Capecitabine, oxaliplatin and radiotherapy: a phase IB neoadjuvant study for esophageal cancer with gene expression analysis.

PURPOSE: To determine the maximal tolerated dose of capecitabine with oxaliplatin + radiotherapy in a phase I study of localized esophageal cancer. PATIENTS AND METHODS: Oxaliplatin (85 mg/m(2)) administered on days 1, 15, and 29. Capecitabine administered twice daily 5 days weekly; dose levels (DL) were 1, 1000; 2, 1250; and 3, 1500 mg/m(2) with 50.4 Gy radiation. RESULTS: Dose-limiting toxicity was reached at DL 3. Carboxylesterase expression in day 2 tumor specimens and induction correlated with response (p

Evaluation of serum iohexol clearance for use in predicting carboplatin clearance in cats.

OBJECTIVE: To determine whether a glomerular filtration rate (GFR) assay based on serum iohexol clearance can be used to predict carboplatin clearance in cats. ANIMALS: 10 cats with tumors. PROCEDURES: GFR was measured concurrently by use of plasma clearance of technetium Tc 99m-labeled diethylenetriaminepentaacetic acid ((99m)Tc-DTPA) to yield GFR(99mTc-DTPA) and serum clearance of iohexol to yield GFR(Iohexol). A single dose of carboplatin was administered IV as a bolus. Dose was calculated by use of a target value for the area under the plasma platinum concentration-versus-time curve (AUC(Target)) and estimation of platinum clearance (CL(PT)) derived from GFR(99mTc-DTPA) as follows: dose = AUC(Target) x 2.6 x GFR(99mTc-DTPA) x body weight, where AUC(Target) is 2.75 min.mg.mL(-1). Plasma platinum concentrations were measured via atomic absorption spectrophotometry. Values for GFR(99mTc-DTPA) and GFR(Iohexol) were compared by use of least-squares regression and Bland-Altman analysis. Least-squares regression was used to determine whether CL(PT) could be predicted from GFR(99mTc-DTPA) or GFR(Iohexol) (or both). RESULTS: GFR(99mTc-DTPA) and GFR(Iohexol) were strongly correlated (r = 0.90), but GFR(Iohexol) values were significantly larger by a factor of approximately 1.4. Platinum clearance had a significant linear relationship to GFR(99mTc-DTPA) (CL(PT) = 2.5 x GFR(99mTc-DTPA)) and to GFR(Iohexol) (CL(PT) = [1.3 x GFR(Iohexol)] + 1.4). CONCLUSIONS AND CLINICAL RELEVANCE: In cats, serum iohexol clearance was an accurate predictor of CL(PT) and can be used to calculate the carboplatin dose as follows: dose = AUC(Target) x ([1.3 x GFR(Iohexol)] + 1.4) x body weight.

A Phase I and pharmacokinetic study of selenomethionine in combination with a fixed dose of irinotecan in solid tumors.

PURPOSE: We conducted a phase I study to determine the recommended dose of selenomethionine (SLM) in combination with irinotecan that consistently results in a protective plasma selenium (Se) concentrations > 15 microM after 1 week of SLM loading. EXPERIMENTAL DESIGN: A 3-3 standard escalation design was followed. SLM was given orally twice daily (BID) for one week (loading) followed by continuous once daily (QD) dosing (maintenance). Seven dose levels of selenomethionine were investigated. Irinotecan was given intravenously at a fixed standard weekly dose, starting on the first day of maintenance SLM. RESULTS: Thirty-one patients were treated on study. Dose limiting diarrhea complicated by sepsis was noted in one of six patients at each of the dose-levels 1 and 7. Dose-levels > or = 5 (4,800 mcg/dose loading maintenance) resulted in day 8 Se concentrations >15 microM while dose-level 7 (7,200 mcg/dose loading and maintenance) resulted in day 8 Se concentrations > 20 muM. No significant variations in SN-38 or biliary index were noted between weeks 1 and 4 of treatment. Despite achieving target Se concentrations, gastrointestinal and bone marrow toxicities were common and irinotecan dose modification was prevalent. Objective responses were seen in two patients and nine patients had disease control for 6 months or longer. CONCLUSIONS: Selenomethionine can be escalated safely to 7,200 mcg BID x 1 week followed by 7,200 mcg QD in combination with a standard dose of irinotecan. No major protection against irinotecan toxicity was established; however, interesting clinical benefits were noted-supporting the investigation of this combination in future efficacy trials.

Analysis of platinum content in biodegradable carboplatin-impregnated beads and retrospective assessment of tolerability for intralesional use of the beads in dogs following excision of subcutaneous sarcomas: 29 cases (2011-2014).

OBJECTIVE To evaluate platinum content in biodegradable carboplatin-impregnated beads and retrospectively assess tolerability and outcome data for dogs treated by intralesional placement of such beads following surgical excision of subcutaneous sarcomas. DESIGN Evaluation study and retrospective case series. SAMPLE 9 carboplatin-impregnated beads and 29 client-owned dogs. PROCEDURES Platinum content in 9 carboplatin-impregnated beads from 3 lots was measured by spectrophotometry, and calculated carboplatin content was compared with the labeled content. Medical records were searched to identify dogs with subcutaneous sarcomas for which treatment included placement of carboplatin-impregnated beads between 2011 and 2014. Signalment, tumor characteristics, surgical and histologic data, adverse events, and local recurrences were recorded. Associations between variables of interest and adverse events or local disease-free interval were analyzed. RESULTS In vitro analysis identified a mean ± SD platinum content of 5.38 ± 0.97 mg/bead. Calculated carboplatin content (10.24 ± 1.84 mg/bead) was significantly greater than the labeled amount (4.6 mg/bead). Bead weight and total platinum content differed significantly among lots, but platinum content per bead weight did not. Mild-to-moderate local adverse events were reported for 11 of 29 tumors; all resolved without additional surgery. No dogs had signs of systemic toxicosis. Overall local disease-free rates 1, 2, and 3 years after surgery were 70%, 70%, and 58%, respectively, as determined by Kaplan-Meier analysis. CONCLUSIONS AND CLINICAL RELEVANCE Carboplatin-impregnated beads were well tolerated; however, results of in vitro tests indicated that caution is needed because of manufacturing inconsistencies.

Efficacy of increasing the therapeutic index of irinotecan, plasma and tissue selenium concentrations is methylselenocysteine dose dependent.

This study was designed to understand the basis for the efficacy of methylselenocysteine (MSC) in increasing the therapeutic index of irinotecan against human tumor xenografts. Nude mice bearing human head and neck squamous cells carcinoma xenografts (FaDu and A253) were treated orally with different doses of MSC and irinotecan. Plasma, tumor and normal tissue samples were collected at different times after MSC treatments and were analyzed for selenium (Se) concentration using electrothermal atomic absorption spectrophotometry. MSC is highly effective in modulating the therapeutic index of irinotecan. Enhanced irinotecan efficacy was greater in FaDu tumors (100% CR) than in A253 tumors (60% CR), and depended on MSC dose with a minimum effective dose of 0.01 mg/dx28. The highest plasma Se concentration was achieved 1h after a single dose and 28 d after daily treatments of MSC. The ability of FaDu tumors to retain Se was significantly better than A253 tumors, and the highest Se concentration in normal tissue was achieved in the liver. Peak plasma and tissue Se concentrations were functions of the dose and duration of MSC treatment. The MSC-dependent increase in Se level in normal tissues may contribute to the protective effect against irinotecan toxicity observed in those tissues. Intratumoral total Se concentration was not found to be predictive of the combination therapy response rates. There is a critical need to develop a method to measure the active metabolite of MSC, rather than total Se.

A phase I and pharmacokinetic study of fixed-dose selenomethionine and irinotecan in solid tumors.

PURPOSE: We conducted a phase I study to determine the maximum tolerated dose (MTD) of irinotecan with fixed, nontoxic high dose of selenomethionine. EXPERIMENTAL DESIGN: Selenomethionine was given orally as a single daily dose containing 2,200 mug of elemental selenium (Se) starting 1 week before the first dose of irinotecan. Irinotecan was given i.v. once weekly x 4 every 6 weeks (one cycle). The starting dose of irinotecan was 125 mg/m(2)/wk. Escalation occurred in cohorts of three patients until the MTD was defined. Pharmacokinetic studies were done for selenium and irinotecan and its metabolites. RESULTS: Three of four evaluable patients at dose level 2 of irinotecan (160 mg/m(2)/wk) had a dose-limiting diarrhea. None of the six evaluable patients at dose level 1 (125 mg/m(2)/wk irinotecan) had a dose-limiting toxicity. One patient with history of irinotecan-refractory colon cancer achieved a partial response. The long half-life of selenium resulted in a prolonged accumulation towards steady-state concentrations. No significant changes in the pharmacokinetics of CPT-11, SN-38, or SN-38G were identified; however, the coadministration of selenomethionine significantly reduced the irinotecan biliary index, which has been associated with gastrointestinal toxicity. CONCLUSIONS: Selenomethionine at 2,200 mug/d did not allow the safe escalation of irinotecan beyond the previously defined MTD of 125 mg/m(2). None of the patients receiving 125 mg/m(2) of irinotecan had grade >2 diarrhea. Unexpected responses and disease stabilizations were noted in a highly refractory population. Further escalation of selenomethionine is recommended in future trials to achieve defined protective serum concentrations of selenium.

A phase 1 trial of intravenous liposomal irinotecan in patients with recurrent high-grade glioma.

PURPOSE: Preclinical activity of irinotecan has been seen in glioma models, but only modest efficacy has been noted in clinical studies, perhaps related to drug distribution and/or pharmacokinetic limitations. In preclinical testing, irinotecan liposome injection (nal-IRI) results in prolongation of drug exposure and higher tissue levels of drug due to slower metabolism and the effect of enhanced permeability and retention. The objective of the current study was to assess the safety and pharmacokinetics (PK) of nal-IRI and to determine the maximum tolerated dose (MTD) in patients with recurrent high-grade glioma stratified based on UGT1A1 genotyping. METHODS: This phase I study stratified patients with recurrent high-grade glioma into 2 groups by UGT1A1 status: homozygous WT ("WT") vs heterozygous WT/*28 ("HT"). Patients who were homozygous *28 were ineligible. The design was a standard 3 + 3 phase I design. WT patients were started at 120 mg/m2 intravenously every 3 weeks with dose increases in 60 mg/m2 increments. HT patients were started at 60 mg/m2, with dose increases in 30 mg/m2 increments. The assessment period for dose-limiting toxicity was 1 cycle (21 days). RESULTS: In the WT cohort (n = 16), the MTD was 120 mg/m2. In the HT cohort (n = 18), the MTD was 150 mg/m2. Dose-limiting toxicity in both cohorts included diarrhea, some with associated dehydration and/or fatigue. PK results were comparable to those seen in other PK studies of nal-IRI; UGT1A1*28 genotype (WT vs. HT) did not affect PK parameters. CONCLUSIONS: Nal-IRI had no unexpected toxicities when given intravenously. Of note, UGT1A1 genotype did not correlate with toxicity or affect PK profile.

Correlation between Ferumoxytol Uptake in Tumor Lesions by MRI and Response to Nanoliposomal Irinotecan in Patients with Advanced Solid Tumors: A Pilot Study.

Purpose: To determine whether deposition characteristics of ferumoxytol (FMX) iron nanoparticles in tumors, identified by quantitative MRI, may predict tumor lesion response to nanoliposomal irinotecan (nal-IRI).Experimental Design: Eligible patients with previously treated solid tumors had FMX-MRI scans before and following (1, 24, and 72 hours) FMX injection. After MRI acquisition, R2* signal was used to calculate FMX levels in plasma, reference tissue, and tumor lesions by comparison with a phantom-based standard curve. Patients then received nal-IRI (70 mg/m2 free base strength) biweekly until progression. Two percutaneous core biopsies were collected from selected tumor lesions 72 hours after FMX or nal-IRI.Results: Iron particle levels were quantified by FMX-MRI in plasma, reference tissues, and tumor lesions in 13 of 15 eligible patients. On the basis of a mechanistic pharmacokinetic model, tissue permeability to FMX correlated with early FMX-MRI signals at 1 and 24 hours, while FMX tissue binding contributed at 72 hours. Higher FMX levels (ranked relative to median value of multiple evaluable lesions from 9 patients) were significantly associated with reduction in lesion size by RECIST v1.1 at early time points (P < 0.001 at 1 hour and P < 0.003 at 24 hours FMX-MRI, one-way ANOVA). No association was observed with post-FMX levels at 72 hours. Irinotecan drug levels in lesions correlated with patient's time on treatment (Spearman ρ = 0.7824; P = 0.0016).Conclusions: Correlation between FMX levels in tumor lesions and nal-IRI activity suggests that lesion permeability to FMX and subsequent tumor uptake may be a useful noninvasive and predictive biomarker for nal-IRI response in patients with solid tumors. Clin Cancer Res; 23(14); 3638-48. ©2017 AACR.

Polyamine catabolism in platinum drug action: Interactions between oxaliplatin and the polyamine analogue N1,N11-diethylnorspermine at the level of spermidine/spermine N1-acetyltransferase.

A great deal of experimental evidence connects induction of polyamine catabolism via spermidine/spermine N1-acetyltransferase (SSAT) to antiproliferative activity and apoptosis. Following our initial observation from gene expression profiling that platinum drugs induce SSAT, we undertook this present study to characterize platinum drug induction of SSAT and other polyamine catabolic enzymes and to examine how these responses might be enhanced with the well-known inducer of SSAT and clinically relevant polyamine analogue, N1,N11-diethylnorspermine (DENSPM). The results obtained in A2780 ovarian cancer cells by real-time quantitative RT-PCR and Northern blot analysis show that a 2-hour exposure of A2780 cells to platinum drugs induces expression of SSAT, a second SSAT (SSAT-2), spermine oxidase, and polyamine oxidase in a dose-dependent manner. At equitoxic doses, oxaliplatin is more effective than cisplatin in SSAT induction. The most affected enzyme, SSAT, increased 15-fold in mRNA expression and 2-fold in enzyme activity. When combined with DENSPM to further induce SSAT and to enhance conversion of mRNA to activity, oxaliplatin increased SSAT mRNA 50-fold and activity, 210-fold. Polyamine pools declined in rough proportion to levels of SSAT induction. At pharmacologically relevant oxaliplatin exposure times (20 hours) and drug concentrations (5 to 15 micromol/L), these responses were increased even further. Combining low-dose DENSPM with oxaliplatin produced a greater than additive inhibition of cell growth based on the sulforhodamine-B assay. Taken together, the findings confirm potent induction of polyamine catabolic enzymes, such as SSAT by platinum drugs, and demonstrate that these biochemical responses as well as growth inhibition can be potentiated by co-treatment with the polyamine analogue DENSPM. With appropriate in vitro and in vivo optimization, these findings could lead to clinically relevant therapeutic strategies.

FL118, a novel camptothecin analogue, overcomes irinotecan and topotecan resistance in human tumor xenograft models.

Irinotecan and topotecan are the only camptothecin analogues approved by the FDA for cancer treatment. However, inherent and/or acquired irinotecan and topotecan resistance is a challenging issue in clinical practice. In this report, we showed that FL118, a novel camptothecin analogue, effectively obliterated human xenograft tumors that acquire irinotecan and topotecan resistance. Consistent with this finding, Pharmacokinetics studies indicated that FL118 rapidly clears from circulation, while effectively accumulating in tumors with a long elimination half-life. Consistent with our previous studies on irinotecan, FL118 exhibited ≥25 fold more effectiveness than topotecan at inhibiting cancer cell growth and colony formation; we further showed that although topotecan can inhibit the expression of survivin, Mcl-1, XIAP or cIAP2, its effectiveness is about 10-100 fold weaker than FL118. Lastly, in contrast to both SN-38 (active metabolite of irinotecan) and topotecan are substrates of the efflux pump proteins P-gp/MDR1 and ABCG2/BCRP, FL118 is not a substrate of P-gp and ABCG2. Consistently, sildenafil, a multiple efflux pump inhibitor, sensitized SN-38 much more than these of the ABCG2-selective inhibitor KO143 in growth inhibition of SW620 and HCT-8 cells. In contrast, both inhibitors showed no effect on FL118 efficacy. Given that both P-gp and ABCG2 express in SW620 and HCT-8 cells and FL118 is not a substrate for P-gp and ABCG2, this suggests that FL118 appears to bypass multiple efflux pump protein-induced resistance, which may contribute to FL118 overcoming irinotecan and topotecan resistance in vivo. These new findings provide renewed perspectives for further development of FL118 for clinical applications.

Tumor priming by Apo2L/TRAIL reduces interstitial fluid pressure and enhances efficacy of liposomal gemcitabine in a patient derived xenograft tumor model.

Interstitial fluid pressure (IFP) is elevated in tumors and high IFP, a negative cancer prognosticator, is known to limit the uptake and efficacy of anti-tumor therapeutics. Approaches that alter the tumor microenvironment and enhance uptake of therapeutics are collectively referred to as tumor "priming". Here we show that the cytotoxic biological therapy Apo2L/TRAIL can prime the tumor microenvironment and significantly lower IFP in three different human tumor xenograft models (Colo205, MiaPaca-2 and a patient gastrointestinal adenocarcinoma tumor xenograft). We found that a single dose of Apo2L/TRAIL resulted in a wave of apoptosis which reached a maximum at 8h post-treatment. Apoptotic debris subsequently disappeared concurrent with an increase in macrophage infiltration. By 24h post-treatment, treated tumors appeared less condensed with widening of the stromal areas which increased at 48 and 72h. Analysis of tumor vasculature demonstrated a significant increase in overall vessel size at 48 and 72h although the number of vessels did not change. Notably, IFP was significantly reduced in these tumors by 48h after Apo2L/TRAIL treatment. Administration of gemcitabine at this time resulted in increased tumor uptake of both gemcitabine and liposomal gemcitabine and significantly improved anti-tumor efficacy of liposomal gemcitabine. These results suggest that Apo2L/TRAIL has a potential as a tumor priming agent and provides a rationale for developing a sequencing schema for combination therapy such that an initial dose of Apo2L/TRAIL would precede administration of gemcitabine or other therapies.

Influence of sex and race on mycophenolic acid pharmacokinetics in stable African American and Caucasian renal transplant recipients.

BACKGROUND AND OBJECTIVES: No evaluation of sex and race influences on mycophenolic acid (MPA) pharmacokinetics and adverse effects (AEs) during enteric-coated mycophenolate sodium (ECMPS) and tacrolimus immunosuppression are available. The primary objective of this study was to investigate the influence of sex and race on MPA and MPA glucuronide (MPAG) pharmacokinetics in stable renal transplant recipients receiving ECMPS and tacrolimus METHODS: The pharmacokinetics of MPA and MPAG and their associated gastrointestinal AEs were investigated in 67 stable renal transplant recipients: 22 African American males (AAMs), 13 African American females (AAFs), 16 Caucasian males (CMs), and 16 Caucasian females (CFs) receiving ECMPS and tacrolimus. A validated gastrointestinal AE rating included diarrhea, dyspepsia, vomiting, and acid-suppressive therapy was completed. Apparent clearance, clearance normalized to body mass index (BMI), area under the concentration-time curve from time zero to 12 h (AUC12) and dose-normalized AUC12 (AUC*) were determined using a statistical model that incorporated gastrointestinal AE and clinical covariates. RESULTS: Males had more rapid apparent MPA clearance (CMs 13.8 ± 6.27 L/h vs. AAMs 10.2 ± 3.73 L/h) than females (CFs 8.70 ± 3.33 L/h and AAFs 9.71 ± 3.94 L/h; p = 0.014) with a race-sex interaction (p = 0.043). Sex differences were observed in MPA clearance/BMI (p = 0.033) and AUC* (p = 0.033). MPA AUC12 was greater than 60 mg·h/L in 57 % of renal transplant recipients (RTR) with 71 % of patients demonstrating gastrointestinal AEs and a higher score noted in females. In all patients, females exhibited 1.40-fold increased gastrointestinal AE scores compared with males (p = 0.024). Race (p = 0.044) and sex (p = 0.005) differences were evident with greater MPAG AUC12 in AAFs and CFs. CONCLUSION: Sex and race differences were evident, with females having slower MPA clearance, higher MPAG AUC12, and more severe gastrointestinal AEs. These findings suggest sex and race should be considered during MPA immunosuppression.

Sunitinib dose escalation overcomes transient resistance in clear cell renal cell carcinoma and is associated with epigenetic modifications.

Sunitinib is considered a first-line therapeutic option for patients with advanced clear cell renal cell carcinoma (ccRCC). Despite sunitinib's clinical efficacy, patients eventually develop drug resistance and disease progression. Herein, we tested the hypothesis whether initial sunitinib resistance may be transient and could be overcome by dose increase. In selected patients initially treated with 50 mg sunitinib and presenting with minimal toxicities, sunitinib dose was escalated to 62.5 mg and/or 75 mg at the time of tumor progression. Mice bearing two different patient-derived ccRCC xenografts (PDX) were treated 5 days per week with a dose-escalation schema (40-60-80 mg/kg sunitinib). Tumor tissues were collected before dose increments for immunohistochemistry analyses and drug levels. Selected intrapatient sunitinib dose escalation was safe and several patients had added progression-free survival. In parallel, our preclinical results showed that PDXs, although initially responsive to sunitinib at 40 mg/kg, eventually developed resistance. When the dose was incrementally increased, again we observed tumor response to sunitinib. A resistant phenotype was associated with transient increase of tumor vasculature despite intratumor sunitinib accumulation at higher dose. In addition, we observed associated changes in the expression of the methyltransferase EZH2 and histone marks at the time of resistance. Furthermore, specific EZH2 inhibition resulted in increased in vitro antitumor effect of sunitinib. Overall, our results suggest that initial sunitinib-induced resistance may be overcome, in part, by increasing the dose, and highlight the potential role of epigenetic changes associated with sunitinib resistance that can represent new targets for therapeutic intervention.

Aflibercept exerts antivascular effects and enhances levels of anthracycline chemotherapy in vivo in human acute myeloid leukemia models.

We examined whether potent vascular endothelial growth factor (VEGF) blockade mediated by aflibercept, a decoy VEGF receptor (VEGFR) 1/2 moiety with stronger affinity for VEGF than bevacizumab, resulted in antileukemia effects and enhanced the efficacy of systemic chemotherapy. The efficacy of aflibercept alone and in combination with doxorubicin was evaluated in human VEGF-expressing acute myeloid leukemia (AML) cell lines and primary cells xenotransplanted into immunodeficient mice. Aflibercept reduced primary VEGF/VEGFR-positive AML colony formation growth in vitro and inhibited AML xenograft growth up to 93% in association with antiangiogenic and antiproliferative effects, hypoxia, and VEGF sequestration in multiple models. High VEGF-A expression by AML cells promoted in vivo xenograft growth and aflibercept sensitivity. Aflibercept therapy slowed disease progression in two systemic human AML xenograft models and reduced peripheral leukemia disease in a primary relapsed AML model in NOD/SCID/IL2Rγnull mice. Combination aflibercept and doxorubicin enhanced antitumor effects in local xenograft models. Sequential aflibercept followed by doxorubicin resulted in progressive anthracycline accumulation in marrow and extramedullary AML sites and resulted in 2-fold higher drug levels 24 hours after administration. In contrast, tissues (tumor, plasma, marrow) treated with chemotherapy only showed progressive drug clearance over time. Combination aflibercept and doxorubicin also resulted in vascular narrowing, decreased vessel number, and perivascular apoptosis. These data suggest that inefficient drug delivery by leukemia-associated vasculature may mediate chemoresistance and support further clinical evaluation of combination aflibercept and anthracycline therapy in refractory/relapsed AML patients.

Pharmacokinetic measurements of IDN 5390 using electrospray ionization tandem mass spectrometry: structure characterization and quantification in dog plasma.

In this report, electrospray ionization tandem mass spectrometry (ESI-MS/MS) for a pharmacokinetic study of IDN 5390, a novel C-seco taxane derivative, which is under preclinical evaluation, has been investigated. Our results showed that IDN 5390 and other taxanes including paclitaxel and IDN 5109 could ionize well in not only positive-, but also in negative-ion mode. Under collision-induced dissociation (CID) conditions, these compounds could fragment into similar M- (molecular), T- (taxane ring) and S- (side chain) series ions. In positive-ion ESI, the formation of both T- and S-series ions involved the breaking of the C-13 ester bond. In negative-ion ESI, however, while the formation mechanism of S-series ions remained the same, the breaking of the C-1' carboxylic ester bond resulted in T-series ions. At optimum collision energy (CE) values, M-, T- and S-series ions of IDN 5390 in both positive- and negative-ion ESI-MS/MS spectra had good intensity. This phenomenon makes both positive- and negative-ion ESI-MS/MS good methods for IDN 5390 metabolite structural characterization, i.e. to reveal the location of modification groups in IDN 5390 metabolites versus IDN 5390 either on the side chain or the taxane ring. A liquid chromatography (LC)/ESI-MS/MS method using the multiple-reaction monitoring (MRM) technique was thereafter developed to quantify IDN 5390 in dog plasma using paclitaxel as internal standard. The method was validated using a concentration range between 5 and 1000 ng/mL and had a limit of detection of 1 ng/mL. The inter-day %CV (%coefficient of variation) of the calibration standards ranged between 4.36 and 9.64%, the intra-day %CV of the calibration standards between 0.61 and 13.44%, and the mean % accuracy of the quality control samples at the low, middle and high end of the concentration curves were 12.5, 6.8 and 9.6%, respectively.