Drug-to-antibody Ratio Research Articles

Efficient elimination of CD103-expressing cells by anti-CD103 antibody drug conjugates in immunocompetent mice.

CD103 plays an important role in the destruction of islet allografts, and previous studies found that a CD103 immunotoxin (M290-Saporin, or M290-SAP) promoted the long-term survival of pancreatic islet allografts. However, systemic toxicity to the host and the bystander effects of M290-SAP obscure the underlying mechanisms of action and restrict its clinical applications. To overcome these shortcomings, anti-CD103 M290 was conjugated to different cytotoxic agents through cleavable or uncleavable linkages to form three distinct antibody-drug conjugates (ADCs): M290-MC-vc-PAB-MMAE, M290-MC-MMAF, and M290-MCC-DM1. The drug-to-antibody ratio (DAR) and the purity of the ADCs were determined by HIC-HPLC and SEC-HPLC, respectively. The binding characteristics, internalization and cytotoxicity of M290 and the corresponding ADCs were evaluated in vitro. The cell depletion efficacies of the various M290-ADCs against CD103-positive cells were then evaluated in vivo. The M290-ADCs maintained the initial binding affinity for the CD103-positive cell surface antigen and then quickly internalized the CD103-positive cell. Surprisingly, all M290-ADCs potently depleted CD103-positive cells in vivo, with high specificity and reduced toxicity. Our findings show that M290-ADCs have potent and selective depletion effects on CD103-expressing cells in immunocompetent mice. These data indicate that M290-ADCs could potentially serve as a therapeutic intervention to block the CD103/E-cadherin pathway.

Innovative native MS methodologies for antibody drug conjugate characterization: High resolution native MS and IM-MS for average DAR and DAR distribution assessment.

Antibody drug conjugates (ADCs) are macromolecules composed of cytotoxic drugs covalently attached via a conditionally stable linker to monoclonal antibodies (mAbs). ADCs are among the most promising next generation of empowered mAbs foreseen to treat cancers. Compared to naked mAbs, ADCs have an increased level of complexity as the heterogeneity of conjugation cumulates with the inherent microvariability of the biomolecule. An increasing need underlying ADC's development and optimization is to improve its analytical and bioanalytical characterization by assessing three main ADC quality attributes: drug distribution, amount of naked antibody, and average drug to antibody ratio (DAR). Here, the analytical potential of native mass spectrometry (MS) and native ion mobility MS (IM-MS) is compared to hydrophobic interaction chromatography (HIC), the reference method for quality control of interchain cysteinyl-linked ADCs. Brentuximab vedotin, first in class and gold standard, was chosen for a proof of principle. High resolution native MS provided accurate mass measurement (<30 ppm) of intact ADCs together with average DAR and drug distribution, confirming the unique ability of native MS for simultaneous detection of mixtures of covalent and noncovalent products. Native IM-MS was next used for the first time to characterize an ADC. IM-MS evidenced ADC multiple drug loading, collisional cross sections measurement of each payload species attesting slight conformational changes. A semiquantitative interpretation of IM-MS data was developed to directly extrapolate average DAR and DAR distribution. Additionally, HIC fractions were collected and analyzed by native MS and IM-MS, assessing the interpretation of each HIC peak. Altogether, our results illustrate how native MS and IM-MS can rapidly assess ADC structural heterogeneity and how easily these methods can be implemented into MS workflows for in-depth ADC analytical characterization.

Development of novel ADCs: conjugation of tubulysin analogues to trastuzumab monitored by dual radiolabeling.

Tubulysins are highly toxic tubulin-targeting agents with a narrow therapeutic window that are interesting for application in antibody-drug conjugates (ADC). For full control over drug-antibody ratio (DAR) and the effect thereof on pharmacokinetics and tumor targeting, a dual-labeling approach was developed, wherein the drug, tubulysin variants, and the antibody, the anti-HER2 monoclonal antibody (mAb) trastuzumab, are radiolabeled. (131)I-radioiodination of two synthetic tubulysin A analogues, the less potent TUB-OH (IC50 > 100 nmol/L) and the potent TUB-OMOM (IC50, ~1 nmol/L), and their direct covalent conjugation to (89)Zr-trastuzumab were established. Radioiodination of tubulysins was 92% to 98% efficient and conversion to N-hydroxysuccinimide (NHS) esters more than 99%; esters were isolated in an overall yield of 68% ± 5% with radiochemical purity of more than 99.5%. Conjugation of (131)I-tubulysin-NHS esters to (89)Zr-trastuzumab was 45% to 55% efficient, resulting in ADCs with 96% to 98% radiochemical purity after size-exclusion chromatography. ADCs were evaluated for their tumor-targeting potential and antitumor effects in nude mice with tumors that were sensitive or resistant to trastuzumab, using ado-trastuzumab emtansine as a reference. ADCs appeared stable in vivo. An average DAR of 2 and 4 conferred pharmacokinetics and tumor-targeting behavior similar to parental trastuzumab. Efficacy studies using single-dose TUB-OMOM-trastuzumab (DAR 4) showed dose-dependent antitumor effects, including complete tumor eradications in trastuzumab-sensitive tumors in vivo. TUB-OMOM-trastuzumab (60 mg/kg) displayed efficacy similar to ado-trastuzumab emtansine (15 mg/kg) yet more effective than trastuzumab. Our findings illustrate the potential of synthetic tubulysins in ADCs for cancer treatment.

Abstract 2651: Impressive efficacy and safety profile of a novel generation duocarmycin-based HER2-targeting ADC

Abstract We have built a linker-drug platform based on a cleavable linker-duocarmycin payload for the development of novel generation antibody-drug conjugates. SYD983, a lead ADC originating from that platform, is a cysteine-coupled HER2-targeting ADC based on trastuzumab. SYD983 is a heterogeneous product that consists of a mixture of naked Ab and ADCs with a drug-to-antibody ratio (DAR) of 2, 4, 6, the mean DAR being 2.0. We have shown that SYD983 binds to HER2, induces antibody-dependent cell-mediated cytotoxicity, and is efficiently internalized into HER2-expressing cells. SYD983 very potently kills HER2-expressing cells in vitro and is inactive in cells that don't express HER2. SYD983 is stable in human and cynomolgus monkey (CM) plasma in vitro but has relatively poor stability in mouse plasma. The latter is due to mouse-specific carboxylesterase (CES1c) since stability of SYD983 in plasma of CES1c knockout mice is similar to that in human and CM plasma. SYD983 could be dosed up to 30 mg/kg in CM in vivo with high exposure and stable kinetics and without severe toxic effects. The CM safety study showed no SYD983-induced thrombocytopenia and no induction of peripheral sensory neuropathy, which both commonly occur in studies with ADCs based on tubulin inhibitors. Finally, to reduce heterogeneity we have further fractionated SYD983 by hydrophobic interaction chromatography resulting in an ADC predominantly containing DAR2 and DAR4 species and we designated the resulting purified and more homogeneous ADC as SYD985. In line with its increased average DAR and the absence of naked Ab, SYD985 (average DAR of 2.7) shows increased potency in vitro compared to SYD983. In vivo, SYD985 showed high anti-tumor activity in two patient-derived xenograft models of HER2 positive metastatic breast cancers which underscores the potential for SYD985 in this indication. We have further initiated a program to directly compare SYD985 to T-DM1 for anti-tumor activity in a series of tumors with different HER2 status of which the results are published in a separate accompanying abstract. In conclusion, the data obtained indicates great potential for SYD985 to become an effective drug for patients with HER2-positive cancers. Clinical studies will further elucidate how the characteristics revealed in the preclinical studies, will translate into a benefit for patients. Taken more generally, we conclude that this novel generation duocarmycin-based LD technology could be used on other mAbs to create effective and safe ADCs to treat different forms of cancer. Citation Format: Willem Dokter, Ruud Ubink, Miranda van der Lee, Monique van der Vleuten, Tanja van Achterberg, Daniëlle Jacobs, Diels van den Dobbelsteen, David Egging, Ellen Mattaar, Patrick Groothuis, Patrick Beusker, Ruud Coumans, Ronald Elgersma, Michel Eppink, Guy de Roo, Gijs Verheijden, Marco Timmers. Impressive efficacy and safety profile of a novel generation duocarmycin-based HER2-targeting ADC. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2651. doi:10.1158/1538-7445.AM2014-2651

Abstract 666: AB-3A4: A novel KAAG1-targeting antibody-drug conjugate is active in models of ovarian carcinoma, triple-negative breast cancer and castration-resistant prostate cancer

Abstract Starting from total RNA prepared from late-stage serous ovarian tumors and low-malignancy potential tumors, a sensitive subtractive cloning technology called STAR was used to identify differentially expressed sequences that were up-regulated in the malignant tumors. This analysis led to the identification of KAAG1, an antigen that is specifically expressed in the vast majority of the ovarian tumors. Monoclonal antibodies (mAbs) that bind to human KAAG1 were generated and one of these, AB-3A4, interacted with KAAG1 expressed on the surface of several ovarian cancer, triple-negative breast cancer (TNBC) and prostate cancer cell lines. Further studies indicated that the AB-3A4/KAAG1 complex was rapidly internalized and co-localized with LAMP1, a marker of lysosomes, indicating that AB-3A4 has potential as an antibody-drug conjugate (ADC). Here we describe preclinical results of AB-3A4 conjugated to the cytotoxic agent monomethyl auristatin E (AB-3A4-vcMMAE). Binding studies with KAAG1-positive cell lines, such as the SKOV-3 (ovarian), MDA-MB-231 (TNBC) and PC-3 (prostate) showed that AB-3A4-vcMMAE interacted with its antigen in a similar manner to the unconjugated AB-3A4. In cytotoxicity assays, AB-3A4-vcMMAE killed cancer cell lines expressing KAAG1 with an IC50 value of 1 - 2 nM, whereas it displayed no specific potency in KAAG1-low or -negative cells. SKOV-3 cells were subcutaneously implanted in SCID mice and allowed to grow to a volume of 150 - 200 mm3 after which four injections of AB-3A4-vcMMAE at 5 mg/kg were administered over two weeks. Rapid and sustained tumor regression was observed for several weeks post-injection. In PC-3 xenografts, a single injection of AB-3A4-vcMMAE at 3 mg/kg was sufficient to cause significant tumor regression and this efficacy was found to be dose-dependent between doses of 1 and 10 mg/kg. In parallel treatment groups, no significant tumor shrinkage was observed with either a control IgG-vcMMAE or a mixture of unconjugated AB-3A4 and free MMAE at a drug-antibody ratio corresponding to that of AB-3A4-vcMMAE. Furthermore, xenografts of TNBC MDA-MB-231 cells were significantly regressed following a single injection of AB-3A4-vcMMAE with no recurrence after several weeks post-treatment. Finally, using an intraperitoneal orthotopic model of ovarian cancer, treatment with AB-3A4-vcMMAE significantly increased the overall survival of mice compared to mice treated with the control ADC. Collectively, our results demonstrate the potent efficacy of AB-3A4-vcMMAE in several disease models and underscore the potential of this novel agent in ovarian cancer, TNBC and castration-resistant prostate cancer, three areas for which very few targeted therapies exist. Citation Format: Gilles B. Tremblay, Anna Moraitis, Dominique Bédard, Adriana Orimoto, Martine Pagé, Anne-Marie Mes-Masson, Mario Filion. AB-3A4: A novel KAAG1-targeting antibody-drug conjugate is active in models of ovarian carcinoma, triple-negative breast cancer and castration-resistant prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 666. doi:10.1158/1538-7445.AM2014-666

Abstract 2645: Advantages of polyacetal polymer-based ADCs: Application to low expression targets

Abstract The application of biodegradable polymers to antibody-drug conjugate (ADC) design can provide numerous advantages, including significantly higher drug-antibody ratios, the use of alternative payloads with potencies considered insufficient for direct conjugation, the improvement of ADC physico-chemical properties, especially for highly hydrophobic payloads, and the potential expansion of protein recognition scaffolds beyond the commonly used IgGs. The basis of the novel polymer-based conjugation system described herein is a hydrophilic, fully biodegradable polyacetal carrier, (poly(1-hydroxymethylethylene hydroxymethylformal) or PHF) modified with chemically orthogonal linkers. A bioconjugation linker is used for efficient covalent attachment of a targeting moiety to the PHF scaffold, while a second, chemically distinct linker is used to attach multiple copies of a drug payload to the polymer to control the mechanism and rate of drug release. Utilizing multiple copies of a proprietary dolastatin derivative chemically conjugated to PHF, we have developed a potent and effective drug conjugation platform for ADC application, which has been named Dolaflexin™. Here, we report the preparation and characterization of a novel trastuzumab DolaflexinTM ADC, employing a maleimide-based bioconjugation approach. The resulting ADC, with a drug-antibody ratio of 20, exhibits enhanced stability and improved pharmacokinetics, with a prolonged plasma half-life and tumor-specific accumulation. Active drug release and accumulation in tumor tissue was also confirmed by LC/MS/MS methods. The activity of this novel trastuzumab-dolaflexin ADC was evaluated in multiple tumor xenograft models with significant variations in target antigen expression levels. Models including BT474 breast cancer, NCI-N87 gastric cancer, and JIMT1 breast cancer models were utilized, and comparisons to a variety of controls and ADC reference standards were made. Significant advantages of the polyacetal polymer-based ADCs in comparison to conventional ADCs, particularly in models with low target antigen expression, were observed. Details of these studies and potential applications for the development of new ADC therapeutics based on this approach will be presented. Citation Format: Alex Yurkovetskiy, Natalya Bodyak, Mao Yin, Joshua D. Thomas, Patrick Conlon, Cheri A. Stevenson, Alex Uttard, LiuLiang Qin, Dmitry R. Gumerov, Elena Ter-Ovaneysan, Venu R. Gurijala, Dennis McGillicuddy, Roberta E. Glynn, Michael DeVit, Laura L. Poling, Peter U. Park, Timothy B. Lowinger. Advantages of polyacetal polymer-based ADCs: Application to low expression targets. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2645. doi:10.1158/1538-7445.AM2014-2645

Abstract 822: Thienoindoles, a novel class of DNA minor groove alkylating agents highly suited for the generation of novel antibody drug conjugates (ADCs)

Abstract The rapidly growing field of Antibody-Drug Conjugates (ADCs) has recently spurred the study of novel drug payloads. In particular, much interest has been paid to the identification of novel cytotoxic agents, which differ in mechanism from anti-tubulin agents, currently the most commonly employed class of drug for ADC coupling. Novel drug payloads for ADC-based therapy should thus ideally possess highly potent cytotoxic activity with a diverse mechanism from tubulin agents, as well as physicochemical properties, which facilitate coupling to antibodies. Duocarmycins are a widely-described class of DNA minor groove binding alkylating agents, examples of which can exhibit picomolar activity against human tumor cell lines, as well as high activity in preclinical tumor models. The clinical development of duocarmycins as drugs in their own right has however been hampered by an extremely limited therapeutic window. Duocarmycins also typically exhibit poor physicochemical profiles, most importantly generally possessing limited aqueous solubility and a propensity to induce protein aggregation, which renders these molecules poorly tractable as optimal ADC payloads. Based on the premise that opportune modification of the duocarmycin scaffold could lead to the discovery of compounds better suited to antibody conjugation, we describe the identification and related proof of concept studies for a novel chemical series based on a proprietary thienoindole scaffold, characterized both by potent antitumor activity and by physicochemical properties that are highly compatible with deployment as antibody payloads. Extensive in vitro profiling within the thienoindole series led to selection of potent cytotoxic compounds suitable for test conjugation to humanized monoclonal antibodies, which were then submitted to in vitro/in vivo profiling. Typically, average drug/antibody ratios (DARs) of 4 could readily be achieved without induction of antibody aggregation/precipitation and without affecting natural antibody-ligand affinity. Efficacy and mechanism of action studies were carried out for thienoindole-ADCs prepared with trastuzumab and with rituximab showing target driven effects in Her2 positive vs. negative breast cancer cell lines and against CD20 positive vs. negative hematological cell lines. PK data indicated long, essentially unaffected plasma half life of our novel ADCs in the mouse. In vivo efficacy studies in the Her2-positive HCC1954 human breast cancer model showed complete tumor regression in mice treated with trastuzumab-ADC with no effects on body weight gain, while unarmed trastuzumab and armed control antibody had little and no effect, respectively. Citation Format: Barbara Valsasina, Fabio Gasparri, Italo Beria, Nicoletta Colombo, Paolo Orsini, Rita Perego, Simona Rizzi, Ulisse Cucchi, Clara Albanese, Aurelio Marsiglio, Ivan Fraietta, Marina Ciomei, Sabrina Cribioli, Carlo Visco, Eduard R. Felder, Antonella Isacchi, Enrico A. Pesenti, Arturo Galvani, Daniele Donati, Michele Caruso. Thienoindoles, a novel class of DNA minor groove alkylating agents highly suited for the generation of novel antibody drug conjugates (ADCs). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 822. doi:10.1158/1538-7445.AM2014-822

Abstract CT206: SN-38 antibody-drug conjugate (ADC) targeting Trop-2, IMMU-132, as a novel platform for the therapy of diverse metastatic solid cancers: Initial clinical results

Abstract IMMU-132 is an ADC of the active metabolite of CPT-11, SN-38, conjugated by a pH-sensitive linker (average drug-antibody ratio = 7.6) to the humanized anti-Trop-2 antibody, hRS7, exhibiting rapid internalization after binding to Trop-2. Trop-2 is a type I transmembrane protein expressed at high prevalence (∼1 x 10*5) and specificity by many carcinomas. We report the results of a Phase I clinical trial of 25 patients with different metastatic cancers (pancreatic, 7; triple-negative breast [TNBC], 4; colorectal [CRC], 3; gastric, 2; small-cell lung [SCLC], 2; esophageal, prostatic, ovarian, non-small-cell lung, renal, tonsillar, urinary bladder, 1 each) after failing a median of 3 prior treatments (some including topoisomerase-I and -II inhibiting drugs). IMMU-132 was administered in repeated 21-day cycles, with each treatment given on days 1 and 8. Dosing started at 8 mg/kg/dose (i.e., 16 mg/kg/cycle), and escalated to 18 mg/kg before encountering dose-limiting neutropenia, in a 3+3 trial design. Fatigue, alopecia, and occasional mild to moderate diarrhea were some of the more common non-hematological toxicities, with 2 patients also reporting a rash. Over 80% of 24 assessable patients had stable disease or tumor shrinkage (17/24 SD; 3/24 PR) among the various metastatic cancers as best response by CT. Three patients (CRC, TNBC, SCLC) have PRs by RECIST; median TTP for all patients, excluding those with pancreatic cancer, is &amp;gt;18 weeks. Neutropenia has been controlled by dose reduction to 8-10 mg/kg/dose (16-20 mg/kg/cycle), which is the Phase II dose. Immunohistochemistry showed strong expression of Trop-2 in most archived patient tumors, but is not detected in serum. Corresponding reductions in blood tumor marker titers (e.g., CEA, CA19-9) reflected tumor responses. No anti-antibody or anti-SN-38 antibodies have been detected despite repeated dosing. Peak and trough assessments of IMMU-132 concentrations in the serum show that the conjugate clears completely within 7 days, an expected finding based on in vitro studies showing 50% of the SN-38 is released in the serum every day. These results indicate that this novel ADC, given in doses ranging from 16-24 mg/kg per cycle, is active in diverse metastatic solid cancers. A Phase II study is ongoing to determine response rates in CRC, TNBC, and SCLC, while also evaluating its potency in other tumor types. Citation Format: Alexander N. Starodub, Allyson J. Ocean, Manish A. Shah, Linda T. Vahdat, Ellen Chuang, Michael J. Guarino, Vincent J. Picozzi, Sajeve S. Thomas, Pius P. Maliakal, Serengulam V. Govindan, William A. Wegener, Robert M. Sharkey, David M. Goldenberg. SN-38 antibody-drug conjugate (ADC) targeting Trop-2, IMMU-132, as a novel platform for the therapy of diverse metastatic solid cancers: Initial clinical results. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr CT206. doi:10.1158/1538-7445.AM2014-CT206

Abstract 2904: SN-38 antibody-drug conjugates as a novel platform for solid cancer therapy: preclinical science

Abstract SN-38 is the active metabolite of the camptothecin prodrug, CPT-11 (irinotecan), which is a solid cancer therapeutic, particularly colorectal cancer (CRC). SN-38 is highly potent (low nM), but its bioavailability is hampered by a low rate of CPT-11 conversion to SN-38 (e.g., &amp;lt;5%), as well as its subsequent detoxification, mainly by UGT1A1 glucoronidation. In an attempt to improve SN-38's bioavailability and therapeutic index, we conjugated it to tumor-targeting humanized monoclonal antibodies (mAbs) using a novel pH-sensitive linker and a maleimide attachment to the mAb's interchain SH groups, achieving a drug-antibody ratio of 7.6. Linker coupling on the 20th position of SN-38 helps maintain SN-38 in the more active lactone form. In human serum, SN-38 is released from the linker with a half-life of ∼24 h, providing ample time for the ADC to localize in tumors. The pH-sensitive linker has the potential to release of SN-38 in the acidic tumor microenvironment by the targeted ADC in the absence of its direct internalization. Studies using two different SN-38-conjugated mAbs targeting CEACAM5 (IMMU-130) and Trop-2 (IMMU-132) show growth inhibition and regression of diverse human solid cancer xenografts in mice given repeated doses (cumulative ≤ 50 mg/kg in mice, or ∼ 4 mg/kg human equivalent dose [HED]), without defining an MTD (CPT-11 conversion is more active in mice, but mice are more tolerant to SN-38 than humans). Dosing regimens using the same total amount of the ADC given once or twice weekly for at least 2 weeks appears to be preferred over the same total amount given once every other week (2 doses). IMMU-130 is a poorly-internalizing mAb that shows good ADC activity in human CRC models expressing CEACAM5, while IMMU-132 internalizes rapidly and is active against CRC, gastric, breast, pancreatic, and prostatic cancers expressing Trop-2; both targets have antigen receptors in the 1 x 10*5 range in most cancer cell lines. Studies to assess tumor and tissue concentrations of SN-38 in xenograft models given the ADC or CPT-11 are ongoing. Toxicity studies performed in relevant animal species found the ADCs were tolerated at HED of up to 60 mg/kg, limited by neutropenia and diarrhea (also dose-limiting for CPT-11 therapy), and with no evidence of selective toxicity to antigen-expressing normal tissues. These results with an ADC having relatively modest toxicity suggest a high therapeutic index. Ongoing Phase I/II clinical trials confirm anticancer activity with a high therapeutic window (less neutropenia and GI toxicity than CPT-11) in cancers expressing the target antigens. Citation Format: David M. Goldenberg, Thomas M. Cardillo, Robert M. Sharkey, William J. McBride, Edmund A. Rossi, Chien-Hsing Chang, Serengulam V. Govindan. SN-38 antibody-drug conjugates as a novel platform for solid cancer therapy: preclinical science. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2904. doi:10.1158/1538-7445.AM2014-2904

Abstract CT211: IMMU-130, an SN-38 antibody-drug conjugate (ADC) targeting CEACAM5, is therapeutically active in metastatic colorectal cancer (mCRC): Initial clinical results of two Phase I studies

Abstract IMMU-130, an ADC of the active metabolite of CPT-11, SN-38, conjugated by a pH-sensitive linker (7.6 average drug-antibody ratio) to the humanized anti-CEACAM5 antibody (labetuzumab), is completing two Phase I trials. In both, eligible patients with advanced mCRC were required to have failed/relapsed standard treatments, one being the topoisomerase-I inhibiting drug, CPT-11 (irinotecan), and an elevated plasma CEA (&amp;gt;5 ng/mL). IMMU-130 was administered every 14 days (EOW) at doses starting from 2.0 mg/kg in the first protocol (IMMU-130-01). Febrile neutropenia occurred in 2 of 3 patients at 24 mg/kg; otherwise at ≤16 mg/kg, neutropenia (≥ Grade 2) was observed in 7 patients, with one also experiencing thrombocytopenia. One patient [of 8 who received &amp;gt; 4 doses (2 cycles)] showed a 40.6% decrease in liver (starting at 7 cm) and lung target lesions (PR by RECIST) for 4.7 months, with no major toxicity, tolerating a total of 18 doses at 16 mg/kg. The study is continuing at 12 mg/kg EOW. Since SN-38 is most effective in S-phase cells, a more protracted exposure could improve efficacy. Thus, in a second Phase I trial (IMMU-130-02), dosing was intensified to twice-weekly, starting at 6 mg/kg/dose for 2 weeks (4 doses) with 1 week off, as a treatment cycle, in a 3+3 trial design. Neutropenia and manageable diarrhea were the major side effects, until dose reduction to 4.0 mg/kg twice-weekly, with early results indicating multiple cycles are well-tolerated. Currently, tumor shrinkage occurred in 3 patients, with 1 in continuing PR (-46%) by RECIST, among 6 patients who completed &amp;gt;4 doses (1 cycle). In both trials, CEA blood titers correlated with tumor response, and high levels did not interfere with therapy. There have been no anti-antibody or anti-SN-38 antibody reactions, based on ELISA tests. In each study, the ADC was cleared by 50% within the first 24 h, which is much longer exposure than with typical doses of the parental molecule, CPT-11. These results indicate that this novel ADC, given in different regimens averaging ∼16-24 mg/kg/cycle, shows therapeutic activity in advanced mCRC patients. Since CEACAM5 has elevated expression in breast and lung cancers, as well as other epithelial tumors, it may be a useful target in other cancers as well. A Phase II trial evaluating twice-weekly dosing and a new regimen, once-weekly x 2 every 21 days, is ongoing in mCRC. Citation Format: Neil H. Segal, Efrat Dotan, Jordan D. Berlin, Alexander N. Starodub, Michael J. Guarino, Leonard B. Saltz, Pius P. Maliakal, Serengulam V. Govindan, William A. Wegener, Robert M. Sharkey, David M. Goldenberg. IMMU-130, an SN-38 antibody-drug conjugate (ADC) targeting CEACAM5, is therapeutically active in metastatic colorectal cancer (mCRC): Initial clinical results of two Phase I studies. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr CT211. doi:10.1158/1538-7445.AM2014-CT211

Statistical modeling of the drug load distribution on trastuzumab emtansine (Kadcyla), a lysine-linked antibody drug conjugate.

Trastuzumab emtansine (Kadcyla) is a recently approved antibody-drug conjugate produced by attachment of the anti-tubulin drug, DM1, to lysine amines via the SMCC linker. The resulting product exhibits a drug load distribution from 0 to 8 drugs per antibody that can be quantified using mass spectrometry. Different statistical models were tested against the experimental data derived from samples produced during process characterization studies to determine best fit. The Poisson distribution gives the best correlation for samples manufactured using the target process conditions (yielding the target average drug to antibody ratio (DAR) of 3.5) as well as those produced under conditions that exceed the allowed manufacturing ranges and yield products with average DAR values that are significantly different from the target (i.e., ≤3.0 or ≥4.0). The Poisson distribution establishes a link between average DAR values and drug load distributions, implying that measurement and control of the former (i.e., via a simple UV spectrophotometric method) could be used to indirectly control the latter in trastuzumab emtansine.

Aldehyde tag coupled with HIPS chemistry enables the production of ADCs conjugated site-specifically to different antibody regions with distinct in vivo efficacy and PK outcomes.

It is becoming increasingly clear that site-specific conjugation offers significant advantages over conventional conjugation chemistries used to make antibody–drug conjugates (ADCs). Site-specific payload placement allows for control over both the drug-to-antibody ratio (DAR) and the conjugation site, both of which play an important role in governing the pharmacokinetics (PK), disposition, and efficacy of the ADC. In addition to the DAR and site of conjugation, linker composition also plays an important role in the properties of an ADC. We have previously reported a novel site-specific conjugation platform comprising linker payloads designed to selectively react with site-specifically engineered aldehyde tags on an antibody backbone. This chemistry results in a stable C–C bond between the antibody and the cytotoxin payload, providing a uniquely stable connection with respect to the other linker chemistries used to generate ADCs. The flexibility and versatility of the aldehyde tag conjugation platform has enabled us to undertake a systematic evaluation of the impact of conjugation site and linker composition on ADC properties. Here, we describe the production and characterization of a panel of ADCs bearing the aldehyde tag at different locations on an IgG1 backbone conjugated using Hydrazino-iso-Pictet-Spengler (HIPS) chemistry. We demonstrate that in a panel of ADCs with aldehyde tags at different locations, the site of conjugation has a dramatic impact on in vivo efficacy and pharmacokinetic behavior in rodents; this advantage translates to an improved safety profile in rats as compared to a conventional lysine conjugate.

Bridging disulfides for stable and defined antibody drug conjugates.

To improve both the homogeneity and the stability of ADCs, we have developed site-specific drug-conjugating reagents that covalently rebridge reduced disulfide bonds. The new reagents comprise a drug, a linker, and a bis-reactive conjugating moiety that is capable of undergoing reaction with both sulfur atoms derived from a reduced disulfide bond in antibodies and antibody fragments. A disulfide rebridging reagent comprising monomethyl auristatin E (MMAE) was prepared and conjugated to trastuzumab (TRA). A 78% conversion of antibody to ADC with a drug to antibody ratio (DAR) of 4 was achieved with no unconjugated antibody remaining. The MMAE rebridging reagent was also conjugated to the interchain disulfide of a Fab derived from proteolytic digestion of TRA, to give a homogeneous single drug conjugated product. The resulting conjugates retained antigen-binding, were stable in serum, and demonstrated potent and antigen-selective cell killing in in vitro and in vivo cancer models. Disulfide rebridging conjugation is a general approach to prepare stable ADCs, which does not require the antibody to be recombinantly re-engineered for site-specific conjugation.

Activity of IMMU-130 anti-CEACAM5-SN-38 antibody-drug conjugate (ADC) on metastatic colorectal cancer (mCRC) having relapsed after CPT-11: Phase I study.

3106 Background: IMMU-130 is an ADC of the humanized anti-CEACAM5 antibody, labetuzumab, linked to the active metabolite of CPT-11, SN-38 (drug-antibody ratio=7.6). In an every other week dosing sc...

IMMU-132, an SN-38 antibody-drug conjugate (ADC) targeting Τrop-2, as a novel platform for the therapy of diverse metastatic solid cancers: Clinical results.

3032 Background: IMMU-132 is an ADC of the internalizing, humanized, anti-Trop-2 antibody, hRS7, conjugated by a pH-sensitive linker, to SN-38, the active metabolite of CPT-11 (mean drug-antibody ratio = 7.6). Trop-2 is a type I transmembrane, calcium-transducing, protein expressed at high density (~1 x 10*5), frequency, and specificity by many human carcinomas, with limited normal tissue expression. Methods: We report the initial Phase I trial of 25 patients (pts) who had failed multiple prior therapies (some including topoisomerase-I/II inhibiting drugs), and the ongoing Phase II extension that focused on pts with colorectal (CRC), small-cell lung (SCLC) and triple-negative breast (TNBC) cancers. Results: Trop-2 is not detected in serum, but was strongly expressed (≥2+) in most archived tumors. In a 3+3 trial design, IMMU-132 was given on days 1 and 8 in repeated 21-day cycles, starting at 8 mg/kg/dose, then 12 and 18 mg/kg before dose-limiting neutropenia. To optimize cumulative treatment with minimal delays, phase II is focusing on 8 and 10 mg/kg (n=22 and 14, respectively). Most common non-hematological toxicities were fatigue (17 ≤G2 ,4 G3), nausea (20 ≤G2), diarrhea (12 ≤G2, 3 G3), alopecia (14), and vomiting (10 ≤G2) ; 2 pts had a rash. Homozygous UGT1A1 *28/*28 was found in 5 pts, 2 of whom had more severe hematological and GI toxicities. Over 80% of 24 assessable pts in Phase I had stable disease or tumor shrinkage (17 SD; 3 PR [CRC, TNBC, SCLC]) as best CT response; median TTP = 18 weeks for all pts, except pancreatic cancer. Of the 36 pts in the Phase II, 14 had their first response assessment by CT: 6 PD, 7 SD; 1 PR (SCLC) by RECIST1.1. Tumor markers (CEA, CA19-9) correlated with responses. No anti-hRS7 or anti-SN-38 antibodies were detected despite dosing over months. The conjugate clears within 7 days, consistent with in vivo animal studies where 50% of the SN-38 is released daily. Conclusions: These results indicate that this novel SN-38-containing ADC is active in metastatic solid cancers, with manageable diarrhea and neutropenia. The Phase II continues, while also accruing in other epithelial tumors. Clinical trial information: NCT01631552.

Transglutaminase-Based Chemo-Enzymatic Conjugation Approach Yields Homogeneous Antibody–Drug Conjugates

Most chemical techniques used to produce antibody-drug conjugates (ADCs) result in a heterogeneous mixture of species with variable drug-to-antibody ratios (DAR) which will potentially display different pharmacokinetics, stability, and safety profiles. Here we investigated two strategies to obtain homogeneous ADCs based on site-specific modification of deglycosylated antibodies by microbial transglutaminase (MTGase), which forms isopeptidic bonds between Gln and Lys residues. We have previously shown that MTGase solely recognizes Gln295 within the heavy chain of IgGs as a substrate and can therefore be exploited to generate ADCs with an exact DAR of 2. The first strategy included the direct, one-step attachment of the antimitotic toxin monomethyl auristatin E (MMAE) to the antibody via different spacer entities with a primary amine functionality that is recognized as a substrate by MTGase. The second strategy was a chemo-enzymatic, two-step approach whereby a reactive spacer entity comprising a bio-orthogonal thiol or azide function was attached to the antibody by MTGase and subsequently reacted with a suitable MMAE-derivative. To this aim, we investigated two different chemical approaches, namely, thiol-maleimide and strain-promoted azide-alkyne cycloaddition (SPAAC). Direct enzymatic attachment of MMAE-spacer derivatives at an 80 molar excess of drug yielded heterogeneous ADCs with a DAR of between 1.0 to 1.6. In contrast to this, the chemo-enzymatic approach only required a 2.5 molar excess of toxin to yield homogeneous ADCs with a DAR of 2.0 in the case of SPAAC and 1.8 for the thiol-maleimide approach. As a proof-of-concept, trastuzumab (Herceptin) was armed with the MMAE via the chemo-enzymatic approach using SPAAC and tested in vitro. Trastuzumab-MMAE efficiently killed BT-474 and SK-BR-3 cells with an IC50 of 89.0 pM and 21.7 pM, respectively. Thus, the chemo-enzymatic approach using MTGase is an elegant strategy to form ADCs with a defined DAR of 2. Furthermore, the approach is directly applicable to a broad variety of antibodies as it does not require prior genetic modifications of the antibody sequence.

In Vitro and In Vivo Evaluation of Cysteine and Site Specific Conjugated Herceptin Antibody-Drug Conjugates

Antibody drug conjugates (ADCs) are monoclonal antibodies designed to deliver a cytotoxic drug selectively to antigen expressing cells. Several components of an ADC including the selection of the antibody, the linker, the cytotoxic drug payload and the site of attachment used to attach the drug to the antibody are critical to the activity and development of the ADC.The cytotoxic drugs or payloads used to make ADCs are typically conjugated to the antibody through cysteine or lysine residues. This results in ADCs that have a heterogeneous number of drugs per antibody. The number of drugs per antibody commonly referred to as the drug to antibody ratio (DAR), can vary between 0 and 8 drugs for a IgG1 antibody. Antibodies with 0 drugs are ineffective and compete with the ADC for binding to the antigen expressing cells. Antibodies with 8 drugs per antibody have reduced in vivo stability, which may contribute to non target related toxicities.In these studies we incorporated a non-natural amino acid, para acetyl phenylalanine, at two unique sites within an antibody against Her2/neu. We covalently attached a cytotoxic drug to these sites to form an ADC which contains two drugs per antibody.We report the results from the first direct preclinical comparison of a site specific non-natural amino acid anti-Her2 ADC and a cysteine conjugated anti-Her2 ADC. We report that the site specific non-natural amino acid anti-Her2 ADCs have superior in vitro serum stability and preclinical toxicology profile in rats as compared to the cysteine conjugated anti-Her2 ADCs. We also demonstrate that the site specific non-natural amino acid anti-Her2 ADCs maintain their in vitro potency and in vivo efficacy against Her2 expressing human tumor cell lines. Our data suggests that site specific non-natural amino acid ADCs may have a superior therapeutic window than cysteine conjugated ADCs.

Insights Into Antibody–Drug Conjugates: Bioanalysis and Biomeasures in Discovery

Author for correspondence: Department of Pharmacokinetics, Dynamics & Metabolism, Pfizer Global Research & Development, Eastern Point Rd, Groton, CT 06340, USA Tel.: +1 860 715 0641 Fax: +1 860 715 9501 E-mail: tracey.clark@pfizer.com Xiaogang Han Department of Pharmacokinetics, Dynamics & Metabolism, Pfizer Global Research & Development, CT, USA Lindsay King Department of Pharmacokinetics, Dynamics & Metabolism, Pfizer Global Research & Development, CT, USA Frank Barletta Department of Pharmacokinetics, Dynamics & Metabolism, Pfizer, NY, USA Antibody–drug conjugate (ADC) therapeutics utilize the specificity of monoclonal antibodies (mAbs) and potency of highly toxic small molecules. ADCs are typically composed of a mAb with a cytotoxin conjugated to it, resulting in a heterogeneous mixture of mAb with various numbers of toxins. Due to this heterogeneity, characterized by the therapeutic drug-to-antibody ratio (DAR), the selection of bioanalytical tools, biomeasure assays and analytes used to understand and develop ADCs can be challenging [1]. Since the therapeutic has both largeand small-molecule components, one can use bioanalytical tools in both spaces. Questions for ADC programs are typically: what should be measured, when, and by which method? Since all assays have limitations [1], a combination of bioanalytical tools is typically used to understand the ADC in vitro/in vivo, understand payload delivery to the site of action and to establish an exposure–response relationship.

Abstract 2856: Pyrrolobenzodiazepine (PBD) dimers - potent next generation warheads in antibody drug conjugates (ADCs) targeted at both solid and haematological tumors.

Abstract The pyrrolobenzodiazepine (PBD) dimers are a class of rationally designed DNA minor groove, sequence selective, cross-linking agents. The non-distortive nature of PBD interstrand cross-links results in their persistence compared to those produced by conventional agents such as the nitrogen mustards and platinum drugs. Members of this class can exhibit picomolar or sub-picomolar activity against a range of human tumour cell lines and demonstrate curative activity in human tumour xenograft models. The fully synthetic PBD dimers are ideally suited for a role in strategies aimed at targeting and releasing highly cytotoxic agents directly at a tumour site such as antibody drug conjugates (ADCs). They combine exquisite potency with a demonstrated therapeutic index (unlike other warheads such as calicheamycin), are not cross-resistant with widely used chemotherapy agents, and their unique mode of action sets them apart from the tubulin binders (maytansinoids and auristatins) that currently dominate the ADC arena but which have the limitation that some tumour types lack sensitivity. Four PBD dimer drug linkers representing different PBD dimer warheads and two different attachment sites (N10 and C2) for the linker on the drug were synthesised. Trastuzumab-ADCs were prepared using these drug linkers with a drug-antibody ratio (DAR) below 3 and with attachment of the cleavable valine-alanine dipeptide linker to cysteine residues. Efficacy was evaluated in vitro against Her2 +ve and -ve cell lines and in vivo against human breast cancer Her2-expressing BT474 xenografts. All four ADCs showed durable complete regressions at 1mg/kg (i.v., qwk x 3) and significant growth delays at 0.3 mg/kg. A PBD-containing ADC was further evaluated against a haematological target. In vitro, the ADC gave a greater than 6-log differential cell killing between an expressing and a non-expressing cell line. In vivo, using the qwk x 3 treatment schedule, durable complete regressions were achieved at a dose of 0.1 mg/kg, whereas the naked antibody had no activity at a dose of 2.5 mg/kg. These data clearly demonstrate that antibody delivery of PBD dimers can result in curative antitumor activity against both solid and haematological tumor targets at low doses and DARs and represent the most promising next-generation ADCs for clinical development. Citation Format: John A. Hartley, Luke Masterson, Stephen Gregson, Thais Cailleau, Ebole Ezeadi, Jean-Noel Levy, Gary Kemp, Arnaud Tiberghien, Elizabeth Dunny, Francois D'Hooge, Lauren Adams, David Williams, Patrick van Berkel, Philip W. Howard. Pyrrolobenzodiazepine (PBD) dimers - potent next generation warheads in antibody drug conjugates (ADCs) targeted at both solid and haematological tumors. [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 2856. doi:10.1158/1538-7445.AM2013-2856

Total Antibody Quantification for MMAE-Conjugated Antibody–Drug Conjugates: Impact of Assay Format and Reagents

Antibody-drug conjugates (ADCs) are target-specific anticancer agents consisting of cytotoxic drugs covalently linked to a monoclonal antibody. The number of ADCs in the clinic is growing, and therefore thorough characterization of the quantitative assays used to measure ADC concentrations in support of pharmacokinetic, efficacy, and safety studies is of increasing importance. Cytotoxic drugs such as the tubulin polymerization inhibiting auristatin, monomethyl auristatin E, have been conjugated to antibodies via cleavable linkers (MC-vc-PAB) through internal cysteines. This results in a heterogeneous mixture of antibody species with drug-to-antibody ratios (DAR) ranging from 0 to 8. In order to characterize the assays used to quantitate total MC-vc-PAB-MMAE ADCs (conjugated and unconjugated antibody), we used purified fractions with defined DARs from 6 therapeutic antibodies to evaluate different assay formats and reagents. Our investigations revealed that for quantitation of total antibody, including all unconjugated and conjugated antibody species, sandwich ELISA formats did not always allow for recovery of all purified DAR fractions (DAR 0-8) to within ±20% of the expected values at the reagent concentrations tested. In evaluating alternative approaches, we found that the recovery of DAR fractions with semihomogeneous assay (SHA) formats, in which sample, capture, and detection reagents are preincubated in solution, were less affected by the antibody's MMAE drug load as compared to traditional stepwise sandwich ELISAs. Thus, choosing the optimal assay format and reagents for total antibody assays is valuable for developing accurate quantitative assays.