ABSTRACT:Starting from d,l-acid and SnCl 2 as catalyst, poly(d,l-lactic acid) (PDLLA) was directly synthesized by melt polycondensation. Under the appropriate conditions such as 0.5 wt % SnCl 2 , 170 -180°C, 70 Pa, and 10 h, the viscosity-average molecular weight (M ) of PDLLA was 4100 Da. PDLLA produced by the most practical method was used as the drug-delivery material for erythromycin and ciprofloxacin. The optimal conditions for the preparation of erythromycin-poly(d,l-lactic acid)-microsphere (ERY-PDLLA-MS) for lung targeting was investigated, and further confirmed by good reappearance tests. DSC and SEM demonstrated that ERY-PDLLA-MS had good spherical shape. The release in vitro of ERY-PDLLA-MS was effective and the half-time (T 1/2 ) was 51.0 h. After 175 h, the accumulated release percentage was 80.0%. The test in vivo showed that ERY-PDLLA-MS was more easily distributed in rabbit lung tissue. When PDLLA was applied in an antibacterial ciprofloxacin drug-delivery microsphere (CIP-P-DLLA-MS), CIP-PDLLA-MS was also characterized with DSC and SEM, and the release T 1/2 in vitro was 24.9 h. After 53.2 h, the accumulated release percentage reached 84.0%, which indicated that CIP-PDLLA-MS was advantageous to long-term release.

Residue depletion of marbofloxacin in broiler chicken after oral administration at 5 mg/kg/day for three consecutive days was studied in this study. The areas under the concentration-time curve from 0 h to ∞ (AUC0-∞ s) of marbofloxacin in tissues and plasma were used to calculate tissue/plasma partition coefficients (PX s). Based on PX s and the other parameters derived from published studies, a flow-limited physiologically based pharmacokinetics (PBPK) model was developed to predict marbofloxacin concentrations, which were then compared with those derived from the residue depletion study so as to validate this model. Considering individual difference in drug disposition, a Monte Carlo simulation included 1000 iterations was further incorporated into the validated model to generate a population PBPK model and to estimate the marbofloxacin residue withdrawal times in edible tissues. The withdrawal periods were compared to those derived from linear regression analysis. The PBPK model presented here successfully predicted the measured concentrations in all tissues. The withdrawal times in all edible tissues derived from the population PBPK model were longer than those from linear regression analysis, and based on the residues in kidney, a withdrawal time of 4 days was estimated for marbofloxacin after oral administration at 5 mg/kg/day for three consecutive days. It was shown that population PBPK model could be used to accurately predict marbofloxacin residue withdrawal time in edible tissues in broiler chickens.

A pH/redox-triggered mesoporous silica nanoparticle (MSN)-based nanoplatform has been fabricated for doxorubicin/paclitaxel (DOX/PTX) codelivery. In this drug-delivery system (DDS), PTX is covalently attached to the surface of DOX loaded MSN via a linker with disulfide bond. By directly attaching PTX to MSN, we can significantly enhance the PTX́s loading degree and achieve the optimum drug loading ratio to DOX, therefore, to generate the best synergistical effect. More importantly, PTX and the linker act as a redox-sensitive “gate” to precisely control the release profile of DOX and PTX. Subsequently, polystyrenesulfonate (PSS) is electrostatically coated to DOX loaded MSN-PTX in microfluidics to achieve acidic pH responsive, because the free amino group on MSN surface has a protonation state at acidic pH, and the electrostatic interaction will be destroyed at pH 5. In addition, PSS can also neutralize the surface zeta potential, thus reduce the nonspecific endocytosis of healthy cells. By evaluating cell viability in cancer cell BT549 and healthy breast cell MCF-10A, we observed that the nanoparticles can selectively release DOX and PTX and eliminate cancer cells, while they will have negligible effect on the healthy breast cells, due to the acidic and redox microenvironment in cancer cells. Overall, we have developed a nanoplatform for precise DOX/PTX combination therapy with high selectivity between cancer cells and healthy cells.

The zeolitic imidazolate framework (ZIF-8), composed of zinc ion and dimethylimidazole, is widely used in drug delivery because of the easy fabrication process and the good biosafety. However, ZIF-8 suffers from low affinity to nonelectric-rich drugs and does not have surface functional groups. Here, to deliver doxorubicin (DOX) with ZIF-8 to specific target sites, DOX was first modified with a pH-sensitive linker containing two carboxyl groups to form the inactive prodrug CAD and subsequently seeded inside ZIF-8 by a 5 min mineralization process. CAD has high affinity to ZIF-8 because of the carboxyl groups and can anchor to the ZIF-8 surface to enable the surface modification with folic acid for tumor targeting. Moreover, the DOX release is precisely controlled by three steps of acidic pH response, with the dissociation of the FA layer, the breakdown of the ZIF-8 structure, and the cleavage of the pH-sensitive linker in prodrug. This novel “prodrug-ZIF-8” strategy has opened a new horizon in drug delivery.