Profiling the relationship between tumor-associated macrophages and pharmacokinetics of liposomal agents in preclinical murine models.

The mononuclear phagocyte system (MPS) has previously been shown to significantly affect the clearance, tumor delivery, and efficacy of nanoparticles (NPs). This study profiled MPS cell infiltration in murine preclinical tumor models and evaluated how these differences may affect tumor disposition of PEGylated liposomal doxorubicin (PLD) in models sensitive and resistant to PLD. Significant differences in MPS presence existed between tumor types (e.g. ovarian versus endometrial), cell lines within the same tumor type, and location of tumor implantation (i.e. flank versus orthotopic xenografts). Further, the differences in MPS presence of SKOV-3 ovarian and HEC1A endometrial orthotopic cancer models may account for the 2.6-fold greater PLD tumor exposure in SKOV-3, despite similar plasma, liver and spleen exposures. These findings suggest that profiling the presence of MPS cells within and between tumor types is important in tumor model selection and in tumor types and patients likely to respond to NP treatment.

A sensitive high performance liquid chromatography assay for the quantification of doxorubicin associated with DNA in tumor and tissues.

Doxorubicin, a widely used anticancer agent, exhibits antitumor activity against a wide variety of malignancies. The drug exerts its cytotoxic effects by binding to and intercalating within the DNA of tumor and tissue cells. However, current assays are unable to accurately determine the concentration of the intracellular active form of doxorubicin. Thus, the development of a sample processing method and a high-performance liquid chromatography (HPLC) methodology was performed in order to quantify doxorubicin that is associated with DNA in tumors and tissues, which provided an intracellular cytotoxic measure of doxorubicin exposure after administration of small molecule and nanoparticle formulations of doxorubicin. The assay uses daunorubicin as an internal standard; liquid-liquid phase extraction to isolate drug associated with DNA; a Shimadzu HPLC with fluorescence detection equipped with a Phenomenex Luna C18 (2µm, 2.0×100mm) analytical column and a gradient mobile phase of 0.1% formic acid in water or acetonitrile for separation and quantification. The assay has a lower limit of detection (LLOQ) of 10ng/mL and is shown to be linear up to 3000ng/mL. The intra- and inter-day precision of the assay expressed as a coefficient of variation (CV%) ranged from 4.01 to 8.81%. Furthermore, the suitability of this assay for measuring doxorubicin associated with DNA in vivo was demonstrated by using it to quantify the doxorubicin concentration within tumor samples from SKOV3 and HEC1A mice obtained 72h after administration of PEGylated liposomal doxorubicin (Doxil(®); PLD) at 6mg/kg IV x 1. This HPLC assay allows for sensitive intracellular quantification of doxorubicin and will be an important tool for future studies evaluating intracellular pharmacokinetics of doxorubicin and various nanoparticle formulations of doxorubicin.

Roles of chemokines CCL2 and CCL5 in the pharmacokinetics of PEGylated liposomal doxorubicin in vivo and in patients with recurrent epithelial ovarian cancer.

Nanoparticles (NPs) are cleared by monocytes and macrophages. Chemokines CCL2 and CCL5 are key mediators for recruitment of these immune cells into tumors and tissues. The purpose of this study was to investigate effects of CCL2 and CCL5 on the pharmacokinetics (PKs) of NPs. Mice deficient in CCL2 or CCL5 demonstrated altered clearance and tissue distribution of polyethylene glycol tagged liposomal doxorubicin (PLD) compared to control mice. The PK studies using mice bearing SKOV3 ovarian cancer xenografts revealed that the presence of tumor cells and higher expression of chemokines were significantly associated with greater clearance of PLD compared to non-tumor bearing mice. Plasma exposure of encapsulated liposomal doxorubicin positively correlated with the total exposure of plasma CCL2 and CCL5 in patients with recurrent epithelial ovarian cancer treated with PLD. These data emphasize that the interplay between PLD and chemokines may have an important role in optimizing PLD therapy. FROM THE CLINICAL EDITOR: The use of nanoparticles as drug delivery carriers is gaining widespread acceptance in the clinical setting. However, the underlying pharmacokinetics of these novel drugs has not really been elucidated. In this interesting article, the authors carried out experiments using mice deficient in CCL2 or CCL5 to study the clearance of liposomal system. They showed the important role the immune system played and would enable better designs of future drug delivery systems.

Meta-analysis of inter-patient pharmacokinetic variability of liposomal and non-liposomal anticancer agents.

A meta-analysis was conducted to evaluate the inter-patient pharmacokinetic (PK) variability of liposomal and small molecule (SM) anticancer agents. Inter-patient PK variability of 9 liposomal and SM formulations of the same drug was evaluated. PK variability was measured as coefficient of variance (CV%) of area under the plasma concentration versus time curve (AUC) and the fold-difference between AUCmax and AUCmin (AUC range). CV% of AUC and AUC ranges were 2.7-fold (P<0.001) and 16.7-fold (P=0.13) greater, respectively, for liposomal compared with SM drugs. There was an inverse linear relationship between the clearance (CL) of liposomal agents and PK variability with a lower CL associated with greater PK variability (R(2)=0.39). PK variability of liposomal agents was greater when evaluated from 0-336 h compared with 0-24h. PK variability of liposomes is significantly greater than SM. The factors associated with the PK variability of liposomal agents need to be evaluated. FROM THE CLINICAL EDITOR: In this meta-analysis, the inter-patient pharmacokinetic variability of 9 liposomal and small molecule anti-cancer agents was studied. The authors determined that several parameters are in favor of the liposomal formulation; however, the PK variability of the formulation was higher compared with small molecule agents, the reason for which remains to be determined in future studies.