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.

8-Chloroadenosine induces apoptosis in human coronary artery endothelial cells through the activation of the unfolded protein response

Infiltration of leukocytes within the vessel at sites of inflammation and the subsequent generation of myeloperoxidase-derived oxidants, including hypochlorous acid, are key characteristics of atherosclerosis. Hypochlorous acid is a potent oxidant that reacts readily with most biological molecules, including DNA and RNA. This results in nucleic acid modification and the formation of different chlorinated products. These products have been used as biomarkers of inflammation, owing to their presence in elevated amounts in different inflammatory fluids and diseased tissue, including atherosclerotic lesions. However, it is not clear whether these materials are simply biomarkers, or could also play a role in the development of chronic inflammatory pathologies. In this study, we examined the reactivity of different chlorinated nucleosides with human coronary artery endothelial cells (HCAEC). Evidence was obtained for the incorporation of each chlorinated nucleoside into the cellular RNA or DNA. However, only 8-chloro-adenosine (8ClA) had a significant effect on the cell viability and metabolic activity. Exposure of HCAEC to 8ClA decreased glycolysis, and resulted in a reduction in ATP, with a corresponding increase in the chlorinated analogue, 8Cl-ATP in the nucleotide pool. 8ClA also induced sustained endoplasmic reticulum stress within the HCAEC, which resulted in activation of the unfolded protein response, the altered expression of antioxidant genes and culminated in the release of calcium into the cytosol and cell death by apoptosis. Taken together, these data provide new insight into pathways by which myeloperoxidase activity and resultant hypochlorous acid generation could promote endothelial cell damage during chronic inflammation, which could be relevant to the progression of atherosclerosis.

The cAMP analogs have potent anti-proliferative effects on medullary thyroid cancer cell lines

The oncogenic activation of the rearranged during transfection (RET) proto-oncogene has a main role in the pathogenesis of medullary thyroid cancer (MTC). Several lines of evidence suggest that RET function could be influenced by cyclic AMP (cAMP)-dependent protein kinase A (PKA) activity. We evaluated the in vitro anti-tumor activity of 8-chloroadenosine-3',5'-cyclic monophosphate (8-Cl-cAMP) and PKA type I-selective cAMP analogs [equimolar combination of the 8-piperidinoadenosine-3',5'-cyclic monophosphate (8-PIP-cAMP) and 8-hexylaminoadenosine-3',5'-cyclic monophosphate (8-HA-cAMP) in MTC cell lines (TT and MZ-CRC-1)]. 8-Cl-cAMP and the PKA I-selective cAMP analogs showed a potent anti-proliferative effect in both cell lines. In detail, 8-Cl-cAMP blocked significantly the transition of TT cell population from G2/M to G0/G1 phase and from G0/G1 to S phase and of MZ-CRC-1 cells from G0/G1 to S phase. Moreover, 8-Cl-cAMP induced apoptosis in both cell lines, as demonstrated by FACS analysis for annexin V-FITC/propidium iodide, the activation of caspase-3 and PARP cleavage. On the other hand, the only effect induced by PKA I-selective cAMP analogs was a delay in G0/G1-S and S-G2/M progression in TT and MZ-CRC-1 cells, respectively. In conclusion, these data demonstrate that cAMP analogs, particularly 8-Cl-cAMP, significantly suppress in vitro MTC proliferation and provide rationale for a potential clinical use of cAMP analogs in the treatment of advanced MTC.

8-Chloroadenosine Sensitivity in Renal Cell Carcinoma Is Associated with AMPK Activation and mTOR Pathway Inhibition

The adenosine analog 8-chloroadenosine has been shown to deplete ATP and inhibit tumor growth in hematological malignancies as well as in lung and breast cancer cell lines. We investigated effects of 8-chloroadenosine on clear cell (cc) renal cell carcinoma (RCC) cell lines. 8-chloroadenosine was effective against ccRCC cell viability in vitro, with IC₅₀ ranging from 2 μM in the most sensitive CAKI-1 to 36 μM in the most resistant RXF-393. Proteomic analysis by reverse-phase protein array revealed that 8-chloroadenosine treatment leads to inhibition of the mTOR pathway. In time-course experiments, 8-chloroadenosine treatment rapidly activated AMPK, measured by AMPK and ACC phosphorylation, and subsequently caused dephosphorylation of p70S6K and ribosomal protein RPS6 in the sensitive cell lines. However, in the resistant cell lines, AMPK activity and the mTOR pathway were unaffected by the treatment. We also noted that the resistant cell lines had elevated basal levels of phospho RPS6 and AKT. Inhibition of PI3K pathway enhanced the efficacy of 8-chloroadenosine across all cell lines. Our observations indicate that 8-chloroadenosine activity is associated with inhibition of the mTOR pathway, and that phospho RPS6 and PI3K pathway activation status may determine resistance. Among solid tumors, RCC is one of the few susceptible to mTOR inhibition. We thus infer that 8-chloroadenosine may be effective in RCC by activating AMPK and inhibiting the mTOR pathway.

Regioselective enzymatic undecylenoylation of 8-chloroadenosine and its analogs with biomass-based 2-methyltetrahydrofuran as solvent

2-Methyltetrahydrofuran (MeTHF), a biomass-derived compound, is a promising medium for biocatalysis and organometallic reactions. The regioselective acylation of 8-chloroadenosine (8-Cl-Ado) and its analogs was carried out in MeTHF with immobilized Penicillium expansum lipase. The lipase displayed more than twofold higher catalytic activity and much better thermostability in MeTHF than in other organic solvents and co-solvent systems. The optimum reaction medium, enzyme dosage, molar ratio of viny ester to nucleoside and reaction temperature for the enzymatic acylation of 8-Cl-Ado were MeTHF, 25 U/mL, 7.5 and 35 °C, respectively, under which the desirable 5'-O-undecylenoyl-8-Cl-Ado was obtained with a yield of 95% and a regioselectivity of >99% in 3 h. In addition, the lipase catalyzed regioselective undecylenoylation of other purine nucleosides, producing 5'-undecylenic acid esters with moderate to high yields (63-94%) and excellent 5'-regioselectivities (94->99%). Use of biomass-derived solvents might open up novel opportunities for sustainable and greener biocatalytic processes.

Integrative gene expression profiling reveals G6PD-mediated resistance to RNA-directed nucleoside analogues in B-cell neoplasms

The nucleoside analogues 8-amino-adenosine and 8-chloro-adenosine have been investigated in the context of B-lineage lymphoid malignancies by our laboratories due to the selective cytotoxicity they exhibit toward multiple myeloma (MM), chronic lymphocytic leukemia (CLL), and mantle cell lymphoma (MCL) cell lines and primary cells. Encouraging pharmacokinetic and pharmacodynamic properties of 8-chloro-adenosine being documented in an ongoing Phase I trial in CLL provide additional impetus for the study of these promising drugs. In order to foster a deeper understanding of the commonalities between their mechanisms of action and gain insight into specific patient cohorts positioned to achieve maximal benefit from treatment, we devised a novel two-tiered chemoinformatic screen to identify molecular determinants of responsiveness to these compounds. This screen entailed: 1) the elucidation of gene expression patterns highly associated with the anti-tumor activity of 8-chloro-adenosine in the NCI-60 cell line panel, 2) characterization of altered transcript abundances between paired MM and MCL cell lines exhibiting differential susceptibility to 8-amino-adenosine, and 3) integration of the resulting datasets. This approach generated a signature of seven unique genes including G6PD which encodes the rate-determining enzyme of the pentose phosphate pathway (PPP), glucose-6-phosphate dehydrogenase. Bioinformatic analysis of primary cell gene expression data demonstrated that G6PD is frequently overexpressed in MM and CLL, highlighting the potential clinical implications of this finding. Utilizing the paired sensitive and resistant MM and MCL cell lines as a model system, we go on to demonstrate through loss-of-function and gain-of-function studies that elevated G6PD expression is necessary to maintain resistance to 8-amino- and 8-chloro-adenosine but insufficient to induce de novo resistance in sensitive cells. Taken together, these results indicate that G6PD activity antagonizes the cytotoxicity of 8-substituted adenosine analogues and suggests that administration of these agents to patients with B-cell malignancies exhibiting normal levels of G6PD expression may be particularly efficacious.

Protein kinase A-independent inhibition of proliferation and induction of apoptosis in human thyroid cancer cells by 8-Cl-adenosine

PURPOSE

Protein kinase A (PKA) affects cell proliferation in many cell types and is a potential target for cancer treatment. PKA activity is stimulated by cAMP and cAMP analogs. One such substance, 8-Cl-cAMP, and its metabolite 8-Cl-adenosine (8-Cl-ADO) are known inhibitors of cancer cell proliferation; however, their mechanism of action is controversial. We have investigated the antiproliferative effects of 8-Cl-cAMP and 8-CL-ADO on human thyroid cancer cells and determined PKA's involvement.

EXPERIMENTAL DESIGN

We employed proliferation and apoptosis assays and PKA activity and cell cycle analysis to understand the effect of 8-Cl-ADO and 8-Cl-cAMP on human thyroid cancer and HeLa cell lines.

RESULTS

8-Cl-ADO inhibited proliferation of all cells, an effect that lasted for at least 4 d. Proliferation was also inhibited by 8-Cl-cAMP, but this inhibition was reduced by 3-isobutyl-1-methylxanthine; both drugs stimulated apoptosis, and 3-isobutyl-1-methylxanthine drastically reduced 8-Cl-cAMP-induced cell death. 8-Cl-ADO induced cell accumulation in G1/S or G2/M cell cycle phases and differentially altered PKA activity and subunit levels. PKA stimulation or inhibition and adenosine receptor agonists or antagonists did not significantly affect proliferation.

CONCLUSIONS

8-Cl-ADO and 8-Cl-cAMP inhibit proliferation, induce cell cycle phase accumulation, and stimulate apoptosis in thyroid cancer cells. The effect of 8-Cl-cAMP is likely due to its metabolite 8-Cl-ADO, and PKA does not appear to have direct involvement in the inhibition of proliferation by 8-Cl-ADO. 8-Cl-ADO may be a useful therapeutic agent to be explored in aggressive thyroid cancer.

8-Chloro-adenosine inhibits growth at least partly by interfering with actin polymerization in cultured human lung cancer cells

A key feature of actin is its ability to bind and hydrolyze ATP. 8-Chloro-adenosine (8-Cl-Ado), which can be phosphorylated to the moiety of 8-Cl-ATP in living cells, inhibits tumor cell proliferation. Therefore we tested the hypothesis that 8-Cl-Ado can interfere with the dynamic state of actin polymerization. We found that 8-Cl-Ado inhibited the growth of human lung cancer cell line A549 and H1299 in culture, and arrested the target cells in G2/M phase evidenced by fluorescence-activated cell sorting (FACS). Immunocytochemistry showed that the normal organization of microfilaments was disrupted in 8-Cl-Ado-exposed cells, which is accompanied by the decrease of cell size and the alteration of cell shape, and by aberrant mitosis and apoptosis in targeted cells. Furthermore, in vitro light scattering assays revealed that 8-Cl-ATP could directly inhibit the transition of G-actin to F-actin. DNase I inhibition assays showed that the G/F-actin ratio, a surrogate marker of actin polymerization status in living cells, was significantly increased in 8-Cl-Ado-exposed A549 and H1299 cells, compared to the G/F-actin ratio in unexposed cells. Taken together, these results indicate that 8-Cl-Ado exposure can alter the dynamic properties of actin polymerization, disrupt the dynamic instability or the rearrangement ability of actin filaments. Therefore, our data suggest that 8-Cl-Ado may exert its cytotoxicity at least partly by interfering with the dynamic instability of microfilaments, which may correlate with its inhibitory effects on cell proliferation and cell death.

8-chloroadenosine induced HL-60 cell growth inhibition, differentiation, and G(0)/G(1) arrest involves attenuated cyclin D1 and telomerase and up-regulated p21(WAF1/CIP1)

8-Chloroadenosine, an active dephosphorylated metabolite of the antineoplastic agent 8-chloroadenosine 3',5'-monophosphate (8-Cl-cAMP), induces growth inhibition in multiple carcinomas. Here we report that 8-chloroadenosine inhibits growth in human promyelocytic leukemia HL-60 cells by a G(0)/G(1) phase arrest and terminates cell differentiation along the granulocytic lineage. The mechanism of 8-chloroadenosine-induced G(0)/G(1) arrest is independent of apoptosis. The expressions of cyclin D1 and c-myc in HL-60 are suppressed by 8-chloroadenosine, whereas the cyclin-dependent kinases inhibitor p21(WAF1/CIP1) is up-regulated. 8-Chloroadenosine has less effect on the expressions of cyclin-dependent kinase (cdk)2 and cdk4, G(1) phase cyclin-dependent kinases, and only moderately induces the expression of transforming growth factor beta1 (TGFbeta1) and the mitotic inhibitor p27(KIP1). Telomerase activity is reduced in extracts of 8-chloroadenosine treated HL-60 cells, but 8-chloroadenosine does not directly inhibit the catalytic activity of telomerase in vitro. Therefore, anti-proliferation of HL-60 cells by 8-chloroadenosine involves coordination of cyclin D1 suppression, reduction of telomerase activity, and up-regulation of p21(WAF1/CIP1) that arrest cell-cycle progression at G(0)/G(1) phase and terminate cell differentiation.

The combination of sulfinosine and 8-Cl-cAMP induces synergistic cell growth inhibition of the human neuroblastoma cell line in vitro

To identify purine analogs that could be effective in treating neuroblastomas, we tested the anticancer properties of sulfinosine, 8-Cl-cAMP and 8-Cl-adenosine in the SK-N-SH cell line. First we examined the effects of these three agents on cell growth inhibition and cell viability by the BrdU and Sulforhodamine B assay. Treatment of SK-N-SH cells with increasing concentrations of these compounds led to a significant inhibition of cell proliferation and decrease of cell viability in a time- and dose-dependent manner at micromolar concentration (<10 microm). Treatment with a combination of sulfinosine and 8-Cl-cAMP resulted in synergistic effects on growth inhibition, cell cycle arrest and induction of apoptosis. Flow-cytometric analysis showed that 8-Cl-cAMP arrested the cells in the G0/G1 phase and sulfinosine blocked cell cycle progression at the G2/M stage, in contrast to the combined effects of both agents that did not arrest growth at any particular phase of the cell cycle. Further analysis of apoptosis induction demonstrated an increase from 17 to 24% of both early and late apoptotic cells and a very low percentage of necrotic cells. These results indicate that apoptosis was the predominant type of cell death after treatment of SK-N-SH cells with both substances, as well as with their combinations.

Complete remission of hairy cell leukemia variant (HCL-v) complicated by red cell aplasia post treatment with rituximab

Hairy cell leukemia variant (HCL-v) is a rare form of a chronic B-cell lymphoproliferative disorder. Unlike typical hairy cell leukemia (HCL) where the complete response (CR) rate to 2-chlorodeoxyadenosine and 2'-deoxycoformycin can approach about 90%, in HCL-v CR is rare and partial response (PR) occurs in approximately 50% with these agents. Rituximab treatment in relapsed or refractory HCL results in a CR of 13% to 53%, but its use in HCL-v has not been reported in the literature to our knowledge. We describe a patient with HCL-v, whose course was previously complicated by pure red cell aplasia who achieved CR after treatment with rituximab. We also briefly review outcomes of treatments used in HCL-v reported in the current literature.

[Mechanisms of sensitization by 8-chloro-adenosine of human tumor cells to TRAIL-induced apoptosis]

OBJECTIVE

To study the effect of 8-chloro-adenosine (8-Cl-Ado) on the sensitivity of human hepatoma and breast cancer cell lines to TRAIL-induced apoptosis in vitro and its mechanisms.

METHODS

Recombinant soluble TRAIL (rsTRAIL) or 8-Cl-Ado was used to treat hepatoma cell line BEL-7402 and breast cancer cell line MCF-7 in vitro. MTT assay was used to evaluate cell viability. The effect of cotreatment with rsTRAIL and 8-Cl-Ado was analyzed. NF-kappaB activity reporter plasmid was designed to measure the activity of transcription factor NF-kappaB. After transient transfection with the reporter plasmid, which contains NF-kappaB-responsive elements, into the cell lines, cells were treated with rsTRAIL and/or 8-Cl-Ado, then the activity of the reporter gene luciferase was determined. Different kinds of caspase inhibitors were used to measure the effect of caspases in the rsTRAIL and/or 8-Cl-Ado induced apoptosis.

RESULTS

8-Cl-Ado could greatly enhance sensitivity of BEL-7402 and MCF-7 cells to reTRAIL. Treatment with 8-Cl-Ado and rsTRAIL inactivated transcription factor NF-kappaB and induced apoptosis in BEL-7402, but not in MCF-7. Caspase family inhibitor could not prevent apoptosis induced by 8-Cl-Ado and rsTRAIL in BEL-7402 cells, however, it could block apoptosis in MCF-7 cells, indicating that two different apoptosis pathways in MCF-7 and BEL-7402 might exist, one was caspase dependent and the other caspase independent. Moreover, all of the inhibitors of caspse-3, -8 and -9 could not block apoptosis induced by the co-treatment.

CONCLUSION

8-chloro-adenosine can enhance the sensitivity of human hepatoma cell line BEL-7402 and breast cancer cell line MCF-7 to rsTRAIL, even though MCF-7 is TRAIL-resistant. 8-Cl-Ado combined with rsTRAIL can trigger different signal pathways in MCF-7 and BEL-7402, which are caspase dependent and independent, respectively.

8-Chloro-cyclic AMP-induced growth inhibition and apoptosis is mediated by p38 mitogen-activated protein kinase activation in HL60 cells

8-Chloro-cyclic AMP (8-Cl-cAMP), which is known to induce growth inhibition, apoptosis, and differentiation in various cancer cell lines, has been studied as a putative anticancer drug. However, the mechanism of anticancer activities of 8-Cl-cAMP has not been fully understood. Previously, we reported that the 8-Cl-cAMP-induced growth inhibition is mediated by protein kinase C (PKC) activation. In this study, we found that p38 mitogen-activated protein kinase (MAPK) also plays important roles during the 8-Cl-cAMP-induced growth inhibition and apoptosis. SB203580 (a p38-specific inhibitor) recovered the 8-Cl-cAMP-induced growth inhibition and apoptosis, whereas other MAPK inhibitors, such as PD98059 (an extracellular signal-regulated kinase-specific inhibitor) and SP600125 (a c-Jun NH2-terminal kinase-specific inhibitor), had no effect. The phosphorylation (activation) of p38 MAPK was increased in a time-dependent manner after 8-Cl-cAMP treatment. Furthermore, SB203580 was able to block PKC activation induced by 8-Cl-cAMP. However, PKC inhibitor (GF109203x) could not attenuate p38 activation, indicating that p38 MAPK activation is upstream of PKC activation during the 8-Cl-cAMP-induced growth inhibition. 8-Chloro-adenosine, a metabolite of 8-Cl-cAMP, also activated p38 MAPK and this activation was blocked by adenosine kinase inhibitor. These results suggest that 8-Cl-cAMP exerts its anticancer activity through p38 MAPK activation and the metabolite(s) of 8-Cl-cAMP mediates this process.

[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.

8-Cl-cAMP and its metabolite, 8-Cl-adenosine induce growth inhibition in mouse fibroblast DT cells through the same pathways: protein kinase C activation and cyclin B down-regulation

8-Chloro-cyclic AMP (8-Cl-cAMP) is known to be most effective in inducing growth inhibition and differentiation of a number of cancer cells. Also, its cellular metabolite, 8-Cl-adenosine was shown to induce growth inhibition in a variety of cell lines. However, the signaling mechanism that governs the effects of 8-Cl-cAMP and/or 8-Cl-adenosine is still uncertain and it is not even sure which of the two is the key molecule that induces growth inhibition. In this study using mouse fibroblast DT cells, it was found that adenosine kinase inhibitor and adenosine deaminase could reverse cellular growth inhibition induced by 8-Cl-cAMP and 8-Cl-adenosine. And 8-Cl-cAMP could not induce growth inhibition in the presence of phosphodiesterase (PDE) inhibitor, but 8-Cl-adenosine could. We also found that protein kinase C (PKC) inhibitor could restore this growth inhibition, and both the 8-Cl-cAMP and 8-Cl-adenosine could activate the enzymatic activity of PKC. Besides, after 8-Cl-cAMP and 8-Cl-adenosine treatment, cyclin B was down-regulated and a CDK inhibitor, p27 was up-regulated in a time-dependent manner. These results suggest that it is not 8-Cl-cAMP but 8-Cl-adenosine which induces growth inhibition, and 8-Cl-cAMP must be metabolized to exert this effect. Furthermore, there might exist signaling cascade such as PKC activation and cyclin B down-regulation after 8-Cl-cAMP and 8-Cl-adenosine treatment.

8-Cl-Adenosine enhances 1,25-dihydroxyvitamin D3-induced growth inhibition without affecting 1,25-dihydroxyvitamin D3-stimulated differentiation of primary mouse epidermal keratinocytes

Background

Epidermal keratinocytes continuously proliferate and differentiate to form the mechanical and water permeability barrier that makes terrestrial life possible. In certain skin diseases, these processes become dysregulated, resulting in abnormal barrier formation. In particular, skin diseases such as psoriasis, actinic keratosis and basal and squamous cell carcinomas are characterized by hyperproliferation and aberrant or absent differentiation of epidermal keratinocytes. We previously demonstrated that 8-Cl-adenosine (8-Cl-Ado) can induce keratinocyte growth arrest without inducing differentiation.

Results

To determine if this agent might be useful in treating hyperproliferative skin disorders, we investigated whether 8-Cl-Ado could enhance the ability of 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], a known keratinocyte differentiating agent and a clinical treatment for psoriasis, to inhibit keratinocyte growth. We found that low concentrations of 8-Cl-Ado and 1,25(OH)₂D₃ appeared to act additively to reduce proliferation of primary mouse epidermal keratinocytes. However, another agent (transforming growth factor-beta) that triggers growth arrest without inducing differentiation also coincidentally inhibits differentiation elicited by other agents; inhibition of differentiation is suboptimal for treating skin disorders, as differentiation is often already reduced. Thus, we determined whether 8-Cl-Ado also decreased keratinocyte differentiation induced by 1,25(OH)₂D₃, as measured using the early and late differentiation markers, keratin 1 protein levels and transglutaminase activity, respectively. 8-Cl-Ado did not affect 1,25(OH)₂D₃-stimulated keratin 1 protein expression or transglutaminase activity.

Conclusions

Our results suggest that 8-Cl-Ado might be useful in combination with differentiating agents for the treatment of hyperproliferative disorders of the skin.

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.

8-Chloro-adenosine sensitizes a human hepatoma cell line to TRAIL-induced apoptosis by caspase-dependent and -independent pathways

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of the tumor necrosis factor (TNF) super-family, induces apoptosis in various cancer cells with little or no effect on normal cells. 8-Chloro-adenosine (8-Cl-Ado) is a potential anti-cancer chemical agent now in clinical trail phase II, though its molecular mechanism remains poorly understood. In the present study, we report that 8-Cl-Ado can promote TRAIL killing activity in the hepatoma cell line BEL-7402 in dose- and time-dependent manner when jointly used in vitro. We showed that the expression of death receptor DR5, but not DR4 was up-regulated and the decoy receptor DcR1 was down-regulated in the cells treated with 8-Cl-Ado and the recombinant soluble TRAIL (rsTRAIL, 95-281 a.a.). Further experiments demonstrated that caspase-family inhibitor z-VAD-fmk prevented the cells from apoptosis induced by co-treatment with 8-Cl-Ado and rsTRAIL for 6 h, however, apoptosis occurred in the cells cultured for 24 h, suggesting that co-treatment induce a caspase-dependent and -independent signaling pathway in the BEL-7402 cells. This phenomenon was confirmed by cleavage analysis of caspase-3 and poly(ADP-ribose) polymerase (PARP), and ROS (reactive oxygen species) assay, respectively. Moreover, transcriptional activity test showed that NF-kappaB was inhibited in the BEL-7402 cells during co-treatment. Our results provided evidence for the first time that 8-Cl-Ado sensitizes the human hepatoma cells BEL-7402 to rsTRAIL-induced apoptosis by up-regulating DR5 expression, inactivating the NF-kappaB activity, and signaling by the caspase-dependent and -independent pathway.

[Inhibition of 8-chloroadenosine on proteasome activity of HL-60 cells]

BACKGROUND & OBJECTIVE

The proteasome is a multicatalytic proteinase complex in eukaryotic cells, and it can be used as a new target for screening anti-tumor drugs according to certain previous researches. The inhibition activity of 8-CA (8-chloroadenosine, a new anti-tumor drug synthesized in our lab) in sarcoma 180, hepatocarcinoma 22, and human gastric carcinoma xenograft tumor has been confirmed. However,the relationship between the mechanism of the inhibition and proteasome is still unclear. The present study was designed to explore the effect of 8-CA on 3 kinds of enzyme activities (chymotrypsin-like activity, trypsin-like activity, and peptidyl-glutamyl- peptide hydrolyzing activity) of 20S proteasome in human progranulocyte leukemia HL-60 cells.

METHODS

HL-60 cells were treated with 8-CA at different concentrations for 24, 48, and 72 hours. Then total protein of HL-60 cells was extracted, and the three enzyme activities of 20S proteasomes in the total protein was examined. And the chymotrypsin-like activity of the purified proteasome from the total protein was also examined by immunoprecipitation. The enzyme activity was indicated by fluorescence absorbance (A) produced by degradation of specific substrates by proteasomes.

RESULTS

In HL-60 cells, three enzyme activities of the proteasomes were significantly inhibited after exposure to 0.1 micromol/L 8-CA for 48 hours; and the inhibition effect was concentration dependent. When the concentration of 8-CA reached 5 micromol/L, the inhibition rates of three proteasome activities (chymotrypsin-like activity,trypsin-like activity,and peptidyl- glutamyl-peptide hydrolyzing activity) were 44.96%, 54.52%, 48.36% for 48 hours and 67.53%, 70.48%, 64.08% for 72 hours, respectively. The inhibition rate of 1 micromol/L and 5 micromol/L 8-CA on chymotrypsin-like proteasome activity of HL-60 cells for 48 hours were 68.14% (P< 0.01) and 92.75% (P< 0.001), respectively.

CONCLUSION

8-CA inhibits proteasome activity of HL-60 cells with a time- and concentration-dependent manner.

Low dose 2-CdA schedule activity in splenic marginal zone lymphomas

Splenic Marginal Zone Lymphoma (SMZL) is a rare clinicopathological entity among marginal zone lymphomas. SMZL is an indolent lymphoma usually treated by splenectomy. A subset of patients is characterized by a more aggressive clinical course and poor prognosis. Treatment of these cases and second-line therapy for relapsed patients have not been yet identified. We report 10 cases treated with cladribrine (5 mg/m(2)/week) for six courses. Six patients (60%) achieved partial response, two patients (20%) achieved a complete response and the two remaining patients did not respond and died as a result of progression of the disease. The treatment was well tolerated. A total of 60% of the patients had an overall survival rate of 48 months and 24 months progression-free-survival was achieved by 37% with a median time of progression-free-survival of 17 months. Interestingly, in addition to a relevant percentage of hematological remission, some patients also experienced a molecular remission. We conclude that this treatment is safe and well tolerated and is able to induce a substantial number of responses. Our results suggest that this schedule is well tolerated and could be an useful alternative to splenectomy.

[The inhibitory effect of 8-chloroadenosine on tumor necrosis factor-induced proto-oncogene expression of retinal pigment epithelial cells]

OBJECTIVE

To investigate the inhibitory effect of 8-chloroadenodine (8-CLA) on tumor necrosis factor-alpha (TNF-alpha)-induced proto-oncogene expression in retinal pigment epithelial (RPE) cells.

METHODS

Primary culture and subculture of health bovine RPE cells were established in vitro. RPE cells were treated with tumor necrosis factor TNF-alpha (13.3 mmol/L) with or without 8-CLA (16 micro mol/L) for 30 minutes or 3 hours, respectively. C-fos and c-myc mRNA expression in RPE cells was detected by Northern blot analysis.

RESULTS

Normal RPE cells expressed c-fos and c-myc mRNA at a low level. After treatment with TNF-alpha, the expression of c-fos and c-myc mRNA was increased by 3.13 and 1.5 fold, respectively, as compared to untreated cells. 8-CLA decreased TNF-alpha-induced c-fos and c-myc mRNA expression by 25.0% and 29.0%, respectively.

CONCLUSIONS

8-CLA can inhibit TNF-alpha-induced c-fos and c-myc mRNA expression in RPE cells. These findings may be useful for exploring new drugs for inhibiting the growth-induced proliferation of RPE.

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.

Synthesis and hybridization properties of RNA containing 8-chloroadenosine

8-Chloroadenosine (8-Cl-Ado) has shown potential as a chemotherapeutic agent for the treatment of multiple myeloma and certain leukemias. 8-Cl-Ado treatment leads to a decrease in global RNA levels and incorporation of the analog into cellular RNA in malignant cells. To investigate the effects of 8-Cl-Ado modifications on RNA structure and function, an 8-Cl-Ado phosphoramidite and controlled-pore glass support were synthesized and used to introduce 8-Cl-Ado at internal and 3'- terminal positions, respectively. RNA oligonucleotides containing 8-chloroadenine (8-Cl-A) residues were synthesized and hybridized with complementary RNA strands. Circular dichroism spectroscopy of the resulting RNA duplexes revealed that the modified nucleobase does not perturb the overall A-form helix geometry. The thermal stabilities of 8-Cl-Ado modified duplexes were determined by UV thermal denaturation analysis and were compared with analogous natural duplexes containing standard and mismatched base pairs. The 8-Cl-Ado modification destabilizes RNA duplexes by approximately 5 kcal/mole, approximately as much as a U:U mismatched base pair. The duplex destabilization of 8-Cl-A may result from perturbation of Watson-Crick base pairing induced by conformational preferences of 8-halogenated nucleosides.

Inactivation of deoxycytidine kinase and overexpression of P-glycoprotein in AraC and daunorubicin double resistant leukemic cell lines

AraC resistance in vitro is explained by inactivation of dCK, while resistance to DNR is described by overexpression of multidrug efflux pumps like Pgp or MRP. Thus far, no correlation between resistance mechanisms in vitro and in patients with AML has been documented. We generated AraC and DNR double resistant cell lines to investigate resistance mechanisms of both agents. In these cell lines involvement of dCK was extensively investigated and Pgp expression and activity was determined. Our data implicate that similar resistance mechanisms like inactivation of dCK coincided by alternatively spliced dCK forms and overexpression of Pgp are induced in single-as well as in double resistant leukemic cell lines.

[8-Chloro-adenosine increases the activity of transcription factor CREB by modification of phosphorylation]

BACKGROUND & OBJECTIVE

8-Chloro-adenosine(8-Cl-Ado) is an anti-tumor drug,which has been investigated and developed recently in China. The molecular mechanism of 8-Cl-Ado is now unclear. This study was conducted to investigate the effect of 8-Cl-Ado on the activity of transcription factor cAMP-response-element-binding protein(CREB) and its correlative mechanism in human promyelocytic leukemia cell line HL-60.

METHODS

MTT method was used to determine IC(50) (the concentration showing 50% of inhibition rate) of 8-Cl-Ado to HL-60. The protein levels and phosphorylated levels of CREB at different time following 8-Cl-Ado stimulation were examined using Western blot analysis. Gel shift assay was performed to examine DNA binding levels of CREB at different time following 8-Cl-Ado stimulation.

RESULTS

(1)The IC(50) of 8-Cl-Ado to HL-60 was about 0.42 micromol/L. (2)8-Cl-Ado increased phosphorylated level of CREB rapidly, which was maximal at 30 minutes, and returned to basal level in 6 hours. The protein level of CREB was constant during 8-Cl-Ado stimulation. (3)8-Cl-Ado did not influence binding level of DNA and CREB.

CONCLUSION

The increase of transcriptional activity of CREB induced by 8-Cl-Ado depends on the increased level of phosphorylated CREB, but is not associated with the protein level and DNA binging level of CREB.

Induction of apoptosis in the human mast cell leukemia cell line HMC-1 by various antineoplastic drugs

Mast cell leukemia (MCL) is a rare disorder characterized by rapid disease progression, resistance against conventional cytoreductive drugs, and short survival. In an attempt to identify drugs that show significant antiproliferative effects on neoplastic mast cells (MC), we exposed the MCL-derived cell line HMC-1 to various cytotoxic drugs including 2-chlorodeoxyadenosine [2CdA], fludarabine and cytosine arabinoside [ARA-C]. The effects of these drugs on 3H-thymidine incorporation, electron microscopic signs of apoptosis, and DNA fragmentation in HMC-1 cells, were analyzed. As assessed by 3H-thymidine incorporation, all drugs produced inhibition of proliferation in HMC-1 cells with the following rank order of potency: ARA-C > doxorubicine > 2-CdA > etoposide > vincristine > fludarabine > cisplatin. Fludarabin, cisplatin, etoposide and 2-CdA also induced ladder-type fragmentation of DNA, endonuclease activity in a Tunel assay, and electron microscopic signs of apoptosis in HMC-1 cells. Together, our data show that various cytostatic drugs can induce apoptosis and inhibition of proliferation in the human MCL cell line HMC-1. Whether these drugs, alone or in combination, are also effective in patients with MCL, remains to be determined.

Synthesis and induction of apoptosis in B cell chronic leukemia by diosgenyl 2-amino-2-deoxy-beta-D-glucopyranoside hydrochloride and its derivatives

2-Acetamido-2-deoxy-D-glucose hydrochloride (D-glucosamine hydrochloride) has been used for the preparation of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-trifluoroacetamido-beta- (4) and 2-tetrachlorophthalimido-alpha,beta-D-glucopyranose (6), which have been transformed into the appropriate bromides and the chloride. Both bromo and chloro sugars were used as a glycosyl donors for the glycosylation of diosgenin [(25R)-spirost-5-en-3beta-ol]. These condensations were conducted under mild conditions, using silver triflate as a promoter, and gave diosgenyl glycosides 9 and 12. Each of them was converted into diosgenyl 2-amino-2-deoxy-beta-D-glucopyranoside hydrochloride (11) and N-acylamido derivatives. The structures of all new glycosides were established by 1H and 13C NMR spectroscopy. These diosgenyl glycosides are the first saponins containing the D-glucosamine residue that have been synthesized. These compounds show promising antitumor activities. The synthetic saponins increase the number of apoptotic B cells, in combination with cladribine (2-CdA), that are isolated from chronic lymphotic leukemia (B-CLL) patients.

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.

Anti-proliferative effects of 8-chloro-cAMP and other cAMP analogs are unrelated to their effects on protein kinase A regulatory subunit expression

Conflicting reports have attributed 8-chloro-cAMP (Cl-cAMP)-mediated inhibition of tumor cell growth to either a toxic 8-chloro-adenosine (Cl-AdR) breakdown product or a Cl-cAMP-mediated decrease in ratio of Type I to Type II regulatory (R) subunits of protein kinase A (PKA). Using the MCF-7 human breast cancer and S49 mouse lymphoma cell lines as models, we show that the effects of Cl-cAMP and other cAMP analogs on growth and R subunit expression are unrelated. MCF-7 cell growth was insensitive to most analogs and inducers of cAMP, but was potently inhibited by Cl-cAMP acting through uptake and phosphorylation of its Cl-AdR breakdown product. Possible roles of adenosine receptors or P(2) purinoceptors in these Cl-cAMP-mediated growth effects were ruled out by studies with agonists and antagonists. Cholera toxin markedly decreased the ratio of Type I to Type II R subunits in MCF-7 cells without affecting growth, while growth inhibitory concentrations of Cl-cAMP or Cl-AdR had insignificant effects on this ratio. In S49 cells, where PKA activation is known to inhibit cell growth, PKA-deficient mutants retained sensitivity to both Cl-cAMP and the related 8-bromo-cAMP. Adenosine kinase (AK)-deficient S49 cells were inhibited only by higher concentrations of these 8-halogenated cAMP analogs. Of the commonly used cAMP analogs, only 8-(4-chlorophenylthio)-cAMP acted purely as a cyclic nucleotide-having no effect on PKA-deficient cells, but strongly inhibiting both wild-type and AK-deficient cells. Where growth inhibitory concentrations of most cAMP analogs reduced RI expression in the AK-deficient mutant, a functionally equivalent concentration of (N(6), O(2'))dibutyryl-cAMP maintained or increased this expression.

Genome-wide expression profiling of 8-chloroadenosine- and 8-chloro-cAMP-treated human neuroblastoma cells using radioactive human cDNA microarray

Previous reports raised question as to whether 8-chloro-cyclic adenosine 3,5-monophosphate (8-Cl-cAMP) is a prodrug for its metabolite, 8-Cl-adenosine which exerts growth inhibition in a broad spectrum of cancer cells. The present study was carried out to clarify overall cellular affects of 8-Cl-cAMP and 8-Cl-adenosine on SK-N-DZ human neuroblastoma cells by systematically characterizing gene expression using radioactive human cDNA microarray. Microarray was prepared with PCR-amplified cDNA of 2,304 known genes spotted on nylon membranes, employing (33)P-labeled cDNAs of SK-N-DZ cells as a probe. The expression levels of approximately 100 cDNAs, representing about 8% of the total DNA elements on the array, were altered in 8-Cl-adenosine- or 8-Cl-cAMP-treated cells, respectively. The genome-wide expression of the two samples exhibited partial overlaps; different sets of up-regulated genes but the same set of down-regulated genes. 8-Cl-adenosine treatment up-regulated genes involved in differentiation and development (LIM protein, connexin 26, neogenin, neurofilament triplet L protein and p21(WAF1/CIP1)) and immune response such as natural killer cells protein 4, and down-regulated ones involved in proliferation and transformation (transforming growth factor-beta, DYRK2, urokinase-type plasminogen activator and proteins involved in transcription and translation) which were in close parallel with those by 8-Cl-cAMP. Our results indicated that the two drugs shared common genomic pathways for the down-regulation of certain genes, but used distinct pathways for the up-regulation of different gene clusters. Based on the findings, we suggest that the anti-cancer activity of 8-Cl-cAMP results at least in part through 8-Cl-adenosine. Thus, the systematic use of DNA arrays can provide insight into the dynamic cellular pathways involved in anticancer activities of chemotherapeutics.

Treatment-induced expression of anti-apoptotic proteins in WSU-CLL, a human chronic lymphocytic leukemia cell line

Bryostatin 1 (bryo 1) has been shown to potentiate the anti-tumor activity of 2-chloro-2-deoxyadenosine (2-CdA) in chronic lymphocytic leukemia (CLL) and in the WSU-CLL cell line. However, like resistant CLL, WSU-CLL cells lose their sensitivity to bryo 1/2-CdA treatment. We report that 2-CdA-induced IAP expression may be a possible mechanism whereby resistance to apoptosis is acquired in these cells. In WSU-CLL cells, three members of the Inhibitors of Apoptosis (IAP) family were identified. Bryo 1 treatment of WSU-CLL cells leads to initiation of the apoptotic cascade and induced a marginal increase in XIAP protein expression. In contrast, 2-CdA treatment, alone or in combination with bryo 1, induced a substantial increase in survivin and XIAP proteins and phosphorylation of BAD. Bryo 1 alone induced caspase-7 and -9 dependent [poly ADP-ribose] polymerase (PARP) cleavage, while sequential treatment with bryo 1 (72 h) followed by 2-CdA (24 h) induced caspase-3,-7, and -9 dependent PARP cleavage and increased apoptosis. Although exposure to bryo 1 initiated apoptotic events, apoptosis was first enhanced by 2-CdA, and then reversed in a time-dependent manner by 2-CdA-induced expression of survival proteins. Taken together, resistance to bryo 1/2-CdA treatment may be the result of 2-CdA-induced IAP inhibition of the intrinsic apoptotic pathway caspases.

Actions of the selective protein kinase C inhibitor PKC412 on B-chronic lymphocytic leukemia cells in vitro

BACKGROUND AND OBJECTIVES

The staurosporine derivative PKC412 (CGP41251) is a more selective inhibitor of the conventional isoforms of protein kinase C (PKC) than is the parent compound. In addition to its growth inhibitory properties, PKC412 reverses the efflux function of the multidrug resistance (MDR)-1 gene product, P-glycoprotein (P-gp).

DESIGN AND METHODS

The in vitro actions of PKC412 were investigated in peripheral blood lymphocytes (PBL) from 4 normal volunteers, B-cell isolates from 3 normal tonsils and 31 patients with B-cell chronic lymphocytic leukemia (B-CLL). Following incubation with PKC412 for 2 days, the viability of B-CLL cells was decreased relative to that of controls (63+/-23% at 1 micromole/L; 52+/-30% at 10 micromole/L; n=20). Normal PBL were significantly more resistant to the drug (91+/-5% viable cells at 1 micromole/L; 73+/-18% at 10 micromole/L; n=4). Thirteen of the B-CLL patients were treated with oral PKC412 in a phase II trial.

RESULTS

PKC activity in malignant cells from these patients showed a reduction post-treatment of 25-96% of their respective pre-treatment levels. Morphologic analysis, as well as in situ assay for DNA strand breaks (TUNEL assay) showed that B-CLL cells were killed by an apoptotic mechanism. In B-CLL cells the mean IC50, for PKC412, as measured by the reduction of 3-(4,5-dimethylthiozol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), was 2.1 micromol/L in 16 samples in which the IC50 were below the maximum concentration of PKC412 used for the assay. In tonsillar B-cells, the mean IC50 was 11 micromol/L whereas PBL cells were resistant. Four of eight and 1/3 B-CLL samples that were resistant to chlorambucil and fludarabine, respectively, were sensitive to PKC412. In 15/31 B-CLL samples a dose-dependent reversal of P-gp-mediated drug efflux by PKC412 was observed. A statistically significant correlation (p<0.001) was observed between P-gp protein expression as measured by FACScan analysis and the reversal of efflux activity by either PKC412 or verapamil. PKC412 increased the sensitivity of B-CLL cells to 2'-chlorodeoxyadenosine and chlorambucil.

INTERPRETATION AND CONCLUSIONS

This study establishes the in vitro cytotoxic and multidrug resistance (MDR) modulatory properties of PKC412 towards malignant cells from B-CLL patients. The direct antitumor activity combined with the potential for P-gp modulation make PKC412 an attractive drug for the treatment of malignancies expressing the MDR phenotype, or in combination with conventional drugs.

8-Cl-adenosine is an active metabolite of 8-Cl-cAMP responsible for its in vitro antiproliferative effects on CHO mutants hypersensitive to cytostatic drugs

8-Cl-cAMP has been undergoing clinical trials as a potential chemotherapy agent, but there is much discussion in the literature as to whether the active agent is 8-Cl-cAMP itself, or its major metabolite, 8-Cl-adenosine. 8-Cl-cAMP is susceptible to the action of serum enzymes such as phosphodiesterases, and its metabolism when administered to cancer patients raises questions as to the mechanism of action of 8-Cl-cAMP. The stability of 8-Cl-cAMP when incubated with serum, and the effects of both 8-Cl-cAMP and 8-Cl-adenosine on the proliferation of variant lines of CHO cells hypersensitive to 8-Cl-cAMP were investigated. A solid-phase extraction (SPE) purification protocol and the HPLC method previously developed were used to determine 8-Cl-cAMP and 8-Cl-adenosine. Heat treatment of serum inactivated the enzymes in the culture medium responsible for activating 8-Cl-cAMP. Under these conditions 8-Cl-cAMP remained stable and there were no traces of its metabolite, 8-Cl-adenosine. Cell culture experiments showed that 8-Cl-cAMP only affected cell growth in medium that contained untreated serum. In contrast, 8-Cl-adenosine was shown to be growth inhibitory in medium containing either heat-treated or untreated serum. HPLC analysis of the culture medium from the cell culture experiments supported the hypothesis that 8-Cl-cAMP was only effective in inhibiting cell growth after metabolism to 8-Cl-adenosine. Thus further studies of this drug and its mechanism of action should focus on 8-Cl-adenosine.

2-CdA in the treatment of hairy cell leukaemia

INTRODUCTION

Hairy cell leukaemia (HCL) is a rare lymphoproliferative disorder. Treatment options available are splenectomy, interferon, DCF and 2-CdA. 2-CdA is considered to have curative potential as proved by the other studies.

METHODS

We gave 2-CdA in a dose of 0.09/kg/day as a continuous infusion in sixteen patients of hairy cell leukaemia.

RESULTS

Three patients developed neutropenia post transfusion. At the end of three months all patients were in remission. Two patients relapsed at the median follow-up of 15 months.

CONCLUSION

2-CdA in HCL can achieve complete remission, prolonged survival and care as well.

8-chloro-cAMP and 8-chloro-adenosine act by the same mechanism in multiple myeloma cells

Previous work with 8-chloro-cAMP (8-Cl-cAMP) has raised questions as to whether it works as a cAMP analogue or as a nucleoside analogue after its conversion to 8-chloro-adenosine (8-Cl-Ado). Although degradation of 8-Cl-cAMP to 8-Cl-Ado in culture medium or plasma has been shown, cellular pharmacology data are missing. The purpose of the present study was to identify the cellular metabolism of these drugs and their actions in a human multiple myeloma cell line. The cells were incubated with either 8-Cl-Ado or 8-Cl-cAMP to follow the cellular metabolism of these agents. Both 8-Cl-cAMP and 8-Cl-Ado incubation resulted in the accumulation of 8-Cl-Ado mono-, di-, and tri-phosphate (8-Cl-ATP), however, the triphosphate was the major cytotoxic metabolite. Accumulation of 8-Cl-ATP was dependent on both the exogenous concentration of 8-Cl-Ado and incubation time. At the 10 microM level of 8-Cl-Ado, >400 microM 8-Cl-ATP accumulated in multiple myeloma cells after continuous incubation for 12 h. Similar incubation with 8-Cl-cAMP also resulted in accumulation of 8-Cl-ATP in the cells, albeit at a lower level. The formation of 8-Cl-ATP from 8-Cl-cAMP was inhibited by >80% in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine in the medium, suggesting extracellular conversion of 8-Cl-cAMP to 8-Cl-Ado. Cells lacking Ado kinase did not accumulate 8-Cl-ATP, either from 8-Cl-Ado or 8-Cl-cAMP, and were resistant to these agents. There was also a decline in the endogenous level of the cellular ATP pool parallel to the accumulation of 8-C1-ATP. The elimination of 8-Cl-ATP was biphasic and slow from the cells. The accumulation of 8-Cl-ATP and a decline in the ATP pool inhibited RNA synthesis but did not affect DNA synthesis for up to 12 h of incubation. Taken together, these data demonstrate that the cytotoxic metabolite of 8-Cl-Ado and 8-Cl-cAMP is 8-Cl-ATP. Hence, 8-Cl-cAMP serves as a prodrug and is converted to 8-Cl-Ado in medium with subsequent phosphorylation to accumulate as 8-Cl-ATP in cells. At the cellular level, 8-Cl-ATP is associated with a decrease in the endogenous ATP pool; at the nuclear level, it inhibits RNA synthesis.

Nucleoside analogues: mechanisms of drug resistance and reversal strategies

Nucleoside analogues (NA) are essential components of AML induction therapy (cytosine arabinoside), effective treatments of lymphoproliferative disorders (fludarabine, cladribine) and are also used in the treatment of some solid tumors (gemcitabine). These important compounds share some general common characteristics, namely in terms of requiring transport by specific membrane transporters, metabolism and interaction with intracellular targets. However, these compounds differ in regard to the types of transporters that most efficiently transport a given compound, and their preferential interaction with certain targets which may explain why some compounds are more effective against rapidly proliferating tumors and others on neoplasia with a more protracted evolution. In this review, we analyze the available data concerning mechanisms of action of and resistance to NA, with particular emphasis on recent advances in the characterization of nucleoside transporters and on the potential role of activating or inactivating enzymes in the induction of clinical resistance to these compounds. We performed an extensive search of published in vitro and clinical data in which the levels of expression of nucleoside-activating or inactivating enzymes have been correlated with tumor response or patient outcome. Strategies aiming to increase the intracellular concentrations of active compounds are presented.

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.

8-Cl-adenosine-induced inhibition of colorectal cancer growth in vitro and in vivo

The cAMP analogue 8-Cl-cAMP induces apoptosis and inhibits proliferation of a wide variety of malignancies in vitro and in vivo with relatively little toxicity. The antitumor effects of this compound are thought to involve its ability to modulate type I protein kinase A (PKAI). However, a nontoxic metabolite of 8-Cl-cAMP, 8-Cl-adenosine, with no known activity against PKAI, exerts growth inhibitory effects in breast, ovary, pancreas, and colorectal cancer cells in vitro and accumulates in xenografted tumors after 8-Cl-cAMP treatment in vivo. To characterize further the antitumor effects of 8-Cl-adenosine in colorectal cancer, we examined its effects on cell growth in vitro (cell number, 3H-thymidine incorporation, and soft agar colony formation) using the isogenically matched colorectal cancer cell lines HCT116, HCT116-E6 (p53-depleted), and 80S14 (p21WAF1/Cip1-null). 8-Cladenosine inhibited cell growth by 89%, 74%, and 79%, respectively in HCT116, HCT116-E6, and 80S14 cells after a 72-hour exposure. Growth inhibition coincided with DNA endoreduplication and subsequent apoptosis. Furthermore, nontoxic doses of 8-Cl-adenosine administered i.p. twice weekly for 4 weeks to athymic mice suppressed growth of HCT116-derived xenografts by 50%. These results show that 8-Cl-adenosine exerts antitumor activity against colorectal cancer independent of p53 and p21WAF1/Cip1.

Peliosis hepatis after treatment with 2-chloro-3'-deoxyadenosine

Peliosis hepatis is an unusual disorder associated with a variety of diseases and treatments. This is the first report of peliosis hepatis associated with administration of 2-chloro-3'-deoxyadenosine. The literature is reviewed.

Induction of apoptosis by 2-chloro-2'deoxyadenosine (2-CdA) alone and in combination with other cytotoxic drugs: synergistic effects on normal and neoplastic lymphocytes by addition of doxorubicin and mitoxantrone

2-CdA is active as a single agent in the treatment of low-grade lymphomas. We analyzed the induction of apoptosis by 2-CdA alone (n=5) and in combination with other drugs in peripheral lymphocytes from 25 patients with leukemic low-grade lymphomas and from 25 healthy volunteers. 2-CdA was tested in 4 escalating concentrations (0.05 microg/ml to 0.4 microg/ml). Linear regressions showed a dose dependent apoptosis rate of 0.29 x microg 2-CdA/ml + 0.11 (r2=0.88, p=0.006) in normal cells and 0.41 x microg 2-CdA/ml + 0.15 (r2=0.88, p=0.005) in leukemic cells. Intracellular metabolization of 2-CdA into 2-CdA-5'mono-, -di- and the active metabolite -triphosphate was analyzed by HPLC and paralleled the dose dependent increase of apoptosis. The combination of 2-CdA with doxorubicin or mitoxantrone had a synergistic effect on the induction of apoptosis (p<0.001) in both normal and neoplastic lymphocytes, whereas 2-CdA plus etoposide or cytosine arabinoside were only additive. Due to the flat slope of the dose response of 2-CdA concentration on apoptosis we assume that higher in vivo dosages of 2-CdA in the treatment of low-grade lymphomas may not result in a higher clinical efficacy. The synergistic lymphocytotoxic effect of 2-CdA combined with doxorubicin or mitoxantrone may be relevant for new treatment approaches.

Cladribine with or without prednisone in the treatment of previously treated and untreated B-cell chronic lymphocytic leukaemia - updated results of the multicentre study of 378 patients

Between January 1992 and January 1999, we treated 378 B-chronic lymphocytic leukaemia (CLL) patients with cladribine (2-CdA), and 255 of the patients were also treated with prednisone. A total of 194 patients were previously untreated, and 184 had relapsed or refractory disease after previous other therapy. Complete response (CR) was obtained in 111 (29.4%) and partial response (PR) in 138 (36.5%) patients, giving an overall response (OR) rate of 65.9%. CR and OR were achieved more frequently in patients in whom 2-CdA was a first-line treatment (45.4% and 82.5% respectively) than in the pretreated group (12.5% and 48.4% respectively) (P < 0.0001). The median duration of OR for previously untreated patients was 14.7 months and for pretreated patients 13.5 months (P = 0.09). The median survival evaluated from the beginning of 2-CdA treatment was shorter in the pretreated group (16.3 months) than in the untreated group (19.4 months) (P < 0.0001). A total of 117 (63.9%) patients died in the pretreated group and 63 (32.6%) in the untreated group. In pretreated patients, 2-CdA + prednisone (P) and 2-CdA alone resulted in similar OR (51.0% and 45.0% respectively; P = 0.4). In contrast, in untreated patients, 2-CdA + P produced a higher OR (85.4%) than 2-CdA alone (72.1%) (P = 0.04). Infections and fever of unknown origin, observed in 91 (49.4%) pretreated and 74 (38.1%) untreated patients (P = 0.03), were the most frequent toxic effects. Our results indicate that 2-CdA is an effective, relatively well-tolerated drug, especially in previously untreated CLL.

[Immunological markers of disease activity in the course of 2-CDA treatment of multiple sclerosis]

52 clinically definite multiple sclerosis (MS) patients were treated with subcutaneous injection of 5 mg 2-CDA in 5 consecutive days. The injection courses were repeated 6 times in one month interval. The MRI pattern and immunological markers were studied in serum and CSF before and after 6 months of treatment. The obtained results suggest that treatment with 2-CDA has not any significant effect on humoral immunological events in multiple sclerosis, what is in contrast to some normalization of cellular immunopathological processes.

The tumor necrosis factor family and and correlation with disease activity and response to treatment in hairy cell leukemia

Hairy cell leukemia (HCL) is a well recognized indolent B-cell lymphoproliferative disorder. HCL cell proliferation is regulated by growth factors and cytokines, of which tumor necrosis factor-alpha (TNF-alpha) may be one of the most important. The mechanism of TNF-alpha-induced HCL cell growth is mediated via 2 receptors, which are present in both cellular and soluble forms. In this study we determined the serum levels of TNF-alpha and their soluble receptors - sTNF-R60 and sTNF-R80 - in 23 HCL patients and correlated them with clinical parameters before and after therapy. Patients were classified according to their clinical status as either "active" at diagnosis or during relapse and "non-active" (responding to therapy with partial and complete remission). Most patients were treated with 2-CDA, following which serum levels of TNF-alpha, sTNF-R60 and sTNF-R80 were significantly decreased, particularly in CR. Significant differences in paired observation values were noted for TNF-alpha and sTNF-R80, indicating a good correlation with the clinical status of disease, but this was not the case for sTNF-R60 (coefficients of correlation between levels of TNF-alpha and sTNF-R80 and of TNF-alpha and sTNF-R60 were r = 0.85 and r= 0.64, respectively). These results suggest that decreases in both TNF-alpha and sTNF-R80 are indicative of response to treatment, while increased levels accompany active disease. Accordingly, we conclude that serum levels of the TNF family, as for the sIL-2R and IL-1 family, may also be used as sensitive markers for monitoring HCL status. Levels may be indicative of the clinical efficacy of therapy and can be used as an indicator of the presence of residual disease.

[2-CDA in treatment of hairy cell leukemia: a comparison between intravenous and subcutaneous administration. Swiss Study Group of Applied Cancer Research]

2-chlorodeoxyadenosine (2-CDA) is very effective in the treatment of patients with hairy-cell leukaemia, with an overall response rate of 80-95%. The standard treatment is a continuous intravenous infusion for 7 days. The bioavailability of 2-CDA after subcutaneous injection is 100%, but the concentration-time profile is completely different compared to continuous intravenous administration. In the present study we compared the intravenous standard treatment (group 1, n = 22; 0.1 mg/kg/d for 7 days, civ.) with subcutaneous administration of 2-CDA (group 2, n = 62; 0.14 mg/kg/d for 5 days, s.c.) in patients with hairy-cell leukaemia. In group 1, 96% (21/22) of patients responded to 2-CDA (complete remission 73%, partial remission 23%) and in the second group 97% were responsive (complete response 76%, 47/62; partial remission 21%, 13/62). The percentage for moderate and severe infections in the trial with intravenous and subcutaneous treatment was 14% and 26% respectively (p = 0.37). We conclude that subcutaneous administration of 2-CDA in patients with hairy-cell leukaemia is feasible and economical and results in comparable responses and toxicity compared to the intravenous standard treatment.

8Cl-cAMP cytotoxicity in both steroid sensitive and insensitive multiple myeloma cell lines is mediated by 8Cl-adenosine

We have examined the cytotoxic effects of cyclic adenosine-3', 5'-monophosphate (cAMP) derivatives on multiple myeloma cells lines and determined that the 8-Chloro substituted derivative (8Cl-cAMP) is one of the most potent. We report here that 8Cl-cAMP is cytotoxic to both steroid sensitive and insensitive myeloma cells with a half maximal concentration of approximately 3 micromol/L. 8Cl-cAMP toxicity in myeloma cells is dependent on phosphodiesterase activity in the serum of cell culture medium. A metabolite of 8Cl-cAMP, 8-Chloro-adenosine (8Cl-AD), kills myeloma cells as effectively as 8Cl-cAMP. Adenosine deaminase (ADA) converts 8Cl-AD into 8Cl-inosine and abrogates the cytotoxic effects of 8Cl-cAMP, 8Cl-AMP, and 8Cl-AD, as does 5-(p-Nitrobenzyl)-6-Thio-Inosine (NBTI), an inhibitor of nucleoside uptake. These data suggest that 8Cl-cAMP must be converted to 8Cl-AD and that 8Cl-AD is the compound that enters the cell. Contrary to glucocorticoid-mediated cell death in myeloma cells, the pathway of 8Cl-AD-mediated cell death appears to be independent of interleukin-6 (IL-6) actions. Although the exact mode of action for this agent is currently unknown, its ability to kill steroid sensitive and insensitive multiple myeloma cells in an IL-6 independent fashion may offer exciting new therapeutic options.

Modulation of apoptosis in human lymphocytes by adenosine analogues

We previously described that 2-chloroadenosine (2CA) and 2-chloro-2'-deoxyadenosine (2CdA) induced apoptosis in human peripheral blood mononuclear cells (PBMC). In this study we tested different adenosine analogues on PBMC and we found that the modifications introduced in the 2CA structure prevented the molecule from exerting its apoptotic effect. On the other hand, substitutions on 2CdA are tolerated, although with a significant decrease in activity.