Recent Advances in Nanotechnology-Based Targeted Delivery Systems of Active Constituents in Natural Medicines for Cancer Treatment

Owing to high efficacy and safety, natural medicines have found their way into the field of cancer therapy over the past few decades. However, the effective ingredients of natural medicines have shortcomings of poor solubility and low bioavailability. Nanoparticles can not only solve the problems above but also have outstanding targeting ability. Targeting preparations can be classified into three levels, which are target tissues, cells, and organelles. On the premise of clarifying the therapeutic purpose of drugs, one or more targeting methods can be selected to achieve more accurate drug delivery and consequently to improve the anti-tumor effects of drugs and reduce toxicity and side effects. The aim of this review is to summarize the research status of natural medicines' nano-preparations in tumor-targeting therapies to provide some references for further accurate and effective cancer treatments.

Physical-Chemical Characterization of Bilayer Membranes Derived from (±) α-Tocopherol-Based Gemini Lipids and Their Interaction with Phosphatidylcholine Bilayers and Lipoplex Formation with Plasmid DNA

Membrane formation and aggregation properties of two series of (±) α-tocopherol-based cationic gemini lipids without and with hydroxyl functionalities at the headgroup region (TnS n = 3, 4, 5, 6, 8, and 12; THnS n = 4, 5, 6, 8, and 12) with varying polymethylene spacer lengths were investigated extensively while comparing with the corresponding properties of the monomeric counterparts (TM and THM). Liposomal suspensions of each cationic lipid were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), zeta potential measurements, and small-angle X-ray diffraction studies. The length of the spacer and the presence of hydroxyl functionalities at the headgroup region strongly contribute to the aggregation behavior of these gemini lipids in water. The interaction of each tocopherol lipid with a model phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC)-derived vesicles, was thoroughly examined by differential scanning calorimetry (DSC) and 1,6-diphenyl-1,3,5-hexatriene (DPH)-doped fluorescence anisotropy measurements. The binding efficiency of the cationic tocopherol liposomes with plasmid DNA (pDNA) was followed by an ethidium bromide (EB) exclusion assay and zeta potential measurements, whereas negatively charged micellar sodium dodecyl sulfate (SDS)-mediated release of the pDNA from various preformed pDNA-liposomal complexes (lipoplex) was studied by an ethidium bromide (EB) reintercalation assay. The structural transformation of pDNA upon complexation with liposome was characterized using circular dichroism (CD) spectroscopic measurements. Gemini lipid-pDNA interactions depend on both the presence of hydroxyl functionalities at the headgroups and the length of the spacer chain between the headgroups. Succinctly, we performed a detailed physical-chemical characterization of the membranes formed from cationic monomeric and gemini lipids bearing tocopherol as their hydrophobic backbone and describe the role of inserting the -OH group at the headgroup of such lipids.

A Fluorescent Self-Reporting Vector with GSH Reduction Responsiveness for Nucleic Acid Delivery

Nonviral gene vectors with stimulus responsiveness and self-reporting properties have broad application prospects in gene therapy. Herein, we developed a nanosized reduction-responsive cationic liposomal vector formed from DNS(Zn), in which a naphthalimide-sulfonamide group was used as the glutathione (GSH)-responsive group to generate a blue fluorescence signal at 458 nm. Macrocyclic polyamine (cyclen) was used as a cationic headgroup to facilitate Zn(II) coordination, which may reduce the cytotoxicity and improve transfection efficiency. The Zn-free and nonresponsive analogues were used for comparison. Fluorescent assays revealed that the GSH response of DNS(Zn) could increase the blue fluorescence signal and improve the DNA release in cells. The title material also showed higher positive ζ-potential than its nonresponsive analogue, resulting in stronger DNA binding ability and better cellular uptake. These advantages made DNS(Zn) a good candidate for nonviral gene delivery, and the transfection efficiency in HeLa cells was distinctly higher than that of its analogue and the commercially available transfection reagent. Besides plasmid DNA, DNS(Zn) could also deliver small interfering RNA (siRNA) with good gene silencing efficiency, extending the application of the liposomes. These results suggest that DNS(Zn) can serve as a highly efficient nucleic acid delivery vector with reduction-responsive fluorescence self-reporting ability in tumor cells.

Zn-Promoted gene transfection efficiency for non-viral vectors: a mechanism study

Mechanism studies revealed that a Zn coordination to cyclen-based cationic polymer may effectively improve the buffering capacity and endosomal escape ability.

Zinc(ii)-cyclen coordinative amphiphiles for enhanced gene delivery

In this study, we developed coordinative amphiphiles for use as novel non-viral DNA vectors. As a modification of a conventional cationic lipid structure, we replaced the cationic head with a zinc(ii)-1,4,7,10-tetraazacyclododecane (Zn-cyclen) complex as a phosphate-directing group, and used biocompatible skeletons (α-tocopherol or cholesterol) as hydrophobic tails. The structure-activity relationship (SAR) was systematically investigated to study the effect of Zn-coordination on the gene transfection between cyclen-based traditional head-tail lipids and Zn(ii)-cyclen coordinative amphiphiles. The results reveal that both Zn-free lipids and Zn-containing amphiphiles could condense DNA into nano-sized particles with appropriate size and zeta-potentials. Agarose gel retardation assay and MTS-based cell viability assays demonstrated that the Zn(ii)-cyclen complex exhibited slightly lower DNA binding ability and much lower cytotoxicity compared to liposome analogues, respectively. Most importantly, in vitro transfection studies showed that the coordination of zinc(ii) to cyclen may dramatically increase the transfection efficiency of the conventional cationic lipid, and α-tocopherol-containing coordinative amphiphile Zn-Cyc-Toc gives the best transfection efficiency, which was enhanced 24.4 times after coordination and was 6.1 times higher than commercial transfection reagent lipofectamine 2000. Mechanism studies confirmed that the DNA complex formed from Zn-Cyc-Toc might induce higher cellular uptake and better endosomal escape ability than the lipoplexes formed from Zn-free lipid Cyc-Toc. This study not only demonstrates that these coordinative amphiphiles might be promising non-viral gene vectors, but also presents a novel strategy to enhance the gene transfection efficiency and biocompatibility of cyclen-based cationic lipids.

Zn-coordination could dramatically enhance the gene transfection efficiency and reduce the cytotoxicity of conventional cyclen-based cationic liposomes.

First synthesis of orthogonally 1,7-diprotected cyclens

Six novel orthogonally 1,7-heterodiprotected cyclen derivatives have been prepared through an efficient and chromatography-free procedure.

Zn(ii)-cyclen complex-based liposomes for gene delivery: the advantage of Zn coordination

Zn-Coordination significantly improves the gene transfection efficiency and reduces the cytotoxicity of cyclen-based cationic liposomes.

A review on cationic lipids with different linkers for gene delivery

Cationic lipids have become known as one of the most versatile tools for the delivery of DNA, RNA and many other therapeutic molecules, and are especially attractive because they can be easily designed, synthesized and characterized. Most of cationic lipids share the common structure of cationic head groups and hydrophobic portions with linker bonds between both domains. The linker bond is an important determinant of the chemical stability and biodegradability of cationic lipid, and further governs its transfection efficiency and cytotoxicity. Based on the structures of linker bonds, they can be grouped into many types, such as ether, ester, amide, carbamate, disulfide, urea, acylhydrazone, phosphate, and other unusual types (carnitine, vinyl ether, ketal, glutamic acid, aspartic acid, malonic acid diamide and dihydroxybenzene). This review summarizes some research results concerning the nature (such as the structure and orientation of linker groups) and density (such as the spacing and the number of linker groups) of linker bond for improving the chemical stability, biodegradability, transfection efficiency and cytotoxicity of cationic lipid to overcome the critical barriers of in vitro and in vivo transfection.

Functionalized Asymmetric Bola-Type Amphiphiles for Efficient Gene and Drug Delivery

The studies of bolaamphiphile-based nanoparticles as delivery vectors are still rudimentary and under development. In this study, several asymmetric bolaamphiphiles containing lysine and another moiety with special functions, such as pH-sensitive or cell-targeting property, were designed and synthesized. The potentials of these bolaamphiphile-based nanoparticles as versatile vectors for both nucleic acids and chemical drugs were studied. With the presence of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), these amphiphiles could be prepared into bolasomes, which showed good DNA binding ability and could condense plasmid DNA into nanoparticles with appropriate size and surface potential. Lys-His, which has a pH-sensitive histidine on one head, exhibited higher transfection efficiency than the symmetric counterpart and comparable efficiency to commercially available transfection reagent. Mechanism studies confirmed that the bolaplexes formed from Lys-His might induce the highest cellular uptake and the best endosomal escape ability. On the other hand, these bolaamphiphiles also exhibited good drug loading ability. The self-assembly vesicles could efficiently encapsulate the hydrophobic anti-cancer drug doxorubicin (DOX) in aqueous solution with high drug loading content and encapsulation efficiency. Confocal laser scanning microscopy (CLSM) experiment and cell viability assay exhibited a controlled release of the drug with the assistance of bolasomes. It was shown that such bolaamphiphiles have great potential as nano-vectors for both drug and gene or their co-delivery.

pH and reduction dual-responsive dipeptide cationic lipids with α-tocopherol hydrophobic tail for efficient gene delivery

A series of tocopherol-based cationic lipid 3a-3f bearing a pH-sensitive imidazole moiety in the dipeptide headgroup and a reduction-responsive disulfide linkage were designed and synthesized. Acid-base titration of these lipids showed good buffering capacities. The liposomes formed from 3 and co-lipid 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) could efficiently bind and condense DNA into nanoparticles. Gel binding and HPLC assays confirmed the encapsulated DNA could release from lipoplexes 3 upon addition of 10 mM glutathione (GSH). MTT assays in HEK 293 cells demonstrated that lipoplexes 3 had low cytotoxicity. The in vitro gene transfection studies showed cationic dipeptide headgroups clearly affected the transfection efficiency (TE), and arginine-histidine based dipeptide lipid 3f give the best TE, which was 30.4 times higher than Lipofectamine 3000 in the presence of 10% serum. Cell-uptake assays indicated that basic amino acid containing dipeptide cationic lipids exhibited more efficient cell uptake than serine and aromatic amino acids based dipeptide lipids. Confocal laser scanning microscopy (CLSM) studies corroborated that 3 could efficiently deliver and release DNA into the nuclei of HeLa cells. These results suggest that tocopherol-based dipeptide cationic lipids with pH and reduction dual-sensitive characteristics might be promising non-viral gene delivery vectors.

Synthesis of α-amino-lipophosphonates as cationic lipids or co-lipids for DNA transfection in dendritic cells

Cationic lipid/co-lipid combinations have been extensively explored in gene delivery as alternatives to viral vectors.

Cationic lipids with a cyclen headgroup: synthesis and structure–activity relationship studies as non-viral gene vectors

The structure–activity relationships of cyclen-based cationic lipids as non-viral gene delivery vectors were studied and clarified.

Fluorescent zinc(ii) complexes for gene delivery and simultaneous monitoring of protein expression

Two new zinc(ii) complexes, [Zn(l-His)(NIP)]+(1) and [Zn(acac)2(NIP)](2) (where NIP is 2-(naphthalen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, acac = acetyl acetone), have been synthesized and characterized by elemental analysis, UV-vis, fluorescence, IR, 1H NMR and electron spray ionization mass spectroscopies. Gel retardation assay, atomic force microscopy and dynamic light scattering studies show that 1 and 2 can induce the condensation of circular plasmid pBR322 DNA into nanometer size particles under ambient conditions. Treatment of 2 with 5 mM EDTA restored 30% of the supercoiled form of DNA, revealing partial reversibility of DNA condensation. The in vitro transfection experiment demonstrates that the complexes can be used to deliver pCMV-tdTomato-N1 plasmid which expresses red fluorescent protein. The confocal studies show that the fluorescent nature of complexes is advantageous for visualizing the intracellular delivery of metal complexes as well as transfection efficiency using two distinct emission windows.

Structure–activity relationship studies of symmetrical cationic bolasomes as non-viral gene vectors

Bolalipids based on lysine or cyclen headgroups were synthesized and their structure–activity relationship as gene delivery vectors was studied.

Functional lipids based on [12]aneN3 and naphthalimide as efficient non-viral gene vectors

Small organic non-viral gene vectors with the structural combinations of (aliphatic chain)–naphthalimide–[12]aneN₃ (11a, b) and naphthalimide–(aliphatic chain)–[12]aneN₃ (12a–c) were synthesized and fully characterized.

Next generation macrocyclic and acyclic cationic lipids for gene transfer: Synthesis and in vitro evaluation

Previously we reported the synthesis and in vitro evaluation of four novel, short-chain cationic lipid gene delivery vectors, characterized by acyclic or macrocyclic hydrophobic regions composed of, or derived from, two 7-carbon chains. Herein we describe a revised synthesis of an expanded library of related cationic lipids to include extended chain analogues, their formulation with plasmid DNA (pDNA) and in vitro delivery into Chinese hamster ovarian (CHO-K1) cells. The formulations were evaluated against each other based on structural differences in the hydrophobic domain and headgroup. Structurally the library is divided into four sets based on lipids derived from two 7- or two 11-carbon hydrophobic chains, C7 and C11 respectively, which possess either a dimethylamine or a trimethylamine derived headgroup. Each set includes four cationic lipids based on an acyclic or macrocyclic, saturated or unsaturated hydrophobic domain. All lipids were co-formulated with the commercial cationic lipid 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine (EPC) in a 1:1 molar ratio, along with one of two distinct neutral co-lipids, cholesterol or 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) in an overall cationic-to-neutral lipid molar ratio of 3:2. Binding of lipid formulations with DNA, and packing morphology associated with the individual lipid-DNA complexes were characterized by gel electrophoresis and small angle X-ray diffraction (SAXD), respectively. As a general trend, lipoplex formulations based on mismatched binary cationic lipids, composed of a shorter C7 lipid and the longer lipid EPC (C14), were generally associated with higher transfection efficiency and lower cytotoxicity than their more closely matched C11/EPC binary lipid formulation counterparts. Furthermore, the cyclic lipids gave transfection levels as high as or greater than their acyclic counterparts, and formulations with cholesterol exhibited higher transfection and lower cytotoxicity than those formulated with DOPE. A number of the lipid formulations with cholesterol as co-lipid performed as well as, or better than Lipofectamine 2000™ and EPC, the two positive controls employed in these studies. These results suggest that our novel cyclic and acyclic cationic lipid vectors are effective nonviral gene transfer agents that warrant further investigation.

Hydroxyl-containing non-viral lipidic gene vectors with macrocyclic polyamine headgroups

The gene transfection abilities and structure–activity relationship of the newly designed hydroxyl-containing cationic lipids were studied in detail.