Human metabolism of [(14)C]indisulam following i.v. infusion in cancer patients

An insight into the interaction between Indisulam and human serum albumin: Spectroscopic method, computer simulation and in vitro cytotoxicity assay

Indisulam (IDM) is a sulfanilamide anticancer agent and has been identified as a molecular glue recently. It shows potential for novel therapies development and brings more hope for curing human diseases. The affinity between molecular glues and plasma protein makes it significant to understand the characteristics of such substances. Therefore, the interaction between IDM and human serum albumin (HSA) was explored through solvent experiments, computer simulation experiments, enzyme kinetics experiments, and cell viability assay. The results revealed that IDM and HSA spontaneously formed stable binary complex with the binding constant of the order 10⁵ M^-1. IDM inserted in the site I of HSA, resulting the change in HSA secondary structure. And π electrons in IDM's benzene rings, as well as van der Waals forces and the H-bond, all helped to stabilize the HSA-IDM complex. The results of molecular dynamic simulation (MD) corresponded with the results from solvent experiment well. For instance, there were approximately 1-5 H-bonds between IDM and HSA. Lys199 and Arg218 were crucial energy contributors in the binding process. The esterase-like activity experiment confirmed that IDM inhibited the catalytic activity of HSA. In addition, cell experiment revealed that serum albumin can significantly reduce the cytotoxicity of IDM towards human embryonic kidney 293T (HEK293T) cells.

Mass spectrometry based identification of geometric isomers during metabolic stability study of a new cytotoxic sulfonamide derivatives supported by quantitative structure-retention relationships

A set of 15 new sulphonamide derivatives, presenting antitumor activity have been subjected to a metabolic stability study. The results showed that besides products of biotransformation, some additional peaks occurred in chromatograms. Tandem mass spectrometry revealed the same mass and fragmentation pathway, suggesting that geometric isomerization occurred. Thus, to support this hypothesis, quantitative structure-retention relationships were applied. Human liver microsomes were used as an in vitro model of metabolism. The biotransformation reactions were tracked by liquid chromatography assay and additionally, fragmentation mass spectra were recorded. In silico molecular modeling at a semi-empirical level was conducted as a starting point for molecular descriptor calculations. A quantitative structure-retention relationship model was built applying multiple linear regression based on selected three-dimensional descriptors. The studied compounds revealed high metabolic stability, with a tendency to form hydroxylated biotransformation products. However, significant chemical instability in conditions simulating human body fluids was noticed. According to literature and MS data geometrical isomerization was suggested. The developed in sillico model was able to describe the relationship between the geometry of isomer pairs and their chromatographic retention properties, thus it supported the hypothesis that the observed pairs of peaks are most likely geometric isomers. However, extensive structural investigations are needed to fully identify isomers' geometry. An effort to describe MS fragmentation pathways of novel chemical structures is often not enough to propose structures of potent metabolites and products of other chemical reactions that can be observed in compound solutions at early drug discovery studies. The results indicate that the relatively non-expensive and not time- and labor-consuming in sillico approach could be a good supportive tool assisting the identification of cis-trans isomers based on retention data. This methodology can be helpful during the structural identification of biotransformation and degradation products of new chemical entities--potential new drugs.

Uridine 5'-diphospho-glucuronosyltransferase genetic polymorphisms and response to cancer chemotherapy

Pharmacogenetics aims to elucidate how genetic variation affects the efficacy and side effects of drugs, with the ultimate goal of personalizing medicine. Clinical studies of the genetic variation in the uridine 5'-diphosphoglucuronosyltransferase gene have demonstrated how reduced-function allele variants can predict the risk of severe toxicity and help identify cancer patients who could benefit from reduced-dose schedules or alternative chemotherapy. Candidate polymorphisms have also been identified in vitro, although the functional consequences of these variants still need to be tested in the clinical setting. Future approaches in uridine 5'-diphosphoglucuronosyltransferase pharmacogenetics include genetic testing prior to drug treatment, genotype-directed dose-escalation studies, study of genetic variation at the haplotype level and genome-wide studies.

Inhibition of carbonic anhydrases with glycosyltriazole benzene sulfonamides

A library of glycoconjugate benzene sulfonamides have been synthesized and investigated for their ability to inhibit the enzymatic activity of physiologically relevant human carbonic anhydrase (hCA) isozymes: hCA I, II, and tumor-associated IX. Our synthetic strategy directly links the known CA pharmacophore (ArSO 2NH 2) to a sugar "tail" moiety through a rigid 1,2,3-triazole linker unit using the Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction or "click chemistry". Many of the glycoconjugates were potent CA inhibitors and exhibited some isozyme selectivity. In particular, the methyl-D-glucuronate triazoles 6 and 14 were potent inhibitors of hCA IX (K(i)s 9.9 and 8.4 nM, respectively) with selectivity also favoring this isozyme. Other exceptional compounds included the deprotected beta-D-ribofuranosyl triazole 15 and alpha-D-mannosyl triazole 17, which were potent and selective hCA II inhibitors (K(i) 7.5 nM and K(i) 2.3 nM, respectively). Collectively, the results confirm that modification of ring size, stereochemical configuration, and chain length in the sugar tail moiety of glycoconjugate CA inhibitors permits tunable potency and selectivity that may constitute an important avenue for the future development of efficacious and selective CA-based therapeutics.

CYP2C9 and CYP2C19 polymorphic forms are related to increased indisulam exposure and higher risk of severe hematologic toxicity

PURPOSE

The anticancer agent indisulam is metabolized by the cytochrome P450 of enzymes CYP2C9 and CYP2C19. Polymorphisms of these enzymes may affect the elimination rate of indisulam. Consequently, variant genotypes may be clinically relevant predictors for the risk of developing severe hematologic toxicity. The purposes of this study were to evaluate the effect of genetic variants of CYP2C9 and CYP2C19 on the pharmacokinetics of indisulam and on clinical outcome and to assess the need for pharmacogenetically guided dose adaptation.

EXPERIMENTAL DESIGN

Pharmacogenetic screening of CYP2C polymorphisms was done in 67 patients treated with indisulam. Pharmacokinetic data were analyzed with a population pharmacokinetic model, in which drug elimination was described by a linear and a Michaelis-Menten pathway. The relationships between allelic variants and the elimination pharmacokinetic parameters (CL, V(max), K(m)) were tested using nonlinear mixed-effects modeling. Polymorphisms causing a high risk of dose-limiting neutropenia were identified in a simulation study.

RESULTS

The Michaelis-Menten elimination rate (V(max)) was decreased by 27% (P<0.0001) for heterozygous CYP2C9*3 mutants. Heterozygous CYP2C19*2 and CYP2C19*3 mutations reduced the linear elimination rate (CL) by 38% (P < 0.0001). The risk of severe neutropenia was significantly increased by these mutations and dose reductions of 50 to 100 mg/m(2) per mutated allele may be required to normalize this risk.

CONCLUSIONS

CYP2C9*3, CYP2C19*2, and CYP2C19*3 polymorphisms resulted in a reduced elimination rate of indisulam. Screening for these CYP2C polymorphisms and subsequent pharmacogenetically guided dose adaptation may assist in the selection of an optimized initial indisulam dosage.

A Semi-Physiological Population Pharmacokinetic Model Describing the Non-linear Disposition of Indisulam

The pharmacokinetic profile of the anti-cancer agent indisulam is non-linear. In addition to non-linear clearance, this may partially be explained by saturable distribution to red blood cells and saturable plasma protein binding. The aims of this study were to develop a semi-physiological population pharmacokinetic model of indisulam and to examine the impact of protein binding and distribution to red blood cells. Indisulam concentrations in plasma, plasma ultrafiltrate and in red blood cells from multiple phase I studies in Caucasian and Japanese patients were used to develop a pharmacokinetic model using NONMEM. This model comprised four physiological compartments: plasma, red blood cells, interstitial fluid and tissue. A simulation study was performed to examine the contribution of physiological processes in indisulam pharmacokinetics. Plasma albumin concentrations were predictive for the maximal protein binding capacity and considerably influenced total plasma concentrations of indisulam, whereas free plasma concentrations remained relatively unaffected. The maximal specific red blood cell binding capacity was 64.0 ( +/-5.9) mg/L and corresponded to the typical red blood cell carbonic anhydrase concentration. Simulation studies demonstrated that the hematocrit does not have a clinically relevant impact on indisulam disposition. This semi-physiological model allowed adequate prediction of the time profiles of indisulam concentrations in all monitored compartments for a large range of dose levels and several treatment regimens. The model has elucidated the mechanism and the role of saturable plasma protein binding and saturable distribution to red blood cells in indisulam pharmacokinetics and provides a basis for rationale PK-PD relationships.