A phase 1 trial of 8-chloro-adenosine in relapsed/refractory acute myeloid leukemia: An evaluation of safety and pharmacokinetics

BACKGROUND

This study evaluated the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of 8-chloro-adenosine (8-Cl-Ado) in patients with relapsed/refractory acute myeloid leukemia (AML).

METHODS

8-Cl-Ado was administered daily for 5 days; the starting dose was 100 mg/m2 , the highest dose tested was 800 mg/m2 . The end points were toxicity, disease response, and PK/PD measurements.

RESULTS

The predominant nonhematologic toxicity was cardiac with grade ≥3 toxicity. Plasma PK in all patients suggested heterogeneity among patients, yet, some dose-dependency for the accumulation of 8-Cl-Ado. Two 8-Cl-Ado metabolites accumulated at similar levels to 8-Cl-Ado. Cellular PK in eight patients indicated accumulation of 8-Cl-ATP, which was associated with AML blast cytoreduction in peripheral blood. The authors determined the RP2D of 8-Cl-Ado to be 400 mg/m2 .

CONCLUSIONS

Given the cardiac adverse events observed, patients require monitoring for arrhythmias and QT interval during infusion. Although peripheral blood cytoreduction was observed, responses were transient, suggesting combination strategies will be required.

Differential regulation of mouse equilibrative nucleoside transporter 1 (mENT1) splice variants by protein kinase CK2

Nucleosides are accumulated by cells via a family of equilibrative transport proteins (ENTs). An alternative splice variant of the most common subtype of mouse ENT (ENT1) has been identified which is missing a protein kinase CK2 (casein kinase 2) consensus site (Ser(254)) in the central intracellular loop of the protein. We hypothesized that this variant (mENT1a) would be less susceptible to modulation by CK2-mediated phosphorylation compared to the variant containing the serine at position 254 (mENT1b). Each splice variant was transfected into nucleoside transporter deficient PK15 cells, and stable transfectants assessed for their ability to bind the ENT1-selective probe [(3)H]nitrobenzylthioinosine (NBMPR) and to mediate the cellular uptake of [(3)H]2-chloroadenosine, with or without treatment with the CK2 selective inhibitor, 4,5,6,7-tetrabromobenzotriazole (TBB). mENT1a had a higher affinity for NBMPR relative to mENT1b - measured both directly by the binding of [(3)H]NBMPR, and indirectly via inhibition of [(3)H]2-chloroadenosine influx by NBMPR. Furthermore, incubation of mENT1b-expressing cells with 10 microM TBB for 48 h decreased both the K(D) and B(max) of [(3)H]NBMPR binding, as well as the V(max) of 2-chloroadenosine uptake, whereas similar treatment of mENT1a-expressing cells with TBB had no effect. PK15 cells transfected with hENT1, which has Ser(254), was similar to mENT1b in its response to TBB. In conclusion, inhibition of CK2 activity, or deletion of Ser(254) from mENT1, enhances transporter affinity for the inhibitor, NBMPR, and reduces the number of ENT1 proteins functioning at the level of the plasma membrane.

Characterization of the effects of adenosine receptor agonists on cerebral blood flow in uninjured and traumatically injured rat brain using continuous arterial spin-labeled magnetic resonance imaging

Hypoperfusion after traumatic brain injury may exacerbate damage. Adenosine, a vasodilator, regulates cerebral blood flow (CBF). Treatment with adenosine receptor agonists has shown benefit in experimental CNS trauma; however, their effects on CBF after injury remain undefined. We used magnetic resonance imaging to assess CBF in uninjured rats both early and at 24 h after intrahippocampal administration of either the nonselective adenosine receptor agonist 2-chloroadenosine (2-CA, 12 nmol) or the A(2A)-receptor agonist 2-p-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarbox-amidoadenosine (CGS 21680, 6 nmol). We also assessed the effects of these agents on cerebral metabolic rate for glucose (CMRglu). We then assessed the effect of 2-CA on CBF at 3.5 to 5 h after controlled cortical impact (CCI). Injection of 2-CA into uninjured rat brain produced marked increases in CBF in ipsilateral hippocampus and cortex versus vehicle (P<0.05); CBF increases persisted even at 24 h. Measurement of hippocampal levels of 2-CA showed persistent increases to 24 h. CGS 21680 produced even more marked global increases in CBF than seen with 2-CA (2-6-fold versus vehicle, P<0.05 in 10/12 regions of interest (ROIs)). Neither agonist altered CMRglu versus vehicle. After CCI, 2-CA increased CBF in ipsilateral hippocampal and hemispheric ROIs (P<0.05 versus vehicle), but the response was attenuated at severe injury levels. We report marked increases in CBF after injection of adenosine receptor agonists into uninjured rat brain despite unaltered CMRglu. 2-Chloroadenosine produced enduring increases in CBF in uninjured brain and attenuated posttraumatic hypoperfusion. Future studies of adenosine-related therapies in CNS injury should address the role of CBF.

[Preparation of 8-chloro-adenosine long circulation liposomes and its pharmacokinetics in rats]

AIM

To prepare 8-chloro-adenosine (8-Cl-A) long circulation liposomes with high entrapped efficiency and prolonged action-time of 8-Cl-A in vivo.

METHODS

To prepare 8-Cl-A long circulation liposomes of nanometer size by improved multiple emulsion. The entrapped efficiency, size and size distribution of 8-Cl-A long circulation liposomes were determined, and its pharmacokinetics in rats was evaluated.

RESULTS

The entrapped efficiency of 8-Cl-A long circulation liposomes was 62.70% and mean diameter of the liposomes was 79.9 nm. The pharmacokinetics studies indicated that 8-Cl-A long circulation liposomes showed higher drug concentration and larger AUC values than that of 8-Cl-A after iv to rats.

CONCLUSION

8-Cl-A long circulation liposomes could prolong the action-time of 8-Cl-A in vivo.

Factors affecting bryostatin 1-enhanced 2-CdA cytotoxicity in resistant B-cell chronic lymphocytic leukemia

Pre-treatment with bryostatin 1 (bryo) has been shown to potentiate the efficacy of (2-chloro-2-deoxyadenosine, cladribine, 2-CdA) in B-cell chronic lymphocytic leukemia (B-CLL) by increasing the ratio of deoxycytidine kinase (dCK) to 5'-nucleotidase (5'-NT) activity. The bryo-induced increase in dCK/5'-NT activity alone has not been a conclusive indication of final clinical outcome. Therefore, we used an ex vivo assay to investigate factors which may affect the bryo-induced enhancement of 2-CdA efficacy in B-CLL patient-derived samples. Bryo-induced increase in dCK/5'-NT was inversely associated with Rai stage CLL (r=-0.86). Increased dCK/5'-NT activity was not correlated with increased efficacy (cell death) or percentage of cellular [8-3H]-2-CdA converted to [8-3H]-2-CdATP ex vivo. Bryo pre-treatment increased the cellular uptake of [8-3H]-2-CdA and incorporation of [8-3H]-2-CdA metabolites into the DNA fraction. Cell death from 2-CdA was inversely correlated with bryo-induced activity of the DNA repair enzyme, DNA-PKcs, (r=-0.77). Thus, the ability of B-CLL to repair damaged DNA may be a more important predictor of the response to bryo/2-CdA and eventual clinical outcome than dCK/5'-NT activity. Additional CLL patients under bryo-2-CdA therapy are needed to verify these important observations.

RNA-directed actions of 8-chloro-adenosine in multiple myeloma cells

The purine analogue, 8-chloro-adenosine (8-Cl-Ado), induces apoptosis in a number of multiple myeloma (MM) cell lines. This ribonucleoside analogue accumulates as a triphosphate and selectively inhibits RNA synthesis without perturbing DNA synthesis. Cellular RNA is synthesized by one of three polymerases (Pol I, II, or III); thus, the inhibition of one or more RNA polymerases may be mediating 8-Cl-Ado cytotoxicity. Here, we have addressed this question by dissecting the RNA-directed actions of 8-Cl-Ado in MM cells. Differential alterations in [(3)H]uridine incorporation were found in the three major classes of RNA after a 20-h exposure with 10 microM 8-Cl-Ado. The synthesis rate of Pol III transcripts, 5 S and tRNA, remained unchanged, whereas Pol I-mediated rRNA synthesis decreased by approximately 20%. In contrast, mRNA synthesis, which is transcribed by Pol II, rapidly declined within 4 h and reached a 50% decrease, which was maintained for 20 h. Parallel to RNA synthesis inhibition, 8-Cl-Ado was maximally incorporated in the mRNA (>13 nmol/mg RNA), which was 5-fold higher than the tRNA and rRNA incorporation. Electrophoretic and radiographic analysis of newly synthesized and processed [(14)C]uridine-labeled transcripts indicated that the analogue blocks transcription elongation. Consistent with that result, high-performance liquid chromatography analysis of micrococcal nuclease and spleen phosphodiesterase-digested RNA demonstrated that the analogue incorporation is at the 3' terminus. In conclusion, our data demonstrate that in MM cells, 8-Cl-Ado is preferentially incorporated into mRNA, suggesting a propensity toward Pol II, and inhibits RNA synthesis by premature transcriptional chain termination.

Plasma and cellular pharmacology of 8-chloro-adenosine in mice and rats

PURPOSE

The nucleoside 8-chloro-adenosine (8-Cl-Ado) is currently being developed for treatment of multiple myeloma and leukemias. Although accumulation of the phosphorylated drug product is known to occur within cell lines, its metabolic fate in plasma or circulating cells in animals is unclear. The purpose of the present study was to determine the pharmacology of 8-Cl-Ado in rodents through examination of plasma and cellular levels of parent drug and metabolites. In addition, we sought to determine whether an inhibitor of adenosine deaminase, 2'-deoxycoformycin (dCF), could enhance intracellular formation of 8-Cl-ATP by preventing degradation of 8-Cl-Ado to 8-Cl-inosine (8-Cl-Ino).

METHODS

A validated HPLC assay permitted simultaneous determination of 8-Cl-Ado, 8-Cl-adenine (8-Cl-Ade), dCF, and 8-Cl-Ino. Radiolabeled cellular nucleotides were obtained from peripheral blood mononuclear cells (PBMC) of both mice and rats using a perchloric acid extraction procedure and were separated by HPLC.

RESULTS

Stability of 8-Cl-Ado in the presence or absence of dCF was examined in fresh plasma from mice, rats and humans. Conversion of 8-Cl-Ado to 8-Cl-Ino was only marginally affected by coincubation with dCF. In CD(2)F(1) mice given 8-Cl-Ado i.p. at 100 mg/kg, there was rapid appearance in plasma of both 8-Cl-Ade and 8-Cl-Ino. The identities of the metabolites were confirmed by mass spectrometry. The plasma [(3)H]8-Cl-Ado concentration 1 h after drug injection was 1.3 micro M in mice while the intracellular levels of [(3)H]8-Cl-AMP and [(3)H]8-Cl-ATP were 1 m M and 350 micro M, respectively. Mice that had received dCF (2 mg/ml) 30 min prior to [(3)H]8-Cl-Ado had 27% less intracellular [(3)H]8-Cl-ATP in PBMC compared to mice without dCF pretreatment. The pharmacokinetics of 8-Cl-Ado were examined in greater detail in Sprague-Dawley rats. Animals were given [(3)H]8-Cl-Ado (42.5 mg/kg, i.v.) by itself or 30 min following injection of dCF (4 mg/kg). Mononuclear cells in mice accumulated 350 or 1200 micro M [(3)H]8-Cl-ATP 1 h after injection of either 50 or 100 mg [(3)H]8-Cl-Ado, respectively. The major metabolite in these cells was the monophosphate, which was four- to sevenfold higher in concentration than the triphosphate metabolite. In rats, [(3)H]8-Cl-AMP concentrations in PBMC were similar to those of the triphosphate metabolite which achieved a peak of 90 micro M 2 h after a bolus injection of 8-Cl-Ado (40 mg/kg). Cellular clearance of 8-Cl-ATP appeared to be slow: 24 h after injection of 8-Cl-Ado the cellular concentration of 8-Cl-ATP was still 40 micro M.

CONCLUSIONS

The use of dCF did not significantly alter 8-Cl-ATP levels in PBMC and is not considered to be a useful therapeutic strategy. Even though a portion of 8-Cl-Ado is metabolically inactivated in plasma, high levels of cytotoxic 8-Cl-ATP accumulated intracellularly in these animals and were retained for a considerable length of time. Further development of 8-Cl-Ado is recommended.

8-Cl-adenosine mediated cytotoxicity and sensitization of T-lymphoblastic leukemia cells to TNFalpha-induced apoptosis is via inactivation of NF-kappaB

These data show that 8-Cl-cAMP is cytotoxic to the lymphoblastic leukemia cell line CEM and its vinblastine selected multidrug resistant derivative, CEM/VLB100 although PKA was not involved in these effects. The cytotoxic effects of 8-Cl-cAMP was abrogated by cotreatment with either ADA or IBMX which indicated a degradation form of 8-Cl-cAMP was needed for this cytotoxicity. CEM and CEM/VLB100 cells displayed a notable sensitivity to 8-Cl-adenosine-induced growth inhibition and apoptosis. 8-Cl-adenosine increased the cytosolic levels of IkappaBalpha which prevented NF-kappaB nuclear translocation. 8-Cl-adenosine also prevented TNFalpha-induced IkB decay and NF-kappaB activation in CEM and CEM/VLB100 cells.

Determination of pharmacokinetics of 8-chloroadenosine and its two major metabolites in dogs by high-performance liquid chromatography

High-performance liquid chromatography was used to measure concentration of 8-chloroadenosine (8-Cl-A) and its two major metabolites 8-chloroadenine (8-Cl-Ad) and 8-chloroinosine (8-Cl-I), and their pharmacokinetics in dogs. 8-Cl-A and its metabolites in serum were treated by deproteinization with acetonitrile, then organic impurities were extracted with dichloromethane, followed by centrifuged and direct injection of the supernatant into the liquid chromatograph. After intravenous injection of 8-Cl-A (30 mg/kg), the parent drug and 8-Cl-I were not detected, but the other metabolite, 8-Cl-Ad, was found at a high concentration for 240 min in dog serum. The main pharmacokinetic parameters of 8-Cl-Ad, t1/2beta and AUC, were 69.30 min and 580 microg min/ml. Our finding indicates that in dogs 8-Cl-A is rapidly metabolized and forms its major metabolites, 8-Cl-Ad and 8-Cl-I. 8-Cl-Ad appeared in many tissues, but 8-Cl-A and 8-Cl-I did not. The concentration of 8-Cl-Ad in dog tissues was highest in the liver and spleen, intermediate in the kidney, intestine, and lowest in the bone marrow, heart, and lungs. However, it was not detected in some liposoluble tissues such as the testes, brain, or uterus. Our study provides useful information for clinical experiment.

Pharmacokinetic-haemodynamic relationships of 2-chloroadenosine at adenosine A1 and A2a receptors in vivo

1. The purpose of the present study was to develop an experimental strategy for the quantification of the cardiovascular effects of non-selective adenosine receptor ligands at the adenosine A1 and A2a receptor in vivo. 2-Chloroadenosine (CADO) was used as a model compound. 2. Three groups of normotensive conscious rats received an short intravenous infusion of 1.4 mg kg-1 CADO during constant infusions of the A1-selective antagonist, 8-cyclopentyltheophylline (CPT; 20 micrograms min-1 kg-1), the A2a-selective antagonist, 8-(3-chlorostyryl) caffeine (CSC; 32 micrograms min-1 kg-1) or the vehicle. The heart rate (HR) and mean arterial blood pressure (MAP) were recorded continuously during the experiment and serial arterial blood samples were taken for analysis of drug concentrations. The ratio MAP/HR was also calculated, which may reflect changes in total peripheral resistance on the assumption that no changes in stroke volume occur. 3. During the infusion of CPT, CADO produced a reduction in both blood pressure and MAP/HR by activation of the A2a receptor. The concentration-effect relationships were described according to the sigmoidal Emax model, yielding potencies based on free drug concentrations (EC50,u) of 61 and 68 ng ml-1 (202 and 225 nM) for the reduction of blood pressure and MAP/HR, respectively. During the infusion of CSC, an EC50,u value of 41 ng ml-1 (136 nM) was observed for the A1 receptor-mediated reduction in heart rate. The in vivo potencies correlated with reported receptor affinities (Ki(A1) = 300 nM and Ki(A2a) = 80 nM). The maximal reductions in MAP/HR and heart rate were comparable to those of full agonists, with the Emax values of -12 +/- 1 x 10(-2) mmHg b.p.m.-1 and -205 b.p.m. respectively. 4. It is concluded that this integrated pharmacokinetic-pharmacodynamic approach can be used to obtain quantitative information on the potency and intrinsic activity of new non-selective adenosine receptor agonists at different receptor subtypes in vivo.

Inhibition of colon tumor cell growth by 8-chloro-cAMP is dependent upon its conversion to 8-chloro-adenosine

Recent interest in site-selective cAMP analogs has focused on the role of 8-chloro-adenosine (8-Cl-adenosine) in the inhibition of tumor cell growth by 8-chloro-cAMP (8-Cl-cAMP) (Van Lookeren Campagne, et al. Cancer Res 1991; 51: 1600-5). We have evaluated 8-Cl-cAMP and 8-Cl-adenosine for their growth inhibitory activity against two human colon adenocarcinoma cell lines, HCT116 and FET. Because these cell lines have been adapted to grow in chemically defined medium we were able to evaluate the effect of serum on 8-Cl-cAMP's growth inhibitory activity. In addition, cells grown in serum-free medium were tested for their sensitivity to 8-Cl-cAMP, serum-activated 8-Cl-cAMP and 8-Cl-adenosine. IC50 values, determined by measuring cell growth using a MTT colorimetric assay, showed that 'serum activation' of 8-Cl-cAMP was required to achieve inhibition of HCT116 (IC50 = 1.3 +/- 0.1 microM) and FET (IC50 = 2.0 +/- 0.1 microM) cell growth. IC50 values were not reached at the highest concentrations tested (IC50 > 500 microM) in the absence of serum, permitting us to conclude that 8-Cl-cAMP does not have growth inhibitory activity between 1.0 and 500 microM doses. HCT116 and FET cells grown in media containing serum and in the presence of 8-Cl-adenosine had IC50 values of 0.6 +/- 0.1 and 0.9 +/- 0.2 microM, respectively. HCT116 and FET cells grown in chemically defined medium containing 8-Cl-adenosine exhibited IC50 values of 1.0 +/- 0.1 and 3.1 microM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral antilymphocyte activity and induction of apoptosis by 2-chloro-2'-arabino-fluoro-2'-deoxyadenosine

2-Chlorodeoxyadenosine (CdA) is active in chronic lymphocytic leukemia, hairy-cell leukemia, and low-grade lymphomas. In part, this spectrum of activity may be attributable to the selective toxicity of CdA to nondividing lymphocytes and monocytes. However, CdA is unstable at acidic pH and is degraded by bacterial nucleoside phosphorylases. The present experiments demonstrate that the 2'-arabino-fluoro derivative of CdA, designated CAFdA, is also directly toxic to quiescent lymphocytes and macrophages. Unlike CdA, CAFdA was stable at pH 2 and resisted degradation by Escherichia coli nucleoside phosphorylase. Cell killing was preceded by the formation of DNA strand breaks and could be prevented by supplementation of the medium with deoxycytidine. The initial DNA damage initiated the pattern of oligonucleosomal DNA fragmentation characteristic of apoptosis. Mutant lymphoblasts, deficient in deoxycytidine kinase, with elevated cytoplasmic 5'-nucleotidase, or with expanded deoxynucleotide pools secondary to increased ribonucleotide reductase activity, were cross-resistant to both CAFdA and CdA toxicity. One-week oral treatment with CAFdA (1 mg/ml in drinking water) achieved an average plasma concentration of 0.56 microM and eliminated 90% of chronic lymphocytic leukemia cells transplanted into severe combined immunodeficiency (scid) mice. Under the same conditions, CdA was much less active. Collectively, these results suggest that CAFdA could be effective as an oral agent in indolent lymphoproliferative diseases and in autoimmune diseases where lymphocyte and monocyte depletion is desirable.

2-Chlorodeoxyadenosine produces a high rate of complete hematologic remission in relapsed acute myeloid leukemia

PURPOSE

The purine analog 2-chlorodeoxyadenosine (2-CDA) was well tolerated and showed promising anti-leukemic activity in a phase I trial conducted at St Jude Children's Research Hospital. To substantiate and extend this result, we performed a phase II trial in a representative group of children and young adults with relapsed acute leukemia.

PATIENTS AND METHODS

Twenty-four patients (median age, 11 years) with acute myeloid or lymphoid leukemia in first or later relapse (acute myeloid leukemia [AML], 17; acute lymphoid leukemia [ALL], seven) were given continuous infusion 2-CDA for 5 days at 8.9 mg/m2/d. Patients with residual blast cells 10 days after treatment received a second course of 2-CDA that was identical to the first. Detailed pharmacokinetic studies were performed on plasma collected from five patients.

RESULTS

Eight (47%) of the 17 patients with AML had complete hematologic remissions (four after the initial course of 2-CDA), and two (12%) had partial remissions, for a total response rate of 59%. Only one child with ALL achieved remission. Seven of the responding patients underwent allogeneic or autologous bone marrow transplantation, with six remaining free of leukemia for a median of 7 months (range, 1 to 11 months). The major form of drug-induced toxicity was hematologic, with severe neutropenia and thrombocytopenia (National Cancer Institute [NCI] grade 3 or 4) developing in 34 of the 36 courses of 2-CDA. In responding patients, the median times to recovery of neutrophil counts greater than 0.5 x 10(9)/L and platelet counts greater than 50 x 10(9)/L were 18 and 21 days, respectively. There were no deaths due to toxicity. The mean steady-state plasma concentration of 2-CDA was 34.6 nmol/L (range, 20 to 54 nmol/L).

CONCLUSION

2-CDA given by prolonged continuous infusion has clinically significant activity against AML and merits further testing in multidrug regimens for this disease.

Determination of 2-chloro-2'-deoxyadenosine in human plasma

The first high performance liquid chromatographic method for determination of the plasma concentration of 2-chloro-2'-deoxyadenosine (CdA) in patients, which is significantly more sensitive than the previously used RIA method, is presented. CdA is a purine analogue with useful clinical activity against lymphoproliferative disorders and it has recently been found to be the single most active agent in the treatment of hairy cell leukaemia. Guaneran (6-nitroimidazol-6-thioguanine) was added to 1 mL plasma as the internal standard and CdA was extracted using ethyl acetate. A Perkin-Elmer C18, 3 mu, 8 cm column was used for the separation of CdA and the internal standard from endogenous compounds in the sample with a mixture of sodium phosphate buffer 10 mM, methanol and acetonitrile (85:10:5, pH = 3.0) as the mobile phase. The sensitivity of the method (1 nM) allows the determination of CdA in plasma 24 h after the administration of 0.14 mg/kg as a 2 h infusion.

On the pharmacokinetics of 2-chloro-2'-deoxyadenosine in humans

The antitumoral effect of 2-chloro-2'-deoxyadenosine (CdA) in the treatment of lymphoproliferative diseases in general and of hairy cell leukemia in particular has recently been demonstrated. Detailed information on the pharmacokinetics of CdA, however, is lacking. The pharmacokinetics of CdA after 2- and 24-h infusions of 0.14 mg/kg was described in 12 patients with lymphoproliferative diseases using a newly developed high-performance liquid chromatography method. The plasma concentration data from individual patients were fitted to a two-compartment model with alpha- and beta-half-lives of 35 +/- 12 (mean +/- SD) min and 6.7 +/- 2.5 h, respectively. The volume of distribution was 9.2 +/- 5.4 liters/kg. The steady-state concentration of CdA during the 24-h infusion was 22.5 +/- 11.1 nM. The areas under the time versus concentration curves were 552 +/- 258 and 588 +/- 185 nM x h, respectively, for the 24- and 2-h infusions. The interindividual variability of the determinants of the plasma pharmacokinetics of CdA was small (the coefficients of variation were between 0.22 and 0.58). At 6.3 +/- 1.5 h after the start of the 2-h infusion, the concentration of CdA was the same as the steady-state concentration during the 24-h infusion. When the mean plasma concentrations of the 12 patients were fitted to a 3-compartment model, the half-lives of the alpha-, beta-, and tau-phases were 8 min, 1 h 6 min, and 6.3 h, respectively. The long terminal half-life of CdA after 2-h infusion supports the use of intermittent infusions.