Pharmacovigilance study of the association between peripheral neuropathy and antibody-drug conjugates using the FDA adverse event reporting system

Antibody-drug conjugates (ADCs) are among the fastest-growing classes of anticancer drugs, making it crucial to evaluate their potential for causing peripheral neuropathy. We analyzed data from the FAERS database (January 1, 2014, to June 30, 2023) using disproportionality and Bayesian methods. We identified 3076 cases of ADC-associated peripheral neuropathy. Our study revealed significant signals for all ADCs (ROR 1.82, 95% CI 1.76-1.89). ADCs with tubulin-binding payloads showed significant peripheral neuropathy signals (ROR 2.31, 95% CI 2.23-2.40), whereas those with DNA-targeting (ROR 0.48, 95% CI 0.39-0.59) and topoisomerase 1 inhibitor (ROR 0.56, 95% CI 0.48-0.66) payloads exhibited non-significant signals. Signals for peripheral sensory neuropathy were 4.83, 2.44, 2.74, and 2.21 (calculated based on IC025) for brentuximab vedotin, trastuzumab emtansine, enfortumab vedotin, and polatuzumab vedotin, while signals for peripheral motor neuropathy were 5.31, 0.34, 2.27, and 0.03, respectively. The median time to onset for all ADCs was 127 days (interquartile range 40-457). Tisotumab vedotin had the highest hospitalization rate at 26.67%, followed by brentuximab vedotin at 25.5%. Trastuzumab emtansine had the highest mortality rate ,with 80 deaths (11.96%) among 669 cases. Based on FAERS database, only ADCs with tubulin-binding payloads exhibited significant peripheral neuropathy signals. Brentuximab vedotin and enfortumab vedotin showed similar profiles for peripheral sensory neuropathy and motor neuropathy. Given the delayed time to onset and potentially poor outcomes, ADC-related peripheral neuropathy warrants significant attention.

Clinical and preclinical advances in PSMA-Directed Antibody-Drug conjugates (ADCs): Current status and hope for the future

Prostate-specific membrane antigen (PSMA) is a type II membrane glycoprotein overexpressed in a variety of tumors, especially in nearly all prostate cancers, which makes it a potentially attractive antigen for targeted cancer therapies. More importantly, PSMA, due to no shedding into circulation and efficient internalization after antibody binding, becomes a potential target for antibody-drug conjugates (ADCs), a valid and emerging paradigm of cancer treatment. Four and eight PSMA-directed ADCs have been or are currently being investigated in clinical trials (three of which failed to confirm the promising results while one is currently being evaluated in an ongoing clinical study) and preclinical studies, respectively, for the treatment of PSMA-positive solid tumors, especially prostate cancer. The present study aims to completely review clinical- and preclinical-stage PSMA-directed ADCs.

The combination of immune checkpoint inhibitors and antibody-drug conjugates in the treatment of urogenital tumors: a review insights from phase 2 and 3 studies

With the high incidence of urogenital tumors worldwide, urinary system tumors are among the top 10 most common tumors in men, with prostate cancer ranking first and bladder cancer fourth. Patients with resistant urogenital tumors often have poor prognosis. In recent years, researchers have discovered numerous specific cancer antigens, which has led to the development of several new anti-cancer drugs. Using protein analysis techniques, researchers developed immune checkpoint inhibitors (ICIs) and antibody-conjugated drugs (ADCs) for the treatment of advanced urogenital tumors. However, tumor resistance often leads to the failure of monotherapy. Therefore, clinical trials of the combination of ICIs and ADCs have been carried out in numerous centers around the world. This article reviewed phase 2 and 3 clinical studies of ICIs, ADCs, and their combination in the treatment of urogenital tumors to highlight safe and effective methods for selecting individualized therapeutic strategies for patients. ICIs activate the immune system, whereas ADCs link monoclonal antibodies to toxins, which can achieve a synergistic effect when the two drugs are combined. This synergistic effect provides multiple advantages for the treatment of urogenital tumors.

Innovative Drug Modalities for the Treatment of Advanced Prostate Cancer

Prostate cancer, a prevalent malignancy affecting the prostate gland, is a significant global health concern. Androgen-deprivation therapy (ADT) has proven effective in controlling advanced disease, with over 50% of patients surviving at the 10-year mark. However, a diverse spectrum of responses exists, and resistance to ADT may emerge over time. This underscores the need to explore innovative treatment strategies for effectively managing prostate cancer progression. Ongoing research endeavors persist in unraveling the complexity of prostate cancer and fostering the development of biologic and innovative approaches, including immunotherapies and targeted therapies. This review aims to provide a valuable synthesis of the dynamic landscape of emerging drug modalities in this context. Interestingly, the complexities posed by prostate cancer not only present a formidable challenge but also serve as a model and an opportunity for translational research and innovative therapies in the field of oncology.

Development and therapeutic evaluation of 5D3(CC-MLN8237)3.2 antibody-theranostic conjugates for PSMA-positive prostate cancer therapy

Prostate cancer (PC) is an aggressive cancer that can progress rapidly and eventually become castrate-resistant prostate cancer (CRPC). Stage IV metastatic castrate-resistant prostate cancer (mCRPC) is an incurable late-stage cancer type with a low 5-year overall survival rate. Targeted therapeutics such as antibody-drug conjugates (ADCs) based on high-affinity monoclonal antibodies and potent drugs conjugated via smart linkers are being developed for PC management. Conjugating further with in vitro or in vivo imaging agents, ADCs can be used as antibody-theranostic conjugates (ATCs) for diagnostic and image-guided drug delivery. In this study, we have developed a novel ATC for PSMA (+) PC therapy utilizing (a) anti-PSMA 5D3 mAb, (b) Aurora A kinase inhibitor, MLN8237, and (c) for the first time using tetrazine (Tz) and trans-cyclooctene (TCO) click chemistry-based conjugation linker (CC linker) in ADC development. The resulting 5D3(CC-MLN8237)3.2 was labeled with suitable fluorophores for in vitro and in vivo imaging. The products were characterized by SDS-PAGE, MALDI-TOF, and DLS and evaluated in vitro by optical imaging, flow cytometry, and WST-8 assay for cytotoxicity in PSMA (+/-) cells. Therapeutic efficacy was determined in human PC xenograft mouse models following a designed treatment schedule. After the treatment study animals were euthanized, and toxicological studies, complete blood count (CBC), blood clinical chemistry analysis, and H&E staining of vital organs were conducted to determine side effects and systemic toxicities. The IC50 values of 5D3(CC-MLN8237)3.2-AF488 in PSMA (+) PC3-PIP and PMSA (-) PC3-Flu cells are 8.17 nM and 161.9 nM, respectively. Pure MLN8237 shows 736.9 nM and 873.4 nM IC50 values for PC3-PIP and PC3-Flu cells, respectively. In vivo study in human xenograft mouse models confirmed high therapeutic efficacy of 5D3(CC-MLN8237)3.2-CF750 with significant control of PSMA (+) tumor growth with minimal systemic toxicity in the treated group compared to PSMA (-) treated and untreated groups. Approximately 70% of PSMA (+) PC3-PIP tumors did not exceed the threshold of the tumor size in the surrogate Kaplan-Meyer analysis. The novel ATC successfully controlled the growth of PSMA (+) tumors in preclinical settings with minimal systemic toxicities. The therapeutic efficacy and favorable safety profile of novel 5D3(CC-MLN8237)3.2 ATC demonstrates their potential use as a theranostic against aggressive PC.

Advances in non-radioactive PSMA-targeted small molecule-drug conjugates in the treatment of prostate cancer

Most patients with advanced prostate cancer (PCa) will develop metastatic castration-resistant prostate cancer (mCRPC) after androgen deprivation therapy, at this time the tumor enters the end stage, and the clinical treatment is very complicated, which requires rationalization of drugs to prolong the life of patients while improving their quality of life. Prostate-specific membrane antigen (PSMA) is a promising biological target for drug delivery in mCRPC due to its high level of specific expression in PCa cell membranes and low expression in normal tissues. Non-radioactive PSMA-targeted small molecule-drug conjugates (SMDCs) are gradually becoming a heat of discovery due to their good affinity and specificity; simple synthesis steps and transport management methods. Non-radioactive PSMA-targeted SMDCs under investigation can be divided into two categories: SMDCs and dual-ligand coupled drugs, among which SMDCs are the most widespread form of this type of conjugate. SMDCs have three key components: cytotoxic load, linker, and small molecule targeting ligands. SMDCs are internalized into the cell after binding to PSMA on the cell membrane and stored in endosomes and lysosomes, where they are usually enzymatically cleaved to allow precise release of cytotoxic molecules and uniform diffusion into the tumor tissue. More than a dozen non-radioactive PSMA-targeted SMDCs have been developed, many of which have shown favorable properties in both in vitro and in vivo evaluations, demonstrating more favorable results than unmodified cytotoxic drugs. Therefore, non-radioactive PSMA-targeted SMDCs have great therapeutic potential for mCRPC as a form of targeted therapy.

The new era of prostate-specific membrane antigen-directed immunotherapies and beyond in advanced prostate cancer: a review

The lack of success in prostate cancer from immune checkpoint inhibitors, which is likely multifactorial, has led to the development and investigation of a number of other novel immunotherapeutic techniques, including antibody-drug conjugates, T-cell redirected bispecific therapies, cancer vaccines and chimeric antigen receptor T-cell therapies. Prostate-specific membrane antigen (PSMA) is a tumour-associated antigen (TAA) that is highly expressed in metastatic prostate cancer and has been validated as an effective target for radionuclide treatment. But while PSMA has thus far been the 'front runner' target for these novel immunotherapeutic techniques, it may not be the ideal target for immunotherapy and there are other potential targetable TAAs that will require further exploration. This review will focus on these various PSMA-directed therapies, as well as other potential targets for immunotherapy beyond PSMA.

Understanding the activity of antibody-drug conjugates in primary and secondary brain tumours

Antibody-drug conjugates (ADCs), a class of targeted cancer therapeutics combining monoclonal antibodies with a cytotoxic payload via a chemical linker, have already been approved for the treatment of several cancer types, with extensive clinical development of novel constructs ongoing. Primary and secondary brain tumours are associated with high mortality and morbidity, necessitating novel treatment approaches. Pharmacotherapy of brain tumours can be limited by restricted drug delivery across the blood-brain or blood-tumour barrier, although data from phase II studies of the HER2-targeted ADC trastuzumab deruxtecan indicate clinically relevant intracranial activity in patients with brain metastases from HER2⁺ breast cancer. However, depatuxizumab mafodotin, an ADC targeting wild-type EGFR and EGFR variant III, did not provide a definitive overall survival benefit in patients with newly diagnosed or recurrent EGFR-amplified glioblastoma in phase II and III trials, despite objective radiological responses in some patients. In this Review, we summarize the available data on the central nervous system activity of ADCs from trials involving patients with primary and secondary brain tumours and discuss their clinical implications. Furthermore, we explore pharmacological determinants of intracranial activity and discuss the optimal design of clinical trials to facilitate development of ADCs for the treatment of gliomas and brain metastases.

Antibody-Drug Conjugates in Prostate Cancer: Where Are we?

Antibody-drug conjugates (ADCs) reflect a new promising approach in prostate cancer, even more so after the practice-changing results in other malignancies, either hematologic or solid. ADCs consist of monoclonal antibodies (mAb) targeted at specific antigens overly expressed on cancer cells compared to normal cells. A cytotoxic payload is attached to the mAb using a stable linker. In prostate cancer, PSMA, STEAP1, TROP2, CD46 and B7-H3 are antigens currently being studied as targets for ADCs. In this paper, we discuss the composition of ADCs and focus on their application and challenges as treatment options in prostate cancer.

Mechanisms of ADC Toxicity and Strategies to Increase ADC Tolerability

Anti-cancer antibody-drug conjugates (ADCs) aim to expand the therapeutic index of traditional chemotherapy by employing the targeting specificity of monoclonal antibodies (mAbs) to increase the efficiency of the delivery of potent cytotoxic agents to malignant cells. In the past three years, the number of ADCs approved by the Food and Drug Administration (FDA) has tripled. Although several ADCs have demonstrated sufficient efficacy and safety to warrant FDA approval, the clinical use of all ADCs leads to substantial toxicity in treated patients, and many ADCs have failed during clinical development due to their unacceptable toxicity profiles. Analysis of the clinical data has demonstrated that dose-limiting toxicities (DLTs) are often shared by different ADCs that deliver the same cytotoxic payload, independent of the antigen that is targeted and/or the type of cancer that is treated. DLTs are commonly associated with cells and tissues that do not express the targeted antigen (i.e., off-target toxicity), and often limit ADC dosage to levels below those required for optimal anti-cancer effects. In this manuscript, we review the fundamental mechanisms contributing to ADC toxicity, we summarize common ADC treatment-related adverse events, and we discuss several approaches to mitigating ADC toxicity.

Prostate-specific Membrane Antigen Biology in Lethal Prostate Cancer and its Therapeutic Implications

CONTEXT

Prostate-specific membrane antigen (PSMA) is a promising, novel theranostic target in advanced prostate cancer (PCa). Multiple PSMA-targeted therapies are currently in clinical development, with some agents showing impressive antitumour activity, although optimal patient selection and therapeutic resistance remain ongoing challenges.

OBJECTIVE

To review the biology of PSMA and recent advances in PSMA-targeted therapies in PCa, and to discuss potential strategies for patient selection and further therapeutic development.

EVIDENCE ACQUISITION

A comprehensive literature search was performed using PubMed and review of American Society of Clinical Oncology and European Society of Medical Oncology annual meeting abstracts up to April 2021.

EVIDENCE SYNTHESIS

PSMA is a largely extracellular protein that is frequently, but heterogeneously, expressed by PCa cells. PSMA expression is associated with disease progression, worse clinical outcomes and the presence of tumour defects in DNA damage repair (DDR). PSMA is also expressed by other cancer cell types and is implicated in glutamate and folate metabolism. It may confer a tumour survival advantage in conditions of cellular stress. PSMA regulation is complex, and recent studies have shed light on interactions with androgen receptor, PI3K/Akt, and DDR signalling. A phase 2 clinical trial has shown that 177Lu-PSMA-617 causes tumour shrinkage and delays disease progression in a significant subset of patients with metastatic castration-resistant PCa in comparison to second-line chemotherapy. Numerous novel PSMA-targeting immunotherapies, small molecules, and antibody therapies are currently in clinical development, including in earlier stages of PCa, with emerging evidence of antitumour activity. To date, the regulation and function of PSMA in PCa cells remain poorly understood.

CONCLUSIONS

There has been rapid recent progress in PSMA-targeted therapies for the management of advanced PCa. Dissection of PSMA biology will help to identify biomarkers for and resistance mechanisms to these therapies and facilitate further therapeutic development to improve PCa patient outcomes.

PATIENT SUMMARY

There have been major advances in the development of therapies targeting a molecule, PSMA, in PCa. Radioactive molecules targeting PSMA can cause tumour shrinkage and delay progression in some patients with lethal disease. Future studies are needed to determine which patients are most likely to respond, and how other treatments can be combined with therapies targeting PSMA so that more patients may benefit.

Targeting signaling pathways in prostate cancer: mechanisms and clinical trials

Prostate cancer (PCa) affects millions of men globally. Due to advances in understanding genomic landscapes and biological functions, the treatment of PCa continues to improve. Recently, various new classes of agents, which include next-generation androgen receptor (AR) signaling inhibitors (abiraterone, enzalutamide, apalutamide, and darolutamide), bone-targeting agents (radium-223 chloride, zoledronic acid), and poly(ADP-ribose) polymerase (PARP) inhibitors (olaparib, rucaparib, and talazoparib) have been developed to treat PCa. Agents targeting other signaling pathways, including cyclin-dependent kinase (CDK)4/6, Ak strain transforming (AKT), wingless-type protein (WNT), and epigenetic marks, have successively entered clinical trials. Furthermore, prostate-specific membrane antigen (PSMA) targeting agents such as ¹⁷⁷Lu-PSMA-617 are promising theranostics that could improve both diagnostic accuracy and therapeutic efficacy. Advanced clinical studies with immune checkpoint inhibitors (ICIs) have shown limited benefits in PCa, whereas subgroups of PCa with mismatch repair (MMR) or CDK12 inactivation may benefit from ICIs treatment. In this review, we summarized the targeted agents of PCa in clinical trials and their underlying mechanisms, and further discussed their limitations and future directions.

Research Trend of Publications Concerning Antibody-Drug Conjugate in Solid Cancer: A Bibliometric Study

Background: Antibody-drug conjugate (ADC) is a promising therapy for solid cancer that has raised global concern. Although several papers have reviewed the current state of ADCs in different solid cancers, a quantitative analysis of the publications in this field is scarce.

Methods: Publications related to ADC in the field of solid cancer were obtained from the Web of Science Core Collection. Data analyses were performed with VOSviewer 1.6.9, HistCite 2.1, CiteSpace V and R package Bibliometrix.

Results: A total of 3,482 records were obtained in the holistic field and 1,197 in the clinical field. Steady growth in the number of publications was observed. The United States was the leading contributor in this field. Krop IE was the most influential author. The most productive institution was Genentech Inc., while Mem Sloan Kettering Canc Ctr was the most cited one. The most impactful journal was the Journal of Clinical Oncology. A total of 37 burst references and five burst references were identified between 2017–2022 in the holistic and clinical fields, respectively. Keywords analysis indicated that ADCs research mainly involved breast cancer, triple-negative breast cancer, ovarian cancer, small cell lung cancer, prostate cancer, gastric cancer, and urothelial carcinoma. ADC agents including trastuzumab emtansine, trastuzumab deruxtecan, sacituzumab govitecan, enfortumab vedotin, and rovalpituzumab tesirine were highly studied. Targets including HER2, trophoblast cell-surface antigen, mesothelin, delta-like ligand 3, and nectin-4 were the major concerns.

Conclusion: This study analyzed publications concerning ADCs in the field of solid cancer with bibliometric analysis. Further clinical trials of ADCs and designs of the next generation of ADCs are the current focuses of the field. Acquired resistance of ADCs and biomarkers for ADC therapy efficacy monitoring are future concerns.

Antibody-Drug Conjugates in Uro-Oncology

Currently available treatment options for patients with refractory metastatic prostate, bladder, or kidney cancers are limited with the prognosis remaining poor. Advances in the pathobiology of tumors has led to the discovery of cancer antigens that may be used as the target for cancer treatment. Antibody-drug conjugates (ADCs) are a relatively new concept in cancer treatment that broaden therapeutic landscape. ADCs are examples of a 'drug delivery into the tumor' system composed of an antigen-directed antibody linked to a cytotoxic drug that may release cytotoxic components after binding to the antigen located on the surface of tumor cells. The clinical properties of drugs are influenced by every component of ADCs. Regarding uro-oncology, enfortumab vedotin (EV) and sacituzumab govitecan (SG) are currently registered for patients with locally advanced or metastatic urothelial cancer following previous treatment with an immune checkpoint inhibitor (iCPI; programmed death receptor-1 [PD-1] or programmed death-ligand 1 [PD-L1]) inhibitor) and platinum-containing chemotherapy. The EV-301 trial showed that EV significantly prolonged the overall survival compared with classic chemotherapy. The TROPHY-U-01 trial conducted to evaluate SG demonstrated promising results as regards the objective response rate and duration of response. The safety and efficacy of ADCs in monotherapy and polytherapy (mainly with iCPIs) for different cancer stages and tumor types are assessed in numerous ongoing clinical trials. The aim of this review is to present new molecular biomarkers, specific mechanisms of action, and ongoing clinical trials of ADCs in genitourinary cancers. In the expert discussion, we assess the place of ADCs in uro-oncology and discuss their clinical value.

Advances in PSMA-targeted therapy for prostate cancer

Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein located on the cell membrane, is specifically and highly expressed in prostate cancer (PCa). Besides, its expression level is related to tumor invasiveness. As a molecular target of PCa, PSMA has been extensively studied in the past two decades. Currently, a great deal of evidence suggests that significant progresses have been made in the PSMA-targeted therapy of PCa. Herein, different PSMA-targeted therapies for PCa are reviewed, including radioligand therapy (177Lu-PSMA-RLT, 225Ac-PSMA-RLT), antibody-drug conjugates (MLN2704, PSMA-MMAE, MEDI3726), cellular immunotherapy (CAR-T, CAR/NK-92, PSMA-targeted BiTE), photodynamic therapy, imaging-guided surgery (radionuclide-guided surgery, fluorescence-guided surgery, multimodal imaging-guided surgery), and ultrasound-mediated nanobubble destruction.

PSMA targeting in metastatic castration-resistant prostate cancer: where are we and where are we going?

Prostate-specific membrane antigen (PSMA) is highly expressed on the membrane of most prostate cancer cells and to a lesser extent in normal tissues. Many vectors targeting this protein have been created over the past decade and numerous clinical studies have positively demonstrated the tolerance and efficacy of radiolabeled prostate-specific membrane antigen ligands for PSMA radioligand therapy (PRLT). Preliminary results are encouraging that PRLT will become an important addition to the current therapeutic options in a number of settings. Improvement in radiopharmaceutical targeting and combination with other oncological agents are under investigation to further improve its therapeutic efficacy. These encouraging results have led to the development of other therapies using PSMA as a target, such as PSMA-targeted chimeric antigen receptor T-cells, PSMA-targeted antibody drug conjugates, and PSMA-targeted bi-specific T-cell-directed therapy. This narrative review details the current state and advancements in prostate-specific membrane antigen targeting in prostate cancer treatment.

Antibodies targeting Prostate-Specific Membrane Antigen positive prostate cancer: from diagnostic imaging to theranostics

PURPOSE OF REVIEW

Targeting Prostate-Specific Membrane Antigen (PSMA) has paved the way for personalized medicine in prostate cancer (PCa) patients. This review aims to highlight the role of PSMA targeting antibodies in PCa, for diagnostic and therapeutic purposes.

RECENT FINDINGS

PSMA Positron Emission Tomography/Computed Tomography has been a game changer in the diagnosis of PCa in the recent decade. Two anti-PSMA monoclonal antibodies have been studied in PCa: 7E11-C35 (limited use) and J591. J591 antibody was used for diagnostic purposes coupled with different radionuclides. Most importantly, it was combined to numerous therapeutic radionuclides such as Lutetium-177 (177Lu), Yttrium-90 (90Y), Indium-111 (111In), and Actinium-225 (225Ac). It was also conjugated to drugs forming antibody-drug conjugates (e.g. MLN2704 and PSMA-ADC). These compounds were tested in recent phase I/II clinical trials.

SUMMARY

PSMA targeting antibodies are very promising for further clinical investigation and continue to be a momentous research area, for both imaging and therapeutic settings. Although some clinical trials resulted in unfavorably safety profiles for some antibodies, they validated PSMA as a crucial immunoconjugate target.

Targeted nanomedicine modalities for prostate cancer treatment

Prostate cancer (PC) is the second most common cause of death amongst men in the USA. Therapy of PC has been transformed in the past decade by introducing novel therapeutics, advanced functional imaging and diagnostic approaches, next generation sequencing, as well as improved application of existing therapies in localized PC. Treatment of PC at the different stages of the disease may include surgery, androgen deprivation therapy (ADT), chemotherapy and radiation therapy. However, although ADT has proven efficacious in PC treatment, its effectiveness may be temporary, as these tumors frequently develop molecular mechanisms of therapy resistance, which allow them to survive and proliferate even under conditions of testosterone deprivation, inhibition of androgen receptor signaling, or cytotoxic drug treatment. Importantly, ADT was found to induce key alterations which frequently result in the formation of metastatic tumors displaying a therapy refractory phenotype. Hence, to overcome these serious therapeutic impediments, novel PC cell-targeted therapeutic strategies are being developed. These include diverse platforms enabling specific enhanced antitumor drug uptake and increased intracellular accumulation. Studies have shown that these novel treatment modalities lead to enhanced antitumor activity and diminished systemic toxicity due to the use of selective targeting and decreased drug doses. The underlying mechanism of targeting and internalization is based upon the interaction between a selective ligand, conjugated to a drug-loaded nanoparticle or directly to an anti-cancer drug, and a specific plasma membrane biomarker, uniquely overexpressed on the surface of PC cells. Another targeted therapeutic approach is the delivery of unique anti-oncogenic signaling pathway-based therapeutic drugs, which are selectively cytotoxic to PC cells. The current paper reviews PC targeted modalities reported in the past 6 years, and discusses both the advantages and limitations of the various targeted treatment strategies.

Treating Prostate Cancer by Antibody-Drug Conjugates

Prostate cancer is the most frequent malignancy in the worldwide male population; it is also one of the most common among all the leading cancer-related death causes. In the last two decades, the therapeutic scenario of metastatic castration-resistant prostate cancer has been enriched by the use of chemotherapy and androgen receptor signaling inhibitors (ARSI) and, more recently, by immunotherapy and poly(ADP–ribose) polymerase (PARP) inhibitors. At the same time, several trials have shown the survival benefits related to the administration of novel ARSIs among patients with non-castration-resistant metastatic disease along with nonmetastatic castration-resistant cancer too. Consequently, the therapeutic course of this malignancy has been radically expanded, ensuring survival benefits never seen before. Among the more recently emerging agents, the so-called “antibody–drug conjugates” (ADCs) are noteworthy because of their clinical practice changing outcomes obtained in the management of other malignancies (including breast cancer). The ADCs are novel compounds consisting of cytotoxic agents (also known as the payload) linked to specific antibodies able to recognize antigens expressed over cancer cells’ surfaces. As for prostate cancer, researchers are focusing on STEAP1, TROP2, PSMA, CD46 and B7-H3 as optimal antigens which may be targeted by ADCs. In this paper, we review the pivotal trials that have currently changed the therapeutic approach to prostate cancer, both in the nonmetastatic castration-resistant and metastatic settings. Therefore, we focus on recently published and ongoing trials designed to investigate the clinical activity of ADCs against prostate malignancy, characterizing these agents. Lastly, we briefly discuss some ADCs-related issues with corresponding strategies to overwhelm them, along with future perspectives for these promising novel compounds.

Small Molecule-Based Prodrug Targeting Prostate Specific Membrane Antigen for the Treatment of Prostate Cancer

Metastatic castration-resistant prostate cancer poses a serious clinical problem with poor outcomes and remains a deadly disease. New targeted treatment options are urgently needed. PSMA is highly expressed in prostate cancer and has been an attractive biomarker for the treatment of prostate cancer. In this study, we explored the feasibility of targeted delivery of an antimitotic drug, monomethyl auristatin E (MMAE), to tumor tissue using a small-molecule based PSMA lig-and. With the aid of Cy5.5, we found that a cleavable linker is vital for the antitumor activity of the ligand-drug conjugate and have developed a new PSMA-targeting prodrug, PSMA-1-VcMMAE. In in vitro studies, PSMA-1-VcMMAE was 48-fold more potent in killing PSMA-positive PC3pip cells than killing PSMA-negative PC3flu cells. In in vivo studies, PSMA-1-VcMMAE significantly inhibited tumor growth leading to prolonged animal survival in different animal models, including metastatic prostate cancer models. Compared to anti-PSMA antibody-MMAE conjugate (PSMA-ADC) and MMAE, PSMA-1-VcMMAE had over a 10-fold improved maximum tolerated dose, resulting in improved therapeutic index. The small molecule-drug conjugates reported here can be easily synthesized and are more cost efficient than anti-body-drug conjugates. The therapeutic profile of the PSMA-1-VcMMAE encourages further clin-ical development for the treatment of advanced prostate cancer.

Immunotherapy in prostate cancer: current state and future perspectives

Metastatic castrate resistant prostate cancer (PCa) remains an incurable entity. In the era of immunotherapy, the complex PCa microenvironment poses a unique challenge to the successful application of this class of agents. However, in the last decade, a tremendous effort has been made to explore this field of therapeutics. In this review, the physiology of the cancer immunity cycle is highlighted in the context of the prostate tumor microenvironment, and the current evidence for use of various classes of immunotherapy agents including vaccines (dendritic cell based, viral vector based and DNA/mRNA based), immune checkpoint inhibitors, Chimeric antigen receptor T cell therapy, antibody-mediated radioimmunotherapy, antibody drug conjugates, and bispecific antibodies, is consolidated. Finally, the future directions for combinatorial approaches to combat PCa are discussed.

Development of 5D3-DM1: A Novel Anti-Prostate-Specific Membrane Antigen Antibody-Drug Conjugate for PSMA-Positive Prostate Cancer Therapy

Prostate cancer (PC) is a potentially high-risk disease and the most common cancer in American men. It is a leading cause of cancer-related deaths in men in the US, second only to lung and bronchus cancer. Advanced and metastatic PC is initially treated with androgen deprivation therapy (ADT), but nearly all cases eventually progress to castrate-resistant prostate cancer (CRPC). CRPC is incurable in the metastatic stage but can be slowed by some conventional chemotherapeutics and second-generation ADT, such as enzalutamide and abiraterone. Therefore, novel therapeutic strategies are urgently needed. Prostate-specific membrane antigen (PSMA) is overexpressed in almost all aggressive PCs. PSMA is widely used as a target for PC imaging and drug delivery. Anti-PSMA monoclonal antibodies (mAbs) have been developed as bioligands for diagnostic imaging and targeted PC therapy. However, these mAbs are successfully used in PC imaging and only a few have gone beyond phase-I for targeted therapy. The 5D3 mAb is a novel, high-affinity, and fast-internalizing anti-PSMA antibody. Importantly, 5D3 mAb demonstrates a unique pattern of cellular localization to the centrosome after internalization in PSMA(+) PC3-PIP cells. These characteristics make 5D3 mAb an ideal bioligand to deliver tubulin inhibitors, such as mertansine, to the cell centrosome, leading to mitotic arrest and elimination of dividing PC cells. We have successfully developed a 5D3 mAb- and mertansine (DM1)-based antibody-drug conjugate (ADC) and evaluated it in vitro for binding affinity, internalization, and cytotoxicity. The in vivo therapeutic efficacy of 5D3-DM1 ADC was evaluated in PSMA(+) PC3-PIP and PSMA(-) PC3-Flu mouse models of human PC. This therapeutic study has revealed that this new anti-PSMA ADC can successfully control the growth of PSMA(+) tumors without inducing systemic toxicity.

Patient Selection Strategies to Maximize Therapeutic Index of Antibody-Drug Conjugates: Prior Approaches and Future Directions

Antibody-drug conjugates (ADC) are targeted agents that have shown promise in treating cancer. A central challenge in development of ADCs is the relatively narrow therapeutic index observed in clinical studies. Patient selection strategies based on expression of the target in tumors have the potential to maximize benefit and provide the best chance of clinical success; however, implementation of biomarker-driven trials can be difficult both practically and scientifically. We conducted a survey of recent clinical experience from early-phase ADC trials completed between 2000 and 2019 to evaluate the different approaches to patient selection currently being used and assess whether there is evidence that target expression is associated with clinical activity. Our analysis of patient selection strategies indicates that optimal trial design for early-stage trials should be based on multiple factors, including prevalence and heterogeneity of target expression among intent-to-treat patients, as well as biological factors influencing expression of cell surface and soluble target. To ensure a high probability of success, early implementation of patient selection strategies centered around target expression are pivotal to development of ADCs. In this review, we propose a strategic approach that can be applied for optimization of trial design.

Targeted Radionuclide Therapy of Prostate Cancer-From Basic Research to Clinical Perspectives

Prostate cancer is the most commonly diagnosed malignancy in men and the second leading cause of cancer-related deaths in Western civilization. Although localized prostate cancer can be treated effectively in different ways, almost all patients progress to the incurable metastatic castration-resistant prostate cancer. Due to the significant mortality and morbidity rate associated with the progression of this disease, there is an urgent need for new and targeted treatments. In this review, we summarize the recent advances in research on identification of prostate tissue-specific antigens for targeted therapy, generation of highly specific and selective molecules targeting these antigens, availability of therapeutic radionuclides for widespread medical applications, and recent achievements in the development of new-generation small-molecule inhibitors and antibody-based strategies for targeted prostate cancer therapy with alpha-, beta-, and Auger electron-emitting radionuclides.

Prostate-specific Membrane Antigen Based Antibody-drug Conjugates for Metastatic Castration-resistance Prostate Cancer

Cancer cells can be selectively targeted by identifying and developing antibodies to specific antigens present on the cancer cell surface. Cytotoxic agents can be conjugated to these antibodies that bind to these cell surface antigens in order to significantly increase the therapeutic index of whichever cytotoxic agent is utilized. This approach of conjugating the cytotoxic drugs to antibodies to target specific surface antigens enhances the anti-tumor activity of antibodies and improves the tumor-to-normal tissue selectivity of chemotherapy. Critical parameters in the development of these antibody-drug conjugates include: 1) selection of most appropriate antigen, 2) the ability of an antibody to be internalized after binding to the antigen, 3) cytotoxic drug potency and 4) stability of the antibody-drug conjugate. For prostate cancer, prostate-specific membrane antigen (PSMA, also known as folate hydrolase-1) is the most validated theragnostic target to date. PSMA is overexpressed on the prostate cancer cell surface, which makes it an even better target for selective drug delivery through conjugated antibodies. Here, we review the PSMA-based antibody-drug conjugates for metastatic castration-resistance prostate cancer (mCRPC).

Trends in Therapeutic Conjugates: Bench to Clinic

In recent years, therapeutic conjugates have attracted considerable attention as a new class of drug due to their unique pharmacological properties, especially from the pharmaceutical community. Their molecular structure tunability, improved targeting specificity, and therapeutic efficacy have been demonstrated in a wide range of research and clinical applications. In this topical review, we summarize selected recent advances in bioconjugation strategies for the development of therapeutic conjugates, their emerging application in clinical settings, as well as perspectives on the direction of future research.

Safety and Efficacy of BIND-014, a Docetaxel Nanoparticle Targeting Prostate-Specific Membrane Antigen for Patients With Metastatic Castration-Resistant Prostate Cancer: A Phase 2 Clinical Trial

Importance

Preferential delivery of docetaxel to tumors by prostate-specific membrane antigen (PSMA)-targeted nanoparticles is clinically effective, and the selective reduction of PSMA-positive circulating tumor cells (CTCs) after treatment has implications for patient selection and disease monitoring.

Objective

To determine the safety and efficacy of BIND-014, a PSMA-directed docetaxel-containing nanoparticle, in patients with metastatic castration-resistant prostate cancer (mCRPC).

Design, Setting, and Participants

A multicenter open-label, phase 2 clinical trial of 42 chemotherapy-naive patients with progressing mCRPC after treatment with abiraterone acetate and/or enzalutamide was conducted from June 24, 2013, to June 10, 2016.

Intervention

Treatment with BIND-014 at a dosage of 60 mg/m2 was given intravenously on day 1 of 21-day cycles in combination with prednisone until disease progression or unacceptable toxic effects occurred.

Main Outcomes and Measures

The primary end point was radiographic progression-free survival according to Prostate Cancer Working Group 2 recommendations and Response Evaluation Criteria in Solid Tumors, version 1.1. Secondary end points included prostate-specific antigen (PSA) response (≥50% reduction from baseline) and changes in CTC number (from ≥5 to <5 cells per 7.5 mL of blood) (CellSearch). Changes in CTC number based on PSMA expression levels on CTCs were also evaluated (Epic Sciences).

Results

Among the 42 patients (81% white), the median age was 66 (range, 50-85) years, and median number of doses received was 6 (range, 1-21). A PSA response was observed in 12 of 40 patients (30%; 95% CI, 18%-45%), measurable disease response in 6 of 19 (32% [95% CI, 15%-54%]), and CTC conversions in 13 of 26 (50%; 95% CI, 32%-68%). Median radiographic progression-free survival was 9.9 (95% CI, 7.1-12.6) months. With use of the Epic Sciences non-EPCAM-based CTC detection platform, CTCs were detected in 16 of 18 patients (89%); 11 of 18 (61%) had CTCs with PSMA expression above the analytical threshold level (PSMA positive) at baseline (range, 0.4-72.4 CTCs/mL). After treatment, PSMA-positive CTCs were preferentially reduced. Treatment-related adverse events included grade 1 or 2 fatigue (29 of 42 patients [69%]), nausea (23 [55%]), neuropathy (14 [33%]), and neutropenic fever (1 [2%]).

Conclusions and Relevance

These findings suggest that treatment with BIND-014 is active and well tolerated in patients with chemotherapy-naive mCRPC. Antitumor activity may be related to PSMA expression levels on CTCs, which suggests that patients who are likely to benefit from this treatment can be identified before treatment is initiated.

Trial Registration

ClinicalTrials.gov Identifier: NCT01812746.

Incorporation of a Hydrophilic Spacer Reduces Hepatic Uptake of HER2-Targeting Affibody-DM1 Drug Conjugates

Affibody molecules are small affinity-engineered scaffold proteins which can be engineered to bind to desired targets. The therapeutic potential of using an affibody molecule targeting HER2, fused to an albumin-binding domain (ABD) and conjugated with the cytotoxic maytansine derivate MC-DM1 (AffiDC), has been validated. Biodistribution studies in mice revealed an elevated hepatic uptake of the AffiDC, but histopathological examination of livers showed no major signs of toxicity. However, previous clinical experience with antibody drug conjugates have revealed a moderate- to high-grade hepatotoxicity in treated patients, which merits efforts to also minimize hepatic uptake of the AffiDCs. In this study, the aim was to reduce the hepatic uptake of AffiDCs and optimize their in vivo targeting properties. We have investigated if incorporation of hydrophilic glutamate-based spacers adjacent to MC-DM1 in the AffiDC, (Z_HER2:2891)₂-ABD-MC-DM1, would counteract the hydrophobic nature of MC-DM1 and, hence, reduce hepatic uptake. Two new AffiDCs including either a triglutamate-spacer-, (Z_HER2:2891)₂-ABD-E₃-MC-DM1, or a hexaglutamate-spacer-, (Z_HER2:2891)₂-ABD-E₆-MC-DM1 next to the site of MC-DM1 conjugation were designed. We radiolabeled the hydrophilized AffiDCs and compared them, both in vitro and in vivo, with the previously investigated (Z_HER2:2891)₂-ABD-MC-DM1 drug conjugate containing no glutamate spacer. All three AffiDCs demonstrated specific binding to HER2 and comparable in vitro cytotoxicity. A comparative biodistribution study of the three radiolabeled AffiDCs showed that the addition of glutamates reduced drug accumulation in the liver while preserving the tumor uptake. These results confirmed the relation between DM1 hydrophobicity and liver accumulation. We believe that the drug development approach described here may also be useful for other affinity protein-based drug conjugates to further improve their in vivo properties and facilitate their clinical translatability.

Prostate-specific Membrane Antigen (PSMA) Expression in the Neovasculature of Gynecologic Malignancies: Implications for PSMA-targeted Therapy

The goal of the study was to examine expression of prostate-specific membrane antigen (PSMA) in neovasculature of gynecologic cancers, as PSMA-targeted therapy has showed a promise in treatment of advanced carcinomas. The study included cervical carcinoma (n=28), vulvar carcinoma (n=20), endometrial carcinoma (n=23), primary ovarian carcinoma (n=21), metastatic ovarian carcinoma (n=25), and normal cervix (n=12) as negative control. All cases were immunostained using anti-CD31 antibody to delineate capillary endothelial cells. In parallel, all cases were immunostained using anti-PSMA antibody. The PSMA staining was assessed in tumor capillaries and in normal tissues and scored as a percentage of CD31 staining. PSMA expression was found in the tumor neovasculature, and no significant expression was identified in vasculature of normal tissues. The extent of PSMA staining in tumor capillaries varied from high expression in ovarian and endometrial cancers, to medium expression in cervical squamous cell carcinomas, and low expression in cervical adenocarcinomas and vulvar cancers. All (100%) cases of primary ovarian carcinoma, ovarian carcinoma metastases, and primary endometrial carcinoma showed PSMA expression in tumor vasculature, which was diffuse in majority of cases. The expression of PSMA in ovarian cancer metastases was similar among different metastatic foci of the same tumor. Fifteen percent of cervical squamous cell carcinoma, 50% of cervical adenocarcinoma, and 75% of vulvar carcinomas showed no capillary expression of PSMA. In conclusion, PSMA is highly and specifically expressed in the neovasculature of ovarian, endometrial, and cervical squamous carcinoma, rendering it a potential therapeutic vascular target.

Passive-specific immunotherapy with monoclonal antibodies for prostate cancer: A systematic review

INTRODUCTION

Treatment of metastatic castration-resistant prostate cancer with conventional therapies is still not successful. Therefore, application of novel biological approaches such as immunotherapy, which appears to be more effective and less toxic, is necessary. Monoclonal antibodies against cancer specific antigens are a kind of immunotherapy that have been approved for specific types of cancer and are being investigated for prostate cancer as well. The aim of this review was to assess the effectiveness and safety of monoclonal antibodies for treatment of advanced prostate cancer.

METHOD

According to the search strategy stated in our systematic review protocol, Scopus, Medline, TRIP, CENTRAL, ProQuest, DART and OpenGrey databases were searched. Data collection and quality assessment were done independently by two authors and any disagreements between the collected data were resolved by a third author. A meta-analysis was not feasible as there was a considerable statistical heterogeneity among the trials. Hence, this review was limited to a narrative analysis of the included studies.

RESULTS

We found 9756 references by applying search strategy in 4 databases of journal articles and 3 databases of grey literature. We then discarded 3957 duplicate citations using Endnote software and 5143 articles due to obvious irrelevancy of their topics in primary screening. In secondary screening of 656 fulltexts, we excluded 538 articles, and finally included 12 trials in this systematic review, updated on 23 June 2017. The overall quality of the studies was fair. In general, results of this systematic review show promising advances in the treatment of prostate cancer patients with monoclonal antibodies against prostate-specific antigens with regard to PSA/disease response. Some of the studies reported pain relief after treatment as well.

CONCLUSION

Currently, the role of immunotherapy in the treatment of advanced prostate cancer still remains debated. Although passive specific immunotherapy could be offered as a novel therapeutic option in the coming years, patients should be informed about the risks and benefits of this therapy. One of the obstacles in this review was the lack of adequate assessment of survival-related endpoints reported in the included studies. Our study provides support for further research in this field.

Expression of Prostate-Specific Membrane Antigen in Tumor-Associated Vasculature Predicts Poor Prognosis in Hepatocellular Carcinoma

INTRODUCTION

Prostate-specific membrane antigen (PSMA) was originally found to be specifically expressed in normal prostate, and its expression was upregulated in almost all stages of prostate cancer. In recent years, PSMA was also found to be expressed in tumor-associated vasculature in many nonprostatic solid tumors. However, the expression pattern of PSMA in hepatocellular carcinoma (HCC) is not well studied.

METHODS

In this study, we examined PSMA expression in 103 HCC tissues using immunohistochemical staining and analyzed the association between PSMA expression and other clinicopathological features and prognosis.

RESULTS

Among the 103 cases, 27 cases (26%) showed PSMA expression in more than 50% of tumor-associated vasculature, 49 cases (48%) showed PSMA expression in less than 50% of vasculature, and 27 cases (26%) did not have detectable PSMA expression. Vascular PSMA expression was associated with several clinicopathological features, such as tumor stage, tumor differentiation, lymph node metastasis, and Ki-67 index. Furthermore, high vascular PSMA expression was also associated with poor prognosis in patients with HCC. Univariate and multivariate analyses showed that high vascular PSMA expression can be used as an independent prognostic marker for HCC.

DISCUSSION

Our study provides the evidence that PSMA is specifically expressed in tumor-associated vasculature of HCC, and vascular PSMA expression may be used as a novel prognostic marker and a vascular therapeutic target for HCC.

A Novel Fully Human Antibody targeting Extracellular Domain of PSMA Inhibits Tumor Growth in Prostate Cancer

Prostate cancer is the most commonly diagnosed malignancy in men and the second leading cause of cancer-related death. It is of vital importance to develop new strategies for prostate cancer therapy. PSMA (prostate-specific membrane antigen) is specifically expressed in prostate cancer and the neovasculature of certain cancer types, thus is considered to be an ideal target for cancer therapy. In our previous study, we have obtained a PSMA-specific single-chain variable fragment (scFv), named gy1, from a large yeast display naïve human scFv library. In this study, we reconstructed the PSMA scFv into a fully human antibody (named PSMAb) and evaluated its characterization both in vitro and in vivo We showed that PSMAb can specifically bind with and internalize into PSMA⁺ cells. The binding affinity of PSMAb is measured to be at nanomolar level, and PSMAb has very good thermostability. In vivo study showed that near IR dye-labeled PSMAb can specifically localize at PSMA⁺ tumors, and the application of PSMAb in vivo significantly inhibited the growth of PSMA⁺ tumors, but not PSMA^- tumors. At the studied doses, no obvious toxicity was observed when applied in vivo, as shown by the relative normal liver and kidney function and normal structure of important organs, shown by hematoxylin and eosin staining. In addition, PSMAb may inhibit tumor growth through antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity mechanisms. Our results indicated that the novel fully human antibody, PSMAb, deserve further study for PSMA-targeted diagnosis and therapy for prostate cancer and other cancer types with vascular PSMA expression.

Phase 1 study of PSMA ADC, an antibody-drug conjugate targeting prostate-specific membrane antigen, in chemotherapy-refractory prostate cancer

BACKGROUND

Prostate-specific membrane antigen (PSMA) is a well-characterized target that is overexpressed selectively on prostate cancer cells. PSMA antibody-drug conjugate (ADC) is a fully human IgG1 monoclonal antibody conjugated to the microtubule disrupting agent monomethyl auristatin E (MMAE), which is designed to specifically bind PSMA-positive cells, internalize, and then release its cytotoxic payload into the cells. PSMA ADC has demonstrated potent and selective antitumor activity in preclinical models of advanced prostate cancer. A Phase 1 study was conducted to assess the safety, pharmacokinetics, and preliminary antitumor effects of PSMA ADC in subjects with treatment-refractory prostate cancer.

METHODS

In this first-in-man dose-escalation study, PSMA ADC was administered by intravenous infusion every three weeks to subjects with progressive metastatic castration-resistant prostate cancer (mCRPC) who were previously treated with docetaxel chemotherapy. The primary endpoint was to establish a maximum tolerated dose (MTD). The study also examined the pharmacokinetics of the study drug, total antibody, and free MMAE. Antitumor effects were assessed by measuring changes in serum prostate-specific antigen (PSA), circulating tumor cells (CTCs), and radiologic imaging.

RESULTS

Fifty-two subjects were administered doses ranging from 0.4 to 2.8 mg/kg. Subjects had a median of two prior chemotherapy regimens and prior treatment with abiraterone and/or enzalutamide. Neutropenia and peripheral neuropathy were identified as important first-cycle and late dose-limiting toxicities, respectively. The dose of 2.5 mg/kg was determined to be the MTD. Pharmacokinetics were approximately dose-proportional with minimal drug accumulation. Reductions in PSA and CTCs in subjects treated with doses of ≥1.8 mg/kg were durable and often concurrent.

CONCLUSIONS

In an extensively pretreated mCRPC population, PSMA ADC demonstrated acceptable toxicity. Antitumor activity was observed over dose ranges up to and including 2.5 mg/kg. The observed anti-tumor activity supported further evaluation of this novel agent for the treatment of advanced metastatic prostate cancer.

Meeting report from the Prostate Cancer Foundation PSMA-directed radionuclide scientific working group

INTRODUCTION

The Prostate Cancer Foundation (PCF) convened a PSMA-Directed Radionuclide Scientific Working Group on November 14, 2017, at Weill Cornell Medicine, New York, NY.

METHODS

The meeting was attended by 35 global investigators with expertise in prostate cancer biology, radionuclide therapy, molecular imaging, prostate-specific membrane antigen (PSMA)-targeted agents, drug development, and prostate cancer clinical trials. The goal of this meeting was to discuss the potential for using PSMA-targeted radionuclide agents for the treatment of advanced prostate cancer and to define the studies and clinical trials necessary for validating and optimizing the use of these agents.

RESULTS

Several major topic areas were discussed including the overview of PSMA biology, lessons and applications of PSMA-targeted PET imaging, the nuances of designing PSMA-targeted radionuclide agents, clinical experiences with PSMA-targeted radionuclides, PCF-funded projects to accelerate PSMA-targeted radionuclide therapy, and barriers to the use of radionuclide treatments in widespread clinical practice.

DISCUSSION

This article reviews the major topics discussed at the meeting with the goal of promoting research that will validate and optimize the use of PSMA-targeted radionuclide therapies for the treatment of advanced prostate cancer.

Inducible expression of cancer-testis antigens in human prostate cancer

Immune tolerance to self-antigens can limit robust anti-tumor immune responses in the use of tumor vaccines. Expression of novel tumor associated antigens can improve immune recognition and lysis of tumor cells. The cancer-testis antigen (CTA) family of proteins has been hypothesized to be an ideal class of antigens due to tumor-restricted expression, a subset of which have been found to induce antibody responses in patients with prostate disease. We demonstrate that CTA expression is highly inducible in five different Prostate Cancer (PC) cell lines using a hypomethylating agent 5-Aza-2′-deoxycytidine (5AZA) and/or a histone deacetylase inhibitor LBH589. These CTAs include NY-ESO1, multiple members of the MAGE and SSX families and NY-SAR35. A subset of CTAs is synergistically induced by the combination of 5AZA and LBH589. We developed an ex vivo organ culture using human PC biopsies for ex vivo drug treatments to evaluate these agents in clinical samples. These assays found significant induction of SSX2 in 9/9 distinct patient samples and NY-SAR35 in 7/9 samples. Further, we identify expression of SSX2 in circulating tumor cells (CTC) from patients with advanced PC. These results indicate that epigenetic modifying agents can induce expression of a broad range of neoantigens in human PC and may serve as a useful adjunctive therapy with novel tumor vaccines and checkpoint inhibitors.

PSMA-homing dsRNA chimeric protein vector kills prostate cancer cells and activates anti-tumor bystander responses

The treatment of metastatic androgen-resistant prostate cancer remains a challenge. We describe a protein vector that selectively delivers synthetic dsRNA, polyinosinic/polycytidylic acid (polyIC), to prostate tumors by targeting prostate specific membrane antigen (PSMA), which is overexpressed on the surface of prostate cancer cells.

The chimeric protein is built from the double stranded RNA (dsRNA) binding domain of PKR tethered to a single chain anti-PSMA antibody. When complexed with polyIC, the chimera demonstrates selective and efficient killing of prostate cancer cells. The treatment causes the targeted cancer cells to undergo apoptosis and to secrete toxic cytokines. In a bystander effect, these cytokines kill neighboring cancer cells that do not necessarily overexpress PSMA, and activate immune cells that enhance the killing effect. The strong effects of the targeted polyIC are demonstrated on both 2D cell cultures and 3D tumor spheroids.

Recent Advances in the Generation of Antibody-Nanomaterial Conjugates

Targeted nanomedicines have significantly changed the way new therapeutics are designed to treat disease. Central to successful therapeutics is the ability to control the dynamics of protein-nanomaterial interactions to enhance the therapeutic effect of the nanomedicine. The aim of this review is to illustrate the diversity and versatility of the conjugation approaches involved in the synthesis of antibody-nanoparticle conjugates, and highlight significant new advances in the field of bioconjugation. Such nanomedicines have found utility as both advanced therapeutic agents, as well as more complex imaging contrast agents that can provide both anatomical and functional information of diseased tissue. While such conjugates show significant promise as next generation targeted nanomedicines, it is recognized that there are in fact no clinically approved targeted therapeutics on the market. This fact is reflected upon within this review, and attempts are made to draw some reasoning from the complexities associated with the bioconjugation chemistry approaches that are typically utilized. Present trends, as well as future directions of next generation targeted nanomedicines are also discussed.

PSMA-targeted polyinosine/polycytosine vector induces prostate tumor regression and invokes an antitumor immune response in mice

There is an urgent need for an effective treatment for metastatic prostate cancer (PC). Prostate tumors invariably overexpress prostate surface membrane antigen (PSMA). We designed a nonviral vector, PEI-PEG-DUPA (PPD), comprising polyethylenimine-polyethyleneglycol (PEI-PEG) tethered to the PSMA ligand, 2-[3-(1, 3-dicarboxy propyl)ureido] pentanedioic acid (DUPA), to treat PC. The purpose of PEI is to bind polyinosinic/polycytosinic acid (polyIC) and allow endosomal release, while DUPA targets PC cells. PolyIC activates multiple pathways that lead to tumor cell death and to the activation of bystander effects that harness the immune system against the tumor, attacking nontargeted neighboring tumor cells and reducing the probability of acquired resistance and disease recurrence. Targeting polyIC directly to tumor cells avoids the toxicity associated with systemic delivery. PPD selectively delivered polyIC into PSMA-overexpressing PC cells, inducing apoptosis, cytokine secretion, and the recruitment of human peripheral blood mononuclear cells (PBMCs). PSMA-overexpressing tumors in nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice with partially reconstituted immune systems were significantly shrunken following PPD/polyIC treatment, in all cases. Half of the tumors showed complete regression. PPD/polyIC invokes antitumor immunity, but unlike many immunotherapies does not need to be personalized for each patient. The potent antitumor effects of PPD/polyIC should spur its development for clinical use.

EpCAM aptamer-functionalized polydopamine-coated mesoporous silica nanoparticles loaded with DM1 for targeted therapy in colorectal cancer

DM1, a maytansine derivative, is a highly potential cytotoxic agent but with severe side effects; therefore, its application in clinical cancer therapy is limited. Here, in order to mitigate this intrinsic drawback of DM1, we developed mesoporous silica nanoparticles (MSNs) loaded with DM1 and surface-decorated with hydrochloride dopamine (PDA), polyethylene glycol (PEG), and epithelial cell adhesion molecule (EpCAM) aptamer (APt) for the targeted treatment of colorectal cancer (CRC). In this system, the PDA coating could be used as pH-sensitive gatekeepers to control the release of DM1 from MSNs in response to the pH stimulus and EpCAM APt-guided active targeting enables the increased delivery of DM1 to CRC as well as a reduction in toxicity and side effects by minimizing the exposure of normal tissues to DM1. Results demonstrated that DM1 inhibited the formation of microtubules and induced apoptosis in tumor cells via caspase signaling. In comparison with the control groups, the MSNs-DM1@PDA-PEG-APt bioconjugates exhibited increased binding ability and much higher cytotoxicity to the CRC SW480 cell line. Furthermore, in vivo assays confirmed the advantages of such a strategy. These findings suggested that MSNs-DM1@PDA-PEG-APt could represent a promising therapeutic platform for EpCAM-positive CRC.

Prostate-Specific Membrane Antigen-Directed Therapy for Metastatic Castration-Resistant Prostate Cancer

Prostate-specific membrane antigen (PSMA) is highly expressed on both benign and malignant prostatic tissue. Prostate-specific membrane antigen-directed therapy is conceptually promising, with a potential to additionally serve as a theranostic model in management of advanced prostate cancer. To date, various approaches have been devised and tested, including radiolabeled PSMA antibodies and inhibitor and antibody-drug conjugates. However, development and progress have faced challenges in determining the optimal combination of payload, PSMA-binding moiety, and linker technology. We review the available clinical data to date in PSMA-directed therapies and discuss the challenges faced.

Intracellular trafficking of new anticancer therapeutics: antibody-drug conjugates

Antibody-drug conjugate (ADC) is a milestone in targeted cancer therapy that comprises of monoclonal antibodies chemically linked to cytotoxic drugs. Internalization of ADC takes place via clathrin-mediated endocytosis, caveolae-mediated endocytosis, and pinocytosis. Conjugation strategies, endocytosis and intracellular trafficking optimization, linkers, and drugs chemistry present a great challenge for researchers to eradicate tumor cells successfully. This inventiveness of endocytosis and intracellular trafficking has given considerable momentum recently to develop specific antibodies and ADCs to treat cancer cells. It is significantly advantageous to emphasize the endocytosis and intracellular trafficking pathways efficiently and to design potent engineered conjugates and biological entities to boost efficient therapies enormously for cancer treatment. Current studies illustrate endocytosis and intracellular trafficking of ADC, protein, and linker strategies in unloading and also concisely evaluate practically applicable ADCs.

Full preclinical validation of the 123I-labeled anti-PSMA antibody fragment ScFvD2B for prostate cancer imaging

Purpose

In the context of prostate cancer (PCa) imaging, the aim of this study was to optimize (in vitro) the specificity and assess preclinically (in vivo) the tumor targeting properties of the ¹²³I-scFvD2B antibody specific for prostate-specific membrane antigen (PSMA).

Experimental Design

The ¹²³I-labeling conditions of the antibody fragment scFvD2B, produced in an eukaryotic system under GMP-compliant conditions, were optimized and assessed for purity and immunoreactivity. The specificity and potency of tumor uptake were tested in three preclinical in vivo models of subcutaneously xenografted human tumors expressing different levels of PSMA (LNCaP, naturally expressing PSMA; PC3-PIP and LS174T-PSMA, transfected with PSMA) or PC3 and LS174T, as negative controls, to assess the clearance, biodistribution and imaging potential of ¹²³I-scFvD2B.

Results

The set conditions of production and radiolabeling yielded a reagent suitable for human delivery thanks to the purity of the formulation and the high immunoreactivity. In all preclinical models ¹²³I-scFvD2B showed specific targeting only to PSMA-positive tumors with the final specific activity ranging up to 1500 MBq/mg. Despite different levels of PSMA expression, biodistribution analyses and SPECT/CT imaging demonstrated similar results and maximal signal-to-background ratios 24 hours after injection.

Conclusions

Due to its in vitro and in vivo properties, ¹²³I-scFvD2B could be a promising tool for the early diagnosis of PCa, and may represent a molecular imaging option to monitor disease progression and assist in the clinical management of PCa patients.

Mipsagargin, a novel thapsigargin-based PSMA-activated prodrug: results of a first-in-man phase I clinical trial in patients with refractory, advanced or metastatic solid tumours

Background:

Mipsagargin (G-202; (8-O-(12-aminododecanoyl)-8-O-debutanoyl thapsigargin)-Asp-γ-Glu-γ-Glu-γ-GluGluOH)) is a novel thapsigargin-based targeted prodrug that is activated by PSMA-mediated cleavage of an inert masking peptide. The active moiety is an inhibitor of the sarcoplasmic/endoplasmic reticulum calcium adenosine triphosphatase (SERCA) pump protein that is necessary for cellular viability. We evaluated the safety of mipsagargin in patients with advanced solid tumours and established a recommended phase II dosing (RP2D) regimen.

Methods:

Patients with advanced solid tumours received mipsagargin by intravenous infusion on days 1, 2 and 3 of 28-day cycles and were allowed to continue participation in the absence of disease progression or unacceptable toxicity. The dosing began at 1.2 mg m⁻² and was escalated using a modified Fibonacci schema to determine maximally tolerated dose (MTD) with an expansion cohort at the RP2D. Plasma was analysed for mipsagargin pharmacokinetics and response was assessed using RECIST criteria.

Results:

A total of 44 patients were treated at doses ranging from 1.2 to 88 mg m⁻², including 28 patients in the dose escalation phase and 16 patients in an expansion cohort. One dose-limiting toxicity (DLT; Grade 3 rash) was observed in the dose escalation portion of the study. At 88 mg m⁻², observations of Grade 2 infusion-related reaction (IRR, 2 patients) and Grade 2 creatinine elevation (1 patient) led to declaration of 66.8 mg m⁻² as the recommended phase II dose (RP2D). Across the study, the most common treatment-related adverse events (AEs) were fatigue, rash, nausea, pyrexia and IRR. Two patients developed treatment-related Grade 3 acute renal failure that was reversible during the treatment-free portion of the cycle. To help ameliorate the IRR and creatinine elevations, a RP2D of 40 mg m⁻² on day 1 and 66.8 mg m⁻² on days 2 and 3 with prophylactic premedications and hydration on each day of infusion was established. Clinical response was not observed, but prolonged disease stabilisation was observed in a subset of patients.

Conclusions:

Mipsagargin demonstrated an acceptable tolerability and favourable pharmacokinetic profile in patients with solid tumours.