Reversible Inhibition of Human Carboxylesterases by Acyl Glucuronides.

Reversible Inhibition of Human Carboxylesterases by Acyl Glucuronides.

Filed under: Drug and Alcohol Rehabilitation

Drug Metab Dispos. 2013 Feb 5;
Inoue NR, Hall A, Lai WG, Williams ET

Carboxylesterases hydrolyze esters, amides, and thioesters to produce carboxylic acids and resulting alcohols, amines, and thiols, respectively. UDP-glucuronosyltransferases are co-localized with carboxylesterases and have the potential to further metabolize carboxylic acids to acyl glucuronides, but it is currently unknown if acyl glucuronides, being esters, also interact with carboxylesterases. OBJECTIVE: This study explores the ability of acyl glucuronides to act as substrates or inhibitors of human carboxylesterases 1 (hCES1) and 2 (hCES2). METHODS: The stability of six acyl glucuronides in the presence of hCES1, hCES2, and buffer alone (100 mM potassium phosphate, pH 7.4, 37 °C) were investigated. Reversible inhibition of 4-nitrophenyl acetate hydrolysis by the acyl glucuronides was also studied. Diclofenac-?-D-glucuronide was used to explore potential time-dependent inactivation. RESULTS: The chemical stability half-life values for CGP 47292-?-D-glucuronide, diclofenac-?-D-glucuronide, (R)-naproxen-?-D-glucuronide, (S)-naproxen-?-D-glucuronide, ibuprofen-?-D-glucuronide (racemic), clopidogrel-?-D-glucuronide, and valproate-?-D-glucuronide were found to be 0.252, 0.537, 0.996, 1.77, 3.67, 5.02, and 15.2 hours, respectively. Diclofenac-?-D-glucuronide, clopidogrel-?-D-glucuronide, ibuprofen-?-D-glucuronide, (R)-naproxen-?-D-glucuronide, and (S)-naproxen-?-D-glucuronide selectively inhibited hCES1 with K(i) values of 4.32 ± 0.47, 24.8 ± 4.2, 355 ± 38, 468 ± 21, 707 ± 64 ?M, respectively, but did not significantly inhibit hCES2. Valproate-?-D-glucuronide and CGP 47292-?-D-glucuronide did not inhibit either hCES. Time-dependent inactivation of hCES1 by diclofenac-?-D-glucuronide was not observed. Lastly, both hCES1 and hCES2 were shown not to catalyze the hydrolysis of the acyl glucuronides studied. CONCLUSION: Drug-drug interaction studies may be warranted for drugs that metabolize to acyl glucuronides due to the potential inhibition of hCESs.
HubMed – drug

 

Intrinsic resistance to JAK2 inhibition in myelofibrosis.

Filed under: Drug and Alcohol Rehabilitation

Clin Cancer Res. 2013 Feb 5;
Kalota A, Jeschke GR, Carroll M, Hexner EO

PURPOSE: Recent results have demonstrated that myeloproliferative neoplasms (MPN) are strongly associated with constitutive activation of the JAK2 tyrosine kinase. However, JAK2 inhibitors currently approved or under development for treating myeloproliferative neoplasms do not selectively deplete the malignant clone, and the inhibition of activity of the drug target (JAK2) has not been rigorously evaluated in clinical studies. Therefore in this study we developed an in vitro assay to gain insight into how effectively JAK2 activity is inhibited in patient samples. EXPERIMENTAL DESIGN: We treated primary cells from normal donors and patients with MPN with JAK2 inhibitors and measured phosphorylation of downstream targets STAT5 and STAT3 by flow cytometry. Obtained results were next correlated with JAK2 V617F allele burden and plasma cytokines level. RESULTS: We observed a dose-dependent decrease in pSTAT5 and pSTAT3 in ex vivo treated granulocytes. However, phosphorylation of STAT3 and STAT5 in cells from patients with myelofibrosis was significantly less inhibited when compared to cells from patients with polycythemia vera, essential thrombocytosis, and normal donors. Sensitivity to inhibition did not correlate with JAK2 V617F clonal burden. Mixing studies using plasma from patients with myelofibrosis did not transfer resistance to sensitive cells. Likewise, no single cytokine measured appeared to account for the observed pattern of resistance. CONCLUSIONS: Taken together these observations suggest that there are cell intrinsic mechanisms that define a priori resistance to JAK2 inhibition in myelofibrosis, and the lesion is localized upstream of STAT3 and STAT5.
HubMed – drug

 

Equivalent benefit of rapamycin and a potent mTOR ATP-competitive inhibitor, MLN0128 (INK128), in a mouse model of tuberous sclerosis.

Filed under: Drug and Alcohol Rehabilitation

Mol Cancer Res. 2013 Feb 5;
Guo Y, Kwiatkowski DJ

Tuberous sclerosis complex (TSC) is a hamartoma syndrome in which brain, renal and lung tumors develop and cause both morbidity and death. Loss of either TSC1 or TSC2 in TSC hamartomas leads to activation of mTORC1. Rapamycin and related drugs have been shown to have clinical benefit for these tumors in TSC patients and those with sporadic forms of TSC-related neoplasms. However, lifelong therapy appears to be required, as tumors are not eliminated by this treatment. We examined the potential benefit of MLN0128, a novel potent mTOR ATP-competitive inhibitor, as a therapeutic strategy for renal cystadenomas that develop in A/J Tsc2+/- mice. Rapamycin given by intraperitoneal injection at 3 mg/kg 3 times per week, and MLN0128 given by gavage at 0.75 mg/kg 5 times per week had equivalent effects in suppressing tumor development during a 4 week treatment period, with an approximate 99% reduction in microscopic tumor cell volume. Marked reduction in activation of mTORC1, and blockade of cell growth was seen with both drugs, while only MLN0128 treatment had effects in blocking mTORC2 and 4EBP1 phosphorylation. However, when either drug was discontinued and mice were observed for two additional months, there was dramatic recovery of tumor growth, with extensive proliferation. Hence, long-lasting tumor growth control is not achieved with transient treatment with either drug, and MLN0128 and rapamycin have equivalent therapeutic benefit in this mouse model. Differences in side-effect profiles might make MLN0128 more attractive for treatment of patients with TSC-related tumors, but will require additional study in humans.
HubMed – drug

 

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