Advanced targeted therapies in cancer: Drug nanocarriers, the future of chemotherapy

Cancer is the second worldwide cause of death, exceeded only by cardiovascular diseases. It is characterized by uncontrolled cell proliferation and an absence of cell death that, except for hematological cancers, generates an abnormal cell mass or tumor. This primary tumor grows thanks to new vascularization and, in time, acquires metastatic potential and spreads to other body sites, which causes metastasis and finally death. Cancer is caused by damage or mutations in the genetic material of the cells due to environmental or inherited factors. While surgery and radiotherapy are the primary treatment used for local and non-metastatic cancers, anti-cancer drugs (chemotherapy, hormone and biological therapies) are the choice currently used in metastatic cancers. Chemotherapy is based on the inhibition of the division of rapidly growing cells, which is a characteristic of the cancerous cells, but unfortunately, it also affects normal cells with fast proliferation rates, such as the hair follicles, bone marrow and gastrointestinal tract cells, generating the characteristic side effects of chemotherapy. The indiscriminate destruction of normal cells, the toxicity of conventional chemotherapeutic drugs, as well as the development of multidrug resistance, support the need to find new effective targeted treatments based on the changes in the molecular biology of the tumor cells. These novel targeted therapies, of increasing interest as evidenced by FDA-approved targeted cancer drugs in recent years, block biologic transduction pathways and/or specific cancer proteins to induce the death of cancer cells by means of apoptosis and stimulation of the immune system, or specifically deliver chemotherapeutic agents to cancer cells, minimizing the undesirable side effects. Although targeted therapies can be achieved directly by altering specific cell signaling by means of monoclonal antibodies or small molecules inhibitors, this review focuses on indirect targeted approaches that mainly deliver chemotherapeutic agents to molecular targets overexpressed on the surface of tumor cells. In particular, we offer a detailed description of different cytotoxic drug carriers, such as liposomes, carbon nanotubes, dendrimers, polymeric micelles, polymeric conjugates and polymeric nanoparticles, in passive and active targeted cancer therapy, by enhancing the permeability and retention or by the functionalization of the surface of the carriers, respectively, emphasizing those that have received FDA approval or are part of the most important clinical studies up to date. These drug carriers not only transport the chemotherapeutic agents to tumors, avoiding normal tissues and reducing toxicity in the rest of the body, but also protect cytotoxic drugs from degradation, increase the half-life, payload and solubility of cytotoxic agents and reduce renal clearance.Despite the many advantages of all the anticancer drug carriers analyzed, only a few of them have reached the FDA approval, in particular, two polymer-protein conjugates, five liposomal formulations and one polymeric nanoparticle are available in the market, in contrast to the sixteen FDA approval of monoclonal antibodies. However, there are numerous clinical trials in progress of polymer-protein and polymer-drug conjugates, liposomal formulations, including immunoliposomes, polymeric micelles and polymeric nanoparticles. Regarding carbon nanotubes or dendrimers, there are no FDA approvals or clinical trials in process up to date due to their unresolved toxicity. Moreover, we analyze in detail the more promising and advanced preclinical studies of the particular case of polymeric nanoparticles as carriers of different cytotoxic agents to active and passive tumor targeting published in the last 5 years, since they have a huge potential in cancer therapy, being one of the most widely studied nano-platforms in this field in the last years. The interest that these formulations have recently achieved is stressed by the fact that 90% of the papers based on cancer therapeutics with polymeric nanoparticles have been published in the last 6 years (PubMed search).Authors acknowledge financial support from University of Salamanca, Spain. AFM work is supported by grants FIS PI13/02846 and RTICC RD12/0036/0001 from Instituto de Salud Carlos III (ISCIII), Spain, and grant SA181U13 from JCyL, Spain. EPH work is supported by grant FS/25-2014 from Fundación en Memoria de D. Samuel Solórzano Barruso, Spain.Peer Reviewe

Adriamycin-loaded albumin-heparin conjugate microspheres for intraperitoneal chemotherapy

Adriamycin-loaded albumin-heparin conjugate microspheres (ADR-AHCMS) were evaluated as possible intraperitoneal (i.p.) delivery systems for site-specific cytotoxic action. The biocompatibility of the microspheres after intraperitoneal injection was tested first. 1 day after i.p. administration of empty as well as drug-loaded AHCMS to male Balb/c mice, only a moderate increase in i.p. neutrophils was measured. 3 days after injection neutrophil levels were comparable with the controls. No significant increases in the numbers of other cell types were observed, indicating an acute inflammatory response which can be considered to be mild. Antitumour efficacy was tested in an L1210 tumour-bearing mouse model and in a CC531 tumour-bearing rat model. The use of ADR-AHCMS leads to longer survival times of mice and improved tumour growth delay in rats, as compared with untreated controls and free drug treated animals. In both animal models higher adriamycin doses were initially tolerated if the drug was formulated in microspheres, although long-term adriamycin toxicity effects were evident in all treated groups. Doses and dosage schedules may be optimized to further reduce the toxic effects of the drug

Nanomedicines as cancer therapeutics: Current status

As of 21st century, cancer is arguably the most complex and challenging disease known to mankind and an inevitable public health concern of this millennium. Nanotechnology, suitably amalgamated with cancer research, has ushered an era of highly personalized and safer medicines which can improve cancer diagnosis and therapy. A wide variety of nanomedicines are currently under investigation, including polymeric/non-polymeric nanoparticles, dendrimers, quantum dots, carbon nanotubes, lipid- and micelle-based nanoparticles. The bases of these nanomedicines in reducing toxicity associated with cancer therapy are their ability to carry a large payload and multivalent-ligand targeting. This imparts specificity for targeting the tissues as well as bypass resistance mechanisms. The major hurdles on these future medicines are potential toxicity of nanoparticles, which imposes the need of extensive regulatory evaluation before nanomedicines could be utilized as cancer therapeutics. This review highlights nanopharmaceuticals that have been investigated in oncology for various applications (diagnosis, therapeutic delivery and theranostics). It also discusses the effects of nano-sized materials on tissues/organ functions, the possibility of overcoming multi-drug resistance by using nanomedicines and their current clinical status

Efficient chemotherapy of rat glioblastoma using Doxorubicin-loaded PLGA nanoparticles with different stabilizers

Background: Chemotherapy of glioblastoma is largely ineffective as the blood-brain barrier (BBB) prevents entry of most anticancer agents into the brain. For an efficient treatment of glioblastomas it is necessary to deliver anti-cancer drugs across the intact BBB. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles coated with poloxamer 188 hold great promise as drug carriers for brain delivery after their intravenous injection. In the present study the anti-tumour efficacy of the surfactant-coated doxorubicin-loaded PLGA nanoparticles against rat glioblastoma 101/8 was investigated using histological and immunohistochemical methods. Methodology: The particles were prepared by a high-pressure solvent evaporation technique using 1% polyvinylalcohol (PLGA/PVA) or human serum albumin (PLGA/HSA) as stabilizers. Additionally, lecithin-containing PLGA/HSA particles (Dox-Lecithin-PLGA/HSA) were prepared. For evaluation of the antitumour efficacy the glioblastoma-bearing rats were treated intravenously with the doxorubicin-loaded nanoparticles coated with poloxamer 188 using the following treatment regimen: 3×2.5 mg/kg on day 2, 5 and 8 after tumour implantation; doxorubicin and poloxamer 188 solutions were used as controls. On day 18, the rats were sacrificed and the antitumour effect was determined by measurement of tumour size, necrotic areas, proliferation index, and expression of GFAP and VEGF as well as Isolectin B4, a marker for the vessel density. Conclusion: The results reveal a considerable anti-tumour effect of the doxorubicin-loaded nanoparticles. The overall best results were observed for Dox-Lecithin-PLGA/HSA. These data demonstrate that the poloxamer 188-coated PLGA nanoparticles enable delivery of doxorubicin across the blood-brain barrier in the therapeutically effective concentrations

Polysaccharide-based self-assembling nanohydrogels: An overview on 25-years research on pullulan

The aim of this overview is to review the evolution of the studies carried out, during more than 25 years, on nanohydrogels obtained by self-assembling of pullulan (PUL) using several hydrophobization strategies. After the first publications, mainly devoted to the preparation and characterization of PUL nanogels, a remarkable number of studies demonstrated how wide can be the field of applications within the main topic of biopharmaceutics. Numerous hydrophilic and lipophilic drugs were entrapped in the nanogel networks, consequently PUL nanogels have been proposed as delivery systems for single drugs and for combination therapies which allowed improvements of pharmacological activities and patient compliance. Furthermore, the large amount of water content allowed loading also proteins which could maintain their native structure and properties. Stimuli-sensitive and stealth PUL nanogel formulations allowed improving the performances of antitumor drugs. These nanohydrogels have also been studied for imaging techniques and for vaccines to be administered by injection and by mucosal application. The studies on PUL nanogels are still in progress and the perspectives for future researches are also addressed

Folate-conjugated nanoparticles as a potent therapeutic approach in targeted cancer therapy

The selective and efficient drug delivery to tumor cells can remarkably improve different cancer therapeutic approaches. There are several nanoparticles (NPs) which can act as a potent drug carrier for cancer therapy. However, the specific drug delivery to cancer cells is an important issue which should be considered before designing new NPs for in vivo application. It has been shown that cancer cells over-express folate receptor (FR) in order to improve their growth. As normal cells express a significantly lower levels of FR compared to tumor cells, it seems that folate molecules can be used as potent targeting moieties in different nanocarrier-based therapeutic approaches. Moreover, there is evidence which implies folate-conjugated NPs can selectively deliver anti-tumor drugs into cancer cells both in vitro and in vivo. In this review, we will discuss about the efficiency of different folate-conjugated NPs in cancer therapy. © 2015, International Society of Oncology and BioMarkers (ISOBM)

Albumin-conjugated PEG liposome enhances tumor distribution of liposomal doxorubicin in rats

To evaluate the effect of coupling of recombinant human serum albumin (rHSA) onto the surface of poly(ethylene glycol)-modified liposorne (PEG liposome) on the in vivo disposition characteristics of liposomal doxorubicin (DXR), the pharmacokinetics and tissue distribution of DXR were evaluated after intravenous administration of rHSA-modified PEG (rHSA/PEG) liposomal DXR into tumor-bearing rats. rHSA/PEG liposome prepared using a hetero-bifunctional cross-linker, N- succinimidyl 3-(2-pyridyldithio) propionate (SPDP), efficiently encapsulated DXR (over 95%). rHSA/PEG liposomal DXR showed longer blood-circulating property than PEG liposornal DXR and the hepatic and splenic clearances of rHSA/PEG liposornal DXR were significantly smaller than those of PEG liposomal DXR. It was also demonstrated that the disposition of DXR to the heart, one of the organs for DXR-related side-effects, was significantly smaller than free DXR. Furthermore, the tumor accumulation of rHSA/PEG liposomal DXR was significantly larger than that of PEG liposomal DXR. The &#34;therapeutic index&#34;, a criterion for therapeutic outcome, for rHSA/PEG fiposornal DXR was significantly higher than PEG liposomal DXR. These results clearly indicate that rHSA-conjugation onto the surface of PEG liposome would be a useful approach to increase the effectiveness and safety of PEG liposomal DXR.</p

Restenosis treatments using nanoparticle-based drug delivery systems

Restenosis, the re-narrowing of a blood vessel after removal of atherosclerotic plaque, is a major limitation of surgical treatments for atherosclerosis. Various attempts to prevent or treat restenosis by pharmacological or mechanical approaches have had limited success in clinical trials. Hence, there is wide interest in developing new strategies to prevent or treat restenosis. This review discusses 'a new-generation therapy' that uses functional nanoparticles to effectively deliver active drug molecules. The potential platforms for nanoparticle-based solutions to restenosis include organic (e.g. polymers, liposomes, and proteins) and inorganic nanoparticles (e.g. layered double hydroxides, titanium oxide nanotubes, and magnetic nanoparticles,). Many in vitro and in vivo studies based on these platforms demonstrate the feasibility and potential of using nanoparticle drug delivery systems for preventing or treating restenosis, but as yet few have reached clinical trials. It is suggested that using inorganic nanoparticles to target deliver multi-functional drugs will be a promising approach to preventing or treating restenosis

The synthesis and characterization of polypeptide-adriamycin conjugates and its complexes with adriamycin. Part I

Poly(α-l-glutamic acid) (PGA) was grafted with amino acid and oligopeptide spacers up to 5 amino acids with the use of N,N'-carbonyldiimidazole and 2,3-dihydro-1,2-benz-isothiazole-3-on-1, 1-dioxide (saccharin) as an additive, and these polypeptides were characterized. The antitumor antibiotic adriamycin was covalently coupled via an amide bond onto PGA and onto the grafted polymers with the use of N-ethoxycarbonyl-2-ethoxy-1, 2-dihydroquinoline (EEDQ); these conjugates were characterized. The conjugates containing Gly—Gly—l-Leu spacer arms did yield free adriamycin upon digestion with papain. Adriamycin gave fairly stable complexes with PGA—adriamycin and branched poly peptide—adriamycin conjugates; these complexes were characterized