M. Laird Forrest

Toxicity of nanomaterials

Nanoscience has matured significantly during the last decade as it has transitioned from bench top science to applied technology. Presently, nanomaterials are used in a wide variety of commercial products such as electronic components, sports equipment, sun creams and biomedical applications. There are few studies of the long-term consequences of nanoparticles on human health, but governmental agencies, including the United States National Institute for Occupational Safety and Health and Japans Ministry of Health, have recently raised the question of whether seemingly innocuous materials such as carbon-based nanotubes should be treated with the same caution afforded known carcinogens such as asbestos. Since nanomaterials are increasing a part of everyday consumer products, manufacturing processes, and medical products, it is imperative that both workers and end-users be protected from inhalation of potentially toxic NPs. It also suggests that NPs may need to be sequestered into products so that the NPs are not released into the atmosphere during the products life or during recycling. Further, non-inhalation routes of NP absorption, including dermal and medical injectables, must be studied in order to understand possible toxic effects. Fewer studies to date have addressed whether the body can eventually eliminate nanomaterials to prevent particle build-up in tissues or organs. This critical review discusses the biophysicochemical properties of various nanomaterials with emphasis on currently available toxicology data and methodologies for evaluating nanoparticle toxicity (286 references).

Effects of nanomaterial physicochemical properties on in vivo toxicity

It is well recognized that physical and chemical properties of materials can alter dramatically at nanoscopic scale, and the growing use of nanotechnologies requires careful assessment of unexpected toxicities and biological interactions. However, most in vivo toxicity concerns focus primarily on pulmonary, oral, and dermal exposures to ultrafine particles. As nanomaterials expand as therapeutics and as diagnostic tools, parenteral administration of engineered nanomaterials should also be recognized as a critical aspect for toxicity consideration. Due to the complex nature of nanomaterials, conflicting studies have led to different views of their safety. Here, the physicochemical properties of four representative nanomaterials (dendrimers, carbon nanotubes, quantum dots, and gold nanoparticles) as it relates to their toxicity after systemic exposure is discussed.

Partial Acetylation of Polyethylenimine Enhances In Vitro Gene Delivery

AbstractPurpose. Polyethylenimine (PEI) is a highly effective gene delivery vector, but because it is an off-the shelf material, its properties may not be optimal. To investigate the effects of the protonation properties of the polymer, we generated PEI derivatives by acetylating varying fractions of the primary and secondary amines to form secondary and tertiary amides, respectively. Methods. Reaction of PEI with increasing amounts of acetic anhydride at 60°C for 4.5 h yielded polymers with 15%, 27%, and 43% of the primary amines modified with acetyl groups. Polymer-DNA complexes were characterized by dynamic light scattering and ζ potential measurements. Cytotoxicity of the polymers was assessed by XTT assay for metabolic activity, and gene delivery efficiency was determined as the relative expression of a luciferase gene in MDA-MB-231 and C2C12 cell lines. Results. Acetylation of PEI decreased the “physiological buffering capacity,” defined as the moles of protons absorbed per mole of nitrogen on titration from pH 7.5 to 4.5, from 0.29 mol H+/mol N to 0.17 mol H+/mol N, 0.12 mol H+/mol N, and 0.090 mol H+/mol N for PEI-Ac15, PEI-Ac27, and PEI-Ac43, respectively. In addition, acetylation decreased the ζ potential of polyplexes from 14 mV to 8-11 mV and increased the polyplex diameter by two- to threefold. Surprisingly, acetylation had a negligible effect on cytotoxicity of the polymers and increased gene delivery effectiveness by up to 21-fold compared to unmodified PEI, both in the presence and absence of serum. Conclusions. Reduction of the buffering capacity of PEI greatly enhanced the gene delivery activity of the polymer. The mechanism is not yet understood, but the enhancement may be caused by more effective polyplex unpackaging, altered endocytic trafficking, and/or increased lipophilicity of acetylated PEI-DNA complexes. Future studies will address these possibilities in more detail.

Nanoparticles for biomedical imaging

Background: Synthetic nanoparticles are emerging as versatile tools in biomedical applications, particularly in the area of biomedical imaging. Nanoparticles 1 – 100 nm in diameter have dimensions comparable to biological functional units. Diverse surface chemistries, unique magnetic properties, tunable absorption and emission properties, and recent advances in the synthesis and engineering of various nanoparticles suggest their potential as probes for early detection of diseases such as cancer. Surface functionalization has expanded further the potential of nanoparticles as probes for molecular imaging. Objective: To summarize emerging research of nanoparticles for biomedical imaging with increased selectivity and reduced nonspecific uptake with increased spatial resolution containing stabilizers conjugated with targeting ligands. Methods: This review summarizes recent technological advances in the synthesis of various nanoparticle probes, and surveys methods to improve the targeting of nanoparticles for their application in biomedical imaging. Conclusion: Structural design of nanomaterials for biomedical imaging continues to expand and diversify. Synthetic methods have aimed to control the size and surface characteristics of nanoparticles to control distribution, half-life and elimination. Although molecular imaging applications using nanoparticles are advancing into clinical applications, challenges such as storage stability and long-term toxicology should continue to be addressed.

Clinical toxicities of nanocarrier systems.

Toxicity of nanocarrier systems involves physiological, physicochemical, and molecular considerations. Nanoparticle exposures through the skin, the respiratory tract, the gastrointestinal tract and the lymphatics have been described. Nanocarrier systems may induce cytotoxicity and/or genotoxicity, whereas their antigenicity is still not well understood. Nanocarrier may alter the physicochemical properties of xenobiotics resulting in pharmaceutical changes in stability, solubility, and pharmacokinetic disposition. In particular, nanocarriers may reduce toxicity of hydrophobic cancer drugs that are solubilized. Nano regulation is still undergoing major changes to encompass environmental, health, and safety issues. The rapid commercialization of nanotechnology requires thoughtful environmental, health and safety research, meaningful, and an open discussion of broader societal impacts, and urgent toxicological oversight action.

In vitro release of the mTOR inhibitor rapamycin from poly(ethylene glycol)-b-poly(ε-caprolactone) micelles

An injectable formulation of rapamycin was prepared using amphiphilic block co-polymer micelles of poly(ethylene glycol)-b-poly(epsilon-caprolactone) (PEG-PCL). Drug-loaded PEG-PCL micelles were prepared by a co-solvent extraction technique. Resulting PEG-PCL micelles were less than 100 nm in diameter and contained rapamycin at 7% to 10% weight and >1 mg/mL. PEG-PCL micelles released rapamycin over several days, t50% 31 h, with no burst release; however, physiological concentrations of serum albumin increased the release rate 3-fold. Alpha-tocopherol, vitamin E, was co-incorporated into PEG-PCL micelles and increased the efficiency of rapamycin encapsulation. The addition of alpha-tocopherol also slowed the release of rapamycin from PEG-PCL micelles in the presence of serum albumin, t50% 39 h.

Lymphatic drug delivery using engineered liposomes and solid lipid nanoparticles.

The lymphatic system plays a crucial role in the immune systems recognition and response to disease, and most solid cancers initially spread from the primary site via the tumors surrounding lymphatics before hematological dissemination. Hence, the lymphatic system is an important target for developing new vaccines, cancer treatments, and diagnostic agents. Targeting the lymphatic system by subcutaneous, intestinal, and pulmonary routes has been evaluated and subsequently utilized to improve lymphatic penetration and retention of drug molecules, reduce drug-related systemic toxicities, and enhance bioavailability of poorly soluble and unstable drugs. Lymphatic imaging is an essential tool for the detection and staging of cancer. New nano-based technologies offer improved detection and characterization of the nodal diseases, while new delivery devices can better target and confine treatments to tumors within the nodal space while sparing healthy tissues. This manuscript reviews recent advances in the field of lymphatic drug delivery and imaging and focuses specifically on the development of liposomes and solid lipid nanoparticles for lymphatic introduction via the subcutaneous, intestinal, and pulmonary routes.

Localized doxorubicin chemotherapy with a biopolymeric nanocarrier improves survival and reduces toxicity in xenografts of human breast cancer.

Patients with metastatic breast cancer have a five-year survival rate of 27% compared to 98% for localized cancer, and the presence of even a few cancer cells in lymph nodes, known as isolated tumor cells or nanometastases, significantly increases the risk of relapse in the absence of aggressive treatment. Therefore, diagnosis and treatment of lymphatic metastases in early breast cancer plays an important role in patient survival. Here, we demonstrate the first description of a delivery system for localized doxorubicin chemotherapy to the breast tissue. The hyaluronan-doxorubicin nanoconjugate exhibits a sustained release characteristic in vitro and in vivo in the breast tissues of rodents bearing human breast cancer xenografts. In addition, the conjugate reduces dose-limiting cardiac toxicity with minimal toxicity observed in normal tissues. Finally, the conjugate dramatically inhibits breast cancer progression in vivo, leading to an increased survival rate. Thus, localized chemotherapy to the breast lymphatics with a nanocarrier may represent an improved strategy for treatment of early stage breast cancers.

Intralymphatic chemotherapy using a hyaluronan-cisplatin conjugate.

BACKGROUND Breast cancers typically spread to regional lymph nodes once they disseminate from the primary tumor, thus adequate evaluation and treatment of the axillary lymph nodes is paramount in early stage disease. One significant problem with current therapy is the side effects chemotherapy agents create systemically, either alone or in combination. The purpose of this study is to determine whether lymphatically targeted cisplatin carriers will increase the localized dose in lymphatic metastases without systemic toxicities. METHODS Hyaluronan (HA) is a highly biocompatible polymer that follows lymphatic drainage from the interstitial spaces. We formed complexes of HA and cisplatin by non-covalent conjugation. Complexes were injected subcutaneously into the upper mammary fat pad of female rats, and the tissue distribution determined. RESULTS Cisplatin-HA contained up to 0.25 w/w of Pt and released drug with a half-life of 10 h in saline. Cisplatin-HA conjugates had high anti-tumor activity in vitro similar to the free drug: cisplatin-HA IC50 7 microg/mL in MCF7 and MDA-MB-231 human breast cancer cells (free cisplatin IC50 7 microg/mL). Cisplatin-HA conjugates were well tolerated in rodents with no signs of injection site morbidity or major organ toxicity after 96 h. The area-under-the-curve of cisplatin in the axially lymph nodes after injection with cisplatin-HA increased 74% compared with normal cisplatin. CONCLUSIONS This study demonstrates a novel intralymphatic drug delivery method in breast cancer to preferentially treat at-risk regional lymph nodes and avoid systemic toxicities. Further in vivo testing related to efficacy of this approach with regard to survival, toxicity, and pharmacokinetics is warranted to support its use in human trials.

Drug delivery to the lymphatic system: importance in future cancer diagnosis and therapies

Cancer is the second leading cause of death in the US. Currently, protocols for cancer treatment include surgery to remove diseased and suspect tissues, focused radiation, systemic chemotherapy, immunotherapy and their combinations. With conventional chemotherapy, it is almost impossible to deliver anticancer drugs specifically to the tumor cells without damaging healthy organs or tissues. Over the past several decades, efforts have been made to improve drug delivery technologies that target anticancer drugs specifically to tumor cells. It has been known for over four decades that the lymphatics are the first site of metastasis for most solid cancers; however, few efforts have been made to localize chemotherapies to lymphatic tissues. Trials of several systemic targeted drug delivery systems based on nanoparticles containing chemotherapeutic agents (e.g., liposomal doxorubicin) have shown similar antitumor activity but better patient tolerance compared with conventional formulations. Animal studies have demonstrated that nanoparticles made of natural or synthetic polymers and liposomal carriers have higher accumulation in the lymph nodes and surrounding lymphatics compared to conventional intravenous therapies. This combination has the potential to both reduce nonspecific organ toxicities and increase the chemotherapeutic dose to the most likely sites of locoregional cancer metastasis.