Peptide Decoration of Nanovehicles to Achieve Active Targeting and Pathology-Responsive Cellular Uptake for Bone Metastasis Chemotherapy

Design of Nanodrug Delivery Systems for Tumor Bone Metastasis

Tumor metastasis is a complex process that is controlled at the molecular level by numerous cytokines. Primary breast and prostate tumors most commonly metastasize to bone, and the development of increasingly accurate targeted nanocarrier systems has become a research focus for more effective anti-bone metastasis therapy. This review summarizes the molecular mechanisms of bone metastasis and the principles and methods for designing bone-targeted nanocarriers and then provides an in-depth review of bone-targeted nanocarriers for the treatment of bone metastasis in the context of chemotherapy, photothermal therapy, gene therapy, and combination therapy. Furthermore, this review also discusses the treatment of metastatic and primary bone tumors, providing directions for the design of nanodelivery systems and future research.

Active targeting schemes for nano-drug delivery systems in osteosarcoma therapeutics

Osteosarcoma, the most common malignant tumor of the bone, seriously influences people's lives and increases their economic burden. Conventional chemotherapy drugs achieve limited therapeutic effects owing to poor targeting and severe systemic toxicity. Nanocarrier-based drug delivery systems can significantly enhance the utilization efficiency of chemotherapeutic drugs through targeting ligand modifications and reduce the occurrence of systemic adverse effects. A variety of ligand-modified nano-drug delivery systems have been developed for different targeting schemes. Here we review the biological characteristics and the main challenges of current drug therapy of OS, and further elaborate on different targeting schemes and ligand selection for nano-drug delivery systems of osteosarcoma, which may provide new horizons for the development of advanced targeted drug delivery systems in the future.

Siglec15 Checkpoint Blockade for Simultaneous Immunochemotherapy and Osteolysis Inhibition in Lung Adenocarcinoma Spinal Metastasis via a Hollow Nanoplatform

Low responsiveness to anti-programmed death-1/programmed death-ligand 1 (anti-PD-1/PD-L1) for solid tumors indicates the presence of other immunosuppressive pathways. Siglec15, a newly discovered immune checkpoint, has been reported to repress immune responses in the tumor microenvironment (TME) and regulate osteoclast differentiation. However, the role of Siglec15 in the treatment for bone metastasis remains unclear. Herein, Siglec15 shows significantly higher expression in lung adenocarcinoma spinal metastasis (LUAD-SM) than in para-cancerous spinal tissues and primary LUAD. Subsequently, a TME-responsive hollow MnO₂ nanoplatform (H-M) loaded with Siglec15 siRNA and cisplatin (H-M@siS15/Cis) is developed, and the surface is modified with an aspartic acid octapeptide (Asp⁸ ), thus allowing H-M to target spinal metastasis. High drug-loading capacity, good biocompatibility, effective tumor accumulation, and efficient Siglec15 silencing are demonstrated. Furthermore, the nanoparticles could reverse immunosuppression caused by tumor cells and tumor-associated macrophages (TAMs) and inhibit osteoclast differentiation via Siglec15 downregulation in vitro. In a LUAD-SM mouse model, H-M@siS15/Cis-Asp⁸ exhibits superior therapeutic efficacy via synergetic immunochemotherapy and osteolysis inhibition. Taken together, this single nanoplatform reveals the therapeutic potential of the new immune checkpoint Siglec15 in LUAD-SM and provides a strategy to treat this disease.

Platinum Nanoparticles in Biomedicine: Preparation, Anti-Cancer Activity, and Drug Delivery Vehicles

Cancer is the main cause of morbidity and mortality worldwide, excluding infectious disease. Because of their lack of specificity in chemotherapy agents are used for cancer treatment, these agents have severe systemic side effects, and gradually lose their therapeutic effects because most cancers become multidrug resistant. Platinum nanoparticles (PtNPs) are relatively new agents that are being tested in cancer therapy. This review covers the various methods for the preparation and physicochemical characterization of PtNPs. PtNPs have been shown to possess some intrinsic anticancer activity, probably due to their antioxidant action, which slows tumor growth. Targeting ligands can be attached to functionalized metal PtNPs to improve their tumor targeting ability. PtNPs-based therapeutic systems can enable the controlled release of drugs, to improve the efficiency and reduce the side effects of cancer therapy. Pt-based materials play a key role in clinical research. Thus, the diagnostic and medical industries are exploring the possibility of using PtNPs as a next-generation anticancer therapeutic agent. Although, biologically prepared nanomaterials exhibit high efficacy with low concentrations, several factors still need to be considered for clinical use of PtNPs such as the source of raw materials, stability, solubility, the method of production, biodistribution, accumulation, controlled release, cell-specific targeting, and toxicological issues to human beings. The development of PtNPs as an anticancer agent is one of the most valuable approaches for cancer treatment. The future of PtNPs in biomedical applications holds great promise, especially in the area of disease diagnosis, early detection, cellular and deep tissue imaging, drug/gene delivery, as well as multifunctional therapeutics.

Sympathetic activity in breast cancer and metastasis: partners in crime

The vast majority of patients with advanced breast cancer present skeletal complications that severely compromise their quality of life. Breast cancer cells are characterized by a strong tropism to the bone niche. After engraftment and colonization of bone, breast cancer cells interact with native bone cells to hinder the normal bone remodeling process and establish an osteolytic "metastatic vicious cycle". The sympathetic nervous system has emerged in recent years as an important modulator of breast cancer progression and metastasis, potentiating and accelerating the onset of the vicious cycle and leading to extensive bone degradation. Furthermore, sympathetic neurotransmitters and their cognate receptors have been shown to promote several hallmarks of breast cancer, such as proliferation, angiogenesis, immune escape, and invasion of the extracellular matrix. In this review, we assembled the current knowledge concerning the complex interactions that take place in the tumor microenvironment, with a special emphasis on sympathetic modulation of breast cancer cells and stromal cells. Notably, the differential action of epinephrine and norepinephrine, through either α- or β-adrenergic receptors, on breast cancer progression prompts careful consideration when designing new therapeutic options. In addition, the contribution of sympathetic innervation to the formation of bone metastatic foci is highlighted. In particular, we address the remarkable ability of adrenergic signaling to condition the native bone remodeling process and modulate the bone vasculature, driving breast cancer cell engraftment in the bone niche. Finally, clinical perspectives and developments on the use of β-adrenergic receptor inhibitors for breast cancer management and treatment are discussed.

Targeted nanomedicines for the treatment of bone disease and regeneration

Targeted delivery by either passive or active targeting of therapeutics to the bone is an attractive treatment for various bone related diseases such as osteoporosis, osteosarcoma, multiple myeloma, and metastatic bone tumors. Engineering novel drug delivery carriers can increase therapeutic efficacy and minimize the risk of side effects. Developmnet of nanocarrier delivery systems is an interesting field of ongoing studies with opportunities to provide more effective therapies. In addition, preclinical nanomedicine research can open new opportunities for preclinical bone-targeted drug delivery; nevertheless, further research is needed to progress these therapies towards clinical applications. In the present review, the latest advancements in targeting moieties and nanocarrier drug delivery systems for the treatment of bone diseases are summarized. We also review the regeneration capability and effective delivery of nanomedicines for orthopedic applications.

Targeting nanoparticles for diagnosis and therapy of bone tumors: Opportunities and challenges

A variety of targeted nanoparticles were developed for the diagnosis and therapy of orthotopic and metastatic bone tumors during the past decade. This critical review will focus on principles and methods in the design of these bone-targeted nanoparticles. Ligands including bisphosphonates, aspartic acid-rich peptides and synthetic polymers were grafted on nanoparticles such as PLGA nanoparticles, liposomes, dendrimers and inorganic nanoparticles for bone targeting. Besides, other ligands such as monoclonal antibodies, peptides and aptamers targeting biomarkers on tumor/bone cells were identified for targeted diagnosis and therapy. Examples of targeted nanoparticles for the early detection of bone metastatic tumors and the ablation of cancer via chemotherapy, photothermal therapy, gene therapy and combination therapy will be intensively reviewed. The development of multifunctional nanoparticles to break down the "vicious" cycle between tumor cell proliferation and bone resorption, and the challenges and perspectives in this area will be discussed.

Dual-targeting liposome modified by glutamic hexapeptide and folic acid for bone metastatic breast cancer

Bone is the most common organ affected by metastatic breast cancer. Targeting delivery of drugs to bone may not only enhance the treatment efficacy, but also reduce the quantity of drug administered. In order to increase the distribution of paclitaxel (PTX) in bone, herein, a novel bone metastasis-targeted glutamic hexapeptide-folic acid (Glu₆-FA) derivative was designed and synthesized as liposome ligand to deliver PTX to bone metastasis effectively. The liposomes were prepared by thin film hydration method and its particle size, zeta potential, encapsulation efficiency, release profile, stability, hemolysis were also characterized. What's more, the anti-tumor effects of PTX-Glu₆-FA-Lip were confirmed by the detection of cell cycle, migration, and further measurement of microtubule stabilization. In addition, the PTX-Glu₆-FA-Lip showed superior targeting ability in vitro and in vivo evaluation as compared to naked PTX, non-coated, singly-modified and co-modified by physical blending liposomes. All the results suggested that Glu₆-FA-modified liposome showed excellent targeting activity to metastatic bone cancer. These findings suggested that Glu₆-FA-Lip was a promising bone metastasis-targeting carrier for the delivery of PTX. This study may therefore be conducive to the field of bone-targeting drugs delivery.

Alendronate-Modified Polymeric Micelles for the Treatment of Breast Cancer Bone Metastasis

Although the prognosis of patients with breast cancer continues to improve, breast cancer metastasis to bones remains high in incidence and challenging to manage. Here, we report the development of bone-homing alendronate (ALN)-anchored biodegradable polymeric micelles for the targeted treatment of metastatic cancer to bone. These micelles exhibited bone protective capacity including the recruitment, differentiation, and resorption activity of the osteoclasts. Encapsulation of docetaxel (DTX), the first-line chemotherapeutic for treatment of metastatic breast cancer, in ALN-modified micelles results in a sustained release, enhanced cytotoxicity, and improved pharmacokinetics. In the syngeneic animal model of late-stage disseminated breast cancer bone metastasis, the treatment with targeted DTX-loaded micelles attenuated the tumorigenesis and significantly improved animal lifespan compared to the conventional surfactant-based formulation (free DTX). These findings indicate potential applications of the osteotropic nanomedicines for bone metastasis treatment.

A Carboxyl-Terminated Dendrimer Enables Osteolytic Lesion Targeting and Photothermal Ablation of Malignant Bone Tumors

Malignant bone tumor accompanied by tumor-associated osteolysis remains a challenging task in clinical practice. Nanomedicines engineered with bone-targeting ligands, such as alendronate and pamidronate, are developed for targeted delivery of therapeutic agents to bone tumors. However, these targeting strategies usually show relatively poor selectivity toward the healthy skeletons and the osteolytic lesions because of the high binding affinity of bisphosphonates with all the bone tissues. Here, we reported a carboxyl-terminated dendrimer as the candidate to preferentially deliver therapeutic nanoparticles to the osteolytic lesions in a malignant bone tumor model. The high density of carboxyl groups on dendrimer surface endow the polymer with natural bone-binding capability. The dendrimer encapsulated with platinum nanoparticle predominantly accumulates at the osteolytic lesions around bone tumors rather than at healthy bone tissues in vivo. The therapeutic experiments reveal that the dendrimer-mediated photothermal therapy efficiently suppresses bone tumors and osteolysis, and the anionic polymer exhibits minimal cytotoxicity and hematologic toxicity. The results suggest that the carboxyl-terminated dendrimer is a promising candidate for selective delivery of therapeutics to the osteolytic lesions and photothermal treatment of malignant bone tumors.

Bortezomib-catechol conjugated prodrug micelles: combining bone targeting and aryl boronate-based pH-responsive drug release for cancer bone-metastasis therapy

The treatment of metastatic tumors is highly desirable in clinics, which has also increased the interest in the design of nanoscale drug delivery systems. Bone metastasis is one of the most common pathways in the metastasis of breast cancer, and it is also an important cause for tumor recurrence and death. The aryl boronate group, as an acid-labile linker, has been introduced into nano-assemblies in recent years. Especially, as a proteasome inhibitor anticancer drug with a boric acid group, bortezomib can facilitate the formation of pH-sensitive aryl boric acid ester linkage with the catecholic group. In this study, bortezomib-loaded micelles with bone targeting properties were constructed for the treatment of breast cancer bone metastasis. The mixed micelles employed alendronate (ALN) as the bone-targeting ligand and encapsulated bortezomib-catechol conjugates as the cargo. In vitro and in vivo studies showed that compared with free drugs or control micelles, these prodrug micelles (ALN-NP) exhibited many favorable properties such as reduced systemic toxicity and improved therapeutic effects. Therefore, ALN-NP is promising as a nanovehicle for bone-targeting delivery of chemotherapeutic drugs. Furthermore, this study offers a novel strategy combining bone targeting and aryl boronate-based pH-responsive drug release for anti-metastasis therapy.

Bisphosphonate conjugation for bone specific drug targeting

Bones provide essential functions and are sites of unique biochemistry and specialized cells, but can also be sites of disease. The treatment of bone disorders and neoplasia has presented difficulties in the past, and improved delivery of drugs to bone remains an important goal for achieving effective treatments. Drug targeting strategies have improved drug localization to bone by taking advantage of the high mineral concentration unique to the bone hydroxyapatite matrix, as well as tissue-specific cell types. The bisphosphonate molecule class binds specifically to hydroxyapatite and inhibits osteoclast resorption of bone, providing direct treatment for degenerative bone disorders, and as emerging evidence suggests, cancer. These bone-binding molecules also provide the opportunity to deliver other drugs specifically to bone by bisphosphonate conjugation. Bisphosphonate bone-targeted therapies have been successful in treatment of osteoporosis, primary and metastatic neoplasms of the bone, and other bone disorders, as well as refining bone imaging. In this review, we focus upon the use of bisphosphonate conjugates with antineoplastic agents, and overview bisphosphonate based imaging agents, nanoparticles, and other drugs. We also discuss linker design potential and the current state of bisphosphonate conjugate research progress. Ongoing investigations continue to expand the possibilities for bone-targeted therapeutics and for extending their reach into clinical practice.

Combating head and neck cancer metastases by targeting Src using multifunctional nanoparticle-based saracatinib

BACKGROUND

Inhibition of metastasis of head and neck squamous cell carcinoma (HNSCC) is one of the most important challenges in cancer treatment. Src, a non-receptor tyrosine kinase, has been implicated as a key promoter in tumor progression and metastasis of HNSCC. However, Src therapy for HNSCC is limited by lack of efficient in vivo delivery and underlying mechanisms remain elusive.

METHODS

Src knockdown cells were achieved by lentiviral-mediated interference. Cell migration and invasion were examined by wound healing and Transwell assays. Protein levels were determined by Western blot and/or immunohistochemistry. The Src inhibitor saracatinib was loaded into self-assembling nanoparticles by the solvent evaporation method. An experimental metastasis mouse model was generated to investigate the drug efficacy in metastasis.

RESULTS

Blockade of Src kinase activity by saracatinib effectively suppressed invasion and metastasis of HNSCC. Mechanistic assessment of the drug effects in HNSCC cells showed that saracatinib induced suppression of Src-dependent invasion/metastasis through downregulating the expression levels of Vimentin and Snail proteins. In tests in mice, saracatinib loaded into the novel multifunctional nanoparticles exhibited superior effects on suppression of HNSCC metastasis compared with the free drug, which is mainly attributed to highly specific and efficient tumor-targeted drug delivery system.

CONCLUSIONS

These findings and advances are of great importance to the development of Src-targeted nanomedicine as a more effective therapy for metastatic HNSCC.

Calcium phosphate-based nanosystems for advanced targeted nanomedicine

Synthetic calcium phosphates (CaPs) are the most widely accepted bioceramics for the repair and reconstruction of bone tissue defects. The recent advancements in materials science have prompted a rapid progress in the preparation of CaPs with nanometric dimensions, tailored surface characteristics, and colloidal stability opening new perspectives in their use for applications not strictly related to bone. In particular, the employment of CaPs nanoparticles as carriers of therapeutic and imaging agents has recently raised great interest in nanomedicine. CaPs nanoparticles, as well as other kinds of nanoparticles, can be engineered to specifically target the site of the disease (cells or organs), thus minimizing their dispersion in the body and undesired organism-nanoparticles interactions. The most promising and efficient approach to improve their specificity is the 'active targeting', where nanoparticles are conjugated with a targeting moiety able to recognize and bind with high efficacy and selectivity to receptors that are highly expressed only in the therapeutic site. The aim of this review is to give an overview on advanced targeted nanomedicine with a focus on the most recent reports on CaP nanoparticles-based systems, specifically designed for the active targeting. The distinctive characteristics of CaP nanoparticles with respect to the other kinds of nanomaterials used in nanomedicine are also discussed.

Two-step polymer- and liposome-enzyme prodrug therapies for cancer: PDEPT and PELT concepts and future perspectives

Polymer-directed enzyme prodrug therapy (PDEPT) and polymer enzyme liposome therapy (PELT) are two-step therapies developed to provide anticancer drugs site-selective intratumoral accumulation and release. Nanomedicines, such as polymer-drug conjugates and liposomal drugs, accumulate in the tumor site due to extravasation-dependent mechanism (enhanced permeability and retention - EPR - effect), and further need to cross the cellular membrane and release their payload in the intracellular compartment. The subsequent administration of a polymer-enzyme conjugate able to accumulate in the tumor tissue and to trigger the extracellular release of the active drug showed promising preclinical results. The development of polymer-enzyme, polymer-drug conjugates and liposomal drugs had undergone a vast advancement over the past decades. Several examples of enzyme mimics for in vivo therapy can be found in the literature. Moreover, polymer therapeutics often present an enzyme-sensitive mechanism of drug release. These nanomedicines can thus be optimal substrates for PDEPT and this review aims to provide new insights and stimuli toward the future perspectives of this promising combination.

Engineered Multifunctional Nanomedicine for Simultaneous Stereotactic Chemotherapy and Inhibited Osteolysis in an Orthotopic Model of Bone Metastasis

A novel multifunctional Ag₂ S quantum dot (QD)-based nanomedicine of alendronate (Ald)/doxorubicin (DOX)@Ag₂ S is developed for highly effective bone tumor therapy in an orthotopic model. The bone-targeting and osteolysis inhibition of Ald and the chemotherapeutic effect of DOX on the bone tumor are in situ visualized by Ag₂ S QDs with emission in the second near-infrared window.

Nanocapsules engineered from polyhedral ZIF-8 templates for bone-targeted hydrophobic drug delivery

Biodegradable nanocapsules for bone-targeted simvastatin delivery were developed by using catechol modified gelatin as wall material and ZIF-8 as templates.

Osteotropic peptide-mediated bone targeting for photothermal treatment of bone tumors

The treatment of bone tumors is a challenging problem due to the inefficient delivery of therapeutics to bone and the bone microenvironment-associated tumor resistance to chemo- and radiotherapy. Here, we developed a bone-targeted nanoparticle, aspartate octapeptide-modified dendritic platinum-copper alloy nanoparticle (Asp-DPCN), for photothermal therapy (PTT) of bone tumors. Asp-DPCN showed much higher affinity toward hydroxyapatite and bone fragments than the non-targeted DPCN in vitro. Furthermore, Asp-DPCN accumulated more efficiently around bone tumors in vivo, and resulted in a higher temperature in bone tumors during PTT. Finally, Asp-DPCN-mediated PTT not only efficiently depressed the tumor growth but also significantly reduced the osteoclastic bone destruction. Our study developed a promising therapeutic approach for the treatment of bone tumors.

Bone and metal targeted polymeric nanoparticles (US20150125391 A1): a patent evaluation

INTRODUCTION

Delivery of therapeutic agents to bone is crucial for the treatment of bone metastasis and other bone diseases. The present invention patent relates to bone- and metal-targeted polymeric nanoparticles for targeting delivery of therapeutic molecules to the pathological tissues in bone or the surgical metal implant-bone tissue interface.

AREAS COVERED

The nanoparticles for drug delivery were fabricated via the assembly of amphiphilic polymers, in which the hydrophilic outer layer was minimal to prolong the circulation time, and the hydrophobic insider core was biodegradable and loaded with therapeutic agents. Bone-targeted elements were conjugated on the nanoparticle surface to enhance their affinity to bone and/or metal implant surface.

EXPERT OPINION

A prolonged, sustained release of therapeutic agents was observed by using the delivery system targeting to bone. The described invention provides a bone-targeted vector to deliver diverse therapeutic agents to bone.

Local and targeted drug delivery for bone regeneration

While experimental bone regeneration approaches commonly employ cells, technological hurdles prevent translation of these therapies. Alternatively, emulating the spatiotemporal cascade of endogenous factors through controlled drug delivery may provide superior bone regenerative approaches. Surgically placed drug depots have clinical indications. Additionally, noninvasive systemic delivery can be used as needed for poorly healing bone injuries. However, a major hurdle for systemic delivery is poor bone biodistribution of drugs. Thus, peptides, aptamers, and phosphate-rich compounds with specificity toward proteins, cells, and molecules within the regenerative bone microenvironment may enable the design of targeted carriers with bone biodistribution greater than that achieved by drug alone. These carriers, combined with osteoregenerative drugs and/or stimuli-sensitive linkers, may enhance bone regeneration while minimizing off-target tissue effects.

Poly(trimethylene carbonate)/Poly(malic acid) Amphiphilic Diblock Copolymers as Biocompatible Nanoparticles

Amphiphilic polycarbonate-poly(hydroxyalkanoate) diblock copolymers, namely, poly(trimethylene carbonate) (PTMC)-b-poly(β-malic acid) (PMLA), are reported for the first time. The synthetic strategy relies on commercially available catalysts and initiator. The controlled ring-opening polymerization (ROP) of trimethylene carbonate (TMC) catalyzed by the organic guanidine base 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), associated with iPrOH as an initiator, provided iPrO-PTMC-OH, which served as a macroinitiator in the controlled ROP of benzyl β-malolactonate (MLABe) catalyzed by the neodymium triflate salt (Nd(OTf)3). The resulting hydrophobic iPrO-PTMC-b-PMLABe-OH copolymers were then hydrogenolyzed into the parent iPrO-PTMC-b-PMLA-OH copolymers. A range of well-defined copolymers, featuring different sizes of segments (Mn,NMR up to 9300 g mol(-1) ; ÐM =1.28-1.40), were thus isolated in gram quantities, as evidenced by NMR spectroscopy, size exclusion chromatography, thermogravimetric analysis, differential scanning calorimetry, and contact angle analyses. Subsequently, PTMC-b-PMLA copolymers with different hydrophilic weight fractions (11-75 %) self-assembled in phosphate-buffered saline upon nanoprecipitation into well-defined nano-objects with Dh =61-176 nm, a polydispersity index <0.25, and a negative surface charge, as characterized by dynamic light scattering and zeta-potential analyses. In addition, these nanoparticles demonstrated no significant effect on cell viability at low concentrations, and a very low cytotoxicity at high concentrations only for PTMC-b-PMLA copolymers exhibiting hydrophilic fractions over 47 %, thus illustrating the potential of these copolymers as promising nanoparticles.

Structural modifications in polymeric micelles to impart multifunctionality for improved drug delivery

Polymeric micelles are macromolecular nanoconstructs which are formed by self-assembly of synthetic amphiphilic block copolymers. These copolymers could be chemically modified to expand their functionality and hence obtain a multifunctional micelle which could serve several functions simultaneously, for example, long circulation time along with active targeting, smart polymeric micelles providing on-demand drug release for example, pH responsive micelles, redox- and light-sensitive micelles, charge-conversion micelles and core/shell cross-linked micelles. Additionally, micelles could be tailored to carry a contrast agent or siRNA/miRNA along with the drug for greater clinical benefit. The focus of the current commentary would be to highlight such chemical modifications which impart multifunctionality to a single carrier and discuss challenges involved in clinical translation of these multifunctional micelles.

Poly(trimethylene carbonate)-based polymers engineered for biodegradable functional biomaterials

This review presents recent examples of applications and functionalization strategies of poly(trimethylene carbonate), its copolymers, and its derivatives to exploit the unique physicochemical properties of the aliphatic polycarbonate backbone.

Intelligent Nanoparticles for Advanced Drug Delivery in Cancer Treatment

Treatment of cancer using nanoparticle-based approaches relies on the rational design of carriers with respect to size, charge, and surface properties. Polymer-based nanomaterials, inorganic materials such as gold, iron oxide, and silica as well as carbon based materials such as carbon nanotubes and graphene are being explored extensively for cancer therapy. The challenges associated with the delivery of these nanoparticles depend greatly on the type of cancer and stage of development. This review highlights design considerations to develop nanoparticle-based approaches for overcoming physiological hurdles in cancer treatment, as well as emerging research in engineering advanced delivery systems for the treatment of primary, metastatic, and multidrug resistant cancers. A growing understanding of cancer biology will continue to foster development of intelligent nanoparticle-based therapeutics that take into account diverse physiological contexts of changing disease states to improve treatment outcomes.