Determination of minocycline in human plasma by high-performance liquid chromatography coupled to tandem mass spectrometry: application to bioequivalence study

Minocycline, a putative neuroprotectant, co-administered with doxorubicin-cyclophosphamide chemotherapy in a xenograft model of triple-negative breast cancer

Minocycline is purported to have neuroprotective properties in experimental models of some human neurologic diseases, and has therefore been identified as a putative neuroprotectant for chemotherapy-induced cognitive impairment (CICI) in breast cancer patients. However, because its mechanism of action is believed to be mediated through anti-inflammatory, anti-apoptotic, and anti-oxidant pathways, co-administration of minocycline with chemotherapeutic agents has the potential to reduce the efficacy of anticancer drugs. The objective of this study is to evaluate the effect of minocycline on the activity of the AC chemotherapeutic regimen (Adriamycin [doxorubicin], Cytoxan [cyclophosphamide]) in in vitro and in vivo models of triple-negative breast cancer (TNBC). Clonogenic and methylthiazol tetrazolium (MTT) assays were used to assess survival and viability in two TNBC cell lines treated with increasing concentrations of AC in the presence or absence of minocycline. Biomarkers of apoptosis, cell stress, and DNA damage were evaluated by western blot. The in vivo effects of AC and minocycline, each alone and in combination, were assessed in a xenograft model of TNBC in female athymic nude mice by weekly tumor volume measurement, body and organ weight measurement, and histopathology. Apoptosis and proliferation were characterized by immunohistochemistry in the xenografts tumors. Brains from tumor-bearing mice were evaluated for microglial activation, glial scars, and the proportion of neural progenitor cells. Data from these in vitro and in vivo studies demonstrate that minocycline does not diminish the cytotoxic and tumor-suppressive effects of this chemotherapeutic drug combination in TNBC cells. Moreover, minocycline appeared to prevent the reduction in doublecortin-positive neural progenitor cells observed in AC-treated mice. We posit that minocycline may be useful clinically for its reported neuroprotective activity in breast cancer patients receiving AC without loss of chemotherapeutic efficacy.

Analysis of a second-generation tetracycline antibiotic minocycline in human plasma by LC-MS/MS

A simple, selective and sensitive LC-MS/MS assay has been developed for the determination of minocycline in human plasma. Plasma samples were prepared by protein precipitation, followed by chromatographic separation on a HyPURITY™ C8 (100 mm × 4.6 mm, 5 µm) column under isocratic conditions. The LOD and LLOQ of the method were 0.50 and 20.0 ng/ml, respectively. The intra-batch and inter-batch precision (% coefficient of variation) across quality control levels was less than 8.0%. For a set of incurred samples the percentage change in concentration was within ± 9.0%. The method was successfully applied to a bioequivalence study of 135 mg minocycline tablet formulation in 14 healthy Indian males. The reproducibility in the measurement of study data was demonstrated by incurred sample reanalysis.

Validated stability-indicating densitometric thin-layer chromatography: Application to stress degradation studies of minocycline

A simple, stability-indicating high-performance thin-layer liquid chromatographic (HPTLC) method for analysis of minocycline was developed and validated. The densitometric analysis was carried out at 345 nm using methanol-acetonitrile-isopropyl alcohol-water (5:4:0.5:0.5, v/v/v/v) as mobile phase. The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase. To achieve good result, plates were sprayed with a 10% (w/v) solution of disodium ethylene diaminetetraacetic acid (EDTA), the pH of which was adjusted to 9.0. Compact spots of minocycline were found at R(f) = 0.30+/-0.02. For proposed procedure, linearity (r = 0.9997), limit of detection (3.7 ng spot(-1)), recovery (99.23-100.16%), and precision (% R.S.D. < or = 0.364) was found to be satisfactory. The drug undergoes acidic and basic degradation, oxidation and photodegradation. All the peaks of degradation products were well resolved from the pure drug with significantly different R(f) values. The acidic and alkaline degradation kinetics of minocycline, evaluated using this method, is found to be of first order.

Improved LC of minocycline drug substance

An isocratic liquid chromatographic method is described for the separation of minocycline and its impurities. This method uses XTerra RP-18, 5 microm (25 cm x 4.6 mm I.D.), a silica-based stationary phase with reduced silanol activity. A mobile phase composed of acetonitrile-0.2 M tetrabutylammonium hydrogen sulphate pH 6.5-0.2 M ethylenediaminetetraacetic acid pH 6.5-water (20:20:20:40; v/v/v/v) was used at a flow rate of 1 ml/min. The column temperature was set at 35 degrees C. UV detection was performed at 280 nm. Optimisation of the separation method and a robustness study were performed by means of a central composite experimental design. The method allows to separate minocycline from known impurities. Some unidentified impurities are also separated. The total time of analysis is less than 20 min.

Liquid chromatographic determination of minocycline in brain-to-plasma distribution studies in the rat

An isocratic reversed-phase high-performance liquid chromatographic procedure was developed for the determination of minocycline in rat plasma and brain and applied to brain-to-blood (plasma) distribution studies. The procedure is based on isolation of the compound and the internal standard (either demeclocycline or tetracycline may be used) from plasma and brain constituents using the Oasis HLB cartridge, with satisfactory recovery and specificity, and separation on a Symmetry Shield RP8 (15 cm x 4.6 mm, 3.5 microm) column coupled with a UV detector set at 350 nm. The assay was linear over a wide range, with a lower limit of quantification of 50 ng ml(-1) or g(-1), using 0.2 ml of plasma and about 200 mg of brain tissue. Precision and accuracy were acceptable. In the rat minocycline crossed the blood-brain barrier slowly, achieving mean brain concentrations between 30 and 40% of the equivalent systemic exposure, regardless of the dose and route of administration.