Crystal Zhang

Impact of drug conjugation on pharmacokinetics and tissue distribution of anti-STEAP1 antibody-drug conjugates in rats.

Antibody-drug conjugates (ADCs) are designed to combine the exquisite specificity of antibodies to target tumor antigens with the cytotoxic potency of chemotherapeutic drugs. In addition to the general chemical stability of the linker, a thorough understanding of the relationship between ADC composition and biological disposition is necessary to ensure that the therapeutic window is not compromised by altered pharmacokinetics (PK), tissue distribution, and/or potential organ toxicity. The six-transmembrane epithelial antigen of prostate 1 (STEAP1) is being pursued as a tumor antigen target. To assess the role of ADC composition in PK, we evaluated plasma and tissue PK profiles in rats, following a single dose, of a humanized anti-STEAP1 IgG1 antibody, a thio-anti-STEAP1 (ThioMab) variant, and two corresponding thioether-linked monomethylauristatin E (MMAE) drug conjugates modified through interchain disulfide cysteine residues (ADC) and engineered cysteines (TDC), respectively. Plasma PK of total antibody measured by enzyme-linked immunosorbent assay (ELISA) revealed ∼45% faster clearance for the ADC relative to the parent antibody, but no apparent difference in clearance between the TDC and unconjugated parent ThioMab. Total antibody clearances of the two unconjugated antibodies were similar, suggesting minimal effects on PK from cysteine mutation. An ELISA specific for MMAE-conjugated antibody indicated that the ADC cleared more rapidly than the TDC, but total antibody ELISA showed comparable clearance for the two drug conjugates. Furthermore, consistent with relative drug load, the ADC had a greater magnitude of drug deconjugation than the TDC in terms of free plasma MMAE levels. Antibody conjugation had a noticeable, albeit minor, impact on tissue distribution with a general trend toward increased hepatic uptake and reduced levels in other highly vascularized organs. Liver uptakes of ADC and TDC at 5 days postinjection were 2-fold and 1.3-fold higher, respectively, relative to the unmodified antibodies. Taken together, these results indicate that the degree of overall structural modification in anti-STEAP1-MMAE conjugates has a corresponding level of impact on both PK and tissue distribution.

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.

Differential Effects of Predosing on Tumor and Tissue Uptake of an 111In-Labeled Anti-TENB2 Antibody–Drug Conjugate

TENB2, also known as tomoregulin or transmembrane protein with epidermal growth factor–like and 2 follistatin-like domains, is a transmembrane proteoglycan overexpressed in human prostate tumors. This protein is a promising target for antimitotic monomethyl auristatin E (MMAE)–based antibody–drug conjugate (ADC) therapy. Nonlinear pharmacokinetics in normal mice suggested that antigen expression in normal tissues may contribute to targeted mediated disposition. We evaluated a predosing strategy with unconjugated antibody to block ADC uptake in target-expressing tissues in a mouse model while striving to preserve tumor uptake and efficacy. Methods: Unconjugated, unlabeled antibody was preadministered to mice bearing the TENB2-expressing human prostate explant model, LuCaP 77, followed by a single administration of 111In-labeled anti-TENB2-MMAE for biodistribution and SPECT/CT studies. A tumor-growth-inhibition study was conducted to determine the pharmacodynamic consequences of predosing. Results: Preadministration of anti-TENB2 at 1 mg/kg significantly increased blood exposure of the radiolabeled ADC and reduced intestinal, hepatic, and splenic uptake while not affecting tumor accretion. Similar tumor-to-heart ratios were measured by SPECT/CT at 24 h with and without the predose. Consistent with this, the preadministration of 0.75 mg/kg did not interfere with efficacy in a tumor-growth study dosed at 0.75 mg or 2.5 mg of ADC per kilogram. Conclusion: Overall, the potential to mask peripheral, nontumor antigen uptake while preserving tumor uptake and efficacy could ameliorate toxicity and may significantly affect future dosing strategies for ADCs.

Mechanism-Based Pharmacokinetic/Pharmacodynamic Model for THIOMAB™ Drug Conjugates

ABSTRACTPurposeTHIOMAB™ drug conjugates (TDCs) with engineered cysteine residues allow site-specific drug conjugation and defined Drug-to-Antibody Ratios (DAR). In order to help elucidate the impact of drug-loading, conjugation site, and subsequent deconjugation on pharmacokinetics and efficacy, we have developed an integrated mathematical model to mechanistically characterize pharmacokinetic behavior and preclinical efficacy of MMAE conjugated TDCs with different DARs. General applicability of the model structure was evaluated with two different TDCs.MethodPharmacokinetics studies were conducted for unconjugated antibody and purified TDCs with DAR-1, 2 and 4 for trastuzumab TDC and Anti-STEAP1 TDC in mice. Total antibody concentrations and individual DAR fractions were measured. Efficacy studies were performed in tumor-bearing mice.ResultsAn integrated model consisting of distinct DAR species (DAR0-4), each described by a two-compartment model was able to capture the experimental data well. Time series measurements of each Individual DAR species allowed for the incorporation of site-specific drug loss through deconjugation and the results suggest a higher deconjugation rate from heavy chain site HC-A114C than the light chain site LC-V205C. Total antibody concentrations showed multi-exponential decline, with a higher clearance associated with higher DAR species. The experimentally observed effects of TDC on tumor growth kinetics were successfully described by linking pharmacokinetic profiles to DAR-dependent killing of tumor cells.ConclusionResults from the integrated model evaluated with two different TDCs highlight the impact of DAR and site of conjugation on pharmacokinetics and efficacy. The model can be used to guide future drug optimization and in-vivo studies.

Preclinical Development of an Anti-NaPi2b (SLC34A2) Antibody Drug Conjugate as a Therapeutic for Non-Small Cell Lung and Ovarian Cancers

Purpose: Antibody–drug conjugates (ADC) selectively deliver a cytotoxic drug to cells expressing an accessible antigenic target. Here, we have appended monomethyl auristatin E (MMAE) to an antibody recognizing the SLC34A2 gene product NaPi2b, the type II sodium–phosphate cotransporter, which is highly expressed on tumor surfaces of the lung, ovary, and thyroid as well as on normal lung pneumocytes. This study evaluated its efficacy and safety in preclinical studies. Experimental Design: The efficacy of anti-NaPi2b ADC was evaluated in mouse ovarian and non–small cell lung cancer (NSCLC) tumor xenograft models, and its toxicity was assessed in rats and cynomolgus monkeys. Results: We show here that an anti-NaPi2b ADC is effective in mouse ovarian and NSCLC tumor xenograft models and well-tolerated in rats and cynomolgus monkeys at levels in excess of therapeutic doses. Despite high levels of expression in normal lung of non-human primate, the cross-reactive ADC exhibited an acceptable safety profile with a dose-limiting toxicity unrelated to normal tissue target expression. The nonproliferative nature of normal pneumocytes, together with the antiproliferative mechanism of MMAE, likely mitigates the potential liability of this normal tissue expression. Conclusions: Overall, our preclinical results suggest that the ADC targeting NaPi2b provides an effective new therapy for the treatment of NSCLC and ovarian cancer and is currently undergoing clinical developments. Clin Cancer Res; 21(22); 5139–50. ©2015 AACR.

An anti-CD3/anti–CLL-1 bispecific antibody for the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is a major unmet medical need. Most patients have poor long-term survival, and treatment has not significantly changed in 40 years. Recently, bispecific antibodies that redirect the cytotoxic activity of effector T cells by binding to CD3, the signaling component of the T-cell receptor, and a tumor target have shown clinical activity. Notably, blinatumomab is approved to treat relapsed/refractory acute lymphoid leukemia. Here we describe the design, discovery, pharmacologic activity, pharmacokinetics, and safety of a CD3 T cell-dependent bispecific (TDB) full-length human IgG1 therapeutic antibody targeting CLL-1 that could potentially be used in humans to treat AML. CLL-1 is prevalent in AML and, unlike other targets such as CD33 and CD123, is not expressed on hematopoietic stem cells providing potential hematopoietic recovery. We selected a high-affinity monkey cross-reactive anti-CLL-1 arm and tested several anti-CD3 arms that varied in affinity, and determined that the high-affinity CD3 arms were up to 100-fold more potent in vitro. However, in mouse models, the efficacy differences were less pronounced, probably because of prolonged exposure to TDB found with lower-affinity CD3 TDBs. In monkeys, assessment of safety and target cell depletion by the high- and low-affinity TDBs revealed that only the low-affinity CD3/CLL1 TDB was well tolerated and able to deplete target cells. Our data suggest that an appropriately engineered CLL-1 TDB could be effective in the treatment of AML.

Development and Translational Application of an Integrated, Mechanistic Model of Antibody-Drug Conjugate Pharmacokinetics.

Antibody drug conjugates (ADC), in which small molecule cytotoxic agents are non-specifically linked to antibodies, can enable targeted delivery of chemotherapeutics to tumor cells. ADCs are often produced and administered as a mixture of conjugated antibodies with different drug to antibody ratios (DAR) resulting in complex and heterogeneous disposition kinetics. We developed a mechanism-based platform model that can describe and predict the complex pharmacokinetic (PK) behavior of ADCs with protease-cleavable valine-citrulline (VC) linker linked to Monomethylmonomethyl auristatin F/E by incorporating known mechanisms of ADC disposition. The model includes explicit representation of all DAR species; DAR-dependent sequential deconjugation of the drug, resulting in the conversion of higher DAR to lower DAR species; and DAR-dependent antibody/ADC clearance. PK profiles of multiple analytes (total antibody, drug-conjugated antibody, and/or antibody-conjugated drug) for different ADC molecules and targets in rodents and cynomolgus monkeys were used for model development. The integrated cross-species model was successful in capturing the multi-analyte PK profiles after administration of purified ADCs with defined DAR species and ADCs with mixtures of DAR. Human PK predictions for DSTP3086S (anti-STEAP1-vc-MMAE) with the platform model agreed well with PK (total antibody and antibody-conjugated drug concentrations) measurements in the dose-ranging phase I clinical study. The integrated model is applicable to various other ADCs with different formats, conjugated drugs, and linkers, and provides a valuable tool for the exploration of mechanisms governing disposition of ADCs and enables translational predictions.

1598PTRANSLATIONAL PKPD OF DNIB0600A, AN ANTI-NAPI2B-VC-MMAE ADC IN OVARIAN AND NSCLC CANCERS

ABSTRACT Aim: Antibody-drug conjugates (ADCs) represent an expanding class of therapeutic molecules in preclinical and clinical development for oncologic indications. Understanding the relationship between pre-clinical to clinical studies with strategic application of pharmacokinetic/pharmacodynamics modeling may allow for optimized dosing strategies for ADCs. NaPi2b is a multi-transmembrane, sodium-dependent phosphate transporter that is expressed in human lung, ovarian, and thyroid cancers. DNIB0600A, which consists of an anti-NaPi2b monoclonal antibody conjugated to the cytotoxic drug MMAE through a cleavable VC linker, is currently in Phase I/II clinical trials. The purpose of this study is to develop a PKPD model based on preclinical data and to utilize the preclinical exposure response relationships to predict clinical outcomes. Methods: DNIB0600A PK was evaluated in normal SCID mice. Dose ranging in-vivo efficacy studies were performed in NaPi2b-expressing xenograft mouse models of ovarian and lung cancers. A semi-mechanistic PKPD model was developed to describe exposure-efficacy relationships in both types of the tumor models. Human PK and PD data were collected from ongoing Phase I/II trials. Results: DNIB0600A demonstrated differential anti-tumor activities in the models, with the ovarian model being more responsive when compared with lung tumor model to NaPi2b ADC treatment. Human efficacious doses for treating ovarian cancer and NSCLC were predicted based on the pre-clinical PKPD relationships. Observed efficacy data from preliminary analysis of Phase I/II trials were in general agreements with model predictions. Conclusions: We built an integrated PKPD model to predict clinical outcome. This approach can be extended to other vc-MMAE based ADCs, and can help in preclinical model validation and ADC optimization. Disclosure: All authors have declared no conflicts of interest.

Abstract 5619: Preclinical development of anti-SLC34A2 antibody drug conjugate as a therapeutic for non-small cell lung and ovarian cancers.

SLC34A2, also known as type II Na/Pi co-transporters NaPi2b or NaPi3b, is a member of solute carrier protein family SLC34. SLC34A2 is highly expressed on cancers of the lung, ovary and thyroid as well as on normal lung pneumocytes, and is a promising target for antigen-directed therapy. Antibody drug conjugates (ADCs) specify the delivery of a cytotoxic drug to cells expressing an accessible antigenic target. Here we have appended monomethyl auristatin E (MMAE) to an antibody recognizing SLC34A2. Anti-SLC34A2-vc-MMAE inhibits tumor growth in multiple ovarian and non-small cell lung cancer xenograft models that express SLC34A2. Anti-SLC34A2 antibody and its conjugate cross-react with both human and monkey, and toxicity studies in monkeys are conducted to identify both target- and MMAE-related effects. Anti-SLC34A2-vc-MMAE was well tolerated in monkeys at efficacious doses and produced dose-related bone marrow suppression and increased apoptosis and mitotic figures consistent with MMAE-related pharmacology. Despite high levels of expression in normal lung of non-human primate, the cross-reactive ADC exhibited an acceptable safety profile with a dose-limiting toxicity unrelated to normal tissue expression. Overall, our preclinical results suggest that the antibody drug conjugate targeting the SLC34A2 may provide an effective new therapy for the treatment of NSCLC and ovarian cancer. Citation Format: Kedan Lin, Crystal Zhang, Eric Harstad, Hajime Hiraragi, Willy Solis, Siao Ping Tsai, Keyang Xu, Maria Hristopoulos, Rayna Venook, Bonnee Rubinfeld, Paul Polakis. Preclinical development of anti-SLC34A2 antibody drug conjugate as a therapeutic for non-small cell lung and ovarian cancers. [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 5619. doi:10.1158/1538-7445.AM2013-5619

Abstract B192: Pharmacokinetic characterization of anti-ETBR antibody drug conjugate in preclinical species.

Purpose. Anti-ETBR-MC-vc-PAB-MMAE (anti-ETBR-vc-E) is an antibody-drug conjugate (ADC) targeting the Endothelin B receptor. It comprises the humanized IgG1 anti-ETBR monoclonal antibody and a potent anti-mitotic agent, monomethyl auristatin E (MMAE), linked through MC-VC-PAB linker. Anti-ETBR antibody and its conjugate cross-react with mouse, rat, cynomolgus monkey and human, which provides an opportunity to compare and evaluate the impact of normal tissue expression on ADC disposition in preclinical species. Methods. Anti-ETBR-vc-E was administered intravenously in mice (0.5 and 5 mg/kg), rats (0.5 and 5 mg/kg), and cynomolgus monkeys (0.3 and 1 mg/kg). The samples were assayed for total antibody and conjugated antibody concentrations in mice and rats while total antibody and antibody-conjugated MMAE concentrations were determined in monkeys. Concentration-time data were used to estimate the pharmacokinetic parameters. Results. The pharmacokinetic behavior of the ADC was characterized by monitoring and comparing total antibody, conjugated antibody, and antibody-conjugated MMAE disposition. The clearances for all three analytes were dose-independent after intravenous administration in mice, rats, or cynomolgus monkeys over the dose range studied. Conjugated antibody and antibody-conjugated MMAE clearances were approximately 2-fold higher than total antibody clearance. Clearance of total antibody in rat was approximately 2-fold higher than in mouse and monkey, with values of 19.4, 7.91, and 8.99 mL/day/kg, respectively. Half-life ranged from 8 to 10 days and volume of distribution ranged from 37 to 40 mL/kg. Conclusions. The pharmacokinetics of anti-ETBR-vc-E total antibody was dose proportional in rodents and monkey suggesting that the presence of cross-reactive antigen in the preclinical species had no impact on clearance. All three species showed a relatively higher deconjugation clearance compared to total antibody clearance. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B192.