Drug Carriers: Not an Innocent Delivery Man

Nucleic acid and oligonucleotide delivery for activating innate immunity in cancer immunotherapy

A group of nucleic acids and oligonucleotides play various roles in the innate immune system. They can stimulate pattern recognition receptors to activate innate immune cells, encode immunostimulatory proteins or peptides, or silence specific genes to block negative regulators of immune cells. Given the limitations of current cancer immunotherapy, there has been increasing interest in harnessing innate immune responses by nucleic acids and oligonucleotides. The poor biopharmaceutical properties of nucleic acids and oligonucleotides make it critical to use carriers that can protect them in circulation, retain them in the tumor microenvironment, and bring them to intracellular targets. Therefore, various gene carriers have been repurposed to deliver nucleic acids and oligonucleotides for cancer immunotherapy and improve their safety and activity. Here, we review recent studies that employed carriers to enhance the functions of nucleic acids and oligonucleotides and overall immune responses to cancer, and discuss remaining challenges and future opportunities in the development of nucleic acid-based immunotherapeutics.

G, Masters AR, Abdel-Aleem JA, Abdelrahman SI, Abdelrahman AA, Lyle LT, Yeo Y. Development of Liposomal Gemcitabine with High Drug Loading Capacity

Liposomes are widely used for systemic delivery of chemotherapeutic agents to reduce their nonspecific side effects. Gemcitabine (Gem) makes a great candidate for liposomal encapsulation due to the short half-life and nonspecific side effects; however, it has been difficult to achieve liposomal Gem with high drug loading capacity. Remote loading, which uses a transmembrane pH gradient to induce an influx of drug and locks the drug in the core as a sulfate complex, does not serve Gem as efficiently as doxorubicin (Dox) due to the low p Ka value of Gem. Existing studies have attempted to improve Gem loading capacity in liposomes by employing lipophilic Gem derivatives or creating a high-concentration gradient for active loading into the hydrophilic cores (small volume loading). In this study, we combine the remote loading approach and small volume loading or hypertonic loading, a new approach to induce the influx of Gem into the preformed liposomes by high osmotic pressure, to achieve a Gem loading capacity of 9.4-10.3 wt % in contrast to 0.14-3.8 wt % of the conventional methods. Liposomal Gem showed a good stability during storage, sustained-release over 120 h in vitro, enhanced cellular uptake, and improved cytotoxicity as compared to free Gem. Liposomal Gem showed a synergistic effect with liposomal Dox on Huh7 hepatocellular carcinoma cells. A mixture of liposomal Gem and liposomal Dox delivered both drugs to the tumor more efficiently than a free drug mixture and showed a relatively good anti-tumor effect in a xenograft model of hepatocellular carcinoma. This study shows that bioactive liposomal Gem with high drug loading capacity can be produced by remote loading combined with additional approaches to increase drug influx into the liposomes.

Albumin-coated nanocrystals for carrier-free delivery of paclitaxel

Nanoparticles are used to deliver anticancer drugs to solid tumors. However, clinical development of nanoparticles is challenging because of their limitations in physicochemical properties, such as low drug loading efficiency and poor circulation stability. Low drug loading not only causes technical difficulty in administration but also increases the amount of co-delivered carrier materials, imposing biological burdens to patients. Poor circulation stability causes loss of pharmacokinetics benefits of nanoparticles. To overcome these challenges, we developed an albumin-coated nanocrystal (NC) formulation of paclitaxel (PTX) with 90% drug loading and high serum stability. The NC was produced by inducing crystallization of PTX in aqueous medium, coating the surface with albumin, and removing extra non-drug ingredients. Among three types of NC produced with different crystallization conditions, NC crystallized in the medium containing Pluronic F-127 then coated with albumin ("Cim-F-alb") had the smallest size and the most native albumin, thus showing the most favorable cell interaction profiles (low uptake by J774A.1 macrophages and high uptake by SPARC+ B16F10 melanoma cells). Cim-F-alb remained more stable in undiluted serum than Abraxane, a commercial albumin-based PTX nanoparticle formulation, while maintaining comparable cytotoxicity to those of Abraxane and solvent-dissolved PTX. In a mouse model of B16F10 melanoma, Cim-F-alb showed higher antitumor efficacy than Abraxane at the same dose. This study demonstrates the feasibility and benefits of delivering an anticancer drug using a carrier-free nanoparticle formulation with good circulation stability.

Polyethylenimine-dermatan sulfate complex, a bioactive biomaterial with unique toxicity to CD146-positive cancer cells

We report unique bioactivity of a polycation-polyanion complex with potential utility for cancer therapy. A complex of disulfide-crosslinked polyethyleneimine (CLPEI), a polycation used for gene complexation, and dermatan sulfate (DS), an anionic polysaccharide to shield excessive cationic charge of the former, has toxicity to a specific group of cancer cell lines, including B16-F10 murine melanoma, A375SM human melanoma, and PC-3 human prostate cancer cells. These CLPEI-DS-sensitive cells express CD146, which binds to the complex via interaction with DS. There is a positive correlation between toxicity and intracellular level of CLPEI, indicating that the CLPEI-DS-sensitivity is attributable to the increased cellular uptake of CLPEI mediated by the DS-CD146 interactions. In vitro studies show that CLPEI-DS complex causes G₀/G₁ phase arrest and apoptotic cell death. In syngeneic and allograft models of B16-F10 melanoma, CLPEI-DS complex administered with a sub-toxic level of doxorubicin potentiates the chemotherapeutic effect of the drug by loosening tumor tissues. Given the unique toxicity, CLPEI-DS complex may be a useful carrier of gene or chemotherapeutics for the therapy of CD146-positive cancers.

Organic nanoparticle systems for spatiotemporal control of multimodal chemotherapy

INTRODUCTION

Chemotherapeutic drugs are used in combination to target multiple mechanisms involved in cancer cell survival and proliferation. Carriers are developed to deliver drug combinations to common target tissues in optimal ratios and desirable sequences. Nanoparticles (NP) have been a popular choice for this purpose due to their ability to increase the circulation half-life and tumor accumulation of a drug. Areas covered: We review organic NP carriers based on polymers, proteins, peptides, and lipids for simultaneous delivery of multiple anticancer drugs, drug/sensitizer combinations, drug/photodynamic therapy or drug/photothermal therapy combinations, and drug/gene therapeutics with examples in the past three years. Sequential delivery of drug combinations, based on either sequential administration or built-in release control, is introduced with an emphasis on the mechanistic understanding of such control. Expert opinion: Recent studies demonstrate how a drug carrier can contribute to co-localizing drug combinations in optimal ratios and dosing sequences to maximize the synergistic effects. We identify several areas for improvement in future research, including the choice of drug combinations, circulation stability of carriers, spatiotemporal control of drug release, and the evaluation and clinical translation of combination delivery.

Polymeric drugs: Advances in the development of pharmacologically active polymers

Synthetic polymers play a critical role in pharmaceutical discovery and development. Current research and applications of pharmaceutical polymers are mainly focused on their functions as excipients and inert carriers of other pharmacologically active agents. This review article surveys recent advances in alternative pharmaceutical use of polymers as pharmacologically active agents known as polymeric drugs. Emphasis is placed on the benefits of polymeric drugs that are associated with their macromolecular character and their ability to explore biologically relevant multivalency processes. We discuss the main therapeutic uses of polymeric drugs as sequestrants, antimicrobials, antivirals, and anticancer and anti-inflammatory agents.