High-performance liquid chromatographic analysis of dianhydrogalactitol in plasma by derivatization with sodium diethyldithiocarbamate

Development and validation of a highly sensitive LC-MS/MS method for determination of brain active agent dianhydrogalactitol in mouse plasma and tissues: Application to a pharmacokinetic study

A sensitive and specific liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed and validated for quantitative analysis of 1,2:5,6-dianhydrogalactitol (DAG) in mouse plasma and tissues. Sodium diethyldithiocarbamate (DDTC) was used as the derivatization reagent to improve its LC-MS/MS behavior. Analytes were separated on a Welch Ultimate XB-CN column with a mobile phase consisting of acetonitrile and 0.1% formic acid solution (65:35). The MS analysis was conducted by positive electrospray ionization in multiple-reaction monitoring (MRM) mode. Good linearity (r² > 0.9958) was observed over the concentration range of 1-1000 ng/mL in plasma and tissue homogenates (brain, liver, heart, spleen, lung and kidney). The intra- and inter-batch precision and accuracy of DAG in plasma and brain samples were all within the acceptable limits. The extraction recovery was stable and no significant matrix effects were observed. The method was successfully applied to study the pharmacokinetic and tissue distribution of DAG in mice after intravenous administration. DAG could cross the blood-brain barrier and had limited liver distribution. Rat primary hepatocytes in vitro experiments demonstrated that DAG had a safe profile in liver.

Determination of epoxides by high-performance liquid chromatography following derivatization with N,N-diethyldithiocarbamate

A reversed-phase, high-performance liquid chromatography (RP-HPLC) method that allows quantitation of low levels of epoxides has been described. The method involved derivatization of epoxides using 100- to 1,000-fold excess N,N-diethyldithiocarbamate (DTC) at 60 degrees C for 20 min at neutral pH. The unreacted DTC was then decomposed to CS(2) and diethyl amine by acidification of the reaction mixture to pH 2 using orthophosphoric acid. The first two steps could be performed in the same reaction vessel by sequential addition of reagents. In the final step, an aliquot (20 microL) of the derivatized sample was analyzed for the presence of stable esters of DTC by RP-HPLC using a Supelcosil LC-18-S (150 x 4.6-mm) column and a mobile phase consisting of 40% (v/v) acetonitrile in water at a flow of 1 mL min(-1). Using UV detection at 278 nm, the epoxides gave linear responses in the concentration range of 0.25 to 50 microM. The method is robust, and as low as 5 pmol of the analyte could be successfully detected and quantified with recoveries of > or =94%. Following a minimal pretreatment such as ultrafiltration (molecular weight cutoff 5,000 Da), the method is suitable for analysis of epoxides in complex physiological fluids (e.g., fetal bovine serum). The method has been rigorously evaluated and adapted in our laboratory for routine analysis and determination of stability of epoxides of 1,3-butadiene and other alkenes added to cell cultures.

Analysis of ifosforamide mustard, the active metabolite of ifosfamide, in plasma

Ifosforamide mustard is the active metabolite of ifosfamide, a cytostatic drug. In this study a sensitive and selective method for the analysis of ifosforamide mustard in plasma is described. The method consists of direct derivatisation of ifosforamide mustard in plasma with diethyldithiocarbamate and subsequent solid-phase extraction of the resulting derivative. The analysis of the derivatisation product was performed by high-performance liquid chromatography with UV detection. The calibration graph was linear in the concentration range 0.45-45 microM and the minimum detectable concentration was 0.45 mumol. The samples were stabilised by addition of semicarbazide and sodium chloride. A patient's plasma sample was analysed by means of the described method. The ifosforamide mustard concentration was 2.3 microM.

Chemical derivatization as a strategy to enhance delectability of agents used in cancer management

The bioanalysis of drugs used in the management of cancer is often complicated by the lack of selectivity and sensitivity. Chemical derivatization of these drugs prior to their chromatographic analysis represents a viable strategy to improve chromatographic resolution and to enhance detectability. This review provides examples of how this approach can meet these objectives. Derivatization of racemic cyclophosphamide with a chiral acylating agent, following hydroxyalkylation to introduce a reactive centre into the molecule, provides the basis for its stereospecific analysis. The analysis of dianhydrogalactitol is described, in which diethyldithiocarbamate is used as a nucleophilic derivatizing agent that improves chromatographic behaviour and analytical sensitivity. The final example that is described is the design and preparation of improved fluorogenic reagents (o-phthalaldehyde analogues) for the derivatization of peptides and application of these reagents to the trace analysis of leu-enkephalin in plasma.

The application of chemical derivatization to clinical drug analysis

The sensitivity and selectivity achievable in the analysis of drug substances from biological matrices is often limited by the physical and chemical properties of the analyte. These limitations are further exacerbated by the inherent reactivity of most drugs in biological systems (i.e., their propensity for undergoing biotransformation). One very powerful approach that has been taken to improve the quality of the analytical methodology is to alter the physico-chemical properties of the drug through chemical modification (derivatization) during some stage of the analytical sequence. This approach has been successfully applied to situations and has resulted in improved chemical stability, analytical selectivity and sensitivity. In most cases, drug analysis from biological fluids involves a chromatographic step; the derivatization reaction can be carried out either prior or subsequent to chromatography. In this paper, examples of the advantages (and limitations) offered by the introduction of a chemical derivatization step in clinical drug analysis will be presented. Specifically, focus will be placed on analysis of chemically-reactive antineoplastic agents and peptides/proteins. The latter represent an emerging class of drugs which present significant analytical challenges. The use of o-phthalaldehyde analogues offering improved derivative stability and increased sensitivity will be described.

Assay for mitolactol and its bifunctional alkylating metabolites in plasma

A method involving precolumn derivatization and high-performance liquid chromatography is described for the measurement of mitolactol levels in plasma. The basis of the assay is the reaction at pH 7.4 and 50 degrees C of mitolactol with diethyldithiocarbamate to form 1,6-bis(diethyldithiocarbamoyl)-2,3,4,5-tetrahydroxyhexane. This derivative is then extracted into chloroform, resolved by normal-phase chromatography, and detected by UV (254 nm) absorbance. The method quantitates the sum of mitolactol and its active bifunctional metabolites, bromoepoxydulcitol and dianhydrogalactitol, in plasma down to concentrations of 0.5 microM. The pharmacokinetic parameters of the drug in mice have been determined following the intraperitoneal injection of either 20 or 100 mg/kg of body weight. Absorption from the peritoneal cavity was largely complete by 5 min. Parameters obtained include a first-order elimination constant, k = 0.92 X 10(-2) min-1 and an apparent volume of distribution, Vd = 0.78 L/kg. For a 100-mg/kg dose, the area under the concentration-time curve was 49 mM X min, and the mean peak drug concentration was reached at 40 min following intraperitoneal injection. Concentrations of mitolactol in total plasma and in plasma ultrafiltrates were identical, indicating that the drug is not (less than 4%) reversibly bound to plasma proteins.

A sensitive assay for the pharmacokinetic investigation of a rapidly hydrolyzing alkylating agent Lycurim (ritrosulfan; R-74; NSC-122 402)

Lycurim [1,4-di(2'-methanesulfonyloxyethylamino)-1,4-dideoxymesoerythri tol dimethane sulfonate] is rapidly hydrolyzed in aqueous media to inactive products according to a second-order reaction. The respective rate constants are: k1 = 9.82 X 10(-2) and k2 = 1.76 X 10(-2) mumol/ml/min. The concentrations of the parent compound and alkylating intermediate(s) were measured by chemical trapping with N,N-diethyldithiocarbamic acid (DDTC). The rate of this reaction is substantially higher: k1 = 2.61 X 10(-1) and K2 = 4.76 X 10(-2) mumol/ml/min. By using 35S-labeled DDTC, alkylating compounds in concentrations as low as 0.04 microgram/ml could be detected in spiked plasma samples. After intracavitary application of 60 mg Lycurim no alkylating activity could be demonstrated in the plasma of patients at any time point.

Some strategies for improving specificity and sensitivity in the analysis of anti-cancer drugs

Some approaches are discussed for introducing specificity and sensitivity into analytical methods for anti-tumour agents which include a liquid chromatographic step. Various modes of HPLC have been exploited to monitor these drugs specifically and at therapeutically low levels. The use of column switching technology and chemical derivatization techniques to enhance both specificity and sensitivity are discussed. Multiple columns (linked through switching valves) containing packings exhibiting different affinities for the analytes cisplatin and riboxamide provide (a) a high degree of selectivity with convenient analysis times, (b) the opportunity for preconcentration of analytes, (c) improved longevity of analytical columns, (d) a solution to the 'general elution problem', and (e) allow direct application of biological fluid to the HPLC system. The use of chemical derivatization techniques (pre- and post-column) to achieve improved sensitivity and altered chromatographic and chemical properties of these and other anti-tumour agents (galactitol, tamoxifen, emetine) is also described. The high chemical reactivity of many anti-tumour agents often requires their rapid derivatization after a biological sample is drawn to prevent chemical degradation in the sample vial. The use of chemical and photochemical derivatization techniques combined with spectrophotometric, fluorometric and voltammetric detectors illustrates the power and utility of derivatization technology in trace drug analysis.

Chemotherapeutic approaches to brain tumors. Experimental observations with dianhydrogalactitol and dibromodulcitol

Dianhydrogalactitol (DAG) or its active cell-killing moiety has a relatively long biological half-life in 9L cells cultured in vitro. The shape of the DAG dose-response curves was similar to that of those observed for most oncolytic agents. The prominent shoulder on the 24-h dose-response curve indicates that 9L cells can accumulate a reasonable amount of DAG-induced sublethal damage before they are killed. The appearance of 9L colonies in petri dishes was delayed 3-5 days after a DAG treatment that killed more than 99% of the cells, an observation not previously made with radiation, hyperthermia, the nitrosoureas, or other chemotherapeutic agents. Comparison of the in vitro exposure integral and the in vivo tumor tissue integral indicated that DAG would have to be administered at a dose in excess of its LD10 to achieve an in vivo 2 log cell kill. The lack of a significant increase in lifespan after a LD10 dose confirmed this prediction. While DAG alone is active against IC ependymoblastoma, it had very limited activity against IC glioma 26; however, the combination of DAG with BCNU was curative in 85%-100% of animals at 120 days. BCNU alone achieved no more than 4%-16% survival at 120 days. The combination of DBD and BCNU was not consistently better than BCNU alone against IC glioma 26. It appears that DAG may have a limited place in CNS chemotherapy for specific kinds of tumors. BCNU-DAG combination studies suggest that we may, under the right conditions, enhance the antitumor activity of the hexitol epoxides by drug combination therapies, although the mechanism for this enhanced antitumor activity is presently unknown.

Urine analysis of platinum species derived from cis-dichlorodiammineplatinum(II) by high-performance liquid chromatography following derivatization with sodium diethyldithiocarbamate

A clinically useful method is described for the quantitative analysis of platinum species derived from cis-dichlorodiammineplatinum(II) in urine. The drug and its biodegradation products are derivatized directly in urine by reaction with sodium diethyldithiocarbamate (DDTC) to form a common product, a 2:1 DDTC-platinum adduct. This complex is stable and can be quantitatively extracted into 0.1 volumes of chloroform. An aliquot of the chloroform layer is then subjected to high-performance liquid chromatography on a muBondapak CN column and the eluent monitored spectrophotometrically at 254 nm. At this wavelength the DDTC-platinum adduct has a molar absorptivity of 43,000, and platinum levels of 25 ng/ml or urine can be detected with a precision of +/- 2.5% and an accuracy of +/- 4%.