Humanized anti-Trop-2 IgG-SN-38 conjugate for effective treatment of diverse epithelial cancers: preclinical studies in human cancer xenograft models and monkeys

Opportunities and Challenges in the Development of Antibody-Drug Conjugate for Triple-Negative Breast Cancer: The Diverse Choices and Changing Needs

Triple-negative breast cancer (TNBC) is a highly heterogeneous breast cancer subtype, which is also characterized by the aggressive phenotype, high recurrence rate, and poor prognosis. Antibody-drug conjugate (ADC) is a monoclonal antibody with a cytotoxic payload connected by a linker. ADC is gaining more and more attention as a targeted anti-cancer agent. Clinical studies of emerging ADC drugs such as sacituzumab govitecan and trastuzumab deruxtecan in patients with metastatic breast cancer (including TNBC) are progressing rapidly. In view of its excellent clinical efficacy and good tolerability, Sacituzumab govitecan gained accelerated approval by the FDA for the treatment of advanced metastatic TNBC in 2020. This review discusses the treatment status and challenges in TNBC, with an emphasis on the current status of ADC development and clinical trials in TNBC and metastatic breast cancer. We also summarize the clinical experience and future exploration directions of ADC development for TNBC patients.

Design and synthesis of novel site-specific antibody-drug conjugates that target TROP2

The approval of Trodelvy® validates TROP2 as a druggable but challenging target for antibody-drug conjugates (ADCs) to treat metastatic triple-negative breast cancer (mTNBC). Here, based on the TROP2-targeted antibody sacituzumab, we designed and developed several site-specific ADC candidates, which employ MMAE (monomethyl auristatin E) as the toxin, via IgG glycoengineering or affinity-directed traceless conjugation. Systematic evaluation of these site-specific ADCs in homogeneity, hydrophilicity, stability, and antitumor efficiency was conducted. The results indicate that the site-specific ADCs gsADC 3b made from one-step glycoengineering exhibit good aggregation stability and in vivo efficacy, providing a new format of ADCs that target TROP2.

Gastrointestinal Toxicity of Antibody Drug Conjugates (ADCs) in Metastatic Breast Cancer: A Pooled Analysis

Trastuzumab emtansine (T-DM1), sacituzumab govitecan (SG), and trastuzumab deruxtecan (T-DXd) are three ADCs approved for the treatment of metastatic breast cancer (MBC). Since gastrointestinal toxicities have been commonly observed with these drugs in clinical trials, a pooled analysis evaluating gastrointestinal adverse events (AEs) in patients with MBC treated with ADCs in clinical trials was performed. PubMed, Embase, and the Cochrane Library were searched from inception until May 2023 for phase II and III clinical trials reporting frequency and severity of gastrointestinal AEs during treatment with ADCs. Data were retrieved for nausea, vomiting, diarrhea, constipation, and abdominal pain: overall and grade 3-4 toxicity rates according to NCI-CTCAE were collected and expressed as proportions. A pre-specified subgroup analysis according to the agent was also carried out. Fourteen studies, comprising 5608 patients, were included in the analysis. Gastrointestinal AEs were frequently registered with SG and T-DXd. A significantly higher frequency of nausea (65.6% with SG, 75% with T-DXd), vomiting (43.7% with SG, 45% with T-DXd), and diarrhea (59.7% with SG, 29% with T-DXd) was noticed with these ADCs compared to TDM-1. Furthermore, diarrhea was more frequently associated with SG (grade 3 in 7.5% of patients), while constipation and abdominal pain were less common. Gastrointestinal AEs, notably nausea and diarrhea, were frequently reported by MBC patients treated with SG and T-DXd in clinical trials. Since these ADCs are administered continuously until disease progression or occurrence of unbearable AEs, gastrointestinal toxicity may have a negative impact on patient quality of life. Therefore, appropriate management of gastrointestinal AEs is mandatory to ensure treatment efficacy and adherence.

Trop2-targeted therapies in solid tumors: advances and future directions

Trophoblast cell surface antigen 2 (Trop2) is overexpressed in a range of solid tumors and participants in multiple oncogenic signaling pathways, making it an attractive therapeutic target. In the past decade, the rapid development of various Trop2-targeted therapies, notably marked by the advent of the antibody-drug conjugate (ADC), revolutionized the outcome for patients facing Trop2-positive tumors with limited treatment opinions, such as triple-negative breast cancer (TNBC). This review provides a comprehensive summary of advances in Trop2-targeted therapies, including ADCs, antibodies, multispecific agents, immunotherapy, cancer vaccines, and small molecular inhibitors, along with in-depth discussions on their designs, mechanisms of action (MOAs), and limitations. Additionally, we emphasize the clinical research progress of these emerging Trop2-targeted agents, focusing on their clinical application and therapeutic efficacy against tumors. Furthermore, we propose directions for future research, such as enhancing our understanding of Trop2's structure and biology, exploring the best combination strategies, and tailoring precision treatment based on Trop2 testing methodologies.

Side effects of drug-antibody conjugates enfortumab-vedotin and sacituzumab-govitecan in targeted therapy in cancer

OBJECTIVE

Antibody-drug conjugates (ADC), enfortumab-vedotin (EV) and sacituzumab-govitecan are new drugs in the treatment of urologic tumors, whose safety profile has not been fully investigated. Therefore, the aim of our study was to evaluate adverse events related to both agents reported to VigiBase, the World Health Organization's global pharmacovigilance database.

METHODS

We employed Bayesian disproportionality analysis based on the information component (IC) to explore the safety profile associated with both therapies. Additionally, we used the proportional reporting ratio approach to examine the safety profile further.

RESULTS

We identified 41,752 reports connected to ADC therapy (EV: n=5359; SG: n=36,393). In the EV subgroup, most reports were associated with dermatologic (38.6%), neurologic adverse events (16.5%), or adverse laboratory assessments (19.4%). In contrast, reports in the SG subgroup were mainly associated with gastrointestinal adverse events (24.2%) and adverse laboratory assessments (39.0%). Adverse laboratory assessments in both cohorts were often based on haematotoxic adverse events.

CONCLUSION

We could provide a comprehensive real-world safety profile of EV and SG using a global pharmacovigilance database. Based on the safety signals explored in this study, further research regarding the impact of these side effects on patient outcomes is justified.

Clinical translation of antibody drug conjugate dosing in solid tumors from preclinical mouse data

Antibody drug conjugates (ADCs) have made impressive strides in the clinic in recent years with 11 Food and Drug Administration approvals, including 6 for the treatment of patients with solid tumors. Despite this success, the development of new agents remains challenging with a high failure rate in the clinic. Here, we show that current approved ADCs for the treatment of patients with solid tumors can all show substantial efficacy in some mouse models when administered at a similar weight-based [milligrams per kilogram (mg/kg)] dosing in mice that is tolerated in the clinic. Mechanistically, equivalent mg/kg dosing results in a similar drug concentration in the tumor and a similar tissue penetration into the tumor due to the unique delivery features of ADCs. Combined with computational approaches, which can account for the complex distribution within the tumor microenvironment, these scaling concepts may aid in the evaluation of new agents and help design therapeutics with maximum clinical efficacy.

Assessment of TROP2, CEACAM5 and DLL3 in metastatic prostate cancer: Expression landscape and molecular correlates

Therapeutic approaches targeting proteins on the surface of cancer cells have emerged as an important strategy for precision oncology. To capitalize on the potential impact of drugs targeting surface proteins, detailed knowledge about the expression patterns of the target proteins in tumor tissues is required. In castration-resistant prostate cancer (CRPC), agents targeting prostate-specific membrane antigen (PSMA) have demonstrated clinical activity. However, PSMA expression is lost in a significant number of CRPC tumors. The identification of additional cell surface targets is necessary to develop new therapeutic approaches. Here, we performed a comprehensive analysis of the expression heterogeneity and co-expression patterns of trophoblast cell-surface antigen 2 (TROP2), delta-like ligand 3 (DLL3), and carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) in CRPC samples from a rapid autopsy cohort. We show that DLL3 and CEACAM5 exhibit the highest expression in neuroendocrine prostate cancer (NEPC), while TROP2 is expressed across different CRPC molecular subtypes, except for NEPC. We further demonstrated that AR alterations were associated with higher expression of PSMA and TROP2. Conversely, PSMA and TROP2 expression was lower in RB1-altered tumors. In addition to genomic alterations, we show a tight correlation between epigenetic states, particularly histone H3 lysine 27 methylation (H3K27me3) at the transcriptional start site and gene body of TACSTD2 (encoding TROP2), DLL3, and CEACAM5, and their respective protein expression in CRPC patient-derived xenografts. Collectively, these findings provide insights into patterns and determinants of expression of TROP2, DLL3, and CEACAM5 with implications for the clinical development of cell surface targeting agents in CRPC.

Sacituzumab Govitecan in Combination With Pembrolizumab for Patients With Metastatic Urothelial Cancer That Progressed After Platinum-Based Chemotherapy: TROPHY-U-01 Cohort 3

PURPOSE

Pembrolizumab is standard therapy for patients with metastatic urothelial cancer (mUC) who progress after first-line platinum-based chemotherapy; however, only approximately 21% of patients respond. Sacituzumab govitecan (SG) is a trophoblast cell surface antigen-2-directed antibody-drug conjugate with US Food and Drug Administration-accelerated approval to treat patients with locally advanced or mUC who previously received platinum-based chemotherapy and a checkpoint inhibitor (CPI). Here, we report the primary analysis of TROPHY-U-01 cohort 3.

METHODS

TROPHY-U-01 (ClinicalTrials.gov identifier: NCT03547973) is a multicohort, open-label phase II study. Patients were CPI-naïve and had mUC progression after platinum-based chemotherapy in the metastatic setting or ≤12 months in the (neo)adjuvant setting. Patients received 10 mg/kg of SG once on days 1 and 8 and 200 mg of pembrolizumab once on day 1 of 21-day cycles. The primary end point was objective response rate (ORR) per central review. Secondary end points included clinical benefit rate (CBR), duration of response (DOR) and progression-free survival (PFS) per central review, and safety.

RESULTS

Cohort 3 included 41 patients (median age 67 years; 83% male; 78% visceral metastases [29% liver]). With a median follow-up of 14.8 months, the ORR was 41% (95% CI, 26.3 to 57.9; 20% complete response rate), CBR was 46% (95% CI, 30.7 to 62.6), median DOR was 11.1 months (95% CI, 4.8 to not estimable [NE]), and median PFS was 5.3 months (95% CI, 3.4 to 10.2). The median overall survival was 12.7 months (range, 10.7-NE). Grade ≥3 treatment-related adverse events occurred in 61% of patients; most common were neutropenia (37%), leukopenia (20%), and diarrhea (20%).

CONCLUSION

SG plus pembrolizumab demonstrated a high response rate with an overall manageable toxicity profile in patients with mUC who progressed after platinum-based chemotherapy. No new safety signals were detected. These data support further evaluation of SG plus CPI in mUC.

UGT1A1 Testing in Breast Cancer: should it become routine practice in patients treated with antibody-drug conjugates?

The use of genetic testing to personalize therapeutic strategies in cancer is rapidly evolving and thus changing the landscape of treatment of oncologic patients. The UGT1A1 gene is an important component for the metabolism and glucoronidation of certain drugs, including irinotecan and sacituzumab govitecan (SG); therefore, various UGT1A1 polymorphisms leading to decreased function of the UGT1A1 enzyme may lead to increased risk of treatment-related side effects. Testing for UGT1A1 polymorphism is not routinely adopted in clinical practice; that is due to the lack of concise studies and recommendations concerning the clinical relevance of this test and its impact on the quality of life of cancer patients. The knowledge regarding UGT1A1 polymorphism and its clinical relevance will be reviewed in this article, as well as the published literature on the association between UGT1A1 polymorphism and the toxicity risk of irinotecan as well as sacituzumab govitecan. The current recommendations and guidelines on UGT1A1 testing will be discussed in detail in the hopes of providing guidance to oncologists in their clinical practice.

Antibody-Drug Conjugates in Triple Negative Breast Cancer

Triple negative breast cancer (TNBC) accounts for 15%-20% of all breast cancer. It is a heterogeneous breast cancer subtype with a poor prognosis. Given these negative features, there is a need for new treatment options beyond conventional chemotherapy in both the early stage and palliative setting. Impressive results have been reported with antibody-drug conjugates (ADCs) that link a cytotoxic payload to a monoclonal antibody, such as sacituzumab govitecan and trastuzumab deruxtecan, in the metastatic stage. The focus of this review is to discuss completed and ongoing trials involving ADCs in TNBC.

Efficacy of Antibody Drug Conjugates Alone and in Combination with other Agents in Metastatic Urothelial Carcinoma: A Scoping Review

INTRODUCTION

Antibody drug conjugates represent a promising class of antineoplastic agents comprised of a monoclonal antibody linked to a potent cytotoxic payload for targeted delivery of chemotherapy to tumors. Various antibody drug conjugates have demonstrated impressive efficacy in patients with metastatic urothelial carcinoma in clinical trials, leading to two FDA approved therapies and several other agents and combinations in clinical development.

MATERIALS AND METHODS

A comprehensive systematic review was undertaken utilizing the principles of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Queried databases included Ovid MEDLINE, Ovid Embase, Web of Science Core Collection and Cochrane CENTRAL Trials. The search sought to identify prospective therapeutic clinical trials in humans with metastatic urothelial carcinoma with a single-arm or randomized controlled trial design investigating antibody drug conjugate-containing regimens.

RESULTS

The literature search yielded 4,929 non-duplicated articles, of which 30 manuscripts and conference abstracts were included, which derived from 15 clinical trials including 19 separate cohorts with efficacy outcome results. Eleven trials investigated ADC monotherapy, while two investigated combination regimens, and the remaining two studies were mixed. Five unique ADC targets were represented including Nectin-4, Trop-2, HER2, Tissue Factor, and SLITRK6. Twelve clinical trial cohorts required prior treatment (63%). Objective response rate was reported for all studies and ranged from 27-52% for ADC monotherapies and 34-75% for ADC plus anti-PD-1 agents. Time to event outcome reporting was highly variable.

CONCLUSION

In addition to enfortumab vedotin and sacituzumab govitecan, various HER2-targeted antibody drug conjugates and ADC-anti-PD-1 combination regimens have demonstrated efficacy in clinical trials and are poised for clinical advancement.

Exploring the next generation of antibody-drug conjugates

Antibody-drug conjugates (ADCs) are a promising cancer treatment modality that enables the selective delivery of highly cytotoxic payloads to tumours. However, realizing the full potential of this platform necessitates innovative molecular designs to tackle several clinical challenges such as drug resistance, tumour heterogeneity and treatment-related adverse effects. Several emerging ADC formats exist, including bispecific ADCs, conditionally active ADCs (also known as probody-drug conjugates), immune-stimulating ADCs, protein-degrader ADCs and dual-drug ADCs, and each offers unique capabilities for tackling these various challenges. For example, probody-drug conjugates can enhance tumour specificity, whereas bispecific ADCs and dual-drug ADCs can address resistance and heterogeneity with enhanced activity. The incorporation of immune-stimulating and protein-degrader ADCs, which have distinct mechanisms of action, into existing treatment strategies could enable multimodal cancer treatment. Despite the promising outlook, the importance of patient stratification and biomarker identification cannot be overstated for these emerging ADCs, as these factors are crucial to identify patients who are most likely to derive benefit. As we continue to deepen our understanding of tumour biology and refine ADC design, we will edge closer to developing truly effective and safe ADCs for patients with treatment-refractory cancers. In this Review, we highlight advances in each ADC component (the monoclonal antibody, payload, linker and conjugation chemistry) and provide more-detailed discussions on selected examples of emerging novel ADCs of each format, enabled by engineering of one or more of these components.

Could a Long-Acting Prodrug of SN-38 be Efficacious in Sacituzumab Govitecan-Resistant Tumors?

We previously proposed that sacituzumab govitecan (SG, Trodelvy®) likely acts as a simple prodrug of systemic SN-38 as well as an antibody drug conjugate (ADC). In the present commentary, we assess whether a long-acting SN-38 prodrug, such as PLX038, might be efficacious in SG-resistant patients. We first describe possible mechanisms of action of SG, with new insights on pharmacokinetics and TROP2 receptor occupancy. We argue that SG is not an optimal conventional ADC and that the amount of systemic SN-38 spontaneously hydrolyzed from the ADC is so high it must have activity. Then, we describe the concept of time-over-target as related to the pharmacology of SG and PLX038 as SN-38 prodrugs. To be clear, we are not in any way suggesting that PLX038 or any SN-38 prodrug is superior to SG as an anticancer agent. Clearly, SG has the benefit over antigen-independent SN-38 prodrugs in that it targets cells with the TROP2 receptor. However, we surmise that PLX038 should be a more efficacious and less toxic prodrug of systemic SN-38 than SG. Finally, we suggest possible mechanisms of SG resistance and how PLX038 might perform in the context of each. Taken together, we argue that-contrary to many opinions-SG does not exclusively act as a conventional ADC, and propose that PLX038 may be efficacious in some settings of SG-resistance.

Sacituzumab Govitecan: A Review in Unresectable or Metastatic HR+/HER2- Breast Cancer

Sacituzumab govitecan (TRODELVY®) is a first-in-class trophoblast cell-surface antigen 2 (Trop-2)-directed antibody and topoisomerase I inhibitor conjugate that is approved globally as monotherapy for the treatment of adults with unresectable locally advanced or metastatic, hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-; defined as immunohistochemistry 0, 1+ or 2+ and in situ hybridization-negative) breast cancer who have received endocrine-based therapy and ≥ 2 additional systemic therapies in the advanced setting. In the phase III TROPiCS-02 trial, intravenous sacituzumab govitecan demonstrated statistically significant and clinically meaningful improvements in progression-free survival and overall survival compared with physician's choice of chemotherapy (capecitabine, eribulin, gemcitabine or vinorelbine) in adults with metastatic HR+/HER2- breast cancer. Sacituzumab govitecan had a generally manageable tolerability profile in these patients; the most common treatment-related grade ≥ 3 adverse events included neutropenia, diarrhoea, leukopenia, anaemia, fatigue and febrile neutropenia. Sacituzumab govitecan carries regulatory warnings for severe neutropenia and severe diarrhoea. Sacituzumab govitecan demonstrated an overall benefit in terms of health-related quality of life. Current evidence indicates that sacituzumab govitecan is an effective treatment option, with a generally manageable tolerability profile, for patients with pre-treated, unresectable locally advanced or metastatic HR+/HER2- breast cancer.

Sacituzumab govitecan plus platinum-based chemotherapy mediates significant antitumor effects in triple-negative breast, urinary bladder, and small-cell lung carcinomas

Sacituzumab govitecan (SG) is an antibody-drug conjugate composed of an anti-Trop-2-directed antibody conjugated with the topoisomerase I inhibitory drug, SN-38, via a proprietary hydrolysable linker. SG has received United States Food and Drug Administration (FDA) approval to treat metastatic triple-negative breast cancer (TNBC), unresectable locally advanced or metastatic hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer, and accelerated approval for metastatic urothelial cancer. We investigated the utility of combining SG with platinum-based chemotherapeutics in TNBC, urinary bladder carcinoma (UBC), and small-cell lung carcinoma (SCLC). SG plus carboplatin or cisplatin produced additive growth-inhibitory effects in vitro that trended towards synergy. Immunoblot analysis of cell lysates suggests perturbation of the cell-cycle and a shift towards pro-apoptotic signaling evidenced by an increased Bax to Bcl-2 ratio and down-regulation of two anti-apoptotic proteins, Mcl-1 and survivin. Significant antitumor effects were observed with SG plus carboplatin in mice bearing TNBC or SCLC tumors compared to all controls (P < 0.0062 and P < 0.0017, respectively) and with SG plus cisplatin in UBC and SCLC tumor-bearing animals (P < 0.0362 and P < 0.0001, respectively). These combinations were well tolerated by the animals. Combining SG with platinum-based chemotherapeutics demonstrates the benefit in these indications and warrants further clinical investigation.

Third-line Treatment for Metastatic Triple-negative Breast Cancer: A Systematic Review and Network Meta-analysis

OBJECTIVE

Metastatic triple-negative breast cancer (mTNBC) is an invasive histologic subtype with a poor prognosis and rapid progression. Currently, there is no standard therapy for the third-line treatment of mTNBC. In this study, we conducted a network meta-analysis to compare regimens and determine treatment outcomes.

METHODS

We performed a systematic search of PubMed, EMBASE, the Cochrane Central Register of Controlled Bases, and the minutes of major conferences. Progression-free survival, overall survival, and objective response rate were analyzed through network meta-analysis using the R software (R Core Team). The efficacy of the treatment regimens was compared using hazard ratios, odds ratios, and 95% CIs.

RESULTS

We evaluated 15 randomized controlled trials involving 6,010 patients. Compared with the physician's choice treatment, sacituzumab govitecan showed significant advantages in progression-free survival and overall survival, with hazard ratio values of 0.41 (95% CI: 0.32-0.52) and 0.48 (95% CI, 0.39-0.60). In terms of objective response rate, sacituzumab govitecan is the best-performing therapy (odds ratio: 10.82; 95% CI: 5.58-20.97). Adverse events among grades 3 to 5 adverse reactions, the incidence of neutropenia and leukopenia in each regimen was higher, whereas the incidence of fever, headache, hypertension, and rash was lower.

CONCLUSION

Compared with the treatment of the physician's choice, sacituzumab govitecan appears more efficacious and is the preferred third-line treatment for mTNBC.

Leveraging TROP2 Antibody-Drug Conjugates in Solid Tumors

Antibody-drug conjugates (ADCs) have become the cornerstone of effective therapeutics in solid and hematological malignancies by harnessing potent cytotoxic payloads with targeted tumoricidal delivery. Since the monumental shift occurred with HER2-targeted ADCs, the discovery of the TROP2 antigen has revolutionized the landscape of ADC development. Moving beyond the traditional ADC design, multiple novel ADCs have successfully shaped and improved survival outcomes in patients with various tumor histologies. Here we review and contrast the clinical impact of the well-known TROP2 ADCs currently in clinical use. We also shed light on upcoming investigational TROP2 ADCs showing promise with novel ADC platforms.

The HER2-directed antibody-drug conjugate DHES0815A in advanced and/or metastatic breast cancer: preclinical characterization and phase 1 trial results

Approved antibody-drug conjugates (ADCs) for HER2-positive breast cancer include trastuzumab emtansine and trastuzumab deruxtecan. To develop a differentiated HER2 ADC, we chose an antibody that does not compete with trastuzumab or pertuzumab for binding, conjugated to a reduced potency PBD (pyrrolobenzodiazepine) dimer payload. PBDs are potent cytotoxic agents that alkylate and cross-link DNA. In our study, the PBD dimer is modified to alkylate, but not cross-link DNA. This HER2 ADC, DHES0815A, demonstrates in vivo efficacy in models of HER2-positive and HER2-low cancers and is well-tolerated in cynomolgus monkey safety studies. Mechanisms of action include induction of DNA damage and apoptosis, activity in non-dividing cells, and bystander activity. A dose-escalation study (ClinicalTrials.gov: NCT03451162) in patients with HER2-positive metastatic breast cancer, with the primary objective of evaluating the safety and tolerability of DHES0815A and secondary objectives of characterizing the pharmacokinetics, objective response rate, duration of response, and formation of anti-DHES0815A antibodies, is reported herein. Despite early signs of anti-tumor activity, patients at higher doses develop persistent, non-resolvable dermal, ocular, and pulmonary toxicities, which led to early termination of the phase 1 trial.

Pharmacokinetics and pharmacodynamics of antibody-drug conjugates for the treatment of patients with breast cancer

INTRODUCTION

Currently three antibody-drug-conjugates (ADC) are approved by the European Medicines Agency (EMA) for treatment of breast cancer (BC) patient: trastuzumab-emtansine, trastuzumab-deruxtecan and sacituzumab-govitecan. ADC are composed of a monoclonal antibody (mAb) targeting a specific antigen, a cytotoxic payload and a linker. Pharmacokinetics (PK) and pharmacodynamics (PD) distinguish ADC from conventional chemotherapy and must be understood by clinicians.

AREAS COVERED

Our review delineates the PK/PD profiles of ADC approved for the treatment of BC with insight for future development. This is an expert opinion literature review based on the EMA's Assessment Reports, enriched by a comprehensive literature search performed on Medline in August 2023.

EXPERT OPINION

All three ADC distributions are described by a two-compartment structure: tissue and serum. Payload concentration peak is immediate but remains at low concentration. The distribution varied for all ADC only with body weight. mAb will be metabolised firstly by the saturable complex formation of ADC/Tumour-Receptor and secondly by binding of FcgRs in immune cells. They are all excreted in the bile and faeces with minimal urine elimination. Dose adjustments, apart from weight, are not recommended. Novel ADC are composed of cleavable linkers with various targets/payloads with the same PK/PD properties, but novel structures of ADC are in development.

Sacituzumab Govitecan as a Second-Line Treatment in Relapsed/Refractory Metastatic Triple-Negative Breast Cancer Patients: A Systematic Review and Meta-analysis

BACKGROUND

Chemotherapy, the only treatment option for metastatic triple-negative breast cancer (mTNBC), showed decreased survival rates. Trophoblast cell surface antigen-2 (Trop-2) could be a possible target for antibody-drug conjugates (ADCs).

OBJECTIVE

Sacituzumab govitecan (SG), an anti-Trop-2 ADC for pretreating relapsed/refractory mTNBC patients, was studied to know the efficacy and safety profile of the drug in mTNBC.

METHODS

The present review searched MEDLINE (via PubMed), WHO Clinical Trial Registry, Clinical Trials.gov, and Cochrane Central Register of Controlled Trials until December 25, 2022. The studies searched comprised randomized trials and observational studies (retrospective [case-control, cross-sectional] and prospective [cohort designs]). Efficacy assessment was performed in terms of complete response (CR), partial response (PR), objective response rate (ORR), stable disease (SD), progressive disease (PD), and clinical benefit rate (CBR), and safety in terms of adverse events.

RESULTS

The overall random-effects pooled prevalence of CR was 4.9 (95% CI: 3.2-7.1), PR was 35.6 (95% CI: 31.5-39.9), ORR was 6.8 (95% CI: 5.9-7.8), SD was 8.0 (95% CI: 6.7-9.4), PD was 5.1 (95% CI: 4.1-6.3), and CBR was 13.4 (95% CI: 11.8-15.1). Adverse events associated with the drug were neutropenia, fatigue, anemia, nausea, and others.

CONCLUSION AND RELEVANCE

This is the first meta-analysis conducted in relapsed/refractory mTNBC patients and found that SG is efficacious but associated with some adverse effects that are related to exposure to the drug. The application of these results will allow clinicians to use SG in the management of patients with mTNBC.

Elucidating the development, characterization, and antitumor potential of a novel humanized antibody against Trop2

Trophoblast cell surface antigen 2 (Trop2) has emerged as a potential target for effective cancer therapy. In this study, we report a novel anti-Trop2 antibody IMB1636, developed using hybridoma technology. It exhibited high affinity and specificity (KD = 0.483 nM) in binding both antigens and cancer cells, as well as human tumor tissues. hIMB1636 could induce endocytosis, and enabled targeted delivery to the tumor site with an in vivo retention time of 264 h. The humanized antibody hIMB1636, acquired using CDR grafting, exhibited the potential to directly inhibit cancer cell proliferation and migration, and to induce ADCC effects. Moreover, hIMB1636 significantly inhibited the growth of MDA-MB-468 xenograft tumors in vivo. Mechanistically, hIMB1636 induced cell cycle arrest and apoptosis by regulating cyclin-related proteins and the caspase cascade. In comparison to commercialized sacituzumab, hIMB1636 recognized a conformational epitope instead of a linear one, bound to antigen and cancer cells with similar binding affinity, induced significantly more potent ADCC effects against cancer cells, and displayed superior antitumor activities both in vitro and in vivo. The data presented in this study highlights the potential of hIMB1636 as a carrier for the formulation of antibody-based conjugates, or as a promising candidate for anticancer therapy.

Targeting Trop2 in solid tumors: a look into structures and novel epitopes

Trophoblast cell surface antigen 2 (Trop2) exhibits limited expression in normal tissues but is over-expressed across various solid tumors. The effectiveness of anti-Trop2 antibody-drug conjugate (ADC) in managing breast cancer validates Trop2 as a promising therapeutic target for cancer treatment. However, excessive toxicity and a low response rate of ADCs pose ongoing challenges. Safer and more effective strategies should be developed for Trop2-positive cancers. The dynamic structural attributes and the oligomeric assembly of Trop2 present formidable obstacles to the progression of innovative targeted therapeutics. In this review, we summarize recent advancements in understanding Trop2's structure and provide an overview of the epitope characteristics of Trop2-targeted agents. Furthermore, we discuss the correlation between anti-Trop2 agents' epitopes and their respective functions, particularly emphasizing their efficacy and specificity in targeted therapies.

ASSESSMENT OF CELL SURFACE TARGETS IN METASTATIC PROSTATE CANCER: EXPRESSION LANDSCAPE AND MOLECULAR CORRELATES

Therapeutic approaches targeting proteins on the surface of cancer cells have emerged as an important strategy for precision oncology. To fully capitalize on the potential impact of drugs targeting surface proteins, detailed knowledge about the expression patterns of the target proteins in tumor tissues is required. In castration-resistant prostate cancer (CRPC), agents targeting prostate-specific membrane antigen (PSMA) have demonstrated clinical activity. However, PSMA expression is lost in a significant number of CRPC tumors, and the identification of additional cell surface targets is necessary in order to develop new therapeutic approaches. Here, we performed a comprehensive analysis of the expression and co-expression patterns of trophoblast cell-surface antigen 2 (TROP2), delta-like ligand 3 (DLL3), and carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) in CRPC samples from a rapid autopsy cohort. We show that DLL3 and CEACAM5 exhibit the highest expression in neuroendocrine prostate cancer (NEPC), while TROP2 is expressed across different CRPC molecular subtypes, except for NEPC. We observed variable intra-tumoral and inter-tumoral heterogeneity and no dominant metastatic site predilections for TROP2, DLL3, and CEACAM5. We further show that AR amplifications were associated with higher expression of PSMA and TROP2 but lower DLL3 and CEACAM5 levels. Conversely, PSMA and TROP2 expression was lower in RB1-altered tumors. In addition to genomic alterations, we demonstrate a tight correlation between epigenetic states, particularly histone H3 lysine 27 methylation (H3K27me3) at the transcriptional start site and gene body of TACSTD2 (encoding TROP2), DLL3, and CEACAM5, and their respective protein expression in CRPC patient-derived xenografts. Collectively, these findings provide novel insights into the patterns and determinants of expression of TROP2, DLL3, and CEACAM5 with important implications for the clinical development of cell surface targeting agents in CRPC.

The clinical development of antibody-drug conjugates for non-small cell lung cancer therapy

Despite the emergence of molecular targeted therapy and immune checkpoint inhibitors as standard first-line treatments for non-small cell lung cancer (NSCLC), their efficacy in some patients is limited by intrinsic and acquired resistance. Antibody-drug conjugates (ADCs), a revolutionary class of antitumor drugs, have displayed promising clinical outcomes in cancer treatment. In 2022, trastuzumab deruxtecan (Enhertu) was approved for treating HER2-mutated NSCLC, thereby underscoring the clinical value of ADCs in NSCLC treatment strategies. An increasing number of ADCs, focusing on NSCLC, are undergoing clinical trials, potentially positioning them as future treatment options. In this review, we encapsulate recent advancements in the clinical research of novel ADCs for treating NSCLC. Subsequently, we discuss the mechanisms of action, clinical efficacy, and associated limitations of these ADCs.

hIMB1636-MMAE, a Novel TROP2-Targeting Antibody-Drug Conjugate Exerting Potent Antitumor Efficacy in Pancreatic Cancer

Herein, we first prepared a novel anti-TROP2 antibody-drug conjugate (ADC) hIMB1636-MMAE using hIMB1636 antibody chemically coupled to monomethyl auristatin E (MMAE) via a Valine-Citrulline linker and then reported its characteristics and antitumor activity. With a DAR of 3.92, it binds specifically to both recombinant antigen (KD ∼ 0.687 nM) and cancer cells and could be internalized by target cells and selectively kill them with IC50 values at nanomolar/subnanomolar levels by inducing apoptosis and G2/M phase arrest. hIMB1636-MMAE also inhibited cell migration, induced ADCC effects, and had bystander effects. It displayed significant tumor-targeting ability and excellent tumor-suppressive effects in vivo, resulting in 5/8 tumor elimination at 12 mg/kg in the T3M4 xenograft model or complete tumor disappearance at 10 mg/kg in BxPc-3 xenografts in nude mice. Its half-life in mice was about 87 h. These data suggested that hIMB1636-MMAE was a promising candidate for the treatment of pancreatic cancer with TROP2 overexpression.

Organic-Solvent-Free "Lego-Like" Modular Preparation of Fab-Nondestructive Antibody-Drug Conjugates with Ultrahigh Drug-to-Antibody Ratio

Antibody-drug conjugates (ADCs) have exciting possibilities in targeted tumor therapy. However, in the existing ADC preparation processes, the random attachment of the payloads to the antigen-binding fragments (Fab) greatly increases the risk of disrupting its antigen recognition ability, while the drug-antibody ratio (DAR) is low, leading to a cumbersome preparation process and low drug delivery efficiency. Herein, poly(glutamic acid) is used to expand the number of drug binding sites, based on the "click chemistry" of azide and DBCO, and the high affinity of Fc-III-4C peptide to the crystalline fragment (Fc) of the monoclonal antibodies. Various antibody-polymer-drug conjugates are obtained with ultrahigh DAR using this organic-solvent-free "Lego-like" modular construction. Among them, aHER2-P-MMAE with DAR of 41.6 achieves tumor growth inhibition (TGI) of 99.7% for both medium-sized and large SKOV-3 ovarian tumors, and aPDL1-P-MMAE (DAR = 40.7) achieves TGI of 98.5% for MC38 colon tumors. In summary, a universal platform is created to prepare Fab-nondestructive ADCs with ultrahigh DAR, which can be used to develop precision medicine for personalized anticancer therapy.

Understanding the promising role of antibody drug conjugates in breast and ovarian cancer

A nascent category of anticancer therapeutic drugs called antibody-drug conjugates (ADCs) relate selectivity of aimed therapy using chemotherapeutic medicines with high cytotoxic power. Progressive linker technology led to the advancement of more efficacious and safer treatments. It offers neoteric as well as encouraging therapeutic strategies for treating cancer. ADCs selectively administer a medication by targeting antigens which are abundantly articulated on the membrane surface of tumor cells. Tumor-specific antigens are differently expressed in breast and ovarian cancers and can be utilized to direct ADCs. Compared to conventional chemotherapeutic drugs, this approach enables optimal tumor targeting while minimizing systemic damage. A cleavable linker improves the ADCs because it allows the toxic payload to be distributed to nearby cells that do not express the target protein, operating on assorted tumors with dissimilar cell aggregation. Presently fifteen ADCs are being studied in breast and ovarian carcinoma preclinically, and assortment of few have already undergone promising early-phase clinical trial testing. Furthermore, Phase I and II studies are investigating a wide variety of ADCs, and preliminary findings are encouraging. An expanding sum of ADCs will probably become feasible therapeutic choices as solo agents or in conjunction with chemotherapeutic agents. This review accentuates the most recent preclinical findings, pharmacodynamics, and upcoming applications of ADCs in breast and ovarian carcinoma.

Antibody drug conjugates: hitting the mark in pancreatic cancer?

Pancreatic cancer is one of the most common causes of cancer-related death, and the 5-year survival rate has only improved marginally over the last decade. Late detection of the disease means that in most cases the disease has advanced locally and/or metastasized, and curative surgery is not possible. Chemotherapy is still the first-line treatment however, this has only had a modest impact in improving survival, with associated toxicities. Therefore, there is an urgent need for targeted approaches to better treat pancreatic cancer, while minimizing treatment-induced side-effects. Antibody drug conjugates (ADCs) are one treatment option that could fill this gap. Here, a monoclonal antibody is used to deliver extremely potent drugs directly to the tumor site to improve on-target killing while reducing off-target toxicity. In this paper, we review the current literature for ADC targets that have been examined in vivo for treating pancreatic cancer, summarize current and on-going clinical trials using ADCs to treat pancreatic cancer and discuss potential strategies to improve their therapeutic window.

Decoding TROP2 in breast cancer: significance, clinical implications, and therapeutic advancements

Breast cancer is a heterogeneous disease characterized by distinct molecular subtypes, varied prognoses, and differential treatment responses. Understanding the molecular landscape and identifying therapeutic targets, such as trophoblast cell-surface antigen 2 (TROP2), is vital. TROP2 is notably overexpressed in breast cancer, playing a significant role in tumor growth, invasion, metastasis, and treatment resistance. While significant progress has been made in targeting TROP2 in breast cancer, several challenges and knowledge gaps remain. These challenges include the heterogeneity of TROP2 expression within breast cancer subtypes, resistance to its targeted therapies, potential off-target effects, limited therapeutic agents, and identifying optimal combination treatments. Integrating findings from clinical trials into clinical practice further complicates the landscape. This review article delves deep into TROP2 in breast cancer, highlighting its expression patterns, clinical implications, and therapeutic advancements. By understanding the role of TROP2, we can pave the way for personalized treatments, and transform the landscape of breast cancer care.

Assessing real-world safety concerns of Sacituzumab govitecan: a disproportionality analysis using spontaneous reports in the FDA adverse event reporting system

Aim

The aim of this study was to identify potential safety concerns associated with Sacituzumab Govitecan (SG), an antibody-drug conjugate targeting trophoblastic cell-surface antigen-2, by analyzing real-world safety data from the largest publicly available worldwide pharmacovigilance database.

Methods

All data obtained from the FDA Adverse Event Reporting System (FAERS) database from the second quarter of 2020 to the fourth quarter of 2022 underwent disproportionality analysis and Bayesian analysis to detect and assess the adverse event signals of SG, considering statistical significance when the lower limit of the 95% CI >1, based on at least 3 reports.

Results

Total of 1072 cases were included. The main safety signals were blood and lymphatic system disorders [ROR(95CI)=7.23 (6.43-8.14)], gastrointestinal disorders [ROR(95CI)=2.01 (1.81-2.22)], and relative infection adverse events, such as neutropenic sepsis [ROR(95CI)=46.02 (27.15-77.99)] and neutropenic colitis [ROR(95CI)=188.02 (120.09-294.37)]. We also noted unexpected serious safety signals, including large intestine perforation [ROR(95CI)=10.77 (3.47-33.45)] and hepatic failure [ROR(95CI)=3.87 (1.45-10.31)], as well as a high signal for pneumonitis [ROR(95CI)=9.93 (5.75-17.12)]. Additionally, age sub-group analysis revealed that geriatric patients (>65 years old) were at an increased risk of neutropenic colitis [ROR(95CI)=282.05 (116.36-683.66)], neutropenic sepsis [ROR(95CI)=101.11 (41.83-244.43)], acute kidney injury [ROR(95CI)=3.29 (1.36-7.94)], and atrial fibrillation [ROR(95CI)=6.91 (2.86-16.69)].

Conclusion

This study provides crucial real-world safety data on SG, complementing existing clinical trial information. Practitioners should identify contributing factors, employ monitoring and intervention strategies, and focus on adverse events like neutropenic sepsis, large intestine perforation, and hepatic failure. Further prospective studies are needed to address these safety concerns for a comprehensive understanding and effective management of associated risks.

Antibody-drug conjugates for urothelial carcinoma

The standard of care for advanced urothelial carcinoma includes platinum chemotherapy and immunotherapy. Antibody-drug conjugates (ADCs), originally developed for hematologic malignancies, involve potent cytotoxic agents linked to antibodies that recognize tumor-specific antigens; this rational drug design allows for more on-target efficacy, while mitigating systemic toxicity. Herein, we review the emerging landscape of ADCs in urothelial carcinoma. The anti-Nectin-4 ADC enfortumab vedotin has demonstrated efficacy in prospective studies in patients with advanced urothelial carcinoma in several settings either alone or in combination with pembrolizumab. The anti-Trop-2 ADC sacituzumab govitecan has also shown efficacy in single-armed studies. Both conjugates have full or accelerated approval from the Food and Drug Administration. Common adverse events include rash and neuropathy for enfortumab vedotin and myelosuppression and diarrhea for sacituzumab govitecan. Several anti-human epidermal growth factor receptor 2 ADCs are in clinical trials, and in localized bladder cancer, the anti-epithelial cell adhesion molecule ADC oportuzumab monatox is being studied in patients refractory to intravesical bacillus calmette-guerin therapy. Antibody-drug conjugates for urothelial carcinoma are approved and emerging as therapies for patients with advanced urothelial carcinoma, filling a prior void for treatment of progressive disease. Ongoing studies are also evaluating these agents in the neoadjuvant and adjuvant settings.

A new era in the treatment of urothelial carcinoma

The advances in targeted therapies, immunotherapy, and the recent emergence of antibody-drug conjugates (ADCs) herald a potential paradigm shift in treating patients with metastatic urothelial cancer. Yet, there are inherent challenges in utilizing these therapies, including the management of treatment-related toxicities. In this special Urologic Oncology: Seminars and Original Investigations issue, we review the latest developments and discuss insights into future research needs.

Clinical perspective: Antibody-drug conjugates for the treatment of HER2-positive breast cancer

Antibody-drug conjugates (ADCs) are a promising class of cancer biopharmaceuticals that exploit the specificity of a monoclonal antibody (mAb) to selectively deliver highly cytotoxic small molecules to targeted cancer cells, leading to an enhanced therapeutic index through increased antitumor activity and decreased off-target toxicity. ADCs hold great promise for the treatment of patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer after the approval and tremendous success of trastuzumab emtansine and trastuzumab deruxtecan, representing a turning point in both HER2-positive breast cancer treatment and ADC technology. Additionally and importantly, a total of 29 ADC candidates are now being investigated in different stages of clinical development for the treatment of HER2-positive breast cancer. The purpose of this review is to provide an insight into the ADC field in cancer treatment and present a comprehensive overview of ADCs approved or under clinical investigation for the treatment of HER2-positive breast cancer.

Antibody-drug conjugates (ADCs) targeting TROP-2 in lung cancer

INTRODUCTION

The advent of antibody-drug conjugates (ADCs) represents a renewed strategy in the era of precision oncology. Several epithelial tumors harbor overexpression of the trophoblast cell-surface antigen 2 (TROP-2), which represents a predictor of poor prognosis and a promising target for anticancer therapy.

AREAS COVERED

In this review, we aim to collect the available preclinical and clinical data regarding anti-TROP-2 ADCs in lung cancer obtained through extensive literature research and screening of the available abstract/posters presented at recent meetings.

EXPERT OPINION

Anti-TROP-2 ADCs represent an innovative upcoming weapon against both non-small cell lung cancer and small cell lung cancer subtypes, pending the results of several ongoing trials. The proper combination and placement of this agent throughout the lung cancer treatment pathway, the identification of potentially predictive biomarkers of benefit, as well as the optimal management and impact of peculiar toxicity (i.e. interstitial lung disease) are the next questions to be answered.

Targeting Trop-2 in cancer: Recent research progress and clinical application

The development of new antitumor drugs depends mainly upon targeting tumor cells precisely. Trophoblast surface antigen 2 (Trop-2) is a type I transmembrane glycoprotein involved in Ca2+ signaling in tumor cells. It is highly expressed in various tumor tissues than in normal tissues and represents a novel and promising molecular target for caner targeted therapy. Up to now, the mechanisms and functions associated with Trop-2 have been extensively studied in a variety of solid tumors. According to these findings, Trop-2 plays an important role in cell proliferation, apoptosis, cell adhesion, epithelial-mesenchymal transition, as well as tumorigenesis and tumor progression. In addition, Trop-2 related drugs are also being developed widely. There are a number of Trop-2 related ADC drugs that have demonstrated potent antitumor activity and are currently been studied, such as Sacituzumab Govitecan (SG) and Datopotamab Deruxtecan (Dato-Dxd). In this study, we reviewed the progress of Trop-2 research in solid tumors. We also sorted out the composition and rationale of Trop-2 related drugs and summarized the related clinical trials. Finally, we discussed the current status of Trop-2 research and expanded our perspectives on its future research directions. Importantly, we found that Trop-2 targeted ADCs have great potential for combination with other antitumor therapies. Trop-2 targeted ADCs can reprogramme tumor microenvironment through multiple signaling pathways, ultimately activating antitumor immunity.

Expression and Therapeutic Targeting of TROP-2 in Treatment-Resistant Prostate Cancer

PURPOSE

Men with metastatic castration-resistant prostate cancer (mCRPC) frequently develop resistance to androgen receptor signaling inhibitor (ARSI) treatment; therefore, new therapies are needed. Trophoblastic cell-surface antigen (TROP-2) is a transmembrane protein identified in prostate cancer and overexpressed in multiple malignancies. TROP-2 is a therapeutic target for antibody-drug conjugates (ADC).

EXPERIMENTAL DESIGN

TROP-2 gene (TACSTD2) expression and markers of treatment resistance from prostate biopsies were analyzed using data from four previously curated cohorts of mCRPC (n = 634) and the PROMOTE study (dbGaP accession phs001141.v1.p1, n = 88). EPCAM or TROP-2-positive circulating tumor cells (CTC) were captured from peripheral blood for comparison of protein (n = 15) and gene expression signatures of treatment resistance (n = 40). We assessed the efficacy of TROP-2-targeting agents in a mouse xenograft model generated from prostate cancer cell lines.

RESULTS

We demonstrated that TACSTD2 is expressed in mCRPC from luminal and basal tumors but at lower levels in patients with neuroendocrine prostate cancer. Patients previously treated with ARSI showed no significant difference in TACSTD2 expression, whereas patients with detectable AR-V7 expression showed increased expression. We observed that TROP-2 can serve as a cell surface target for isolating CTCs, which may serve as a predictive biomarker for ADCs. We also demonstrated that prostate cancer cell line xenografts can be targeted specifically by labeled anti-TROP-2 agents in vivo.

CONCLUSIONS

These results support further studies on TROP-2 as a therapeutic and diagnostic target for mCRPC.

Structure-Activity Relationships of Bis-Intercalating Peptides and Their Application as Antibody-Drug Conjugate Payloads

Synthetic analogs based on the DNA bis-intercalating natural product peptides sandramycin and quinaldopeptin were investigated as antibody drug conjugate (ADC) payloads. Synthesis, biophysical characterization, and in vitro potency of 34 new analogs are described. Conjugation of an initial drug-linker derived from a novel bis-intercalating peptide produced an ADC that was hydrophobic and prone to aggregation. Two strategies were employed to improve ADC physiochemical properties: addition of a solubilizing group in the linker and the use of an enzymatically cleavable hydrophilic mask on the payload itself. All ADCs showed potent in vitro cytotoxicity in high antigen expressing cells; however, masked ADCs were less potent than payload matched unmasked ADCs in lower antigen expressing cell lines. Two pilot in vivo studies were conducted using stochastically conjugated DAR4 anti-FRα ADCs, which showed toxicity even at low doses, and site-specific conjugated (THIOMAB) DAR2 anti-cMet ADCs that were well tolerated and highly efficacious.

Precision Medicine in Bladder Cancer: Present Challenges and Future Directions

Bladder cancer (BC) is characterized by significant histopathologic and molecular heterogeneity. The discovery of molecular pathways and knowledge of cellular mechanisms have grown exponentially and may allow for better disease classification, prognostication, and development of novel and more efficacious noninvasive detection and surveillance strategies, as well as selection of therapeutic targets, which can be used in BC, particularly in a neoadjuvant or adjuvant setting. This article outlines recent advances in the molecular pathology of BC with a better understanding and deeper focus on the development and deployment of promising biomarkers and therapeutic avenues that may soon make a transition into the domain of precision medicine and clinical management for patients with BC.

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.

Advances in Targeted Therapy of Breast Cancer with Antibody-Drug Conjugate

Antibody-drug conjugates (ADCs) are a potential and promising therapy for a wide variety of cancers, including breast cancer. ADC-based drugs represent a rapidly growing field of breast cancer therapy. Various ADC drug therapies have progressed over the past decade and have generated diverse opportunities for designing of state-of-the-art ADCs. Clinical progress with ADCs for the targeted therapy of breast cancer have shown promise. Off-target toxicities and drug resistance to ADC-based therapy have hampered effective therapy development due to the intracellular mechanism of action and limited antigen expression on breast tumors. However, innovative non-internalizing ADCs targeting the tumor microenvironment (TME) component and extracellular payload delivery mechanisms have led to reduced drug resistance and enhanced ADC effectiveness. Novel ADC drugs may deliver potent cytotoxic agents to breast tumor cells with reduced off-target effects, which may overcome difficulties related to delivery efficiency and enhance the therapeutic efficacy of cytotoxic cancer drugs for breast cancer therapy. This review discusses the development of ADC-based targeted breast cancer therapy and the clinical translation of ADC drugs for breast cancer treatment.

Recent advances in SN-38 drug delivery system

DNA topoisomerase I plays a key role in lubricatingthe wheels of DNA replication or RNA transcription through breaking and reconnecting DNA single-strand. It is widely known that camptothecin and its derivatives (CPTs) have inhibitory effects on topoisomerases I, and have obtained some clinical benefits in cancer treatment. The potent cytotoxicity makes 7-ethyl-10-hydroxycamptothecin (SN-38) become a brilliant star among these derivatives. However, some undesirable physical and chemical properties of this compound, including poor solubility and stability, seriously hinder its effective delivery to tumor sites. In recent years, strategies to alleviate these defects have aroused extensive research interest. By focusing on the loading mechanism, basic nanodrug delivery systems with SN-38 loaded, like nanoparticles, liposomes and micelles, are demonstrated here. Additionally, functionalized nanodrug delivery systems of SN-38 including prodrug and active targeted nanodrug delivery systems and delivery systems designed to overcome drug resistance are also reviewed. At last, challenges for future research in formulation development and clinical translation of SN-38 drug delivery system are discussed.

Overview of Trop-2 in Cancer: From Pre-Clinical Studies to Future Directions in Clinical Settings

Trophoblast cell surface antigen-2 (Trop-2) is a glycoprotein that was first described as a membrane marker of trophoblast cells and was associated with regenerative abilities. Trop-2 overexpression was also described in several tumour types. Nevertheless, the therapeutic potential of Trop-2 was widely recognized and clinical studies with drug–antibody conjugates have been initiated in various cancer types. Recently, these efforts have been rewarded with the approval of sacituzumab govitecan from both the Food and Drug Administration (FDA) and European Medicines Agency (EMA), for metastatic triple-negative breast cancer patients. In our work, we briefly summarize the various characteristics of cancer cells overexpressing Trop-2, the pre-clinical activities of specific inhibitors, and the role of anti-Trop-2 therapy in current clinical practice. We also review the ongoing clinical trials to provide a snapshot of the future developments of these therapies.

Antitumor activities of a defucosylated anti‑EpCAM monoclonal antibody in colorectal carcinoma xenograft models

Epithelial cell adhesion molecule (EpCAM) is a type I transmembrane glycoprotein, which is highly expressed on tumor cells. As EpCAM plays a crucial role in cell adhesion, survival, proliferation, stemness, and tumorigenesis, it has been considered as a promising target for tumor diagnosis and therapy. Anti‑EpCAM monoclonal antibodies (mAbs) have been developed and have previously demonstrated promising outcomes in several clinical trials. An anti‑EpCAM mAb, EpMab‑37 (mouse IgG₁, kappa) was previously developed by the authors, using the cell‑based immunization and screening method. In the present study, a defucosylated version of anti‑EpCAM mAb (EpMab‑37‑mG2a‑f) was generated to evaluate the antitumor activity against EpCAM‑positive cells. EpMab‑37‑mG_2a‑f recognized EpCAM‑overexpressing CHO‑K1 (CHO/EpCAM) cells with a moderate binding‑affinity [dissociation constant (K_D)=2.2x10^‑8 M] using flow cytometry. EpMab‑37‑mG_2a‑f exhibited potent antibody‑dependent cellular cytotoxicity (ADCC) and complement‑dependent cytotoxicity (CDC) for CHO/EpCAM cells by murine splenocytes and complements, respectively. Furthermore, the administration of EpMab‑37‑mG_2a‑f significantly suppressed CHO/EpCAM xenograft tumor development compared with the control mouse IgG. EpMab‑37‑mG_2a‑f also exhibited a moderate binding‑affinity (K_D=1.5x10^‑8 M) and high ADCC and CDC activities for a colorectal cancer cell line (Caco‑2 cells). The administration of EpMab‑37‑mG_2a‑f to Caco‑2 tumor‑bearing mice significantly suppressed tumor development compared with the control. By contrast, EpMab‑37‑mG_2a‑f never suppressed the xenograft tumor growth of Caco‑2 cells in which EpCAM was knocked out. On the whole, these results indicate that EpMab‑37‑mG_2a‑f may exert antitumor activities against EpCAM‑positive cancers and may thus be a promising therapeutic regimen for colorectal cancer.

Antibody-drug conjugates and predictive biomarkers in advanced urothelial carcinoma

The use of antibody-drug conjugates (ADCs) is expanding in several malignancies, including urothelial carcinoma where two of these medications have been approved for use and several others remain under study. ADCs act by binding to specific cell surface proteins, delivering anticancer agents directly to the target cells. Preclinical studies suggest that loss of these surface proteins alters sensitivity to therapy and expression of target proteins vary significantly based on the tumor subtype, prior therapies and other characteristics. However, use of biomarkers to predict treatment response have not been regularly included in clinical trials and clinician practice. In this review we summarize what is known about potential predictive biomarkers for ADCs in UC and discuss potential areas where use of biomarkers may improve patient care.

Antibody-Drug Conjugate Sacituzumab Govitecan Drives Efficient Tissue Penetration and Rapid Intracellular Drug Release

Antibody-drug conjugates (ADC) are a rapidly growing class of targeted cancer treatments, but the field has experienced significant challenges from their complex design. This study examined the multiscale distribution of sacituzumab govitecan (SG; Trodelvy), a recently clinically approved ADC, to clarify the mechanism(s) of efficacy given its unique design strategy. We employed a multiscale quantitative pharmacokinetic approach, including near-infrared fluorescence imaging, single-cell flow cytometry measurements, payload distribution via γH2AX pharmacodynamic staining, and a novel dual-labeled fluorescent technique to track the ADC and payload in a high trophoblast cell-surface antigen 2 expression xenograft model of gastric cancer (NCI-N87). We found that rapid release of the SN-38 payload from the hydrolysable linker inside cells imparts more DNA damage in vitro and in vivo than an ADC with a more stable enzyme cleavable linker. With SG, little to no extracellular payload release in the tumor was observed using a dual-labeled fluorescence technique, although bystander effects were detected. The high dosing regimen allowed the clinical dose to reach the majority of cancer cells, which has been linked to improved efficacy. In addition, the impact of multiple doses (day 1 and day 8) of a 21-day cycle was found to further improve tissue penetration despite not changing tumor uptake [percent injected dose per gram (%ID/g)] of the ADC. These results show increased ADC efficacy with SG can be attributed to efficient tumor penetration and intracellular linker cleavage after ADC internalization. This quantitative approach to study multiscale delivery can be used to inform the design of next-generation ADCs and prodrugs for other targets.

Advances in Trop2-targeted therapy: Novel agents and opportunities beyond breast cancer

Trop2 is a transmembrane glycoprotein and calcium signal transducer with limited expression in normal human tissues. It is consistently overexpressed in a variety of malignant tumors and participates in several oncogenic signaling pathways that lead to tumor development, invasion, and metastasis. As a result, Trop2 has become an attractive therapeutic target in cancer treatment. The anti-Trop2 antibody-drug conjugate (Trodelvy™, sacituzumab govitecan) has been approved to treat metastatic triple-negative breast cancer. However, it is still unclear whether the success observed in Trop2-positive breast cancer could be replicated in other tumor types, owing to the differences in the expression levels and functions of Trop2 across cancer types. In this review, we summarize the recent progress on the structures and functions of Trop2 and highlight the potential diagnostic and therapeutic value of Trop2 beyond breast cancer. In addition, the promising novel Trop2-targeted agents in the clinic were discussed, which will likely alter the therapeutic landscape of Trop2-positive tumors in the future.

Antibody-drug conjugates targeting Trop-2: Clinical developments in early breast cancer therapy

Although breast cancer has a good prognosis compared with various cancers, metastatic breast cancer has an aggressive disease course and remains incurable. Therefore, treatment of early breast cancer to prevent recurrence and metastasis is crucial. Recently, the development of anti-cancer drugs, such as targeted agents and immuno-oncology, has been accelerating. Antibody-drug conjugates (ADCs) are also building a new paradigm. Particularly, ADCs targeting Trop-2 were approved for their efficacy in metastatic triple-negative breast cancer patients who received ≥2 prior systemic therapies and showed significant results in heavily pretreated hormone receptor-positive/HER2-negative breast cancer. In this brief review, we provide an overview of ongoing clinical trials of ADCs targeting Trop-2 in early breast cancer, specifically sacituzumab govitecan.

SN-38 Sensitizes BRCA-Proficient Ovarian Cancers to PARP Inhibitors through Inhibiting Homologous Recombination Repair

As a multifunctional protein posttranslational modification enzyme in eukaryotic cells, Poly-ADP-ribose polymerase (PARP) acts as a DNA damage sensor, which helps to repair DNA damage through recruiting repair proteins to the DNA break sites. PARP inhibitors offer a significant clinical benefit for ovarian cancer with BRCA1/2 mutations. However, the majority of ovarian cancer patients harbor wild-type (WT) BRCA1/2 status, which narrows its clinical application. Here, we identified a small compound, SN-38, a CPT analog, which sensitizes BRCA-proficient ovarian cancer cells to PARP inhibitor treatment by inhibiting homologous recombination (HR) repair. SN-38 treatment greatly enhanced PARP inhibitor olaparib induced DNA double-strand breaks (DSBs) and DNA replication stress. Meanwhile, the combination of SN-38 and olaparib synergistically induced apoptosis in ovarian cancer. Furthermore, combination administration of SN-38 and olaparib induced synergistic antitumor efficacy in an ovarian cancer xenograft model in vivo. Therefore, our study provides a novel therapeutic strategy to optimize PARP inhibitor therapy for patients with BRCA-proficient ovarian cancer.

Small-molecule inhibitors, immune checkpoint inhibitors, and more: FDA-approved novel therapeutic drugs for solid tumors from 1991 to 2021

The United States Food and Drug Administration (US FDA) has always been a forerunner in drug evaluation and supervision. Over the past 31 years, 1050 drugs (excluding vaccines, cell-based therapies, and gene therapy products) have been approved as new molecular entities (NMEs) or biologics license applications (BLAs). A total of 228 of these 1050 drugs were identified as cancer therapeutics or cancer-related drugs, and 120 of them were classified as therapeutic drugs for solid tumors according to their initial indications. These drugs have evolved from small molecules with broad-spectrum antitumor properties in the early stage to monoclonal antibodies (mAbs) and antibody‒drug conjugates (ADCs) with a more precise targeting effect during the most recent decade. These drugs have extended indications for other malignancies, constituting a cancer treatment system for monotherapy or combined therapy. However, the available targets are still mainly limited to receptor tyrosine kinases (RTKs), restricting the development of antitumor drugs. In this review, these 120 drugs are summarized and classified according to the initial indications, characteristics, or functions. Additionally, RTK-targeted therapies and immune checkpoint-based immunotherapies are also discussed. Our analysis of existing challenges and potential opportunities in drug development may advance solid tumor treatment in the future.