (100 mm × 3.0 mm, 1.7 μm; Waters Corp., Milford, MA, USA) using isocratic elution with CO₂/methanol as the mobile phase. The single-run analysis time was as short as 3.5 min. The sample preparation for protein removal was accomplished using a simple methanol precipitation method. The lower limit of quantification (LLOQ) of azacitidine was 20 ng/mL. The intra-day and inter-day precisions were less than 15%, and the relative error (RE) was within ±15% for the medium- and high-concentration quality control (QC) samples and within ±20% for the low-concentration QC samples. Finally, the developed method was successfully applied to a pharmacokinetic study in rats following the intravenous administration of azacitidine.

Remodeling genomes with artificial transcription factors (ATFs)

Chromatin structure plays a pivotal role in defining which regions of the genome are accessible for effective transcription. Chromatin-remodeling agents are able to relax this structure, facilitating the access of transcription factors into the DNA. Herein, we describe a new method, which combines artificial transcription factors (ATFs) and chromatin-remodeling agents to specifically reactivate silenced regions of the genome and reprogram cellular phenotypes.

A phase II study of 5-day intravenous azacitidine in patients with myelodysplastic syndromes

The approved 7-day schedule of subcutaneous azacitidine for myelodysplastic syndrome is associated with injection site reactions and bruising and may be inconvenient because of the need for weekend doses. Although pharmacokinetic data with IV azacitidine suggests equivalence, there are no efficacy data published. Patients with all myelodysplastic syndromes (MDS) FAB subtypes were enrolled and received 75 mg/m(2)/d of azacitidine by 20-min intravenous infusion for 5 days in every 28 days. Global methylation studies were performed at baseline and prior to Cycle 3. Twenty-five patients were enrolled and 22 were evaluable. Median age was 69.5 years; 9 (41%) patients had lower-risk disease (IPSS Low or Int-1) and 13 (59%) had higher-risk disease (IPSS Int-2 or High). Twenty-seven percent of patients responded (5 CRs and 1 PR). The median time to response was 108 days. The median PFS was 339 days (11.3 months), the median OS was 444 days (14.8 months) and the median duration of response (DOR) was 450 days (15.0 months). Global methylation studies suggest a greater degree of demethylation in responders. This regimen appeared to offer a PR + CR rate and median DOR somewhat similar to what has been reported with the 7-day subcutaneous regimen; however, OS was shorter.

Evolution of decitabine development: accomplishments, ongoing investigations, and future strategies

Decitabine (5-aza-2'-deoxycytidine) is a hypomethylating agent with a dual mechanism of action: reactivation of silenced genes and differentiation at low doses, and cytotoxicity at high doses. The original studies in the 1980s used decitabine as a classical anticancer drug, at its maximum clinically tolerated dose, 1500 to 2500 mg/m(2) per course. At these doses, decitabine was found to be active in leukemia, but was associated with delayed and prolonged myelosuppression. After a better understanding of epigenetics in cancer and the role of decitabine in epigenetic (hypomethylating) therapy was gained, it was reevaluated at approximately 1/20th of the previous doses (ie, at 'optimal biologic' doses that modulate hypomethylation). In these dose schedules of decitabine (100 to 150 mg/m(2) per course), the drug was found to be active with manageable side effects in patients with myelodysplastic syndromes (MDS) and other myeloid tumors. Optimizing dosing schedules of decitabine to maximize hypomethylation (low dose, high dose intensity, and multiple cycles) have further improved results, suggesting that decitabine is an active therapy that alters the natural course of MDS. Combination therapies that augment the epigenetic effect of decitabine will likely improve responses and extend its use for the treatment of other malignancies.

Oral decitabine reactivates expression of the methylated gamma-globin gene in Papio anubis

The silencing of tumor suppressor genes associated with increased DNA methylation of the promoter regions is a frequent observation in many forms of cancer. Reactivation of these genes using pharmacological inhibitors of DNA methyltransferase such as 5-aza-2'-deoxycytidine (decitabine) is a worthwhile therapeutic goal. The effectiveness and tolerability of low-dose intravenous and subcutaneous decitabine regimens to demethylate and reactivate expression of the methylated gamma-globin gene in baboons and in patients with sickle cell disease led to successful trials of low-dose regimens of this drug in patients with myelodysplastic syndrome. Since these low-dose regimens are well-tolerated with minimal toxicity, they are suitable for chronic dosing to maintain promoter hypomethylation and expression of target genes. The development of an orally administered therapy using DNA methyltransferase inhibitors would facilitate such chronic approaches to therapy. We tested the ability of decitabine and a new salt derivative, decitabine mesylate, to reactivate the methylated gamma-globin gene in baboons when administered orally. Our results demonstrate that oral administration of these drugs at doses 17-34 times optimal subcutaneous doses of decitabine reactivates fetal hemoglobin, demethylates the epsilon- and gamma-globin gene promoters, and increases histone acetylation of these promoters in baboons (Papio anubis).

Phase I Study of Decitabine Alone or in Combination With Valproic Acid in Acute Myeloid Leukemia

Purpose

To determine an optimal biologic dose (OBD) of decitabine as a single agent and then the maximum-tolerated dose (MTD) of valproic acid (VA) combined with decitabine in acute myeloid leukemia (AML).

Patients and Methods

Twenty-five patients (median age, 70 years) were enrolled; 12 were untreated and 13 had relapsed AML. To determine an OBD (based on a gene re-expression end point), 14 patients received decitabine alone for 10 days. To determine the MTD, 11 patients received decitabine (at OBD, days 1 through 10) plus dose-escalating VA (days 5 through 21).

Results

The OBD of decitabine was 20 mg/m2/d intravenously, with limited nonhematologic toxicity. In patients treated with decitabine plus VA, dose-limiting encephalopathy occurred in two of two patients at VA 25 mg/kg/d and one of six patients at VA 20 mg/kg/d. Drug-induced re-expression of estrogen receptor (ER) was associated with clinical response (P ≤ .05). ER promoter demethylation, global DNA hypomethylation, depletion of DNA methyltransferase enzyme, and histone hyperacetylation were also observed. In an intent-to-treat analysis, the response rate was 44% (11 of 25). Of 21 assessable patients, 11 (52%) responded: four with morphologic and cytogenetic complete remission (CR; each had complex karyotype), four with incomplete CR, and three with partial remission. In untreated AML, four of nine assessable patients achieved CR. Clinical responses appeared similar for decitabine alone or with VA.

Conclusion

Low-dose decitabine was safe and showed encouraging clinical and biologic activity in AML, but the addition of VA led to encephalopathy at relatively low doses. On the basis of these results, additional studies of decitabine (20 mg/m2/d for 10 days) alone or with an alternative deacetylating agent are warranted.

Pharmacokinetics of decitabine administered as a 3-h infusion to patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS)

PURPOSE

In this study, pharmacokinetics (PK) of decitabine administered as a 3-h intravenous infusion of 15 mg/m2 every 8 h for 3 days (cycles repeated every 6 weeks) was evaluated in patients with MDS or AML.

METHODS

The PK of this dosing regimen was evaluated in sixteen patients with MDS or AML. Plasma samples were obtained pre-dose and during the first 8-h dosing interval on each dosing day during Cycle 1, and at pre-dose and just prior to the end of infusion during Cycle 2. PK samples were assayed for decitabine by a sensitive and specific validated liquid chromatography-tandem mass spectrometry method.

RESULTS

The mean maximum observed plasma concentration (Cmax), 64.8-77.0 ng/ml, and the mean area under the plasma concentration-time curve (AUC0-infinity), 152-163 ng h/ml, were unchanged during dosing of decitabine for 3 days. The time to the maximum concentration (Tmax) generally occurred at the end of infusion. The mean values for terminal phase elimination half-life (0.62-0.78 h), total body clearance (125-132 l/h per m2), and volume of distribution at steady state (62.7-89.2 l/m2), remained unchanged during the every 8 h dosing (P>0.05). Cycles 1 and 2 Cmax values for days 1, 2, and 3 were not significantly different as determined by paired two-tailed t test (P>0.05). The primary toxicity of decitabine was myelosuppression, which was observed in all patients. Two deaths, from sepsis, were considered possibly related to decitabine.

CONCLUSIONS

Decitabine dosed at 15 mg/m2 iv every 8 h for 3 days resulted in a predictable and manageable toxicity profile in patients with MDS/AML. The repeated dosing did not result in systemic accumulation of the drug, and decitabine PK remained unchanged from cycle to cycle.

Azacitidine pharmacokinetics in an adolescent patient with renal compromise

Azacitidine pharmacokinetic parameters in adolescent patients with renal compromise are not available from the medical literature. We describe a 14-year-old with myelodysplastic syndrome treated with subcutaneous 5-azacitidine for disease relapse 2 years after hematopoietic stem cell transplant. Because of renal compromise, malnutrition, and poor functional status, pharmacokinetic parameters were projected from existing literature data to select the patient's first azacitidine treatment course (1.5 mg/kg/d for 7 d). Posttreatment azacitidine plasma concentrations used to calculate patient-specific pharmacokinetic parameters corroborated initial estimates and systemic exposure associated with therapeutic benefit in adults and permitted individualization of treatment.

Decitabine and vitamin D3 differentially affect hematopoietic transcription factors to induce monocytic differentiation

Standard chemotherapy is not curative for many patients with acute myeloid leukemia (AML). New treatment strategies combining demethylating agents, such as decitabine, and drugs that induce myelomonocytic differentiation (i.e. Vitamin D3) may re-establish functional hematopoiesis in these patients. We studied the effects of decitabine alone or in combination with Vitamin D3 (VD3) on U937 cells and AML blasts. Preincubation with decitabine (0.1-1 microM) and subsequent exposure to VD3 (3 nM) synergistically induced monocytic differentiation. To elucidate the mechanisms of decitabine- and VD3-induced monocytic differentiation, we investigated the effects of the two drugs on transcription factors implicated in monocytic differentiation. Northern and Western blotting showed that decitabine induced transcription of c-jun but not PU.1, while VD3 increased PU.1, IRF8, and C/EBPbeta but not c-jun. Using electromobility shift assays, we demonstrated increased DNA binding of nuclear proteins from decitabine- and VD3-induced U937 cells to the CD11b promoter. In addition, we investigated whether the myeloid transcription factor Sp1 played a role in decitabine- and VD3-induced CD14 expression. Indeed, we found that mithramycin A, a specific inhibitor of Sp1, inhibited both VD3- and decitabine-induced upregulation of CD14, which is in line with previous data showing that Sp1 is critical for CD14 promoter activity. Induction of CD11b and/or CD14 by decitabine and/or VD3 was confirmed in primary AML patient samples at the time of diagnosis. In conclusion, decitabine synergizes with Vitamin D3 to induce CD11b and CD14 expression, likely by enhancing PU.1/c-jun and Sp1 transcriptional activity.

Combined DNA methyltransferase and histone deacetylase inhibition in the treatment of myeloid neoplasms

Optimal reexpression of most genes silenced through promoter methylation requires the sequential application of DNA methyltransferase inhibitors followed by histone deacetylase inhibitors in tumor cell cultures. Patients with myelodysplastic syndrome or acute myeloid leukemia (AML) were treated with the methyltransferase inhibitor 5-azacitidine (aza-CR) followed by the histone deacetylase inhibitor sodium phenylbutyrate. Major responses associated with cytogenetic complete response developed in patients receiving prolonged dosing schedules of aza-CR. Bisulfite sequencing of the p15 promoter in marrow DNA during the first cycle of treatment showed heterogeneous allelic demethylation in three responding patients, suggesting ongoing demethylation within the tumor clone, but no demethylation in two nonresponders. Six of six responding patients with pretreatment methylation of p15 or CDH-1 promoters reversed methylation during the first cycle of therapy (methylation-specific PCR), whereas none of six nonresponders showed any demethylation. Gene demethylation correlated with the area under the aza-CR plasma concentration-time curve. Administration of both drugs was associated with induction of acetylation of histones H3 and H4. This study provides the first demonstration that molecular mechanisms responsible for responses to DNA methyltransferase/histone deacetylase inhibitor combinations may include reversal of aberrant epigenetic gene silencing. The promising percentage of major hematologic responses justifies the testing of such combinations in prospective randomized trials.

A pharmacodynamic study of 5-azacytidine in the P39 cell line

OBJECTIVE

5-azacytidine (azacytidine), a DNA hypomethylating agent, was recently approved as the first therapeutic agent for the treatment of myelodysplastic syndromes. The present subcutaneous dosing schedule, 75 mg/m(2) for 7/28 days, is based on early clinical studies and may constitute a practical problem for patients. The present in vitro study aimed at evaluating the pharmacodynamics of azacytidine, thereby providing a rationale for clinical dose-finding studies.

METHODS

P39 cells were incubated with 0.1, 0.5, and 1 microM azacytidine daily for 24, 48, and 72 hours, followed by 48 hours in drug-free medium. The effects of azacytidine on cell growth, proliferation, apoptosis, cell cycle status, and promoter methylation of E-cadherin, ER, and HIC genes were studied.

RESULTS

Azacytidine decreased cell growth and proliferation, increased apoptosis, and affected cell cycle status in a dose-dependent manner. However, the exposure time, 24 to 72 hours, at doses between 0.5 and 1 microM, did not significantly affect any of these variables. Using first-order exponential pharmacokinetic model, we found that the effect of 1, 2, or 3 microM over 24 hours did not differ from that of 0.5 to 1 microM given over 48 to 72 hours. Induction of promoter hypomethylation was observed already after 24 hours of exposure with >or=0.5 microM azacytidine with no clear dose-effect relationship.

CONCLUSION

Our results indicate that optimal cellular effects of azacytidine might be achieved by shorter exposure times. The model provides information about the relation between azacytidine dose intensity and exposure time on malignant myeloid cells, which could serve as a rationale for further clinical development of practical, safe, and cost-effective dosing schedules.

Characterization of decomposition products and preclinical and low dose clinical pharmacokinetics of decitabine (5-aza-2'-deoxycytidine) by a new liquid chromatography/tandem mass spectrometry quantification method

Aberrant DNA methylation patterns resulting in gene transcriptional repression are observed in numerous cancers. Decitabine, a DNA methyltransferase inhibitor, is being clinically evaluated in patients with hematologic malignancies and solid tumors. Decitabine is rather unstable and decomposes to 1-beta-D-2'-deoxyribofuranosyl-3-guanylurea under basic conditions and several additional unknown products under neutral conditions. This has greatly limited application of pharmacokinetic assays to clinical development of decitabine. In this paper, a high-performance liquid chromatography/ultraviolet multi-stage mass spectrometry (HPLC-UV-MSn) study of the decomposition of decitabine in water and human plasma revealed that these previously unknown products are isomers of the intermediates formyl-1-beta-D-2'-deoxyribofuranosyl-3-guanylurea and 1-beta-D-2'-deoxyribofuranosyl-3-guanylurea. A HPLC tandem mass spectrometry (MS/MS) method for the determination of decitabine concentrations in human and rat plasma has been developed. This method was based on a specific fragmentation pathway of the molecular ion of decitabine at m/z 229 to generate a unique fragment ion at m/z 113 under collision-induced dissociation. Separation of decitabine and the stable internal standard dihydro-5-aza-cytidine from the endogenous interfering substance in plasma extract was carried out on a C18 Aquasil column under an isocratic elution with a mobile phase consisting of 5% water/acetonitrile and 10 mM ammonium formate. The detection of decitabine was via selected reaction monitoring (SRM, 229 > 113), and its ionization was enhanced by post-column addition of acetonitrile. Effects of sample preparation and handling parameters on the stability of decitabine were also evaluated in human plasma at various temperatures. The accuracy and precision of this assay showed a coefficient of variation of <15% over the range of 0.5-25 ng for rat plasma and 0.1-25 ng for human plasma injected on-column. Pharmacokinetics of decitabine in rats following intravenous doses of 1.0 and 5.0 mg/kg were characterized. In the rat, plasma concentration-time profiles were found to follow a biexponential decline and the pharmacokinetics was dose-independent. Application of this decitabine pharmacokinetic assay to human studies is therefore justified and ongoing.

Decitabine

Decitabine is a hypomethylating agent. Its action in DNA leads to the reactivation of tumour suppressor genes and the subsequent differentiation of cancer cells. In a randomised, phase III trial in patients (n = 170) with myelodysplastic syndromes (MDS), intravenous decitabine (45 mg/m(2)/day for 3 consecutive days every 6 weeks) combined with supportive care achieved a higher response rate (including eight complete and seven partial responses) than supportive care alone, which achieved no responses (17% vs 0%; p < 0.001). The median times to response and duration of response were 3.3 and 10.3 months in the phase III trial. In three phase II studies in patients (n = 29-87) with MDS treated with decitabine (40 or 50 mg/m(2)/day for 3 days every 5-6 weeks), the percentage of patients achieving a complete or partial response or an improvement ranged from 26% to 49%, and the median duration of response or improvement ranged from 4.9 to 8.3 months. The main adverse event associated with decitabine is myelosuppression.

Azacitidine: a novel agent for myelodysplastic syndromes

PURPOSE

The pharmacology, pharmacokinetics, clinical efficacy, dosage and administration, and safety of azacitidine are reviewed.

SUMMARY

Azacitidine is the first drug in a new class of compounds, known as DNA hypomethylating agents, to receive FDA-approved labeling for the treatment of myelodysplastic syndromes. It exerts its antineoplastic activity by causing a direct cytotoxic effect on abnormally proliferating hematopoietic cell lines by interfering with nucleic acid metabolism. Azacitidine is rapidly absorbed following subcutaneous injection, with peak plasma concentrations achieved within 30 minutes of administration. Based on promising results in Phase I-II testing, azacitidine entered Phase III testing in all subtypes of myelodysplastic syndromes. Azacitidine was compared with best supportive care, the previous standard therapy for myelodysplastic syndromes, demonstrating improvements in hematologic response, delaying time to progression to acute myelogenous leukemia, and increasing overall survival. Azacitidine is available as sterile lyophilized powder in single-use vials for reconstitution. The recommended dosage of azacitidine for the first treatment cycle is 75 mg/m(2) daily for seven days. The treatment cycle should be repeated every four weeks for a minimum of four cycles. Overall, azacitidine appears to be well tolerated, with the most common adverse effects being myelosuppression, nausea, and vomiting.

CONCLUSION

Azacitidine is the first DNA hypomethylating agent approved by FDA for the treatment of myelodysplastic syndromes and has demonstrated superior efficacy and improvements in patients' quality of life and bone marrow function over supportive care.

Pharmacology of 5-Aza-2'-deoxycytidine (decitabine)

The preclinical pharmacology of 5-aza-2'-deoxycytidine (decitabine, 5AZA-CdR) is reviewed. 5AZA-CdR, an analogue of deoxycytidine, is a prodrug that requires metabolic activation by deoxycytidine kinase. The active inhibitor in the cell is its triphosphate form (5AZA-dCTP), which incorporates very readily into DNA to produce an inhibition of DNA methyltransferase. The mechanism responsible for the antileukemic action of 5AZA-CdR is related to its reversal of epigenetic silencing by aberrant DNA methylation of genes that suppress leukemiogenesis. 5AZA-CdR is an S-phase-specific agent. At concentrations in the range of micromolars this analogue can induce terminal differentiation and loss of clonogenicity of human leukemic cells. Drug resistance to 5AZA-CdR occurs primarily by reduction in deoxycytidine kinase activity or increase in the activity of cytidine deaminase, the enzyme that inactivates this analogue. 5AZA-CdR is a very potent antileukemic agent in animal models, more effective than the related antileukemic drug, cytosine arabinoside. In humans, 5AZA-CdR has a short half-life of 15 to 25 minutes due to rapid inactivation by liver cytidine deaminase. The major toxicity produced by 5AZA-CdR is myelosuppression. Preliminary clinical studies in patients with hematologic malignancies indicate that 5AZA-CdR is an active chemotherapeutic agent. The optimal dose-schedule for this interesting epigenetic agent with a novel mechanism of action remains to be determined. Translation of the pharmacology of 5AZA-CdR into therapeutic regimens based on scientific rationale can be used to obtain this objective.

5-azacytidine and decitabine monotherapies of myelodysplastic disorders

OBJECTIVE

To review and differentiate the pharmacology, toxicology, pharmacokinetics, and results of major clinical trials of 5-azacytidine (5-AzaC) and 5-aza-2'-deoxycytidine (decitabine) therapy of myelodysplastic disorders.

DATA SOURCES

A PubMed/MEDLINE search was conducted (1966-October 2004) using the following terms: DNA methylation, myelodysplastic disorders, 5-azacytidine, and 5-aza-2'-deoxycytidine (decitabine). Additional data sources included bibliographies from identified articles and manufacturer information.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials for the treatment of various malignancies by hypomethylating agents were selected from data sources. All published, major clinical trials evaluating 5-AzaC or decitabine in myelodysplastic disorders and transformed myeloid leukemia treatment were included.

DATA SYNTHESIS

Myelodysplastic disorders are a group of bone marrow stem cell hyperplasias and dysplasias that result in ineffective hematopoiesis. Myelodysplastic disorders and transformed leukemia have poor prognosis and minimal response to chemotherapy. DNA hypomethylating agents have been shown to improve overall response rates (increased neutrophil, leukocyte, and platelet counts), time to leukemic progression, and quality of life compared with supportive therapy. The incidence of the most common adverse effects (nausea, vomiting, myelosuppression) can be reduced by low-dose, continuous, or extended-interval infusion.

CONCLUSIONS

Since appropriate dosing schedules of decitabine are being investigated, comparison of the clinical effectiveness of 5-AzaC and decitabine would be premature at this time. DNA hypomethylating agents show promise as monotherapies of myelodysplastic disorders and transformed leukemia and may be useful as a component of combination chemotherapy of various malignancies.

Bioavailability of azacitidine subcutaneous versus intravenous in patients with the myelodysplastic syndromes

The primary objectives of this study were to characterize the absolute bioavailability of azacitidine after subcutaneous (SC) administration and to compare the single-dose pharmacokinetics of azacitidine following SC and intravenous (IV) administration. Six patients with myelodysplastic syndromes were randomly assigned according to a crossover design to treatment A, consisting of azacitidine administered as a single 75-mg/m(2) SC dose, or treatment B, consisting of azacitidine administered as a single 75-mg/m(2) IV infusion dose over 10 minutes. A minimum of 7 days and a maximum of 28 days were permitted between treatments. The study demonstrated good bioavailability of a SC azacitidine dose compared to an IV infusion treatment. The exposure profiles following SC drug administration illustrate measurable azacitidine levels with bioavailability (AUC) values within 89% of those measured following IV administration (range, 70%-112%). The median IV half-life was 0.36 +/- 0.02 hours compared to 0.69 +/- 0.14 hours for SC administration. Regardless of the route of administration, a single dose of azacitidine, 75 mg/m(2), was generally well tolerated.

Pharmacokinetics of 5-Azacitidine Administered With Phenylbutyrate in Patients With Refractory Solid Tumors or Hematologic Malignancies

Purpose

To characterize the pharmacokinetic behavior of 5-azacitidine (5-AC), a cytidine nucleoside analog, when given with phenylbutyrate, a histone deaceytlase inhibitor.

Patients and Methods

Pharmacokinetic data were obtained from two trials involving patients with solid tumor and hematologic malignancies. 5-AC at doses ranging from 10 to 75 mg/m2/d was administered once daily as a subcutaneous injection for 5 to 21 days in combination with phenylbutyrate administered as a continuous intravenous infusion for varying dose and duration every 28 or 35 days. Serial plasma samples were collected up to 24 hours after 5-AC administration. 5-AC was quantitated using a validated liquid chromatograph/tandem mass spectrometry method.

Results

5-AC was rapidly absorbed with the mean Tmaxoccurring at 0.47 hour. Average maximum concentration (Cmax) and area under the curve (AUC0-∞) values increased in a dose-proportionate manner with increasing dose from 10 to 75 mg/m2/d; the mean ± SD Cmaxand AUC0-∞at 10 mg/m2/d were 776 ± 459 nM and 1,355 ± 1,125 h*nM, respectively, and at 75 mg/m2/d were 4,871 ± 1,398 nM and 6,582 ± 2,560 h*nM, respectively. Despite a short terminal half-life of 1.5 ± 2.3 hours, inhibition of DNA methyl transferase activity in tumors of patients receiving 5-AC has been documented.

Conclusion

5-AC is rapidly absorbed and eliminated when administered subcutaneously. Sufficient 5-AC exposure is achieved to produce pharmacodynamic effects in tumors.

Quantification of 5-azacytidine in plasma by electrospray tandem mass spectrometry coupled with high-performance liquid chromatography

5-Azacytidine (5AC), a nucleoside analogue and hypomethylating agent, has anticancer properties and has been utilized in the treatment of various malignancies. 5AC is unstable and rapidly hydrolyzed to several by-products, including 5-azacytosine and 5-azauracil. A sensitive, reliable method was developed to quantitate 5AC using LC/MS/MS to perform pharmacokinetic and pharmacodynamic studies on 5AC combination therapy trials. Blood samples were collected in a heparinized tube and immediately processed for storage. To increase the stability of 5AC in plasma, 25 ng/mL tetrahydrouridine was added to the plasma and snap frozen. Plasma samples were extracted using acetonitrile then cleaned up by Oasis MCX ion exchange solid-phase extraction cartridges. 5AC was separated on an YMC Jsphr M80 C(18) column with gradient elution of ammonium acetate (2 mM) with 0.1% formic acid and methanol mobile phase. 5AC elutes at 5.0 +/- 0.2 min with a total run time of 30 min. Identification was through positive-ion mode and multiple reaction monitoring mode at m/z+ 244.9-->113.0 for 5AC and m/z+ 242.0-->126.0 for 5-methyl-2'-deoxycytidine, the internal standard. The lower limit of quantitation of 5AC was 5 ng/mL in human plasma, and linearity was observed from 5 to 500 ng/mL fitted by linear regression with 1/x weight. This method is 50 times more sensitive than previously published assays and successfully allows studies to characterize the pharmacokinetics and pharmacodynamics of 5AC.

Azacitidine

Azacitidine, a pyrimidine analogue, is an antineoplastic agent that acts mainly by causing hypomethylation of cytosine residues in newly replicated DNA and has shown efficacy in the treatment of myelodysplatic syndromes (MDS). In a randomised controlled trial in patients with MDS (n=191), subcutaneous azacitidine 75-100 mg/m2/day in 7-day cycles every 28 days with continuing supportive care produced a significantly higher response rate (including reductions in rate of transformation to acute myeloid leukaemia and transfusion requirements) than that seen with supportive care alone (60% vs 5%; p<0.001). Patients (n=49) who were switched from supportive care to azacitidine after 4 months also showed a 47% response rate. The clinical response in patients receiving azacitidine was associated with significant (p<or=0.015) improvements in several measures of health-related quality of life, including those assessing fatigue and physical functioning, compared with those in supportive care recipients. Given the grim prognosis of MDS patients, azacitidine was generally well tolerated, with common, but transient, myelotoxicity. Adverse events did not increase in severity or frequency during the course of the treatment.

Decitabine. MGI Pharma Inc/SuperGen Inc

Decitabine is a DNA methyltransferase inhibitor under development by SuperGen Inc and MGI Pharma Inc for the potential treatment of a range of hematological malignancies, including myelodysplastic syndrome, solid tumors and sickle cell disease.

Decitabine

Decitabine [NSC 127716, DAC, dezocitidine, Aza dC, 2'-deoxy-5-azacytidine, Dacogen( trade mark )] is a deoxycytidine and cytarabine derivative with potent antileukaemic activity, originated by Pharmachemie. This antimetabolite is able to induce in vitro gene activation and cellular differentiation by a mechanism involving DNA hypomethylation. Decitabine has been studied in several phase II trials for solid tumours as well as in different types of leukaemia. The drug has been shown to have very limited efficacy against solid tumours. However, decitabine exhibits higher activity for the treatment of haematological malignancies. SuperGen announced that it had entered a Cooperative Research and Development Agreement (CRADA) with the US National Cancer Institute (NCI) in May 2000. SuperGen will supply decitabine to the NCI, which will initiate and sponsor clinical trials in patients with solid tumours and haematological malignancies. The NCI will also conduct studies on decitabine's mechanism of action. SuperGen had previously acquired worldwide rights to decitabine from Pharmachemie in the third quarter of 1999 for 4 million US dollars worth of SuperGen shares and income from manufacture upon the launch of decitabine. The drug is undergoing two phase II trials for the treatment of cytomegalovirus leukaemia (CML) in the US, one of which will assess the safety, response rate, duration of response, and survival of decitabine (injection) in combination with imatinib mesylate (oral). SuperGen initiated a phase II clinical study of decitabine in combination with imatinib mesylate in June 2003 that will be conducted under SuperGen's CRADA with the National Cancer Institute and will take place at the MD Anderson Cancer Center in the US. Approximately 80 patients with CML will be enrolled in the study. This followed on decitabine's orphan drug status for the same indication, which was granted by the US FDA in 2002. In addition, the European Commission has granted orphan drug status to decitabine for MDS treatment in February 2003. In March 2003, SuperGen announced that patient enrolment was completed for its open-label, phase III trial comparing decitabine with standard care therapy for treatment of advanced myelodysplastic syndrome, which was initiated in March 2001. The study will be conducted at 22 medical centres in the US and will enrol a total of 160 patients. A pivotal trial is also underway in Europe for the same indication and is aiming to enrol 220 patients. In addition, decitabine is undergoing phase II trials for the treatment of non-small cell lung cancer (NSCLC) in Canada and for prostate cancer in the US. In July 2003, SuperGen was issued a US patent relating to decitabine as part of a combination therapy with other anticancer agents to treat ovarian, breast, prostate, gastric, lung, pancreatic and colon cancers through the correction of DNA hypermethylation. SuperGen was issued a US patent (No. 6 191 119) in 2001 covering the use of decitabine in combination with rubitecan and antibiotic agents, including doxorubicin.

Pharmacological approach for optimization of the dose schedule of 5-Aza-2’-deoxycytidine (Decitabine) for the therapy of leukemia

5-Aza-2'-deoxycytidine (5-Aza-CdR; Decitabine) is an active antineoplastic agent in patients with leukemia. Since 5-Aza-CdR is an S phase specific agent and has a short plasma half-life, its antileukemic activity is dose schedule-dependent. Leukemia patients who are candidates for 5-Aza-CdR therapy following relapse after therapy with cytosine arabinoside are at greater risk for the problem of drug resistance since these cytosine nucleoside analogues are metabolized by the same enzymes. Due to its unique mechanism of action of demethylating DNA, 5-Aza-CdR has the potential to activate tumor (growth) suppressor and differentiation genes that have been accidentally silenced by DNA methylation in leukemic cells. All these factors should be taken into account in the design of the optimal dose schedule of this analogue. The optimal dose schedule of 5-Aza-CdR should be based on the kinetic parameters of deoxycytidine kinase, its pharmacokinetics, its effects on DNA methylation and the cell cycle parameters of the leukemic cells and the normal hematopoietic stem cells. Since granulocytopenia is the major toxic effect produced by 5-Aza-CdR, the use of hematopoietic growth factors to shorten the duration of leukopenia should be investigated. Another approach which we are investigating is to use the methods of gene therapy to insert the cytidine deaminase gene into normal hematopoietic progenitor cells so as to make them drug resistant to 5-Aza-CdR. The use of other agents that can induce the differentiation of leukemic cells in combination with 5-Aza-CdR may have the potential to increase the clinical effectiveness of this analogue for the therapy of leukemia.

Phase I and pharmacological trial of fazarabine (Ara-AC) with granulocyte colony-stimulating factor

Fazarabine (1-beta-D-arabinofuranosyl-5-aza-cytosine, or Ara-AC) is a nucleoside analogue that consists of the arabinoside ring of 1-beta-D-arabinofuranosylcytosine and the pyrimidine base of 5-azacytidine. In Phase I and Phase II trials, neutropenia was dose limiting, with minimal nonhematological toxicity. The in vitro cytotoxic concentrations of Ara-AC could not be achieved in these studies; neutropenia precluded dose escalation. The objectives of this study were: to determine either the maximum tolerated dose of Ara-AC or to safely achieve target plasma levels of 2-5 microgram/ml when Ara-AC was administered as a 24-h infusion with granulocyte colony-stimulating factor (G-CSF) to patients with advanced refractory malignancies; to characterize the pharmacokinetic behavior of Ara-AC with G-CSF; and to define the relationship of Ara-AC pharmacokinetics to toxicity. Twenty-four patients received 67 courses of Ara-AC at doses of 54-112 mg/m2/h. Dose-limiting toxicity was approached but not reached. Grade 3 or 4 neutropenia and nausea were the principle side effects. Steady-state plasma concentrations exceeded the minimum target concentration of 2 microgram/ml in all patients who received >/=78 mg/m2/h for 24 h. The maximum target concentration was approached during administration of 112 mg/m2/h for 24 h. The mean steady-state clearance was 475 +/- 103 ml/min/m2 and did not change with dose. One partial response was seen. One patient received 16 courses and another received 7 courses of therapy before progression. Ara-AC can be safely administered in doses that result in plasma concentrations of 2-5 microgram/ml, if it is given with G-CSF. Phase II trials of Ara-AC in selected malignancies are planned.

Cerebrospinal fluid pharmacokinetics and toxicology of intraventricular and intrathecal arabinosyl-5-azacytosine (fazarabine, NSC 281272) in the nonhuman primate

Arabinosyl-5-azacytosine (AAC), a new nucleoside antimetabolite, is broadly active in preclinical tumor screening evaluations. To assess the potential for intrathecal use of this drug, we studied the toxicity and pharmacokinetics of intrathecal and intraventricular administration in nonhuman primates. Four adult male rhesus monkeys were given single 10 mg intrathecal (n = 1) or intraventricular (n = 3) doses of AAC to determine its acute toxicity and pharmacokinetic parameters. An additional 3 animals were given four weekly 10 mg intrathecal doses to assess the systemic and neurologic toxicity associated with chronic administration. Disappearance from the cerebrospinal fluid (CSF) was biexponential, and CSF clearance was 0.2 ml/min, which exceeds the rate of CSF bulk flow by 5-fold. The peak CSF concentration and area under the concentration x time curve achieved with the intraventricular administration of 10 mg were one hundred, and fifty fold greater, respectively, than those achieved after an intravenous dose of 200 mg/kg (1500-2400 mg) in prior experiments. No clinically evident neurotoxicity was observed in either the single or the weekly x 4 dose groups. A slight, transient CSF pleocytosis and increased CSF protein was observed. Systemic toxicity was limited to one animal in the weekly x 4 dose group who demonstrated a mild and transient decrease in his peripheral leukocyte count unassociated with a change in his hematocrit or platelet count. These studies in nonhuman primates demonstrate a clear pharmacokinetic advantage for intrathecal vs systemic administration of AAC. This is demonstrated by a 50-fold greater CSF drug exposure with an intrathecal or intraventricular dose 1/200th of that which can be given systemically.(ABSTRACT TRUNCATED AT 250 WORDS)

2'-deoxy-5-azacytidine increases binding of cisplatin to DNA by a mechanism independent of DNA hypomethylation

The chemotherapeutic agents 2'-deoxy-5-azacytidine (DAC) and cisplatin (cDDP) have been shown in vitro to be synergystic in their cytotoxicity toward human tumour cells. We have investigated possible molecular mechanisms underlying this synergy using the plasmid pSVE3 in vitro and after transfection into CMT3 cells. Increased binding of cDDP to DAC-substituted DNA generated in vivo was confirmed by flameless atomic absorption spectrophotometry (FAAS). The plasmid used in these experiments was unmethylated suggesting that DAC was effective in enhancing cDDP binding to DNA without acting as a hypomethylating agent, but by directly changing the topology of DNA. The role of DNA methylation in cDDP binding was studied using methylated and unmethylated plasmid incubated in vitro with cDDP. Restriction analyses and FAAS measurement of bound platinum indicated that methylated DNA bound more cDDP than unmethylated DNA. In addition, in vivo studies confirmed the in vitro observations since replication of methylated plasmid was inhibited to a greater extent than unmethylated plasmid.

Clinical pharmacology of 1-beta-D-arabinofuranosyl-5-azacytosine (fazarabine) following 72-hour infusion

The clinical pharmacology of fazarabine (1-beta-D-arabinofuranosyl-5-azacytosine), a structural analogue of 1-beta-D-arabinofuranosylcytosine (ara-C) and 5-azacytidine, was assessed in 14 patients with various malignancies during a phase I trial. Since the starting dose for the protocol was low (0.2 mg/m2/hr over a 72-hr continuous iv infusion), a radioimmunoassay (RIA) using commercially available ara-C antibody and [3H]ara-C was developed to measure the anticipated low plasma drug levels. The assay could be used to measure fazarabine accurately in plasma and urine with a sensitivity of 0.08 ng/ml. The RIA does not require extraction of samples. Using both RIA and HPLC, similar results were obtained in plasma samples from a patient receiving a high dose (180 mg/m2/hr) of fazarabine. The assay is simple, sensitive, reproducible, and specific. Following the infusion, plasma levels declined triphasically with a terminal half-life of 5.7 +/- 2.0 hr. The AUC was linearly related to dose. When the various doses were normalized to 1.75 mg/m2/hr (the maximum tolerated dose as determined from the phase I trial) the mean AUC value was 4232 +/- 987 (ng/ml)hr. Plasma steady-state drug levels (CPss) were achieved in 2-4 hr and were linearly dependent to dose. Also, when normalized, the mean CPss was 58 +/- 13 ng/ml, which is within the reported concentration range necessary for inhibiting malignant cell growth. Total clearance was rapid, 528 +/- 138 ml/(m2.min), and not dose-related.

Phase I and pharmacokinetic study of arabinofuranosyl-5-azacytosine (fazarabine, NSC 281272)

A Phase I clinical trial of 1-beta-D-arabinofuranosyl-5-azacytosine (ara-AC or fazarabine) given as a 72-h continuous infusion on a 21-day cycle was conducted in 27 adult patients with refractory cancer. The major toxicity was reversible granulocytopenia and thrombocytopenia. Dose-limiting toxicity was observed at a dose rate of 1.96 mg/m2/h in which Grade IV leukopenia (WBC less than 1,000/mm3) occurred in 4 of 11 patients and Grade IV thrombocytopenia (platelets less than 25,000/mm3) occurred in 3 of 11 patients. Plasma steady-state levels ranged from 0.13 to 0.6 microM for doses of 1.25 to 5.94 mg/m2/h. Mean total body clearance was 647 ml/min/m2. Minor clinical responses were seen in one patient with testicular cancer, one patient with colon cancer, one patient with breast cancer, and one patient with acute nonlymphocytic leukemia. Another patient with adenocarcinoma of unknown primary had stable disease during 13 cycles of therapy. Based on the results of this study, the recommended dose for Phase II studies of 1-beta-D-arabinofuranosyl-5-azacytosine administered as a 72-h continuous infusion is 2.0 mg/m2/h (48 mg/m2/day).

Comparison of antineoplastic activity of cytosine arabinoside and 5-aza-2'-deoxycytidine against human leukemic cells of different phenotype

A comparison of the cellular and molecular pharmacology of the deoxycytidine analogues cytosine arabinoside (Ara-C) and 5-aza-2'-deoxycytidine (5-AZA-CdR) on human myeloid (HL-60), T-cell (Molt-3) and B-cell (RPMI-8392) leukemic cell lines was investigated. Ara-C was a more potent inhibitor of growth than 5-AZA-CdR. In a colony assay, 5-AZA-CdR was a more potent cytotoxic agent than Ara-C for both the myeloid and B-cell leukemic cells, but not for the T-cell leukemic cells. The total cellular uptake of 5-AZA-CdR was greater than Ara-C for the myeloid and B-cell leukemic cells, whereas for the T-cells the uptake of the arabinosyl analogue was greater. Ara-C produced a potent inhibition of DNA synthesis, whereas no inhibition was detected with 5-AZA-CdR during a short incubation. In contrast, 5-AZA-CdR produced a potent inhibition of DNA methylation whereas Ara-C produced a slight increase in the methylation of DNA. This study shows that there are significant differences in the antineoplastic activity of Ara-C and 5-AZA-CdR against human leukemic cell lines of different phenotype and that these differences are related to differences in the metabolism of these two deoxycytidine analogues and to their effects on DNA synthesis and methylation.

Phase I trial and pharmacokinetic evaluation of fazarabine in children

A phase I trial of fazarabine (1-beta-D-arabinofuranosyl-5-azacytosine, NSC 281272) administered as a 24-h continuous infusion was performed in 16 children with refractory malignancies. Dose-limiting toxicity consisting of reversible granulocytopenia and thrombocytopenia was observed in 4 of 4 solid tumor patients treated at the starting dose of 20 mg/m2/h. Subsequent patients were treated at a dose of 15 mg/m2/h which was determined to be the maximum tolerated dose. Moderate nausea and vomiting were the only other toxicities observed. Plasma steady-state concentrations of fazarabine were attained by 2-4 h in all patients and were 1.8 and 2.5 microM at the 15- and 20-mg/m2/h doses, respectively. The total body clearance of fazarabine was 571 and 550 ml/min/m2 at the 15- and 20-mg/m2/h doses, respectively. In three of four patients evaluated, fazarabine was detectable in the cerebrospinal fluid (CSF). Steady-state CSF concentrations ranged from 0.29 to 0.74 microM in these three individuals and the steady-state CSF:plasma ratios ranged from 0.22-0.25. Both the plasma and CSF steady-state concentrations were within the 0.1 to 1 microM range reported to be cytotoxic in vitro against the Molt-4 human T-lymphoblastic leukemia cell line. Based on the above, the optimal dose for phase II trials of fazarabine administered as a 24-h infusion is 15 mg/m2/h (360 mg/m2/day).

Cellular metabolism of 5,6-dihydro-5-azacytidine and its incorporation into DNA and RNA of human lymphoid cells CEM/O and CEM/dCk(-)

5,6-Dihydro-5-azacytidine (DHAC) is a hydrolytically stable analog of 5-azacytidine (5-aza-C) that has antileukemic activity against experimental leukemias and, like 5-aza-C, causes DNA hypomethylation. We report the cellular metabolism of DHAC and its incorporation into nucleic acids in the CCRF/CEM/O and deoxycytidine kinase mutant CCRF/CEM/dCk(-) human lymphoid cell lines. The cells were incubated with their respective IC50 concentrations for 24 h, then aliquot samples were removed at predetermined intervals and extracted for nucleotides. The acid-soluble extracts of the cells were assayed on HPLC for nucleotides of DHAC. The major anabolite of [3H]DHAC, [3H]DHACTP, peaked at 110.3 +/- 30.7 microM in CEM/O and at 96.3 +/- 41.9 microM in CEM/dCk(-) cells at 9 and 12 h, respectively. The intracellular concentrations of the deoxyribonucleoside triphosphate, [3H]DHAdCTP, peaked at 13.5 +/- 7.7 microM at 4 h in CEM/O and at 80.8 +/- 13.8 microM at 12 h, a 6-fold greater cellular concentration, in the dCk mutant cell line. The amount of DHAC anabolites incorporated into CEM/O nucleic acids reached a plateau in RNA at 552.6 +/- 7.8 pmol/10(7) cells and in DNA at 64.55 +/- 10.0 pmol/10(7) cells. In CEM/dCk(-) cells, DHAC anabolites reached a plateau in RNA and DNA at 4,256.3 +/- 631.0 and 395.5 +/- 145.4 pmol/10(7) cells, respectively. Thus, with equitoxic treatments of DHAC, the incorporation of its analog anabolites into RNA and DNA was 8- and 6-fold greater in CEM/dCk(-) cells. DNA methylation levels were depressed equally despite a 6-fold greater incorporation of the analog in DNA in the CEM/dCk(-) cells indicating that hypomethylation may be saturated after DHAC treatment. The DNA methylation levels reached a nadir of 0.19% and 0.20% methyl-C (percentage of methylation) in the two cell lines at 6 and 12 h after the beginning of drug treatment and remained relatively constant for the duration of the 24-h treatment. A curve-linear relationship was obtained between the DNA methylation levels in both cell lines and the amounts of DHAC anabolite incorporated into DNA.

Cellular metabolism of 1-beta-D-arabinofuranosyl-5-azacytosine and incorporation into DNA and RNA of human lymphoid CEM/0 and CEM/dCk(-) cells

1-beta-D-arabinosyl-5-azacytosine (ara-AC) is a relatively new antitumor agent under clinical investigation, which has the 2'-beta arabinosyl configuration found in the tumoricidal drug ara-C and the nitrogen substitution in the 5-position of the pyrimidine ring found in 5-azacytidine (5-aza-C). The present study examined the cellular metabolism and the effect on DNA methylation of ara-AC in human CCRF/CEM cells sensitive and resistant to ara-C. The triphosphate anabolite of the drug, ara-ACTP, was the major anabolite in the CEM cellular extracts, peaking at 50.6 +/- 23 microM 4 h after incubation with IC50 concentrations (0.25 microM) of [3H]ara-AC. The mono- and diphosphate anabolites accumulated 10-fold lower cellular concentrations than ara-ACTP. The nucleoside triphosphate (NTP) pools and, especially, cellular ATP declined significantly by 9 h after the initiation of drug treatment and remained depleted for the 24-h treatment. The drug anabolite was gradually incorporated into both RNA and DNA, peaking in CEM/0 at 3.44 and 0.14 nmol/10(7) cells, respectively. The DNA methylation levels in these cells declined rapidly after treatment with ara-AC, attaining a nadir plateau at 29% of control methylation value. The deoxycytidine kinase (dCK) mutant CEM cell line [CEM/dCk(-)] neither activated ara-AC at appreciable levels nor induced DNA hypomethylation at low concentrations (0.25-1 microM). However, the drug was activated at 0.2-1 microM extracellular concentrations of ara-AC, probably by an as yet unknown nucleoside kinase at approximately 10% of the amount in CEM/0 cells. Ara-AC appears to mediate its cytotoxic action through the accumulation of its triphosphate anabolite, ara-ACTP, and the subsequent incorporation into nucleic acids. DNA methylation may also contribute to its cytotoxicity.

Preclinical pharmacology of arabinosyl-5-azacytidine in nonhuman primates

The plasma and cerebrospinal fluid (CSF) pharmacokinetics of arabinosyl-5-azacytidine (AAC) were studied in rhesus monkeys following a 15-min, 1-h, or 12-h i.v. infusion of 200 mg/kg. No clinically significant toxicity was observed with these schedules. The plasma elimination of AAC is rapid and characterized by a triphasic decay with t1/2 alpha = 3.6-5.4 min, t1/2 beta = 18-24 min, and t1/2 gamma = 94-144 min for the above infusion schedules. The CSF penetration of AAC as measured by the CSF:plasma Css ratio for the 12-h infusion was 0.15. The stability of AAC in pooled plasma, phosphate buffered saline, and RPMI 1640 culture media at 37 degrees C was compared with the terminal half-life of AAC observed in vivo. The shorter in vitro AAC half-life in plasma with or without tetrahydrouridine versus that in phosphate buffered saline suggests that the terminal half-life of AAC in vivo is most likely a result of enhanced nucleophilic attack and hydrolytic degradation of the unstable triazine ring in plasma. A triexponential equation modeling the disappearance of AAC was constructed from the in vivo experimental data. Use of this equation in computer-aided simulations of current Phase I doses and schedules of AAC correctly predicts the human plasma concentrations which have been observed. The preclinical pharmacokinetic data provided here may be useful in helping to develop rational human studies with specific concentration x time goals.

[Prodrugs]

Prodrugs are pharmacologically inert and nontoxic chemical compounds which are transformed in vivo into pharmacologically and therapeutically active compounds, i.e. drugs. Prodrugs are used to solve problems which cannot be solved by the drugs themselves. There are three types of problems: problems arising before the drug enters the body (solubilization, stabilization and improved acceptability); problems associated with the penetration and fate of the drug in the body (absorption, barrier crossing, duration of action); problems relating to the therapeutic target (selective local delivery). The principal prodrugs that solve these problems and the mechanisms of the solutions they provide are described and discussed.

Biochemical pharmacology of 5,6-dihydro-5-azacytidine (DHAC) and DNA hypomethylation in tumor (L1210)-bearing mice

Dihydro-5-azacytidine (DHAC) is a hydrolytically stable congener of 5-azacytidine, which retains antileukemic activity against experimental leukemias. The biochemical pharmacology of DHAC was studied in tumor-bearing mice in order to elucidate the mode of action of this drug. We found that after an LD10 dose of DHAC, the plasma peak concentration achieved was 317 microM and was eliminated biexponentially, with a t1/2 alpha of 1.03 h and a t1/2 beta of 5 h. By 4 h, an unidentified metabolite of [3H]DHAC peaked and was eliminated biexponentially, with a t1/2 alpha of 1.06 h and a t1/2 beta of 10.6 h. [3H]DHACTP was the major anabolite in the L1210/0 cells, and was also eliminated biexponentially, with a t1/2 alpha of 4.3 h and a t1/2 beta of 12.2 h. An unknown anabolite of [3H]DHAC that eluted 5 min after [3H]DHACTP, between UTP and ATP, peaked at 3 h and could possibly be the deoxy-derivative [3H]DHAdCTP. A tissue distribution study revealed that the liver, L1210/0, and lung accumulate the most radioactivity per gram of wet tissue. Methylation studies showed that an LD10 dose of [3H]DHAC resulted in a 25.06% hypomethylation of DNA in L1210/0 cells and a 46.32% hypomethylation in a deoxycytidine kinase mutant cell line L1210/dCK(-), compared with their respective controls.

Biochemistry of azacitidine: a review

Azacitidine is a pyrimidine ring analog of cytidine that is incorporated into RNA causing alteration in RNA synthesis and processing and resulting in inhibition of protein synthesis. Azacitidine as the deoxynucleotide is also incorporated into DNA inhibiting its synthesis and blocking cytosine methylation by noncompetitive inhibition of DNA methyltransferase. The resulting hypomethylation of DNA is thought to induce gene activation and expression and cell differentiation. This may be an underlying factor in azacitidine's antileukemic activity and also contributes to its carcinogenic and tumor-promoting properties in experimental models.