HPMA Copolymer-Conjugated Pirarubicin in Multimodal Treatment of a Patient with Stage IV Prostate Cancer and Extensive Lung and Bone Metastases

Metal ions and nanomaterials for targeted bone cancer immunotherapy

Bone cancer remains a significant challenge in oncology, with limited success in current therapeutic approaches, particularly immunotherapy. Emerging research highlights the potential of integrating metal ions and nanomaterials for targeted immunotherapy in bone cancer. Metal ions, including calcium, magnesium, and zinc, play a significant role in modulating immune responses within the tumor microenvironment, affecting essential pathways necessary for immune activation. Meanwhile, nanomaterials, particularly metallic nanoparticles, offer precise drug delivery and immune system modulation, improving the efficacy of immunotherapeutic agents. This review explores the synergistic effects of metal ion-nanomaterial conjugates, discussing their role in enhancing immune cell activation, particularly T-cells and macrophages, and their potential for controlled drug release. We highlight preclinical advancements in bone cancer treatment using metal ion-responsive nanoparticles, and address current challenges such as biocompatibility and toxicity. Finally, we discuss the future prospects of these technologies in personalized and precision medicine, aiming to revolutionize bone cancer immunotherapy.

Long circulating liposomal platform utilizing hydrophilic polymer-based surface modification: preparation, characterisation, and biological evaluation

Liposomes are one of the most important drug delivery vectors, nowadays used in clinics. In general, polyethylene glycol (PEG) is used to ensure the stealth properties of the liposomes. Here, we have employed hydrophilic, biocompatible and highly non-fouling N-(2-hydroxypropyl) methacrylamide (HPMA)-based copolymers containing hydrophobic cholesterol anchors for the surface modification of liposomes, which were prepared by the method of lipid film hydration and extrusion through 100 nm polycarbonate filters. Efficient surface modification of liposomes was confirmed by transmission electron microscopy, atomic force microscopy, and gradient ultracentrifugation. The ability of long-term circulation in the vascular bed was demonstrated in rabbits after i.v. application of fluorescently labelled liposomes. Compared to PEGylated liposomes, HPMA-based copolymer-modified liposomes did not induce specific antibody formation and did not activate murine and human complement. Compared with PEGylated liposomes, HPMA-based copolymer-modified liposomes showed a better long-circulating effect after repeated administration. HPMA-based copolymer-modified liposomes thus represent suitable new candidates for a generation of safer and improved liposomal drug delivery platforms.

Targeting endothelial permeability in the EPR effect

The characteristics of the primary tumor blood vessels and the tumor microenvironment drive the enhanced permeability and retention (EPR) effect, which confers an advantage towards enhanced delivery of anti-cancer nanomedicine and has shown beneficial effects in preclinical models. Increased vascular permeability is a landmark feature of the tumor vessels and an important driver of the EPR. The main focus of this review is the endothelial regulation of vascular permeability. We discuss current challenges of targeting vascular permeability towards clinical translation and summarize the structural components and mechanisms of endothelial permeability, the principal mediators and signaling players, the targeted approaches that have been used and their outcomes to date. We also critically discuss the effects of the tumor-infiltrating immune cells, their interplay with the tumor vessels and the impact of immune responses on nanomedicine delivery, the impact of anti-angiogenic and tumor-stroma targeting approaches, and desirable nanoparticle design approaches for greater translational benefit.

Case Report: Tumor-to-tumor metastasis with prostate cancer metastatic to lung cancer: the first reported case

Tumor-to-tumor metastasis (TTM) occurs rarely in tumor progression, but this event has significant clinical implications. Although the impact of TTM on patient prognosis and survival has been increasingly recognized, understanding of TTM biology and treatment is limited. Prostate cancer is among the most common malignancies threatening male health. Prostate cancer can potentially metastasize to primary lung Cancer; however, this is an exceedingly rare event. We here report for the first time a case of TTM from a prostate cancer to a coexisting primary lung cancer.

Dye labeling for optical imaging biases drug carriers' biodistribution and tumor uptake

Biodistribution analyses of nanocarriers are often performed with optical imaging. Though dye tags can interact with transporters, e.g., organic anion transporting polypeptides (OATPs), their influence on biodistribution was hardly studied. Therefore, this study compared tumor cell uptake and biodistribution (in A431 tumor-bearing mice) of four near-infrared fluorescent dyes (AF750, IRDye750, Cy7, DY-750) and dye-labeled poly(N-(2-hydroxypropyl)methacrylamide)-based nanocarriers (dye-pHPMAs). Tumor cell uptake of hydrophobic dyes (Cy7, DY-750) was higher than that of hydrophilic dyes (AF750, IRDye750), and was actively mediated but not related to OATPs. Free dyes' elimination depended on their hydrophobicity, and tumor uptake correlated with blood circulation times. Dye-pHPMAs circulated longer and accumulated stronger in tumors than free dyes. Dye labeling significantly influenced nanocarriers' tumor accumulation and biodistribution. Therefore, low-interference dyes and further exploration of dye tags are required to achieve the most unbiased results possible. In our assessment, AF750 and IRDye750 best qualified for labeling hydrophilic nanocarriers.

Enhanced Permeability and Retention Effect as a Ubiquitous and Epoch-Making Phenomenon for the Selective Drug Targeting of Solid Tumors

In 1979, development of the first polymer drug SMANCS [styrene-co-maleic acid (SMA) copolymer conjugated to neocarzinostatin (NCS)] by Maeda and colleagues was a breakthrough in the cancer field. When SMANCS was administered to mice, drug accumulation in tumors was markedly increased compared with accumulation of the parental drug NCS. This momentous result led to discovery of the enhanced permeability and retention effect (EPR effect) in 1986. Later, the EPR effect became known worldwide, especially in nanomedicine, and is still believed to be a universal mechanism for tumor-selective accumulation of nanomedicines. Some research groups recently characterized the EPR effect as a controversial concept and stated that it has not been fully demonstrated in clinical settings, but this erroneous belief is due to non-standard drug design and use of inappropriate tumor models in investigations. Many research groups recently provided solid evidence of the EPR effect in human cancers (e.g., renal and breast), with significant diversity and heterogeneity in various patients. In this review, we focus on the dynamics of the EPR effect and restoring tumor blood flow by using EPR effect enhancers. We also discuss new applications of EPR-based nanomedicine in boron neutron capture therapy and photodynamic therapy for solid tumors.

Polymeric Carriers for Delivery of RNA Cancer Therapeutics

As research uncovers the underpinnings of cancer biology, new targeted therapies have been developed. Many of these therapies are small molecules, such as kinase inhibitors, that target specific proteins; however, only 1% of the genome encodes for proteins and only a subset of these proteins has ‘druggable’ active binding sites. In recent decades, RNA therapeutics have gained popularity due to their ability to affect targets that small molecules cannot. Additionally, they can be manufactured more rapidly and cost-effectively than small molecules or recombinant proteins. RNA therapeutics can be synthesised chemically and altered quickly, which can enable a more personalised approach to cancer treatment. Even though a wide range of RNA therapeutics are being developed for various indications in the oncology setting, none has reached the clinic to date. One of the main reasons for this is attributed to the lack of safe and effective delivery systems for this type of therapeutic. This review focuses on current strategies to overcome these challenges and enable the clinical utility of these novel therapeutic agents in the cancer clinic.

Inducible endothelial leakiness in nanotherapeutic applications

All intravenous delivered nanomedicine needs to escape from the blood vessel to exert their therapeutic efficacy at their designated site of action. Failure to do so increases the possibility of detrimental side effects and negates their therapeutic intent. Many powerful anticancer nanomedicine strategies rely solely on the tumor derived enhanced permeability and retention (EPR) effect for the only mode of escaping from the tumor vasculature. However, not all tumors have the EPR effect nor can the EPR effect be induced or controlled for its location and timeliness. In recent years, there have been exciting developments along the lines of inducing endothelial leakiness at the tumor to decrease the dependence of EPR. Physical disruption of the endothelial-endothelial cell junctions with coordinated biological intrinsic pathways have been proposed that includes various modalities like ultrasound, radiotherapy, heat and even nanoparticles, appear to show good progress towards the goal of inducing endothelial leakiness. This review explains the intricate and complex biological background behind the endothelial cells with linkages on how updated reported nanomedicine strategies managed to induce endothelial leakiness. This review will also end off with fresh insights on where the future of inducible endothelial leakiness holds.

Enhanced Permeability and Retention Effect: A key facilitator for solid tumor targeting by nanoparticles

Exploring the enhanced permeability and retention (EPR) effect through therapeutic nanoparticles has been a subject of considerable interest in tumor biology. This passive targeting based phenomenon exploits the leaky blood vasculature and the defective lymphatic drainage system of the heterogeneous tumor microenvironment resulting in enhanced preferential accumulation of the nanoparticles within the tumor tissues. This article reviews the fundamental studies to assess how the EPR effect plays an essential role in passive targeting. Further, it summarizes various therapeutic modalities of nanoformulation including chemo-photodynamic therapy, intravascular drug release, and photothermal immunotherapy to combat cancer using enhanced EPR effect in neoplasia region.

Simultaneous Delivery of Doxorubicin and Protease Inhibitor Derivative to Solid Tumors via Star-Shaped Polymer Nanomedicines Overcomes P-gp- and STAT3-Mediated Chemoresistance

The derivative of protease inhibitor ritonavir (5-methyl-4-oxohexanoic acid ritonavir ester; RD) was recently recognized as a potent P-gp inhibitor and cancerostatic drug inhibiting the proteasome and STAT3 signaling. Therefore, we designed high-molecular-weight HPMA copolymer conjugates with a PAMAM dendrimer core bearing both doxorubicin (Dox) and RD (Star-RD + Dox) to increase the circulation half-life to maximize simultaneous delivery of Dox and RD into the tumor. Star-RD inhibited P-gp activity, potently sensitizing both low- and high-P-gp-expressing cancer cells to the cytostatic and proapoptotic activity of Dox in vitro. Star-RD + Dox possessed higher cytostatic and proapoptotic activities compared to Star-Dox and the equivalent mixture of Star-Dox and Star-RD in vitro. Star-RD + Dox efficiently inhibited STAT3 signaling and induced caspase-3 activation and DNA fragmentation in cancer cells in vivo. Importantly, Star-RD + Dox was found to have superior antitumor activity in terms of tumor growth inhibition and increased survival of mice bearing P-gp-expressing tumors.

Effect of Tumor Targeted-Anthracycline Nanomedicine, HPMA Copolymer-Conjugated Pirarubicin (P-THP) against Gynecological Malignancies

Anthracyclines are important for the treatment of gynecological malignancies, but their effects are modest, and one of the major reasons is the lack of a tumor-targeting property. To overcome this drawback, a poly (hydroxypropyl meta-acrylamide) conjugated with tetrahydropyraryl doxorubicin (P-THP) has been developed, which exhibits a highly tumor-specific accumulation owing to the enhanced permeability and retention effect. The effect of P-THP has been confirmed by using various cell lines and solid tumor models, while its effect on gynecological malignancies have not been investigated. In this regard, human uterine sarcoma cell line with metastatic potential MEA-SA C9 high, epithelial ovarian cancer cell line A2780 and its cisplatin-resistant line A2780cis, and DOX-resistant line A2780ADR were used in this study, and the therapeutic effect as well as the safety profiles of P-THP were investigated compared to native THP, cisplatin, and paclitaxel, which are commonly used for gynecological malignancies, both in vitro and in vivo. Similar to native THP, a dose-dependent toxicity of P-THP was identified in all cell lines. Moreover, the IC50 values in the 3 h following P-THP were 1.5–10 times higher than those at 72 h, though the intracellular uptake of P-THP in all cells were 2–10-fold less than THP. In vivo studies using xenograft tumor models revealed that P-THP significantly suppressed the MES-SA C9 high, A2780, and A2780cis tumor growth at the dose of 15 mg/kg (THP equivalent), which is three times above the maximal tolerance dose of native THP, while no body weight loss or acute death occurred. However, in A2780ADR cells and the xenograft model, no significant difference in the therapeutic effect was observed between THP and P-THP, suggesting that P-THP exhibits its effect depending on the release of the active free THP in tumor tissues, and thus the internalization into tumor cells. These findings indicates that P-THP has the potential as a therapeutic for gynecological malignancies to improve the therapeutic outcomes and survival rates of patients, even in refractory patients.

Tumor Stimulus-Responsive Biodegradable Diblock Copolymer Conjugates as Efficient Anti-Cancer Nanomedicines

Biodegradable nanomedicines are widely studied as candidates for the effective treatment of various cancerous diseases. Here, we present the design, synthesis and evaluation of biodegradable polymer-based nanomedicines tailored for tumor-associated stimuli-sensitive drug release and polymer system degradation. Diblock polymer systems were developed, which enabled the release of the carrier drug, pirarubicin, via a pH-sensitive spacer allowing for the restoration of the drug cytotoxicity solely in the tumor tissue. Moreover, the tailored design enables the matrix-metalloproteinases- or reduction-driven degradation of the polymer system into the polymer chains excretable from the body by glomerular filtration. Diblock nanomedicines take advantage of an enhanced EPR effect during the initial phase of nanomedicine pharmacokinetics and should be easily removed from the body after tumor microenvironment-associated biodegradation after fulfilling their role as a drug carrier. In parallel with the similar release profiles of diblock nanomedicine to linear polymer conjugates, these diblock polymer conjugates showed a comparable in vitro cytotoxicity, intracellular uptake, and intratumor penetration properties. More importantly, the diblock nanomedicines showed a remarkable in vivo anti-tumor efficacy, which was far more superior than conventional linear polymer conjugates. These findings suggested the advanced potential of diblock polymer conjugates for anticancer polymer therapeutics.

Translational Strategies to Target Metastatic Bone Disease

Metastatic bone disease is a common and devastating complication to cancer, confounding treatments and recovery efforts and presenting a significant barrier to de-escalating the adverse outcomes associated with disease progression. Despite significant advances in the field, bone metastases remain presently incurable and contribute heavily to cancer-associated morbidity and mortality. Mechanisms associated with metastatic bone disease perpetuation and paralleled disruption of bone remodeling are highlighted to convey how they provide the foundation for therapeutic targets to stem disease escalation. The focus of this review aims to describe the preclinical modeling and diagnostic evaluation of metastatic bone disease as well as discuss the range of therapeutic modalities used clinically and how they may impact skeletal tissue.

The Enhanced Permeability and Retention (EPR) Effect: The Significance of the Concept and Methods to Enhance Its Application

Chemotherapy for human solid tumors in clinical practice is far from satisfactory. Despite the discovery and synthesis of hundreds of thousands of anticancer compounds targeting various crucial units in cancer cell proliferation and metabolism, the fundamental problem is the lack of targeting delivery of these compounds selectively into solid tumor tissue to maintain an effective concentration level for a certain length of time for drug-tumor interaction to execute anticancer activities. The enhanced permeability and retention effect (EPR effect) describes a universal pathophysiological phenomenon and mechanism in which macromolecular compounds such as albumin and other polymer-conjugated drugs beyond certain sizes (above 40 kDa) can progressively accumulate in the tumor vascularized area and thus achieve targeting delivery and retention of anticancer compounds into solid tumor tissue. Targeting therapy via the EPR effect in clinical practice is not always successful since the strength of the EPR effect varies depending on the type and location of tumors, status of blood perfusion in tumors, and the physical-chemical properties of macromolecular anticancer agents. This review highlights the significance of the concept and mechanism of the EPR effect and discusses methods for better utilizing the EPR effect in developing smarter macromolecular nanomedicine to achieve a satisfactory outcome in clinical applications.

Development of a Selective Tumor-Targeted Drug Delivery System: Hydroxypropyl-Acrylamide Polymer-Conjugated Pirarubicin (P-THP) for Pediatric Solid Tumors

Simple Summary

Hydroxypropyl acrylamide polymer-conjugated pirarubicin (P-THP), an innovative polymer-conjugated anticancer agent, theoretically has highly tumor-specific distribution via the enhanced permeability and retention (EPR) effect. While anthracyclines are extremely important in the treatment of most pediatric solid tumors, P-THP may serve as a less toxic and more effective substitute for conventional anthracyclines in both newly diagnosed and refractory/recurrent pediatric cancers.

Abstract

Most pediatric cancers are highly chemo-sensitive, and cytotoxic chemotherapy has always been the mainstay of treatment. Anthracyclines are highly effective against most types of childhood cancer, such as neuroblastoma, hepatoblastoma, nephroblastoma, rhabdomyosarcoma, Ewing sarcoma, and so forth. However, acute and chronic cardiotoxicity, one of the major disadvantages of anthracycline use, limits their utility and effectiveness. Hydroxypropyl acrylamide polymer-conjugated pirarubicin (P-THP), which targets tumor tissue highly selectively via the enhanced permeability and retention (EPR) effect, and secondarily releases active pirarubicin molecules quickly into the acidic environment surrounding the tumor. Although, the latter rarely occurs in the non-acidic environment surrounding normal tissue. This mechanism has the potential to minimize acute and chronic toxicities, including cardiotoxicity, as well as maximize the efficacy of chemotherapy through synergy with tumor-targeting accumulation of the active molecules and possible dose-escalation. Simply replacing doxorubicin with P-THP in a given regimen can improve outcomes in anthracycline-sensitive pediatric cancers with little risk of adverse effects, such as cardiotoxicity. As cancer is a dynamic disease showing intra-tumoral heterogeneity during its course, continued parallel development of cytotoxic agents and molecular targeting agents is necessary to find potentially more effective treatments.

EPR-Effect Enhancers Strongly Potentiate Tumor-Targeted Delivery of Nanomedicines to Advanced Cancers: Further Extension to Enhancement of the Therapeutic Effect

For more than three decades, enhanced permeability and retention (EPR)-effect-based nanomedicines have received considerable attention for tumor-selective treatment of solid tumors. However, treatment of advanced cancers remains a huge challenge in clinical situations because of occluded or embolized tumor blood vessels, which lead to so-called heterogeneity of the EPR effect. We previously developed a method to restore impaired blood flow in blood vessels by using nitric oxide donors and other agents called EPR-effect enhancers. Here, we show that two novel EPR-effect enhancers—isosorbide dinitrate (ISDN, Nitrol^®) and sildenafil citrate—strongly potentiated delivery of three macromolecular drugs to tumors: a complex of poly(styrene-co-maleic acid) (SMA) and cisplatin, named Smaplatin^® (chemotherapy); poly(N-(2-hydroxypropyl)methacrylamide) polymer-conjugated zinc protoporphyrin (photodynamic therapy and imaging); and SMA glucosamine-conjugated boric acid complex (boron neutron capture therapy). We tested these nanodrugs in mice with advanced C26 tumors. When these nanomedicines were administered together with ISDN or sildenafil, tumor delivery and thus positive therapeutic results increased two- to four-fold in tumors with diameters of 15 mm or more. These results confirmed the rationale for using EPR-effect enhancers to restore tumor blood flow. In conclusion, all EPR-effect enhancers tested showed great potential for application in cancer therapy.

Polymer-Based Drug-Free Therapeutics for Anticancer, Anti-Inflammatory, and Antibacterial Treatment

This paper summarizes the area of biomedicinal polymers, which serve as nanomedicines even though they do not contain any anticancer or antiinflammatory drugs. These polymer nanomedicines with unique design are in the literature highlighted as a novel class of therapeutics called "drug-free macromolecular therapeutics." Their therapeutic efficacy is based on the tailored multiple presentations of biologically active vectors, i.e., peptides, oligopeptides, or oligosaccharides. Thus, they enable, for example, to directly induce the apoptosis of malignant cells by the crosslinking of surface slowly internalizing receptors, or to deplete the efficacy of tumor-associated proteins. The precise biorecognition of natural binding motifs by multiple vectors on the polymer construct remains the crucial part in the designing of these drug-free nanomedicines. Here, the rationales, designs, synthetic approaches, and therapeutic potential of drug-free macromolecular therapeutics consisting of various active vectors are described in detail. Recent developments and achievements for namely B-cell lymphoma treatment, Gal-3-positive tumors, inflammative liver injury, and bacterial treatment are reviewed and highlighted. Finally, a possible future prospect within this highly exciting new field of nanomedicine research is presented.

Polymer-ritonavir derivate nanomedicine with pH-sensitive activation possesses potent anti-tumor activity in vivo via inhibition of proteasome and STAT3 signaling

Drug repurposing is a promising strategy for identifying new applications for approved drugs. Here, we describe a polymer biomaterial composed of the antiretroviral drug ritonavir derivative (5-methyl-4-oxohexanoic acid ritonavir ester; RD), covalently bound to HPMA copolymer carrier via a pH-sensitive hydrazone bond (P-RD). Apart from being more potent inhibitor of P-glycoprotein in comparison to ritonavir, we found RD to have considerable cytostatic activity in six mice (IC₅₀ ~ 2.3-17.4 μM) and six human (IC₅₀ ~ 4.3-8.7 μM) cancer cell lines, and that RD inhibits the migration and invasiveness of cancer cells in vitro. Importantly, RD inhibits STAT3 phosphorylation in CT26 cells in vitro and in vivo, and expression of the NF-κB p65 subunit, Bcl-2 and Mcl-1 in vitro. RD also dampens chymotrypsin-like and trypsin-like proteasome activity and induces ER stress as documented by induction of PERK phosphorylation and expression of ATF4 and CHOP. P-RD nanomedicine showed powerful antitumor activity in CT26 and B16F10 tumor-bearing mice, which, moreover, synergized with IL-2-based immunotherapy. P-RD proved very promising therapeutic activity also in human FaDu xenografts and negligible toxicity predetermining these nanomedicines as side-effect free nanosystem. The therapeutic potential could be highly increased using the fine-tuned combination with other drugs, i.e. doxorubicin, attached to the same polymer system. Finally, we summarize that described polymer nanomedicines fulfilled all the requirements as potential candidates for deep preclinical investigation.

The 35th Anniversary of the Discovery of EPR Effect: A New Wave of Nanomedicines for Tumor-Targeted Drug Delivery-Personal Remarks and Future Prospects

This Special Issue on the enhanced permeability and retention (EPR) effect commemorates the 35th anniversary of its discovery, the original 1986 Matsumura and Maeda finding being published in Cancer Research as a new concept in cancer chemotherapy. My review here describes the history and heterogeneity of the EPR effect, which involves defective tumor blood vessels and blood flow. We reported that restoring obstructed tumor blood flow overcomes impaired drug delivery, leading to improved EPR effects. I also discuss gaps between small animal cancers used in experimental models and large clinical cancers in humans, which usually involve heterogeneous EPR effects, vascular abnormalities in multiple necrotic foci, and tumor emboli. Here, I emphasize arterial infusion of oily formulations of nanodrugs into tumor-feeding arteries, which is the most tumor-selective drug delivery method, with tumor/blood ratios of 100-fold. This method is literally the most personalized medicine because arterial infusions differ for each patient, and drug doses infused depend on tumor size and anatomy in each patient. Future developments in EPR effect-based treatment will range from chemotherapy to photodynamic therapy, boron neutron capture therapy, and therapies for free radical diseases. This review focuses on our own work, which stimulated numerous scientists to perform research in nanotechnology and drug delivery systems, thereby spawning a new cancer treatment era.

HPMA Copolymer-Based Nanomedicines in Controlled Drug Delivery

Recently, numerous polymer materials have been employed as drug carrier systems in medicinal research, and their detailed properties have been thoroughly evaluated. Water-soluble polymer carriers play a significant role between these studied polymer systems as they are advantageously applied as carriers of low-molecular-weight drugs and compounds, e.g., cytostatic agents, anti-inflammatory drugs, antimicrobial molecules, or multidrug resistance inhibitors. Covalent attachment of carried molecules using a biodegradable spacer is strongly preferred, as such design ensures the controlled release of the drug in the place of a desired pharmacological effect in a reasonable time-dependent manner. Importantly, the synthetic polymer biomaterials based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers are recognized drug carriers with unique properties that nominate them among the most serious nanomedicines candidates for human clinical trials. This review focuses on advances in the development of HPMA copolymer-based nanomedicines within the passive and active targeting into the place of desired pharmacological effect, tumors, inflammation or bacterial infection sites. Specifically, this review highlights the safety issues of HPMA polymer-based drug carriers concerning the structure of nanomedicines. The main impact consists of the improvement of targeting ability, especially concerning the enhanced and permeability retention (EPR) effect.

Factors affecting the dynamics and heterogeneity of the EPR effect: pathophysiological and pathoanatomic features, drug formulations and physicochemical factors

INTRODUCTION

The enhanced permeability and retention (EPR) effect serves as the foundation of anticancer nanomedicine design. EPR effect-based drug delivery is an effective strategy for most solid tumors. However, the degree of efficacy depends on the pathophysiological conditions of tumors, drug formulations, and other factors.

AREAS COVERED

Vascular mediators including nitric oxide, bradykinin , and prostaglandins are vital for facilitating and maintaining EPR effect dynamics. Progression to large, advanced cancers may induce activated blood coagulation cascades, which lead to thrombus formation in tumor vasculature. Rapidly growing tumors cause obstructed or suppressed blood flow in tumor vasculature related to embolism or occluded blood vessels. The resulting limited tumor blood flow leads to less drug delivered to tumors, i.e. no or poor EPR effect. High stromal content also suppresses vascular permeability and drug diffusion. Restoring obstructed tumor blood flow and improving tumor vascular permeability via vascular mediators will improve drug delivery and the EPR effect. Physicochemical features of nanomedicines also influence therapeutic outcomes and are vital for the EPR effect.

EXPERT OPINION

The tumor microenvironment, especially tumor blood flow, is critical for a potent EPR effect. A rational strategy for circumventing EPR effect barriers must include restoring tumor blood flow.

HPMA-Based Copolymers Carrying STAT3 Inhibitor Cucurbitacin-D as Stimulus-Sensitive Nanomedicines for Oncotherapy

The study describes the synthesis, physicochemical properties, and biological evaluation of polymer therapeutics based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers intended for a tumor-targeted immuno-oncotherapy. Water-soluble linear and cholesterol-containing HPMA precursors were synthesized using controlled reversible addition–fragmentation chain transfer polymerization to reach molecular weight M_n about 2 × 10⁴ g·mol⁻¹ and low dispersity. These linear or self-assembled micellar conjugates, containing immunomodulatory agent cucurbitacin-D (CuD) or the anticancer drug doxorubicin (Dox) covalently bound by the hydrolytically degradable hydrazone bond, showed a hydrodynamic size of 10–30 nm in aqueous solutions. The CuD-containing conjugates were stable in conditions mimicking blood. Importantly, a massive release of active CuD in buffer mimicking the acidic tumor environment was observed. In vitro, both the linear (LP-CuD) and the micellar (MP-CuD) conjugates carrying CuD showed cytostatic/cytotoxic activity against several cancer cell lines. In a murine metastatic and difficult-to-treat 4T1 mammary carcinoma, only LP-CuD showed an anticancer effect. Indeed, the co-treatment with Dox-containing micellar polymer conjugate and LP-CuD showed potentiation of the anticancer effect. The results indicate that the binding of CuD, characterized by prominent hydrophobic nature and low bioavailability, to the polymer carrier allows a safe and effective delivery. Therefore, the conjugate could serve as a potential component of immuno-oncotherapy schemes within the next preclinical evaluation.

Recent Advances in Nanomedicine for the Diagnosis and Treatment of Prostate Cancer Bone Metastasis

Patients with advanced prostate cancer can develop painful and debilitating bone metastases. Currently available interventions for prostate cancer bone metastases, including chemotherapy, bisphosphonates, and radiopharmaceuticals, are only palliative. They can relieve pain, reduce complications (e.g., bone fractures), and improve quality of life, but they do not significantly improve survival times. Therefore, additional strategies to enhance the diagnosis and treatment of prostate cancer bone metastases are needed. Nanotechnology is a versatile platform that has been used to increase the specificity and therapeutic efficacy of various treatments for prostate cancer bone metastases. In this review, we summarize preclinical research that utilizes nanotechnology to develop novel diagnostic imaging tools, translational models, and therapies to combat prostate cancer bone metastases.

Cytarabine nanotherapeutics with increased stability and enhanced lymphoma uptake for tailored highly effective therapy of mantle cell lymphoma

Mantle cell lymphoma (MCL) is a rare subtype of B-cell non-Hodgkin lymphoma (B-NHL) with chronically relapsing clinical course. Implementation of cytarabine (araC) into induction and salvage regimen became standard of care for majority of MCL patients. In this study, tailored N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer nanotherapeutics containing covalently bound araC (araC co-polymers) were designed, synthesized and evaluated for their anti-lymphoma efficacy in vivo using a panel of six patient-derived lymphoma xenografts (PDX) derived from newly diagnosed and relapsed / refractory (R/R) MCL. While free araC led to temporary inhibition of growth of MCL tumors, araC co-polymers induced long-term disappearance of the engrafted lymphomas with no observed toxicity even in the case of PDX models derived from patients, who relapsed after high-dose araC-based treatments. The results provide sound preclinical rationale for the use of HPMA-based araC co-polymers in induction, salvage or palliative therapy of MCL patients.

Phosphorylcholine-Grafted Molecular Bottlebrush-Doxorubicin Conjugates: High Structural Stability, Long Circulation in Blood, and Efficient Anticancer Activity

Controlling the particle structure of tumor-targeting nanomedicines in vivo remains challenging but must be achieved to control their in vivo fate and functions. Molecular bottlebrushes (MBs), where brush side chains are densely grafted from a main chain, have recently received attention as building blocks of polymer-based prodrugs because their rigid structure would be expected to demonstrate high structural stability in vivo. Here, we synthesized a poly(methacryloyloxyethyl phosphorylcholine) (pMPC)-grafted molecular bottlebrush (PCMB) conjugated with a cancer drug, doxorubicin (DOX), via an acid-cleavable hydrazone bond. A pMPC-based linear polymer (LP) conjugated with DOX was also prepared for comparison. We confirmed the lack of structural transition in the PCMB between before and after conjugation with DOX using small-angle light and X-ray scattering techniques, whereas the structure of LP was significantly influenced by DOX conjugation and transformed from a random-coil structure to a large agglomerate via hydrophobic interactions among DOXs. Although PCMB-DOX and LP-DOX showed comparable tissue permeability, pharmacokinetics, and ability to accumulate in tumor tissues, the antitumor efficacy of PCMB-DOX was better than that of LP-DOX. This was presumably due to the formation of LP-DOX agglomerates. The diffusion of cleaved DOX would be restricted in the hydrophobic core of the agglomerate, resulting in the DOX release at the tumor site being compromised. In contrast to LP-DOX, DOX release from PCMB-DOX was not compromised after accumulation in tumor tissues because it did not form such an agglomerate, resulting in the strong antitumor effect. We have demonstrated the potential of MBs as building blocks of drug carriers and believe that these findings can contribute to the design of polymer-based nanomedicines.

Polymer-conjugated glucosamine complexed with boric acid shows tumor-selective accumulation and simultaneous inhibition of glycolysis

We synthesized unique water-soluble synthetic-polymer, styrene-maleic acid copolymer (SMA) conjugated glucosamine (SG); which formed a stable complex with boric acid (BA). This complex had a mean particle size of 15 nm by light scattering, and single peak in gel permeation chromatography. The particles were taken up by tumor cells five times faster than free BA in vitro and liberated BA at acidic tumor pH (5-7). Liberated BA inhibited glycolysis and resulted in tumor suppression in vivo. Intravenously injected SGB-complex did bind with albumin, and plasma half-life was about 8 h in mice, and accumulated to tumor tissues about 10 times more than in normal organs. IC₅₀ of SGB-complex for HeLa cells under pO₂ of 6-9% was about 20 μg/ml (free BA equivalent), 150 times more potent than free BA. Neutron irradiation of human oral cancer cells with SGB-complex resulted in 16 times greater cell-killing than that without SGB-complex. In vivo antitumor effect was evaluated after neutron irradiation only once in SCC VII tumor bearing mice and significant tumor suppression was confirmed. These results indicate that SGB-complex is a unique multifunctional anticancer agent with much more potent activity under low pO₂ conditions as in large advanced cancers.

Overcoming resistance to rituximab in relapsed non-Hodgkin lymphomas by antibody-polymer drug conjugates actively targeted by anti-CD38 daratumumab

B-cell non-Hodgkin lymphomas (B-NHL) represent the most common type of hematologic malignancies in the Western hemisphere. The therapy of all B-NHL is based on the combination of different genotoxic cytostatics and anti-CD20 monoclonal antibody (mAb) rituximab. Unfortunately, many patients relapse after the mentioned front-line treatment approaches. The therapy of patients with relapsed/refractory (R/R) B-NHL represents an unmet medical need. We designed, developed and tested novel actively targeted hybrid mAb-polymer-drug conjugate (APDC) containing anti-CD20, anti-CD38 or anti-CD19 mAbs. Biocompatible copolymers based on N-(2-hydroxypropyl)methacrylamide (HPMA) with cytostatic agent doxorubicin attached via stimuli-sensitive hydrazone bond were employed for the mAb grafting. Anti-lymphoma efficacy of the APDC nanotherapeutics was evaluated in vivo on a panel of three patient-derived lymphoma xenografts derived from two patients with R/R B-NHL and one patient with so far untreated B-NHL. In both PDX models derived from patients with R/R B-NHL, the targeting with anti-CD38 antibody daratumumab demonstrated highly improved anti-lymphoma efficacy compared to the targeting with anti-CD20 rituximab, two experimental anti-CD19 antibodies and non-targeted controls. The results represent a proof-of-concept of a new algorithm of personalized anti-tumor therapy based on highly innovative APDC biomaterials.

Polymer nanomedicines

Polymer nanomedicines (macromolecular therapeutics, polymer-drug conjugates, drug-free macromolecular therapeutics) are a group of biologically active compounds that are characterized by their large molecular weight. This review focuses on bioconjugates of water-soluble macromolecules with low molecular weight drugs and selected proteins. After analyzing the design principles, different structures of polymer carriers are discussed followed by the examination of the efficacy of the conjugates in animal models and challenges for their translation into the clinic. Two innovative directions in macromolecular therapeutics that depend on receptor crosslinking are highlighted: a) Combination chemotherapy of backbone degradable polymer-drug conjugates with immune checkpoint blockade by multivalent polymer peptide antagonists; and b) Drug-free macromolecular therapeutics, a new paradigm in drug delivery.

Exploiting the dynamics of the EPR effect and strategies to improve the therapeutic effects of nanomedicines by using EPR effect enhancers

The enhanced permeability and retention (EPR) effect is a unique phenomenon of solid tumors that is related to their particular anatomical and pathophysiological characteristics, e.g. defective vascular architecture; large gaps between endothelial cells in blood vessels; abundant vascular mediators such as bradykinin, nitric oxide, carbon monoxide, and vascular endothelial growth factor; and impaired lymphatic recovery. These features lead to tumor tissues showing considerable extravasation of plasma components and nanomedicines. These data comprise the basic theory underlying the development of macromolecular agents or nanomedicines. The EPR effect is not necessarily valid for all solid tumors, because tumor blood flow and vascular permeability vary greatly. Tumor blood flow is frequently obstructed as tumor size increases, as often seen clinically; early stage, small tumors show a more uniform EPR effect, whereas advanced large tumor show heterogeneity in EPR effect. Accordingly, it would be very important to apply enhancers of EPR effect in clinical setting to make EPR effect more uniform. In this review, we discuss the EPR effect: its history, factors involved, and dynamics and heterogeneity. Strategies to overcome the EPR effect's heterogeneity may guarantee better therapeutic outcomes of drug delivery to advanced cancers.

HPMA-based polymeric conjugates in anticancer therapeutics

Polymer therapeutics has gained prominence due to an attractive structural polymer chemistry and its applications in diseases therapy. In this review, we discussed the development and capabilities of N-(2-hydroxypropyl) methacrylamide (HPMA) and HPMA-drug conjugates in cancer therapy. The design, architecture, and structural properties of HPMA make it a versatile system for the synthesis of polymeric conjugations for biomedical applications. Research suggests that HPMA could be a possible alternative for polymers such polyethylene glycol (PEG) in biomedical applications. Although numerous clinical trials of HPMA-drug conjugates are ongoing, yet no product has been successfully brought to the market. Thus, further research is required to develop HPMA-drug conjugates as successful cancer therapeutics.

Development of (G3-C12)-mediated camptothecin polymeric prodrug targeting to Galectin-3 receptor against androgen-independent prostate cancer

The development of small molecule anticancer drugs, with low water solubility and high toxicity, into polymeric prodrugs has developed into a promising strategy in clinical application. In this study, we synthesized a novel G3-C12-mediated esterase-sensitive tumor-targeting polymeric prodrug of camptothecin (CPT), P(OEGMA-co-CPT-co-G3-C12), and explored its anticancer activity against androgen-independent prostate cancer in vitro and in vivo. Compared to free CPT, the multifunctional polymeric prodrug demonstrated improved water solubility and stability, higher intracellular uptake, and enhanced cytotoxicity in DU145 cells in vitro. Furthermore, it displayed an improved accumulation in the tumor and an enhanced anticancer activity in vivo. Hence, P(OEGMA-co-CPT-co-G3-C12) could be a promising drug in the treatment of androgen-independent prostate cancer.

Rutin protects against pirarubicin-induced cardiotoxicity by adjusting microRNA-125b-1-3p-mediated JunD signaling pathway

Pirarubicin (THP), an anthracycline drug, is widely used as a basic therapeutic agent for the treatment of carcinoma and lymphatic malignant tumor. However, it exerts irreversible cardiotoxicity in varying degrees. At present, dexrazoxane (DZR) is the only cardioprotective agent used to treat anthracycline drug-induced cardiotoxicity, but it may reduce the anticancer effect of anthracycline drugs, causing severe granulocytopenia and other adverse reactions. Therefore, it is necessary to discover more effective and less toxic drugs for the treatment of THP-induced cardiotoxicity. The present study aimed to investigate the effects and possible mechanisms of rutin (RUT) against THP-induced cardiomyocyte injury. An in vitro cardiomyocyte injury model of THP-treated murine immortalized cardiomyocytes (HL-1) was used in this study. The results showed that RUT markedly increased the viability of HL-1 cells through protection against THP-induced cardiomyocyte injury. Furthermore, RUT significantly inhibited myocardial oxidative insult by adjusting the levels of intracellular reactive oxygen species (ROS). Our data also indicated that RUT activated JunD signaling pathways, thereby affecting the expression levels of some apoptotic proteins by decreasing miR-125b-1-3p expression level. In addition, intracellular ROS level significantly increased in HL-1 cells treated with THP after miR-125b-1-3p mimic transfection, whereas the expression of JunD was downregulated and that of some apoptotic proteins was upregulated. However, this effect was markedly reversed by RUT. Therefore, we inferred that the protective effect of RUT on THP cardiotoxicity was achieved through regulation of the JunD gene by miR-125b-1-3p. This experiment revealed the protective effect of RUT on THP-induced cardiotoxicity at the non-coding RNA level and provided a theoretical foundation for the application of RUT as a protective agent against THP cardiotoxicity.

Fluorescence Imaging as a Tool in Preclinical Evaluation of Polymer-Based Nano-DDS Systems Intended for Cancer Treatment

Targeted drug delivery using nano-sized carrier systems with targeting functions to malignant and inflammatory tissue and tailored controlled drug release inside targeted tissues or cells has been and is still intensively studied. A detailed understanding of the correlation between the pharmacokinetic properties and structure of the nano-sized carrier is crucial for the successful transition of targeted drug delivery nanomedicines into clinical practice. In preclinical research in particular, fluorescence imaging has become one of the most commonly used powerful imaging tools. Increasing numbers of suitable fluorescent dyes that are excitable in the visible to near-infrared (NIR) wavelengths of the spectrum and the non-invasive nature of the method have significantly expanded the applicability of fluorescence imaging. This chapter summarizes non-invasive fluorescence-based imaging methods and discusses their potential advantages and limitations in the field of drug delivery, especially in anticancer therapy. This chapter focuses on fluorescent imaging from the cellular level up to the highly sophisticated three-dimensional imaging modality at a systemic level. Moreover, we describe the possibility for simultaneous treatment and imaging using fluorescence theranostics and the combination of different imaging techniques, e.g., fluorescence imaging with computed tomography.

Superior Penetration and Cytotoxicity of HPMA Copolymer Conjugates of Pirarubicin in Tumor Cell Spheroid

N-(2-Hydroxypropyl)methacrylamide copolymer conjugates of pirarubicin (THP), P-THP, accumulates selectively in solid tumor tissue by the enhanced permeability and retention (EPR) effect. Despite of high accumulation in solid tumors, some macromolecular antitumor agents show poor therapeutic outcome because of poor tissue diffusion into the tumor as well as obstructed tumor blood flow. Here, we confirmed that cellular uptake of P-THP was 25 times less than that of free THP at 1-4 h incubation time in vitro. The passage of P-THP through the confluent tight-monolayer cells junction was 12 times higher than free THP, and P-THP penetrated deeper into the tumor cell spheroid (1.3-1.7-fold) than free THP in 4 h. In addition, P-THP showed cytotoxicity comparable to that of free THP to tumor-cells in spheroid form, despite of 7 times lower cytotoxicity of P-THP to the monolayer cells to that of free THP in vitro. These results indicate that P-THP administration can exhibit deeper diffusion into the tumor cell spheroid than free THP. As a consequence, P-THP exhibits more efficient antitumor activity than free THP in vivo, which is also supported by better pharmacokinetics and tumor accumulation of P-THP than free THP.

Polymer Nanoplatforms at Work in Prostate Cancer Therapy

Prostate cancer (PCa) is the most common male urogenital malignancy worldwide. Surgery, endocrine therapy, radiotherapy, and chemotherapy are the main clinical management options for PCa. However, these three therapies each have limitations. For example, surgery is not suitable for the advanced PCa patients with extensive metastases, and radiotherapy causes serious side effects. Primary endocrine therapy promotes the progression of hormone‐sensitive PCa into the castration‐resistant prostate cancer. Therefore, considering these drawbacks, chemotherapy has become an effective and extensive treatment for PCa. Among the modern therapeutic strategies against advanced PCa, polymer‐nanocarrier‐incorporated formulations have gradually emerged due to their well‐controlled release profiles and improved tumor targeting abilities. The drug delivery systems based on polymer nanoplatforms passively target tumors via the enhanced permeability and retention effect. Simultaneously, stimuli‐responsive polymer nanoplatforms unload cargoes in response to certain stimuli in the tumor area. Furthermore, the active targeting ligand‐conjugated polymer nanoformulations against PCa‐specific markers have also achieved great success in PCa therapies. Herein, the advanced polymer nanoplatforms for PCa therapy are reviewed, while the future development of polymer nanoplatforms for PCa therapy is also predicted.

A Literature Review of Proton Beam Therapy for Prostate Cancer in Japan

Aim: Patients of proton beam therapy (PBT) for prostate cancer had been continuously growing in number due to its promising characteristics of high dose distribution in the tumor target and a sharp distal fall-off. Considering the large number of proton beam facilities in Japan, the further increase of patients undergoing this treatment is due to the emendations by Japanese National Health Insurance (NHI) and the development of medical equipment and technology, it is necessary to know what kind of research and advancements has been done on proton therapy for prostate cancer in the country. For these reasons, this literature review was conducted. The aim of this review is to identify and discuss research studies of proton beam therapy for prostate cancer in Japan. These include observational, interventional, and secondary data analysis of published articles. Method: A literature review on published works related to proton beam therapy for prostate cancer in Japan was conducted using articles that were gathered in the PubMed database of June 2018. We went through abstracts and manuscripts written in English with the keywords ‘proton beam therapy’, ‘prostate cancer’, and ‘Japan’. Results: A total of 23 articles were included. Fourteen articles were observational studies, most of which focused on the adverse effects of Proton Beam Therapy (PBT). Seven articles were interventional studies related on treatment planning, equipment parts, as well as target positioning. Two were secondary data analysis. The included studies were published in 13 different journals by different institutions using various equipment. Conclusion: Despite the favorable results of proton beam therapy, future research should include more patients and longer follow-up schedules to clarify the definitive role of PBT, yet, up to recent retrospective studies, included in this paper, concluded that PBT can be a suitable treatment option for localized prostate cancer. In addition, interventional studies were conducted by several institutions to further embellish proton therapy.

Optimizing the Cu-RDRP ofN-(2-hydroxypropyl) methacrylamide toward biomedical applications

Aqueous Cu-RDRP ofN-(2-hydroxypropyl) methacrylamide was optimized to achieve co(polymers) of low dispersity and controlled molecular weight at high conversions.

Biorecognition: A key to drug-free macromolecular therapeutics

This review highlights a new paradigm in macromolecular nanomedicine - drug-free macromolecular therapeutics (DFMT). The effectiveness of the new system is based on biorecognition events without the participation of low molecular weight drugs. Apoptosis of cells can be initiated by the biorecognition of complementary peptide/oligonucleotide motifs at the cell surface resulting in the crosslinking of slowly internalizing receptors. B-cell CD20 receptors and Non-Hodgkin lymphoma (NHL) were chosen as the first target. Exposing cells to a conjugate of one motif with a targeting ligand decorates the cells with this motif. Further exposure of decorated cells to a macromolecule (synthetic polymer or human serum albumin) containing multiple copies of the complementary motif as grafts results in receptor crosslinking and apoptosis induction in vitro and in vivo. The review focuses on recent developments and explores the mechanism of action of DFMT. The altered molecular signaling pathways demonstrated the great potential of DFMT to overcome rituximab resistance resulting from either down-regulation of CD20 or endocytosis and trogocytosis of rituximab/CD20 complexes. The suitability of this approach for the treatment of blood borne cancers is confirmed. In addition, the widespread applicability of DFMT as a new concept in macromolecular therapeutics for numerous diseases is exposed.

Nanotherapeutics with suitable properties for advanced anticancer therapy based on HPMA copolymer-bound ritonavir via pH-sensitive spacers

Ritonavir (RIT) is a widely used antiviral drug that acts as an HIV protease inhibitor with emerging potential in anticancer therapies. RIT causes inhibition of P-glycoprotein, which plays an important role in multidrug resistance (MDR) in cancer cells when overexpressed. Moreover, RIT causes mitochondrial dysfunction, leading to decreased ATP production and reduction of caveolin I expression, which can affect cell migration and tumor progression. To increase its direct antitumor activity, decrease severe side effects induced by the use of free RIT and improve its pharmacokinetics, ritonavir 5-methyl-4-oxohexanoate (RTV) was synthesized and conjugated to a tumor-targeted polymer carrier based on a N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer. Here we demonstrated that polymer-bound RTV enhanced the internalization of polymer-RTV conjugates, differing in RTV content from 4 to 15 wt%, in HeLa cancer cells compared with polymer without RTV. The most efficient influx and internalization properties were determined for the polymer conjugate bearing 11 wt% of RTV. This conjugate was internalized by cells using both caveolin- and clathrin-dependent endocytic pathways in contrast to the RTV-free polymer, which was preferentially internalized only by clathrin-mediated endocytosis. Moreover, we found the co-localization of the RTV-conjugate with mitochondria and a significant decrease of ATP production in treated cells. Thus, the impact on mitochondrial mechanism can influence the function of ATP-dependent P-glycoprotein and also the cell viability of MDR cancer cells. Overall, this study demonstrated that the polymer-RTV conjugate is a promising polymer-based nanotherapeutic, suitable for antitumor combination therapy with other anticancer drugs and a potential mitochondrial drug delivery system.

Shell-Sheddable Poly(N-2-hydroxypropyl methacrylamide) Polymeric Micelles for Dual-Sensitive Release of Doxorubicin

Poly(ethylene glycol) (PEG) shell-sheddable micelles are proved to be effective tools for rapid intracellular drug delivery. However, some adverse factors, such as the potential immunogenicity and the accelerated blood clearance, might be accompanied with the traditional PEG sheddable micelles. Here, a poly(N-2-hydroxypropyl methacrylamide) (PHPMA) sheddable block copolymer containing disulfide bonds on the main chain is prepared to form pH- and reduction-dual-responsive micelles. The most optimal synthetic route of the block copolymer is selected from three potential pathways. Doxorubicin is loaded via an acid-labile hydrazone bond to achieve high drug loading content and to prevent premature drug release. As expected, as-prepared shell-sheddable micelles exhibit faster intracellular drug release and more satisfactory in vitro anticancer efficacy than the nonsheddable counterpart did. This design provides a feasible guideline for the efficient synthesis of similar shell-sheddable micelles consisting of PHPMA coatings.