Success Of Antibody-drug Conjugates Research Articles

Abstract LB275: Reactivation of mitotic arrest upon targeting TACC3 restores immunogenic cell death and T-DM1 response in HER2-positive breast cancer

Abstract Immunogenic cell death (ICD) is a specific form of cell death that is characterized by the release of danger-associated molecular patterns (DAMPs), such as cell surface exposure of calreticulin, ATP and HMGB1 release, and can be induced by several different anti-cancer therapies. This, in turn, evokes a strong anti-tumor immune response, leading to reduced tumor growth. Despite being the first and one of the most successful antibody-drug conjugates (ADCs) approved for refractory HER2-positive breast cancer, little is known if response and resistance to trastuzumab emtansine (T-DM1) involves ICD modulation that can be leveraged to enhance T-DM1 response. Here we report that T-DM1 induces spindle assembly checkpoint (SAC)-dependent ICD in sensitive cells, mediated by its payload by inducing eIF2α phosphorylation, surface exposure of calreticulin, ATP and HMGB1 release, and secretion of ICD-related cytokines, all of which are lost in resistance. Accordingly, ICD-related gene signatures correlate with clinical response to T-DM1-containing therapy in pre-treatment samples, and increased infiltration of anti-tumor CD8+ T cells is correlated with better T-DM1 response in post-treatment samples. We found that transforming acidic coiled-coil containing 3 (TACC3) is overexpressed in T-DM1 resistant cells, and that T-DM1 responsive patients have reduced TACC3 protein while the non-responders exhibited increased TACC3 expression during T-DM1 treatment. Notably, genetic or pharmacological inhibition of TACC3 revives T-DM1-induced SAC activation and induction of ICD markers in vitro. TACC3 inhibition elicits ICD in vivo as shown by vaccination assay. It also potentiates T-DM1 in the human HER2-overexpressing MMTV-huHER2#5 (Fo5) transgenic model by activating ICD markers, release of cytokines and inducing dendritic cell (DC) maturation and enhancing infiltration of cytotoxic T cells. Together, our results show that ICD is a key mechanism of action of T-DM1 which is lost in resistance, and that targeting TACC3 restores T-DM1-mediated ICD and overcomes resistance. Citation Format: Ozge Saatci, Mustafa Emre Gedik, Nathaniel Oberholtzer, Meral Uner, Ozge Akbulut, Metin Cetin, Mertkaya Aras, Kubra Ibis, Burcu Caliskan, Erden Banoglu, Stefan Wiemann, Aysegul Uner, Sercan Aksoy, Shikhar Mehrotra, Ozgur Sahin. Reactivation of mitotic arrest upon targeting TACC3 restores immunogenic cell death and T-DM1 response in HER2-positive breast cancer [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 LB275.

Abstract 5814: EPriL macrocycles as a platform for the rapid generation of effective kinase degrader antibody conjugates (DACs)

Abstract The therapeutic success of antibody drug conjugates (ADCs) drives a continuous search for novel payloads that can increase therapeutic window and thereby widen the applications for ADCs. Recently, heterobifunctional degraders have gained great interest as payloads, and degrader antibody conjugates (DACs) are seen as a novel therapeutic modality. Heterobifunctional degraders consist of a small molecule ligand that binds a target (protein of interest or POI), a spacer and an E3 ligase ligand, which can catalyze target degradation. Owing to their catalytic activity, degraders can have better potency than the equivalent inhibitors, making them suitable as ADC payload [1]. Degrader payloads can target a wider variety of mechanisms than classic payloads, which use the same antitumor strategies as chemotherapy, such as tubulin binding or topoisomerase inhibition. Since many FDA-approved targeted therapies are based on the inhibition of protein kinases, we investigated degraders of these kinases as DAC payloads. Kinase DACs could bring enhanced targeting and therefore better therapeutic window to a field where classic ADC payloads have often shown substantial toxicities. As many heterobifunctional degraders show poor cell membrane penetration, their inhibitory potential could be increased as part of a DAC, where endocytic uptake is followed by intracellular release of the degrader payload. To identify kinase degrader payloads, we present a workflow based on a platform called Energetically Privileged Ligands (EPriLs). EPriLs are macrocycle scaffolds that bind non-covalently in the kinase ATP pocket. Their unique binding mode avoids contacts with amino acid positions where resistance to kinase inhibitors frequently occurs. EPriL macrocycles can be decorated appropriately to rationally design specific inhibitors for many therapeutically relevant kinases, and provide synthetic handles to couple them to VHL or CRBN ligands to generate effective kinase degraders. Here we describe how EPriL kinase degraders can be developed into effective DACs, using consecutive libraries of EPriL ligands, spacers, E3 ligase ligands and linkers. First, suitable degraders are identified, based on rapid and deep target degradation and potent antiproliferative activity on target cell lines. Degraders are then transformed into maleimide-linked degraders using convenient attachment of enzymatically cleavable linkers. In a medium throughput fashion, these maleimides are coupled to antibodies to generate DACs, which are tested for stability and biological potency. Applying this workflow to various well-validated kinase targets in oncology resulted in a promising kinase targeting DAC with favorable ADME properties, clear potentiation compared to the parent degrader, and increased selectivity for tumor cell lines. 1] Dragovich et al., Chem. Soc. Rev. (2022) 51, 3886-3897. Citation Format: Joost C. Uitdehaag, Jos e Man, Michelle Muller, Freek an Cauter, Sander an Gemert, Milan Hoffmann, Yvonne G. an Mil, Winfried R. Mulder, Martine B. Prinsen, Jan Gerard Sterrenburg, Diep Vu, Joeri e Wit, Erik Ensing, Rogier C. Buijsman. EPriL macrocycles as a platform for the rapid generation of effective kinase degrader antibody conjugates (DACs) [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 5814.

Abstract 3210: Raptamer-drug conjugates as molecularly targeted cancer therapeutics

Abstract The use of aptamers as a therapeutic targeting moiety holds the promise of building on the success of antibody-drug conjugates (ADCs). While ADCs are an attractive modality, they face limitations, including limited penetration into solid tumors and a complicated production process for large-scale manufacturing. Aptamers have several potential advantages over antibodies as a targeting moiety including: (i) a smaller size that enables better tumor penetration; (ii) chemical synthesis which allows rapid scale-up and ease of incorporating modifications; (iii) a superior safety profile from lack of immunogenicity and (iv) room temperature stability. Therefore, the use of aptamers in conjunction with drugs (similar to ADCs) holds promise for development of targeted therapeutics. We have identified a novel therapeutic target for certain cancers (COF-01) using proteomics data and immunohistochemistry from patient-derived tumors. Both the COF-01 protein and related mRNA expression was shown to be significantly increased in non-small cell lung cancer, head and neck cancer and pancreatic cancer. Here, we present a new therapeutic approach that targets COF-01-positive cancer cells using next generation aptamer conjugates. We performed a cell- and protein-based selection using our proprietary bead-based combinatorial libraries to generate next-generation base-modified ssDNA aptamers (Raptamers) against COF-01. Binding affinities of the COF-01 Raptamer candidates were determined by concentration curves using biolayer interferometry. The dissociation constants for the COF-01 Raptamers ranged from 80 nM - 200 nM. COF-01-specific Raptamer-drug conjugates (Rap-DCs) were developed by conjugating the Raptamers to monomethyl auristatin E via a cleavable linker. In vitro efficacy data showed the COF-01 Rap-DC can selectively induce cytotoxicity in different types of COF-01-positive human cancer cells (A431, CAL 27, BxPC-3). There was a significant decrease in cell viability of COF-01-positive cells when compared to COF-01-negative control cells (IC50 values ranged from 5.19 nM - 14.11 nM). In vivo efficacy testing in a COF-01-postive cell-derived xenograft mouse model showed a significant decrease in tumor volume in animals treated with the COF-01 Rap-DC when compared to saline- and erlotinib-treated controls. This provides proof-of concept for the use of high-affinity Raptamers against novel molecular targets, such as COF-01. This platform can be used to develop Rap-DCs against emergent neo-antigens on cancer cells that have escaped chemotherapy. Citation Format: Stephanie P. Vega, Nancy E. Ward, Uksha Saini, Leniher Castan-Chibas, Garima Kaushik, Daniel Ciznadija, Dev Chatterjee, Michael J. Heffernan, Atul Varadhachary, Michael Ritchie. Raptamer-drug conjugates as molecularly targeted cancer therapeutics [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 3210.

Small Molecule-Drug Conjugates: Opportunities for the Development of Targeted Anticancer Drugs.

Conventional chemotherapy is insufficient for precise cancer treatment due to its lack of selectivity and inevitable side effects. Targeted drugs have emerged as a promising solution for precise cancer treatment. A common strategy is to conjugate therapeutic agents with ligands that can specifically bind to tumor cells, providing targeted therapy. Similar to the more successful antibody drug conjugates (ADCs), small molecule drug conjugates (SMDCs) are another promising class of targeted drugs, consisting of three parts: targeting ligand, cleavable linker and payload. Compared to ADCs, SMDCs have the advantages of smaller size, better permeability, simpler preparation process and non-immunogenicity, making them a promising alternative to ADCs. This review describes the characteristics of the targeting ligand, linker and payload of SMDCs and the criteria for selecting a suitable one. We also discuss recently reported SMDCs and list some successful SMDCs that have entered clinical trials.

Neutrophil elastase as a versatile cleavage enzyme for activation of αvβ3 integrin-targeted small molecule drug conjugates with different payload classes in the tumor microenvironment.

Introduction: The development of bioconjugates for the targeted delivery of anticancer agents is gaining momentum after recent success of antibody drug conjugates (ADCs) in the clinic. Smaller format conjugates may have several advantages including better tumor penetration; however, cellular uptake and trafficking may be substantially different from ADCs. To fully leverage the potential of small molecule drug conjugates (SMDCs) with potent binding molecules mediating tumor homing, novel linker chemistries susceptible for efficient extracellular activation and payload release in the tumor microenvironment (TME) need to be explored. Methods: We designed a novel class of SMDCs, which target αvβ3 integrins for tumor homing and are cleaved by neutrophil elastase (NE), a serine protease active in the TME. A peptidomimetic αvβ3 ligand was attached via optimized linkers composed of substrate peptide sequences of NE connected to different functional groups of various payload classes, such as camptothecins, monomethyl auristatin E, kinesin spindle protein inhibitors (KSPi) and cyclin-dependent kinase 9 inhibitors (CDK-9i). Results: NE-mediated cleavage was found compatible with the diverse linker attachments via hindered ester bonds, amide bonds and sulfoximide bonds. Efficient and traceless release of the respective payloads was demonstrated in biochemical assays. The newly designed SMDCs were highly stable in buffer as well as in rat and human plasma. Cytotoxicity of the SMDCs in cancer cell lines was clearly dependent on NE. IC50 values were in the nanomolar or sub-nanomolar range across several cancer cell lines reaching similar potencies as compared to the respective payloads only in the presence of NE. In vivo pharmacokinetics evaluating SMDC and free payload exposures in rat and particularly the robust efficacy with good tolerability in triple negative breast and small cell lung cancer murine models demonstrate the utility of this approach for selective delivery of payloads to the tumor. Discussion: These results highlight the broad scope of potential payloads and suitable conjugation chemistries paving the way for future SMDCs harnessing the safety features of targeted delivery approaches in combination with NE cleavage in the TME.

Abstract 2171: A multivariate biomarker predicts sacituzumab govitecan response in solid tumors

Abstract Despite the recent clinical success of antibody drug conjugates (ADC) in oncology, predictive biomarkers are lacking, potentially limiting their impact. Herein, we evaluated the ability of candidate biomarkers alone and in combination to predict objective response rates observed in solid tumor patients treated with the TROP2-targeted ADC, sacituzumab govitecan (SG), as determined in the IMMU-12-01 basket trial. We leveraged available next generation sequencing (NGS)-based molecular profiling data from an independent advanced solid tumor cohort (n = 23,968) and developed a multivariate biomarker algorithm that produced biomarker positive rates correlating with the objective response rates (ORR) observed in IMMU-12-01. Candidate biomarkers evaluated included TROP2 gene expression, proliferation (by gene expression) and tumor cellularity. Notably, while TROP2 gene expression was highly correlated with protein expression across 45 tumor types (r = 0.93), TROP2 gene expression alone did not significantly predict ORR across 9 tumor types (r = 0.40, p = 0.29). In contrast, a biomarker algorithm combining TROP2 and proliferation by gene expression with tumor cellularity strongly predicted response both when using tumor type-specific biomarker rates in a discovery cohort (r = 0.83, p = 0.006) and in an independent validation cohort (r = 0.82, p = 0.007). These results indicate that the multivariate biomarker accounts for 67% of the variability observed in response rates and may thus identify patients likely to benefit from SG. Among tumor types with objective responses in IMMU-12-01, biomarker positive rates ranged from 9.9% in colorectal cancer to 57.4% in bladder cancer. Additional tumor types with biomarker positive rates >30% included cancers of the head and neck, cervix, salivary gland, skin (non-melanoma) and ovary, all with positive biomarker rates >30%. Interestingly, most tumor types had biomarker positive rates >5%, suggesting the potential for a tumor type-agnostic approach to patient selection. Considering SG and other ADC’s mechanism of action, a plausible model for response is that (1) higher target expression increases ADC drug delivery, (2) higher tumor cellularity increases ADC bystander effect and (3) higher tumor cell proliferation increases tumor cell death. In summary, we uncovered a novel biomarker algorithm capable of predicting SG response across solid tumors that may be generalizable to ADCs as a class, with the potential to further optimize use and maximize benefit. Citation Format: Nickolay A. Khazanov, Laura E. Lamb, Daniel H. Hovelson, Kat Kwiatkowski, D. Bryan Johnson, Daniel R. Rhodes, Scott A. Tomlins. A multivariate biomarker predicts sacituzumab govitecan response in solid tumors [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 2171.

Antibody-Drug Conjugates in Prostate Cancer: A Systematic Review.

The prognosis in the setting of metastatic castration-resistant prostate cancer patients (mCRPC) remains limited. Therefore, novel treatment strategies remain an unmet need. Antibody-drug conjugates (ADC) emerged as a new drug concept with the potential to deliver a cytotoxic payload with limited off-target toxicity and potentially bystander effect. Following the success of ADCs in breast cancer and urothelial tumours, their activity in prostate cancer is now under investigation. Thus, the aim of this systematic review was to identify published and ongoing prospective clinical trials regarding ADC treatment in prostate cancer. A systematic search of PubMed, MEDLINE, and Web of Science was conducted as per PRISMA guidelines to identify prospective clinical trials of ADCin prostate cancer. Trials are currently ongoing on ClinicalTrials.gov and in the EU. The Clinical Trials Register was also identified. Abstracts, publications in languages other than English, review articles, retrospective analyses, and phase I trials were excluded. A total of six phase I/II prospective clinical trials already published were included. Seven ongoing trials were also identified. All studies were in the refractory/advanced tumour setting, and two included only mCRPC patients. The ADC targets were prostate-specific membrane antigen (PSMA), trophoblast cell surface antigen-2 (TROP-2), six-transmembrane epithelial antigen of prostate-1 (STEAP-1), tissue factor (TF), delta-like protein 3 (DLL-3), B7-H3 family of proteins (B7-H3), and human epidermal growth factor receptor 2 (HER2). Regarding the efficacy of PSMA ADC treatment in the second-line or beyond mCRPC setting, a PSA ≥ 50% decline rate in 14% of all treated patients was reported. One patient achieved a complete response with TROP-2 ADC. Overall, a wide range of safety issues were raised, particularly in connection with neuropathy and hematologic toxicity. Novel therapies have been changing the scope of treatment in mCRPC. ADCs seem to provide efficacy benefits, even with potential toxicity. The results of most prospective ongoing studies are still awaited, and a longer follow-up time is warranted to evaluate the real impact of ADCs in PCa.

Antibody-Drug Conjugates for the Treatment of HER2-Positive Breast Cancer.

Human epidermal growth factor receptor 2 (HER2) receptor tyrosine kinase is overexpressed in 20-30% of breast cancers and is associated with poor prognosis and worse overall patient survival. Most women with HER2-positive breast cancer receive neoadjuvant chemotherapy plus HER2-targeted therapies. The development of HER2-directed therapeutics is an important advancement in targeting invasive breast cancer. Despite the efficacy of anti-HER2 monoclonal antibodies, they are still being combined with adjuvant chemotherapy to improve overall patient outcomes. Recently, significant progress has been made towards the development of a class of therapeutics known as antibody-drug conjugates (ADCs), which leverage the high specificity of HER2-targeted monoclonal antibodies with the potent cytotoxic effects of various small molecules, such as tubulin inhibitors and topoisomerase inhibitors. To date, two HER2-targeting ADCs have been approved by the FDA for the treatment of HER2-positive breast cancer: Ado-trastuzumab emtansine (T-DM1; Kadcyla®) and fam-trastuzumab deruxtecan-nxki (T-Dxd; Enhertu®). Kadcyla and Enhertu are approved for use as a second-line treatment after trastuzumab-taxane-based therapy in patients with HER2-positive breast cancer. The success of ADCs in the treatment of HER2-positive breast cancer provides novel therapeutic advancements in the management of the disease. In this review, we discuss the basic biology of HER2, its downstream signaling pathways, currently available anti-HER2 therapeutic modalities and their mechanisms of action, and the latest clinical and safety characteristics of ADCs used for the treatment of HER2-positive breast cancer.

Effect of Conjugation Site and Technique on the Stability and Pharmacokinetics of Antibody-Drug Conjugates.

Appropriate selection of conjugation sites and conjugation technologies is now widely accepted as crucial for the success of antibody-drug conjugates (ADCs). Herein, we present ADCs conjugated by different conjugation methods to different conjugation positions being systematically characterized by multiple in vitro assays as well as in vivo pharmacokinetic (PK) analyses in transgenic Tg276 mice. Conjugation to cysteines, genetically introduced at positions N325, L328, S239, D265, and S442, was compared to enzymatic conjugation via microbial transglutaminase (mTG) either to C-terminal light (LC) or heavy chain (HC) recognition motifs or to endogenous position Q295 of a native antibody. All conjugations yielded homogeneous DAR 2 ADCs with similar hydrophobicity, thermal stability, human neonatal Fc receptor (huFcRn) binding, and serum stability properties, but with pronounced differences in their PK profiles. mTG-conjugated ADC variants conjugated either to Q295 or to LC recognition motifs showed superior PK behavior. Within the panel of engineered cysteine variants L328 showed a similar PK profile compared to previously described S239 but superior PK compared to S442, D265, and N325. While all positions were first tested with trastuzumab, L328 and mTG LC were further evaluated with additional antibody scaffolds derived from clinically evaluated monoclonal antibodies (mAb). Based on PK analyses, this study confirms the newly described position L328 as favorable site for cysteine conjugation, comparable to the well-established engineered cysteine position S239, and emphasizes the favorable position Q295 of native antibodies and the tagged LC antibody variant for enzymatic conjugations via mTG. In addition, hemizygous Tg276 mice are evaluated as an adequate model for ADC pharmacokinetics, facilitating the selection of suitable ADC candidates early in the drug discovery process.

Selective Delivery of Doxorubicin to EGFR+ Cancer Cells by Cetuximab-DNA Conjugates.

Doxorubicin is a hydrophobic anticancer drug that has poor selectivity, due to the lack of active targeting capability. Here, learning lessons from the success of antibody-drug conjugates, we have designed a new doxorubicin delivery system without conjugating doxorubicin to antibody directly. In this setup, cetuximab, an antibody that targets the epidermal growth factor receptor (EGFR) in cancer cells, was conjugated to a single-stranded DNA with a carefully designed sequence in a site-selective manner by using the DNA-templated protein conjugation (DTPC) method. The DNA duplex in the conjugates serves as a carrier of doxorubicin through noncovalent intercalation, and cetuximab functions as the targeting agent; this could drastically decrease systemic toxicity and potentially avoid under- or overdosing. The size of conjugates loaded with doxorubicin was about 8.77 or 16.61 nm when characterized by dynamic light scattering and atomic force microscopy, respectively. In vitro cytotoxicity and selective cancer cell killing was investigated against two EGFR+ cell lines (KB and MDA-MB-231) and one EGFR- cell line (NIH-3T3). Cytotoxicity and flow cytometry data showed that doxorubicin loaded in cetuximab-DNA conjugates was more potent in terms of cell cytotoxicity than free doxorubicin in EGFR-overexpressed cell lines, thus suggesting that the conjugates were more selectively and easily taken up into cells, followed by rapid release of doxorubicin from the system into the cytoplasm from endosomes.

Abstract 2343: Comprehensive evaluation of antibody-drug conjugate targets for drug development across tumor types: Analysis from TCGA

Abstract Introduction: Cancer cells over-express proteins on their cell surface that can be exploited as drug targets and has led to development of two successful Anti-body Drug Conjugates (ADCs), Brentuximab and Trastuzumab Emtansine. Because a strong correlation exists between mRNA levels and protein expression we analyzed RNAseq data from TCGA to look at known ADC targets as a proof-of-concept to discovering new therapeutic targets. Methods: We used mRNA expressions (transcripts per million, TPM) from publicly available RNA sequencing data from the Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) project to analyze the expression of ADC targets in tumor and normal tissues. We chose thirty-seven targets with known ADCs in clinical development. Graphs were generated to show distribution of each gene's expression across all tumor and normal tissue types in TCGA and GTEx. Potential targets were determined based on tumor expression of at least two times the highest expression in any normal tissue. Proteins known to be secreted in the blood stream at high levels were excluded as they are unlikely to make a good ADC target (eg. AFP, FOLH1). Results: Using ERBB2 as the prototype gene, we were able to detect over-expression in all tumors that have HER-2 ove-rexpression in the literature including breast, bladder, NSCLC, Gastroesophageal, endometrial, HNSCC, ovarian, and colon cancer. Other genes with overexpression in select tumors including BSG (RCC, Melanoma, ACC), CD70 (RCC, DLBCL, mesothelioma, cervical), ENPP3 (RCC, endometrial, breast, lung adeno), FGFR2 (breast, gastric), FOLR1 (ovarian, lung adeno), GPNMB (lung, melanoma, HNSCC, renal), MSLN (lung adeno, mesothelioma, ovarian), SLC39A6 (breast), TDGF1 (thymoma, testicular, adrenocortical) were discovered as well. Tumors exhibited a significantly higher expression compared to normal tissue for ERBB2: breast cancer vs normal breast: p < 0.001; bladder cancer vs normal bladder: p < 0.001; lung adenocarcinoma vs normal lung: p < 0.001; ovarian cancer vs normal ovary: p < 0.001. Conclusion: Overall, this large-scale analysis from TCGA reveals that RNA-seq can be used as an initial screen to identify novel targets for ADCs. Further analysis will identify previously unappreciated targets that can be exploited for drug development across diverse cancers. Further confirmation with protein expression is warranted. Citation Format: Roman Groisberg, Jason Rosznik, Funda Meric-Bernstam, Vivek Subbiah. Comprehensive evaluation of antibody-drug conjugate targets for drug development across tumor types: Analysis from TCGA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2343.

QSurface: fast identification of surface expression markers in cancers

BackgroundCell surface proteins have provided useful targets and biomarkers for advanced cancer therapies. The recent clinical success of antibody-drug conjugates (ADCs) highlights the importance of finding selective surface antigens for given cancer subtypes. We thus attempted to develop stand-alone software for the analysis of the cell surface transcriptome of patient cancer samples and to prioritize lineage- and/or mutation-specific over-expression markers in cancer cells.ResultsA total of 519 genes were selected as surface proteins, and their expression was profiled in 14 cancer subtypes using patient sample transcriptome data. Lineage/mutation-oriented analysis was used to identify subtype-specific surface markers with statistical confidence. Experimental validation confirmed the unique over-expression of predicted surface markers (MUC4, MSLN, and SLC7A11) in lung cancer cells at the protein level. The differential cell surface gene expression of cell lines may differ from that of tissue samples due to the absence of the tumor microenvironment.ConclusionsIn the present study, advanced 3D models of lung cell lines successfully reproduced the predicted patterns, demonstrating the physiological relevance of cell line-based 3D models in validating surface markers from patient tumor data. Also QSurface software is freely available at http://compbio.sookmyung.ac.kr/~qsurface.

Practical Considerations, Challenges, and Limitations of Bioconjugation via Azide-Alkyne Cycloaddition.

Interrogating biological systems is often limited by access to biological probes. The emergence of "click chemistry" has revolutionized bioconjugate chemistry by providing facile reaction conditions amenable to both biologic molecules and small molecule probes such as fluorophores, toxins, or therapeutics. One particularly popular version is the copper-catalyzed azide-alkyne cycloaddition (AAC) reaction, which has spawned new alternatives such as the strain-promoted azide-alkyne cycloaddition reaction, among others. This focused review highlights practical approaches to AAC reactions for the synthesis of peptide or protein bioconjugates and contrasts current challenges and limitations in light of recent advances in the field. The conical success of antibody drug conjugates has expanded the toolbox of linkers and payloads to facilitate practical applications of bioconjugation to create novel therapeutics and biologic probes. The AAC reaction in particular is poised to enable a large set of functionalized molecules as a combinatorial approach to high-throughput bioconjugate generation, screening, and honing of lead compounds.

A novel anti-CD22 scFv\u2013apoptin fusion protein induces apoptosis in malignant B-cells

CD22 marker is a highly internalizing antigen which is located on the surface of B-cells and is being used as a promising target for treatment of B cell malignancies. Monoclonal antibodies targeting CD22 have been introduced and some are currently under investigation in clinical trials. Building on the success of antibody drug conjugates, we developed a fusion protein consisting of a novel anti-CD22 scFv and apoptin and tested binding and therapeutic effects in lymphoma cells. The recombinant protein was expressed in E. coli and successfully purified and refolded. In vitro binding analysis by immunofluorescence and flow cytometry demonstrated that the recombinant protein specifically binds to CD22 positive Raji cells but not to CD22 negative Jurkat cells. The cytotoxic properties of scFv–apoptin were assessed by an MTT assay and Annexin V/PI flow cytometry analysis and showed that the recombinant protein induced apoptosis preferentially in Raji cells with no detectable effects in Jurkat cells. Our findings indicated that the recombinant anti-CD22 scFv–apoptin fusion protein could successfully cross the cell membrane and induce apoptosis with high specificity, make it as a promising molecule for immunotherapy of B-cell malignancies.

Detection and Specific Elimination of EGFR+ Ovarian Cancer Cells Using a Near Infrared Photoimmunotheranostic Approach

Targeted theranostics is an alternative strategy in cancer management that aims to improve cancer detection and treatment simultaneously. This approach combines potent therapeutic and diagnostic agents with the specificity of different cell receptor ligands in one product. The success of antibody drug conjugates (ADCs) in clinical practice has encouraged the development of antibody theranostics conjugates (ATCs). However, the generation of homogeneous and pharmaceutically-acceptable ATCs remains a major challenge. The aim of this study is to detect and eliminate ovarian cancer cells on-demand using an ATC directed to EGFR. An ATC with a defined drug-to-antibody ratio was generated by the site-directed conjugation of IRDye®700 to a self-labeling protein (SNAP-tag) fused to an EGFR-specific antibody fragment (scFv-425). In vitro and ex vivo imaging showed that the ATC based on scFv-425 is suitable for the highly specific detection of EGFR+ ovarian cancer cell, human tissues and ascites samples. The construct was also able to eliminate EGFR+ cells and human ascites cells with IC50 values of 45-66 nM and 40-90 nM, respectively. Our experiments provide a framework to create a versatile technology platform for the development of ATCs for precise detection and treatment of ovarian cancer cells.

Abstract 2056: Development of quaternary amine linkers for ADCs: Application to auristatin E and tubulysin

Abstract The recent clinical success of antibody-drug conjugates (ADCs) has spawned an increased effort to identify new technologies, and the development of new drug-linker chemistry is vital to expand the scope of conjugatable payloads. The tertiary amine functional group is a common structural motif present in many bioactive compounds, including antimitotics of the auristatin and tubulysin classes. Traditionally, conjugation of tertiary amines required drug derivatization or modification to remove an N-alkyl group, thus creating a readily conjugatable secondary amine. However, identifying appropriate modifications that do not compromise the activity of the drug is frequently time consuming and often unsuccessful. To eliminate the need for such structural modifications, we sought a method for stable conjugation and facile release through the tertiary amine functional group by creating linkers with a quaternary amine point of attachment. To validate the linker strategy, quaternary amine-based cleavable linkers bearing auristatin E were synthesized and evaluated as ADCs. The conjugates were stable in rodent plasma, and were potent and immunologically specific both in vitro and in vivo in a Hodgkin lymphoma xenograft model. A second application of this technology has been demonstrated with tubulysins, another class of potent antimitotics containing a tertiary amine at the N-terminus. A cleavable quaternary amine linker containing a tubulysin analog was synthesized and ADCs were prepared and evaluated. The tubulysin conjugates were potent and immunologically specific across a panel of cancer cell lines, including multiple MDR-positive lines. Furthermore, the tubulysin conjugate displayed ‘bystander activity’ in an in vitro co-culture assay. The quaternary amine linkers represent an advance in linker technology and will enable the evaluation of drug classes previously inaccessible as ADCs. Citation Format: Patrick J. Burke, Joseph Z. Hamilton, Thomas A. Pires, Jocelyn R. Setter, Joshua H. Hunter, Julia H. Cochran, Brian E. Toki, Peter D. Senter, Robert P. Lyon, Scott C. Jeffrey. Development of quaternary amine linkers for ADCs: Application to auristatin E and tubulysin. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2056.

Design of a Small-Molecule Drug Conjugate for Prostate Cancer Targeted Theranostics.

Targeted therapy has become an effective strategy of precision medicine for cancer treatment. Based on the success of antibody-drug conjugates (ADCs), here we report a theranostic design of small-molecule drug conjugates (T-SMDCs) for targeted imaging and chemotherapy of prostate cancer. The structure of T-SMDCs built upon a polyethylene glycol (PEG) scaffold consists of (i) a chelating moiety for positron emission tomography (PET) imaging when labeled with (68)Ga, a positron-emitting radioisotope; (ii) a prostate specific membrane antigen (PSMA) specific ligand for prostate cancer targeting; and (iii) a cytotoxic drug (DM1) for chemotherapy. For proof-of-concept, such a T-SMDC, NO3A-DM1-Lys-Urea-Glu, was synthesized and evaluated. The chemical modification of Lys-Urea-Glu for the construction of the conjugate did not compromise its specific binding affinity to PSMA. The PSMA-mediated internalization of (68)Ga-labeled NO3A-DM1-Lys-Urea-Glu displayed a time-dependent manner, allowing the desired drug delivery and release within tumor cells. The antiproliferative activity of the T-SMDC showed a positive correlation with the PSMA expression level. Small animal PET imaging with (68)Ga-labeled NO3A-DM1-Lys-Urea-Glu exhibited significantly higher uptake (p < 0.01) in the PSMA positive PC3-PIP tumors (4.30 ± 0.20%ID/g) at 1 h postinjection than in the PSMA negative PC3-Flu tumors (1.12 ± 0.42%ID/g). Taken together, we have successfully designed and synthesized a T-SMDC system for prostate cancer targeted imaging and therapy.

Abstract 648: Optimization of a PEGylated glucuronide-auristatin linker for antibody-drug conjugates

Abstract The clinical success of antibody-drug conjugates (ADCs) brentuximab vedotin and ado-trastuzumab emtansine has led to an increased effort to identify new antibody payloads and develop improved linker technologies. Most antibody payloads impart significant hydrophobicity to the ADC resulting in accelerated plasma clearance and diminished in vivo activity, particularly for conjugates with high drug to antibody ratios (DAR). Consequently, drug-linkers have been designed to minimize or mask hydrophobicity, enabling a higher DAR and improved pharmacokinetic properties, translating to enhanced in vivo potency. We recently reported on the incorporation of a discrete PEG polymer as a side chain in the β-glucuronide-monomethylauristatin E (MMAE) linker to provide homogeneous DAR 8 conjugates with decreased plasma clearance and increased antitumor activity in xenograft models relative to a non-PEGylated control. The PEG-glucuronide-MMAE lead has now been optimized by minimizing the size of the PEG side chain and incorporating a self-stabilizing maleimide to prevent payload de-conjugation in vivo. Multiple PEG-glucuronide-MMAE linker constructs were prepared with PEG size varying from 0 to 24 ethylene oxide units, and uniform DAR 8 ADCs were evaluated. PEG size had small but variable effects in vitro, with diminished activity observed in some cell lines. In contrast, a clear relationship was observed between PEG length and plasma pharmacokinetics. Longer PEG chains resulted in slower clearance, with a ‘threshold’ length beyond which clearance was not impacted. Conjugates bearing PEG of sufficient length to minimize ADC plasma clearance provided a wider therapeutic window relative to conjugates bearing shorter PEGs. Thus, sufficient masking of drug hydrophobicity is a viable strategy to provide uniform DAR 8 ADCs that preserve ADC pharmacokinetics and increase potency through higher drug loading. Citation Format: Patrick J. Burke, Joseph Z. Hamilton, Scott C. Jeffrey, Joshua H. Hunter, Svetlana O. Doronina, Nicole M. Okeley, Martha E. Anderson, Peter D. Senter, Robert P. Lyon. Optimization of a PEGylated glucuronide-auristatin linker for antibody-drug conjugates. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 648. doi:10.1158/1538-7445.AM2015-648

Abstract 4634: Anthracycline based antibody-drug conjugates (ADCs) for the treatment of non-Hodgkin's lymphoma are effective in cell lines resistant to auristatin based ADCs.

Abstract Anthracyclines are one of the most widely used classes of chemotherapy. With current success of antibody drug conjugates in the clinic, we were interested in anthracycline-based antibody-drug conjugates (ADCs). Anthracyclines currently used in systemic chemotherapy were ineffective as the ADC drug probably due to low potency of the drug. PNU-159682 was identified as a metabolic product of nemorubicin that was 700 to 2400 more potent in in vivo cytotoxicity assays than nemorubicin. We were interested to see if we could develop an effective anthracycline-based ADC using PNU-159682. For these proof of concept studies we selected the clinically validated linker maleimidocaproyl-valine-citrulline-p-aminobenzoyloxycarbonyl (MC-vc-PAB) used in the approved ADC brentuximab vedotin [anti-CD30-MC-vc-PAB-monomethyl auristatin E (MMAE)] and attached it to the primary alcohol of PNU-159682 to make NMS-249. For antibodies we selected the anti-CD22 and anti-CD79b antibodies that have been shown to be effective as MC-vc-PAB-MMAE ADCs in phase 1 clinical trials for the treatment of NHL. In xenograft models of NHL anti-CD22-NMS249 was as effective or more effective as anti-CD22-MC-vcPAB-MMAE. In particular WSU-DLCL2, where anti-CD22-MC-vc-PAB-MMAE was least effective, show the greatest difference between the two ADCs. To further explore if these the anti-CD22-NMS249 could be used for patients that had progressed on auristatin-based ADC, we developed two cell lines that were resistant to anti-CD22-MC-vc-PAB-MMAE by consistently treating xenograft models with increase amounts of ADC. After removing the resistant tumors and culturing the cells in vitro the cell lines retained their resistance in vivo to anti-CD22-MC-vc-PAB-MMAE but were also resistance to anti-CD79b-MC-vc-PAB-MMAE. This suggests the resistance was not target related and we found that CD22 expression was maintained in the resistant cell lines. Anti-CD22-NMS249 maintained its efficacy in the resistant cell lines. Microarray and FACs showed that the resistant cells lines were up-regulated in MDR1 (PgP). We found that in vivo, unlike other anthacyclines, PNU-159682 was not a PgP substrate this may explain the ability of the anti-CD22-NMS249 to overcome the resistance to anti-CD22-MC-vc-PAB-MMAE. These studies provide poof of concept for an anthracycline ADC that could be use in patients that have failed auristatin-based therapies. Citation Format: Andrew G. Polson, Bing Zheng, MaryAnn Go, Jeffery Lau, Shang-Fan Yu, Susan Spencer, Robert Cohen, Michele Caruso, John Flygare, Paul Polakis. Anthracycline based antibody-drug conjugates (ADCs) for the treatment of non-Hodgkin's lymphoma are effective in cell lines resistant to auristatin based ADCs. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4634. doi:10.1158/1538-7445.AM2013-4634

An integrated approach to identify normal tissue expression of targets for antibody‐drug conjugates: case study of TENB2

The success of antibody-drug conjugates (ADCs) depends on the therapeutic window rendered by the differential expression between normal and pathological tissues. The ability to identify and visualize target expression in normal tissues could reveal causes for target-mediated clearance observed in pharmacokinetic characterization. TENB2 is a prostate cancer target associated with the progression of poorly differentiated and androgen-independent tumour types, and ADCs specific for TENB2 are candidate therapeutics. The objective of this study was to locate antigen expression of TENB2 in normal tissues, thereby elucidating the underlying causes of target-mediated clearance. A series of pharmacokinetics, tissue distribution and mass balance studies were conducted in mice using a radiolabelled anti-TENB2 ADC. These data were complemented by non-invasive single photon emission computed tomography - X-ray computed tomography imaging and immunohistochemistry. The intestines were identified as a saturable and specific antigen sink that contributes, at least in part, to the rapid target-mediated clearance of the anti-TENB2 antibody and its drug conjugate in rodents. As a proof of concept, we also demonstrated the selective disposition of the ADC in a tumoural environment in vivo using the LuCaP 77 transplant mouse model. High tumour uptake was observed despite the presence of the antigen sink, and antigen specificity was confirmed by antigen blockade. Our findings provide the anatomical location and biological interpretation of target-mediated clearance of anti-TENB2 antibodies and corresponding drug conjugates. Further investigations may be beneficial in addressing the relative contributions to ADC disposition from antigen expression in both normal and pathological tissues.