Antibody-drug Conjugates Platform Research Articles

DNA self-assembly-mediated high drug-antibody ratio ADC platform for targeted tumor therapy and imaging

Antibody-drug conjugates (ADCs) achieve therapeutic effects through toxin delivery inside cells, targeting high-abundance antigens. However, tumor heterogeneity and the low abundance of tumor-specific antigens underscore the urgent requirement for developing a flexible, multifunctional, and high-capacity drug-delivery platform. The current study developed a self-assembled ADC platform called the high drug–antibody-ratio ADC (HD-ADC). Cytotoxic payloads were efficiently conjugated into a 12-arm deoxyribonucleic acid (DNA) branched junction via DNA-mediated precise self-assembly to achieve a high drug–antibody ratio (DAR). Anti-EGFR HD-ADC showed strong efficacy in causing cytotoxicity and suppressing tumor growth in an A431 xenograft mouse model. Furthermore, the Cy5-conjugated HD-ADC platform was a simple and effective method for improving fluorescent signal detection, enabling the detection of targets—such as neoantigens—with ultralow-expression levels. The HD-ADC platform supports the assembly of various functional components, providing the foundation for usage across multiple antibody-mediated targeted therapies and diagnostics.

Abstract LB025: CKD-703, a novel antibody-drug conjugate targeting cMET with an enhanced therapeutic index in solid tumors

Abstract In our pursuit of advancing cancer therapeutics, we introduce CKD-703, a groundbreaking cMET-targeting antibody drug conjugate (ADC) designed to strategically address the challenges posed by cMET overexpression and alteration in various solid tumors. Recognizing the pivotal role of tolerability and efficacy in shaping the therapeutic landscape of ADC, CKD-703 represents a significant advancement, aiming to widen the therapeutic index of cMET-targeted therapies. As we develop CKD-703, an innovative cMET-targeting ADC, we acknowledge the oncogenic potential of cMET alterations, particularly in non-small cell lung cancer (NSCLC), and the prevalent elevation of cMET across various cancers. Antibody drug conjugates targeting cMET (cMET-ADCs) have shown its therapeutic potential in treating cMET positive tumors, irrespective of their dependency on cMET signaling. Clinical success, however, has often been limited to NSCLC patients with the highest cMET levels. In light of this, CKD-703 is crafted to not only improve tolerability but also enhance efficacy, thereby broadening its application to a diverse patient population, including those with moderate cMET expression. To develop a novel cMET-ADC, Chong Kun Dang leverages Synaffix's ADC platform technology, incorporating glycan remodeling to achieve site-specific conjugation of the linker-payload to the antibody and ensuring a homogeneous drug-antibody ratio. These unique characteristics enhance CKD-703's stability in the bloodstream, minimizing the concentration of liberated free payload and significantly improving tolerability. The uniform DAR of CKD-703 contributes to improved pharmacokinetics, ensuring a consistent and sustained therapeutic effect. In comparison to benchmark antibodies, CKD-703 exhibits superior binding affinity to cMET and efficient internalization, resulting in enhanced therapeutic efficacy. This is evidenced in preclinical experiments which performed in several animal models that can mimic the complexities of cMET positive tumors with varying expression levels. The GLP toxicity studies of CKD-703 are ongoing. In conclusion, CKD-703 is a novel cMET-targeting ADC designed to overcome the limitations observed in existing cMET-ADCs in clinical trials as well as significantly improve tolerability and efficacy. By strategically addressing challenges associated with moderate cMET expression levels, CKD-703 emerges as a promising therapeutic candidate, aiming to broaden the therapeutic index in cMET-overexpressing solid tumors. This study highlights the importance of tailored approaches to diverse patient populations in advancing the development of CKD-703 in the pursuit of precision cancer therapies. Citation Format: Kwanwoo Lee, Sue-Youn Kim, Hye-Jin Hong, Eunjeong Park, Jungok Park, Seong-Ho Hong, Daekwon Bae, Nina Ha, Sohn-Ji Yeon, Inchang Hwang, Semi Kim, Yoonseok Lee, Ju-Hee Lee. CKD-703, a novel antibody-drug conjugate targeting cMET with an enhanced therapeutic index in solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB025.

Abstract 5805: A novel platform of diversified payloads to drive ADC innovation

Abstract First generation of antibody drug conjugates (ADCs) for anticancer therapy has been described more than two decades ago with gemtuzumab-ozogamicin receiving the first approval in 2000. Over the last 4 years, 8 new ADCs got FDA approval essentially due to the innovation on the linker improving the disposition in patients and the manufacturability together with the technical advantages in the engineering of biologics and the introduction of new cytotoxic payloads such as deruxtecan. In the future, next generation ADCs will be developed exploring payloads beyond the currently used cytotoxins to improve safety, efficacy and durability of responses and therefore the short- and long-term therapeutic benefit to patients. Nerviano Medical Sciences (NMS) generated a portfolio of novel and diversified payload linkers leveraging on its proprietary chemical collection that includes cytotoxic and targeted payloads. A rigorous screening funnel has been applied considering diversification in terms of MoAs, pharmacokinetic properties, mechanism of resistance and combinability with other therapies to identify the optimal match with specific tumor types and targets, generating a new class of ADCs with improved selectivity and efficacy for hard-to-treat cancers even in chemoresistant settings. NMS ADC platform incorporates 1) our patent protected payload linker NMS-P945, a duocarmycin like DNA minor groove binder and alkylating agent inducing DNA damage, acting in chemoresistant cells with bystander effect and immunogenic cell death properties and generating ADCs highly efficacious in mouse xenograft models and safe when administered in NHP, 2) novel anthracyclines (PNU-682 derivatives) with an improved stability and safety profile and 3) targeted molecules with different mechanism of action including payloads active in synthetic lethality contexts. Payload linkers with different functionalization generated from each payload have been evaluated for chemical stability, sensitivity to lysosomal protease cleavage, and conjugability to monoclonal antibodies. The ADCs, generated with proof-of-concept antibodies (e.g. Trastuzumab), were characterized in terms of Drug to Antibody Ratio (DAR), aggregation level, plasma stability, antigen binding and differential antiproliferative activity in target positive vs target negative tumor cells. The best products resulting from the screening funnel have been subjected to a multidimensional analysis taking into consideration payload properties, tumor features and antigen expression in selected populations with the aim of identifying tumor types particularly sensitive to the payload. Our multidimensional approach coupling new payload linker with innovative MoA to careful selection of patients will allow to reach unprecedented efficacy and safety profile. Citation Format: Paolo Orsini, Matteo Salsa, Simona Rizzi, Ulisse Cucchi, Daniela Faiardi, Alessia Burocchi, Antonella Ciavolella, Rosita Lupi, Fabio Gasparri, Barbara Valsasina. A novel platform of diversified payloads to drive ADC innovation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5805.

Abstract 3143: The ADC payload PNU-159682 is highly active in a wide range of cancer indications by inducing DNA damage and cell death via a distinct mode of action

Abstract During the last decade antibody-drug-conjugates (ADCs) have become an important and validated treatment modality for cancer patients. Here, we introduce a unique next generation ADC platform based on Sortase-mediated antibody conjugation (SMAC-Technology) yielding in very homogenous and stable drug conjugates with limited systemic, but powerful anti-tumor activity. The highly potent payload used is a proprietary derivative of the Anthracycline PNU-159682. Our PNU-159682-based ADCs are known to not only induce DNA damage in the target cell, but importantly also trigger immunogenic cell death and thus, stimulating anti-tumor immunity offering untapped combination potential. ADCs based on the SMAC-Technology platform currently undergo clinical development. In this work, we present functional studies that were performed to further elucidate the mode of action (MoA) of the ADC payload PNU-159682 and to investigate any potential liabilities with respect to sensitivity, which could limit treatment options for cancer patients. Flow cytometry-based readouts verified that PNU-EDA, a derivative of PNU-159682, is a highly potent inducer of DNA damage, cell cycle arrest and cell death. Interestingly, PNU-EDA arrests cells and inhibits DNA synthesis in S-phase in contrast to other Anthracyclines such as Doxorubicin, which leads to a block in the G2/M-phase. High-throughput cell line panel sensitivity screens confirmed that the activity of PNU-EDA is broad and not restricted to specific cancer indications. Notably, a correlation between lower potency and increased ABCB1 (MDR1) expression levels was observed for PNU-EDA, but not for parental PNU-159682. More detailed mechanistic insights were obtained by performing a genome-wide CRISPR-Cas9 KO screen, which revealed a partial dependency of the PNU-EDA potency on the proficiency of the TC-NER DNA damage repair mechanism. This finding further highlights a distinct MoA of PNU-159682 compared to Doxorubicin or other DNA-targeting compounds such as Cisplatin. Overall, our screens and mechanistic studies verified that PNU-159682-based ADCs efficiently kill cancer cells via a particular MoA and thereby, offer highly promising therapeutic options to a diverse and large population of cancer patients. Citation Format: Monika Kaiser, Ulrike Fiedler, Daniel Gerlach, Norbert Kraut, Lukas Bammert. The ADC payload PNU-159682 is highly active in a wide range of cancer indications by inducing DNA damage and cell death via a distinct mode of action [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3143.

Development of a Novel DNA Mono-alkylator Platform for Antibody-Drug Conjugates.

Although microtubule inhibitors (MTI) remain a therapeutically valuable payload option for antibody-drug conjugates (ADC), some cancers do not respond to MTI-based ADCs. Efforts to fill this therapeutic gap have led to a recent expansion of the ADC payload "toolbox" to include payloads with novel mechanisms of action such as topoisomerase inhibition and DNA cross-linking. We present here the development of a novel DNA mono-alkylator ADC platform that exhibits sustained tumor growth suppression at single doses in MTI-resistant tumors and is well tolerated in the rat upon repeat dosing. A phosphoramidate prodrug of the payload enables low ADC aggregation even at drug-to-antibody ratios of 5:1 while still delivering a bystander-capable payload that is effective in multidrug resistant (MDR)-overexpressing cell lines. The platform was comparable in xenograft studies to the clinical benchmark DNA mono-alkylator ADC platform DGN459 but with a significantly better tolerability profile in rats. Thus, the activity and tolerability profile of this new platform make it a viable option for the development of ADCs.

Albumin-ruthenium catalyst conjugate for bio-orthogonal uncaging of alloc group.

The employment of antibodies as a targeted drug delivery vehicle has proven successful which is exemplified by the emergence of antibody-drug conjugates (ADCs). However, ADCs are not without their shortcomings. Improvements may be made to the ADC platform by decoupling the cytotoxic drug from the delivery vehicle and conjugating an organometallic catalyst in its place. The resulting protein-metal catalyst conjugate was designed to uncage the masked cytotoxin administered as a separate entity. Macropinocytosis of albumin by cancerous cells suggests the potential of albumin acting as the tumor-targeting delivery vehicle. Herein reported are the first preparation and demonstration of ruthenium catalysts with cyclopentadienyl and quinoline-based ligands conjugated to albumin. The effective uncaging abilities were demonstrated on allyloxy carbamate (alloc)-protected rhodamine 110 and doxorubicin, providing a promising catalytic scaffold for the advancement of selective drug delivery methods in the future.

Validation of ADC Platform for Protein Concentration and the Drug-Antibody Ratio (DAR) using Variable Pathlength Technology

Antibody Drug Conjugates (ADCs) are biopharmaceutical drugs which are designed to treat cancer by targeting and killing the cancerous cells while leaving the healthy tissue intact. ADCs are comprised of an antibody connected to a cytotoxic drug by a linkerThe antibody targets a specific antigen which is present in cancerous cells but not healthy cells. The ADC binds to the cancer cell and becomes internalized where the cytotoxic drug is released and kills the cancer cell. Two important pieces of information required about the ADC are the protein concentration and the Drug-Antibody Ratio (DAR). The DAR is the number of drug molecules attached to the antibody. It is important during the manufacturing steps to ensure that the process is proceeding as expected and that there is not more or less drug present than required.

Design and Evaluation of Phosphonamidate-Linked Exatecan Constructs for Highly Loaded, Stable, and Efficacious Antibody-Drug Conjugates.

Topoisomerase I (TOP1) Inhibitors constitute an emerging payload class to engineer antibody-drug conjugates (ADC) as next-generation biopharmaceutical for cancer treatment. Existing ADCs are using camptothecin payloads with lower potency and suffer from limited stability in circulation. With this study, we introduce a novel camptothecin-based linker-payload platform based on the highly potent camptothecin derivative exatecan. First, we describe general challenges that arise from the hydrophobic combination of exatecan and established dipeptidyl p-aminobenzyl-carbamate (PAB) cleavage sites such as reduced antibody conjugation yields and ADC aggregation. After evaluating several linker-payload structures, we identified ethynyl-phosphonamidates in combination with a discrete PEG24 chain to compensate for the hydrophobic PAB-exatecan moiety. Furthermore, we demonstrate that the identified linker-payload structure enables the construction of highly loaded DAR8 ADCs with excellent solubility properties. Head-to-head comparison with Enhertu, an approved camptothecin-based ADC, revealed improved target-mediated killing of tumor cells, excellent bystander killing, drastically improved linker stability in vitro and in vivo and superior in vivo efficacy over four tested dose levels in a xenograft model. Moreover, we show that ADCs based on the novel exatecan linker-payload platform exhibit antibody-like pharmacokinetic properties, even when the ADCs are highly loaded with eight drug molecules per antibody. This ADC platform constitutes a new and general solution to deliver TOP1 inhibitors with highest efficiency to the site of the tumor, independent of the antibody and its target, and is thereby broadly applicable to various cancer indications.

Site-Specific Dolasynthen Antibody-Drug Conjugates Exhibit Consistent Pharmacokinetic Profiles across a Wide Range of Drug-to-Antibody Ratios.

Key defining attributes of an antibody-drug conjugate (ADC) include the choice of the targeting antibody, linker, payload, and the drug-to-antibody ratio (DAR). Historically, most ADC platforms have used the same DAR for all targets, regardless of target characteristics. However, recent studies and modeling suggest that the optimal DAR can depend on target expression level and intratumoral heterogeneity, target internalization and trafficking, and characteristics of the linker and payload. An ADC platform that enables DAR optimization could improve the success rate of clinical candidates. Here we report a systematic exploration of DAR across a wide range, by combining THIOMAB protein engineering technology with Dolasynthen, an auristatin-based platform with monomeric and trimeric variants. This approach enabled the generation of homogeneous, site-specific ADCs spanning a discrete range of DARs 2, 4, 6, 12, and 18 by conjugation of trastuzumab IgG1 THIOMAB constructs with 1, 2, or 3 engineered cysteines to monomeric or trimeric Dolasynthen. All ADCs had physicochemical properties that translated to excellent in vivo pharmacology. Following a single dose of ADCs in a HER2 xenograft model with moderate antigen expression, our data demonstrated comparable pharmacokinetics for the conjugates across all DARs and dose-dependent efficacy of all test articles. These results demonstrate that the Dolasynthen platform enables the generation of ADCs with a broad range of DAR values and with comparable physiochemical, pharmacologic, and pharmacokinetics profiles; thus, the Dolasynthen platform enables the empirical determination of the optimal DAR for a clinical candidate for a given target.

Self‐Assembled L–DNA Linkers for Rapid Construction of Multi‐Specific Antibody‐Drug Conjugates Library

AbstractOne of the key challenges of improving clinical outcomes of antibody drug conjugates (ADCs) is overcoming cancer resistance to the antibody and/or drug components of ADCs, and hence the need for ADC platforms with high combinatory flexibility. Here, we introduce the use of self‐assembled left‐handed DNA (L–DNA) oligonucleotides to link combinatory single‐domain antibodies and toxin payloads for tunable and adaptive delivery of ADCs. We demonstrate that the method allows convenient construction of a library of ADCs with multi‐specific targeting, multi‐specific payloads, and exact drug‐antibody ratio. The newly constructed ADCs with L–DNA scaffold showed favorable properties of in vitro cell cytotoxicity and in vivo suppression and eradication of solid tumors. Collectively, our data suggest that the L–DNA based modular ADC (MADC) platform is a viable option for generating therapeutic ADCs and for potentially expanding ADC therapeutic window via multi‐specificity.

Self-Assembled L-DNA Linkers for Rapid Construction of Multi-Specific Antibody-Drug Conjugates Library.

One of the key challenges of improving clinical outcomes of antibody drug conjugates (ADCs) is overcoming cancer resistance to the antibody and/or drug components of ADCs, and hence the need for ADC platforms with high combinatory flexibility. Here, we introduce the use of self-assembled left-handed DNA (L-DNA) oligonucleotides to link combinatory single-domain antibodies and toxin payloads for tunable and adaptive delivery of ADCs. We demonstrate that the method allows convenient construction of a library of ADCs with multi-specific targeting, multi-specific payloads, and exact drug-antibody ratio. The newly constructed ADCs with L-DNA scaffold showed favorable properties of in vitro cell cytotoxicity and in vivo suppression and eradication of solid tumors. Collectively, our data suggest that the L-DNA based modular ADC (MADC) platform is a viable option for generating therapeutic ADCs and for potentially expanding ADC therapeutic window via multi-specificity.

Abstract 2012: A novel antibody-drug conjugate platform enabling high drug-to-antibody ratios and greater payload flexibility

Abstract Historically, increasing the drug-to-antibody ratio (DAR) in an antibody-drug conjugate (ADC) significantly raises aggregation propensity as a result of the hydrophobicity of the payload. Consequently, DARs are commonly limited to 4, forcing developers to incorporate very high potency payloads to achieve the required efficacy. This, combined with chemical instability and off-target uptake, often results in dose-limiting toxicities and narrow therapeutic indexes. In this study, we used a novel and flexible multivalent linker technology to construct two ADCs targeting HER-2 with the monoclonal antibody, trastuzumab and interchain cysteine bioconjugation. One ADC incorporated monomethyl auristatin E (MMAE) as the drug payload at average DAR 16 whilst the second incorporated the camptothecin analog, SN38, as the drug payload also at average DAR 16. The ADCs were characterized by liquid chromatography-mass spectrometry (LC-MS), size-exclusion chromatography (SEC), hydrophobic interaction chromatography (HIC) and SDS-PAGE and were then tested for efficacy in a range of HER-2 positive cell lines in vitro, and tumor growth inhibition studies using NCI-N87 cells in a mouse xenograft. Both ADCs remained > 95% monomeric (no aggregation) and demonstrated greater chemical stability in ex-vivo serum stability studies compared to comparator ADC constructs utilizing a clinically validated linker and the same payload release chemistry. In in vitro cell killing studies, the ADCs demonstrated target-specific cell killing with the SN38 average DAR 16 ADC achieving a disproportionate 30-fold increase in IC50 (by ADC concentration) compared to a DAR 8 comparator. Dose dependent tumor growth inhibition was observed in an HER-2 positive NCI-N87 mouse xenograft model with no change in mouse body weight, and good systemic exposure. These data demonstrate our capability, using a novel multivalent linker technology, to construct ADCs with DARs considerably greater than DAR 8 which are chemically stable, shield payloads from hydrophobic interactions (no aggregation), demonstrate good in vivo exposure profiles and which are highly efficacious in vitro and in vivo. Higher DARs will permit the incorporation of lower potency and targeted small molecule payloads into ADCs which will result in targeted cancer therapeutics with wider therapeutic indexes through the delivery of greater concentrations of payload to the tumor microenvironment and lower, payload-associated, dose-limiting toxicity. Citation Format: Ludovic Juen, Adam J. Collier, Anthony W. Tolcher, Myriam M. Ouberai. A novel antibody-drug conjugate platform enabling high drug-to-antibody ratios and greater payload flexibility [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2012.

Abstract 1405: Novel ADC platform delivers promising in vivo activity and safety

Abstract The physiochemical properties of an antibody-drug conjugate (ADC) are one key design attribute that can impacts its stability and pharmacokinetics/pharmacodynamics and are one of the key design attributes. Typically, ADCs with better hydrophilicity are less prone to aggregation, and have lower systemic clearance, and greater anti-tumor activities and thus a larger therapeutic index. However, the need to incorporate lipophilic payloads with an enhanced bystander effects has posed significant challenges to ADC and linker design, especially at drug-antibody ratios of 8 and even 16higher. Here we present a novel ADC platform that can greatly improveimproves the hydrophilicity, physiochemical stability, and pharmacokinetics of ADCs conjugated to lipophilic payloads such as exatecan, MMAE, SN38 and EErribulin. All payloads which are allare expect to exhibit strong bystander effects.By introducing PEG, polyhydroxyl and/or polycarboxyl groups, we generated hydrophilic linkers that enable site specific and, highly homogeneous conjugation of payloads to multiple prototypical antibodies at DAR 4, 8 and even 16. Compared. These ADCs were evaluated for their binding affinity, hydrophilicity, physiochemical stability, in vitro and in vivo anti-tumor activities, tolerability, and pharmacokinetics. In addition, comparisons were made with with theirthe corresponding naked unconjugated parent antibodies and conventional vedotin- and deruxtecan-based ADCs., these ADCs were evaluated for their binding affinity, hydrophilicity, physiochemical stability, in vitro and in vivo anti-tumor activities, tolerability, and pharmacokinetics. These novel ADCs were found to be stable at 37℃ for up to 30 days, after for at least 5 cycles of freeze-thaw, and at concentrations as high as 100 mg/mL, as assessed by visual inspection, hydrophobic interaction chromatography and size exclusion chromatography. Binding affinities of these ADCs to target-positive cell lines were similar to their corresponding naked unconjugated parent antibodies. These ADCs demonstrated strong tumor growth inhibition with single or repeated dosing in multiple tumor xenograft mouse models. The pharmacokinetic profiles of these ADCs are similar to those of the naked respective parent unconjugated antibodies. Assessments of ADCs using these new platform linkers in cynomolgus monkeys demonstrated showed better tolerability than ADCs using the traditional drug linkers.In summary, our novel ADC platform enables conjugation of hydrophobic payloads at high DARs as high as 8 or 16 with favorable physiochemical properties, results in robust pharmacokinetics, strong potency in vivo, and better tolerability. Therefore the potential for a meaningful therapeutic window may be realized through this novel ADC platform. Citation Format: Haidong Liu, Wenke Qi, Lei Wang, Guobao Wang, Xinyue Chen, Julia Gavrilyuk, Tae Han, Baiteng Zhao, Xiao Shang. Novel ADC platform delivers promising in vivo activity and safety [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1405.

Abstract 1738: XMT-2056, a well-tolerated, Immunosynthen-based STING-agonist antibody-drug conjugate which induces anti-tumor immune activity

Abstract STING pathway agonism has emerged as a potential therapeutic mechanism to stimulate an innate anti-tumor immune response. However, the systemic administration of a free STING agonist may be limited by toxicity, and broad biodistribution may not be ideal. Antibody-drug conjugates (ADCs) constitute a proven therapeutic modality that enables tumor-targeted delivery and thus is ideally suited to systemic administration with reduced toxicity. To develop an optimized STING-agonist ADC platform, we designed a novel STING-agonist specifically tailored for use in an ADC. Determination of the co-crystal structure confirmed that the agonist binds to the closed, or ‘active', conformation of the STING homodimer. The resulting Immunosynthen platform, which was developed specifically for the selected STING agonist payload, was used to generate XMT-2056, a tumor antigen-targeted STING-agonist ADC with excellent drug-like properties and >100-fold increased potency as compared to the free STING-agonist payload. In mice, XMT-2056 induced robust anti-tumor immune activity, with only minimal increases in systemic cytokine levels, and exhibited significant benefit over the benchmark free STING-agonist payload in both regards. Additionally, in vitro and in vivo studies demonstrate that XMT-2056 is able to activate the STING pathway in both tumor-resident immune cells and tumor cells, offering a potential advantage over other innate immune activating pathways. XMT-2056 was well-tolerated in non-human primates at significantly higher exposure levels than those required for anti-tumor activity, and the ADC exhibited favorable pharmacokinetics after repeat doses. Together these data support the clinical development of XMT-2056. Citation Format: Jeremy R. Duvall, Raghida A. Bukhalid, Naniye M. Cetinbas, Kalli C. Catcott, Kelly Slocum, Kenneth Avocetien, Keith W. Bentley, Stephen Bradley, Susan Clardy, Scott D. Collins, Elizabeth Ditty, Timothy Eitas, Brian D. Jones, Eugene W. Kelleher, Winnie Lee, Travis Monnell, Rebecca Mosher, Marina Protopopova, LiuLiang Qin, Pamela Shaw, Elena Ter-Ovanesyan, Joshua D. Thomas, Phonphimon Wongthida, Ling Xu, Liping Yang, Jeffrey Zurita, Dorin Toader, Marc Damelin, Timothy B. Lowinger. XMT-2056, a well-tolerated, Immunosynthen-based STING-agonist antibody-drug conjugate which induces anti-tumor immune activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1738.

Dolaflexin: A Novel Antibody-Drug Conjugate Platform Featuring High Drug Loading and a Controlled Bystander Effect.

After significant effort over the last 30 years, antibody-drug conjugates (ADC) have recently gained momentum as a therapeutic modality, and nine ADCs have been approved by the FDA to date, with additional ADCs in late stages of development. Here, we introduce dolaflexin, a novel ADC technology that overcomes key limitations of the most common ADC platforms with two key features: a higher drug-to-antibody ratio and a novel auristatin with a controlled bystander effect. The novel, cell permeable payload, auristatin F-hydroxypropylamide, undergoes metabolic conversion to the highly potent, but less cell permeable auristatin F to balance the bystander effect through drug trapping within target cells. We conducted studies in mice, rats, and cynomolgus monkeys to complement in vitro characterization and contrasted the performance of dolaflexin with regard to antitumor activity, pharmacokinetic properties, and safety in comparison with the ADC platform utilized in the approved ADC ado-trastuzumab emtansine (T-DM1). A HER2-targeted dolaflexin ADC was shown to have a much lower threshold of antigen expression for potent cell killing in vitro, was effective in vivo in tumors with low HER2 expression, and induced tumor regressions in a xenograft model that is resistant to T-DM1.

Development of Highly Optimized Antibody-Drug Conjugates against CD33 and CD123 for Acute Myeloid Leukemia.

Mortality due to acute myeloid leukemia (AML) remains high, and the management of relapsed or refractory AML continues to be therapeutically challenging. The reapproval of Mylotarg, an anti-CD33-calicheamicin antibody-drug conjugate (ADC), has provided a proof of concept for an ADC-based therapeutic for AML. Several other ADCs have since entered clinical development of AML, but have met with limited success. We sought to develop a next-generation ADC for AML with a wide therapeutic index (TI) that overcomes the shortcomings of previous generations of ADCs. We compared the TI of our novel CD33-targeted ADC platform with other currently available CD33-targeted ADCs in preclinical models of AML. Next, using this next-generation ADC platform, we performed a head-to-head comparison of two attractive AML antigens, CD33 and CD123. Our novel ADC platform offered improved safety and TI when compared with certain currently available ADC platforms in preclinical models of AML. Differentiation between the CD33- and CD123-targeted ADCs was observed in safety studies conducted in cynomolgus monkeys. The CD33-targeted ADC produced severe hematologic toxicity, whereas minimal hematologic toxicity was observed with the CD123-targeted ADC at the same doses and exposures. The improved toxicity profile of an ADC targeting CD123 over CD33 was consistent with the more restricted expression of CD123 in normal tissues. We optimized all components of ADC design (i.e., leukemia antigen, antibody, and linker-payload) to develop an ADC that has the potential to translate into an effective new therapy against AML.

Abstract 6706: Systemic administration of STING agonist antibody-drug conjugates elicit potent anti-tumor immune responses with minimal induction of circulating cytokines

Abstract STING pathway agonism has emerged as a potential therapeutic mechanism to stimulate an innate anti-tumor immune response. While in principle systemic administration of a STING agonist would have many therapeutic benefits, including the delivery of STING to all tumor lesions, such an approach may be limited by toxicity. Antibody-drug conjugates (ADCs) constitute a proven therapeutic modality that is ideally suited to enable systemic administration without associated toxicity concerns via a targeted delivery strategy. Herein, we demonstrate that systemically administered STING agonist ADCs have greater anti-tumor activity as well as greatly improved tolerability compared to an intravenously (IV) administered, unconjugated (free) agonist. We generated novel STING agonist ADCs by leveraging our Immunosynthen platform, in which the chemical scaffold for bioconjugation is optimized for the STING agonist, resulting in an ADC that has desirable physicochemical and drug-like properties. We have studied the in vitro activity and mechanism of action of STING agonist ADCs in monoculture and co-culture systems. STING agonist ADCs were at least 100-fold more potent in inducing interferon and cytokines as well as tumor cell-killing relative to free agonist. STING agonist ADCs against several targets (antigens) have been evaluated for anti-tumor activity and pharmacodynamic and pharmacokinetic properties in multiple xenograft and syngeneic models. A single administration of STING agonist ADC resulted in target-dependent, durable, and complete regressions. Importantly, the STING agonist ADC led to an increase in tumor-localized inflammatory cytokines and significant immune cell infiltration, while levels of systemic cytokines remained low. In contrast, IV administered free agonist induced up to 100-fold higher levels of systemic cytokines with concomitant body weight loss but only modest tumor growth delay. In summary, Immunosynthen represents a novel STING agonist ADC platform. We have demonstrated target-dependent anti-tumor immune responses in vitro and in vivo for multiple targets, tumor models, and mouse strains. In each case the STING agonist ADC was more active and better tolerated than the IV administered free agonist. Citation Format: Raghida A. Bukhalid, Jeremy R. Duvall, Naniye Malli Cetinbas, Kalli C. Catcott, Kenneth Avocetien, Keith W. Bentley, Stephen Bradley, Tyler Carter, Chen-Ni Chin, Susan Clardy, Scott D. Collins, Timothy Eitas, Brian D. Jones, Eugene W. Kelleher, Rebecca Mosher, Mark Nazzaro, Marina Protopopova, Pamela Shaw, Kelly Slocum, Elena Ter-Ovanesyan, LiuLiang Qin, Joshua D. Thomas, Ling Xu, Liping Yang, Jeffrey Zurita, Dorin Toader, Marc Damelin, Timothy B. Lowinger. Systemic administration of STING agonist antibody-drug conjugates elicit potent anti-tumor immune responses with minimal induction of circulating cytokines [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6706.

The Evolution of Antibody-Drug Conjugates: A Positive Inflexion Point.

In 2019, an important inflection point occurred when the U.S. Food and Drug Administration approved three new antibody-drug conjugates (ADCs) for the treatment of malignancies, including urothelial cancer (enfortumab vedotin-ejfv), diffuse large B-cell lymphoma (polatuzumab vedotin-piiq), and HER2 breast cancer (fam-trastuzumab deruxtecan-nxki), and expanded the indication for ado-trastuzumab emtansine to early breast cancer. This near doubling in the number of approved ADCs within 1 year validates the ADC platform and represents a successful evolution over the past 30 years. ADCs were born in an era when systemic therapy for cancer was largely cytotoxic chemotherapy. Many of the investigational cytotoxic agents were determined to be too toxic for oral and intravenous use. The agents were especially potent, with inhibitory concentrations that inhibited 50% of cells in the nanomolar and picomolar range but had poor therapeutic indexes when administered systemically. Now, over the last 30 years, we have seen an evolution of the many aspects of this complex platform with better antigen target selection, more sophisticated chemistry for the linkers, a growing diversity of payloads from cytotoxic chemotherapy to targeted therapies and immunostimulants, and, with the recent series of regulatory approvals, a buoyed sense of optimism for the technology. Nonetheless, we have not fully realized the full potential of this platform. In this review, the many components of ADCs will be discussed, the difficulties encountered will be highlighted, the innovative strategies that are being used to improve them will be assessed, and the direction that the field is going will be considered.

Redox-Responsive Polymeric RNAi Based on Multivalent Conjugation of siRNA for Improved Intracellular Delivery.

Learning from the design concept of antibody-drug conjugates (ADCs), we attempted to construct siRNA conjugated polymer brush by attaching a multiple of siRNA to the units of poly(amino acids) [poly(lysine) derivatives] through an intracellular cleavable disulfide bond. Note that the disulfide linkage is stable at extracellular milieu yet subjected to cleavage into free thiol residues at the intracellular reducing compartments. Consequently, ready release of arrays of active siRNA was achieved selectively in the intracellular compartments. Furthermore, tumor-targeted cyclic Asp-Gly-Arg (RGD) was conjugated to the aforementioned polymer brush in view that the RGD receptors (αVβ3 and αVβ5 integrins) were overexpressed over a wide spectrum of cancerous cells. Our subsequent results have achieved potent gene silencing in cultured cancerous cells from our proposed siRNA delivery construct. To our best knowledge, our proposed conjugate should be the first example of using an ADC platform in successful intracellular transportation of larger macromolecular biological payloads rather than small molecular chemotherapeutic drugs. Hence, the proposed strategy may serve as a promising avenue for targeted delivery of macromolecular pharmaceutical payloads.

Abstract 2687: Dolasynthen–a novel, homogeneous Auristatin F hydroxypropyl amide antibody-drug conjugate platform

Abstract Dolasynthen is a novel, fully synthetic, structurally homogeneous platform that enables the construction of ADCs with tunable drug-to-antibody ratios (DAR), from a low of 2 to a high of 24. The resulting ADCs exhibit excellent physicochemical properties and fully homogeneous conjugates can be created through a variety of bioconjugation chemistries. Analogous to our first platform, Dolaflexin®, Dolasynthen is loaded with the proprietary payload Auristatin F hydroxypropylamide (AF-HPA) with precisely defined numbers of the cytotoxin per Dolasynthen scaffold.Studies that evaluate the tolerability and efficacy of Dolasynthen in preclinical models are described herein. ADCs containing a range of DAR values were generated following conjugation of Dolasynthen to two different monoclonal antibodies. The DAR of the ADCs was achieved by controlled reduction of native disulfide bonds in IgG1 antibodies, chromatographic fractionation, or through use of site-specific conjugation technologies. ADCs with both DAR6 and DAR12 were evaluated in vitro and also in vivo in the mouse, rat and monkey, for efficacy, tolerability and PK. Dolasynthen conjugates had excellent physicochemical properties and displayed the expected cell binding and in vitro cytotoxicities. In vivo pharmacology of Dolasynthen ADCs in in vivo xenograft models showed dose-dependent tumor growth inhibition at low mg/kg mAb doses. Tolerability in the rat at multiple doses was determined, including histopathological evaluation. Dolasynthen ADCs showed excellent PK characteristics in mouse, rat and NHP. Overall, the Dolasynthen platform appears to offer significant potential for clinical application. Citation Format: Dorin Toader, Marc Damelin, Anouk Dirksen, Shawn P. Fesler, Scott D. Collins, Barrett J. Nehilla, Jian Xu, Ling Xu, Kalli C. Cattcott, Alex Uttard, Winnie Lee, Susan Clardy, Cheri A. Stevenson, LiuLiang Qin, Patrick R. Conlon, Mariya V. Kozytska, Chen-Ni Chin, David H. Lee, Timothy B. Lowinger. Dolasynthen–a novel, homogeneous Auristatin F hydroxypropyl amide antibody-drug conjugate platform [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2687.