Stimuli-responsive (nano)architectures for phytochemical delivery in cancer therapy

The use of phytochemicals for purpose of cancer therapy has been accelerated due to resistance of tumor cells to conventional chemotherapy drugs and therefore, monotherapy does not cause significant improvement in the prognosis and survival of patients. Therefore, administration of natural products alone or in combination with chemotherapy drugs due to various mechanisms of action has been suggested. However, cancer therapy using phytochemicals requires more attention because of poor bioavailability of compounds and lack of specific accumulation at tumor site. Hence, nanocarriers for specific delivery of phytochemicals in tumor therapy has been suggested. The pharmacokinetic profile of natural products and their therapeutic indices can be improved. The nanocarriers can improve potential of natural products in crossing over BBB and also, promote internalization in cancer cells through endocytosis. Moreover, (nano)platforms can deliver both natural and synthetic anti-cancer drugs in combination cancer therapy. The surface functionalization of nanostructures with ligands improves ability in internalization in tumor cells and improving cytotoxicity of natural compounds. Interestingly, stimuli-responsive nanostructures that respond to endogenous and exogenous stimuli have been employed for delivery of natural compounds in cancer therapy. The decrease in pH in tumor microenvironment causes degradation of bonds in nanostructures to release cargo and when changes in GSH levels occur, it also mediates drug release from nanocarriers. Moreover, enzymes in the tumor microenvironment such as MMP-2 can mediate drug release from nanocarriers and more progresses in targeted drug delivery obtained by application of nanoparticles that are responsive to exogenous stimulus including light.

Guanidine-modified nanoparticles as robust BTZ delivery carriers and activators of immune responses

Dendritic cells (DCs), the primary antigen-presenting cells in the immune system, play a critical role in regulating tumor immune responses. However, the tumor immunosuppressive microenvironment severely impedes the process of antigen-presenting and DC maturation, thereby limiting the efficacy of cancer immunotherapy. In this work, a pH-responsive polymer nanocarrier (PAG) modified with aminoguanidine (AG) was constructed for the efficient delivery of bortezomib (BTZ) through bidentate hydrogen bonds and electrostatic adsorption formed between guanidine groups of PAG and boronic acid groups of BTZ. The obtained PAG/BTZ nanoparticles exhibited pH-responsive release of BTZ and AG in the acidic tumor microenvironment. On the one hand, BTZ induced potent immune activation by eliciting immunogenic cell death (ICD) and releasing damage-associated molecular patterns. On the other hand, the cationic AG significantly promoted antigen uptake by DCs and activated DC maturation. As a result, PAG/BTZ significantly stimulated tumoral infiltration of cytotoxic T lymphocytes (CTLs) and triggered robust antitumor immune responses. Thus, it showed potent antitumor efficacy when synergizing with an immune checkpoint-blocking antibody.

The tumor EPR effect for cancer drug delivery: Current status, limitations, and alternatives

Over the past three decades, the enhanced permeability and retention (EPR) effect has been considered the basis of tumor-targeted drug delivery. Various cancer nanomedicines, including macromolecular drugs, have been designed to utilize this mechanism for preferential extravasation and accumulation in solid tumors. However, such nanomedicines have not yet achieved convincing therapeutic benefits in clinics. Increasing evidence suggests that the EPR effect is over-represented in human tumors, especially in metastatic tumors. This review covers the evolution of the concept, the heterogeneity and limitation of the EPR effect in clinical realities, and prospects for alternative strategies independent of the EPR effect.

Exploring pH dependent delivery of 5-fluorouracil from functionalized multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) can be applied for pH-sensitive delivery of anticancer drugs. Due to the importance of 5-fluorouracil (5-FU) in different tumor therapy regimens, it has been widely used in different pH dependent drug delivery systems. To investigate the pH effects on loading (and release) of 5-FU on (and from) the functionalized MWCNTs and propose the optimum condition for drug delivery, both macroscopic and microscopic studies were carried out using chromatography and molecular dynamic simulation at different conditions. For both levels of studies, different analytical approaches were performed to assess the validity of the methods. The experimental results revealed that 5-FU has more binding affinity to the surface of the nanocarrier at physiological pH (pH = 7.4) and showed more release at acidic conditions (pH = 5.0). Meanwhile it has been observed that basic pH (pH = 9.0) can lead to a dramatic decrease effect on loading of the drug. The results of this study can be used to suggest the optimum pH levels for nanocarbon based formulations of 5-FU in cancer therapy.

Redox-sensitive nanoparticles based on xylan-lipoic acid conjugate for tumor targeted drug delivery of niclosamide in cancer therapy

In this study, novel redox-sensitive nanoparticles based on xylan-lipoic acid (Xyl-LA) conjugate were developed for tumor targeted delivery of niclosamide (Nic) in cancer therapy. The niclosamide loaded xylan-lipoic acid conjugate nanoparticles (Xyl-LA/Nic NPs) showed redox responsive behaviour in presence of reductive glutathione (GSH), which indicate their suitability for intracellular drug release. The obtained Xyl-LA/Nic NPs exhibited uniform particle size (196 ± 1.64 nm), high loading capacity (~28.6 wt %) and excellent blood compatibility. The anticancer activity of the Niclosamide and the Xyl-LA/Nic NPs against the colon carcinoma cell lines (HCT-15, Colo-320) were evaluated by MTT assay and the overall results indicate that the Xyl-LA/Nic NPs significantly enhanced the therapeutic efficiency of niclosamide in cancer therapy.

Polyphenol-cisplatin complexation forming core-shell nanoparticles with improved tumor accumulation and dual-responsive drug release for enhanced cancer chemotherapy

Cisplatin (CDDP) is a potent first-line antitumor drug but suffers severe side effects and poor pharmacokinetics. Its complexation with polycarboxylic acids, such as polyglutamic acids, is generally used to fabricate nanoformulations for CDDP delivery; however, the multiple strong complexations makes intracellular drug release slow. Herein, we report a novel polyphenol-metal coordination method to fabricate CDDP-incorporated core-shell nanoparticles, which are stable in blood circulation but dissociate in the tumor. Methoxyl-PEG terminated with one or two gallic acids (PEG-GA or PEG-GA2) complexed CDDP and produced well-defined nanoparticles (PEG-GAx/Pt) with CDDP loading contents as high as 17.7% to 29.8%. The PEG-GAx/Pt nanoparticles were very stable in the physiological conditions and had slow blood clearance and efficient tumor accumulation, but dissociated quickly and released CDDP in response to the tumor acidity or elevated levels of reactive oxygen species (ROS). PEG-GAx/Pt nanoparticles exhibited improved antitumor efficiency against 4 T1 breast cancer and A549 lung carcinoma with much-reduced toxicity compared to free CDDP. The work demonstrates a new strategy of cisplatin-polyphenol coordination for developing platinum drugs' nanomedicines.

Tumor extravasation and infiltration as barriers of nanomedicine for high efficacy: The current status and transcytosis strategy

Nanotechnology-based drug delivery platforms have been explored for cancer treatments and resulted in several nanomedicines in clinical uses and many in clinical trials. However, current nanomedicines have not met the expected clinical therapeutic efficacy. Thus, improving therapeutic efficacy is the foremost pressing task of nanomedicine research. An effective nanomedicine must overcome biological barriers to go through at least five steps to deliver an effective drug into the cytosol of all the cancer cells in a tumor. Of these barriers, nanomedicine extravasation into and infiltration throughout the tumor are the two main unsolved blockages. Up to now, almost all the nanomedicines are designed to rely on the high permeability of tumor blood vessels to extravasate into tumor interstitium, i.e., the enhanced permeability and retention (EPR) effect or so-called "passive tumor accumulation"; however, the EPR features are not so characteristic in human tumors as in the animal tumor models. Following extravasation, the large size nanomedicines are almost motionless in the densely packed tumor microenvironment, making them restricted in the periphery of tumor blood vessels rather than infiltrating in the tumors and thus inaccessible to the distal but highly malignant cells. Recently, we demonstrated using nanocarriers to induce transcytosis of endothelial and cancer cells to enable nanomedicines to actively extravasate into and infiltrate in solid tumors, which led to radically increased anticancer activity. In this perspective, we make a brief discussion about how active transcytosis can be employed to overcome the difficulties, as mentioned above, and solve the inherent extravasation and infiltration dilemmas of nanomedicines.

Poly-isoprenylated ifosfamide analogs: Preactivated antitumor agents as free formulation or nanoassemblies

Oxazaphosphorines including cyclophosphamide, trofosfamide and ifosfamide (IFO) belong to the alkylating agent class and are indicated in the treatment of numerous cancers. However, IFO is subject to limiting side-effects in high-dose protocols. To circumvent IFO drawbacks in clinical practices, preactivated IFO analogs were designed to by-pass the toxic metabolic pathway. Among these IFO analogs, some of them showed the ability to self-assemble due to the use of a poly-isoprenyloxy chain as preactivating moiety. We present here, the in vitro activity of the nanoassembly formulations of preactivated IFO derivatives with a C-4 geranyloxy, farnesyloxy and squalenoxy substituent on a large panel of tumor cell lines. The chemical and colloidal stabilities of the geranyloxy-IFO (G-IFO), farnesyloxy-IFO (F-IFO) and squalenoxy-IFO (SQ-IFO) NAs were further evaluated in comparison to their free formulation. Finally, pharmacokinetic parameters and maximal tolerated dose of the most potent preactivated IFO analog (G-IFO) were determined and compared to IFO, paving the way to in vivo studies.

Tumor vessel normalization by the PI3K inhibitor HS-173 enhances drug delivery

Tumor vessels are leaky and immature, which causes poor oxygen and nutrient supply to tumor vessels and results in cancer cell metastasis to distant organs. This instability of tumor blood vessels also makes it difficult for anticancer drugs to penetrate and reach tumors. Numerous tumor vessel normalization approaches have been investigated for improving drug delivery into tumors. In this study, we investigated whether phosphoinositide 3-kinase (PI3K) inhibitors are able to improve vascular structure and function over the prolonged period necessary to achieve effective vessel normalization. The PI3K inhibitors, HS-173 and BEZ235 potently suppressed tumor growth and hypoxia, and increased tumor apoptosis in animal models. PI3K inhibitors also induced a regular, flat monolayer of endothelial cells (ECs) in vessels, improving stability of vessel structure, and normalized tumor vessels by increasing vascular maturity, pericyte coverage, basement membrane thickness, and tight-junctions. These effects resulted in a decrease in tumor vessel tortuosity and vessel thinning, and improved vessel function and blood flow. The tumor vessel stabilization effect of the PI3K inhibitor HS-173 also decreased the number of metastatic lung nodules in vivo metastasis model. Furthermore, HS-173 improved the delivery of doxorubicin into the tumor region, enhancing its anticancer effects. Mechanistic studies suggested that PI3K inhibitor HS-173-induced vessel normalization reflected changes in endothelial Notch signaling. Taken together, our findings indicate that vessel normalization by PI3K inhibitors restrained tumor growth and metastasis while improving chemotherapy by enhancing drug delivery into the tumor, suggesting that HS-173 may have a therapeutic value as an enhancer or an anticancer drug.

Connexin hemichannel induced vascular leak suggests a new paradigm for cancer therapy

It is 40 years since cancer growth was correlated with neovascularisation. Anti-angiogenic drugs remain at the forefront of cancer investigations but progress has been disappointing and unexpected toxicities are emerging. Gap junction channels are implicated in lesion spread following injury, with channel blockers shown to improve healing; in particular preventing vascular disruption and/or restoring vascular integrity. Here we briefly review connexin roles in vascular leak and endothelial cell death that occurs following acute wounds and during chronic disease, and how connexin channel regulation has been used to ameliorate vascular disruption. We then review chronic inflammatory disorders and trauma in the eye, concluding that vascular disruption under these conditions mimics that seen in tumours, and can be prevented with connexin hemichannel modulation. We apply this knowledge to tumour vessel biology, proposing that contrary to current opinion, these data suggest a need to protect, maintain and/or restore cancer vasculature. This may lead to reduced tumour hypoxia, promote the survival of normal cells, and enable improved therapeutic delivery or more effective radiation therapy.