In vitro comparison of O4-benzylfolate modulated, BCNU-induced toxicity in human bone marrow using CFU-GM and tumor cell lines

Understanding the correlation between in vitro and in vivo immunotoxicity tests for nanomedicines

Preclinical characterization of novel nanotechnology-based formulations is often challenged by physicochemical characteristics, sterility/sterilization issues, safety and efficacy. Such challenges are not unique to nanomedicine, as they are common in the development of small and macromolecular drugs. However, due to the lack of a general consensus on critical characterization parameters, a shortage of harmonized protocols to support testing, and the vast variety of engineered nanomaterials, the translation of nanomedicines into clinic is particularly complex. Understanding the immune compatibility of nanoformulations has been identified as one of the important factors in (pre)clinical development and requires reliable in vitro and in vivo immunotoxicity tests. The generally low sensitivity of standard in vivo toxicity tests to immunotoxicities, inter-species variability in the structure and function of the immune system, high costs and relatively low throughput of in vivo tests, and ethical concerns about animal use underscore the need for trustworthy in vitro assays. Here, we consider the correlation (or lack thereof) between in vitro and in vivo immunotoxicity tests as a mean to identify useful in vitro assays. We review literature examples and case studies from the experience of the NCI Nanotechnology Characterization Lab, and highlight assays where predictability has been demonstrated for a variety of nanomaterials and assays with high potential for predictability in vivo.

Plasma and CNS pharmacokinetics of O4-benzylfolic acid (O4BF) and metabolite in a non-human primate model

PURPOSE

O(6)-alkylguanine-DNA alkyltransferase (AGT) repairs DNA damage from alkylating agents by transferring the alkyl adducts from the O(6)-position of guanine in DNA to AGT. The folate analog O(4)-benzylfolic acid (O(4)BF) is an inhibitor of AGT with reported selectivity of the alpha-folate receptor in tumors. We studied plasma and cerebrospinal fluid (CSF) pharmacokinetics and CSF penetration of O(4)BF in a non-human primate model.

METHODS

Rhesus monkeys (Macaca mulatta) received O(4)BF (10-50 mg/kg) intravenously, and serial blood and CSF samples were obtained. Analyte concentrations in plasma were measured by HPLC/photo diode array, and an HPLC/MS/MS assay was used for CSF samples.

RESULTS

A putative metabolite of O(4)BF was detected in plasma and CSF. O(4)BF and the metabolite inactivated purified AGT with ED(50) of 0.04 mcM. The median clearance of O(4)BF was 8 ml/min/kg and half-life was 1.1 h. The metabolite had a substantially longer half-life (>20 h) and greater AUC than O(4)BF. The AUC of the metabolite increased disproportionately to the dose of O(4)BF, suggesting saturable elimination. CSF penetration of O(4)BF and its metabolite was < 1%. At the 50 mg/kg dose level, the C(max) in CSF for O(4)BF was less than 0.09 mcM and for the metabolite the C(max) ranged from 0.02 to 0.04 mcM (O(4)BF equivalents).

CONCLUSIONS

Concentrations of O(4)BF and the metabolite in CSF exceeded the ED(50) of AGT; however, recently reported lack of receptor specificity and pharmacokinetic data suggesting saturable elimination of both O(4)BF and its metabolite may limit dose-escalation and future clinical development of this agent.