Efficacy of oral cytarabine ocfosfate and etoposide in the treatment of elderly patients with higher-risk myelodysplastic syndromes compared to that in elderly acute myeloid leukemia patients.

BACKGROUND: Elderly acute myeloid leukemia (AML) patients and patients with higher-risk myelodysplastic syndromes (MDS) have a much poorer prognosis than younger patients despite intensive chemotherapy. METHODS: Ten patients with higher-risk MDS and 12 patients with AML over 65 years of age were enrolled into this study and received oral induction therapy with cytarabine ocfosfate and etoposide. RESULTS: The therapy response rates were 60% in the MDS group and 41.7% in the AML group. The difference in overall survival among MDS and AML patients was not statistically significant. The difference in the median survival times of the responsive and nonresponsive groups, which included MDS and AML patients, was statistically significant (790 and 174 days, respectively). CONCLUSIONS: Based on a comparison of the data of this therapy in elderly higher-risk MDS patients versus elderly AML patients, we conclude that this therapy is well tolerated and can be cost-effective and useful for higher-risk MDS in elderly patients.

A novel cytarabine crystalline lipid prodrug: hexadecyloxypropyl cytarabine 3',5'-cyclic monophosphate for proliferative vitreoretinopathy.

PURPOSE: The objectives of this study were to synthesize and characterize two types of cytarabine (Ara-C) lipid produgs and evaluate the prodrugs for sustained intraocular delivery after administration by intravitreal injection. METHODS: Hexadecyloxypropyl cytarabine 5'-monophosphate (HDP-P-Ara-C) and hexadecyloxypropyl cytarabine 3',5'-cyclic monophosphate (HDP-cP-Ara-C) were synthesized starting from cytarabine (1-ß-D-arabinofuranosylcytosine). Their vitreal clearance profile was simulated using a custom dissolution chamber, in vitro cytotoxicity was evaluated using cell proliferation assays, and in vivo ocular properties in rat and rabbit eyes were assessed using biomicroscopy, indirect ophthalmoscopy, tonometry, electroretinography, and histology. RESULTS: HDP-P-Ara-C was cleared from the dissolution chamber (flow rate 2 µL/min) within 7 days. In contrast, HDP-cP-Ara-C, a much more insoluble prodrug, was still detectable 36 days after the dissolution process was started. HDP-P-Ara-C had a 50% cytotoxicity concentration of 52±2.6 µM in human retinal pigment epithelium (ARPE-19) and 32±2.2 µM in a rat Müller cell line, rMC-1. The 50% cytotoxicity concentration values for HDP-cP-Ara-C in ARPE-19 and rMC-1 cells were 50 µM and 25 µM, respectively. HDP-P-Ara-C was not detectable 2 weeks after the highest intravitreal dose (228 µg/rat eye) was injected, and no ocular toxicity was found. With HDP-cP-Ara-C, the drug depot was visible for 26 weeks following a single intravitreal injection (800 µg/rabbit eye). For both compounds, the electroretinogram, intraocular pressure, and other toxicity studies were negative except for the highest dose of HDP-cP-Ara-C (800 µg/eye), which had focal toxicity from the direct touch of the retina and decreased dark adapted a-waves and decreased flicker electroretinogram amplitudes (generalized estimating equations, p=0.039 and 0.01). CONCLUSIONS: The cyclic monophosphate prodrug, HDP-cP-Ara-C, was found to have physiochemical properties better suited for sustained delivery of cytarabine to posterior segments of the eye. These properties included limited aqueous solubility, in vitro antiproliferative activity, and good tolerability after injection into rabbit eyes.

Antibacterial FANA oligonucleotides as a novel approach for managing the Huanglongbing pathosystem.

Candidatus Liberibacter asiaticus (CLas), a bacterium transmitted by the Asian citrus psyllid, Diaphorina citri, is the causal agent of citrus greening disease, or Huanglongbng (HLB). Currently, vector population suppression with insecticides and tree removal are the most effective strategies for managing the HLB pathosystem. In this study, we assessed the bactericidal capabilities of 2'-deoxy-2'-fluoro-D-arabinonucleic acid antisense oligonucleotides (FANA ASO) both in vitro and in vivo by (1) confirming their capacity to penetrate insect cells, (2) silencing bacterial essential genes, and (3) quantifying reductions in bacterial titer and D. citri transmission. We confirmed that FANA ASO are able to penetrate insect cells without the use of a delivery agent. Expression of an essential gene in the D. citri endosymbiont, Wolbachia (wDi), significantly decreased by 30% following incubation with a wDi-specific FANA ASO. Viability of isolated wDi cells also decreased in response to the FANA ASO treatment. Delivery of a CLas-specific FANA ASO to infected adult D. citri in feeding assays resulted in significant silencing of a CLas essential gene. CLas relative density and transmission were significantly lower among D. citri fed FANA ASO in diet compared to untreated insects. Root infusions of a CLas-specific FANA ASO into infected Citrus trees significantly reduced CLas titer during a 30-day trial. Our results suggest that FANA ASO targeting insect-transmitted plant bacteria or insect endosymbionts may be useful tool for integrated management of agricultural pathogens.

Antineovascular therapy with angiogenic vessel-targeted polyethyleneglycol-shielded liposomal DPP-CNDAC.

Causing damage to angiogenic vessels is a promising approach for cancer chemotherapy. The present study is a codification of a designed liposomal drug delivery system (DDS) for antineovascular therapy (ANET) with 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (CNDAC). The authors have previously reported that liposomalized 5'-O-dipalmitoylphosphatidyl CNDAC (DPP-CNDAC), a phospholipid derivative of the novel antitumor nucleoside CNDAC, is quite useful for ANET. DPP-CNDAC liposomes modified with APRPG, a peptide having affinity toward angiogenic vessels, efficiently suppressed tumor growth by damaging angiogenic endothelial cells. In the present study, the authors masked the hydrophilic moiety of DPP-CNDAC, namely, CNDAC, on the liposomal surface with APRPG-polyethyleneglycol (PEG) conjugate to improve the availability of DPP-CNDAC liposomes. The use of the APRPG-PEG conjugate attenuated the negative zeta-potential of the DPP-CNDAC liposomes and reduced the agglutinability of them in the presence of serum. These effects improved the blood level of DPP-CNDAC liposomes in colon 26 NL-17 tumor-bearing BALB/c male mice, resulting in enhanced accumulation of them in the tumor. Laser scanning microscopic observations indicated that APRPG-PEG-modified DPP-CNDAC liposomes (LipCNDAC/APRPG-PEG) colocalized with angiogenic vessels and strongly induced apoptosis of tumor cells, whereas PEG-modified DPP-CNDAC liposomes (LipCNDAC/PEG) did not. In fact, LipCNDAC/APRPG-PEG suppressed the tumor growth more strongly compared to LipCNDAC/PEG and increased significantly the life span of the mice. The present study is a good example of an effective liposomal DDS for ANET that is characterized by: (i) phospholipid derivatization of a certain anticancer drug to suit the liposomal formulation; (ii) PEG-shielding for masking undesirable properties of the drug on the liposomal surface; and (iii) active targeting to angiogenic endothelial cells using a specific probe.

The value of oral cytarabine ocfosfate and etoposide in the treatment of refractory and elderly AML patients.

Twenty-one acute myeloid leukemia (AML) patients were enrolled and received oral induction therapy with cytarabine ocfosfate (SPAC) and etoposide (EP). The median age was 69 years (range: 33-86). There were 11 patients with de novo AML and 10 AML cases that had evolved from myelodysplastic syndromes. Seventeen patients had abnormal karyotypes including eight complex abnormalities, various complications, and 7 of 21 had a poor performance status (PS) with Eastern Cooperative Oncology Group (ECOG) scores of 3-4. All patients completed induction therapy without severe adverse events. Seven achieved complete remission (CR), and two achieved partial remission (PR). Uni- and multivariate analyses demonstrated a positive and significant correlation between the results of therapy (CR +/- PR) and overall survival. The plasma concentrations of cytosine arabinoside (ara-C) in some cases were higher than those previously reported, indicating the accumulation of ara-C with increasing numbers of days of SPAC administration. We conclude that this therapy is well tolerated and useful for refractory and elderly AML patients.

Phase I clinical investigation of fludarabine phosphate by a loading-dose and continuous-infusion schedule.

Fludarabine phosphate was studied in a phase I trial of a loading-dose/continuous-infusion schedule. The schedule was chosen to rapidly achieve and maintain concentrations that have been shown in vitro to achieve maximal inhibition of cell growth. The initial level was a loading dose of 20 mg/m2 followed by a 48-hour continuous iv (CIV) infusion of 30 mg/m2 every 24 hours. For the single-dose escalation, the loading dose was held constant while the CIV dose was increased to 45 mg/m2/24 hours for 48 hours. The dose-limiting toxicity was myelosuppression, especially leukopenia. No other significant toxicity was encountered. The maximum tolerated dose was 20 mg/m2 by iv push followed by a 48-hour CIV infusion of 30 mg/m2/24 hours for 48 hours. The recommended starting dose for phase II trials is 20 mg/m2 by iv push followed by a 48-hour CIV infusion of 30 mg/m2/24 hours. This dose level achieved the target plasma levels in the 2 patients studied.

Antiproliferative effects of 9-beta-D-arabinofuranosyladenine 5'-monophosphate and related compounds in combination with adenosine deaminase inhibitors against mouse leukemia L1210/C2 cells in culture.

The antiproliferative activity of 9-beta-D-arabinofuranosyladenine 5'-monophosphate against a cultured line of mouse leukemia cells (L1210/C2) was enhanced by addition of either 2'-deoxycoformycin or erythro-9-(2-hydroxy-3-nonyl)adenine. The activity of 9-beta-D-arabinofuranosyladenine 5'-monophosphate, alone or in combination with either of the two inhibitors of adenosine deaminase, was comparable to that of 9-beta-D-arabinofuranosyladenine (ara-A), apparently reflecting the rapid conversion of 9-beta-D-arabinofuranosyladenine 5'-monophosphate to ara-A by L1210/C2 cells. Several ara-A analogs were assayed for antiproliferative activity against L1210/C2 cells; of these, only 9-beta-D-arabinofuranosyladenine 5'-O-methylphosphate and 2'-deoxy-2'-amino-9-beta-D-arabinofuraosyladenine were active. Addition of 2'-deoxycoformycin to cell culture fluids enhanced the activity of 9-beta-D-arabinofuranosyladenine 5'-O-methylphosphate suggesting conversion to an adenosine deaminase-sensitive intermediate, presumably ara-A.

Clinical pharmacology of 1-beta-D-arabinofuranosylcytosine-5'-stearylphosphate, an orally administered long-acting derivative of low-dose 1-beta-D-arabinofuranosylcytosine.

1-beta-D-Arabinofuranosylcytosine-5'-stearylphosphate (cytarabine ocfosfate, stearyl-ara-CMP) is a newly synthesized 5'-alkylphosphate derivative of 1-beta-D-arabinofuranosylcytosine (ara-C), which is lipophilic, resistant to inactivation by deamination, and orally active. Pharmacology of this drug was studied in patients with hematological malignancies. The concentrations of stearyl-ara-CMP, ara-C (its active metabolite), and 1-beta-D-arabinofuranosyluracil (ara-U, its inactive metabolite) were determined by radioimmunoassay. When six patients received a single p.o. dose of the drug (500 mg/m2), stearyl-ara-CMP, ara-C, and ara-U could be detected in the plasma for at least 72 h afterwards. The plasma disappearance curve of stearyl-ara-CMP corresponded to a one-compartment open model with first-order absorption kinetics. The peak plasma level (Cmax) was 322 +/- 218 nM, and the predicted time to reach Cmax (Tmax) was 6.5 +/- 4.5 h, while the elimination half-life (t1/2) was very long (32.0 +/- 8.4 h). The plasma ara-C level increased slowly to a Cmax of 26.3 +/- 12.7 nM (Tmax, 13.3 +/- 4.7 h) after stearyl-ara-CMP administration. This level was quite low compared with that achieved by low-dose s.c. ara-C therapy, but ara-C persisted longer in the plasma in the former case, and the area under the curve was similar for both regimens. For ara-U, the Cmax, Tmax, and t1/2 were 483 +/- 315 nM, 23.6 +/- 4.0 h, and 19.6 +/- 5.3 h, respectively. No stearyl-ara-CMP was detected in the urine, and only 8.0% of the administered dose was excreted as ara-C and ara-U within 72 h. The stearyl-ara-CMP concentration in the cerebrospinal fluid was below the limit of detection in three patients without meningeal involvement at 6 h. During clinical use of stearyl-ara-CMP, macrocytic anemia was observed, and some patients also developed megaloblastic change of their erythroblasts, suggesting a mild and persistent cytostatic effect. In conclusion, p.o. therapy with stearyl-ara-CMP achieved prolonged maintenance of the plasma drug level. Thus, the drug released a very low dose of ara-C over a long period in plasma and tissues and had a prolonged mild antineoplastic effect in patients with hematological malignancies.

Pharmacokinetics of Ara-CMP-Stearate (YNK01): phase I study of the oral Ara-C derivative.

Ara-CMP-Stearate (1-beta-D-arabinofuranosylcytosine-5'-stearylphosphate, YNK 01, Fosteabine) is the orally applicable prodrug of cytosine-arabinoside (Ara-C). During a phase I study in patients with advanced low-grade non-Hodgkin lymphomas or acute myeloid leukemia, the pharmacokinetic parameters of Ara-CMP-Stearate (kindly provided by ASTA Medica, Frankfurt, Germany) were determined by HPLC analysis. Seventy-two hours after a first starting dose which served for the determination of baseline pharmacokinetic parameters, Ara-CMP-Stearate was administered over 14 days by daily oral application. Ara-CMP-Stearate was started at a dose of 100 mg/day and was escalated in subsequent patients to 200 mg/day and 300 mg/day. Plasma and urine concentrations of Ara-CMP-Stearate, Ara-C and Ara-U were measured during the initial treatment phase and within 72 h after the end of the 14-day treatment cycle. So far six patients have been treated with 100 mg/day, three with 200 mg/day and another six with 300 mg/day. One patient was treated consecutively with 100 mg, 300 mg and 600 mg. Fitting the results of the plasma concentration measurements of Ara-CMP-Stearate to a one-compartment model, the following pharmacokinetic parameters were obtained (average and variation coefficient VC). Ara-CMP-Stearate dose-independent parameters: lag time = 1.04 h (0.57); tmax = 5.72 h (0.30); t1/2 = 9.4 h (0.36). Dose-dependent parameters: at 100 mg: AUC = 1099 ng/h/ml (0.31); concentration(max) = 53.8 ng/ml (0.28); at 200 mg: AUC = 2753 ng/h/ml (0.32); concentration(max) = 154.8 ng/ml (0.46); at 300 mg: AUC = 2940 ng/h/ml (0.66); concentration(max) = 160.0 ng/ml (0.59). The long lag time and late tmax can be explained by resorption in the distal part of the small intestine. No Ara-CMP-Stearate was detected in urine samples (limit of detection = 500 pg/ml). Pharmacokinetic parameters of Ara-C following Ara-CMP-Stearate application showed the following characteristics: t1/2 = 24.3 h (0.39); AUC (100 mg) = 262 ng/h/ml (0.93); AUC (200 mg) = 502 ng/h/ml (0.87); AUC (300 mg) = 898 ng/h/ml (1.07). Since Ara-CMP-Stearate causes intravascular hemolysis after intravenous administration, it was not possible to determine its bioavailability by comparing the AUC after oral and i.v. application. Instead, the renal elimination of Ara-U, as the main metabolite of Ara-C was measured during the first 72-h period and after the last application.(ABSTRACT TRUNCATED AT 400 WORDS)

Results of a phase II trial of a combination of oral cytarabine ocfosfate (YNK01) and interferon alpha-2b for the treatment of chronic myelogenous leukemia patients in chronic phase.

Cytarabine ocfosfate (YNK01) is a prodrug analogue of cytarabine which is resistant to systemic deamination after oral administration. Following initial studies indicating significant anti-tumour activity of YNK01 a phase II trial was initiated in order to assess the tolerability and efficacy of a combination of this agent with interferon alpha-2b (IFN-alpha2b) in recently diagnosed chronic phase CML patients (n = 98). The treatment was subdivided into cycles consisting of 4 weeks of continuous administration of IFN-alpha-2b (3 MU/m(2)/day 1st week and then 5 MU/m(2)/day) and 14 days of oral YNK01 (600 mg/day 1st cycle). At the end of each cycle the dose of YNK01 was adjusted according to the blood count observed during the previous 4 weeks. The median time from diagnosis to inclusion in the trial was 2 months (range 6 days to 7.5 months). At 12 weeks, 62 patients (63%; 95% CI, 54-73) achieved a complete hematological response. At 24 weeks, of 98 patients, two achieved a complete cytogenetic response, 14 a partial response (16% major cytogenetic response rate; 95% CI, 9-24) and 34 a minor response; 19 patients were not evaluable for cytogenetic response. During the trial, 20 patients progressed to accelerated (6) or blastic phases (14). The median time to progression was 15 months (range 2-38 months). At 3 years the overall survival was 79% (95% CI, 70-88). Although the complete hematological response rate compared favorably with the 40% response rate previously obtained with the subcutaneous formulation of Ara-c, the cytogenetic response rate was less than expected. Most of the patients experienced side-effects and all permanently stopped YNK01. Although the combination seems attractive the initial dose of 600 mg per day is probably too high and should be reconsidered in further trials.

Galactosylated poly(L-lysine) as a hepatotropic carrier of 9-beta-D-arabinofuranosyladenine 5'-monophosphate.

D-Galactopyranosyl residues were coupled to poly(L-lysine) and the antiviral agents arabinofuranosyladenine 5'-monophosphate (ara-AMP) and acyclovir were conjugated with this glycosylated polymer. In mice the ara-AMP conjugate accomplished a selective drug delivery to liver cells.

The effect of YNK-01 (an oral prodrug of cytarabine) on hepatocellular carcinoma.

Thirty-two patients with hepatocellular carcinoma (HCC) were treated with YNK-01, a prodrug of cytarabine for oral administration. A dose of 200 mg/d of YNK-01 was administered to 17 cases and 300 mg/d to 15 cases. One course was 2 weeks in duration, and this was repeated every 4 weeks for as long as the patients were able to tolerate it. There were five partial responses (15%) and 13 patients with no change (41%). A higher partial response rate was observed in the 300 mg/d group (27%) compared with the 200 mg/d group (6%). The average durations of partial response and no change were approximately 4 and 3 months, respectively. The main side effects of YNK-01 were anemia, leukopenia, thrombocytopenia, and symptoms of the alimentary tract (nausea, anorexia, diarrhea, etc). These results suggest that YNK-01 is a potentially useful oral agent for chemotherapy of hepatocellular carcinoma.

Acyclovir and vidarabine monophosphate: comparison of iontophoretic and intravenous administration for the treatment of HSV-1 stromal keratitis.

We determined the therapeutic efficacy of iontophoretic application of acyclovir and vidarabine monophosphate (ara-AMP) for the treatment of herpes simplex virus (HSV) type 1-induced stromal keratitis in rabbits. The therapeutic efficacy of intravenous administration of acyclovir was assessed in the same model. Stromal keratitis was produced by intrastromal injection of 10 microliters purified HSV-1, McKrae strain. Treatment began the first day after intrastromal injection. Iontophoresis (0.5 mAmp for four minutes) of 3.4 percent (0.1 M) ara-AMP and 5.0 percent (0.22 M) acyclovir was performed once daily for five consecutive days in two treatment groups. Intravenous administration of 50 mg acyclovir/kg was performed twice daily for eight consecutive days. Intravenous administration of NaCl (0.14 M) and ocular iontophoresis of NaCl (0.14 M) were performed as controls in the two treatment groups. At least two scorers performed a single masked evaluation of the disease severity (lesion scoring) of the conjunctiva, corneal epithelium, stroma, and iris by still lamp examination. The eyes were scored daily for 12 consecutive days, and then every other day up to day 22. Iontophoresis of acyclovir or ara-AMP significantly reduced the course of the disease compared with iontophoresis of NaCl. Intravenous administration of acyclovir significantly reduced the disease compared with intravenous NaCl. This suggests that iontophoresis of acyclovir or ara-AMP either alone or in combination with intravenous administration of acyclovir may be of value in the treatment of HSV-1 stromal keratitis.

Drug targeting in antiviral chemotherapy. A chemically stable conjugate of 9-beta-D-arabinofuranosyl-adenine 5'-monophosphate with lactosaminated albumin accomplishes a selective delivery of the drug to liver cells.

With the aim of improving the chemotherapeutic index of 9-beta-D-arabinofuranosyl-adenine 5' monophosphate (ara-AMP) in the treatment of chronic hepatitis B, this drug was conjugated with lactosaminated serum albumin (L-SA), a neoglycoprotein which only enters into hepatocytes. We used a L-SA-ara-AMP conjugate which, in contrast to those previously employed, has the advantage of remaining soluble after lyophilization. We found in mice that: (I) this new conjugate was quite stable in the bloodstream where only a small part of ara-AMP was released; (II) after administration of the conjugate labelled in the drug moiety both acid insoluble and soluble radioactivities were several times higher in liver than in other organs; (III) in mice with Ectromelia virus hepatitis, the conjugate inhibited virus DNA synthesis in liver without affecting cellular DNA synthesis in intestine and bone marrow; (IV) the conjugate did not display any recognizable sign of acute toxicity even at doses several fold higher than those pharmacologically active; and (V) when prepared with homologous albumin it was not immunogenic.

Treatment of patients with advanced chronic myelogenous leukemia with interferon-alpha-2b and continuous oral cytarabine ocfosfate (YNK01): a pilot study.

The efficacy of continuous oral cytarabine ocfosfate (YNK01) (300 mg/day) in combination with interferon alpha (IFNalpha, 5x10(6) IU/day) was evaluated in patients with advanced chronic myelogenous leukemia, who previously failed to respond to IFNalpha-based therapies. Dose escalations up to 900 mg YNK01 were allowed in patients who failed to respond. In view of our results, four patients developed a complete hematological response after YNK01 was started. Among those who initially responded to YNK01, one complete cytogenetic response was achieved 18 months later. Although the data are preliminary, this is the first study showing that continuous administration of YNK01 along with IFNalpha is effective in patients with advanced chronic myelogenous leukemia.

Treatment of acute myeloid leukemia and myelodysplastic syndrome with orally administered cytarabine ocfosfate and granulocyte colony-stimulating factor.

Cytarabine ocfosfate (SPAC) was administered orally to 19 patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). SPAC was administered at doses of 200-300 mg/day for more than 14 days with granulocyte colony-stimulating factor (G-CSF). Four of the 12 patients with AML and 1 of the 7 patients with MDS achieved complete remission (CR) after one cycle of SPAC treatment. Especially, 3 of the 6 patients with newly diagnosed AML achieved CR. Major side effects of SPAC were myelosuppression and tolerable gastrointestinal disorders. The treatment with SPAC is a therapeutic option in elderly patients or patients with organ failure.

Bone marrow cytogenetic complete remission achieved by interferon-alpha plus cytarabine ocfosfate therapy in a patient with chronic myelogenous leukemia during extramedullary blast crisis.

We report a case of chronic myelogenous leukemia (CML) in which the bone marrow achieved cytogenetic complete remission (CCR) achieved by treatment with interferon-alpha and oral cytarabine ocfosfate after extramedullary blast crisis. A 51-year-old Japanese man diagnosed with CML was treated with interferon-alpha. Two months later; lymph node swellings developed in his neck and inguinal regions. Lymph node biopsy revealed the infiltration of blast cells showing bcr-abl fusion signal by fluorescence in situ hybridization analysis. Bone marrow aspiration and cytogenetic analysis demonstrated that his bone marrow was still in the chronic phase, with minor cytogenetic response. Continuing interferon-alpha for 6 months in combination with oral cytarabine ocfosfate resulted in the disappearance of the neck lymph node swellings followed by CCR in the bone marrow. However, rapid reenlargement of the neck and inguinal lymph nodes was noted 2 months after CCR despite maintaining medullary remission with major cytogenetic response. Finally, medullary crisis was noted 13 months from the initial development of the extramedullary crisis. This case suggests that interferon-alpha plus cytarabine ocfosfate therapy may be of benefit in the treatment of extramedullary blast crisis of CML.

Combined oral administration of etoposide and arabinofuranosylcytosine-5'-stearylphosphate enhances the antitumor effect against P388 ascites tumors.

We investigated the antitumor effect of oral administration of etoposide and arabinofuranosylcytosine-5'-stearylphosphate (C18PCA) against P388 ascites tumors in B6D2F1 mice. Etoposide (25 mg/kg) and C18PCA (5 mg/kg) were given orally on days 1-5 after tumor inoculation. The median life span of the mice treated with etoposide or C18PCA alone was 19.5 and 18 days, respectively. The combination of both drugs significantly extended the median life span to 33 days. To clarify this enhancement of the increase in median life span, we examined intracellular deoxyribonucleoside triphosphate (dNTP) pools, cell-cycle distribution, DNA fragmentation, and the time course of the plasma drug concentration. Etoposide had no effect on intracellular dNTP pools in this experimental system, whereas treatment of cells with C18PCA or with the combination of both drugs resulted in a significant increase in dTTP pools to values ranging from 1.8- to 2.0-fold higher than the control levels. There was a significant increase in cells in the S + G2/M phase when cells had been treated with both etoposide and C18PCA. Agarose-gel electrophoresis of the extracted DNA revealed that C18PCA enhanced the fragmentation of DNA, with a length of about 180 bp being induced by etoposide. The plasma peak levels of etoposide (1000 nM) and ara-C (50 nM) were observed at 20 and 30 min after the simultaneous administration of both drugs, respectively. The plasma etoposide level gradually decreased to 10% of the peak level at 240 min after administration. On the other hand, the plasma concentration of ara-C was maintained at above 20 nM at 240 min. These observations suggest that C18PCA and etoposide act on P388 murine leukemic cells by accumulating cells in the S + G2/M phase. Even if the plasma concentration of ara-C is low, the repair of DNA damage by etoposide may be hindered in the presence of ara-C following an increase in DNA fragmentation.

Characteristic antitumor activity of cytarabine ocfosfate against human colorectal adenocarcinoma xenografts in nude mice.

The antitumor activity of cytarabine ocfosfate (SPAC) was tested against human colorectal, gastric and lung adenocarcinoma xenografts in nude mice in comparison with the activities of various antitumor drugs used clinically. SPAC showed higher therapeutic efficacy against human colorectal adenocarcinoma xenografts than against human gastric and lung adenocarcinoma xenografts. SPAC was effective against three of four human colorectal adenocarcinoma xenografts, with efficacy higher than that of 1-beta-D-arabinofuranosylcytosine, fluorouracil, cisplatin, doxorubicin, pirarubicin and vindesine sulfate, but lower than that of mitomycin C and cyclophosphamide. These results indicate that SPAC may be useful for induction and/or postoperative chemotherapy against colorectal adenocarcinomas.

A severe hepatic disorder with myelodysplastic syndrome, treated with cytarabine ocfosfate, in a dog.

An 8-year-old female Shih Tzu was presented with weight loss and vomiting. Alanine aminotransferase was high and abdominal radiographs revealed hepato- and splenomegaly. Mild anaemia, neutrophilia with left shift, eosinophilia, a thrombocytosis with dysplastic features of eosinophils and platelets, were detected. The animal was initially considered to have hepatitis and was treated accordingly, but clinical signs persisted. Histological examination of liver biopsy samples showed disruption of the hepatic lobule, with extensive infiltration by haemopoietic cells. Further investigation of the bone marrow suggested a diagnosis of myelodysplastic syndrome. The animal was treated with cytarabine ocfosfate, a prodrug of cytosine arabinoside, and appeared to recover.