Efficacy Of Antibody-drug Conjugates Research Articles

Abstract 1848: Targeting FZD7-positive cancers using a novel antibody-drug conjugate

Abstract WNT signaling is frequently dysregulated in cancers. However, pan-WNT inhibitors regularly induce adverse effects in patients, mostly notably in bone, creating a need for more specific WNT-pathway targeting strategies. Frizzled-7 (FZD7), a cell-surface receptor for WNT proteins, is a strong target candidate due to its high expression pattern in many tumor types (including but not limited to breast, ovarian, liver, gastric, and skin cancers) and low to modest expression in few normal adult tissues. We validated FZD7 protein expression in primary patient melanomas and breast and ovarian tumor samples, and developed an antibody-drug conjugate (ADC) that targets human FZD7, hereafter referred to as “FZD7 ADC.” Our ADC consists of a chimeric human-mouse IgG1 antibody conjugated to four molecules of antimitotic drug, monomethyl auristatin E (MMAE), by cleavable valine-citrulline linkers. By flow cytometry, we confirmed that the antibody component binds FZD7 and does not cross-react with the other nine human FZD receptors, FZD(1-6,8-10). We have identified MA-148 and PA-1 as human ovary-derived cancer cell lines responsive to our ADC. We also generated a negative control line, MA-148 FZD7-KO, by CRISPR/Cas9 knockout. In a cell viability assay, we demonstrated FZD7 ADC efficacy in inducing direct, FZD7-dependent cytotoxicity. A single dose of ADC killed MA-148 and PA-1 cells in vitro, with an IC50 of ~0.76 ug/mL (~5 nM) in both lines. MA-148 FZD7-KO cells exhibited an IC50 of ~9 ug/mL (~60 nM). Here, we established a therapeutic window in which our ADC specifically kills FZD7-positive cells. We are currently evaluating FZD7 ADC tumor-killing efficacy in vivo. Because our ADC only binds human FZD7, and not mouse Fzd7, we are utilizing a xenograft model in female nude mice. In a preliminary three-armed study, we established subcutaneous human MA-148-Luciferase (Luc) tumors in mice and treated with a PBS control, 1 mg/kg FZD7 ADC (~0.15 nmole), or 3 mg/kg FZD7 ADC (~0.5 nmole), n = 3-5 per group. We performed an identical study with mice bearing MA-148 FZD7-KO-Luc tumors in parallel. Treatments were delivered twice per week by tail vein injection. Tumor size was measured weekly by an IVIS Spectrum after intraperitoneal luciferin injection. After eight doses over 27 days, MA-148-Luc tumors treated with 3 mg/kg FZD7 ADC completely or partially regressed compared to the control tumors (p = 0.0101 by one-way ANOVA and Tukey's multiple comparisons test). The 1 mg/kg dose did not produce a therapeutic effect in the MA-148-Luc. Importantly, the negative-control MA-148 FZD7-KO-Luc tumors treated with 3- or 1 mg/kg of ADC were not statistically different from the control tumors. Here, we have established a therapeutic FZD7 ADC dose for tumor regression and demonstrated its specificity to FZD7-positive tumors in vivo. Our data show that the FZD7 ADC is an effective strategy to combat cancers expressing FZD7. Citation Format: Myan Do, Christina C. Wu, Stephen Adams, Dennis Carson, Sunil Advani, Karl Willert. Targeting FZD7-positive cancers using a novel antibody-drug conjugate [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 1848.

Linker Design Impacts Antibody-Drug Conjugate Pharmacokinetics and Efficacy via Modulating the Stability and Payload Release Efficiency.

The development of antibody-drug conjugates (ADCs) has significantly been advanced in the past decade given the improvement of payloads, linkers and conjugation methods. In particular, linker design plays a critical role in modulating ADC stability in the systemic circulation and payload release efficiency in the tumors, which thus affects ADC pharmacokinetic (PK), efficacy and toxicity profiles. Previously, we have investigated key linker parameters such as conjugation chemistry (e.g., maleimide vs. disulfide), linker length and linker steric hindrance and their impacts on PK and efficacy profiles. Herein, we discuss our perspectives on development of integrated strategies for linker design to achieve a balance between ADC stability and payload release efficiency for desired efficacy in antigen-expressing xenograft models. The strategies have been successfully applied to the design of site-specific THIOMABTM antibody-drug conjugates (TDCs) with different payloads. We also propose to conduct dose fractionation studies to gain guidance for optimal dosing regimens of ADCs in pre-clinical models.

Therapeutic Potential of Antibody-Drug Conjugate-Based Therapy in Head and Neck Cancer: A Systematic Review.

Simple SummaryHead and neck cancer (HNC) is a complex and extremely heterogeneous disease that includes a wide variety of cancer subtypes. Despite notable advances in understanding the molecular mechanisms involved in the disease, which allowed the increase of the therapeutic armamentarium, HNC treatment remains very challenging. In fact, to date the average 5-year survival rate for this disease is around 65%; hence, HNC continues to be one of the most aggressive solid tumors. Surgical removal is the first treatment of choice for HCN; however, in addition to this treatment modality, a broad spectrum of new therapies has been developed so far, ranging from multimodal chemotherapy to targeted and immune-therapy, mainly through the use of antibodies. In this work, we systematically reviewed the progress obtained in antibody-drug conjugate (ADC) development for the treatment of HNC.Background: Antibody-drug conjugates (ADCs) are designed to deliver potent cytotoxic agents into tumor tissues. During the last two decades, a plethora of ADCs have been successfully developed and used for several indications, including hematologic and solid tumors. In this work, we systematically reviewed the progress in ADC development for the treatment of HNC. Methods: This review was registered in PROSPERO database. A comprehensive search was conducted following PRISMA guidelines and using PubMed, Scopus and Web of Science database. Results: In total, 19 studies were included. Due to the significant heterogeneity of the outcome measures, meta-analysis was not performed, and data were summarized in tables. HNC results are poorly represented in the cohorts of completed clinical trials; published data are mostly focused on safety evaluation rather than efficacy of ADCs. Conclusions: Although several novel agents against a wide range of different antigens were investigated, showing promising results at a preclinical level, most of the targets reported in this review are not specific for HNC; hence, the development of ADCs tailored for the HNC phenotype could open up new therapeutic perspectives. Moreover, the results from the present systematic review call attention to how limited is the application of current clinical trials in HNC.

Efficient Labeling of Native Human IgG by Proximity-Based Sortase-Mediated Isopeptide Ligation.

Antibody-drug conjugates (ADCs) have demonstrated great therapeutic potential due to their ability to target the delivery of potent cytotoxins. However, the heterogeneous nature of conventional drug conjugation strategies can affect the safety, efficacy, and stability of ADCs. Site-specific conjugations can resolve these issues, but often require genetic modification of Immunoglobulin G (IgG), which can impact yield or cost of production, or require undesirable chemical linkages. Here, we describe a near-traceless conjugation method that enables the efficient modification of native IgG, without the need for genetic engineering or glycan modification. This method utilizes engineered variants of sortase A to catalyze noncanonical isopeptide ligation. Sortase A was fused to an antibody-binding domain to improve ligation efficiency. Antibody labeling is limited to five lysine residues on the heavy chain and one on the light chain of human IgG1. The ADCs exhibit conserved antigen and Fc-receptor interactions, as well as potent cytolytic activity.

Quantitative Evaluation of the Effect of Antigen Expression Level on Antibody-Drug Conjugate Exposure in Solid Tumor.

Antibody-drug conjugates (ADCs) rely on high expression of target antigens on cancer cells to effectively enter the cell and release a cytotoxic payload. Previous studies have shown that ADC efficacy is not always tied to antigen expression. However, our recent in vitro study suggests a linear relationship between antigen expression and the intracellular levels of the ADC payload. In this study, we have explored the relationship between antigen expression and intratumoral ADC exposure in vivo. Using trastuzumab-vc-MMAE (T-vc-MMAE) and four cell lines with varying expression of human epithelial growth factor receptor 2 (HER2), the pharmacokinetics of total trastuzumab, released ("free") MMAE, and total MMAE were evaluated in a tumor xenograft model. Nude mice were implanted with tumors originating from BT-474, MDA-MB-453, MCF-7, and MDA-MB-468 cell lines and dosed with 10 mg/kg or 1 mg/kg of ADC. Observed data were mathematically characterized using a mechanism-based PK model. A strong positive correlation was observed between antigen expression levels and free/total MMAE exposure (R2 ≥ 0.91) (total MMAE being the sum of released and conjugated MMAE) within the tumor, but not for total trastuzumab exposure. The PK model was able to recapitulate plasma PK through simulation; however, the tumor PK was overpredicted or underpredicted in some cases potentially due to differences in tumor vasculature or extracellular matrix conditions. Our results indicate a linear relationship between antigen expression and tumor exposure of free/total ADC payload in vivo, validating our previous finding in vitro, while also revealing the need to understand complex physiology of the tumor to predict tumor PK of ADC and its components. Our findings also support the concept of antigen expression screening in patients for targeted therapies like ADCs to achieve the maximum therapeutic benefit of the treatment.

Tandem-Cleavage Linkers Improve the In Vivo Stability and Tolerability of Antibody-Drug Conjugates.

Although peptide motifs represent the majority of cleavable linkers used in clinical-stage antibody-drug conjugates (ADCs), the sequences are often sensitive to cleavage by extracellular enzymes, such as elastase, which leads to systemic release of the cytotoxic payload. This action reduces the therapeutic index by causing off-target toxicities that can be dose-limiting. For example, a common side-effect of ADCs made using peptide-cleavable linkers is myelosuppression, including neutropenia. Only a few reports describe methods for optimizing peptide linkers to maintain efficient and potent tumor payload delivery while enhancing circulating stability. Herein, we address these critical limitations through the development of a tandem-cleavage linker strategy, where two sequential enzymatic cleavage events mediate payload release. We prepared dipeptides that are protected from degradation in the circulation by a sterically encumbering glucuronide moiety. Upon ADC internalization and lysosomal degradation, the monosaccharide is removed and the exposed dipeptide is degraded, which liberates the attached payload inside the target cell. We used CD79b-targeted monomethyl auristatin E (MMAE) conjugates as our model system and compared the stability, efficacy, and tolerability of ADCs made with tandem-cleavage linkers to ADCs made using standard technology with the vedotin linker. The results, where rat studies showed dramatically improved tolerability in the hematopoietic compartment, highlight the role that linker stability plays in efficacy and tolerability and also offer a means of improving an ADC's therapeutic index for improved patient outcomes.

Unlocking the potential of antibody-drug conjugates for cancer therapy.

Nine different antibody-drug conjugates (ADCs) are currently approved as cancer treatments, with dozens more in preclinical and clinical development. The primary goal of ADCs is to improve the therapeutic index of antineoplastic agents by restricting their systemic delivery to cells that express the target antigen of interest. Advances in synthetic biochemistry have ushered in a new generation of ADCs, which promise to improve upon the tissue specificity and cytotoxicity of their predecessors. Many of these drugs have impressive activity against treatment-refractory cancers, although hurdles impeding their broader use remain, including systemic toxicity, inadequate biomarkers for patient selection, acquired resistance and unknown benefit in combination with other cancer therapies. Emerging evidence indicates that the efficacy of a given ADC depends on the intricacies of how the antibody, linker and payload components interact with the tumour and its microenvironment, all of which have important clinical implications. In this Review, we discuss the current state of knowledge regarding the design, mechanism of action and clinical efficacy of ADCs as well as the apparent limitations of this treatment class. We then propose a path forward by highlighting several hypotheses and novel strategies to maximize the potential benefit that ADCs can provide to patients with cancer.

Extracellular vesicles as modifiers of antibody‐drug conjugate efficacy

Antibody‐drug conjugates (ADCs) are a new class of anti‐cancer drugs that consist of a monoclonal antibody, a highly potent small‐molecule cytotoxic drug, and a chemical linker between the two. ADCs can selectively deliver cytotoxic drugs to cancer cells leading to a reduced systemic exposure and a wider therapeutic window. To date, nine ADCs have received marketing approval, and over 100 are being investigated in nearly 600 clinical trials. The target antigens of at least eight out of the nine approved anti‐cancer ADCs and of 69 investigational ADCs are present on extracellular vesicles (EVs) (tiny particles produced by almost all types of cells) that may carry their contents into local and distant cells. Therefore, the EVs have a potential to mediate both the anti‐cancer effects and the adverse effects of ADCs. In this overview, we discuss the mechanisms of action of ADCs and the resistance mechanisms to them, the EV‐mediated resistance mechanisms to small molecule anti‐cancer drugs and anti‐cancer monoclonal antibodies, and the EVs as modifiers of ADC efficacy and safety.

Synergistic therapeutic benefit by combining the antibody drug conjugate, depatux-m with temozolomide in pre-clinical models of glioblastoma with overexpression of EGFR.

Depatux-m is an antibody drug conjugate (ADC) that targets and inhibits growth of cancer cells overexpressing the epidermal growth factor receptor (EGFR) or the 2-7 deletion mutant (EGFRvIII) in tumor models in vitro and in vivo. Treatment of patients suffering from relapsed/refractory glioblastoma (GBM) with a combination of depatux-m and temozolomide (TMZ) tended to increase overall survival. As a first step to understand the nature of the interaction between the two drugs, we investigated whether the interaction was synergistic, additive or antagonistic. The efficacy of ADCs, antibodies, TMZ and radiation was tested in xenograft models of GBM, U-87MG and U-87MG EGFRvIII. Both models express EGFR. U-87MG EGFRvIII was transduced to express EGFRvIII. Changes in tumor volume, biomarkers of cell death and apoptosis after treatment were used to measure efficacy of the various treatments. Synergism of depatux-m and TMZ was verified in three-dimensional cultures of U-87MG and U-87MG EGFRvIII by the method of Chou and Talalay. Combined with TMZ and radiotherapy (RT), depatux-m inhibited xenograft growth of U-87MG and U-87MG EGFRvIII more than either treatment with depatux-m or TMZ + RT. Durability of the response to depatux-m + TMZ + RT or depatux-m + TMZ was more pronounced in U-87MG EGFRvIII than in U-87MG. Efficacy of depatux-m + TMZ was synergistic in U-87MG EGFRvIII and additive in U-87MG. Adding depatux-m enhances the efficacy of standard of care therapy in preclinical models of GBM. Durability of response to depatux-m + TMZ in vivo and synergy of the drug-drug interaction correlates with the amount of antigen expressed by the tumor cells.

Assessments of the In Vitro and In Vivo Linker Stability and Catabolic Fate for the Ortho Hydroxy-Protected Aryl Sulfate Linker by Immuno-Affinity Capture Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometric Assay.

Antibody–drug conjugate (ADC) linkers play an important role in determining the safety and efficacy of ADC. The Ortho Hydroxy-Protected Aryl Sulfate (OHPAS) linker is a newly developed linker in the form of a di-aryl sulfate structure consisting of phenolic payload and self-immolative group (SIG). In this study, using two bioanalytical approaches (namely “bottom-up” and “middle-up” approaches) via the liquid chromatography-quadrupole time-of-flight mass spectrometric (LC-qTOF-MS) method, in vitro and in vivo linker stability experiments were conducted for the OHPAS linker. For comparison, the valine-citrulline-p-aminobenzyloxycarbonyl (VC-PABC) linker was also evaluated under the same experimental conditions. In addition, the catabolite identification experiments at the subunit intact protein level were simultaneously performed to evaluate the catabolic fate of ADCs. As a result, the OHPAS linker was stable in the in vitro mouse/human plasma as well as in vivo pharmacokinetic studies in mice, whereas the VC-PABC linker was relatively unstable in mice in vitro and in vivo. This is because the VC-PABC linker was sensitive to a hydrolytic enzyme called carboxylesterase 1c (Ces1c) in mouse plasma. In conclusion, the OHPAS linker appears to be a good linker for ADC, and further experiments would be warranted to demonstrate the efficacy and toxicity related to the OHPAS linker.

Tumor volumes as a predictor of response to the anti-EGFR antibody drug conjugate depatuxizumab mafadotin.

BackgroundThe adverse impact of increasing brain tumor size on the efficacy of antibody-drug conjugates (ADCs) was investigated preclinically then validated with clinical data.Methods—Preclinical studyThe impact of tumor size on ADC tumor delivery and treatment response was evaluated in an EGFR-amplified patient-derived glioblastoma (GBM) model following treatment with Depatuxizumab mafadotin (Depatux-M). Biodistribution and imaging studies correlated drug distribution with starting treatment volume and anti-tumor activity.Methods—Clinical studyM12-356 was a Phase I study of Depatux-M in patients with GBM. Blinded volumetric analysis of baseline tumor volumes of M12-356 patients was undertaken by two reviewers and results correlated with response and survival.ResultsPreclinically, imaging and biodistribution studies showed specific and significantly higher tumor uptake of zirconium-89 labeled Depatux-M (89Zr-Depatux-M) in mice with smaller tumor volume (~98 mm3) versus those with larger volumes (~365 mm3); concordantly, mice with tumor volumes ≤100 mm3 at treatment commencement had significantly better growth inhibition by Depatux-M (93% vs 27%, P < .001) and significantly longer overall survival (P < .0001) compared to tumors ≥400 mm3. Clinically, patients with tumor volumes <25 cm3 had significantly higher response rates (17% vs. 0%, P = .009) and longer overall survival (0.5 vs 0.89 years, P = .001) than tumors above 25 cm3.ConclusionBoth preclinical and clinical data showed intra-tumoral concentration and efficacy of Depatux-m inversely correlated with tumor size. This finding merit further investigation with pretreatment tumor volume as a predictor for response to ADCs, in both gliomas and other solid tumors.

Antibody Co-Administration Can Improve Systemic and Local Distribution of Antibody-Drug Conjugates to Increase In Vivo Efficacy.

Several antibody-drug conjugates (ADC) showing strong clinical responses in solid tumors target high expression antigens (HER2, TROP2, Nectin-4, and folate receptor alpha/FRα). Highly expressed tumor antigens often have significant low-level expression in normal tissues, resulting in the potential for target-mediated drug disposition (TMDD) and increased clearance. However, ADCs often do not cross-react with normal tissue in animal models used to test efficacy (typically mice), and the impact of ADC binding to normal tissue antigens on tumor response remains unclear. An antibody that cross-reacts with human and murine FRα was generated and tested in an animal model where the antibody/ADC bind both human tumor FRα and mouse FRα in normal tissue. Previous work has demonstrated that a "carrier" dose of unconjugated antibody can improve the tumor penetration of ADCs with high expression target-antigens. A carrier dose was employed to study the impact on cross-reactive ADC clearance, distribution, and efficacy. Co-administration of unconjugated anti-FRα antibody with the ADC-improved efficacy, even in low expression models where co-administration normally lowers efficacy. By reducing target-antigen-mediated clearance in normal tissue, the co-administered antibody increased systemic exposure, improved tumor tissue penetration, reduced target-antigen-mediated uptake in normal tissue, and increased ADC efficacy. However, payload potency and tumor antigen saturation are also critical to efficacy, as shown with reduced efficacy using too high of a carrier dose. The judicious use of higher antibody doses, either through lower DAR or carrier doses, can improve the therapeutic window by increasing efficacy while lowering target-mediated toxicity in normal tissue.

Novel Therapies for the Treatment of Patients with Relapsed/Refractory Multiple Myeloma: A Review of Clinical Trials

Introduction: Multiple myeloma (MM) is a neoplastic proliferation of plasma cells. It is the second most common hematological malignancy in the US. Although it is associated with poor prognosis, newer therapies have improved outcomes in MM patients. This review aims to describe novel therapies used for the treatment of relapsed/refractory multiple myeloma (RRMM). Methods: A literature search was performed on Embase and clinicaltrials.gov using the keyword "Multiple Myeloma" from 1/1/2016 to 6/25/2020 for identifying ongoing clinical trials in the treatment of RRMM. After detailed scrutiny, we included 23 ongoing clinical trials (N=4362). We excluded case reports, case series, review articles, meta-analysis, and observational studies. Results: We summarized the interim results from ongoing clinical trials evaluating treatment of RRMM under following newer categories of drugs: Immunomodulatory drugs In a phase 1b/IIa trial (NCT02773030, N=51) evaluating the efficacy of a novel immunomodulators, iberdomide CC-220 + dexamethasone (Dex) yielded an overall response rate (ORR) of 31%, clinical benefit (CB) was seen in 51% of the patients, and disease control (DC) in 88% of the patients and it was well tolerated by RRMM patients. There are other ongoing clinical trials evaluating the efficacy of Avadomide (CC-122), CC-92480 in RRMM. Alkylating agents In a phase I/II trial (NCT01897714, N=45), melphalan-flufenamide (melflufan) + Dex yielded an ORR of 31%, it was well tolerated with 49% CB. Phase III OCEAN trial (NCT03151811, N=450) is currently ongoing to compare melflufen + Dex vs. pomalidomide (Pom) + Dex. Apoptotic agents A phase 3 trial BELLINI (NCT02755597, N=291) evaluated the efficacy of veneteclox (Ven, Bcl-2 inhibitor) by randomizing patients to either Ven or Placebo arm. With a median follow up of 28.6 months (m), progression free survival (PFS) was 23.2m in the Ven arm vs. 11.4m in placebo. The interim results from a phase I/II trial (NCT03314181, N=104) of Ven + daratumumab (Dara) + Dex showed ORR of 96% with ≥ very good partial response (VGPR) of 96%. The addition of Bortezomib (Bor) to VenDaraDex had a slightly low ORR of 92%, with ≥VGPR of 79%. Another phase I/II trial (NCT01794520, N=117) is in progress to assess the efficacy and safety of Ven as monotherapy. Monoclonal Antibodies (MoAb) A phase I/II trial (NCT01421186, N=91) evaluated the efficacy of MOR202, which is a novel MoAb. MOR202 was evaluated in three arms; MOR202 + Dex, MOR202 + Lenalidomide (Len) + Dex and MOR202 + Pom + Dex. The interim analysis showed the ORR of 65% with MOR202 + Len + Dex which was better than ORR of 48% with MOR202 + Pom + Dex, while the use of MOR202 + Dex yielded only 28% ORR. Antibody-drug conjugate (ADC) Four ongoing trials are evaluating the efficacy of ADC (belantamab mafodotin), and the interim results are available for two trials. In phase II DREAMM-2 trial (NCT03525678, N=221) evaluating 2 doses of GSK2857916, 2.5mg/kg dose yielded ORR of 31% while 3.4mg/kg showed ORR of 34%. Another phase I trial (NCT02064387, N=79) evaluated belantamab mafodotin in RRMM and other hematologic malignancies expressing B-cell maturation antigen (BCMA). The results were promising with ORR of 60%. Bispecific T-cell engagers (BiTE) Phase I trial of BiTE AMG 420 (NCT02514239, N=43) showed favorable results with ORR 70%, and CR 12%. The interim results from another phase I trial (NCT03486067, N=115) which evaluated the efficacy of BiTE CC-93269 showed 43% ORR and CR 17%. CAR-T Cell therapy CAR-T cell therapy is also being studied in RRMM with JNJ-68284528 directed against BCMA in a phase Ib trial (NCT03548207, N=118). The interim analysis of 29 response evaluable patients out of 118 reported 100% ORR with stringent CR 76%. PK13 Inhibitors In a phase I/II study (NCT00401011, N=84) evaluating perifosine + Bor +/- Dex, ORR of 41% was observed in Bor RR patients, and therapy was well tolerated with PFS of 6.4m and mOS of 25m. Conclusion: This review demonstrates novel and promising therapies which are currently in early phase clinical trials for the treatment of RRMM. Based on interim results, Iberdomide, melflufan, Ven, MoAb MOR202, ADC belantamab mafodotin, BiTE Molecule AMG 420, BCMA CAR-T cell therapy and perifosine have shown promising early activity and safety data in RRMM patients. Additional exploratory clinical trials are needed to confirm the efficacy and safety of these agents. Disclosures Anwer: Incyte, Seattle Genetics, Acetylon Pharmaceuticals, AbbVie Pharma, Astellas Pharma, Celegene, Millennium Pharmaceuticals.: Honoraria, Research Funding, Speakers Bureau.

Rapid Analysis of Reduced Antibody Drug Conjugate by Online LC-MS/MS with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Antibody drug conjugates (ADCs), which harness the high targeting specificity of monoclonal antibodies (mAb) with the potency of small molecule therapeutics, are one of the fastest growing pharmaceutical classes. Nevertheless, ADC conjugation techniques and processes may introduce intrinsic heterogeneity including primary sequence variants, varied drug-to-antibody ratio (DAR) species, and drug positional isomers, which must be monitored to ensure the safety and efficacy of ADCs. Liquid chromatography coupled to mass spectrometry (LC-MS) is a powerful tool for characterization of ADCs. However, the conventional bottom-up MS analysis workflows require an enzymatic digestion step which can be time consuming and may introduce artifactual modifications. Herein, we develop an online LC-MS/MS method for rapid analysis of reduced ADCs without digestion, enabling determination of DAR, characterization of the primary sequence, and localization of the drug conjugation site of the ADC using high-resolution Fourier transform ion cyclotron resonance (FTICR) MS. Specifically, a model cysteine-linked ADC was reduced to generate six unique subunits: light chain (Lc) without drug (Lc0), Lc with 1 drug (Lc1), heavy chain (Hc) without drug (Hc0), and Hc with 1-3 drugs (Hc1-3, respectively). A concurrent reduction strategy is applied to assess ADC subunits in both the partially reduced (intrachain disulfide bonds remain intact) and fully reduced (all disulfide bonds are cleaved) forms. The entire procedure including the sample preparation and LC-MS/MS takes less than 55 min, enabling rapid multiattribute analysis of ADCs.

Mechanistic Modeling of Intra-Tumor Spatial Distribution of Antibody-Drug Conjugates: Insights into Dosing Strategies in Oncology.

Antibody drug conjugates (ADCs) provide targeted delivery of cytotoxic agents directly inside tumor cells. However, many ADCs targeting solid tumors have exhibited limited clinical efficacy, in part, due to insufficient penetration within tumors. To better understand the relationship between ADC tumor penetration and efficacy, previously applied Krogh cylinder models that explore tumor growth dynamics following ADC administration in preclinical species were expanded to a clinical framework by integrating clinical pharmacokinetics, tumor penetration, and tumor growth inhibition. The objective of this framework is to link ADC tumor penetration and distribution to clinical efficacy. The model was validated by comparing virtual patient population simulations to observed overall response rates from trastuzumab‐DM1 treated patients with metastatic breast cancer. To capture clinical outcomes, we expanded upon previous Krogh cylinder models to include the additional mechanism of heterogeneous tumor growth inhibition spatially across the tumor. This expansion mechanistically captures clinical response rates by describing heterogeneous ADC binding and tumor cell killing; high binding and tumor cell death close to capillaries vs. low binding, and high tumor cell proliferation far from capillaries. Sensitivity analyses suggest that clinical efficacy could be optimized through dose fractionation, and that clinical efficacy is primarily dependent on the ADC‐target affinity, payload potency, and tumor growth rate. This work offers a mechanistic basis to predict and optimize ADC clinical efficacy for solid tumors, allowing dosing strategy optimization to improve patient outcomes.

LRRC15 antibody-drug conjugates show promise as osteosarcoma therapeutics in preclinical studies.

Osteosarcoma (OS), the most common bone tumor in children and adolescents, has high rates of metastasis leading to poor survival. Leucine-rich repeat containing 15 (LRRC15), a transmembrane protein whose expression is modulated by TGFβ, was recently shown to be highly expressed on the surface of OS tumor cells. Here, we evaluate a novel antibody-drug conjugate (ADC) targeting LRRC15 in OS human cell lines and murine xenografts. We compare this new ADC, which is conjugated to the anthracycline derivative PNU-159682 (PNU), to a previously studied LRRC15 ADC that is conjugated to the tubulin inhibitor monomethyl auristatin E (MMAE), since anthracyclines are standard of care in OS. We evaluated LRRC15 expression in OS cells using Western blots and flow cytometry, and analyzed the epigenetic landscape of the LRRC15 locus using chromatin immunoprecipitation. Efficacy of ADCs on cell growth was analyzed by IncuCyte live cell imaging. Intramuscular xenograft tumor growth was assessed by bioluminescence imaging and hematoxylin and eosin staining. LRRC15-PNU is more effective at inhibiting growth in vitro and in vivo than an isotype antibody control or the LRRC15-MMAE ADC in two high LRRC15 expressing OS cell lines. Low expressing cell lines are not sensitive to either ADC. Importantly, cells with low LRRC15 expression are amenable to re-expression after TGFβ treatment, suggesting a potential to sensitize insensitive OS cells to LRRC15 ADC treatment. In vivo, LRRC15-PNU had cure rates of 40-100% in OS xenograft models. Overall, LRRC15-directed ADCs are a promising new avenue for OS treatment.

PF-06804103, A Site-specific Anti-HER2 Antibody-Drug Conjugate for the Treatment of HER2-expressing Breast, Gastric, and Lung Cancers.

The approval of ado-trastuzumab emtansine (T-DM1) in HER2+ metastatic breast cancer validated HER2 as a target for HER2-specific antibody-drug conjugates (ADC). Despite its demonstrated clinical efficacy, certain inherent properties within T-DM1 hamper this compound from achieving the full potential of targeting HER2-expressing solid tumors with ADCs. Here, we detail the discovery of PF-06804103, an anti-HER2 ADC designed to have a widened therapeutic window compared with T-DM1. We utilized an empirical conjugation site screening campaign to identify the engineered ĸkK183C and K290C residues as those that maximized in vivo ADC stability, efficacy, and safety for a four drug-antibody ratio (DAR) ADC with this linker-payload combination. PF-06804103 incorporates the following novel design elements: (i) a new auristatin payload with optimized pharmacodynamic properties, (ii) a cleavable linker for optimized payload release and enhanced antitumor efficacy, and (iii) an engineered cysteine site-specific conjugation approach that overcomes the traditional safety liabilities of conventional conjugates and generates a homogenous drug product with a DAR of 4. PF-06804103 shows (i) an enhanced efficacy against low HER2-expressing breast, gastric, and lung tumor models, (ii) overcomes in vitro- and in vivo-acquired T-DM1 resistance, and (iii) an improved safety profile by enhancing ADC stability, pharmacokinetic parameters, and reducing off-target toxicities. Herein, we showcase our platform approach in optimizing ADC design, resulting in the generation of the anti-HER2 ADC, PF-06804103. The design elements of identifying novel sites of conjugation employed in this study serve as a platform for developing optimized ADCs against other tumor-specific targets.

Tumour-associated macrophages process drug and radio-conjugates of the dead tumour cell-targeting APOMAB® antibody

APOMAB (chDAB4) is a dead tumour cell-targeting antibody which has been used preclinically as a diagnostic agent and therapeutically as a radioimmunotherapy and antibody drug conjugate (ADC). However, little is known of the intra-tumour processing of chDAB4 when bound to dead tumour cells. In this study we examine the role of macrophages in the in vitro and in vivo processing of radiolabelled chDAB4 and a chDAB4 ADC.We found that chDAB4 binds to macrophages in vitro, resulting in the killing of macrophages when using the ADC, chDAB4-SG3249. Free drug released by the macrophage processing of chDAB4-SG3249 could result in killing of ‘bystander’ Lewis lung (LL2) carcinoma cells. Furthermore, macrophages phagocytosed chDAB4-bound dead LL2 cells and were killed when they phagocytosed chDAB4-SG3249-bound dead LL2 cells in vitro. In vivo, we found markedly different tumour retention of chDAB4 in the LL2 tumour model depending on whether it was radiolabelled with a residualising radionuclide (89Zr), which is retained intracellularly, or a non-residualising radionuclide (124I), which can diffuse out of the cell. This prolonged retention of 89Zr vs124I indicated intra-tumoral processing of chDAB4 in vivo. The tumour uptake of 89Zr-chDAB4 was reduced after macrophage depletion, which also reduced the efficacy of the chDAB4 ADC in vivo. This study shows that macrophages can process chDAB4 and chDAB4 ADC in vitro and shows the importance of tumour-associated macrophages in the tumour retention of chDAB4 and the efficacy of chDAB4 ADC in vivo.

A novel semi-mechanistic tumor growth fraction model for translation of preclinical efficacy of anti-glypican 3 antibody drug conjugate to human.

The growing fraction (GF) of tumor has been reported as one of the predictive markers of the efficacy of chemotherapeutics. Therefore, a semi-mechanistic model has been developed that describes tumor growth on the basis of cell cycle, allowing the incorporation of the GF of a tumor in pharmacokinetic/pharmacodynamic (PK/PD) modeling. Efficacy data of anti-glypican 3 (GPC3) antibody drug conjugate (ADC) in a hepatocellular carcinoma (HCC) patient derived xenograft (PDX) model was used for evaluation of this proposed model. Our model was able to describe the kinetics of growth inhibition of HCC PDX models following treatment with anti-GPC3 ADC remarkably well. The estimated tumurostatic concentrations were used in tandem with human PKs translated from cynomolgus monkey for prediction of the efficacious dose. The projected efficacious human dose of anti-GPC3 ADC was in the range 0.20-0.63 mg/kg for the Q3W dosing regimen, with a median dose of 0.50 mg/kg. This publication is the first step in evaluating the applicability of GF in PK/PD modeling of ADCs. The authors are hopeful that incorporation of GF will result in an improved translation of the preclinical efficacy of ADCs to clinical settings and thereby better prediction of the efficacious human dose.

Development of 5D3-DM1: A Novel Anti-Prostate-Specific Membrane Antigen Antibody-Drug Conjugate for PSMA-Positive Prostate Cancer Therapy.

Prostate cancer (PC) is a potentially high-risk disease and the most common cancer in American men. It is a leading cause of cancer-related deaths in men in the US, second only to lung and bronchus cancer. Advanced and metastatic PC is initially treated with androgen deprivation therapy (ADT), but nearly all cases eventually progress to castrate-resistant prostate cancer (CRPC). CRPC is incurable in the metastatic stage but can be slowed by some conventional chemotherapeutics and second-generation ADT, such as enzalutamide and abiraterone. Therefore, novel therapeutic strategies are urgently needed. Prostate-specific membrane antigen (PSMA) is overexpressed in almost all aggressive PCs. PSMA is widely used as a target for PC imaging and drug delivery. Anti-PSMA monoclonal antibodies (mAbs) have been developed as bioligands for diagnostic imaging and targeted PC therapy. However, these mAbs are successfully used in PC imaging and only a few have gone beyond phase-I for targeted therapy. The 5D3 mAb is a novel, high-affinity, and fast-internalizing anti-PSMA antibody. Importantly, 5D3 mAb demonstrates a unique pattern of cellular localization to the centrosome after internalization in PSMA(+) PC3-PIP cells. These characteristics make 5D3 mAb an ideal bioligand to deliver tubulin inhibitors, such as mertansine, to the cell centrosome, leading to mitotic arrest and elimination of dividing PC cells. We have successfully developed a 5D3 mAb- and mertansine (DM1)-based antibody-drug conjugate (ADC) and evaluated it in vitro for binding affinity, internalization, and cytotoxicity. The in vivo therapeutic efficacy of 5D3-DM1 ADC was evaluated in PSMA(+) PC3-PIP and PSMA(-) PC3-Flu mouse models of human PC. This therapeutic study has revealed that this new anti-PSMA ADC can successfully control the growth of PSMA(+) tumors without inducing systemic toxicity.