Targeting CDK9 for treatment of colorectal cancer.

Colorectal cancer (CRC) remains one of the most lethal human malignancies, and pursuit of new therapeutic targets for treatment has been a major research focus. Cyclin-dependent kinase 9 (CDK9), which plays a crucial role in transcription, has emerged as a target for cancer treatment. CDKI-73, one of the most potent and pharmacologically superior CDK9 inhibitors, has demonstrated excellent anti-tumour efficacy against several types of cancers. In this study, we evaluated its therapeutic potential against CRC. CDKI-73 elicited high cytotoxicity against all colon cancer cell lines tested. Cell cycle and apoptosis analysis in HCT 116 and HT29 cells revealed that CDKI-73 induced cell death without accumulation of DNA at any phase of the cell cycle. Moreover, it caused depolarisation of mitochondrial membrane, leading to caspase-independent apoptosis. Knockdown by shRNA demonstrated the CDK9-targeted mechanism of CDKI-73, which also affected the Mnk/eIF4E signalling axis. In addition, RT-qPCR analysis showed that CDKI-73 down-regulated multiple pro-survival factors at the mRNA level. Its in vivo anti-tumour efficacy was further evaluated in Balb/c nude mice bearing HCT 116 xenograft tumours. CDKI-73 significantly inhibited tumour growth (***P < 0.001) without overt toxicity. Analysis of the tumour tissues collected from the xenografted animals confirmed that the in vivo anti-tumour efficacy was associated with CDK9 targeting of CDKI-73. Overall, this study provides compelling evidence that CDKI-73 is a promising drug candidate for treating colorectal cancer.

Bioanalysis and Stability of Polymyxins.

Clinical use of the polymyxin antibiotics began approximately 10 years after their discovery in the late 1940s. Their concentrations in biological fluids were measured using microbiological methods. These methods were reasonably accurate for measuring the active polymyxin base, such as polymyxin B and colistin (polymyxin E), but were used inappropriately for measuring the concentrations of "colistin" in humans or animals following the administration of colistimethate, also known as colistin methanesulphonate (CMS). The use of polymyxins for systemic infections waned in the 1970s because of their toxicity and the preference for other antibiotics, but their value for treating infections caused by several important Gram-negative pathogens becoming resistant to other antibiotics was realized in the mid-1990s. The lack of adequate pharmacokinetic and pharmacodynamic knowledge spurred the development of methods more specific for measuring polymyxin B and colistin after their administrations as sulphate salts, and of colistin and CMS after the administration of CMS sodium. These methods have been based on high-performance liquid chromatography, detection and quantification of fluorescent derivatives of the polymyxin bases, or of the bases themselves with detection and quantification by mass spectrometry.

Discovery of N-Phenyl-4-(1H-pyrrol-3-yl)pyrimidin-2-amine Derivatives as Potent Mnk2 Inhibitors: Design, Synthesis, SAR Analysis, and Evaluation of in vitro Anti-leukaemic Activity.

BACKGROUND: Aberrant expression of eukaryotic translation initiation factor 4E (eIF4E) is common in many types of cancer including acute myeloid leukaemia (AML). Phosphorylation of eIF4E by MAPK-interacting kinases (Mnks) is essential for the eIF4E-mediated oncogenic activity. As such, the pharmacological inhibition of Mnks can be an effective strategy for the treatment of cancer. METHODS: A series of N-phenyl-4-(1H-pyrrol-3-yl)pyrimidin-2-amine derivatives was designed and synthesised. The Mnk inhibitory activity of these derivatives as well as their anti-proliferative activity against MV4-11 AML cells was determined. RESULTS: These compounds were identified as potent Mnk2 inhibitors. Most of them demonstrated potent anti-proliferative activity against MV4-11 AML cells. The cellular mechanistic studies of the representative inhibitors revealed that they reduced the level of phosphorylated eIF4E and induced apoptosis by down-regulating the anti-apoptotic protein myeloid cell leukaemia 1 (Mcl-1) and by cleaving poly(ADP-ribose)polymerase (PARP). The lead compound 7k possessed desirable pharmacokinetic properties and oral bioavailability. CONCLUSION: This work proposes that exploration of the structural diversity in the context of Nphenyl- 4-(1H-pyrrol-3-yl)pyrimidin-2-amine would offer potent and selective Mnk inhibitors.

Enantioselectivity in the tissue distribution of perhexiline contributes to different effects on hepatic histology and peripheral neural function in rats.

Perhexiline, a chiral drug, is a potent antiischemic agent whose clinical utility is limited by hepatic and neural toxicities. It inhibits mitochondrial carnitine palmitoyltransferase-1, however, excessive inhibition predisposes toward tissue steatosis. This pilot study investigated the distribution of the two enantiomers and their toxicological potential. Dark Agouti rats (n = 4 per group) were administered vehicle or 200 mg/kg daily of racemic, (+)- or (-)-perhexiline maleate orally for 8 weeks. Plasma biochemical liver function tests and Von Frey assessments of peripheral neural function were performed. Hepatic and neuronal histology, including lipid and glycogen content, was assessed using electron microscopy. Concentrations of the perhexiline enantiomers and metabolites were quantified in plasma, liver and heart. Plasma perhexiline concentrations following administration of racemate, (+)- or (-)-enantiomer were within the mid-upper clinical therapeutic range. There was extensive uptake of both enantiomers into liver and heart, with 2.5- to 4.5-fold greater net uptake of (+)- compared to (-)-perhexiline (P < .05) when administered as pure enantiomers, but not when administered as racemate. There was no biochemical or gross histological evidence of hepatotoxicity. However, livers of animals administered (+)-perhexiline had higher lipid (P < .01) and lower glycogen (P < .05) content, compared to those administered (-)-perhexiline. Animals administered racemic perhexiline had reduced peripheral neural function (P < .05) compared to controls or animals administered (-)-perhexiline. For the same plasma concentrations, differences in tissue distribution may contribute to disparities in the effects of (+)- and (-)-perhexiline on hepatic histology and neural function.

Dual Inhibition of Mnk2 and FLT3 for potential treatment of acute myeloid leukaemia.

The discovery of novel anti-AML therapeutic agents is urgently needed, but the complex heterogeneity of the disease has so far hampered the development of a curative treatment. FLT3 inhibitors have shown therapeutic potential in clinical trials; but a monotherapy regimen has been associated with resistance mediated by the activation of parallel signalling circuitry, including MAPK and mTOR. Therefore, inhibiting a nexus of the two signalling pathways along with inhibition of FLT3 might be advantageous. Herein, we propose that a dual inhibition of FLT3 and Mnk would provide a better clinical option for AML patients compared to targeting FLT3 alone. Thus, a series of N-phenyl-4-(thiazol-5-yl)pyrimidin-2-amines and 4-(indol-3-yl)-N-phenylpyrimidin-2-amines were prepared. Potent Mnk2 inhibitors, FLT3 inhibitors, and dual inhibitors of Mnk2 and FLT3 were identified and their anti-proliferative activities assessed against MV4-11 AML cell lines. Dual inhibition of FLT3 and Mnk2 caused the increased apoptotic cell death of MV4-11 cells compared to inhibition of FLT3 or Mnk2 alone.

The association between total phthalate concentration and non-communicable diseases and chronic inflammation in South Australian urban dwelling men.

OBJECTIVE: To investigate associations between urinary total phthalate concentration, chronic low-grade inflammation and non-communicable diseases in a cohort of South Australian men. METHODS: 1504 men aged 39-84 years who provided a urinary sample at the follow-up visit of the Men Androgen Inflammation Lifestyle Environment and Stress (MAILES) study, a randomly-selected group of urban-dwelling, community-based men from Adelaide, Australia (n = 2038; study participation rate: 78.1%). Total phthalate concentration was quantified in fasting morning urine samples. Chronic diseases were assessed through self-report questionnaire or directly measured using standardised clinical and laboratory procedures. Inflammatory biomarkers were assayed by ELISA or spectroscopy. Multivariable linear and logistic regression models were applied to determine associations of log-transformed urinary phthalate concentration with inflammation and chronic disease. RESULTS: Total phthalates were detected in 99.6% of urinary samples; geometric mean (95% CI) was 114.1 (109.5-118.9)µg/g creatinine. Higher total phthalate levels were associated with higher levels of hs-CRP, IL-6 (all p < 0.05) and TNF-α but not MPO. Urinary total phthalate concentrations were positively associated with cardiovascular disease, type-2-diabetes and hypertension. Comparing extreme quartiles of total phthalate, prevalence ratios were 1.78 (95% CI 1.17 - 2.71, p-trend = 0.001) for cardiovascular disease and 1.84 (95%CI 1.34 - 2.51, p-trend = 0.001) for type-2-diabetes and 1.14 (95%CI 1.01 - 1.29, p-trend = 0.013) for hypertension. Total phthalates and asthma and depression were not significantly associated. CONCLUSION: A positive association between total phthalates and cardiovascular disease, type-2-diabetes, hypertension and increased levels of chronic low-grade inflammatory biomarkers was observed in urban-dwelling Australian men.

Effect of Garlic, Gingko, and St. John's Wort Extracts on the Pharmacokinetics of Fexofenadine: A Mechanistic Study.

The aim of this study was to determine the effects of garlic and ginkgo herbal extracts on the pharmacokinetics of the P-glycoprotein (P-gp)/organic anion-transporting polypeptides (Oatps) substrate fexofenadine. Male rats were dosed orally with garlic (120 mg/kg), ginkgo (17 mg/kg), St. John's wort (SJW; 1000 mg/kg; positive control), or Milli-Q water for 14 days. On day 15, rats either were administered fexofenadine (orally or i.v.), had their livers isolated and perfused with fexofenadine, or had their small intestines divided into four segments (SI-SIV) and analyzed for P-gp and Oatp1a5. In vivo, SJW increased the clearance of i.v. administered fexofenadine by 28%. Garlic increased the area under the curve0-∞ and maximum plasma concentration of orally administered fexofenadine by 47% and 85%, respectively. Ginkgo and SJW had no effect on the oral absorption of fexofenadine. In the perfused liver, garlic, ginkgo, and SJW increased the biliary clearance of fexofenadine with respect to perfusate by 71%, 121%, and 234%, respectively. SJW increased the biliary clearance relative to the liver concentration by 64%. The ratio of liver to perfusate concentrations significantly increased in all treated groups. The expression of Oatp1a5 in SI was increased by garlic (88%) and SJW (63%). There were no significant changes in the expression of P-gp. Induction of intestinal Oatp1a5 by garlic may explain the increased absorption of orally administered fexofenadine. Ginkgo had no effect on the expression of intestinal P-gp or Oatp1a5. A dual inductive effect by SJW on opposing intestinal epithelial transport by Oatp1a5 and P-gp remains a possibility.

Targeting CDK9: a promising therapeutic opportunity in prostate cancer.

Cyclin-dependent kinase 9 (CDK9) is a key transcriptional regulator and a lucrative target for cancer treatment. Targeting CDK9 can effectively confine the hyperactivity of androgen receptor and the constitutive expression of anti-apoptotic proteins; both being main causes of prostate cancer (PCa) development and progression. In castrate-resistant PCa, traditional therapies that only target androgen receptor (AR) have become obsolete due to reprograming in AR activity to make the cells independent of androgen. CDK9 inhibitors may provide a new and better therapeutic opportunity over traditional treatment options by targeting both androgen receptor activity and anti-apoptotic proteins, improving the chances of positive outcomes, especially in patients with the advanced disease. This review focuses on biological functions of CDK9, its involvement with AR and the potential for therapeutic opportunities in PCa treatment.

Unveiling new chemical scaffolds as Mnk inhibitors.

The discovery of small molecules that selectively inhibit Mnks is considered of paramount importance towards deciphering the exact role of these proteins in carcinogenesis and to further validate them as anti-cancer drug targets. However, the dearth of structural information of Mnks is a major hurdle. This study unveils the 7H-pyrrolo[2,3-d]pyrimidine derivatives as potent inhibitors of Mnks. ATP and substrate competition assays showed that this scaffold interacts with the ATP binding site, but not with the substrate site. Screened against a panel of cancer cells, Mnk inhibitors were most potent against MV4-11 acute myeloid leukemia cells. The induction of apoptosis was shown to be mediated by downregulation of Mcl-1.

The association of socio-demographic status, lifestyle factors and dietary patterns with total urinary phthalates in Australian men.

OBJECTIVE: To investigate the associations between socio-demographic status, lifestyle factors, dietary patterns and urinary total phthalate concentration in a cohort of South Australian men. METHOD: We randomly selected 1527 males aged 39 to 84 from wave two of the Men Androgen Inflammation Lifestyle Environment and Stress (MAILES) study. Total phthalate concentration was examined in fasting morning urine samples. Socio-demographic and lifestyle factors were assessed by questionnaire. Food intake was assessed by food frequency questionnaire (FFQ). Dietary patterns were constructed using factor analysis. RESULTS: Total phthalates were detected in 99.6% of the urine samples. The overall geometric mean (95% CI) of total phthalate concentration was 112.4 (107.5-117.5) ng/mL. The least square geometric means (LSGMs) of total phthalate concentration were significantly higher among people who were obese (127.8 ng/mL), consuming less than two serves fruit per day (125.7 ng/mL) and drinking more than one can (375mL) of carbonated soft drink per day (131.9 ng/mL). Two dietary patterns were identified: a prudent dietary pattern and a western dietary pattern. Both the western dietary pattern (p = 0.002) and multiple lifestyle risk factors including smoking, obesity, insufficient physical activity and the highest quartile of the western dietary pattern (p<0.001), were positively associated with total phthalate levels. There was no significant relationship between total phthalate concentration and socio-demographic status. CONCLUSION: Phthalate exposure is ubiquitous and positively associated with lifestyle risk factors in urban dwelling Australian men.

Comparison of CYP2D metabolism and hepatotoxicity of the myocardial metabolic agent perhexiline in Sprague-Dawley and Dark Agouti rats.

1. Perhexiline, a chiral anti-anginal agent, may be useful to develop new cardiovascular therapies, despite its potential hepatotoxicity. 2. This study compared Dark Agouti (DA) and Sprague-Dawley (SD) rats, as models of perhexiline's metabolism and hepatotoxicity in humans. Rats (n = 4/group) received vehicle or 200 mg/kg/d of racemic perhexiline maleate for 8 weeks. Plasma and liver samples were collected to determine concentrations of perhexiline and its metabolites, hepatic function and histology. 3. Median (range) plasma and liver perhexiline concentrations in SD rats were 0.09 (0.04-0.13) mg/L and 5.42 (0.92-8.22) ng/mg, respectively. In comparison, DA rats showed higher (p < 0.05) plasma 0.50 (0.16-1.13) mg/L and liver 24.5 (9.40-54.7) ng/mg perhexiline concentrations, respectively, 2.5- and 3.7-fold higher cis-OH-perhexiline concentrations, respectively (p < 0.05), and lower plasma metabolic ratio (0.89 versus 1.55, p < 0.05). In both strains, the (+):(-) enantiomer ratio was 2:1. Perhexiline increased plasma LDH concentrations in DA rats (p < 0.05), but had no effect on plasma biochemistry in SD rats. Liver histology revealed lower glycogen content in perhexiline-treated SD rats (p < 0.05), but no effects on lipid content in either strain. 4. DA rats appeared more similar to humans with respect to plasma perhexiline concentrations, metabolic ratio, enantioselective disposition and biochemical changes suggestive of perhexiline-induced toxicity.

Cohort profile: The men androgen inflammation lifestyle environment and stress (MAILES) study.

The Men Androgen Inflammation Lifestyle Environment and Stress (MAILES) Study was established in 2009 to investigate the associations of sex steroids, inflammation, environmental and psychosocial factors with cardio-metabolic disease risk in men. The study population consists of 2569 men from the harmonisation of two studies: all participants of the Florey Adelaide Male Ageing Study (FAMAS) and eligible male participants of the North West Adelaide Health Study (NWAHS). The cohort has so far participated in three stages of the MAILES Study: MAILES1 (FAMAS Wave 1, from 2002-2005, and NWAHS Wave 2, from 2004-2006); MAILES2 (FAMAS Wave 2, from 2007-2010, and NWAHS Wave 3, from 2008-2010); and MAILES3 (a computer-assisted telephone interview (CATI) survey of all participants in the study, conducted in 2010). Data have been collected on a comprehensive range of physical, psychosocial and demographic issues relating to a number of chronic conditions (including cardiovascular disease, diabetes, arthritis and mental health) and health-related risk factors (including obesity, blood pressure, smoking, diet, alcohol intake and inflammatory markers), as well as on current and past health status and medication.

Stability of Myrmecia pilosula (Jack Jumper) Ant venom for use in immunotherapy.

Allergy to Myrmecia pilosula (Jack Jumper Ant) venom is common in Australia, affecting ∼2.7% of some communities. Venom immunotherapy is a highly effective treatment, but for the venom to be widely distributed for clinical use, the stability and shelf-life of formulated Jack Jumper Ant venom must be demonstrated. HPLC-UV, ELISA Inhibition, SDS-PAGE and SDS-PAGE Immunoblot were used to assess venom stability under conditions of varying temperature, pH and in the presence of various stabilising agents. Optimal stability occurred between pH 8 and 10, however the presence of benzyl alcohol within this pH range resulted in a cloudy appearance within 3 days, so a pH of 6 was used. Increasing polysorbate 80 concentrations accelerated the degradation of allergenic peptides in 100 µg/mL venom, but improved stability at concentrations of 1 µg/mL or less. Sucrose reduced degradation of allergens Myr p 1 and Myr p 3, whilst glycerol was destabilizing. In the presence of 22% sucrose, 1.1mg/mL Jack Jumper Ant venom was stable at -18 °C and 4 °C for 12 months; following dilution to 100 µg/mL with 0.9% sodium chloride, 10mM phosphate (pH 6), 0.05% polysorbate 80 and 0.9% benzyl alcohol (giving 2% sucrose), venom was stable for 7 days when stored at 4 °C. Concentrated Jack Jumper Ant venom can be stored in 22% sucrose for 12 months, and after dilution to 100 µg/mL for clinical use, it should be discarded after 7 days.

Inhibition of morphine metabolism by ketamine.

Clinical observation of a synergistic effect of ketamine on morphine analgesia remains controversial. Although a pharmacodynamic basis for an interaction has been explored in animal and clinical studies, the possibility of a pharmacokinetic mechanism has not been investigated. Whereas both morphine and morphine-6-glucuronide are effective analgesics, morphine-3-glucuronide (M3G) lacks activity. Thus, changes in the metabolism and disposition of morphine may result in an altered response. First, we investigated the interaction between morphine and ketamine in the isolated perfused rat liver preparation. The clearance of morphine was decreased from 16.8 +/- 4.6 ml/min in the control period to 7.7 +/- 2.8 ml/min in the ketamine-treatment period, with the formation clearance of M3G decreasing from 8.0 +/- 4.1 ml/min to 2.1 +/- 1.1 ml/min. Fractional conversion of morphine to M3G was significantly decreased from 0.46 +/- 0.17 in the control period to 0.28 +/- 0.14 upon the addition of ketamine. The possible mechanism of the interaction was further investigated in vitro with rat liver microsomes as the enzyme source. The formation of M3G followed single-enzyme Michaelis-Menten kinetics, with a mean apparent K(m) of 2.18 +/- 0.45 mM and V(max) of 8.67 +/- 0.59 nmol/min/mg. Ketamine inhibited morphine 3-glucuronidation noncompetitively, with a mean K(i) value of 33.3 +/- 7.9 microM. The results demonstrate that ketamine inhibits the glucuronidation of morphine in a rat model.

Elucidation of the pharmacokinetic/pharmacodynamic determinant of colistin activity against Pseudomonas aeruginosa in murine thigh and lung infection models.

Colistin is increasingly used as last-line therapy against Gram-negative pathogens. The pharmacokinetic (PK)/pharmacodynamic (PD) index that best correlates with the efficacy of colistin remains undefined. The activity of colistin against three strains of Pseudomonas aeruginosa was studied in neutropenic mouse thigh and lung infection models. The PKs of unbound colistin were determined from single-dose PK studies together with extensive plasma protein binding analyses. Dose-fractionation studies were conducted over 24 h with a dose range of 5 to 160 mg/kg of body weight/day. The bacterial burden in the thigh or lung was measured at 24 h after the initiation of treatment. Relationships between antibacterial effect and measures of exposure to unbound (f) colistin (area under the concentration-time curve [fAUC/MIC], maximum concentration of drug in plasma [fC(max)]/MIC, and the time that the concentration in plasma is greater than the MIC [fT > MIC]) were examined by using an inhibitory sigmoid maximum-effect model. Nonlinearity in the PKs of colistin, including its plasma protein binding, was observed. The PK/PD index that correlated best with its efficacy was fAUC/MIC in both the thigh infection model (R(2) = 87%) and the lung infection model (R(2) = 89%). The fAUC/MIC targets required to achieve 1-log and 2-log kill against the three strains were 15.6 to 22.8 and 27.6 to 36.1, respectively, in the thigh infection model, while the corresponding values were 12.2 to 16.7 and 36.9 to 45.9 in the lung infection model. The findings of this in vivo study indicate the importance of achieving adequate time-averaged exposure to colistin. The results will facilitate efforts to define the more rational design of dosage regimens for humans.

Effect of St John's wort on the disposition of fexofenadine in the isolated perfused rat liver.

OBJECTIVES: This study examined the effects of St John's wort (Hypericum perforatum) on the disposition of fexofenadine, a substrate of P-glycoprotein/organic anion transporting polypeptide, in the isolated perfused rat liver. METHODS: Male Sprague-Dawley rats were given St John's wort, 1000 mg/kg, by intragastric gavage once daily for 14 days. On day 15, livers were isolated surgically and perfused in a recirculating system with fexofenadine (2 microg/ml), either alone or following addition of ciclosporin (0.5 microg/ml) 5 min before the addition of fexofenadine. Perfusate samples and bile were collected for 60 min. Fexofenadine in perfusate, bile and the homogenised livers was measured by HPLC. KEY FINDINGS: Administration of St John's wort significantly increased biliary clearance with respect to perfusate and biliary clearance with respect to the concentration in the liver, by 74% and 71%, respectively. This was reversed by ciclosporin. CONCLUSIONS: St John's wort enhanced the elimination of fexofenadine into the bile. This could be because it increases the activity of P-glycoprotein on the canalicular membrane of hepatocytes.

Renal disposition of colistin in the isolated perfused rat kidney.

Nephrotoxicity is an important limitation to the clinical use of colistin against Pseudomonas aeruginosa and other gram-negative pathogens. Previous work reported net tubular reabsorption of colistin by the kidney in vivo, but there is no knowledge of its disposition within the kidney. This study investigated the renal disposition and potential transport mechanisms of colistin in the isolated perfused rat kidney (IPK) model by perfusing with colistin sulfate alone (2 microg/ml) or in the presence of potential inhibitors (tetraethylammonium [TEA], glycine-glycine [Gly-Gly], or hydrochloric acid [HCl]) at three different concentrations. When perfused alone, the renal clearances (CL(R)) for colistin A and B (the major components of colistin) in control kidneys were constant and low (mean values < 0.05 ml/min throughout the perfusion). The mean clearance ratios [CR, defined as CL(R)/(f(u) x GFR), where f(u) is the fraction of drug unbound in perfusate and GFR is the glomerular filtration rate] were significantly less than 1. It was concluded that there is net tubular reabsorption of colistin, and this exceeded the reabsorption of water. Less than 10% eliminated from perfusate was recovered in urine, suggesting considerable renal accumulation of colistin. The CR values for colistin were significantly increased when perfused with TEA (500 microM), Gly-Gly (833 microM), and HCl (2,500, 5,000, and 10,000 microM). It is proposed that renal reabsorption of colistin may involve organic cation transporters (inhibited by TEA) and peptide transporters (inhibited by Gly-Gly) and that the process is sensitive to the pH of urine.

Comparison of once-, twice- and thrice-daily dosing of colistin on antibacterial effect and emergence of resistance: studies with Pseudomonas aeruginosa in an in vitro pharmacodynamic model.

OBJECTIVES: The optimal dosing regimen for colistin methanesulphonate (CMS) against Pseudomonas aeruginosa is unknown. CMS is converted in vivo to its active form, colistin. We evaluated three colistin dosage regimens in an in vitro pharmacokinetic/pharmacodynamic model. METHODS: Three intermittent dosage regimens involving 8, 12 and 24 h dosage intervals (Cmax of 3.0, 4.5 or 9.0 mg/L, respectively) were employed. Antibacterial activity and emergence of resistance were investigated over 72 h using two strains of P. aeruginosa: ATCC 27853 and 19056. The areas under the killing curves (AUBC(0-72)) and population analysis profiles (AUCPAP) were used to compare regimens. RESULTS: No difference in bacterial killing was observed among different regimens. For ATCC 27853, substantial killing was observed after the first dose with less killing after subsequent doses irrespective of regimen; regrowth to between 5.95 and 7.49 log10 cfu/mL occurred by 72 h (growth control 7.46 log10 cfu/mL). AUCPAPs at 72 h for the 12 hourly (4.08 +/- 1.54) and 24 hourly (4.16 +/- 2.48) regimens were substantially higher than that for both the growth control (1.63 +/- 0.08) and 8 hourly regimen (2.30 +/- 0.87). For 19056, bacterial numbers at 72 h with each regimen (1.32-2.75 log10 cfu/mL) were far below that of the growth control (7.79 log10 cfu/mL); AUCPAPs could not be measured effectively due to the substantial killing. CONCLUSIONS: No difference in overall bacterial kill was observed when the recommended maximum daily dose was administered at 8, 12 or 24 h intervals. However, the 8 hourly regimen appeared most effective at minimizing emergence of resistance.

Subacute toxicity of colistin methanesulfonate in rats: comparison of various intravenous dosage regimens.

The relative nephro- and neurotoxicity of colistin methanesulfonate (CMS) was investigated with rats during 7 days of intravenous administration in regimens mimicking twice- and once-daily dosing of a clinically relevant dose for humans. Histological examination revealed more-severe renal lesions with the regimen corresponding to once-daily dosing, indicating that the potential for renal toxicity may be greater with extended-interval dosing.

Determination of colistin in human plasma, urine and other biological samples using LC-MS/MS.

A liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed to quantify colistin in human plasma and urine, and perfusate and urine from the isolated perfused rat kidney (IPK). Solid phase extraction (SPE) preceded chromatography on a Synergi Fusion-RP column with a mobile phase of acetonitrile, water and acetic acid (80/19/1) at 0.2mL/min. Ions were generated using electrospray ionization and detected in the positive-ion mode. Multiple reaction monitoring was performed using precursor-product ion combinations. Calibration curves were linear from 0.028microg/mL (human plasma, IPK perfusate and urine)/0.056microg/mL (human urine) to 1.78microg/mL (all four media) for colistin A sulfate; corresponding values for colistin B sulfate were 0.016/0.032 to 1.01microg/mL. Accuracy and precision were within 10%. The LLOQ for colistin A sulfate was 0.028microg/mL in human plasma, IPK perfusate and urine and 0.056microg/mL in human urine; corresponding values for colistin B sulfate were 0.016 and 0.032microg/mL. The low sample volume, short analysis time and low LLOQ are ideal for pre-clinical and human pharmacokinetic studies of colistin.