Mouse Strains Influence Clearance and Efficacy of Antibody and Antibody-Drug Conjugate Via Fc-FcγR Interaction.

To provide a better understanding of the pharmacokinetics-pharmacodynamics relationships of antibody-based drugs, we analyzed several chimeric and humanized monoclonal antibodies or antibody-drug conjugates (ADC) for PK and efficacy among four strains of mice. Notably, antibodies and ADCs displayed a dose-dependent drug disposition profile in the plasma of NSG mice. The increased clearance rate in NSG mice resulted in the reduction of antitumor activity of ADCs. Furthermore, we identified that the abnormal clearance was mediated by Fc-FcγR interaction by comparing antibodies that lack FcγR binding capacity. We also found a high percentage of FcγR-expressing macrophages in the bone marrow, spleen, and liver of NSG mice, which may be responsible for the abnormal distribution of antibodies. Overall, these findings suggest that preclinical evaluation of efficacy and pharmacokinetics of antibodies and ADCs need to consider mouse strain-induced variations.

Characterization of SGN-CD123A, A Potent CD123-Directed Antibody-Drug Conjugate for Acute Myeloid Leukemia.

Treatment choices for acute myelogenous leukemia (AML) patients resistant to conventional chemotherapies are limited and novel therapeutic agents are needed. IL3 receptor alpha (IL3Rα, or CD123) is expressed on the majority of AML blasts, and there is evidence that its expression is increased on leukemic relative to normal hematopoietic stem cells, which makes it an attractive target for antibody-based therapy. Here, we report the generation and preclinical characterization of SGN-CD123A, an antibody-drug conjugate using the pyrrolobenzodiazepine dimer (PBD) linker and a humanized CD123 antibody with engineered cysteines for site-specific conjugation. Mechanistically, SGN-CD123A induces activation of DNA damage response pathways, cell-cycle changes, and apoptosis in AML cells. In vitro, SGN-CD123A-mediated potent cytotoxicity of 11/12 CD123+ AML cell lines and 20/23 primary samples from AML patients, including those with unfavorable cytogenetic profiles or FLT3 mutations. In vivo, SGN-CD123A treatment led to AML eradication in a disseminated disease model, remission in a subcutaneous xenograft model, and significant growth delay in a multidrug resistance xenograft model. Moreover, SGN-CD123A also resulted in durable complete remission of a patient-derived xenograft AML model. When combined with a FLT3 inhibitor quizartinib, SGN-CD123A enhanced the activity of quizartinib against two FLT3-mutated xenograft models. Overall, these data demonstrate that SGN-CD123A is a potent antileukemic agent, supporting an ongoing trial to evaluate its safety and efficacy in AML patients (NCT02848248). Mol Cancer Ther; 17(2); 554-64. ©2017 AACR.

Tumor-Associated Macrophages Can Contribute to Antitumor Activity through FcγR-Mediated Processing of Antibody-Drug Conjugates.

The primary mechanism of antibody-drug conjugates (ADC) is targeted delivery of a cytotoxic payload to tumor cells via cancer-associated membrane receptors. However, the tumor microenvironment likely plays a role in ADC penetration, distribution, and processing and thus impacts the overall antitumor activity. Here, we report on the potential contribution of Fc-FcγR interactions between ADCs and tumor-associated macrophages (TAM) to the preclinical antitumor activities of ADCs. In the CD30+ L-428 Hodgkin lymphoma model, anti-CD30-vcMMAE and a non-binding control (hIgG-vcMMAE) demonstrated similar antitumor activity as well as similar payload release in the tumors. IHC analysis revealed L-428 tumors contained highly abundant TAMs, which were confirmed to bind ADCs by IHC and flow cytometry. The infiltration of TAMs was further found to correlate with the antitumor activity of the non-binding hIgG-vcMMAE in five additional xenograft models. hIgG1V1-vcMMAE, bearing a mutation in the Fc region which ablates Fc gamma receptor (FcγR) binding, lost antitumor activity in three TAM-high xenograft models, suggesting Fc-FcγR interactions modulate the TAM-ADC interaction. Our results suggest that TAMs can contribute to ADC processing through FcγR interaction in preclinical tumor models and may represent an important additional mechanism for drug release from ADCs. Correlative studies in clinical trials will further shed light on whether TAMs play a role in patients' response to ADC therapies. Mol Cancer Ther; 16(7); 1347-54. ©2017 AACR.

Intracellular Released Payload Influences Potency and Bystander-Killing Effects of Antibody-Drug Conjugates in Preclinical Models.

Antibody-drug conjugates (ADC) comprise targeting antibodies armed with potent small-molecule payloads. ADCs demonstrate specific cell killing in clinic, but the basis of their antitumor activity is not fully understood. In this study, we investigated the degree to which payload release predicts ADC activity in vitro and in vivo ADCs were generated to target different receptors on the anaplastic large cell lymphoma line L-82, but delivered the same cytotoxic payload (monomethyl auristatin E, MMAE), and we found that the intracellular concentration of released MMAE correlated with in vitro ADC-mediated cytotoxicity independent of target expression or drug:antibody ratios. Intratumoral MMAE concentrations consistently correlated with the extent of tumor growth inhibition in tumor xenograft models. In addition, we developed a robust admixed tumor model consisting of CD30(+) and CD30(-) cancer cells to study how heterogeneity of target antigen expression, a phenomenon often observed in cancer specimens, affects the treatment response. CD30-targeting ADC delivering membrane permeable MMAE or pyrrolobenzodiazepine dimers demonstrated potent bystander killing of neighboring CD30(-) cells. In contrast, a less membrane permeable payload, MMAF, failed to mediate bystander killing in vivo, suggesting local diffusion and distribution of released payloads represents a potential mechanism of ADC-mediated bystander killing. Collectively, our findings establish that the biophysical properties and amount of released payloads are chief factors determining the overall ADC potency and bystander killing. Cancer Res; 76(9); 2710-9. ©2016 AACR.

Antibody-conjugated drug assay for protease-cleavable antibody-drug conjugates.

BACKGROUND: Antibody-drug conjugates (ADCs) require multiple assays to characterize their PK. These assays can separately evaluate the ADC by quantifying the antibody or the conjugated drug and may give different answers due to assay measurement differences, heterogeneous nature of ADCs and potential biotransformations that occur in vivo. RESULTS: We present a new version of the antibody-conjugated drug assay for valine-citrulline-linked monomethylauristatin E (vcMMAE) ADCs. A stable isotope-labeled internal standard, protein A affinity capture and solid-phase cleavage of MMAE using papain was used prior to LC-MS/MS analysis. CONCLUSION: The assay was used to assess the difference in ex vivo drug-linker stability of native-cysteine versus engineered cysteine ADCs and to determine the number of drugs per antibody of a native-cysteine ADC in vivo.

The fucosylation inhibitor, 2-fluorofucose, inhibits vaso-occlusion, leukocyte-endothelium interactions and NF-ĸB activation in transgenic sickle mice.

2-Fluorofucose (2FF) blocks the fucosylation and the tethering of sialyl-Lewisx tetrasaccharide and structural variants on leukocytes and red blood cells to P- and E-selectins on activated endothelial cell surfaces. Because P- and E-selectin are required for vaso-occlusion in murine sickle cell disease (SCD), we investigated whether 2FF would inhibit vaso-occlusion in SCD mice. Microvascular stasis was measured in subcutaneous venules in NY1DD and HbSS-Townes SCD mice with dorsal skin-fold chambers after infusion of hemoglobin or exposure to hypoxia/reoxygenation. 2FF in drinking water or administered by gavage inhibited stasis in sickle mice in a dose-responsive manner. Significant inhibitory effects on stasis were seen 1 day post-treatment. 2FF treatment of SCD mice also significantly reduced leukocyte rolling and adhesion along the vessel walls of SCD mice and the static adhesion of neutrophils and sickle red blood cells isolated from 2FF-treated SCD mice to resting and activated endothelial cells. Total white blood cell counts increased in response to 2FF. NF-ĸB activation and VCAM-1 and E-selectin expression were inhibited in the livers of SCD mice consistent with an overall decrease in vascular inflammation and ischemia-reperfusion physiology. Pretreatment with 2FF completely eliminated heme-induced lethality in HbSS-Townes mice, consistent with the observed anti-inflammatory and anti-adhesive properties of 2FF in SCD mice. These data suggest that 2FF may be beneficial for preventing or treating vaso-occlusive crises in SCD patients.

SGN-LIV1A: a novel antibody-drug conjugate targeting LIV-1 for the treatment of metastatic breast cancer.

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.

SGN-CD33A: a novel CD33-targeting antibody-drug conjugate using a pyrrolobenzodiazepine dimer is active in models of drug-resistant AML.

Outcomes in acute myeloid leukemia (AML) remain unsatisfactory, and novel treatments are urgently needed. One strategy explores antibodies and their drug conjugates, particularly those targeting CD33. Emerging data with gemtuzumab ozogamicin (GO) demonstrate target validity and activity in some patients with AML, but efficacy is limited by heterogeneous drug conjugation, linker instability, and a high incidence of multidrug resistance. We describe here the development of SGN-CD33A, a humanized anti-CD33 antibody with engineered cysteines conjugated to a highly potent, synthetic DNA cross-linking pyrrolobenzodiazepine dimer via a protease-cleavable linker. The use of engineered cysteine residues at the sites of drug linker attachment results in a drug loading of approximately 2 pyrrolobenzodiazepine dimers per antibody. In preclinical testing, SGN-CD33A is more potent than GO against a panel of AML cell lines and primary AML cells in vitro and in xenotransplantation studies in mice. Unlike GO, antileukemic activity is observed with SGN-CD33A in AML models with the multidrug-resistant phenotype. Mechanistic studies indicate that the cytotoxic effects of SGN-CD33A involve DNA damage with ensuing cell cycle arrest and apoptotic cell death. Together, these data suggest that SGN-CD33A has CD33-directed antitumor activity and support clinical testing of this novel therapeutic in patients with AML.

Development of orally active inhibitors of protein and cellular fucosylation.

The key role played by fucose in glycoprotein and cellular function has prompted significant research toward identifying recombinant and biochemical strategies for blocking its incorporation into proteins and membrane structures. Technologies surrounding engineered cell lines have evolved for the inhibition of in vitro fucosylation, but they are not applicable for in vivo use and drug development. To address this, we screened a panel of fucose analogues and identified 2-fluorofucose and 5-alkynylfucose derivatives that depleted cells of GDP-fucose, the substrate used by fucosyltransferases to incorporate fucose into protein and cellular glycans. The inhibitors were used in vitro to generate fucose-deficient antibodies with enhanced antibody-dependent cellular cytotoxicity activities. When given orally to mice, 2-fluorofucose inhibited fucosylation of endogenously produced antibodies, tumor xenograft membranes, and neutrophil adhesion glycans. We show that oral 2-fluorofucose treatment afforded complete protection from tumor engraftment in a syngeneic tumor vaccine model, inhibited neutrophil extravasation, and delayed the outgrowth of tumor xenografts in immune-deficient mice. The results point to several potential therapeutic applications for molecules that selectively block the endogenous generation of fucosylated glycan structures.

Orally active fumagillin analogues: transformations of a reactive warhead in the gastric environment.

Semisynthetic analogues of fumagillin, 1, inhibit methionine aminopeptidase-2 (MetAP2) and have entered the clinic for the treatment of cancer. An optimized fumagillin analogue, 3 (PPI-2458), was found to be orally active, despite containing a spiroepoxide function that formed a covalent linkage to the target protein. In aqueous acid, 3 underwent ring-opening addition of water and HCl, leading to four products, 4-7, which were characterized in detail. The chlorohydrin, but not the diol, products inhibited MetAP2 under weakly basic conditions, suggesting reversion to epoxide as a step in the mechanism. In agreement, chlorohydrin 6 was shown to revert rapidly to 3 in rat plasma. In an ex vivo assay, rats treated with purified acid degradants demonstrated inhibition of MetAP2 that correlated with the biochemical activity of the compounds. Taken together, the results indicate that degradation of the parent compound was compensated by the formation of active equivalents leading to a pharmacologically useful level of MetAP2 inhibition.

Intracellular activation of SGN-35, a potent anti-CD30 antibody-drug conjugate.

PURPOSE: SGN-35 is an antibody-drug conjugate (ADC) containing the potent antimitotic drug, monomethylauristatin E (MMAE), linked to the anti-CD30 monoclonal antibody, cAC10. As previously shown, SGN-35 treatment regresses and cures established Hodgkin lymphoma and anaplastic large cell lymphoma xenografts. Recently, the ADC has been shown to possess pronounced activity in clinical trials. Here, we investigate the molecular basis for the activities of SGN-35 by determining the extent of targeted intracellular drug release and retention, and bystander activities. EXPERIMENTAL DESIGN: SGN-35 was prepared with (14)C-labeled MMAE. Intracellular ADC activation on CD30(+) and negative cell lines was determined using a combination of radiometric and liquid chromatograhpy/mass spectrometry-based assays. The bystander activity of SGN-35 was determined using mixed tumor cell cultures consisting of CD30(+) and CD30(-) lines. RESULTS: SGN-35 treatment of CD30(+) cells leads to efficient intracellular release of chemically unmodified MMAE, with intracellular concentrations of MMAE in the range of 500 nmol/L. This was due to specific ADC binding, uptake, MMAE retention, and receptor recycling or resynthesis. MMAE accounts for the total detectable released drug from CD30(+) cells, and has a half-life of retention of 15 to 20 h. Cytotoxicity studies with mixtures of CD30(+) and CD30(-) cell lines indicated that diffusible released MMAE from CD30(+) cells was able to kill cocultivated CD30(-) cells. CONCLUSIONS: MMAE is efficiently released from SGN-35 within CD30(+) cancer cells and, due to its membrane permeability, is able to exert cytotoxic activity on bystander cells. This provides mechanistic insight into the pronounced preclinical and clinical antitumor activities observed with SGN-35.

Carbamate analogues of fumagillin as potent, targeted inhibitors of methionine aminopeptidase-2.

Inhibition of methionine aminopeptidase-2 (MetAP2) represents a novel approach to antiangiogenic therapy. We describe the synthesis and activity of fumagillin analogues that address the pharmacokinetic and safety liabilities of earlier candidates in this compound class. Two-step elaboration of fumagillol with amines yielded a diverse series of carbamates at C6 of the cyclohexane spiroepoxide. The most potent of these compounds exhibited subnanomolar inhibition of cell proliferation in HUVEC and BAEC assays. Although a range of functionalities were tolerated at this position, alpha-trisubstituted amines possessed markedly decreased inhibitory activity, and this could be rationalized by modeling based on the known fumagillin-MetAP2 crystal structure. The lead compound resulting from these studies, (3R,4S,5S,6R)-5-methoxy-4-((2R,3R)-2-methyl-3-(3-methylbut-2-enyl)oxiran-2-yl)-1-oxaspiro[2.5]octan-6-yl (R)-1-amino-3-methyl-1-oxobutan-2-ylcarbamate, (PPI-2458), demonstrated an improved pharmacokinetic profile relative to the earlier clinical candidate TNP-470, and has advanced into phase I clinical studies in non-Hodgkin's lymphoma and solid cancers.

Design, synthesis and selection of DNA-encoded small-molecule libraries.

Biochemical combinatorial techniques such as phage display, RNA display and oligonucleotide aptamers have proven to be reliable methods for generation of ligands to protein targets. Adapting these techniques to small synthetic molecules has been a long-sought goal. We report the synthesis and interrogation of an 800-million-member DNA-encoded library in which small molecules are covalently attached to an encoding oligonucleotide. The library was assembled by a combination of chemical and enzymatic synthesis, and interrogated by affinity selection. We describe methods for the selection and deconvolution of the chemical display library, and the discovery of inhibitors for two enzymes: Aurora A kinase and p38 MAP kinase.

The pharmacologic basis for antibody-auristatin conjugate activity.

Antibody-drug conjugates (ADCs) made with auristatin antimitotic agents have shown significant preclinical and clinical oncology activity. SGN-75 is composed of the anti-CD70 antibody h1F6 conjugated to monomethylauristatin F through a noncleavable maleimidocaproyl linkage. To understand the pharmacologic basis of the activity of this ADC, its pharmacokinetics and biodistribution were evaluated in a mouse xenograft model with use of a dual-radiolabeled ADC. The concentrations of antibody, total auristatin (conjugated plus unconjugated), and unconjugated auristatin were measured simultaneously in serum, tumor, and 16 normal tissues. Serum pharmacokinetic parameters for antibody and total auristatin were similar with very little unconjugated auristatin observed, demonstrating a high degree of stability. The kinetic values in normal tissues generally tracked with serum: the first time point (1 h) had the highest antibody and total auristatin concentrations with low unconjugated auristatin concentrations, with the exception of organs expected to be involved in hepatobiliary clearance of the ADC, where total and unconjugated auristatin concentrations peaked at 4 h and then rapidly decreased. In tumors, antibody concentrations were maximal at 1 day, with total auristatin increasing until 2 days. Intratumoral unconjugated auristatin was a substantial fraction of the total auristatin and reached concentrations much higher than in normal tissues. The exposure of the tumor to total and unconjugated auristatin was tens to hundreds times higher than normal tissue exposure. The data establish the pharmacologic basis of activity of the ADC through specific tumor targeting, intratumoral auristatin retention, and ADC stability in the systemic circulation.

Contribution of linker stability to the activities of anticancer immunoconjugates.

The linker component of antibody-drug conjugates (ADC) is a key feature in developing optimized therapeutic agents that are highly active at well tolerated doses. For maximal intratumoral drug delivery, linkers are required that are highly stable in the systemic circulation, yet allow for efficient drug release at the target site. In this respect, amide bond-based technologies constitute a technological advancement, since the linker half-lives in circulation ( t 1/2 approximately 7 days) are much longer than earlier generation linkers that break down within 1-2 days. The amide linkers, some of which contain peptides, are appended to the mAb carriers through thioether/maleimide adducts. Here, we describe that use of a bromoacetamidecaproyl (bac) in place of the maleimidocaproyl (mc) increases the plasma stability of resulting thioether ADCs. One such ADC, 1F6-C4v2-bac-MMAF, which is directed against the CD70 antigen on lymphomas and renal cell carcinoma, was prepared containing a bac thioether spacer between the drug (MMAF) and the mAb carrier (1F6-C4v2). There was no measurable systemic drug release from this ADC for 2 weeks postadministration in mice. In order to assess the impact of improving linker stability beyond mc containing ADCs, a series of mc and bac-linked 1F6-MMAF conjugates were compared for tolerability, intratumoral drug delivery, and therapeutic efficacy in nude mice with renal cell carcinoma xenografts. There were no statistically significant efficacy differences between sets of mc and bac containing ADCs, although the bac linker technology led to 25% higher intratumoral drug exposure over a 7 day period compared to the corresponding mc linker. The mechanism of drug release from maleimide-adducts likely involves a retro-Michael reaction that takes place in plasma, based on in vitro studies demonstrating that some of the released drug-maleimide derivative became covalently bound to cysteine-34 of serum albumin. In summary, the data indicate that new linkers can be obtained with improved in vivo stability by replacing the maleimide with an acetamide, but the resulting ADCs had similar tolerability and activity profiles.