The transferrin receptor and the targeted delivery of therapeutic agents against cancer

Transferrin-modified liposomes triggered with ultrasound to treat HeLa cells

Targeted liposomes are designed to target specific receptors overexpressed on the surfaces of cancer cells. This technique ensures site-specific drug delivery to reduce undesirable side effects while enhancing the efficiency of the encapsulated therapeutics. Upon reaching the tumor site, these liposomes can be triggered to release their content in a controlled manner using ultrasound (US). In this study, drug release from pegylated calcein-loaded liposomes modified with transferrin (Tf) and triggered with US was evaluated. Low-frequency ultrasound at 20-kHz using three different power densities (6.2 mW/cm2, 9 mW/cm2 and 10 mW/cm2) was found to increase calcein release. In addition, transferrin-conjugated pegylated liposomes (Tf-PEG liposomes) were found to be more sonosensitive compared to the non-targeted (control) liposomes. Calcein uptake by HeLa cells was found to be significantly higher with the Tf-PEG liposomes compared to the non-targeted control liposomes. This uptake was further enhanced following the exposure to low-frequency ultrasound (at 35 kHz). These findings show that targeted liposomes triggered with US have promising potential as a safe and effective drug delivery platform.

Are trace element concentrations suitable biomarkers for the diagnosis of cancer?

Despite advances in cancer research, cancer is still one of the leading causes of death worldwide. An early diagnosis substantially increases the survival rate and treatment success. Thus, it is important to establish biomarkers which could reliably identify cancer patients. As cancer is associated with changes in the systemic trace element status and distribution, serum concentrations of selenium, iron, copper, and zinc could contribute to an early diagnosis. To test this hypothesis, case control studies measuring trace elements in cancer patients vs. matched controls were selected and discussed focusing on lung, prostate, breast, and colorectal cancer. Overall, cancer patients had elevated serum copper and diminished zinc levels, while selenium and iron did not show consistent changes for all four cancer types. Within the tumor tissue, mainly copper and selenium are accumulating. Whether these concentrations also predict the survival probability of cancer patients needs to be further investigated.

Cancer Selective Target Degradation by Folate-Caged PROTACs

PROTACs (proteolysis targeting chimeras) are an emerging class of promising therapeutic modalities that degrade intracellular protein targets by hijacking the cellular ubiquitin-proteasome system. However, potential toxicity of PROTACs in normal cells due to the off-tissue on-target degradation effect limits their clinical applications. Precise control of a PROTAC's on-target degradation activity in a tissue-selective manner could minimize potential toxicity/side-effects. To this end, we developed a cancer cell selective delivery strategy for PROTACs by conjugating a folate group to a ligand of the VHL E3 ubiquitin ligase, to achieve targeted degradation of proteins of interest (POIs) in cancer cells versus noncancerous normal cells. We show that our folate-PROTACs, including BRD PROTAC (folate-ARV-771), MEK PROTAC (folate-MS432), and ALK PROTAC (folate-MS99), are capable of degrading BRDs, MEKs, and ALK, respectively, in a folate receptor-dependent manner in cancer cells. This design provides a generalizable platform for PROTACs to achieve selective degradation of POIs in cancer cells.

Nanotechnology Based Approach for Hepatocellular Carcinoma Targeting

Hepatocellular carcinoma (HCC) is the primary liver cancer that has shown a high incidence and mortality rate worldwide among several types of cancers. A large variety of chemotherapeutic agents employed for the treatment have a limited success rate owing to their limited site-specific drug targeting ability. Thus, there is a demand to develop novel approaches for the treatment of HCC. With advancements in nanotechnology-based drug delivery approaches, the challenges of conventional chemotherapy have been continuously decreasing. Nanomedicines constituted of lipidic and polymeric composites provide a better platform for delivering and opening new pathways for HCC treatment. A score of nanocarriers such as surface-engineered liposomes, nanoparticles, nanotubes, micelles, quantum dots, etc., has been investigated in the treatment of HCC. These nanocarriers are considered to be highly effective clinically for delivering chemotherapeutic drugs with high site-specificity ability and therapeutic efficiency. The present review highlights the current focus on the application of nanocarrier systems using various ligand-based receptor-specific targeting strategies for the treatment and management of HCC. Moreover, the article has also included information on the current clinically approved drug therapy for hepatocellular carcinoma treatment and updates of regulatory requirements for approval of such nanomedicines.

O-GlcNAcylation enhances sensitivity to RSL3-induced ferroptosis via the YAP/TFRC pathway in liver cancer

Ferroptosis is a form of regulated cell death characterized by iron-dependent accumulation of lipid hydroperoxides to lethal levels. YAP has been reported to play a pivotal role in controlling ferroptotic death, and the expression of YAP is enhanced and stabilized by O-GlcNAcylation. However, whether O-GlcNAcylation can increase the sensitivity of hepatocellular carcinoma (HCC) cells to ferroptosis remains unknown. In the present study, we found that O-GlcNAcylation increased the sensitivity of HCC cells to ferroptosis via YAP. Moreover, YAP increased the iron concentration in HCC cells through transcriptional elevation of TFRC via its O-GlcNAcylation. With YAP knockdown or YAP-T241 mutation, the increased sensitivity to ferroptosis induced by O-GlcNAcylation was abolished. In addition, the xenograft assay confirmed that O-GlcNAcylation increased ferroptosis sensitivity via TFRC in vivo. In summary, we are the first to find that O-GlcNAcylation can increase ferroptosis sensitivity in HCC cells via YAP/TFRC. Our work will provide a new basis for clinical therapeutic strategies for HCC patients.

Iron at the Interface of Hepatocellular Carcinoma

Cancer incidence and mortality are rapidly growing, with liver cancer being the sixth most diagnosed cancer worldwide and the third leading cause of cancer death in 2020. A number of risk factors have been identified that trigger the progression to hepatocellular carcinoma. In this review, we focus on iron as a potential risk factor for liver carcinogenesis. Molecules involved in the regulation of iron metabolism are often upregulated in cancer cells, in order to provide a supply of this essential trace element for all stages of tumor development, survival, proliferation, and metastasis. Thus, cellular and systemic iron levels must be tightly regulated to prevent or delay liver cancer progression. Disorders associated with dysregulated iron metabolism are characterized with increased susceptibility to hepatocellular carcinoma. This review discusses the association of iron with metabolic disorders such as hereditary hemochromatosis, non-alcoholic fatty liver disease, obesity, and type 2 diabetes, in the background of hepatocellular carcinoma.

Apoferritin: a potential nanocarrier for cancer imaging and drug delivery

Introduction: As a protein-based biomaterial for potential cancer targeting delivery, apoferritin has recently attracted interest.Areas covered: In this review, we discuss the development of this cage-like protein as an endogenous nanocarrier that can hold molecules in its cavity. We present the specific characterizations and formulations of apoferritin nanocarriers, and outline the recent progress of the protein as an appropriate tumor-delivery vehicle in different therapeutic strategies to treat solid tumors. Finally, we propose how the application for cancer drug repurposing delivery within apoferritin could expand cancer treatment in the future.Expert opinion: Being a ubiquitous iron storage protein that exists in many living organisms, apoferritin is promising as a cancer tumor-targeting nanocarrier. By exploiting its versatility, apoferritin could be used for cancer repurposed drug delivery and could reduce the high cost of new drug discovery development and shorten the formulation process.

Regression of Melanoma Following Intravenous Injection of Plumbagin Entrapped in Transferrin-Conjugated, Lipid-Polymer Hybrid Nanoparticles

BACKGROUND

Plumbagin, a naphthoquinone extracted from the officinal leadwort presenting promising anti-cancer properties, has its therapeutic potential limited by its inability to reach tumors in a specific way at a therapeutic concentration following systemic injection. The purpose of this study is to assess whether a novel tumor-targeted, lipid-polymer hybrid nanoparticle formulation of plumbagin would suppress the growth of B16-F10 melanoma in vitro and in vivo.

METHODS

Novel lipid-polymer hybrid nanoparticles entrapping plumbagin and conjugated with transferrin, whose receptors are present in abundance on many cancer cells, have been developed. Their cellular uptake, anti-proliferative and apoptosis efficacy were assessed on various cancer cell lines in vitro. Their therapeutic efficacy was evaluated in vivo after tail vein injection to mice bearing B16-F10 melanoma tumors.

RESULTS

The transferrin-bearing lipid-polymer hybrid nanoparticles loaded with plumbagin resulted in the disappearance of 40% of B16-F10 tumors and regression of 10% of the tumors following intravenous administration. They were well tolerated by the mice.

CONCLUSION

These therapeutic effects, therefore, make transferrin-bearing lipid-polymer hybrid nanoparticles entrapping plumbagin a highly promising anti-cancer nanomedicine.

Iron metabolism: an emerging therapeutic target underlying the anti-cancer effect of quercetin

Iron, an essential micronutrient for all kinds of cells, is essential for the balance of body internal environment. Notably, cancer cells exhibit a strong dependence on iron and require a large amount of iron for proliferation. A growing number of studies suggested that iron metabolism imbalance and subsequent excess iron accumulation are closely related to the occurrence and progression of cancer. Precisely, excess iron promotes the development of cancer due to the pro-oxidative nature of iron and its damaging effects on DNA. Simultaneously, tumor cells acquire large amounts of iron to maintain rapid growth and proliferation. Therefore, targeting iron metabolism may provide a new way for the treatment of cancer. Quercetin, a natural flavonoid, has long been regarded as potential drug for cancer treatments owing to its anti-inflammatory, antioxidant and anti-tumor effects. It is proven that quercetin possesses a high iron-chelating capacity, depriving cancer cells of iron or altering iron metabolism. Herein, we conduct a review on the mechanisms of iron imbalance in tumors and the role of quercetin in iron chelation, which will provide insight into the potential for quercetin as an anti-cancer drug.

Onco-Receptors Targeting in Lung Cancer via Application of Surface-Modified and Hybrid Nanoparticles: A Cross-Disciplinary Review

Lung cancer is among the most prevalent and leading causes of death worldwide. The major reason for high mortality is the late diagnosis of the disease, and in most cases, lung cancer is diagnosed at fourth stage in which the cancer has metastasized to almost all vital organs. The other reason for higher mortality is the uptake of the chemotherapeutic agents by the healthy cells, which in turn increases the chances of cytotoxicity to the healthy body cells. The complex pathophysiology of lung cancer provides various pathways to target the cancerous cells. In this regard, upregulated onco-receptors on the cell surface of tumor including epidermal growth factor receptor (EGFR), integrins, transferrin receptor (TFR), folate receptor (FR), cluster of differentiation 44 (CD44) receptor, etc. could be exploited for the inhibition of pathways and tumor-specific drug targeting. Further, cancer borne immunological targets like T-lymphocytes, myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), and dendritic cells could serve as a target site to modulate tumor activity through targeting various surface-expressed receptors or interfering with immune cell-specific pathways. Hence, novel approaches are required for both the diagnosis and treatment of lung cancers. In this context, several researchers have employed various targeted delivery approaches to overcome the problems allied with the conventional diagnosis of and therapy methods used against lung cancer. Nanoparticles are cell nonspecific in biological systems, and may cause unwanted deleterious effects in the body. Therefore, nanodrug delivery systems (NDDSs) need further advancement to overcome the problem of toxicity in the treatment of lung cancer. Moreover, the route of nanomedicines’ delivery to lungs plays a vital role in localizing the drug concentration to target the lung cancer. Surface-modified nanoparticles and hybrid nanoparticles have a wide range of applications in the field of theranostics. This cross-disciplinary review summarizes the current knowledge of the pathways implicated in the different classes of lung cancer with an emphasis on the clinical implications of the increasing number of actionable molecular targets. Furthermore, it focuses specifically on the significance and emerging role of surface functionalized and hybrid nanomaterials as drug delivery systems through citing recent examples targeted at lung cancer treatment.

Ferroptosis/pyroptosis dual-inductive combinational anti-cancer therapy achieved by transferrin decorated nanoMOF

Non-apoptotic cell death such as ferroptosis and pyroptosis has shed new light on cancer treatment, whereas combinational therapy using both these mechanisms has not yet been fully explored. Herein, a dual-inductive nano-system to realize ferroptosis/pyroptosis mediated anti-cancer effects is presented. The nanodrug (Tf-LipoMof@PL) is constructed with a piperlongumine (PL) loaded metal-organic framework (MOF) coated with transferrin decorated pH sensitive lipid layer. Intracellular iron was enriched with an iron-containing MOF, whose endocytosis can be further facilitated by transferrin decorated on the lipid layer, which provides a prerequisite for the occurrence of ferroptosis and pyroptosis. Piperlongumine as the ferroptosis inducer can strengthen the ferroptotic cell death, and provide H2O2 for the dual induction system to increase ROS generation through Fenton reaction. On the basis of validation of both ferroptosis and pyroptosis, the dual-inductive nanodrug demonstrated ideal anticancer effects in the xenograft mice model, which proved that the ferroptosis/pyroptosis dual-inductive nanoplatform could be an effective and promising anticancer modality.

Peptide-Functionalized Nanoparticles-Encapsulated Cyclin-Dependent Kinases Inhibitor Seliciclib in Transferrin Receptor Overexpressed Cancer Cells

Seliciclib, a broad cyclin-dependent kinases (CDKs) inhibitor, exerts its potential role in cancer therapy. For taking advantage of overexpressive transferrin receptor (TfR) on most cancer cells, T7 peptide, a TfR targeting ligand, was selected as a targeting ligand to facilitate nanoparticles (NPs) internalization in cancer cells. In this study, poly(d,l-lactide-co-glycolide) (PLGA) was conjugated with maleimide poly(ethylene glycol) amine (Mal-PEG-NH₂) to form PLGA-PEG-maleimide copolymer. The synthesized copolymer was used to prepare NPs for encapsulation of seliciclib which was further decorated by T7 peptide. The result shows that the better cellular uptake was achieved by T7 peptide-modified NPs particularly in TfR-high expressed cancer cells in order of MDA-MB-231 breast cancer cells > SKOV-3 ovarian cancer cells > U87-MG glioma cells. Both SKOV-3 and U87-MG cells are more sensitive to encapsulated seliciclib in T7-decorated NPs than to free seliciclib, and that IC₅₀ values were lowered for encapsulated seliciclib.

Antibodies Targeting the Transferrin Receptor 1 (TfR1) as Direct Anti-cancer Agents

The transferrin receptor 1 (TfR1), also known as cluster of differentiation 71 (CD71), is a type II transmembrane glycoprotein that binds transferrin (Tf) and performs a critical role in cellular iron uptake through the interaction with iron-bound Tf. Iron is required for multiple cellular processes and is essential for DNA synthesis and, thus, cellular proliferation. Due to its central role in cancer cell pathology, malignant cells often overexpress TfR1 and this increased expression can be associated with poor prognosis in different types of cancer. The elevated levels of TfR1 expression on malignant cells, together with its extracellular accessibility, ability to internalize, and central role in cancer cell pathology make this receptor an attractive target for antibody-mediated therapy. The TfR1 can be targeted by antibodies for cancer therapy in two distinct ways: (1) indirectly through the use of antibodies conjugated to anti-cancer agents that are internalized by receptor-mediated endocytosis or (2) directly through the use of antibodies that disrupt the function of the receptor and/or induce Fc effector functions, such as antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cell-mediated phagocytosis (ADCP), or complement-dependent cytotoxicity (CDC). Although TfR1 has been used extensively as a target for antibody-mediated cancer therapy over the years, interest continues to increase for both targeting the receptor for delivery purposes and for its use as direct anti-cancer agents. This review focuses on the developments in the use of antibodies targeting TfR1 as direct anti-tumor agents.

Novel method for screening functional antibody with comprehensive analysis of its immunoliposome

Development of monoclonal antibody is critical for targeted drug delivery because its characteristics determine improved therapeutic efficacy and reduced side-effect. Antibody therapeutics target surface molecules; hence, internalization is desired for drug delivery. As an antibody–drug conjugate, a critical parameter is drug-to-antibody ratio wherein the quantity of drugs attached to the antibody influences the antibody structure, stability, and efficacy. Here, we established a cell-based immunotoxin screening system to facilitate the isolation of functional antibodies with internalization capacities, and discovered an anti-human CD71 monoclonal antibody. To overcome the limitation of drug-to-antibody ratio, we employed the encapsulation capacity of liposome, and developed anti-CD71 antibody-conjugated liposome that demonstrated antigen–antibody dependent cellular uptake when its synthesis was optimized. Furthermore, anti-CD71 antibody-conjugated liposome encapsulating doxorubicin demonstrated antigen–antibody dependent cytotoxicity. In summary, this study demonstrates the powerful pipeline to discover novel functional antibodies, and the optimal method to synthesize immunoliposomes. This versatile technology offers a rapid and direct approach to generate antibodies suitable for drug delivery modalities.

Smart Nanocarriers for Targeted Cancer Therapy

Cancer is considered one of the most threatening diseases worldwide. Although many therapeutic approaches have been developed and optimized for ameliorating patient's conditions and life expectancy, however, it frequently remains an incurable pathology. Notably, conventional treatments may reveal inefficient in the presence of metastasis development, multidrug resistance and inability to achieve targeted drug delivery. In the last decades, nanomedicine has gained a prominent role, due to many properties ascribable to nanomaterials. It is worth mentioning their small size, their ability to be loaded with small drugs and bioactive molecules and the possibility to be functionalized for tumor targeting. Natural vehicles have been exploited, such as exosomes, and designed, such as liposomes. Biomimetic nanomaterials have been engineered, by modification with biological membrane coating. Several nanoparticles have already entered clinical trials and some liposomal formulations have been approved for therapeutic applications. In this review, natural and synthetic nanocarriers functionalized for actively targeting cancer cells will be described, focusing on their advantages with respect to conventional treatments. Recent innovations related to biomimetic nanoparticles camouflaged with membranes isolated from different types of cells will be reported, together with their promising applications. Finally, a short overview on the latest advances in carrier-free nanomaterials will be provided.

Crosstalk between Macrophages, T Cells, and Iron Metabolism in Tumor Microenvironment

Leukocytes, including macrophages and T cells, represent key players in the human immune system, which plays a considerable role in the development and progression of tumors by immune surveillance or immune escape. Boosting the recruitment of leukocytes into the tumor microenvironment and promoting their antitumor responses have been hot areas of research in recent years. Although immunotherapy has manifested a certain level of success in some malignancies, the overall effectiveness is far from satisfactory. Iron is an essential trace element required in multiple, normal cellular processes, such as DNA synthesis and repair, cellular respiration, metabolism, and signaling, while dysregulated iron metabolism has been declared one of the metabolic hallmarks of malignant cancer cells. Furthermore, iron is implicated in the modulation of innate and adaptive immune responses, and elucidating the targeted regulation of iron metabolism may have the potential to benefit antitumor immunity and cancer treatment. In the present review, we briefly summarize the roles of leukocytes and iron metabolism in tumorigenesis, as well as their crosstalk in the tumor microenvironment. The combination of immunotherapy with targeted regulation of iron and iron-dependent regulated cell death (ferroptosis) may be a focus of future research.

Multi-Targeted Anticancer Activity of Imidazolate Phosphane Gold(I) Compounds by Inhibition of DHFR and TrxR in Breast Cancer Cells

A class of phosphane gold(I) compounds, made of azoles and phosphane ligands, was evaluated for a screening on the regards of Breast Cancer cell panels (BC). The compounds possess N-Au-P or Cl-Au-P bonds around the central metal, and they differ for the presence of aprotic or protic polar groups in the azoles and/or the phosphane moieties to tune their hydrophilicity. Among the six candidates, only the compounds having the P-Au-N environment and not displaying neither the hydroxyl nor carboxyl groups in the ligands were found active. The compounds were screened by MTT tests in SKBR3, A17, and MDA-MB231 cancer cells, and two compounds (namely the 4,5-dicyano-imidazolate-1yl-gold(I)-(triphenylphosphane, 5, and 4,5-dichloro-imidazolate-1yl-gold(I)-triphenylphosphane, 6) were found very cytotoxic, with the most active with an IC₅₀ value of 3.46 μM in MDA-MB231 cells. By performing enzymatic assays in the treated cells lysates, the residual enzymatic activity of dihydrofolate reductase (DHFR) has been measured after cell treatment for 4 or 12 h in comparison with control cells. Upon 12 h of treatment, the activity of DHFR was significantly reduced in both SKBR3 and A17 cells by compounds 5 and 6, but not in human MDA-MB231 cells; interestingly, it was found remarkably high after 4 h of treatment, revealing a time dependence for the DHFR enzymatic assays. The DHFR inhibition data have been compared to those for the thioredoxin reductase (TrxR), the most recognized molecular target for gold compounds. For this latter, similar residual activities (i.e., 37 and 49% for the match of SKBR3 cells and compound 5 or 6, respectively) were found. Binding studies on the regards of ct-DNA (calf-thymus-DNA) and of plasma transporters proteins, such as BSA (bovine serum albumin) and ATF (apo transferrin), were performed. As expected for gold compounds, the data support strong binding to proteins (K_sv values range: 1.51 ÷ 2.46 × 10⁴ M⁻¹) and a weaker interaction with ct-DNA's minor groove (K_sv values range: 1.55 ÷ 6.12 × 10³ M⁻¹).

Rab7-harboring vesicles are carriers of the transferrin receptor through the biosynthetic secretory pathway

The biosynthetic secretory pathway is particularly challenging to investigate as it is underrepresented compared to the abundance of the other intracellular trafficking routes. Here, we combined the retention using selective hook (RUSH) to a CRISPR-Cas9 gene editing approach (eRUSH) and identified Rab7-harboring vesicles as an important intermediate compartment of the Golgi-to-plasma membrane transport of neosynthesized transferrin receptor (TfR). These vesicles did not exhibit degradative properties and were not associated to Rab6A-harboring vesicles. Rab7A was transiently associated to neosynthetic TfR-containing post-Golgi vesicles but dissociated before fusion with the plasma membrane. Together, our study reveals a role for Rab7 in the biosynthetic secretory pathway of the TfR, highlighting the diversity of the secretory vesicles' nature.

Current status and future directions of hepatocellular carcinoma-targeted nanoparticles and nanomedicine

INTRODUCTION

Hepatocellular carcinoma (HCC) is a major health problem worldwide. Conventional therapies covering either chemotherapy or combination therapy still have sub-optimal responses with significant adverse effects and toxicity. Moreover, tumor cells usually acquire resistance quickly for traditional approaches, limiting their use in HCC. Interest in nanomedicine due to minimal systemic toxicity and a high degree of target-specific drug-delivery have pulled the attention of health scientists in this area of therapeutics.

AREA COVERED

The review covers the incidence and epidemiology of HCC, proposed molecular drug targets, mechanistic approach and emergence of nanomedicines including nanoparticles, lipidic nanoparticles, vesicular-based nanocarrier, virus-like particles with momentous therapeutic aspects including biocompatibility, and toxicity of nanocarriers along with conclusions and future perspective, with an efficient approach to safely cross physiological barriers to reach the target site for treating liver cancer.

EXPERT OPINION

Remarkable outcomes have recently been observed for the therapeutic efficacy of nanocarriers with respect to a specific drug target against the treatment of HCC by existing under trial drugs.

The evolution of polymer conjugation and drug targeting for the delivery of proteins and bioactive molecules

Polymer conjugation can be considered one of the leading approaches within the vast field of nanotechnology-based drug delivery systems. In fact, such technology can be exploited for delivering an active molecule, such as a small drug, a protein, or genetic material, or it can be applied to other drug delivery systems as a strategy to improve their in vivo behavior or pharmacokinetic activities such as prolonging the half-life of a drug, conferring stealth properties, providing external stimuli responsiveness, and so on. If on the one hand, polymer conjugation with biotech drug is considered the linchpin of the protein delivery field boasting several products in clinical use, on the other, despite dedicated research, conjugation with low molecular weight drugs has not yet achieved the milestone of the first clinical approval. Some of the primary reasons for this debacle are the difficulties connected to achieving selective targeting to diseased tissue, organs, or cells, which is the main goal not only of polymer conjugation but of all delivery systems of small drugs. In light of the need to achieve better drug targeting, researchers are striving to identify more sophisticated, biocompatible delivery approaches and to open new horizons for drug targeting methodologies leading to successful clinical applications. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

A bird's eye view of the advanced approaches and strategies for overshadowing triple negative breast cancer

Triple negative breast cancer (TNBC) is one of the most aggressive form of breast cancer. It is characterized by the absence of estrogen, progesterone and human epidermal growth factor receptors. The main issue with TNBC is that it exhibits poor prognosis, high risk of relapse, short progression-free survival and low overall survival in patients. This is because the conventional therapy used for managing TNBC has issues pertaining to poor bioavailability, lower cellular uptake, increased off-target effects and development of resistance. To overcome such pitfalls, several other approaches are explored. In this context, the present manuscript showcases three of the most widely used approaches which are (i) nanotechnology-based approach; (ii) gene therapy approach and (iii) Phytochemical-based approach. The ultimate focus is to present and explain the insightful reports based on these approaches. Further, the review also expounds on the identified molecular targets and novel targeting ligands which are explored for managing TNBC effectively. Thus, in a nutshell, the review tries to highlight these existing treatment approaches which might inspire for future development of novel therapies with a potential of overshadowing TNBC.

Iron: An Essential Element of Cancer Metabolism

Cancer cells undergo considerable metabolic changes to foster uncontrolled proliferation in a hostile environment characterized by nutrient deprivation, poor vascularization and immune infiltration. While metabolic reprogramming has been recognized as a hallmark of cancer, the role of micronutrients in shaping these adaptations remains scarcely investigated. In particular, the broad electron-transferring abilities of iron make it a versatile cofactor that is involved in a myriad of biochemical reactions vital to cellular homeostasis, including cell respiration and DNA replication. In cancer patients, systemic iron metabolism is commonly altered. Moreover, cancer cells deploy diverse mechanisms to increase iron bioavailability to fuel tumor growth. Although iron itself can readily participate in redox reactions enabling vital processes, its reactivity also gives rise to reactive oxygen species (ROS). Hence, cancer cells further rely on antioxidant mechanisms to withstand such stress. The present review provides an overview of the common alterations of iron metabolism occurring in cancer and the mechanisms through which iron promotes tumor growth.

Iron Dysregulation in Human Cancer: Altered Metabolism, Biomarkers for Diagnosis, Prognosis, Monitoring and Rationale for Therapy

Simple Summary

Iron is the more abundant metal ion in humans. It is essential for life as it has a role in various cellular processes involved, for instance, in cell metabolism and DNA synthesis. These functions are crucial for cell proliferation, and it is therefore not surprising that iron is accumulated in tumors. In this review, we describe normal and altered iron homeostasis mechanisms. We also provide a vision of iron-related proteins with altered expression in cancers and discuss their potential as diagnostic and/or prognostic biomarkers. Finally, we give an overview of therapeutic strategies acting on iron metabolism to fight against cancers.

Abstract

Iron (Fe) is a trace element that plays essential roles in various biological processes such as DNA synthesis and repair, as well as cellular energy production and oxygen transport, and it is currently widely recognized that iron homeostasis is dysregulated in many cancers. Indeed, several iron homeostasis proteins may be responsible for malignant tumor initiation, proliferation, and for the metastatic spread of tumors. A large number of studies demonstrated the potential clinical value of utilizing these deregulated proteins as prognostic and/or predictive biomarkers of malignancy and/or response to anticancer treatments. Additionally, the iron present in cancer cells and the importance of iron in ferroptosis cell death signaling pathways prompted the development of therapeutic strategies against advanced stage or resistant cancers. In this review, we select relevant and promising studies in the field of iron metabolism in cancer research and clinical oncology. Besides this, we discuss some co-existing discrepant findings. We also present and discuss the latest lines of research related to targeting iron, or its regulatory pathways, as potential promising anticancer strategies for human therapy. Iron chelators, such as deferoxamine or iron-oxide-based nanoparticles, which are already tested in clinical trials, alone or in combination with chemotherapy, are also reported.

Effective ferroptotic small-cell lung cancer cell death from SLC7A11 inhibition by sulforaphane

Small-cell lung cancer (SCLC) is a highly aggressive cancer with poor prognosis, due to a lack of therapeutic targets. Sulforaphane (SFN) is an isothiocyanate derived from cruciferous vegetables and has shown anticancer effects against numerous types of cancer. However, its anticancer effect against SCLC remains unclear. The present study aimed to demonstrate the anticancer effects of SFN in SCLC cells by investigating cell death (ferroptosis, necroptosis and caspase inhibition). The human SCLC cell lines NCI-H69, NCI-H69AR (H69AR) and NCI-H82 and the normal bronchial epithelial cell line, 16HBE14o- were used to determine cell growth and cytotoxicity, evaluate the levels of iron and glutathione, and quantify lipid peroxidation following treatment with SFN. mRNA expression levels of cystine/glutamate antiporter xCT (SLC7A11), a key component of the cysteine/glutamate antiporter, were measured using reverse transcription-quantitative PCR, while the levels of SLC7A11 protein were measured using western blot analysis. Following the addition of SFN to the cell culture, cell growth was significantly inhibited, and cell death was shown in SCLC and multidrug-resistant H69AR cells. The ferroptotic effects of SFN were confirmed following culture with the ferroptosis inhibitor, ferrostatin-1, and deferoxamine; iron levels were elevated, which resulted in the accumulation of lipid reactive oxygen species. The mRNA and protein expression levels of SLC7A11 were significantly lower in SFN-treated cells compared with that in the control cells (P<0.0001 and P=0.0006, respectively). These results indicated that the anticancer effects of SFN may be caused by ferroptosis in the SCLC cells, which was hypothesized to be triggered from the inhibition of mRNA and protein expression levels of SLC7A11. In conclusion, the present study demonstrated that SFN-induced cell death was mediated via ferroptosis and inhibition of the mRNA and protein expression levels of SLC7A11 in SCLC cells. The anticancer effects of SFN may provide novel options for SCLC treatment.

A Method for Targeted Nonviral siRNA Delivery in Cancer and Inflammatory Diseases

Small interfering RNA (siRNA)-based therapy has been subject of intense research since the discovery of RNA interference (RNAi), providing a tool to potentially silence any chosen gene. Nevertheless, efficient delivery still presents a major hurdle to translating this promising technology into medical practice. Here, we describe a straightforward method to prepare and characterize an effective delivery system consisting of low-molecular-weight polyethylenimine (PEI) and transferrin (Tf). Tf-PEI polyplexes are not only able to successfully transport and protect the sensitive nucleic acid payload from degradation but also to selectively deliver the siRNA to transferrin receptor (TfR)-overexpressing cells, playing key roles in the pathology of numerous cancer types as well as inflammatory diseases.

Ligand-Targeted Delivery of Photosensitizers for Cancer Treatment

Photodynamic therapy (PDT) is a promising cancer treatment which involves a photosensitizer (PS), light at a specific wavelength for PS activation and oxygen, which combine to elicit cell death. While the illumination required to activate a PS imparts a certain amount of selectivity to PDT treatments, poor tumor accumulation and cell internalization are still inherent properties of most intravenously administered PSs. As a result, common consequences of PDT include skin photosensitivity. To overcome the mentioned issues, PSs may be tailored to specifically target overexpressed biomarkers of tumors. This active targeting can be achieved by direct conjugation of the PS to a ligand with enhanced affinity for a target overexpressed on cancer cells and/or other cells of the tumor microenvironment. Alternatively, PSs may be incorporated into ligand-targeted nanocarriers, which may also encompass multi-functionalities, including diagnosis and therapy. In this review, we highlight the major advances in active targeting of PSs, either by means of ligand-derived bioconjugates or by exploiting ligand-targeting nanocarriers.

A selective drug delivery system based on phospholipid-type nanobubbles for lung cancer therapy

Aim: To develop a micelle-type nanobubble decorated with fluorescein-5-isothiocyanate-conjugated transferrin, with encapsulation of paclitaxel (PTX@FT-NB) for lung cancer treatment. Materials & methods: PTX@FT-NBs were characterized to determine their physicochemical properties, structural stability and cytotoxicity. Lung cancer cell and mouse xenograft tumor models were used to evaluate the therapeutic effectiveness of PTX@FT-NB. Results: The PTX@FT-NBs not only showed selective targeting to lung cancer cells but also inhibited tumor growth significantly via paclitaxel release. Furthermore, paclitaxel-induced microtubule stabilization demonstrated the release of the drug from PTX@FT-NB in the targeted tumor cell both in vitro and in vivo. Conclusion: PTX@FT-NB has the potential as an anticancer nanocarrier against lung cancer cells because of its specific targeting and better drug delivery capacity.

Receptor-based targeting of engineered nanocarrier against solid tumors: Recent progress and challenges ahead

Background In past few decades, the research on engineered nanocarriers (NCs) has gained significant attention in cancer therapy due to selective delivery of drug molecules on the diseased cells thereby preventing unwanted uptake into healthy cells to cause toxicity. Scope of review The applicability of enhanced permeability and retention (EPR) effect for the delivery of nanomedicines in cancer therapy has gained limited success due to poor accessibility of the drugs to the target cells where non-specific payload delivery to the off target region lack substantial reward over the conventional therapeutic systems. Major conclusions In spite of the fact, nanomedicines fabricated from the biocompatible nanocarriers have reduced targeting potential for meaningful clinical benefits. However, over expression of receptors on the tumor cells provides opportunity to design functional nanomedicine to bind substantially and deliver therapeutics to the cells or tissues of interest by alleviating the bio-toxicity and unwanted effects. This critique will give insight into the over expressed receptor in various tumor and targeting potential of functional nanomedicine as new therapeutic avenues for effective treatment. General significance This review shortly shed light on EPR-based drug targeting using nanomedicinal strategies, their limitation, and advances in therapeutic targeting to the tumor cells.

Genetic recombination of poly(l-lysine) functionalized apoferritin nanocages that resemble viral capsid nanometer-sized platforms for gene therapy

Currently, bioengineered apoferritin nanocages with flexible protein shells and functionalized modifications have become an attractive approach for efficient anti-tumor therapy. Here, we modified the N-terminus of H-chain subunits in apoferritin with different amounts of lysine via genetic recombination to obtain a poly(l-lysine) modified H-chain apoferritin (nL-HFn) nanocage for siRNA delivery and gene therapy. To achieve excellent cellular affinity and uptake, the nanocarriers were internalized through transferrin receptor-mediated endocytosis, then escaped from the endosome for cytoplasmic transport. Compared with natural apoferritin, the siRNA-loaded genetic recombination NPs modified with lysine exhibit stronger RNA-interference and antitumor efficiency both in vitro and in 4T1 tumor model mice. Therefore, bioengineered apoferritin nanocages modified with lysine might be a promising platform for nucleic acid drug delivery.

Artemisinins as a novel anti-cancer therapy: Targeting a global cancer pandemic through drug repurposing

Artemisinins are a unique class of antimalarial drugs with significant potential for drug repurposing for a wide range of diseases including cancer. Cancer is a leading cause of death globally and the majority of cancer related deaths occur in Low and Middle Income Countries (LMICs) where conventional treatment options are often limited by financial cost. Drug repurposing can significantly shorten new therapeutic discovery pathways, ensuring greater accessibility and affordability globally. Artemisinins have an excellent safety and tolerability profile as well as being affordable for deployment in Low and Middle Class Income Countries at around USD1 per daily dose. Robust, well designed clinical trials of artemisinin drug repurposing are indicated for a variety of different cancers and treatment settings.

Extracellular Vesicle-Based Nucleic Acid Delivery: Current Advances and Future Perspectives in Cancer Therapeutic Strategies

Extracellular vesicles (EVs) are sophisticated and sensitive messengers released by cells to communicate with and influence distant and neighboring cells via selective transfer of bioactive content, including protein lipids and nucleic acids. EVs have therefore attracted broad interest as new and refined potential therapeutic systems in many diseases, including cancer, due to their low immunogenicity, non-toxicity, and elevated bioavailability. They might serve as safe and effective vehicles for the transport of therapeutic molecules to specific tissues and cells. In this review, we focus on EVs as a vehicle for gene therapy in cancer. We describe recent developments in EV engineering to achieve efficient intracellular delivery of cancer therapeutics and avoid off-target effects, to provide an overview of the potential applications of EV-mediated gene therapy and the most promising biomedical advances.

Pharmacokinetics of inhaled nanotherapeutics for pulmonary delivery

Pulmonary delivery of lipid-based nanotherapeutics by inhalation presents an advantageous alternative to oral and intravenous routes of administration that avoids enzymatic degradation in gastrointestinal tract and hepatic first pass metabolism and also limits off-target adverse side effects upon heathy tissues. For lung-related indications, inhalation provides localized delivery in order to enhance therapeutic efficacy at the site of action. Optimization of physicochemical properties, selected drug and inhalation format can greatly influence the pharmacokinetic behavior of inhaled nanoparticle systems and their payloads. The present review analyzes a wide range of nanoparticle systems, their formulations and consequent effect on pharmacokinetic distribution of delivered active components after inhalation.

From Iron Chelation to Overload as a Therapeutic Strategy to Induce Ferroptosis in Leukemic Cells

Despite its crucial importance in numerous physiological processes, iron also causes oxidative stress and damage which can promote the growth and proliferation of leukemic cells. Iron metabolism is strictly regulated and the related therapeutic approaches to date have been to restrict iron availability to tumor cells. However, since a new form of iron-catalyzed cell death has been described, termed ferroptosis, and subsequently better understood, iron excess is thought to represent an opportunity to selectively kill leukemic cells and spare normal hematopoietic cells, based on their differential iron needs. This review summarizes the physiology of iron metabolism and its deregulation in leukemia, the known ferrotoposis pathways, and therapeutic strategies to target the altered iron metabolism in leukemia for the purposes of initiating ferroptosis in these cancer cells.

Targeting Receptors on Cancer Cells with Protein Toxins

Cancer cells frequently upregulate surface receptors that promote growth and survival. These receptors constitute valid targets for intervention. One strategy involves the delivery of toxic payloads with the goal of killing those cancer cells with high receptor levels. Delivery can be accomplished by attaching a toxic payload to either a receptor-binding antibody or a receptor-binding ligand. Generally, the cell-binding domain of the toxin is replaced with a ligand or antibody that dictates a new binding specificity. The advantage of this “immunotoxin” approach lies in the potency of these chimeric molecules for killing cancer cells. However, receptor expression on normal tissue represents a significant obstacle to therapeutic intervention.

Iron and Cancer: 2020 Vision

New and provocative insights into the relationships between iron and cancer have been uncovered in recent years. These include delineation of connections that link cellular iron to DNA repair, genomic integrity, and oncogenic signaling as well as the discovery of ferroptosis, a novel iron-dependent form of cell death. In parallel, new molecules and pathways that regulate iron influx, intracellular iron trafficking, and egress in normal cells, and their perturbations in cancer have been discovered. In addition, insights into the unique properties of iron handling in tumor-initiating cells (cancer stem cells), novel contributions of the tumor microenvironment to the uptake and regulation of iron in cancer cells, and new therapeutic modalities that leverage the iron dependence of cancer have emerged.

Advances in biomedical and pharmaceutical applications of protein-stabilized gold nanoclusters

The interest in using gold nanoclusters (AuNCs) as imaging probes is growing, covering wide ranges of applications. The stabilization of AuNCs with protein ligands enhances their biomedical and pharmaceutical applications. This is due to the biocompatibility, water solubility and bioactivity of proteins. Different factors can control the optical properties of AuNCs such as protein size, amino acids content and conformational structure. Controlling the synthesis conditions can result in tuning the AuNCs excitation, emission, fluorescence intensity and physicochemical properties to fulfill different applications. NIR-emitting protein-stabilized AuNCs are promising as imaging agents for targeting and visualization of cancer in vitro and in vivo. They are promising to be included as an important part of multifunctional theranostic nanosystems, due to their potential dual functions as imaging and photosensitizing agent for photodynamic therapy. Additionally, the protein around AuNCs represents a rich environment of active functional groups that are susceptible for conjugation with various biomolecules. Protein-AuNCs can act as fluorescent probes for rapid and selective analysis of different analytes in solution, cells or biological fluids. In conclusion, the variability of protein-AuNC applications can advance research in different biomedical and pharmaceutical fields.

Engineering Mesoporous Silica Nanoparticles for Targeted Alpha Therapy against Breast Cancer

Targeted alpha therapy, where highly cytotoxic doses are delivered to tumor cells while sparing surrounding healthy tissue, has emerged as a promising treatment against cancer. Radionuclide conjugation with targeting vectors and dose confinement, however, are still limiting factors for the widespread application of this therapy. In the current study, we developed multifunctional silica nanoconstructs for targeted alpha therapy that show targeting capabilities against breast cancer cells, cytotoxic responses at therapeutic dosages, and enhanced clearance. The silica nanoparticles were conjugated to transferrin, which promoted particle accumulation in cancerous cells, and 3,4,3-LI(1,2-HOPO), a chelator with high selectivity and binding affinity for f-block elements. High cytotoxic effects were observed when the nanoparticles were loaded with ²²⁵Ac, a clinically relevant radioisotope. Lastly, in vivo studies in mice showed that the administration of radionuclides with nanoparticles enhanced their excretion and minimized their deposition in bones. These results highlight the potential of multifunctional silica nanoparticles as delivery systems for targeted alpha therapy and offer insight into design rules for the development of new nanotherapeutic agents.

Endocytosis, signal transduction and proteolytic cleaving of human holotransferrin in Entamoeba histolytica

Amoebiasis is a parasitic infection of the human large intestine caused by Entamoeba histolytica; this disease mainly affects people from developing countries. To survive, this primitive protozoan has a high demand for iron, and it uses host iron proteins upon invasion. Transferrin (Tf) is a plasma iron-binding protein that transports and delivers iron to all cells. Iron-loaded Tf (holoTf) in humans can support the proliferation of amoebae in vitro by binding to an amoebic TfR (EhTfR), and amoebae endocytose it inside clathrin-coated vesicles. In this study, it was found that EhTfR phosphorylation is required for human holoTf endocytosis by E. histolytica. Once this complex is endocytosed, human holoTf could be degraded with a nutritional purpose by cysteine proteases. HoloTf endocytosis initiates the activation of the mitogen-activated protein kinases (MAPKs) and focal adhesion kinase (FAK) pathways, which induce cell proliferation with phosphoinositide 3-kinase (PI-3 K) and Ca²⁺ involvement. In the first minutes after holoTf is endocytosed, several proteins are phosphorylated including transketolase, enolase, L-myo-inositol-1-phosphate synthase and phosphoglucomutase, which control carbohydrate metabolism, and heat shock protein-70. The study of these proteins and their signal transduction pathways could be useful for developing future therapies.

Multiplexed non-invasive tumor imaging of glucose metabolism and receptor-ligand engagement using dark quencher FRET acceptor

Rationale: Following an ever-increased focus on personalized medicine, there is a continuing need to develop preclinical molecular imaging modalities to guide the development and optimization of targeted therapies. Near-Infrared (NIR) Macroscopic Fluorescence Lifetime Förster Resonance Energy Transfer (MFLI-FRET) imaging offers a unique method to robustly quantify receptor-ligand engagement in live intact animals, which is critical to assess the delivery efficacy of therapeutics. However, to date, non-invasive imaging approaches that can simultaneously measure cellular drug delivery efficacy and metabolic response are lacking. A major challenge for the implementation of concurrent optical and MFLI-FRET in vivo whole-body preclinical imaging is the spectral crowding and cross-contamination between fluorescent probes. Methods: We report on a strategy that relies on a dark quencher enabling simultaneous assessment of receptor-ligand engagement and tumor metabolism in intact live mice. Several optical imaging approaches, such as in vitro NIR FLI microscopy (FLIM) and in vivo wide-field MFLI, were used to validate a novel donor-dark quencher FRET pair. IRDye 800CW 2-deoxyglucose (2-DG) imaging was multiplexed with MFLI-FRET of NIR-labeled transferrin FRET pair (Tf-AF700/Tf-QC-1) to monitor tumor metabolism and probe uptake in breast tumor xenografts in intact live nude mice. Immunohistochemistry was used to validate in vivo imaging results. Results: First, we establish that IRDye QC-1 (QC-1) is an effective NIR dark acceptor for the FRET-induced quenching of donor Alexa Fluor 700 (AF700). Second, we report on simultaneous in vivo imaging of the metabolic probe 2-DG and MFLI-FRET imaging of Tf-AF700/Tf-QC-1 uptake in tumors. Such multiplexed imaging revealed an inverse relationship between 2-DG uptake and Tf intracellular delivery, suggesting that 2-DG signal may predict the efficacy of intracellular targeted delivery. Conclusions: Overall, our methodology enables for the first time simultaneous non-invasive monitoring of intracellular drug delivery and metabolic response in preclinical studies.

Application of advances in endocytosis and membrane trafficking to drug delivery

Multidisciplinary research efforts in the field of drug delivery have led to the development of a variety of drug delivery systems (DDS) designed for site-specific delivery of diagnostic and therapeutic agents. Since efficient uptake of drug carriers into target cells is central to effective drug delivery, a comprehensive understanding of the biological pathways for cellular internalization of DDS can facilitate the development of DDS capable of precise tissue targeting and enhanced therapeutic outcomes. Diverse methods have been applied to study the internalization mechanisms responsible for endocytotic uptake of extracellular materials, which are also the principal pathways exploited by many DDS. Chemical inhibitors remain the most commonly used method to explore endocytotic internalization mechanisms, although genetic methods are increasingly accessible and may constitute more specific approaches. This review highlights the molecular basis of internalization pathways most relevant to internalization of DDS, and the principal methods used to study each route. This review also showcases examples of DDS that are internalized by each route, and reviews the general effects of biophysical properties of DDS on the internalization efficiency. Finally, options for intracellular trafficking and targeting of internalized DDS are briefly reviewed, representing an additional opportunity for multi-level targeting to achieve further specificity and therapeutic efficacy.

NIR Photodynamic Destruction of PDAC and HNSCC Nodules Using Triple-Receptor-Targeted Photoimmuno-Nanoconjugates: Targeting Heterogeneity in Cancer

Receptor heterogeneity in cancer is a major limitation of molecular targeting for cancer therapeutics. Single-receptor-targeted treatment exerts selection pressures that result in treatment escape for low-receptor-expressing tumor subpopulations. To overcome this potential for heterogeneity-driven resistance to molecular targeted photodynamic therapy (PDT), we present for the first time a triple-receptor-targeted photoimmuno-nanoconjugate (TR-PIN) platform. TR-PIN functionalization with cetuximab, holo-transferrin, and trastuzumab conferred specificity for epidermal growth factor receptor (EGFR), transferrin receptor (TfR), and human epidermal growth factor receptor 2 (HER-2), respectively. The TR-PINs exhibited up to a 24-fold improvement in cancer cell binding compared with EGFR-specific cetuximab-targeted PINs (Cet-PINs) in low-EGFR-expressing cell lines. Photodestruction using TR-PINs was significantly higher than the monotargeted Cet-PINs in heterocellular 3D in vitro models of heterogeneous pancreatic ductal adenocarcinoma (PDAC; MIA PaCa-2 cells) and heterogeneous head and neck squamous cell carcinoma (HNSCC, SCC9 cells) containing low-EGFR-expressing T47D (high TfR) or SKOV-3 (high HER-2) cells. Through their capacity for multiple tumor target recognition, TR-PINs can serve as a unique and amenable platform for the effective photodynamic eradication of diverse tumor subpopulations in heterogeneous cancers to mitigate escape for more complete and durable treatment responses.