Repression of sphingosine kinase (SK)-interacting protein (SKIP) in acute myeloid leukemia diminishes SK activity and its re-expression restores SK function.

Previous studies have shown that sphingosine kinase interacting protein (SKIP) inhibits sphingosine kinase (SK) function in fibroblasts. SK phosphorylates sphingosine producing the potent signaling molecule sphingosine-1-phosphate (S1P). SKIP gene (SPHKAP) expression is silenced by hypermethylation of its promoter in acute myeloid leukemia (AML). However, why SKIP activity is silenced in primary AML cells is unclear. Here, we investigated the consequences of SKIP down-regulation in AML primary cells and the effects of SKIP re-expression in leukemic cell lines. Using targeted ultra-HPLC-tandem MS (UPLC-MS/MS), we measured sphingolipids (including S1P and ceramides) in AML and control cells. Primary AML cells had significantly lower SK activity and intracellular S1P concentrations than control cells, and SKIP-transfected leukemia cell lines exhibited increased SK activity. These findings show that SKIP re-expression enhances SK activity in leukemia cells. Furthermore, other bioactive sphingolipids such as ceramide were also down-regulated in primary AML cells. Of note, SKIP re-expression in leukemia cells increased ceramide levels 2-fold, inactivated the key signaling protein extracellular signal-regulated kinase, and increased apoptosis following serum deprivation or chemotherapy. These results indicate that SKIP down-regulation in AML reduces SK activity and ceramide levels, an effect that ultimately inhibits apoptosis in leukemia cells. The findings of our study contrast with previous results indicating that SKIP inhibits SK function in fibroblasts and therefore challenge the notion that SKIP always inhibits SK activity.

Lesional-targeting of neuroprotection to the inflammatory penumbra in experimental multiple sclerosis.

Progressive multiple sclerosis is associated with metabolic failure of the axon and excitotoxicity that leads to chronic neurodegeneration. Global sodium-channel blockade causes side effects that can limit its use for neuroprotection in multiple sclerosis. Through selective targeting of drugs to lesions we aimed to improve the potential therapeutic window for treatment. This was assessed in the relapsing-progressive experimental autoimmune encephalomyelitis ABH mouse model of multiple sclerosis using conventional sodium channel blockers and a novel central nervous system-excluded sodium channel blocker (CFM6104) that was synthesized with properties that selectively target the inflammatory penumbra in experimental autoimmune encephalomyelitis lesions. Carbamazepine and oxcarbazepine were not immunosuppressive in lymphocyte-driven autoimmunity, but slowed the accumulation of disability in experimental autoimmune encephalomyelitis when administered during periods of the inflammatory penumbra after active lesion formation, and was shown to limit the development of neurodegeneration during optic neuritis in myelin-specific T cell receptor transgenic mice. CFM6104 was shown to be a state-selective, sodium channel blocker and a fluorescent p-glycoprotein substrate that was traceable. This compound was >90% excluded from the central nervous system in normal mice, but entered the central nervous system during the inflammatory phase in experimental autoimmune encephalomyelitis mice. This occurs after the focal and selective downregulation of endothelial p-glycoprotein at the blood-brain barrier that occurs in both experimental autoimmune encephalomyelitis and multiple sclerosis lesions. CFM6104 significantly slowed down the accumulation of disability and nerve loss in experimental autoimmune encephalomyelitis. Therapeutic-targeting of drugs to lesions may reduce the potential side effect profile of neuroprotective agents that can influence neurotransmission. This class of agents inhibit microglial activity and neural sodium loading, which are both thought to contribute to progressive neurodegeneration in multiple sclerosis and possibly other neurodegenerative diseases.

Methylseleninic acid inhibits HDAC activity in diffuse large B-cell lymphoma cell lines.

PURPOSE: Selenium is a trace element that is fundamental to human health. Research has mainly focussed on its role in cancer prevention, but recent evidence supports its role in established cancer, with high concentrations inducing tumour cell death and non-toxic concentrations sensitising cells to chemotherapy. However, the precise mechanism of selenium action is not clear. The effect of methylseleninic acid (MSA), an organic selenium compound, on histone deacetylase (HDAC) activity in diffuse large B-cell lymphoma cell lines is reported here. METHODS: Lymphoma cell lines were exposed to MSA under normoxic and hypoxic conditions. Protein expression was determined by western blotting, HDAC activity and VEGF concentration by fluorimetric and electrochemiluminescence assays, respectively, and intracellular selenium metabolites quantified by mass spectrometry. RESULTS: MSA inhibited HDAC activity, which resulted in the acetylation of histone H3 and α-tubulin. However, cellular metabolism of MSA to methylselenol was required for this effect. Dimethylselenide, the methylation product of methylselenol, was found to be the major intracellular metabolite. MSA also inhibited HIF-1α expression and VEGF secretion, a possible consequence of HDAC inhibition. CONCLUSION: The ability of methylselenol to inhibit HDAC activity has not been previously reported, thus providing a novel mechanism of selenium action.

Capabilities of HPLC with APEX-Q nebulisation ICP-MS and ESI MS/MS to compare selenium uptake and speciation of non-malignant with different B cell lymphoma lines.

The formation of intracellular dimethylselenide (DMSe) as a product of exposure of non-malignant (PBMCs) and lymphoma (RL and DHL-4) cell lines to methylseleninic acid (MSA) at clinical levels is suggested here for the first time. This was achieved by analysis of cell lysates by HPLC coupled to ICP-MS via APEX-Q nebulisation, enabling limits of detection for target methyl-Se species which are up to 12-fold lower than those obtained with conventional nebulisation. Methyl-Se-glutathione (CH3Se-SG), although detected in lysates of cells exposed to MSA, was found to be a reaction product of MSA with glutathione. This was confirmed by HPLC-ESI MS (MS) analysis of lysates of control cells (unexposed to Se) spiked with MSA. The MS/MS data obtained by collision-induced dissociation fragmentation of the ion m/z 402 (for [M+H](+) 8°Se) were consistent with the presence of CH3Se-SG. Formation of DMSe was not detected by HPLC-ICP-MS in these spiked lysates, and it was found to require live cells in cell media containing MSA. Interestingly, the ratio of DMSe to CH3Se-SG was significantly higher in lymphoma cells exposed to MSA in comparison to non-malignant cells. Moreover, maximum Se uptake levels in lymphoma cell lines seemed to be reached much earlier (after 10 min of MSA exposure) than in non-malignant cells. Finally, the GC-TOF-MS speciation data obtained for cell headspace suggested that the major Se species (dimethyldiselenide) appeared to be present in lymphoma cell headspace at significantly higher concentrations than in non-malignant cell headspace after only 10 min of exposure to MSA. Evidence for the presence of dimethylselenidesulfide in lymphoma cell headspace is also provided for the first time.

The association of CCND1 overexpression and cisplatin resistance in testicular germ cell tumors and other cancers.

Development of chemoresistance limits the clinical efficiency of platinum-based therapy. Although many resistance mechanisms have been demonstrated, genetic/molecular alterations responsible for drug resistance in the majority of clinical cases have not been identified. We analyzed three pairs of testicular germ cell tumor cell lines using Affymetrix expression microarrays and revealed a limited number of differentially expressed genes across the cell lines when comparing the parental and resistant cells. Among them, CCND1 was the most significantly differentially expressed gene. Analysis of testicular germ cell tumor clinical samples by quantitative reverse transcription PCR analysis revealed that overall expression of CCND1 was significantly higher in resistant cases compared with sensitive samples (P < 0.0001). We also found that CCND1 was dramatically overexpressed both in induced and intrinsically resistant samples of ovarian and prostate cancer. Finally combined CCND1 knockdown using small-interfering RNA and cisplatin treatment inhibited cell growth in vitro significantly more effectively than any of these single treatments. Therefore, deregulation of CCND1 may be a major cause of cisplatin resistance in testicular germ cell tumors and may also be implicated in ovarian and prostate cancers. CCND1 could be potentially used as a marker for treatment stratification and as a molecular target to improve the treatment of platinum-resistant tumors.

Identification of genomic changes associated with cisplatin resistance in testicular germ cell tumor cell lines.

Since the introduction of cisplatin into the clinic, the treatment of patients with a variety of solid tumors including testicular germ cell tumors, ovarian and lung cancers, has dramatically improved. One of the main causes for therapeutic failure in these malignancies is the development of drug resistance. Testicular germ cell tumors (TGCTs), the most common malignancy in young men, exhibit extreme sensitivity to cisplatin-based chemotherapy, making them an ideal model for investigating the mechanisms of cisplatin chemo-sensitivity and resistance. TGCT development and pathogenesis have been well studied but little is known about the genetic background in chemo-resistant cases. We investigated genomic differences between three TGCT parental cell lines and their cisplatin resistant derivatives. Using 10K single nucleotide polymorphism (SNP) microarray analysis, we identified two small chromosomal regions with consistent copy number changes across all three pairs of resistant cell lines. These were an 8.7 Mb region at 6q26-27, which displayed consistent copy number gain and a 0.3 Mb deletion involving 4 SNPs at 10p14. Both the chromosomal gain and loss were confirmed by fluorescence in situ hybridization. The significance of these regions should be further investigated as they may contain key genes involved in the development of chemo- resistance to cisplatin-based treatment in TGCTs and other cancers.

Chemosensitization of B-cell lymphomas by methylseleninic acid involves nuclear factor-kappaB inhibition and the rapid generation of other selenium species.

Although recent reports suggest that selenium can modulate the activity of cytotoxic drugs, the mechanism underlying this activity remains unclear. This has been investigated using a panel of human B-cell lymphoma cell lines. The cytotoxic effects of chemotherapeutic agents (e.g., doxorubicin, etoposide, 4-hydroperoxycyclophosphamide, melphalan, and 1-beta-d-arabinofuranosylcytosine) were increased by up to 2.5-fold when combined with minimally toxic concentrations (EC(5-10)) of the organic selenium compound, methylseleninic acid (MSA). DNA strand breaks were identified using comet assays, but the measured genotoxic activity of the combinations did not explain the observed synergistic effects in cell death. However, minimally toxic (EC(10)) concentrations of MSA induced a 50% decrease in nuclear factor-kappaB (NF-kappaB) activity after an exposure of 5 h, similar to that obtained with the specific NF-kappaB inhibitor, BAY 11-7082. Combinations of BAY 11-7082 with these cytotoxic drugs also resulted in synergism, suggesting that the chemosensitizing activity of MSA is mediated, at least in part, by its effects on NF-kappaB. Basal intracellular selenium concentration was higher in a MSA-sensitive cell line. After exposure to MSA, methylselenocysteine and selenomethionine were identified as the main intracellular species generated. Volatile selenium species, trapped using solid-phase microextraction fibers, were identified as dimethylselenide and dimethyldiselenide. These volatile species are thought to be the most biologically active forms of selenium. Taken together, these results show that the NF-kappaB pathway is one target for MSA underlying the interaction between MSA and chemotherapy. These data encourage the further clinical development of selenium as a potential modulator of cytotoxic drug activity in B-cell lymphomas.

The proteasome inhibitor bortezomib acts independently of p53 and induces cell death via apoptosis and mitotic catastrophe in B-cell lymphoma cell lines.

Bortezomib is a proteasome inhibitor with proven efficacy in multiple myeloma and non-Hodgkin's lymphoma. This study reports the effects of bortezomib in B-cell lymphoma cell lines with differing sensitivity to bortezomib to investigate factors that influence sensitivity. Bortezomib induced a time- and concentration-dependent reduction in cell viability in five lymphoma cell lines, with EC(50) values ranging from 6 nmol/L (DHL-7 cells) to 25 nmol/L (DHL-4 cells) after 72 h. Bortezomib cytotoxicity was independent of p53 function, as all cell lines exhibited mutations by sequence analysis. The difference in sensitivity was not explained by proteasome or nuclear factor-kappaB (NF-kappaB) inhibition as these were similar in the most and least sensitive cells. NF-kappaB inhibition was less marked than that of a specific NF-kappaB inhibitor, Bay 11-7082. Cell cycle analysis showed a marked G(2)-arrested population in the least sensitive DHL-4 line only, an effect that was not present with Bay 11-7082 treatment. Conversely, in DHL-7 cells, bortezomib treatment resulted in cells moving into an aberrant mitosis, indicative of mitotic catastrophe that may contribute to increased sensitivity to bortezomib. These studies show that although bortezomib treatment had similar effects on apoptotic and NF-kappaB signaling pathways in these cell lines, different cell cycle effects were observed and induction of a further mechanism of cell death, mitotic catastrophe, was observed in the more sensitive cell line, which may provide some pointers to the difference in sensitivity between cell lines. An improved understanding of how DHL-7 cells abrogate the G(2)-M cell cycle checkpoint may help identify targets to increase the efficacy of bortezomib.

Structure-activity relationships of aryloxyalkanoic acid hydroxyamides as potent inhibitors of histone deacetylase.

Syntheses of aryloxyalkanoic acid hydroxyamides are described, all of which are potent inhibitors of histone deacetylase, some being more potent in vitro than trichostatin A (IC(50)=3 nM). Variation of the substituents on the benzene ring as well as fusion of a second ring have marked effects on potency, in vitro IC(50) values down to 1 nM being obtained.

Bortezomib therapy in patients with relapsed or refractory lymphoma: potential correlation of in vitro sensitivity and tumor necrosis factor alpha response with clinical activity.

PURPOSE: To determine the efficacy of bortezomib in patients with lymphoid malignancy, correlating clinical response with effect on plasma cytokines and in vitro activity in primary cultures. PATIENTS AND METHODS: Patients received bortezomib (1.3 mg/m2) on days 1, 4, 8, and 11 of a 3-week cycle. Plasma tumor necrosis factor alpha (TNF-alpha) and interleukin-6 were measured before each treatment, and bortezomib activity was examined in patient samples grown in primary culture. RESULTS: Fifty-one patients received a total of 193 cycles of treatment. Twenty-four patients had mantle cell lymphoma (MCL), 13 had follicular lymphoma (FL), six had lymphoplasmacytic lymphoma, six had Hodgkin's disease (HD), and one each had diffuse large B-cell lymphoma and adult T-cell leukemia/lymphoma. Patients were heavily pretreated with a median of four previous therapies. Significant grade 3 to 4 toxicities were thrombocytopenia (n = 22), fatigue (n = 10), and peripheral neuropathy (n = 3). Seven patients with MCL responded to treatment (one complete response, six partial responses [PRs]; overall response rate, 29%). Two patients with FL achieved a late PR 3 months after discontinuing therapy. Two patients with Waldenström's macroglobulinemia and one patient with HD achieved a PR. MCL primary cultures demonstrated greater sensitivity to bortezomib than FL (median 50% effective concentration for viability, 209 nmol/L v 1,311 nmol/L, respectively; P = .07), which correlated with clinical response. A median reduction in plasma TNF-alpha of 98% was observed in six patients with MCL who responded to bortezomib compared with a reduction of 38% in six nonresponders (P = .07). CONCLUSION: Bortezomib demonstrates encouraging efficacy in MCL in heavily pretreated individuals. Response was associated with a reduction in plasma TNF-alpha and in vitro sensitivity in a small number of patients.

Aromatic sulfide inhibitors of histone deacetylase based on arylsulfinyl-2,4-hexadienoic acid hydroxyamides.

The synthesis of a novel series of potent inhibitors of histone deacetylases is described, based on arylsulfinyl-2,4-hexadienoic acid hydroxyamides and their derivatives. In vitro IC(50) values down to 40 nM were obtained, and several compounds showed inhibition of CEM (human leukemic) cell viability with IC(50) of approximately 1.5 microM, comparable to or better than that of suberoylanilide hydroxamic acid, an inhibitor of histone deacetylase currently in clinical trials.

Stability of morphine sulphate and diamorphine hydrochloride in intrasite gel.

Several studies have reported that opioids applied topically to painful ulcers produce an analgesic effect. It is unknown whether these opioids (usually mixed with hydrogels) are stable and, if so, for how long. We investigated the stability of morphine sulphate and diamorphine hydrochloride, each mixed with intrasite gel at a concentration of 1.25 mg/mL. Samples were prepared in the laboratory and then stored in plastic containers in the dark, at room temperature, in conditions of normal day/night at room temperature, and at 4 degrees C. Aliquots were collected from each container over a 28-day period and analysed using HPLC. No known degradation products were measured in the morphine-intrasite gel mixture stored for up to 28 days, irrespective of the temperature and whether or not samples were exposed to light, suggesting that morphine remains stable. Diamorphine, breaks down to morphine and no other degradation products are measurable.

Morphine analgesia in cancer pain: role of the glucuronides.

Preclinical data and limited studies in humans have suggested that morphine-6-glucuronide (M6G) has analgesic activity and morphine-3-glucuronide (M3G), contributes adversely to the therapeutic effect of morphine. This open point-prevalence study in 103 patients on oral morphine for cancer-related pain investigated the correlations between morphine doses, metabolites, and the degree of pain relief or toxicity. Morphine, M6G, and M3G were assayed by high-performance liquid chromatography on a single blood sample taken between two and four hours after dose. Pain, analgesia, and toxicity were recorded on numerical and visual analog scales. Patients received a median dose of 60 (range, 10 to 620) mg per day morphine, for a median of 4.1 weeks (range, 0.2 to 46.0 weeks). Ml3G:M6G ratios fell within a narrow range, with a median value of 4.39 (interquartile range, 3.78 to 6.96; range, 2.18 to 14.95). There were no significant correlations between M3G:M6G and morphine dose, or any measure of analgesia. The correlation between plasma concentration and pain score (i.e., better analgesia) was stronger for M6G (r = 0.308, p < 0.01) than morphine (r = 0.197, p = 0.05). These data suggest that M6G contributes significantly to the analgesic potency of oral morphine. No evidence was found for differences in M3G. M6G ratios contributing to analgesia or toxicity.

Lack of pharmacokinetic interaction between 5-fluorouracil and oxaliplatin.

OBJECTIVE: Our objective was to investigate the influence of oxaliplatin on the pharmacokinetics of 5-fluorouracil (5FU) administered in a bolus plus infusional regimen. PATIENTS AND METHODS: All patients had advanced/metastatic colorectal cancer. In study 1, 19 patients were studied after bolus (400 mg/m(2)) plus a 22-hour infusion (600 mg/m(2)) of 5FU/leucovorin in the standard de Gramont regimen or the same regimen with oxaliplatin (85 mg/m(2)) given before 5FU. In study 2, 12 patients were studied for 2 treatment cycles, with 5FU given in a modified de Gramont regimen comprising bolus (400 mg/m(2)) plus a 46-hour infusion (2400 mg/m(2)) of 5FU. During 1 of these cycles, oxaliplatin (85 mg/m(2)) was given before 5FU. RESULTS: The coadministration of oxaliplatin did not significantly alter 5FU area under the plasma concentration-time curve from 0 to 1 hour, area under the plasma concentration-time curve from time 0 to the last time point, or steady-state concentration in either the de Gramont (11.6 +/- 3.8 mg/L x h(-1), 14.9 +/- 4.2 mg x h/L, and 0.17 +/- 0.06 mg/L, respectively, for 5FU alone versus 9.4 +/- 2.6 mg/L x h(-1), 13.3 +/- 2.3 mg x h/L, and 0.16 +/- 0.04, respectively, for 5FU plus oxaliplatin) or modified de Gramont regimens (13.4 +/- 2.2 mg x h/L, 35.4 +/- 4.2 mg x h/L, and 0.46 +/- 0.08 mg/L, respectively, for 5FU alone versus 13.9 +/- 3.3 mg x h/L, 38.1 +/- 7.4 mg x h/L, and 0.53 +/- 0.12, respectively, for 5FU plus oxaliplatin). The inclusion of oxaliplatin coadministration as a covariate in a NONMEM analysis did not result in any change in the objective function or mean values for the following derived parameters: maximum velocity (1590 mg x h(-1)), day 1 Michaelis-Menten constant (7.8 mg x h(-1)), and day 2 Michaelis-Menten constant (11.9 mg x h(-1)). CONCLUSIONS: The coadministration of oxaliplatin in either the standard or modified de Gramont regimen does not significantly affect the pharmacokinetics of 5FU.

The bioavailability of morphine applied topically to cutaneous ulcers.

A number of studies have reported the analgesic effect of morphine when applied topically to painful skin ulcers. It has been suggested that morphine may exert a local action, as opioid receptors have been demonstrated on peripheral nerve terminals. In this study, we investigated the bioavailability of topically applied morphine to cutaneous ulcers. Six hospice inpatients with skin ulcers were given morphine sulfate 10 mg in Intrasite gel topically and morphine sulfate 10 mg subcutaneously over 4 hours, at least 48 hours apart, in randomized order. Morphine, morphine-6-glucuronide (M6G), and morphine-3-glucuronide (M3G) were determined in plasma using a specific HPLC method. In five patients morphine and its metabolites were undetectable when applied topically. In one patient (with the largest ulcer), morphine and M6G were detected. The calculated morphine and M6G bioavailability in this patient were 20% and 21%, respectively. M3G was also detected but was below the lower limit of quantitation. When applied topically to ulcers, morphine was not absorbed in the majority of patients, suggesting any analgesic effect would be mediated locally rather than systemically. However, in ulcers with a large surface area, systemic absorption may occur.

s-thalidomide has a greater effect on apoptosis than angiogenesis in a multiple myeloma cell line.

s-Thalidomide has proven efficacy in multiple myeloma. Although it has both antiangiogenic and pro-apoptotic effects, its primary mode of therapeutic action remains unclear. We have investigated the changes to the expression of genes involved with these cellular processes following culture with s-thalidomide in the U266 MM cell line. Cells were cultured with s-thalidomide (0-1000 microM), and cell parameters, including apoptosis, were assessed on day 3. RNA was extracted from cells cultured for 24 h at the IC(50) concentration of s-thalidomide, and changes to gene expression were investigated by microarray methodologies. A reduction in cell viability was observed in U266 cells cultured with s-thalidomide (IC(50): 362 microM), which were mirrored by significant increases in apoptosis (for example, 200 microM on day 3: 40.3+/-3.1% vs. 3.2+/-0.4% on day 0; P<0.001). There were changes in the expression profile of genes involved in angiogenesis and apoptosis, but the changes were most dramatic in the apoptotic genes. In particular, the expression of I-kappaB kinase was decreased by two-fold, which was associated with a four-fold decrease in NF-kappaB expression. These data correlated with immunoblotting analyses, which showed significant increases in I-kappaB protein levels and decreased NF-kappaB activity. Additionally, the Bax : Bcl-2 ratio was significantly increased. Our data suggest that both angiogenic and apoptotic genes and proteins are affected by s-thalidomide. Additionally, a dramatic decrease in Bcl-2 expression with s-thalidomide suggests a possible enhancement of cytotoxic effect if combined with other cytotoxic agents.

The schedule-dependent effects of etoposide in leukaemic cell lines: a function of concentration and duration.

PURPOSE: Etoposide is a commonly used anticancer agent that is highly schedule-dependent. The in vitro activity of etoposide (0-10 microM) was investigated in a panel of leukaemic cell lines. METHODS: Cells were cultured with etoposide in drug schedules of equal exposure duration (ED, durationxconcentration), and the effects of drug exposure on cell parameters, including cell cycle distribution, were assessed over an 8-day period. RESULTS: Proliferation assays indicated a concentration- and duration-dependent induction of cell death by etoposide in CEM and HL60 cells, and flow cytometric analysis indicated that this cell kill was by apoptosis. Efficacy was also dependent upon schedule, with more cell kill seen in schedules of longer duration. As an example, accumulative percent cell kill resulting from a continuous exposure to 0.05 microM etoposide was significantly greater than that in cultures involving either a 4-day exposure to 0.1 microM or a single-day exposure to 0.4 microM etoposide (193.4+/-15.9% vs 125.2+/-5.4% vs 42.3+/-5.9%, respectively; P<0.001 in all cases; equi-ED 0.4 microM.days). Efficacy was also dependent upon the ED of the schedule. At very low concentrations, the initial enhancement of cytotoxicity mediated by increasing duration would gradually and paradoxically be lost in the more protracted schedules (e.g. accumulative percent cell kill 66.4+/-7.4%, 158.3+/-12.0% and 40.1+/-6.0% with 100 n M for 2 days, 33 n M for 6 days and 25 n M for 8 days, respectively; P<0.001 in all cases; equi-ED 0.2 microM x days). CONCLUSIONS: Our results confirm the schedule-dependency of etoposide in vitro, highlighting the importance of total duration of drug exposure in determining cytotoxicity, and emphasizing the requirement to achieve a cytotoxic concentration in longer exposures. It is therefore crucial to ensure that etoposide regimens used clinically involve doses that are effectively cytotoxic.

Phase I and pharmacokinetic study of intravenous irinotecan plus oral ciclosporin in patients with fuorouracil-refractory metastatic colon cancer.

PURPOSE: To assess the safety and toxicity profile of escalating doses of intravenous irinotecan, in combination with a fixed dose of oral ciclosporin (Cs) and to determine the pharmacokinetic profile of irinotecan and its metabolites. PATIENTS AND METHODS: Patients with fluorouracil-refractory metastatic colorectal cancer received escalating doses of intravenous irinotecan from 40 to 125 mg/m(2) every 2 weeks in combination with a fixed dose of oral Cs (5 mg/kg bid for 3 days). Pharmacokinetic analysis of plasma irinotecan and its metabolites SN38 and SN38G was performed during paired cycles with and without Cs. RESULTS: Thirty-seven patients were treated. Dose-limiting toxicity of grade 4 neutropenia was seen at an irinotecan dose of 125 mg/m(2). There was no grade 4 diarrhea, and only one patient experienced grade 3 diarrhea. Toxicities caused by Cs were generally mild. Pharmacokinetic studies demonstrated that irinotecan clearance was reduced from 13.4 to 5.8 L/h/m(2) and area under the curve (AUC)(0-tn) was increased 2.2-fold by the coadministration of Cs. Similar significant increases in AUC(0-24h) were seen for both SN38 and SN38G (2.2-fold and 2.3-fold, respectively) in the presence of Cs. Antitumor activity was seen at every irinotecan dose level. CONCLUSION: The maximum tolerated irinotecan dose and recommended dose for phase II studies is 100 mg/m(2) every 2 weeks. Dose-limiting diarrhea was not seen during this study, supporting the hypothesis that pharmacokinetic modulation of irinotecan by Cs may improve its therapeutic index. Further studies using this combination are warranted.