Targeting of muramyl dipeptide to macrophages by gelatin conjugation to enhance their in vivo antitumor activity

Biodegradable Polymers for Microencapsulation Systems

Environmentally friendly alternatives have become sought after upon the development of scientific research and industrial processes. Recent trends suggest biodegradable polymers as the most promising solution for synthetic microcapsule systems. Safety, efficiency, biocompatibility, and biodegradability are some of the properties that biodegradable systems in microencapsulation can provide for a broad spectrum of applications. The controlled release of encapsulated active agents is a research field that, over the years, has been constantly innovating due to the promising applications in the areas of pharmaceutical, cosmetic, textile industry, among others. This article presents an overview of different polymers with potential for microcapsule synthesis, namely, biodegradable polymers. First, natural polymers are discussed, which are divided into two categories: polysaccharide-based polymers (cellulose, starch, chitosan, and alginate) and protein polymers (gelatin). Second, synthetic polymers are described, where biodegradable polymers such as polyesters, polyamides, among others appear as examples. For each polymer, this review presents its origin, relevant properties, applications, and examples found in the literature regarding its use in biodegradable microencapsulation systems.

Harnessing the untapped potential of nucleotide-binding oligomerization domain ligands for cancer immunotherapy

In the last decade, cancer immunotherapy has emerged as an effective alternative to traditional therapies such as chemotherapy and radiation. In contrast to the latter, cancer immunotherapy has the potential to distinguish between cancer and healthy cells, and thus to avoid severe and intolerable side‐effects, since the cancer cells are effectively eliminated by stimulated immune cells. The cytosolic nucleotide‐binding oligomerization domains 1 and 2 receptors (NOD1 and NOD2) are important components of the innate immune system and constitute interesting targets in terms of strengthening the immune response against cancer cells. Many NOD ligands have been synthesized, in particular NOD2 agonists that exhibit favorable immunostimulatory and anticancer activity. Among them, mifamurtide has already been approved in Europe by the European Medicine Agency for treating patients with osteosarcoma in combination with chemotherapy after complete surgical removal of the primary tumor. This review is focused on NOD receptors as promising targets in cancer immunotherapy as well as summarizing current knowledge of the various NOD ligands exhibiting antitumor and even antimetastatic activity in vitro and in vivo.

Inhibition of liver metastasis by targeting of immunomodulators using mannosylated liposome carriers

Mannosylated liposomes were prepared by incorporating cholesten-5-yloxy-N-(4-((1-imino-2-beta-D-thiomannosylethyl)amino)butyl)formamide (Man-C4-Chol) into small unilamellar liposomes consisting of cholesterol and distearoyl phosphatidylcholine (DSPC). The biodistribution of liposomes labeled with [3H]cholesteryl hexadecyl ether was examined in mice. The rate and extent of the hepatic uptake of those [3H]liposomes increased proportionally on increasing the mixing ratio of Man-C4-Chol. Their hepatic uptake was reduced by increasing the administered dose due to the limited number of mannose receptors. The liver uptake of [3H]Man-liposomes was preferentially mediated by liver non-parenchymal cells (NPC) and significantly inhibited by co-injection with an excess of Man-BSA, indicating the involvement of a mannose receptor-mediated mechanism in the hepatic uptake of Man-liposomes. Muramyl dipeptide (MDP), an immunomodulator, was also incorporated into the liposomes and its inhibitory effect in an experimental liver metastasis model was examined. In contrast to free MDP treatment, which showed little effect on the inhibition of metastasis, liposomal MDP significantly reduced the number of metastatic colonies in the liver. Active targeting of MDP to liver NPC by Man-liposomes resulted in more effective inhibition than delivery of MDP by liposomes without mannose. Treatment with MDP/Man-liposomes further increased the survival of the tumor-bearing mice. These results suggest that Man-liposomes are effective carriers for targeted delivery of bioactive compounds to liver NPC.

Selective activation of antitumor activity of macrophages by the delivery of muramyl dipeptide using a novel polynucleotide-based carrier recognized by scavenger receptors

We have shown that muramyl dipeptide (MDP) conjugated to a 10-mer polyguanylic acid (PolyG) is specifically internalized by macrophages through scavenger receptor (SCR)-mediated endocytosis. Macrophages activated by PolyG-MDP displayed about 20-fold higher cytotoxic activity against nonmacrophage tumor cells compared to that elicited by free MDP. The PolyG-MDP was found to trigger the secretion of higher levels of interleukin-6, interleukin-1alpha, TNF-alpha, and nitric oxide in comparison to free MDP. Addition of antibodies directed against IL-6 and TNF-alpha to macrophage culture completely abrogated the tumoricidal response of PolyG-MDP, indicating that these two cytokines are primarily responsible for bioefficacy. This general approach of PolyG as a vehicle may find wide application in the delivery of genes and antisense oligonucleotides to macrophages.

In vivo fate of folate-BSA in non-tumor- and tumor-bearing mice

KB tumor cells exhibit an increased number of folate receptors on their membrane. This receptor has been proposed as a promising target for tumor drug targeting. Therefore, the disposition of folate-conjugated bovine serum albumin (folate-BSA) was examined as a model system for drug targeting. Nude mice which had received KB tumor cell transplants were given bolus intravenous administration of either 111In-labeled folate-BSA (111In-folate-BSA; 1 mg/kg) or unmodified 111In-BSA (111In-BSA; 1 mg/kg). The disposition characteristics and pharmacokinetics of 111In-folate-BSA were compared with those of the 111In-BSA as a control. The half-life of the beta-phase of 111ln-folate-BSA in plasma was 140 min. The tumor uptake rate index for 111In-folate-BSA was 0.46 microL/min/g, and that for 111In-BSA was 0.32 microL/min/g. This index of 111In-folate-BSA was slightly higher than that of 111In-BSA in vivo, by a factor of 1.4. In vivo experiments showed folate-BSA has a relatively long plasma duration. 111In-folate-BSA also showed selective distribution to tumors, but not as great as recent results from in vitro experiments. Therefore, the low vascular permeability of BSA into solid tumor tissue and inhibition of folate-mediated 111In-folate-BSA uptake by tumor cells from the blood may be the rate-limiting factor of distribution.