Over the last decade, significant progress has been made in the field of drug delivery. The advent of engineered nanoparticles has allowed us to circumvent the initial limitations to drug delivery such as pharmacokinetics and solubility. However, in spite of significant advances to tumor targeting, an effective treatment strategy for malignant tumors still remains elusive. Tumors possess distinct physiological features which allow them to resist traditional treatment approaches. This combined with the complexity of the biological system presents significant hurdles to the site-specific delivery of therapeutic drugs. One of the key features of engineered nanoparticles is that these can be tailored to execute specific functions. With this review, we hope to provide the reader with a clear understanding and knowledge of biological barriers and the methods to exploit these characteristics to design multifunctional nanocarriers, effect useful dosing regimens and subsequently improve therapeutic outcomes in the clinic.

This work aimed to develop solid lipid nanoparticles (SLN) co-loaded with doxorubicin and α-tocopherol succinate (TS) and to evaluate its potential to overcome drug resistance and to increase antitumoral effect in MCF-7/Adr and NCI/Adr cancer cell lines. The SLN were prepared by a hot homogenization method and characterized for size, zeta potential, entrapment efficiency (EE), and drug loading (DL). The cytotoxicity of SLN or penetration was evaluated in MCF-7/Adr and NCI/adr as a monolayer or spheroid cancer cell model. The SLN showed a size in the range of 74-80nm, negative zeta potential, EE of 99%, and DL of 67mg/g. The SLN co-loaded with Dox and TS showed a stronger cytotoxicity against MCF-7/Adr and NCI/Adr cells. In the monolayer model, the doxorubicin co-localization as a free and encapsulated form was higher for the encapsulated drug in MCF-7/Adr and NCI/adr, suggesting a bypassing of P-glycoprotein bomb efflux. For cancer cell spheroids, the SLN co-loaded with doxorubicin and TS showed a prominent cytotoxicity and a greater penetration of doxorubicin.

Over the last few decades, the most popular platform to perform high-throughput screening for viable anti-neoplastic compounds has been monolayer cell culture. However, cells in monolayer culture lose many of their in vivo characteristics. As a result, this platform provides a limited predictive value in determining the clinical outcome of the compounds of interest. Using a technique known as 3D spheroid culture, may be the answer to this conundrum. Spheroids have been shown to mimic the tissue-like properties of tumors necessary for the proper evaluation of compounds. In this review, production of cancer cell spheroids, utilization of these spheroids in understanding various therapeutic mechanisms and the potential for their use in high-throughput screening of drugs and drug-delivery systems are discussed in detail.

Liposomes have come a long way since their conception in the 1960s, when they were envisioned primarily for drug delivery. Besides serving the important function of the delivery of a variety of drugs, liposomes offer a platform for the co-delivery of a range of therapeutic and diagnostic agents with different physicochemical properties. They are also amenable to the addition of various targeting moieties such as proteins, sugars, and antibodies for selective targeting at a desired site, including tumors. Currently, the design of stimuli-sensitive liposomes for drug delivery is a lively area of research. Compared to conventional liposomes, stimuli-sensitive nanoplatforms respond to local conditions that are characteristics of the pathological area of interest, allowing the release of active agents at the targeted site. Acidic pH, abnormal levels of enzymes, temperature, altered redox potential, and external magnetic field are examples of internal and external stimuli exploited in the design of stimuli-sensitive liposomes. The penetration of the liposomes into the cells can be enhanced with the help of a variety of cell penetrating peptides, which can be incorporated into the liposomes with the help of various lipid-polymer conjugates. Liposomes are now being employed in diagnostics as well. Imaging of a tumor can be made easier by the inclusion of fluorescent probes. They can also be used for gamma or MR imaging using chelated reporter metals and incorporating them either into the core of the liposome or in the lipid bilayer facing outwards. In this chapter, we discuss methods that are commonly used for the preparation of liposomes with a vast range of functions to meet a variety of needs in diagnostics and drug delivery.

Purpose To develop transferrin (Tf)-targeted delivery systems for the pro-apoptotic drug, NCL-240, and to evaluate the efficacy of this delivery system in ovarian cancer NCI/ADR-RES cells, grown in vitro in a 3D spheroid model. Methods Tf-targeted PEG-PE-based micellar and ePC/CHOL-based liposomal delivery systems for NCL-240 were prepared. NCI/ADR-RES cells were used to generate spheroids by a non-adhesive liquid overlay technique. Spheroid growth and development were monitored by size (diameter) analysis and H&E staining. The targeted formulations were compared to untargeted ones in terms of their degree of spheroid association and penetration. A cell viability analysis with NCL-240-loaded micelles and liposomes was performed to assess the effectiveness of Tf-targeting. Results Tf-targeted polymeric micelles and Tf-targeted liposomes loaded with NCL-240 were prepared. NCI/ADR-RES cells generated spheroids that demonstrated the presence of a distinct necrotic core along with proliferating cells in the spheroid periphery, partly mimicking in vivo tumors. The Tf-targeted micelles and liposomes had a deeper spheroid penetration as compared to the untargeted delivery systems. Cell viability studies using the spheroid model demonstrated that Tf-mediated targeting markedly improved the cytotoxicity profile of NCL-240. Conclusion Transferrin targeting enhanced delivery and effectiveness of micelles and liposomes loaded with NCL-240 against NCI/ADR-RES cancer cells in a 3D spheroid model.

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