Category: Preclinical Development
Purpose: In the preclinical evaluation of biomolecules, one of the goals is to quantitatively determine the relationships between drug concentrations in the blood (systemic pharmacokinetics; PK) and drug responses (pharmacodynamics; PD) at the site of action. As an example, our recent investigation using the subcutaneous application of a linear probe in rodent indicates that microdialysis can be successfully implemented to determine the biodistribution profiles of MTX and 7-OH-MTX in peripheral tissues and a tumor . In the present study, we wanted to investigate the subcutaneous PK profile of MTX and 7-OH-MTX in non-human primates.
Methods: We investigated the in vitro recovery of Methotrexate (MTX, MW=454 g/mol) and its major active metabolite, 7-OH-MTX, by placing a linear probe (CMA 30) in a petri dish containing different concentrations of MTX (1, 10, 100 µM) and 7-OH-MTX.
In the cynomolgus primate (Macaca fascicularis), after placement of the subcutaneous linear probes (right and left sides of the dorsum), the plasma and dialysate concentration-time profiles of MTX were obtained after oral and intravenous administration of MTX (10 mg/kg and 1 mg/kg) to determine the pharmacokinetic parameters of the drug. Drug concentrations were quantified using HPLC.
Results: The mean in vitro recovery of MTX after equilibration time was found to be approximately 39 ± 3.5%. Similar results were observed for 7-OH-MTX.
In the cynomolgus primate, the mean subcutaneous dialysate concentration of the parent drug reached a peak with a delay of 20 min after intravenous administration and exhibited a prolonged elimination half-life at its terminal phase. Additionally, there was a significantly lower subcutaneous drug level compared to the plasma level. The -OH-MTX metabolite was detectable in plasma and the elimination half-life in the terminal phase of 7-OH-MTX was clearly prolonged (more than 3-fold) compared to that of the parent compound. The right-side and left-side subcutaneous dialysate concentrations reached a peak with a delay of 40 min, and the exposure level of the drug was significantly lower subcutaneously compared to the plasma exposure.
Conclusion: The ability of the microdialysis technique to monitor unbound extracellular levels of both endogenous and exogenous compounds, has led to its use of the microdialysis technique in the research of PK and PD properties of both old and new drugs. In PK studies, a notable advantage of this technique is the time course determination of the bioactive levels in the target tissue, especially for centrally acting, antimicrobial, and antineoplastic drugs. This permits the simultaneous determination of a local drug level and its pharmacological effects and the study of a PK/PD correlation. These types of experiments can help to elucidate the mechanisms of action of various drugs and to optimize dosing regimen.
 Effect of drug transporter inhibitors on the pharmacokinetics and tissue distribution of methotrexate in normal and tumor-bearing mice: a microdialysis study. Cancer Chem. Pharmacol. (2009) 66 (1):159-169.