Antibody-Drug Conjugates for Cancer Therapy

Insights into Modern Therapeutic Approaches in Pediatric Acute Leukemias

Pediatric cancers predominantly constitute lymphomas and leukemias. Recently, our knowledge and awareness about genetic diversities, and their consequences in these diseases, have greatly expanded. Modern solutions are focused on mobilizing and impacting a patient’s immune system. Strategies to stimulate the immune system, to prime an antitumor response, are of intense interest. Amid those types of therapies are chimeric antigen receptor T (CAR-T) cells, bispecific antibodies, and antibody–drug conjugates (ADC), which have already been approved in the treatment of acute lymphoblastic leukemia (ALL)/acute myeloid leukemia (AML). In addition, immune checkpoint inhibitors (ICIs), the pattern recognition receptors (PRRs), i.e., NOD-like receptors (NLRs), Toll-like receptors (TLRs), and several kinds of therapy antibodies are well on their way to showing significant benefits for patients with these diseases. This review summarizes the current knowledge of modern methods used in selected pediatric malignancies and presents therapies that may hold promise for the future.

Current status of immunotherapy for non-small cell lung cancer

Nowadays, lung cancer is still the deadliest oncological disease in the world. Among them, non-small cell lung cancer (NSCLC) accounts for 80%∼85% of all lung cancers, and its 5-year survival rate is less than 15%, making the situation critical. In the past decades, despite some clinical advances in conventional treatments, the overall survival rate of NSCLC is still not optimistic due to its unique physiological conditions and the frequent occurrence of tumor escape. In recent years, immunotherapy has become a new hot spot in lung cancer research, including antibody therapy and cell therapy, which have been developed and utilized one after another, especially immune checkpoint inhibitor (ICI). These approaches have effectively improved the overall survival rate and objective response rate of NSCLC patients by enhancing the immune capacity of the body and targeting tumor cells more effectively, which is more specific and less toxic compared with conventional chemotherapy, and providing more strategies for NSCLC treatment. In this paper, we reviewed the relevant targets, clinical progress and adverse reaction in monoclonal antibodies, antibody-drug conjugates, ICI, bispecific antibodies, T-cell receptor engineered T cell therapy (TCR-T), Chimeric antigen receptor T-cell immunotherapy (CAR-T), and also report on their combination therapy from the immune-related background to provide better NSCLC treatment and prospective.

Novel ADCs and Strategies to Overcome Resistance to Anti-HER2 ADCs

During recent years, a number of new compounds against HER2 have reached clinics, improving the prognosis and quality of life of HER2-positive breast cancer patients. Nonetheless, resistance to standard-of-care drugs has motivated the development of novel agents, such as new antibody-drug conjugates (ADCs). The latter are a group of drugs that benefit from the potency of cytotoxic agents whose action is specifically guided to the tumor by the target-specific antibody. Two anti-HER2 ADCs have reached the clinic: trastuzumab-emtansine and, more recently, trastuzumab-deruxtecan. In addition, several other HER2-targeted ADCs are in preclinical or clinical development, some of them with promising signs of activity. In the present review, the structure, mechanism of action, and potential resistance to all these ADCs will be described. Specific attention will be given to discussing novel strategies to circumvent resistance to ADCs.

Synthesis and evaluation of highly releasable and structurally stable antibody-SN-38-conjugates

Camptothecins, traditional chemotherapy drugs, have been clinically used in antibody-drug conjugates (ADCs), which refreshes the recognition that ADCs preferably incorporate highly potent payloads. However, SN-38, active metabolite of irinotecan from camptothecins, tended to be incorporated into ADCs with an unstable acid sensitive bond, not with the widely used Cathepsin B (CTSB) sensitive bond, which may pose the risk of off-target. Herein, we reported a novel strategy to construct highly releasable and structurally stable SN-38-conjugates, in which CTSB linkers directly connected to the 10-OH group through ether bond, not to the common 20-OH group of lactones of SN-38. In this paper, rapid release of SN-38 was skillfully demonstrated by utilizing the fluorescence properties of SN-38. The SN-38-ether-ADC displayed highly stable serum stability with the half-life over 10 days. Moreover, the drug-antibody-ratio (DAR) of ADC could be elevated to 7.1 through the introduction of polyethylene glycol (PEG) moieties without aggregation. The optimized ADC exhibited potent in vitro activities up to 5.5 nM, comparable to SN-38. Moreover, this ADC group significantly delayed tumor growth in vivo. In conclusion, the novel strategy has the potential to promote the development of SN38-ADCs and enrich the conjugation approaches for hydroxyl-bearing payloads.

Versatile and Robust Method for Antibody Conjugation to Nanoparticles with High Targeting Efficiency

The application of antibodies in nanomedicine is now standard practice in research since it represents an innovative approach to deliver chemotherapy agents selectively to tumors. The variety of targets or markers that are overexpressed in different types of cancers results in a high demand for antibody conjugated-nanoparticles, which are versatile and easily customizable. Considering up-scaling, the synthesis of antibody-conjugated nanoparticles should be simple and highly reproducible. Here, we developed a facile coating strategy to produce antibody-conjugated nanoparticles using 'click chemistry' and further evaluated their selectivity towards cancer cells expressing different markers. Our approach was consistently repeated for the conjugation of antibodies against CD44 and EGFR, which are prominent cancer cell markers. The functionalized particles presented excellent cell specificity towards CD44 and EGFR overexpressing cells, respectively. Our results indicated that the developed coating method is reproducible, versatile, and non-toxic, and can be used for particle functionalization with different antibodies. This grafting strategy can be applied to a wide range of nanoparticles and will contribute to the development of future targeted drug delivery systems.

Antibody Drug Conjugates in Glioblastoma - Is There a Future for Them?

Glioblastoma (GBM) is an aggressive and fatal malignancy that despite decades of trials has limited therapeutic options. Antibody drug conjugates (ADCs) are composed of a monoclonal antibody which specifically recognizes a cellular surface antigen linked to a cytotoxic payload. ADCs have demonstrated superior efficacy and/or reduced toxicity in a range of haematological and solid tumors resulting in nine ADCs receiving regulatory approval. ADCs have also been explored in patients with brain tumours but with limited success to date. While earlier generations ADCs in glioma patients have had limited success and high toxicity, newer and improved ADCs characterised by low immunogenicity and more effective payloads have shown promise in a range of tumour types. These newer ADCs have also been tested in glioma patients, however, with mixed results. Factors affecting the effectiveness of ADCs to target the CNS include the blood brain barrier which acts as a physical and biochemical barrier, the pro-cancerogenic and immunosuppressive tumor microenvironment and tumour characteristics like tumour volume and antigen expression. In this paper we review the data regarding the ongoing the development of ADCs in glioma patients as well as potential strategies to overcome these barriers to maximise their therapeutic potential.

Antibody drug conjugates in non-small cell lung cancer: An emerging therapeutic approach

The current standard-of-care for the treatment of advanced non-small cell lung cancer (NSCLC) incorporates targeted therapies, immune-checkpoint inhibitors (ICI) and systemic chemotherapy. Antibody-drug conjugates (ADC) are a class of anti-cancer therapy capable of transporting cytotoxic drugs directly to tumour cells, thus harnessing the strengths of both cytotoxic chemotherapy and targeted therapy. In this review we provide a comprehensive review the design, mode of action, and mechanisms of resistance to ADCs in NSCLC. We also summarize the clinical development of several promising ADCs in early phase clinical trials for the treatment NSCLC. including ADCs against well-established targets (e.g.HER2 in breast cancer, Nectin4 in urothelial cancer), novel antigenic targets (e.g. HER3, TROP2, PTK7, CEACAM5), as well as promising combinations with agents known to be active in NSCLC such as tyrosine kinase inhibitors and ICI therapy, as a strategy to overcome mechanisms of resistance to ADC therapy.

A New Kid on the Block: Sacituzumab Govitecan for the Treatment of Breast Cancer and Other Solid Tumors

Human trophoblast cell-surface antigen-2 (Trop-2) is a membrane glycoprotein involved in cell proliferation and motility, frequently overexpressed in epithelial tumors. Thus, it represents an attractive target for anticancer therapies. Sacituzumab govitecan (SG) is a third-generation antibody-drug conjugate, consisting of an anti-Trop-2 monoclonal antibody (hRS7), a hydrolyzable linker, and a cytotoxin (SN38), which inhibits topoisomerase 1. Specific pharmacological features, such as the high antibody to payload ratio, the ultra-toxic nature of SN38, and the capacity to kill surrounding tumor cells (the bystander effect), make SG a very promising drug for cancer treatment. Indeed, unprecedented results have been observed with SG in patients with heavily pretreated advanced triple-negative breast cancer and urothelial carcinomas, and the drug has already received approval for these indications. These results are coupled with a manageable toxicity profile, with neutropenia and diarrhea as the most frequent adverse events, mainly of grades 1-2. While several trials are exploring SG activity in different tumor types and settings, potential biomarkers of response are under investigation. Among these, Trop-2 overexpression and the presence of BRCA1/2 mutations seem to be the most promising. We review the available literature concerning SG, with a focus on its toxicity spectrum and possible biomarkers of its response.

A phase 1 study of LY3076226, a fibroblast growth factor receptor 3 (FGFR3) antibody-drug conjugate, in patients with advanced or metastatic cancer

Background We report a Phase 1 study of LY3076226, an antibody-drug conjugate composed of human IgG1 monoclonal antibody against the human FGFR3 attached with a cleavable linker to the maytansine derivative DM4 in patients with advanced or metastatic cancer. Methods This study was comprised of two parts: (A) dose escalation in patients with advanced or metastatic cancer and (B) dose expansion in patients with urothelial carcinoma with locally determined FGFR3 alterations. The dose range of LY3076226 tested was 0.2-5.0 mg/kg as an intravenous infusion on Day 1 of each 21-day cycle. The primary objective was to determine a recommended phase 2 dose (RP2D). Results Twenty-five patients were enrolled (Part A: 22, Part B: 3) and received ≥ 1 dose of LY3076226. No dose-limiting toxicities were reported. LY3076226 was generally well tolerated; most of the toxicities were Grade 1 or 2. Two patients experienced treatment-related Grade 3 toxicity (embolism and decreased platelet count). Four patients experienced serious adverse events (not treatment-related), all in Part A. Dose-proportional exposure was observed, with an estimated half-life of 2-7 days. No responses were seen with LY3076226 treatment. Stable disease persisting for > 6 months was observed in 1 patient receiving 3.2 mg/kg of LY3076226. Conclusion The study demonstrates acceptable safety and tolerability of LY3076226 up to the 5.0 mg/kg dose. Recruitment was stopped due to pipeline prioritization. Dose escalation of LY3076226 beyond 5.0 mg/kg in patients with advanced tumors may be possible. The trial was registered on August 19, 2015 under identifier NCT02529553 with ClinicalTrials.gov.

Perspectives on the development of antibody-drug conjugates targeting ROR1 for hematological and solid cancers

Antibody–drug conjugates (ADCs) are targeted therapeutics generated by conjugation of cytotoxic small molecules to monoclonal antibodies (mAbs) via chemical linkers. Due to their selective delivery of toxic payloads to antigen-positive cancer cells, ADCs demonstrate wider therapeutic indexes compared with conventional chemotherapy. After decades of intensive research and development, significant advances have been made in the field, leading to a total of 10 U.S. food and drug administration (FDA)-approved ADCs to treat cancer patients. Currently, ~80 ADCs targeting different antigens are under clinical evaluation for treatment of either hematological or solid malignancies. Notably, three ADCs targeting the same oncofetal protein, receptor tyrosine kinase like orphan receptor 1 (ROR1), have attracted considerable attention when they were acquired or licensed successively in the fourth quarter of 2020 by three major pharmaceutical companies. Apparently, ROR1 has emerged as an attractive target for cancer therapy. Since all the components of ADCs, including the antibody, linker and payload, as well as the conjugation method, play critical roles in ADC’s efficacy and performance, their choice and combination will determine how far they can be advanced. This review summarizes the design and development of current anti-ROR1 ADCs and highlights an emerging trend to target ROR1 for cancer therapy.

An intelligent cell-selective polymersome-DM1 nanotoxin toward triple negative breast cancer

Antibody-drug conjugates (ADCs) are among the most significant advances in clinical cancer treatments, however, they are haunted with fundamental issues like low drug/antibody ratio (DAR), need of large amount of antibody, and complex chemistry. Targeted nanomedicines while offering a promising alternative to ADCs are afflicted with drug leakage and inferior cancer-specificity. Herein, we developed an intelligent cell-selective nanotoxin based on anti-CD44 antibody-polymersome-DM1 conjugates (aCD44-AP-DM1) for potent treatment of solid tumors. DM1 was simultaneously coupled to vesicular membrane via disulfide bonds during self-assembly and anti-CD44 antibody was facilely clicked onto polymersome surface, tailor-making an optimal aCD44-AP-DM1 with a controlled antibody density of 5.0, extraordinary DAR of 275, zero drug leakage and rapid reduction-responsive DM1 release. aCD44-AP-DM1 displayed a high specificity and exceptional cytotoxicity toward MDA-MB-231 triple negative breast cancer, SMMC-7721 hepatocellular carcinoma and A549 non-small cell lung cancer cells with half-maximal inhibitory concentrations (IC₅₀) of 21.4, 3.7 and 64.6 ng/mL, respectively, 3.6-47.2-fold exceeding non-targeted P-DM1. Intriguingly, the systemic administration of aCD44-AP-DM1 significantly suppressed subcutaneous MDA-MB-231 tumor xenografts in nude mice while intratumoral injection achieved complete tumor eradication in four out of five mice, without causing toxicity. This intelligent cell-selective nanotoxin has emerged as a better platform over ADCs for targeted cancer therapy.

Antibody-Antineoplastic Conjugates in Gynecological Malignancies: Current Status and Future Perspectives

In the last decade, antibody-drug conjugates (ADCs), normally formed by a humanized antibody and a small drug via a chemical cleavable or non-cleavable linker, have emerged as a potential treatment strategy in cancer disease. They allow to get a selective delivery of the chemotherapeutic agents at the tumor level, and, consequently, to improve the antitumor efficacy and, especially to decrease chemotherapy-related toxicity. Currently, nine antibody-drug conjugate-based formulations have been already approved and more than 80 are under clinical trials for the treatment of several tumors, especially breast cancer, lymphomas, and multiple myeloma. To date, no ADCs have been approved for the treatment of gynecological formulations, but many formulations have been developed and have reached the clinical stage, especially for the treatment of ovarian cancer, an aggressive disease with a low five-year survival rate. This manuscript analyzes the ADCs formulations that are under clinical research in the treatment of gynecological carcinomas, specifically ovarian, endometrial, and cervical tumors.

On-Demand Drug Release from Click-Refillable Drug Depots

Stimuli-responsive, on-demand release of drugs from drug-eluting depots could transform the treatment of many local diseases, providing intricate control over local dosing. However, conventional on-demand drug release approaches rely on locally implanted drug depots, which become spent over time and cannot be refilled or reused without invasive procedures. New strategies to noninvasively refill drug-eluting depots followed by on-demand release could transform clinical therapy. Here we report an on-demand drug delivery paradigm that combines bioorthogonal click chemistry to locally enrich protodrugs at a prelabeled site and light-triggered drug release at the target tissue. This approach begins with introduction of the targetable depot through local injection of chemically reactive azide groups that anchor to the extracellular matrix. The anchored azide groups then capture blood-circulating protodrugs through bioorthogonal click chemistry. After local capture and retention, active drugs can be released through external light irradiation. In this report, a photoresponsive protodrug was constructed consisting of the chemotherapeutic doxorubicin (Dox), conjugated to dibenzocyclooctyne (DBCO) through a photocleavable ortho-nitrobenzyl linker. The protodrug exhibited excellent on-demand light-triggered Dox release properties and light-mediated in vitro cytotoxicity in U87 glioblastoma cell lines. Furthermore, in a live animal setting, azide depots formed in mice through intradermal injection of activated azide-NHS esters. After i.v. administration, the protodrug was captured by the azide depots with intricate local specificity, which could be increased with multiple refills. Finally, doxorubicin could be released from the depot upon light irradiation. Multiple rounds of depot refilling and light-mediated release of active drug were accomplished, indicating that this system has the potential for multiple rounds of treatment. Taken together, these in vitro and in vivo proof of concept studies establish a novel method for in vivo targeting and on-demand delivery of cytotoxic drugs at target tissues.

Abscopal Effect and Drug-Induced Xenogenization: A Strategic Alliance in Cancer Treatment?

The current state of cancer treatment is still far from being satisfactory considering the strong impairment of patients' quality of life and the high lethality of malignant diseases. Therefore, it is critical for innovative approaches to be tested in the near future. In view of the crucial role that is played by tumor immunity, the present review provides essential information on the immune-mediated effects potentially generated by the interplay between ionizing radiation and cytotoxic antitumor agents when interacting with target malignant cells. Therefore, the radiation-dependent abscopal effect (i.e., a biological effect of ionizing radiation that occurs outside the irradiated field), the influence of cancer chemotherapy on the antigenic pattern of target neoplastic cells, and the immunogenic cell death (ICD) caused by anticancer agents are the main topics of this presentation. It is widely accepted that tumor immunity plays a fundamental role in generating an abscopal effect and that anticancer drugs can profoundly influence not only the host immune responses, but also the immunogenic pattern of malignant cells. Remarkably, several anticancer drugs impact both the abscopal effect and ICD. In addition, certain classes of anticancer agents are able to amplify already expressed tumor-associated antigens (TAA). More importantly, other drugs, especially triazenes, induce the appearance of new tumor neoantigens (TNA), a phenomenon that we termed drug-induced xenogenization (DIX). The adoption of the abscopal effect is proposed as a potential therapeutic modality when properly applied concomitantly with drug-induced increase in tumor cell immunogenicity and ICD. Although little to no preclinical or clinical studies are presently available on this subject, we discuss this issue in terms of potential mechanisms and therapeutic benefits. Upcoming investigations are aimed at evaluating how chemical anticancer drugs, radiation, and immunotherapies are interacting and cooperate in evoking the abscopal effect, tumor xenogenization and ICD, paving the way for new and possibly successful approaches in cancer therapy.

Co-delivery systems: hope for clinical application?

Cancer is a multidimensional and challenging disease to handle. Current statistics reveal that we are far from satisfying cancer treatment. Taking advantage of different therapeutic agents that affect multiple pathways has been established as highly productive. Nevertheless, owing to several hindrances to conventional combination therapy, such as lack of tumor targeting, non-uniform pharmacokinetic of the combined drugs, and off-target side effects, it is well documented that this treatment approach is unlikely to address all the difficulties observed in monotherapy. Co-delivery systems could enhance the therapeutic efficacy of the combination therapy by targeting cancer cells and improving the pharmacokinetic and physicochemical properties of the therapeutic agents. Nevertheless, it seems that present knowledge in responding to the challenges in cancer treatment is still inadequate and far from optimal treatment, which highlights the urgent need for systematic studies direct to identify various aspects of co-delivery systems. Accordingly, to gather informative data, save time, and achieve superior results, the following steps are necessary: (1) implementing computational methods to predict drug-drug interactions (DDIs) in vitro and in vivo, (2) meticulous cancer studies at the cellular and molecular levels to obtain specific criteria for selecting preclinical and clinical models, (3) extensive physiological and pharmacokinetic study of nanocarriers behavior in preclinical models, and (4) finding the optimal formulation and analyzing its behavior in cellular and animal models facilitates bridging in vivo models to clinical trials. This review aims to deliver an overview of co-delivery systems, rationales, and suggestions for further studies in this field.

Translational Development of a Zr-89-Labeled Inhibitor of Prostate-specific Membrane Antigen for PET Imaging in Prostate Cancer

Purpose

We present here a Zr-89-labeled inhibitor of prostate-specific membrane antigen (PSMA) as a complement to the already established F-18- or Ga-68-ligands.

Procedures

The precursor PSMA-DFO (ABX) was used for Zr-89-labeling. This is not an antibody, but a peptide analogue of the precursor for the production of [¹⁷⁷Lu]Lu-PSMA-617. The ligand [⁸⁹Zr]Zr-PSMA-DFO was compared with [⁶⁸Ga]Ga-PSMA-11 and [¹⁸F]F-JK-PSMA-7 in vitro by determination of the K_d value, cellular uptake, internalization in LNCaP cells, biodistribution studies with LNCaP prostate tumor xenografts in mice, and in vivo by small-animal PET imaging in LNCaP tumor mouse models. A first-in-human PET was performed with [⁸⁹Zr]Zr-PSMA-DFO on a patient presenting with a biochemical recurrence after brachytherapy and an ambiguous intraprostatic finding with [¹⁸F]F-JK-PSMA-7 but histologically benign cells in a prostate biopsy 7 months previously.

Results

[⁸⁹Zr]Zr-PSMA-DFO was prepared with a radiochemical purity ≥ 99.9% and a very high in vitro stability for up to 7 days at 37 °C. All radiotracers showed similar specific cellular binding and internalization, in vitro and comparable tumor uptake in biodistribution experiments during the first 5 h. The [⁸⁹Zr]Zr-PSMA-DFO achieved significantly higher tumor/background ratios in LNCaP tumor xenografts (tumor/blood: 309 ± 89, tumor/muscle: 450 ± 38) after 24 h than [⁶⁸Ga]Ga-PSMA-11 (tumor/blood: 112 ± 57, tumor/muscle: 58 ± 36) or [¹⁸F]F-JK-PSMA-7 (tumor/blood: 175 ± 30, tumor/muscle: 114 ± 14) after 4 h (p < 0.01). Small-animal PET imaging demonstrated in vivo that tumor visualization with [⁸⁹Zr]Zr-PSMA-DFO is comparable to [⁶⁸Ga]Ga-PSMA-11 or [¹⁸F]F-JK-PSMA-7 at early time points (1 h p.i.) and that PET scans up to 48 h p.i. clearly visualized the tumor at late time points. A late [⁸⁹Zr]Zr-PSMA-DFO PET scan on a patient with biochemical recurrence (BCR) had demonstrated intensive tracer accumulation in the right (SUV_max 13.25, 48 h p.i.) and in the left prostate lobe (SUV max 9.47), a repeat biopsy revealed cancer cells on both sides.

Conclusion

[⁸⁹Zr]Zr-PSMA-DFO is a promising PSMA PET tracer for detection of tumor areas with lower PSMA expression and thus warrants further clinical evaluation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11307-021-01632-x.

Strategies and Approaches for Discovery of Small Molecule Disruptors of Biofilm Physiology

Biofilms, the predominant growth mode of microorganisms, pose a significant risk to human health. The protective biofilm matrix, typically composed of exopolysaccharides, proteins, nucleic acids, and lipids, combined with biofilm-grown bacteria’s heterogenous physiology, leads to enhanced fitness and tolerance to traditional methods for treatment. There is a need to identify biofilm inhibitors using diverse approaches and targeting different stages of biofilm formation. This review discusses discovery strategies that successfully identified a wide range of inhibitors and the processes used to characterize their inhibition mechanism and further improvement. Additionally, we examine the structure–activity relationship (SAR) for some of these inhibitors to optimize inhibitor activity.

Impact of Endocytosis Mechanisms for the Receptors Targeted by the Currently Approved Antibody-Drug Conjugates (ADCs)-A Necessity for Future ADC Research and Development

Biologically-based therapies increasingly rely on the endocytic cycle of internalization and exocytosis of target receptors for cancer therapies. However, receptor trafficking pathways (endosomal sorting (recycling, lysosome localization) and lateral membrane movement) are often dysfunctional in cancer. Antibody-drug conjugates (ADCs) have revitalized the concept of targeted chemotherapy by coupling inhibitory antibodies to cytotoxic payloads. Significant advances in ADC technology and format, and target biology have hastened the FDA approval of nine ADCs (four since 2019). Although the links between aberrant endocytic machinery and cancer are emerging, the impact of dysregulated internalization processes of ADC targets and response rates or resistance have not been well studied. This is despite the reliance on ADC uptake and trafficking to lysosomes for linker cleavage and payload release. In this review, we describe what is known about all the target antigens for the currently approved ADCs. Specifically, internalization efficiency and relevant intracellular sorting activities are described for each receptor under normal processes, and when complexed to an ADC. In addition, we discuss aberrant endocytic processes that have been directly linked to preclinical ADC resistance mechanisms. The implications of endocytosis in regard to therapeutic effectiveness in the clinic are also described. Unexpectedly, information on endocytosis is scarce (absent for two receptors). Moreover, much of what is known about endocytosis is not in the context of receptor-ADC/antibody complexes. This review provides a deeper understanding of the pertinent principles of receptor endocytosis for the currently approved ADCs.

Nanoparticles for Targeted Drug Delivery to Cancer Stem Cells: A Review of Recent Advances

Cancer stem cells (CSCs) are a subpopulation of cells that can initiate, self-renew, and sustain tumor growth. CSCs are responsible for tumor metastasis, recurrence, and drug resistance in cancer therapy. CSCs reside within a niche maintained by multiple unique factors in the microenvironment. These factors include hypoxia, excessive levels of angiogenesis, a change of mitochondrial activity from aerobic aspiration to aerobic glycolysis, an upregulated expression of CSC biomarkers and stem cell signaling, and an elevated synthesis of the cytochromes P450 family of enzymes responsible for drug clearance. Antibodies and ligands targeting the unique factors that maintain the niche are utilized for the delivery of anticancer therapeutics to CSCs. In this regard, nanomaterials, specifically nanoparticles (NPs), are extremely useful as carriers for the delivery of anticancer agents to CSCs. This review covers the biology of CSCs and advances in the design and synthesis of NPs as a carrier in targeting cancer drugs to the CSC subpopulation of cancer cells. This review includes the development of synthetic and natural polymeric NPs, lipid NPs, inorganic NPs, self-assembling protein NPs, antibody-drug conjugates, and extracellular nanovesicles for CSC targeting.

Linker Design Impacts Antibody-Drug Conjugate Pharmacokinetics and Efficacy via Modulating the Stability and Payload Release Efficiency

The development of antibody-drug conjugates (ADCs) has significantly been advanced in the past decade given the improvement of payloads, linkers and conjugation methods. In particular, linker design plays a critical role in modulating ADC stability in the systemic circulation and payload release efficiency in the tumors, which thus affects ADC pharmacokinetic (PK), efficacy and toxicity profiles. Previously, we have investigated key linker parameters such as conjugation chemistry (e.g., maleimide vs. disulfide), linker length and linker steric hindrance and their impacts on PK and efficacy profiles. Herein, we discuss our perspectives on development of integrated strategies for linker design to achieve a balance between ADC stability and payload release efficiency for desired efficacy in antigen-expressing xenograft models. The strategies have been successfully applied to the design of site-specific THIOMAB^TM antibody-drug conjugates (TDCs) with different payloads. We also propose to conduct dose fractionation studies to gain guidance for optimal dosing regimens of ADCs in pre-clinical models.

Breast cancer immunotherapy: Current and novel approaches

The crucial role of the immune system in the progression/regression of breast cancer (BC) should always be taken into account. Various immunotherapy approaches have been investigated for BC, including tumor-targeting antibodies (bispecific antibodies), adoptive T cell therapy, vaccines, and immune checkpoint blockade such as anti-PD-1. In addition, a combination of conventional chemotherapy and immunotherapy approaches contributes to improving patients' overall survival rates. Although encouraging outcomes have been reported in most clinical trials of immunotherapy, some obstacles should still be resolved in this regard. Recently, personalized immunotherapy has been proposed as a potential complementary medicine with immunotherapy and chemotherapy for overcoming BC. Accordingly, this review discusses the brief association of these methods and future directions in BC immunotherapy.

A Review on Cancer Immunotherapy and Applications of Nanotechnology to Chemoimmunotherapy of Different Cancers

Clinically, different approaches are adopted worldwide for the treatment of cancer, which still ranks second among all causes of death. Immunotherapy for cancer treatment has been the focus of attention in recent years, aiming for an eventual antitumoral effect through the immune system response to cancer cells both prophylactically and therapeutically. The application of nanoparticulate delivery systems for cancer immunotherapy, which is defined as the use of immune system features in cancer treatment, is currently the focus of research. Nanomedicines and nanoparticulate macromolecule delivery for cancer therapy is believed to facilitate selective cytotoxicity based on passive or active targeting to tumors resulting in improved therapeutic efficacy and reduced side effects. Today, with more than 55 different nanomedicines in the market, it is possible to provide more effective cancer diagnosis and treatment by using nanotechnology. Cancer immunotherapy uses the body's immune system to respond to cancer cells; however, this may lead to increased immune response and immunogenicity. Selectivity and targeting to cancer cells and tumors may lead the way to safer immunotherapy and nanotechnology-based delivery approaches that can help achieve the desired success in cancer treatment.

Exatecan Antibody Drug Conjugates Based on a Hydrophilic Polysarcosine Drug-Linker Platform

We herein report the development and evaluation of a novel HER2-targeting antibody-drug conjugate (ADC) based on the topoisomerase I inhibitor payload exatecan, using our hydrophilic monodisperse polysarcosine (PSAR) drug-linker platform (PSARlink). In vitro and in vivo experiments were conducted in breast and gastric cancer models to characterize this original ADC and gain insight about the drug-linker structure-activity relationship. The inclusion of the PSAR hydrophobicity masking entity efficiently reduced the overall hydrophobicity of the conjugate and yielded an ADC sharing the same pharmacokinetic profile as the unconjugated antibody despite the high drug-load of the camptothecin-derived payload (drug-antibody ratio of 8). Tra-Exa-PSAR10 demonstrated strong anti-tumor activity at 1 mg/kg in an NCI-N87 xenograft model, outperforming the FDA-approved ADC DS-8201a (Enhertu), while being well tolerated in mice at a dose of 100 mg/kg. In vitro experiments showed that this exatecan-based ADC demonstrated higher bystander killing effect than DS-8201a and overcame resistance to T-DM1 (Kadcyla) in preclinical HER2+ breast and esophageal models, suggesting potential activity in heterogeneous and resistant tumors. In summary, the polysarcosine-based hydrophobicity masking approach allowsfor the generation of highly conjugated exatecan-based ADCs having excellent physicochemical properties, an improved pharmacokinetic profile, and potent in vivo anti-tumor activity.

Fermentation, Purification, and Tumor Inhibition of a Disulfide-Stabilized Diabody Against Fibroblast Growth Factor-2

Angiogenesis is considered one of the hallmarks of cancer and plays a critical role in the development of tumor. Fibroblast growth factor 2 (FGF-2) is a member of the FGF family and participates in excessive cancer cell proliferation and tumor angiogenesis. Thus, targeting FGF-2 was considered to be a promising anti-tumor strategy. A disulfide-stabilized diabody (ds-Diabody) against FGF-2 was produced in Pichia pastoris (GS115) by fermentation and the anti-tumor activity was analyzed. The novel 10-L fed batch fermentation with newly designed media was established, and the maximum production of the ds-Diabody against FGF-2 reached 210.4 mg/L. The ds-Diabody against FGF-2 was purified by Ni²⁺ affinity chromatography and DEAE anion exchange chromatography. The recombinant ds-Diabody against FGF-2 could effectively inhibit proliferation, migration, and invasion of melanoma and glioma tumor cells stimulated by FGF-2. Furthermore, xenograft tumor model assays showed that the ds-Diabody against FGF-2 had potent antitumor activity in nude mice by inhibiting tumor growth and angiogenesis. The tumor growth inhibition rate of melanoma and glioma was about 70 and 45%, respectively. The tumor angiogenesis inhibition rate of melanoma and glioma was about 64 and 51%, respectively. The results revealed that the recombinant ds-Diabody against FGF-2 may be a promising anti-tumor drug for cancer therapy.

An Overview of Potential Therapeutic Agents Targeting WNT/PCP Signaling

Since the discovery of the proto-oncogene Wnt1 (Int1) in 1982, WNT signaling has been identified as one of the most important pathways that regulates a wide range of fundamental developmental and physiological processes in multicellular organisms. The canonical WNT signaling pathway depends on the stabilization and translocation of β-catenin and plays important roles in development and homeostasis. The WNT/planar cell polarity (WNT/PCP) signaling, also known as one of the β-catenin-independent WNT pathways, conveys directional information to coordinate polarized cell behaviors. Similar to WNT/β-catenin signaling, disruption or aberrant activation of WNT/PCP signaling also underlies a variety of developmental defects and cancers. However, the pharmacological targeting of WNT/PCP signaling for therapeutic purposes remains largely unexplored. In this review, we briefly discuss WNT/PCP signaling in development and disease and summarize the known drugs/inhibitors targeting this pathway.

Thomas O, Barraja P, Gaudêncio SP, Bertoni F. Marine Anticancer Agents: An Overview with a Particular Focus on Their Chemical Classes

The marine environment is a rich source of biologically active molecules for the treatment of human diseases, especially cancer. The adaptation to unique environmental conditions led marine organisms to evolve different pathways than their terrestrial counterparts, thus producing unique chemicals with a broad diversity and complexity. So far, more than 36,000 compounds have been isolated from marine micro- and macro-organisms including but not limited to fungi, bacteria, microalgae, macroalgae, sponges, corals, mollusks and tunicates, with hundreds of new marine natural products (MNPs) being discovered every year. Marine-based pharmaceuticals have started to impact modern pharmacology and different anti-cancer drugs derived from marine compounds have been approved for clinical use, such as: cytarabine, vidarabine, nelarabine (prodrug of ara-G), fludarabine phosphate (pro-drug of ara-A), trabectedin, eribulin mesylate, brentuximab vedotin, polatuzumab vedotin, enfortumab vedotin, belantamab mafodotin, plitidepsin, and lurbinectedin. This review focuses on the bioactive molecules derived from the marine environment with anticancer activity, discussing their families, origin, structural features and therapeutic use.