Quantifying ADC bystander payload penetration with cellular resolution using pharmacodynamic mapping

Beyond Cytotoxic Potency: Disposition Features Required to Design ADC Payload

Antibody-drug conjugates (ADCs) have demonstrated impressive clinical usefulness in treating several types of cancer, with the notion of widening of the therapeutic index of the cytotoxic payload through the minimization of the systemic toxicity. Therefore, choosing the most appropriate payload molecule is a particularly important part of the early design phase of ADC development, especially given the highly competitive environment ADCs find themselves in today. The focus of the current review is to describe critical attributes/considerations needed in the discovery and ultimately development of cytotoxic payloads in support of ADC design. In addition to potency, several key dispositional characteristics including solubility, permeability and bystander effect, pharmacokinetics, metabolism, and drug-drug interactions, are described as being an integral part of the integrated activities required in the design of clinically safe and useful ADC therapeutic agents.

Sustained and Localized Drug Depot Release Using Radiation-Activated Scintillating Nanoparticles

Clinical treatment of cancer commonly incorporates X-ray radiation therapy (XRT), and developing spatially precise radiation-activatable drug delivery strategies may improve XRT efficacy while limiting off-target toxicities associated with systemically administered drugs. Nevertheless, achieving this has been challenging thus far because strategies typically rely on radical species with short lifespans, and the inherent nature of hypoxic and acidic tumor microenvironments may encourage spatially heterogeneous effects. It is hypothesized that the challenge could be bypassed by using scintillating nanoparticles that emit light upon X-ray absorption, locally forming therapeutic drug depots in tumor tissues. Thus a nanoparticle platform (Scintillating nanoparticle Drug Depot; SciDD) that enables the local release of cytotoxic payloads only after activation by XRT is developed, thereby limiting off-target toxicity. As a proof-of-principle, SciDD is used to deliver a microtubule-destabilizing payload MMAE (monomethyl auristatin E). With as little as a 2 Gy local irradiation to tumors, MMAE payloads are released effectively to kill tumor cells. XRT-mediated drug release is demonstrated in multiple mouse cancer models and showed efficacy over XRT alone (p < 0.0001). This work shows that SciDD can act as a local drug depot with spatiotemporally controlled release of cancer therapeutics.

A B7-H4-Targeting Antibody-Drug Conjugate Shows Antitumor Activity in PARPi and Platinum-Resistant Cancers with B7-H4 Expression

PURPOSE

Platinum and PARP inhibitors (PARPi) demonstrate activity in breast and ovarian cancers, but drug resistance ultimately emerges. Here, we examine B7-H4 expression in primary and recurrent high-grade serous ovarian carcinoma (HGSOC) and the activity of a B7-H4-directed antibody-drug conjugate (B7-H4-ADC), using a pyrrolobenzodiazepine-dimer payload, in PARPi- and platinum-resistant HGSOC patient-derived xenograft (PDX) models.

EXPERIMENTAL DESIGN

B7-H4 expression was quantified by flow cytometry and IHC. B7-H4-ADC efficacy was tested against multiple cell lines in vitro and PDX in vivo. The effect of B7-H4-ADC on cell cycle, DNA damage, and apoptosis was measured using flow cytometry.

RESULTS

B7-H4 is overexpressed in 92% of HGSOC tumors at diagnosis (n = 12), persisted in recurrent matched samples after platinum treatment, and was expressed at similar levels across metastatic sites after acquired multi-drug resistance (n = 4). Treatment with B7-H4-ADC resulted in target-specific growth inhibition of multiple ovarian and breast cancer cell lines. In platinum- or PARPi-resistant ovarian cancer cells, B7-H4-ADC significantly decreased viability and colony formation while increasing cell-cycle arrest and DNA damage, ultimately leading to apoptosis. Single-dose B7-H4-ADC led to tumor regression in 65.5% of breast and ovarian PDX models (n = 29), with reduced activity in B7-H4 low or negative models. In PARPi and platinum-resistant HGSOC PDX models, scheduled B7-H4-ADC dosing led to sustained tumor regression and increased survival.

CONCLUSIONS

These data support B7-H4 as an attractive ADC target for treatment of drug-resistant HGSOC and provide evidence for activity of an ADC with a DNA-damaging payload in this population. See related commentary by Veneziani et al., p. 1434.

What influences the activity of Degrader-Antibody conjugates (DACs)

The targeted protein degradation (TPD) technology employing proteolysis-targeting chimeras (PROTACs) has been widely applied in drug chemistry and chemical biology for the treatment of cancer and other diseases. PROTACs have demonstrated significant advantages in targeting undruggable targets and overcoming drug resistance. However, despite the efficient degradation of targeted proteins achieved by PROTACs, they still face challenges related to selectivity between normal and cancer cells, as well as issues with poor membrane permeability due to their substantial molecular weight. Additionally, the noteworthy toxicity resulting from off-target effects also needs to be addressed. To solve these issues, Degrader-Antibody Conjugates (DACs) have been developed, leveraging the targeting and internalization capabilities of antibodies. In this review, we elucidates the characteristics and distinctions between DACs, and traditional Antibody-drug conjugates (ADCs). Meanwhile, we emphasizes the significance of DACs in facilitating the delivery of PROTACs and delves into the impact of various components on DAC activity. These components include antibody targets, drug-antibody ratio (DAR), linker types, PROTACs targets, PROTACs connections, and E3 ligase ligands. The review also explores the suitability of different targets (antibody targets or PROTACs targets) for DACs, providing insights to guide the design of PROTACs better suited for antibody conjugation.

Improving Intracellular Delivery of an Antibody-Drug Conjugate Targeting Carcinoembryonic Antigen Increases Efficacy at Clinically Relevant Doses In Vivo

Solid tumor antibody-drug conjugates (ADC) have experienced more clinical success in the last 5 years than the previous 18-year span since the first ADC approval in 2000. While recent advances in protein engineering, linker design, and payload variations have played a role in this success, high expression and readily internalized targets have also been crucial to solid tumor therapy. However, these factors are also paradoxically connected to poor tissue penetration and lower efficacy. Previous work shows that potent ADCs can benefit from slower internalization under subsaturating doses to improve tissue penetration and increase tumor response. In contrast, faster internalization is predicted to increase efficacy under higher, tumor saturating doses. In this work, the intracellular delivery of SN-38 conjugated to an anti-carcinoembryonic antigen (anti-CEA) antibody (Ab) is increased by coadministering a noncompeting (cross-linking) anti-CEA Ab to improve efficacy in a colorectal carcinoma animal model. The SN-38 payload enables broad tumor saturation with clinically-tolerable doses, and under these saturating conditions, using a second CEA receptor cross-linking Ab yields faster internalization, which increases tumor killing efficacy. Our spheroid results show indirect bystander killing can also occur, but the more efficient direct cell killing from targeted intracellular payload release drives a greater tumor response. These results provide a strategy to increase therapeutic effectiveness with improved intracellular delivery under tumor saturating doses with the potential to expand the ADC target repertoire.

Spatiotemporal Quantification of HER2-targeting Antibody-Drug Conjugate Bystander Activity and Enhancement of Solid Tumor Penetration

PURPOSE

Antibody-drug conjugate (ADC) has had a transformative effect on the treatment of many solid tumors, yet it remains unclear how ADCs exert bystander activity in the tumor microenvironment.

EXPERIMENTAL DESIGN

Here, we directly visualized and spatiotemporally quantified the intratumor biodistribution and pharmacokinetics of different ADC components by developing dual-labeled fluorescent probes.

RESULTS

Mechanistically, we found that tumor penetration of ADCs is distinctly affected by their ability to breach the binding site barrier (BSB) in perivascular regions of tumor vasculature, and bystander activity of ADC can only partially breach BSB. Furthermore, bystander activity of ADCs can work in synergy with coadministration of their parental antibodies, leading to fully bypassing BSBs and enhancing tumor penetration via a two-step process.

CONCLUSIONS

These promising preclinical data allowed us to initiate a phase I/II clinical study of coadministration of RC48 and trastuzumab in patients with malignant stomach cancer to further evaluate this treatment strategy in humans.

Drug conjugates for the treatment of lung cancer: from drug discovery to clinical practice

A drug conjugate consists of a cytotoxic drug bound via a linker to a targeted ligand, allowing the targeted delivery of the drug to one or more tumor sites. This approach simultaneously reduces drug toxicity and increases efficacy, with a powerful combination of efficient killing and precise targeting. Antibody‒drug conjugates (ADCs) are the best-known type of drug conjugate, combining the specificity of antibodies with the cytotoxicity of chemotherapeutic drugs to reduce adverse reactions by preferentially targeting the payload to the tumor. The structure of ADCs has also provided inspiration for the development of additional drug conjugates. In recent years, drug conjugates such as ADCs, peptide‒drug conjugates (PDCs) and radionuclide drug conjugates (RDCs) have been approved by the Food and Drug Administration (FDA). The scope and application of drug conjugates have been expanding, including combination therapy and precise drug delivery, and a variety of new conjugation technology concepts have emerged. Additionally, new conjugation technology-based drugs have been developed in industry. In addition to chemotherapy, targeted therapy and immunotherapy, drug conjugate therapy has undergone continuous development and made significant progress in treating lung cancer in recent years, offering a promising strategy for the treatment of this disease. In this review, we discuss recent advances in the use of drug conjugates for lung cancer treatment, including structure-based drug design, mechanisms of action, clinical trials, and side effects. Furthermore, challenges, potential approaches and future prospects are presented.

HER2-targeted therapies in cancer: a systematic review

Abnormal alterations in human epidermal growth factor receptor 2 (HER2, neu, and erbB2) are associated with the development of many tumors. It is currently a crucial treatment for multiple cancers. Advanced in molecular biology and further exploration of the HER2-mediated pathway have promoted the development of medicine design and combination drug regimens. An increasing number of HER2-targeted drugs including specific monoclonal antibodies, tyrosine kinase inhibitors (TKIs), and antibody-drug conjugates (ADCs) have been approved by the U.S. Food and Drug Administration. The emergence of ADCs, has significantly transformed the treatment landscape for various tumors, such as breast, gastric, and bladder cancer. Classic monoclonal antibodies and novel TKIs have not only demonstrated remarkable efficacy, but also expanded their indications, with ADCs in particular exhibiting profound clinical applications. Moreover the concept of low HER2 expression signifies a breakthrough in HER2-targeted therapy, indicating that an increasing number of tumors and patients will benefit from this approach. This article, provides a comprehensive review of the underlying mechanism of action, representative drugs, corresponding clinical trials, recent advancements, and future research directions pertaining to HER2-targeted therapy.

Impact of tissue penetration and albumin binding on design of T cell targeted bispecific agents

Bispecific agents are a rapidly growing class of cancer therapeutics, and immune targeted bispecific agents have the potential to expand functionality well beyond monoclonal antibody agents. Humabodies⁎ are fully human single domain antibodies that can be linked in a modular fashion to form multispecific therapeutics. However, the effect of heterogeneous delivery on the efficacy of crosslinking bispecific agents is currently unclear. In this work, we utilize a PSMA-CD137 Humabody with an albumin binding half-life extension (HLE) domain to determine the impact of tissue penetration on T cell activating bispecific agents. Using heterotypic spheroids, we demonstrate that increased tissue penetration results in higher T cell activation at sub-saturating concentrations. Next, we tested the effect of two different albumin binding moieties on tissue distribution using albumin-specific HLE domains with varying affinities for albumin and a non-specific lipophilic dye. The results show that a specific binding mechanism to albumin does not influence tissue penetration, but a non-specific mechanism reduced both spheroid uptake and distribution in the presence of albumin. These results highlight the potential importance of tissue penetration on bispecific agent efficacy and describe how the design parameters including albumin-binding domains can be selected to maximize the efficacy of bispecific agents.

Targeting HER2 and FGFR-positive cancer cells with a bispecific cytotoxic conjugate combining anti-HER2 Affibody and FGF2

Breast cancer remains a significant global health challenge, necessitating the development of effective targeted therapies. This study aimed to create bispecific targeting molecules against HER2 and FGFR1, two receptors known to play crucial roles in breast cancer progression. By combining the high-affinity Affibody ZHER2:2891 and a modified, stable form of fibroblast growth factor 2 (FGF2), we successfully generated bispecific proteins capable of simultaneously recognizing HER2 and FGFR1. Two variants were designed: AfHER2-sFGF2 with a shorter linker and AfHER2-lFGF2 with a longer linker between the HER2 and FGFR1-recognizing proteins. Both proteins exhibited selective binding to HER2 and FGFR1, with AfHER2-lFGF2 demonstrating simultaneous binding to both receptors. AfHER2-lFGF2 exhibited superior internalization compared to FGF2 in FGFR-positive cells and significantly increased internalization compared to AfHER2 in HER2-positive cells. To enhance their therapeutic potential, highly potent cytotoxic agent MMAE was conjugated to the targeting proteins, resulting in protein-drug conjugates. The bispecific AfHER2-lFGF2-vcMMAE conjugate demonstrated exceptional cytotoxic activity against HER2-positive, FGFR-positive, and dual-positive cancer cell lines that was significantly higher compared to monospecific conjugates. These data indicate the beneficial effect of simultaneous targeting of HER2 and FGFR1 in precise anticancer medicine and contribute valuable insights into the design and potential of bispecific targeting molecules for breast cancer treatment.

The Evolving Landscape of Antibody-Drug Conjugates: In Depth Analysis of Recent Research Progress

Antibody-drug conjugates (ADCs) are targeted immunoconjugate constructs that integrate the potency of cytotoxic drugs with the selectivity of monoclonal antibodies, minimizing damage to healthy cells and reducing systemic toxicity. Their design allows for higher doses of the cytotoxic drug to be administered, potentially increasing efficacy. They are currently among the most promising drug classes in oncology, with efforts to expand their application for nononcological indications and in combination therapies. Here we provide a detailed overview of the recent advances in ADC research and consider future directions and challenges in promoting this promising platform to widespread therapeutic use. We examine data from the CAS Content Collection, the largest human-curated collection of published scientific information, and analyze the publication landscape of recent research to reveal the exploration trends in published documents and to provide insights into the scientific advances in the area. We also discuss the evolution of the key concepts in the field, the major technologies, and their development pipelines with company research focuses, disease targets, development stages, and publication and investment trends. A comprehensive concept map has been created based on the documents in the CAS Content Collection. We hope that this report can serve as a useful resource for understanding the current state of knowledge in the field of ADCs and the remaining challenges to fulfill their potential.

SGN-B7H4V, an investigational vedotin ADC directed to the immune checkpoint ligand B7-H4, shows promising activity in preclinical models

BACKGROUND

SGN-B7H4V is a novel investigational vedotin antibody-drug conjugate (ADC) comprising a B7-H4-directed human monoclonal antibody conjugated to the cytotoxic payload monomethyl auristatin E (MMAE) via a protease-cleavable maleimidocaproyl valine citrulline (mc-vc) linker. This vedotin linker-payload system has been clinically validated in multiple Food and Drug Administration approved agents including brentuximab vedotin, enfortumab vedotin, and tisotumab vedotin. B7-H4 is an immune checkpoint ligand with elevated expression on a variety of solid tumors, including breast, ovarian, and endometrial tumors, and limited normal tissue expression. SGN-B7H4V is designed to induce direct cytotoxicity against target cells by binding to B7-H4 on the surface of target cells and releasing the cytotoxic payload MMAE upon internalization of the B7-H4/ADC complex.

METHODS

B7-H4 expression was characterized by immunohistochemistry across multiple solid tumor types. The ability of SGN-B7H4V to kill B7-H4-expressing tumor cells in vitro and in vivo in a variety of xenograft tumor models was also evaluated. Finally, the antitumor activity of SGN-B7H4V as monotherapy and in combination with an anti-programmed cell death-1 (PD-1) agent was evaluated using an immunocompetent murine B7-H4-expressing Renca tumor model.

RESULTS

Immunohistochemistry confirmed B7-H4 expression across multiple solid tumors, with the highest prevalence in breast, endometrial, and ovarian tumors. In vitro, SGN-B7H4V killed B7-H4-expressing tumor cells by MMAE-mediated direct cytotoxicity and antibody-mediated effector functions including antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis. In vivo, SGN-B7H4V demonstrated strong antitumor activity in multiple xenograft models of breast and ovarian cancer, including xenograft tumors with heterogeneous B7-H4 expression, consistent with the ability of vedotin ADCs to elicit a bystander effect. In an immunocompetent murine B7-H4-expressing tumor model, SGN-B7H4V drove robust antitumor activity as a monotherapy that was enhanced when combined with an anti-PD-1 agent.

CONCLUSION

The immune checkpoint ligand B7-H4 is a promising molecular target expressed by multiple solid tumors. SGN-B7H4V demonstrates robust antitumor activity in preclinical models through multiple potential mechanisms. Altogether, these preclinical data support the evaluation of SGN-B7H4V as a monotherapy in the ongoing phase 1 study of SGN-B7H4V in advanced solid tumors (NCT05194072) and potential future clinical combinations with immunotherapies.

Mechanistically Weighted Metric to Predict In Vivo Antibody-Receptor Occupancy: An Analytical Approach

In situ clinical measurement of receptor occupancy (RO) is challenging, particularly for solid tumors, necessitating the use of mathematical models that predict tumor receptor occupancy to guide dose decisions. A potency metric, average free tissue target to initial target ratio (AFTIR), was previously described based on a mechanistic compartmental model and is informative for near-saturating dose regimens. However, the metric fails at clinically relevant subsaturating antibody doses, as compartmental models cannot capture the spatial heterogeneity of distribution faced by some antibodies in solid tumors. Here we employ a partial differential equation (PDE) Krogh cylinder model to simulate spatiotemporal receptor occupancy and derive an analytical solution, a mechanistically weighted global AFTIR, that can better predict receptor occupancy regardless of dosing regimen. In addition to the four key parameters previously identified, a fifth key parameter, the absolute receptor density (targets/cell), is incorporated into the mechanistic AFTIR metric. Receptor density can influence equilibrium intratumoral drug concentration relative to whether the dose is saturating or not, thereby influencing the tumor penetration depth of the antibody. We derive mechanistic RO predictions based on distinct patterns of antibody tumor penetration, presented as a global AFTIR metric guided by a Thiele Modulus and a local saturation potential (drug equivalent of binding potential for positron emissions tomography imaging) and validate the results using rigorous global and local sensitivity analysis. This generalized AFTIR serves as a more accurate analytical metric to aid clinical dose decisions and rational design of antibody-based therapeutics without the need for extensive PDE simulations. SIGNIFICANCE STATEMENT: Determining antibody-receptor occupancy (RO) is critical for dosing decisions in pharmaceutical development, but direct clinical measurement of RO is often challenging and invasive, particularly for solid tumors. Significant efforts have been made to develop mathematical models and simplified analytical metrics of RO, but these often require complex computer simulations. Here we present a mathematically rigorous but simplified analytical model to accurately predict RO across a range of affinities, doses, drug, and tumor properties.

Antibody Drug Conjugates in Bladder Cancer: Current Milestones and Future Perspectives

OPINION STATEMENT

Over the last several years, the treatment landscape of urothelial carcinoma has witnessed an unprecedented expansion of therapeutic options including checkpoint inhibitors, tyrosine kinase inhibitors, and antibody drug conjugates (ADC). Early trial data has shown that ADCs are safer and potentially effective treatment options in advanced bladder cancer as well as in the early disease. In particular, enfortumab-vedotin (EV) has shown promising results with a recent cohort of a clinical trial demonstrating that EV is effective as neoadjuvant monotherapy as well as in combination with pembrolizumab in metastatic setting. Similar promising results have been shown by other classes of ADC in other trials including sacituzumab-govitecan (SG) and oportuzumab monatox (OM). ADCs are likely to become a mainstay treatment option in the urothelial carcinoma playbook as either a monotherapy or combination therapy. The cost of the drug presents a real challenge, but further trial data may justify the use of the drug as mainstay treatment.

Antibody-Drug Conjugates for the Treatment of Renal Cancer: A Scoping Review on Current Evidence and Clinical Perspectives

Antibody-drug conjugates (ADCs) are complex chemical structures composed of a monoclonal antibody, serving as a link to target cells, which is conjugated with a potent cytotoxic drug (i.e., payload) through a chemical linker. Inspired by Paul Ehrlich's concept of the ideal anticancer drug as a "magic bullet", ADCs are also highly specific anticancer agents, as they have been demonstrated to recognize, bind, and neutralize cancer cells, limiting injuries to normal cells. ADCs are among the newest pharmacologic breakthroughs in treating solid and hematologic malignancies. Indeed, in recent years, various ADCs have been approved by the Food and Drug Administration and European Medicines Agency for the treatment of several cancers, resulting in a "practice-changing" approach. However, despite these successes, no ADC is approved for treating patients affected by renal cell carcinoma (RCC). In the present paper, we thoroughly reviewed the current literature and summarized preclinical studies and clinical trials that evaluated the activity and toxicity profile of ADCs in RCC patients. Moreover, we scrutinized the potential causes that, until now, hampered the therapeutical success of ADCs in those patients. Finally, we discussed novel strategies that would improve the development of ADCs and their efficacy in treating RCC patients.

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.

Pharmacokinetics and Pharmacodynamics of TAK-164 Antibody Drug Conjugate Coadministered with Unconjugated Antibody

The development of new antibody-drug conjugates (ADCs) has led to the approval of 7 ADCs by the FDA in 4 years. Given the impact of intratumoral distribution on efficacy of these therapeutics, coadministration of unconjugated antibody with ADC has been shown to improve distribution and efficacy of several ADCs in high and moderately expressed tumor target systems by increasing tissue penetration. However, the benefit of coadministration in low expression systems is less clear. TAK-164, an ADC composed of an anti-GCC antibody (5F9) conjugated to a DGN549 payload, has demonstrated heterogeneous distribution and bystander killing. Here, we evaluated the impact of 5F9 coadministration on distribution and efficacy of TAK-164 in a primary human tumor xenograft mouse model. Coadministration was found to improve the distribution of TAK-164 within the tumor, but it had no significant impact (increase or decrease) on efficacy. Experimental and computational evidence indicates that this was not a result of tumor saturation, increased binding to perivascular cells, or compensatory bystander effects. Rather, the cellular potency of DGN549 was matched with the single-cell uptake of TAK-164 making its IC50 close to its equilibrium binding affinity (KD), and as such, coadministration dilutes total DGN549 in cells below the maximum cytotoxic concentration, thereby offsetting an increased number of targeted cells with decreased ability to kill each cell. These results provide new insights on matching payload potency to ADC delivery to help identify when increasing tumor penetration is beneficial for improving ADC efficacy and demonstrate how mechanistic simulations can be leveraged to design clinically effective ADCs.

ADME and DMPK considerations for the discovery and development of antibody drug conjugates (ADCs)

 The therapeutic concept of antibody drug conjugates (ADCs) is to selectively target tumour cells with small molecule cytotoxic drugs to maximise cell kill benefit and minimise healthy tissue toxicity.An ADC generally consists of an antibody that targets a protein on the surface of tumour cells chemically linked to a warhead small molecule cytotoxic drug.To deliver the warhead to the tumour cell, the antibody must bind to the target protein and in general be internalised into the cell. Following internalisation, the cytotoxic agent can be released in the endosomal or lysosomal compartment (via different mechanisms). Diffusion or transport out of the endosome or lysosome allows the cytotoxic drug to express its cell-killing pharmacology. Alternatively, some ADCs (e.g. EDB-ADCs) rely on extracellular cleavage releasing membrane permeable warheads.One potentially important aspect of the ADC mechanism is the 'bystander effect' whereby the cytotoxic drug released in the targeted cell can diffuse out of that cell and into other (non-target expressing) tumour cells to exert its cytotoxic effect. This is important as solid tumours tend to be heterogeneous and not all cells in a tumour will express the targeted protein.The combination of large and small molecule aspects in an ADC poses significant challenges to the disposition scientist in describing the ADME properties of the entire molecule.This article will review the ADC landscape and the ADME properties of successful ADCs, with the aim of outlining best practice and providing a perspective of how the field can further facilitate the discovery and development of these important therapeutic modalities.

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.

Design of high avidity and low affinity antibodies for in situ control of antibody drug conjugate targeting

Antibody-Drug Conjugates (ADCs) have rapidly expanded in the clinic, with 7 new approvals in 3 years. For solid tumors, high doses of ADCs improve tissue penetration and efficacy. These doses are enabled by lower drug-to-antibody ratios and/or co-administration of unconjugated antibody carrier doses to avoid payload toxicity. While effective for highly expressed targets, these strategies may not maintain efficacy with lower target expression. To address this issue, a carrier dose that adjusts binding in situ according to cellular expression was designed using computational modeling. Previous studies demonstrated that coadministration of unconjugated antibody with the corresponding ADC at an 8:1 ratio improves ADCs efficacy in high HER2 expressing tumors. By designing a High Avidity, Low Affinity (HALA) carrier antibody, ADC binding is partially blocked in high expression cells, improving tissue penetration. In contrast, the HALA antibody cannot compete with the ADC in low expressing cells, allowing ADC binding to the majority of receptors. Thus, the amount of competition from the carrier dose automatically adjusts to expression levels, allowing tailored competition between different patients/metastases. The computational model highlights two dimensionless numbers, the Thiele modulus and a newly defined competition number, to design an optimal HALA antibody carrier dose for any target.

Degrader-antibody conjugates

Degrader-antibody conjugates (DACs) are novel entities that combine a proteolysis targeting chimera (PROTAC) payload with a monoclonal antibody via some type of chemical linker. This review provides a current summary of the DAC field. Many general aspects associated with the creation and biological performance of traditional cytotoxic antibody-drug conjugates (ADCs) are initially presented. These characteristics are subsequently compared and contrasted with related parameters that impact DAC generation and biological activity. Several examples of DACs assembled from both the scientific and the patent literature are utilized to highlight differing strategies for DAC creation, and specific challenges associated with DAC construction are documented. Collectively, the assembled examples demonstrate that biologically-active DACs can be successfully prepared using a variety of PROTAC payloads which employ diverse E3 ligases to degrade multiple protein targets.

Predictive Simulations in Preclinical Oncology to Guide the Translation of Biologics

Preclinical in vivo studies form the cornerstone of drug development and translation, bridging in vitro experiments with first-in-human trials. However, despite the utility of animal models, translation from the bench to bedside remains difficult, particularly for biologics and agents with unique mechanisms of action. The limitations of these animal models may advance agents that are ineffective in the clinic, or worse, screen out compounds that would be successful drugs. One reason for such failure is that animal models often allow clinically intolerable doses, which can undermine translation from otherwise promising efficacy studies. Other times, tolerability makes it challenging to identify the necessary dose range for clinical testing. With the ability to predict pharmacokinetic and pharmacodynamic responses, mechanistic simulations can help advance candidates from in vitro to in vivo and clinical studies. Here, we use basic insights into drug disposition to analyze the dosing of antibody drug conjugates (ADC) and checkpoint inhibitor dosing (PD-1 and PD-L1) in the clinic. The results demonstrate how simulations can identify the most promising clinical compounds rather than the most effective in vitro and preclinical in vivo agents. Likewise, the importance of quantifying absolute target expression and antibody internalization is critical to accurately scale dosing. These predictive models are capable of simulating clinical scenarios and providing results that can be validated and updated along the entire development pipeline starting in drug discovery. Combined with experimental approaches, simulations can guide the selection of compounds at early stages that are predicted to have the highest efficacy in the clinic.

Maximizing response to intratumoral immunotherapy in mice by tuning local retention

Direct injection of therapies into tumors has emerged as an administration route capable of achieving high local drug exposure and strong anti-tumor response. A diverse array of immune agonists ranging in size and target are under development as local immunotherapies. However, due to the relatively recent adoption of intratumoral administration, the pharmacokinetics of locally-injected biologics remains poorly defined, limiting rational design of tumor-localized immunotherapies. Here we define a pharmacokinetic framework for biologics injected intratumorally that can predict tumor exposure and effectiveness. We find empirically and computationally that extending the tumor exposure of locally-injected interleukin-2 by increasing molecular size and/or improving matrix-targeting affinity improves therapeutic efficacy in mice. By tracking the distribution of intratumorally-injected proteins using positron emission tomography, we observe size-dependent enhancement in tumor exposure occurs by slowing the rate of diffusive escape from the tumor and by increasing partitioning to an apparent viscous region of the tumor. In elucidating how molecular weight and matrix binding interplay to determine tumor exposure, our model can aid in the design of intratumoral therapies to exert maximal therapeutic effect.

Antibody-drug conjugates: Resurgent anticancer agents with multi-targeted therapeutic potential

Antibody-drug conjugates (ADCs) constitute a relatively new group of anticancer agents, whose first appearance took place about two decades ago, but a renewed interest occurred in recent years, following the success of anti-cancer immunotherapy with monoclonal antibodies. Indeed, an ADC combines the selectivity of a monoclonal antibody with the cell killing properties of a chemotherapeutic agent (payload), joined together through an appropriate linker. The antibody moiety targets a specific cell surface antigen expressed by tumor cells and/or cells of the tumor microenvironment and acts as a carrier that delivers the cytotoxic payload within the tumor mass. Despite advantages in terms of selectivity and potency, the development of ADCs is not devoid of challenges, due to: i) low tumor selectivity when the target antigens are not exclusively expressed by cancer cells; ii) premature release of the cytotoxic drug into the bloodstream as a consequence of linker instability; iii) development of tumor resistance mechanisms to the payload. All these factors may result in lack of efficacy and/or in no safety improvement compared to unconjugated cytotoxic agents. Nevertheless, the development of antibodies engineered to remain inert until activated in the tumor (e.g., antibodies activated proteolytically after internalization or by the acidic conditions of the tumor microenvironment) together with the discovery of innovative targets and cytotoxic or immunomodulatory payloads, have allowed the design of next-generation ADCs that are expected to possess improved therapeutic properties. This review provides an overview of approved ADCs, with related advantages and limitations, and of novel targets exploited by ADCs that are presently under clinical investigation.

Simulating the Selection of Resistant Cells with Bystander Killing and Antibody Coadministration in Heterogeneous Human Epidermal Growth Factor Receptor 2-Positive Tumors

Intratumoral heterogeneity is a leading cause of treatment failure resulting in tumor recurrence. For the antibody-drug conjugate (ADC) ado-trastuzumab emtansine (T-DM1), two major types of resistance include changes in human epidermal growth factor receptor 2 (HER2) expression and reduced payload sensitivity, which is often exacerbated by heterogenous HER2 expression and ADC distribution during treatment. ADCs with bystander payloads, such as trastuzumab-monomethyl auristatin E (T-MMAE), can reach and kill adjacent cells with lower receptor expression that cannot be targeted directly with the ADC. Additionally, coadministration of T-DM1 with its unconjugated antibody, trastuzumab, can improve distribution and minimize heterogeneous delivery. However, the effectiveness of trastuzumab coadministration and ADC bystander killing in heterogenous tumors in reducing the selection of resistant cells is not well understood. Here, we use an agent-based model to predict outcomes with these different regimens. The simulations demonstrate that both T-DM1 and T-MMAE benefit from trastuzumab coadministration for tumors with high average receptor expression (up to 70% and 40% decrease in average tumor volume, respectively), with greater benefit for nonbystander payloads. However, the benefit decreases as receptor expression is reduced, reversing at low concentrations (up to 360% and 430% increase in average tumor volume for T-DM1 and T-MMAE, respectively) for this mechanism that impacts both ADC distribution and efficacy. For tumors with intrinsic payload resistance, coadministration uniformly exhibits better efficacy than ADC monotherapy (50%-70% and 19%-36% decrease in average tumor volume for T-DM1 and T-MMAE, respectively). Finally, we demonstrate that several regimens select for resistant cells at clinical tolerable doses, which highlights the need to pursue other mechanisms of action for durable treatment responses. SIGNIFICANCE STATEMENT: Experimental evidence demonstrates heterogeneity in the distribution of both the antibody-drug conjugate and the target receptor in the tumor microenvironment, which can promote the selection of resistant cells and lead to recurrence. This study quantifies the impact of increasing the antibody dose and utilizing bystander payloads in heterogeneous tumors. Alternative cell-killing mechanisms are needed to avoid enriching resistant cell populations.

Cellular-Resolution Imaging of Bystander Payload Tissue Penetration from Antibody-Drug Conjugates

After several notable clinical failures in early generations, antibody-drug conjugates (ADCs) have made significant gains with seven new FDA-approvals within the last 3 years. These successes have been driven by a shift towards mechanistically informed ADC design, where the payload, linker, drug-to-antibody ratio, and conjugation are increasingly tailored to a specific target and clinical indication. However, fundamental aspects needed for design, such as payload distribution, remain incompletely understood. Payloads are often classified as 'bystander' or 'non-bystander' depending on their ability to diffuse out of targeted cells into adjacent cells that may be antigen negative or more distant from tumor vessels, helping to overcome heterogeneous distribution. Seven of the eleven FDA-approved ADCs employ these bystander payloads, but the depth of penetration and cytotoxic effects as a function of physicochemical properties and mechanism of action have not been fully characterized. Here, we utilized tumor spheroids and pharmacodynamic marker staining to quantify tissue penetration of the three major classes of agents: microtubule inhibitors, DNA-damaging agents, and topoisomerase inhibitors. PAMPA data and co-culture assays were performed to compare to the 3D tissue culture data. The results demonstrate a spectrum in bystander potential and tissue penetration depending on the physicochemical properties and potency of the payload. Generally, directly targeted cells show a greater response even with bystander payloads, consistent with the benefit of deeper ADC penetration. These results are compared to computational simulations to help scale the data from in vitro and preclinical animal models to the clinic.

Antibody-Drug Conjugates: Functional Principles and Applications in Oncology and Beyond

In the era of precision medicine, antibody-based therapeutics are rapidly enriched with emerging advances and new proof-of-concept formats. In this context, antibody-drug conjugates (ADCs) have evolved to merge the high selectivity and specificity of monoclonal antibodies (mAbs) with the cytotoxic potency of attached payloads. So far, ten ADCs have been approved by FDA for oncological indications and many others are currently being tested in clinical and preclinical level. This paper summarizes the essential components of ADCs, from their functional principles and structure up to their limitations and resistance mechanisms, focusing on all latest bioengineering breakthroughs such as bispecific mAbs, dual-drug platforms as well as novel linkers and conjugation chemistries. In continuation of our recent review on anticancer implication of ADC's technology, further insights regarding their potential usage outside of the oncological spectrum are also presented. Better understanding of immunoconjugates could maximize their efficacy and optimize their safety, extending their use in everyday clinical practice.

A phase I/II study of rovalpituzumab tesirine in delta-like 3-expressing advanced solid tumors

Delta-like protein 3 (DLL3) is highly expressed in solid tumors, including neuroendocrine carcinomas/neuroendocrine tumors (NEC/NET). Rovalpituzumab tesirine (Rova-T) is a DLL3-targeting antibody-drug conjugate. Patients with NECs and other advanced DLL3-expressing tumors were enrolled in this phase I/II study (NCT02709889). The primary endpoint was safety. Two hundred patients were enrolled: 101 with NEC/NET (large-cell NEC, gastroenteropancreatic NEC, neuroendocrine prostate cancer, and other NEC/NET) and 99 with other solid tumors (melanoma, medullary thyroid cancer [MTC], glioblastoma, and other). The recommended phase II dose (RP2D) was 0.3 mg/kg every 6 weeks (q6w) for two cycles. At the RP2D, grade 3/4 adverse events included anemia (17%), thrombocytopenia (15%), and elevated aspartate aminotransferase (8%). Responses were confirmed in 15/145 patients (10%) treated at 0.3 mg/kg, including 9/69 patients (13%) with NEC/NET. Rova-T at 0.3 mg/kg q6w had manageable toxicity, with antitumor activity observed in patients with NEC/NET, melanoma, MTC, and glioblastoma.