Abstract Background The clinical benefit of anti-spike mAbs for prophylaxis and treatment of SARS-CoV-2 is now well established (Baum 2020, Loo 2022, Westendorf 2022, Jones 2021, Kreuzberger 2021, Cathcart 2021, Hirsch 2022, Shi 2020); However, the evolution of SARS CoV-2 due to immune pressure has compromised the utility of all previously approved mAbs which target the variable, immune dominant receptor binding domain of the Spike protein. Despite the success of vaccination protecting the general population, the immunocompromised and elderly remain at high risk of serious disease and mortality from SARS CoV-2 infection. Therefore, there is a need to develop mAbs that remain active across current and emergent SARS CoV-2 variants for such populations. Methods The Generate Platform uses machine learning (ML) models to generate therapeutics with desirable properties. We used this platform to explore the amino acid sequence landscape compatible with the binding conformation and breadth of neutralization for mAbs targeting the conserved S-2 stem helix of Spike. While S-2 directed antibodies can broadly neutralize diverse coronaviruses, they are generally limited by potency. We employed an iterative computation- experimentation loop to design antibodies that bind to the S-2 stem helix, optimizing for potency, breadth and developability. Results The Generate Platform was employed to identify S-2 targeted Spike antibodies with high potency and breadth of neutralization resulting in GB-0669. GB-0669 exhibits sub-nM neutralization against all SARS-CoV-2 variants and Omicron sublineages including the highly immune evasive strain XBB. GB-0669 also displays sub-nM neutralization against sarbecoviruses associated with previous epidemics (SARS-CoV-1) and those of pandemic potential (WIV1, bat SARS-like coronavirus). The GB 0669 epitope was mapped by co-crystallization and is consistent with the observed breadth; all key interactions are >99% conserved with no evidence of immune escape. Conclusion GB-0669, a novel mAB targeting the conserved S-2 region of Spike, is hypothesized to be effective for prophylaxis of COVID-19 across all Omicron sublineages and future variants as well as CoVs with pandemic potential. Disclosures Francesco Borriello, MD PhD, Generate Biomedicines: Employee Gevorg Grigoryan, PhD, Generate Biomedicines: Chief Technology Officer|Generate Biomedicines: Ownership Interest|Generate Biomedicines: Stocks/Bonds Daria Hazuda, PhD, Generate Biomedicines: Employee|Generate Biomedicines: Stocks/Bonds|Merck and Co: Employee|Merck and Co: Stocks/Bonds Nathan H. Joh, PhD, Generate Biomedicines: Employee at Generate Biomedicines

Supplementary Table 1: Surface antigen density impacts in vitro potency of anti-LIV-1 ADC . MCF-7 ATCC cells from three sources with varying levels of LIV-1 expression were tested with SGN-LIV1A for cytotoxicity. Lower antigen density resulted in decreased potency.

BackgroundPD-1/PD-L1 immune checkpoint inhibitors have transformed oncology, but a significant unmet need persists for patients with relapsed/refractory tumors following PD-1/PD-L1 treatment. PD-L1 is expressed in patients across a broad spectrum of tumor types and displays limited normal tissue expression, highlighting the potential of PD-L1 as a target for antibody-drug conjugates (ADCs) in addition to its role as an immune checkpoint. SGN-PDL1V is a PD-L1-directed ADC currently under preclinical investigation, which is comprised of an anti-PD-L1 antibody conjugated to the vedotin drug-linker. The vedotin drug-linker, consists of the microtubule disrupting agent, monomethyl auristatin E (MMAE), and a protease-cleavable peptide linker, which has been clinically validated in multiple ADC programs including brentuximab vedotin, enfortumab vedotin and polatuzumab vedotin.1–3 The proposed SGN-PDL1V primary mechanism of action is direct cytotoxicity against PD-L1-expressing malignant cells through delivery of the MMAE payload. Additionally, MMAE induces immunogenic cell death, leading to subsequent immune activation in the tumor microenvironment.4 Here, we characterize the preclinical activity and tolerability of SGN-PDL1V.MethodsSGN-PDL1V cytotoxicity was evaluated using PD-L1 expressing tumor cell lines in vitro and xenograft tumor models in vivo. Inhibition of the PD-1/PD-L1 immune checkpoint was assessed in a luminescent reporter system in vitro and a syngeneic tumor model in vivo. The tolerability and safety profile of SGN-PDL1V was determined in a non-human primate study.ResultsIn vitro, SGN-PDL1V demonstrated internalization and potent cytotoxic activity against PD-L1 expressing tumor cells. In vivo, SGN-PDL1V achieved tumor regressions in multiple tumor xenograft models at doses as low as 1 mg/kg when dosed weekly for a total of three doses. This activity was observed in immunocompromised mice, which lack responses to PD-1/PD-L1 inhibition. Notably, activity was observed even in xenograft models with low, heterogeneous PD-L1 expression, supporting the possibility to treat patients across a wide range of PD-L1 expression levels. Additionally, SGN-PDL1V exhibited potential to inhibit the PD-1/PD-L1 checkpoint in vitro and in vivo. The tolerability and safety profile of SGN-PDL1V were assessed in a non-human primate study and found to be comparable to other FDA-approved vedotin ADCs.ConclusionsSGN-PDL1V is a promising PD-L1 directed ADC with a unique cytotoxic mechanism of action among other PD-L1-targeted therapeutics. SGN-PDL1V demonstrated robust activity in multiple preclinical models and comparable tolerability and safety profile to other vedotin ADCs in non-human primates. Collectively, these data support further evaluation of SGN-PDL1V in a planned, first-in-human Phase 1 study.AcknowledgementsWe would like to thank Kerry Klussman for assay support and Jamie Mitchell for conjugation support.Trial RegistrationN/AReferencesSenter PD, Sievers EL. The discovery and development of brentuximab vedotin for use in relapsed Hodgkin lymphoma and systemic anaplastic large cell lymphoma. Nat Biotechnol 2012;30(7):631–7. Epub 2012/07/12. doi: 10.1038/nbt.2289. PubMed PMID: 22781692.Rosenberg JE, O'Donnell PH, Balar AV, McGregor BA, Heath EI, Yu EY, et al. Pivotal trial of enfortumab vedotin in urothelial carcinoma after platinum and anti-programmed death 1/Programmed death ligand 1 therapy. J Clin Oncol 2019;37(29):2592–600. Epub 2019/07/30. doi: 10.1200/JCO.19.01140. PubMed PMID: 31356140; PubMed Central PMCID: PMC6784850.Tilly H, Morschhauser F, Bartlett NL, Mehta A, Salles G, Haioun C, et al. Polatuzumab vedotin in combination with immunochemotherapy in patients with previously untreated diffuse large B-cell lymphoma: an open-label, non-randomised, phase 1b-2 study. Lancet Oncol 2019;20(7):998–1010. Epub 2019/05/19. doi: 10.1016/S1470-2045(19)30091-9. PubMed PMID: 31101489.Klussman K, Tenn E, Higgins S, Mazahreh R, Snead K, Hamilton J, Grogan B, Sigurjonsson J, Cao A, Gardai S, Liu B. 618 Vedotin ADCs induce ER stress and elicit hallmarks of ICD across multiple cancer indications. J Immunother Cancer 2020;8(Suppl 3):A372. DOI:10.1136/jitc-2020-SITC2020.0618.Ethics ApprovalAll animal studies were conducted in accordance with protocols reviewed and approved by the Institutional Animal Care and Use Committee at Seagen or the external testing facility that conducted the studies.

Patients with relapsed/triple class refractory (refractory to a proteasome inhibitor, immunomodulatory drug or anti-CD38 antibody) multiple myeloma (MM) have limited treatment options. Versatile therapies, such as unconjugated antibodies (Abs), that are well tolerated and can be combined with multiple modalities are critical for the MM treatment landscape. SEA-BCMA is an investigational, humanized, nonfucosylated IgG1 monoclonal Ab targeting B-cell maturation antigen (BCMA) on malignant plasma cells. Preclinical data show that SEA-BCMA blocks BCMA-mediated pro-survival and proliferative cell signaling and mediates antibody-dependent cellular phagocytosis and enhanced antibody-dependent cellular cytotoxicity via increased binding to activating Fc receptor, FcγRIIIa (Van Epps 2018). A phase 1, open-label, multicenter study to evaluate the safety, tolerability, and antitumor activity of SEA-BCMA in adults with relapsed or refractory MM (SGNBCMA-001; NCT03582033) is ongoing. To support maximal ligand blocking and immune effector engagement by SEA-BCMA, we investigated its binding and saturation pharmacodynamics (PD) in patients enrolled in dose escalation and currently recruiting dose expansion cohorts.

Abstract Despite a number of new therapies for multiple myeloma (MM) most patients relapse, require multiple lines of therapy, and ultimately succumb to disease. Therapies that are well tolerated and active remain an unmet need. Currently, successful MM therapies combine agents with different mechanisms of action and safety profiles. Therapeutic antibodies have recently altered the MM treatment paradigm, allowing patients to achieve deeper responses with minimal added toxicity. SEA-BCMA is a humanized afucosylated IgG1 antibody targeting BCMA, which shows preclinical evidence of encouraging activity and tolerability. BCMA is expressed at the surface of plasma cells, and induces proliferative signals through the binding of its ligands APRIL and BAFF. SEA-BCMA acts through three mechanisms of action. One, it engages in increased binding to FcγRIII through SEA technology leading to enhanced antibody dependent cellular cytotoxicity. Two, it mediates antibody dependent cellular phagocytosis. Three, it blocks the proliferative signals from BCMA ligand binding. This antibody shows activity in all seven tumor xenograft models tested, inducing tumor delays at doses as low as 0.1mg/kg, and generating prolonged survival and durable regressions with repeat dosing. SEA-BCMA is active on tumor xenografts expressing as few as 2000 surface copies of BCMA antigen. Both effector function and ligand blocking contribute to overall in vivo activity. In the absence of effector cell recruitment, ligand blocking alone can induce prolonged durable regressions. In addition, SEA-BCMA can target MM cells in the presence of soluble BCMA. SEA-BCMA is tolerated up to 100mg/kg in cynomolgus monkey, reflecting lack of toxicity from cellular interactions with the Fc portion of the Ab, since SEA-BCMA does not bind to the cynomolgus monkey antigen. SEA-BCMA displays a 12-day half-life in these animals. In vitro testing with human PBMCs or bone marrow mononuclear cells induced minimal cytokine production in the presence of BCMA target. In summary, SEA-BCMA is highly active and well tolerated in preclinical models and is a strong candidate for treatment of MM patients. Citation Format: Heather Van Epps, Martha Anderson, Changpu Yu, Kerry Klussman, Lori Westendorf, Chris Carosino, Luke Manlove, Julia Cochran, Jason Neale, Dennis Benjamin, Maureen Ryan. SEA-BCMA: A highly active enhanced antibody for multiple myeloma [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 3833.

Microtubule-organizing centers (MTOCs) form, anchor, and stabilize the polarized network of microtubules in a cell. The central MTOC is the centrosome that duplicates during the cell cycle and assembles a bipolar spindle during mitosis to capture and segregate sister chromatids. Yet, despite their importance in cell biology, the physical structure of MTOCs is poorly understood. Here we determine the molecular architecture of the core of the yeast spindle pole body (SPB) by Bayesian integrative structure modeling based on in vivo fluorescence resonance energy transfer (FRET), small-angle x-ray scattering (SAXS), x-ray crystallography, electron microscopy, and two-hybrid analysis. The model is validated by several methods that include a genetic analysis of the conserved PACT domain that recruits Spc110, a protein related to pericentrin, to the SPB. The model suggests that calmodulin can act as a protein cross-linker and Spc29 is an extended, flexible protein. The model led to the identification of a single, essential heptad in the coiled-coil of Spc110 and a minimal PACT domain. It also led to a proposed pathway for the integration of Spc110 into the SPB.

Patients with relapsed/refractory B-cell malignancies such as non-Hodgkin lymphoma (B-NHL) or acute lymphoblastic leukemia have a poor prognosis. Despite measurable clinical activity with new targeted therapies, many patients do not achieve a complete or durable response suggesting an opportunity to improve upon existing therapies. Here we describe SGN-CD19B, a pyrrolobenzodiazepine (PBD)-based anti-CD19 antibody drug conjugate (ADC) being investigated for treatment of B-cell malignancies, which has improved potency compared with other ADCs. CD19-expressing tumor cells rapidly internalize SGN-CD19B, and the released PBD drug induces DNA damage, resulting in G2/M cell cycle arrest and cell death. SGN-CD19B demonstrated activity against a broad panel of malignant B-cell lines and induced durable regressions in mice bearing xenografts derived from these B-cell malignancies. A single dose of SGN-CD19B induced durable regressions at 300 μg/kg (3 μg/kg drug equivalents); combination with rituximab decreased the curative dose to 100 μg/kg (1 μg/kg drug equivalents). These doses are significantly lower than the level of drug required with other ADC payloads. In cynomolgus monkeys, SGN-CD19B effectively depleted CD20+ B lymphocytes in peripheral blood and lymphoid tissues confirming that SGN-CD19B is pharmacodynamically active at well-tolerated doses. In summary, preclinical studies show SGN-CD19B is a highly active ADC, which releases a DNA cross-linking agent rather than a microtubule inhibitor. The distinct mechanism of action, broad potency, and potential to combine with rituximab suggest that SGN-CD19B may offer unique clinical opportunities in B-cell malignancies. A phase 1 clinical trial is in progress to investigate the therapeutic potential of SGN-CD19B in relapsed/refractory B-NHL. This trial was registered at www.clinicaltrials.gov as #NCT02702141.

Denintuzumab Mafodotin (SGN-CD19A) is an antibody-drug conjugate (ADC) composed of an anti-CD19 antibody attached to a synthetic cytotoxic agent, monomethyl auristatin F (MMAF). The ADC binds CD19, internalizes, and releases cys-mcMMAF, which ultimately results in G2-M growth arrest and induction of apoptosis in targeted cells (Law et. al. AACR 2011). SGN-CD19A has shown convincing antitumor activity in relapsed/refractory non-Hodgkin lymphoma patients, resulting in a significant number of objective responses, including complete responses with prolonged durability (Moskowitz et. al. Blood 2015). To further characterize the anti-tumor activity of SGN-CD19A, we evaluated whether immune-mediated cell killing and immunogenic cell death (ICD) act in addition to the previously described apoptotic cell death. We then examined whether these mechanisms of cell death are augmented by clinically approved CD20 antibodies. Our results show that SGN-CD19A supports immune-mediated killing of lymphoma cell lines in vitro through antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Assessment of disseminated and subcutaneous tumor xenografts showed that SGN-CD19A activity is reduced when the wild type antibody is replaced with IgG variants that lack effector function. We also found depletion of macrophage or NK cells eliminates the improved survival conferred by the parental antibody of SGN-CD19A. Together these data provide strong evidence that effector function contributes to activity of SGN-CD19A in vivo. Next, we implemented an in vitro system pairing lymphoblastoid cell lines (LCLs) with autologous PBMC to investigate the effect of SGN-CD19A-mediated cell death on immune activation. Treatment of LCL with SGN-CD19A drove hallmarks of ICD as indicated by activation of the ER stress response along with upregulation of surface calreticulin. In vitro co-culture of SGN-CD19A treated LCL with autologous PBMC resulted in heightened monocyte activation and expansion of LCL-reactive cytotoxic T cells supporting a role for SGN-CD19A in augmenting anti-tumor immune responses. Finally, we evaluated the anti-tumor activity of SGN-CD19A in the presence and absence of clinically relevant CD20 antibodies. Results showed that CD20-targeted antibodies impact internalization of CD19 antigen leading to improved drug delivery of SGN-CD19A. Blocking B cell signaling inhibits the effect of CD20 antibodies on CD19 and SGN-CD19A. The improved anti-tumor activity observed with SGN-CD19A plus CD20 therapeutics was confirmed in vivo using rituximab. In conclusion, our results demonstrate SGN-CD19A is a multifunctional ADC capable of eliciting cell killing through immune-mediated mechanisms as well as delivery of the cytotoxic payload, cys-mcMMAF. Importantly, the described mechanisms of SGN-CD19A activity are further augmented by CD20 antibodies. These studies support the ongoing clinical evaluation of SGN-CD19A, which is currently being tested in randomized Phase II clinical trials in combination with R-ICE (NCT02592876) as well as R-CHOP (NCT02855359). Disclosures Van Epps: Seattle Genetics: Employment. Heiser:Seattle Genetics: Employment. Cao:Seattle Genetics: Employment. Klussman:Seattle Genetics: Employment. Yu:Seattle Genetics: Employment. Stone:Seattle Genetics: Employment. Neale:Seattle Genetics: Employment. Gardai:Seattle Genetics: Employment. Law:Seattle Genetics, Inc.: Employment, Equity Ownership. Ryan:Seattle Genetics: Employment.

Patients with relapsed or refractory B-cell non-Hodgkin lymphoma (r/r NHL) have a poor prognosis. Despite measurable clinical activity seen with new targeted therapies, most r/r NHL patients do not achieve a complete or durable response suggesting there is room to improve upon existing clinical candidates.

Abstract SGN-CD19A is an antibody drug conjugate (ADC) that recognizes CD19, a B-cell specific marker expressed in B-cell malignancies including non-Hodgkin lymphoma (NHL). SGN-CD19A is currently in a phase I clinical trial for adult patients with relapsed refractory B-cell NHL (CT.gov NCT01786135) in which it has shown evidence of single-agent activity (1). This ADC binds CD19, internalizes, and releases cys-mcMMAF, which ultimately induces apoptosis in targeted cells (2). Lymphoma tumor xenografts treated with SGN-CD19A show growth delay in a dose dependent manner. Here we show that SGN-CD19A in combination with standard of care [rituximab/ifosfamide/carboplatin/etoposide (R-ICE), rituximab/cyclophosphamide/doxorubicin/vincristine/prednisone (R-CHOP), or components] exceeds the activity of SGN-CD19A alone and results in impressive anti-tumor activity in multiple xenograft models. It was notable that in some xenograft models, SGN-CD19A + R-CHOP or SGN-CD19A + R-ICE yielded activity that was similar to SGN-CD19A plus rituximab alone. This strong interaction between rituximab and SGN-CD19A was modeled in vitro. SGN-CD19A synergized with rituximab, in the absence of cross-linking, to cause decreased cell viability in NHL cell lines. These data suggest that cell autonomous signaling contributes to the unique interaction between rituximab and SGN-CD19A. Our in vivo and in vitro data support R-CHOP, R-ICE, or rituximab as viable combination therapies for NHL patients with SGN-CD19A. 1) Uma Borate et al. A first-in-human phase 1 study of the antibody-drug conjugate SGN-CD19A in relapsed or refractory B-lineage acute leukemia and highly aggressive lymphoma. Blood 2013 122:1437 2) Che-Leung Law et al. Preclinical characterization of an auristatin-based anti-CD19 drug conjugate, SGN-19A. Abstract number 625. In: Proceedings of the 102th Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Citation Format: Heather A. Van Epps, Kerry Klussman, Martha Anderson, Weiping Zeng, Devra Olson, Maureen Ryan, Tina Albertson, Che-Leung Law. Preclinical results of SGN-CD19A in combination with R-ICE or R-CHOP in non-Hodgkin lymphoma models. [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 2541. doi:10.1158/1538-7445.AM2015-2541

Abstract In this article, we describe a novel antibody–drug conjugate (ADC; SGN–LIV1A), targeting the zinc transporter LIV-1 (SLC39A6) for the treatment of metastatic breast cancer. LIV-1 was previously known to be expressed by estrogen receptor–positive breast cancers. In this study, we show that LIV-1 expression is maintained after hormonal therapy in primary and metastatic sites and is also upregulated in triple-negative breast cancers. In addition to breast cancer, other indications showing LIV-1 expression include melanoma, prostate, ovarian, and uterine cancer. SGN–LIV1A consists of a humanized antibody conjugated through a proteolytically cleavable linker to monomethyl auristatin E, a potent microtubule-disrupting agent. When bound to surface-expressed LIV-1 on immortalized cell lines, this ADC is internalized and traffics to the lysozome. SGN–LIV1A displays specific in vitro cytotoxic activity against LIV-1–expressing cancer cells. In vitro results are recapitulated in vivo where antitumor activity is demonstrated in tumor models of breast and cervical cancer lineages. These results support the clinical evaluation of SGN–LIV1A as a novel therapeutic agent for patients with LIV-1–expressing cancer. Mol Cancer Ther; 13(12); 2991–3000. ©2014 AACR.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC LIV-1, also known as SLC39A6 or ZIP6, is a member of the zinc transporter family and was first identified as an estrogen-inducible gene in breast cancer derived cell lines. LIV-1, as a downstream target of STAT3, promotes the epithelial to mesenchymal transition that is important in the malignant progression to metastasis. Consistent with its role in cancer, we determined by immunohistochemical (IHC) analysis that LIV-1 is expressed in subtypes of metastatic breast cancers (ER+/HER2-, HER2+ and triple negative). In healthy human tissues, LIV-1 expression is limited to four hormonally-regulated organs. The broad expression of LIV-1 in metastatic breast cancer in combination with the limited expression in vital organs makes LIV-1 an excellent target for an antibody-drug conjugate (ADC). SGN-LIV1A is an ADC consisting of a humanized anti-LIV-1 mAb conjugated to the microtubule-disrupting agent, monomethyl auristatin E, via a protease-cleavable linker. In vitro, SGN-LIV1A shows target specific internalization and cytotoxic activity against a breast cancer cell line. In vivo studies also demonstrate antitumor activity of SGN-LIV1A in preclinical xenograft models with significant delay of tumor growth compared to control groups. These findings support further evaluation and development of SGN-LIVA as a therapeutic for the treatment of metastatic breast cancer. Citation Format: Django Sussman, Leia M. Smith, Martha E. Anderson, Steve Duniho, Joshua H. Hunter, Heather Kostner, Jamie B. Miyamoto, Albina Nesterova, Lori Westendorf, Heather A. Van Epps, Nancy Whiting, Dennis R. Benjamin. SGN-LIV1A: a development stage antibody drug-conjugate targeting LIV-1 for the treatment of metastatic breast cancer. [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 3962. doi:10.1158/1538-7445.AM2013-3962

Abstract LIV-1, also known as SLC39A6 or ZIP6, is a member of the zinc transporter family and was first identified as an estrogen-inducible gene in breast cancer derived cell lines. LIV-1, as a downstream target of STAT3, promotes the epithelial to mesenchymal transition that is important in the malignant progression to metastasis. Consistent with its role in cancer, we determined by immunohistochemical (IHC) analysis that LIV-1 is expressed in subtypes of metastatic breast cancers (ER+/HER2-, HER2+ and triple negative). In healthy human tissues, LIV-1 expression is limited to four hormonally-regulated organs. The broad expression of LIV-1 in metastatic breast cancer in combination with the limited expression in vital organs makes LIV-1 an excellent target for an antibody-drug conjugate (ADC). SGN-LIV1A is an ADC consisting of a humanized anti-LIV-1 mAb conjugated to the microtubule-disrupting agent, monomethyl auristatin E, via a protease-cleavable linker. In vitro, SGN-LIV1A shows target specific internalization and cytotoxic activity against a breast cancer cell line. In vivo studies also demonstrate antitumor activity of SGN-LIV1A in preclinical xenograft models with significant delay of tumor growth compared to control groups. These findings support further evaluation and development of SGN-LIVA as a therapeutic for the treatment of metastatic breast cancer. Citation Format: Django Sussman, Leia M. Smith, Martha E. Anderson, Steve Duniho, Joshua H. Hunter, Heather Kostner, Jamie B. Miyamoto, Albina Nesterova, Lori Westendorf, Heather A. Van Epps, Nancy Whiting, Dennis R. Benjamin. SGN-LIV1A: a development stage antibody drug-conjugate targeting LIV-1 for the treatment of metastatic breast cancer. [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 3962. doi:10.1158/1538-7445.AM2013-3962

Antibody-drug conjugates (ADCs) are designed to deliver a targeted, potent payload directly to the tumor cell. This targeted cytoxicity can greatly augment the antitumor activity of a naked antibody and reduce the off target toxicity of free drug. Cancers of the head and neck, pancreas, bladder, lung, ovary and breast show frequent expression of integrin α6, suggesting they may be amenable to therapeutic targeting with an anti-integrin β6 ADC. We identified a therapeutic antibody that is optimal for drug delivery by screening a large panel of anti-integrin β6 ADCs on antigen-positive tumor lines. Monoclonal antibody 15H3 showed consistent potency as an ADC on solid tumor cell lines representative of the target indications. The ADC activity of 15H3 was detectable using either monomethyl auristatin E with a protease-cleavable linker (vcMMAE) or monomethyl auristatin F (mcMMAF), which requires antibody degradation. 15H3 was selected as the lead and humanized for in vivo testing. Humanized 15H3 (h15H3) retained all the properties of the mouse parental antibody, including the ability to cross-bind multiple species (human, monkey, rat, and mouse integrin α6). In vitro analysis showed that h15H3-vcMMAE and h15H3-mcMMAF internalize within a few hours and result in antigen-specific cytotoxicity of carcinoma lines. In vivo studies of integrin-α6 positive xenografts demonstrated antitumor activity. Our data suggest that integrin β6 is a promising potential ADC target for antigen-positive solid tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4630. doi:1538-7445.AM2012-4630