br Pharmacokinetics and biodistribution of encapsulated
3.4. Pharmacokinetics and biodistribution of encapsulated and non-encapsulated CBZ
PEBCA-CBZ and non-encapsulated CBZ (15 mg/kg) were in-travenously (i.v.) injected into the tail vein of mice bearing the MAS98.12 tumor. Blood samples were taken approximately 2 min after injection, and 1, 4, 24 and 96 h after injection, and the plasma samples were analyzed for CBZ using an LC-MS/MS method. The CBZ con-centrations at almost all time points were at least 10-fold higher in mice receiving PEBCA-CBZ compared to mice receiving free CBZ (Fig. 4A).
The plasma concentration/time curves for both PEBCA-CBZ and CBZ indicate an initial distribution phase, followed by a terminal elimination phase. The low number of data points did not allow de-termination of distribution or elimination Okadaic acid through non-linear regression. Interpolation based on the two first data points (up to 1 h) indicate distribution half-lives in the range of approximately 50 min and 30 min for PEBCA-CBZ and CBZ, respectively. Similarly, calculation of the elimination half-lives based upon the mean values of the two last time points (24 and 96 h) indicates half-lives of this phase of about 60 h for both compounds. The higher plasma concentration observed after administration of PEBCA-CBZ compared to CBZ suggests a lower dis-tribution volume and lower total clearance for PEBCA-CBZ compared to CBZ. This is consistent with the NP formulation being less able to escape the vascular compartment, and elimination of NPs primarily through the reticuloendothelial system.
Fig. 2. Treatment efficacy and toxicity studied in mice bearing MAS98.12 PDX breast tumors. Tumor growth inhibition (A) and body weight change (B) after treatment. PEBCA-CBZ and CBZ were injected 2 × 15 mg CBZ/ kg body weight at day 33 and 36, indicated by the red arrows. Empty PEBCA NPs (same dose as PEBCA-CBZ) and saline were used as negative controls (mean ± SEM; n = 8–9 tumors/ 5–6 mice). Tumor size is relative to the size mea-sured at time of randomization. Non-palpable tumors at day 57 after implantation are indicated as com-plete remissions. The statistical p-value of Welch t-test of areas under the curves is indicated (p = 0.02). (For interpretation of the references to colour in this figure legend, the reader is referred to the web ver-sion of this article.)
Fig. 3. Biodistribution of PEBCA particles containing the fluorescent dye NR668 measured in MAS98.12 tumor-bearing mice. Whole body images were obtained with IVIS 1, 4, 24 and 96 h after i.v. administration of the NPs; colour scale on the right indicates radian efficiency × 109 (A). Ex vivo fluorescence images of isolated organs were obtained 24 h after injection (B). Quantification of fluorescence intensity as relative radiant efficiency per region of interest pixel data of tissues collected 24 h after injection (C). Mean values obtained for 2 animals; error bars show SD values. PEBCA-CBZ: PEBCA containing CBZ and NR668; PEBCA: PEBCA containing NR668, but not CBZ. LNs: lymph nodes. The tumor data are enlarged in the inset.
The CBZ concentrations were measured in tumor, liver, spleen, lymph nodes, and kidney following a single injection of PEBCA-CBZ and CBZ (15 mg/kg). The results obtained with samples taken 24 and 96 h after injections are shown in Fig. 4B and C, respectively. The data are given as ng CBZ/mg tissue; for researchers wanting to have data as % ID/mg the injected dose was 0.27–0.30 mg CBZ. The highest amount of drug per mg tissue was obtained in spleen. However, when assuming that the mass of liver is approximately 13 times that of spleen in mice  the data in Fig. 4 indicates that the liver/spleen ratio of PEBCA-CBZ is 2.1 at 24 h after injection and 4.4 at 96 h after injection, de-monstrating that liver is taking up the largest part of these NPs. The amounts of CBZ in the tumor samples measured as ng CBZ/mg tissue were 20% (24 h) and 1.4% (96 h) of that in liver after injection of PEBCA-CBZ.
The concentration of CBZ was significantly higher (t-test; p-value < .01) in all tissues analyzed at 24 h following injection of par-ticle bound (PEBCA-CBZ) as compared to free drug (CBZ), with the largest differences observed in liver and spleen which contained the highest amounts of PEBCA-CBZ. In the samples obtained 96 h after in-jection, CBZ could be detected (i.e. being above the LOQ of the LC-MS/ MS method; calculated to be 0.19 ng/ml) in all tissues analyzed after injection of PEBCA-CBZ. Following injection of free CBZ, the CBZ content was below the LOQ for all tissues except tumor tissue 96 h after injection, such that the CBZ content could be estimated in tumor tissue only (Fig. 4C). The CBZ content measured in tumors 24 h after injection of PEBCA-CBZ was approx. 1.2% of the injected dose. This was reduced