Design and in vitro characterization of lipids with a pH-sensitive conformational switch and their liposomes for anticancer drug delivery

Author

Shen Zhao, University of the PacificFollow

Date of Award

2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Pharmaceutical and Chemical Sciences

First Advisor

Xin Guo

First Committee Member

Xiaoling Li

Second Committee Member

Bhaskara R. Jasti

Third Committee Member

Lisa A. Wrischnik

Abstract

The traditional anticancer drugs are distributed in vivo through systemic blood circulation with a very small portion reaching the tumor site. Targeted drug delivery systems are developed in efforts to concentrate the drug molecules in the tissue of interest while reducing the drug distribution to healthy tissues to reduce the side effects. Liposomes are colloidal systems composed of amphiphilic molecules that assemble into vesicle structures in aqueous media. They are common carriers for targeted drug delivery with the advantages of low toxicity, low immunogenicity and the ability of encapsulating both lipophilic and hydrophilic drugs.

Prior research indicated the advantages of triggered release in drug delivery systems. As a specific example, a series of trans-2-aminocyclohexanol based lipids (flipids) have been reported to illustrate a promising strategy to render pH-triggered drug delivery systems: pH-triggered conformational switch. Based on the foregoing, we hypothesize that incorporation of lipids with a pH-sensitive conformational switch and a long-saturated lipid tail can improve the anticancer activities of stealth liposomes. In this study, six new flipids with C-16 saturated hydrocarbon tails were designed. Such lipids were synthesized with high yields by introducing a catalyst (Copper (II) tetrafluoroborate) at a key step of the synthetic scheme.

pH-sensitive liposomes (fliposomes) composed of flipids were prepared and loaded with the anticancer drug doxorubicin with high encapsulation efficiency. The physicochemical properties of doxorubicin-loaded fliposomes were characterized and their pH-dependent leakage were investigated. The results showed that among all groups fliposomes containing the C-16 trans-2-morpholylcyclohexanol-based flipid (Mor-C16) exhibited the largest increase of release as the pH dropped form pH 7.4 to 6.0, indicating its good potential of serving as a component in pH-triggered drug delivery systems.

Three-dimensional multicellular spheroids (3D MCS) are self-assembled microscale tissue analogs in vitro. They better mimic the native and complex tumor microenvironment than the conventional two-dimensional cell culture systems. In this dissertation study, 3D MCS of six different human cancer cells were successfully cultured and their growing conditions were optimized to obtain 3D MCS of tight structure and reproducible size. The constructed 3D MCS carried heterogeneously distributed live and apoptotic cells as well as acidic inside pH based on confocal microscopic imaging studies.

The penetration of doxorubicin-loaded Mor-C16 fliposomes into 3D MCS was imaged by confocal microscopy in comparison to doxorubicin-loaded non pH-sensitive liposomes and free doxorubicin. The anticancer activities of doxorubicin-loaded Mor-C16 fliposomes against 3D MCS of three different cell lines was also evaluated by cell viability. Both the fliposome and the non pH-sensitive liposome formulations more efficiently penetrated into two of the three types of 3D MCS compared to free doxorubicin after 4h drug exposure. However, doxorubicin-loaded Mor-C16 fliposome imposed higher cytotoxicity to all three types of 3D MCS compared to doxorubicin-loaded non pH-sensitive liposome over 72 h drug exposure. Taken together, we propose that fliposomes achieved superior activity against 3D MCS by efficient penetration into 3D MCS, followed by enhanced release of the anticancer drug doxorubicin.

Pages

129

Recommended Citation

Zhao, Shen. (2018). Design and in vitro characterization of lipids with a pH-sensitive conformational switch and their liposomes for anticancer drug delivery. University of the Pacific, Dissertation. https://scholarlycommons.pacific.edu/uop_etds/3574