Building Machine Learning Small Molecule Melting Points and Solubility Models Using CCDC Melting Points Dataset

Predicting solubility of small molecules is a very difficult undertaking due to the lack of reliable and consistent experimental solubility data. It is well known that for a molecule in a crystal lattice to be dissolved, it must, first, dissociate from the lattice and then, second, be solvated. The melting point of a compound is proportional to the lattice energy, and the octanol-water partition coefficient (log P) is a measure of the compound's solvation efficiency. The CCDC's melting point dataset of almost one hundred thousand compounds was utilized to create widely applicable machine learning models of small molecule melting points. Using the general solubility equation, the aqueous thermodynamic solubilities of the same compounds can be predicted. The global model could be easily localized by adding additional melting point measurements for a chemical series of interest.

Indexing Ultrafast Shape-Based Descriptors in MongoDB to Identify TLR4 Pathway Agonists

A method is presented for an ultrafast shape-based search workflow for the screening of large compound collections, i.e., those of vendors. The three-dimensional shape of a molecule dictates its biological activity by enabling the molecule to fit into binding pockets of proteins. Quite often, distinctly different chemical compounds that have similar shapes can bind in a similar way. OpenEye pioneered an algorithm for comparing shapes of molecules by overlaying them in a computer and measuring differences between a query molecule and a target molecule. Overlaying shapes is a computationally intensive process and represents a bottleneck in searching for similar molecules. More recent publications describe alternative methods of overlaying molecules, which are accomplished by comparing shape-based descriptors. These methods were implemented in the Open Drug Discovery Toolkit (ODDT) package. We utilized a combination of open-source software packages like ODDT and RDkit to implement a workflow for ultrafast conformer generation and matching that does not require storing precomputed conformers on the file system or in memory. Moreover, the generated descriptors could be optionally stored in MongoDB for performing searches in the future. To speed up the search, we created a set of indexes from the transformed shape-based descriptors. We are in the process of calculating descriptors for multiple vendors, including Enamine's "REAL" collection of 1.2 billion compounds. Currently, the shape similarity search on more than 70 million compounds takes less than 8 s! We exemplified our methodology with the screen of compounds that can act as putative TLR4 agonists. The search was based on a literature-known small-molecule TLR4 agonist series. In due course, we identified compounds with novel structural motifs that were active in mouse and human TLR4 reporter cell lines.

NOTCH3-targeted antibody drug conjugates regress tumors by inducing apoptosis in receptor cells and through transendocytosis into ligand cells

Aberrant NOTCH3 signaling and overexpression is oncogenic, associated with cancer stem cells and drug resistance, yet therapeutic targeting remains elusive. Here, we develop NOTCH3-targeted antibody drug conjugates (NOTCH3-ADCs) by bioconjugation of an auristatin microtubule inhibitor through a protease cleavable linker to two antibodies with differential abilities to inhibit signaling. The signaling inhibitory antibody rapidly induces ligand-independent receptor clustering and internalization through both caveolin and clathrin-mediated pathways. The non-inhibitory antibody also efficiently endocytoses via clathrin without inducing receptor clustering but with slower lysosomal co-localization kinetics. In addition, DLL4 ligand binding to the NOTCH3 receptor mediates transendocytosis of NOTCH3-ADCs into ligand-expressing cells. NOTCH3-ADCs internalize into receptor and ligand cells independent of signaling and induce cell death in both cell types representing an atypical mechanism of ADC cytotoxicity. Treatment of xenografts with NOTCH3-ADCs leads to sustained tumor regressions, outperforms standard-of-care chemotherapy, and allows targeting of tumors that overexpress NOTCH3 independent of signaling inhibition.

NOTCH3 receptor is overexpressed in breast, lung, and ovarian tumors

Newly generated NOTCH3-targeted antibody drug conjugates are efficacious and safe

NOTCH3 antibodies internalize through different routes depending on signaling status

NOTCH3 antibody intercellular trafficking occurs by transendocytosis into ligand cells

Development of Highly Optimized Antibody-Drug Conjugates against CD33 and CD123 for Acute Myeloid Leukemia

PURPOSE

Mortality due to acute myeloid leukemia (AML) remains high, and the management of relapsed or refractory AML continues to be therapeutically challenging. The reapproval of Mylotarg, an anti-CD33-calicheamicin antibody-drug conjugate (ADC), has provided a proof of concept for an ADC-based therapeutic for AML. Several other ADCs have since entered clinical development of AML, but have met with limited success. We sought to develop a next-generation ADC for AML with a wide therapeutic index (TI) that overcomes the shortcomings of previous generations of ADCs.

EXPERIMENTAL DESIGN

We compared the TI of our novel CD33-targeted ADC platform with other currently available CD33-targeted ADCs in preclinical models of AML. Next, using this next-generation ADC platform, we performed a head-to-head comparison of two attractive AML antigens, CD33 and CD123.

RESULTS

Our novel ADC platform offered improved safety and TI when compared with certain currently available ADC platforms in preclinical models of AML. Differentiation between the CD33- and CD123-targeted ADCs was observed in safety studies conducted in cynomolgus monkeys. The CD33-targeted ADC produced severe hematologic toxicity, whereas minimal hematologic toxicity was observed with the CD123-targeted ADC at the same doses and exposures. The improved toxicity profile of an ADC targeting CD123 over CD33 was consistent with the more restricted expression of CD123 in normal tissues.

CONCLUSIONS

We optimized all components of ADC design (i.e., leukemia antigen, antibody, and linker-payload) to develop an ADC that has the potential to translate into an effective new therapy against AML.

Abstract 935: Generation and preclinical characterization of CD123-CPI antibody-drug conjugate (ADC)

CD123 is expressed on cancer cells in a variety of hematologic malignancies including acute myeloid leukemia (AML). CD123 is frequently expressed on leukemic blasts and leukemic stem cells (LSCs), a cell population associated with relapse in patients, but there is minimal or no expression on most normal hematopoietic cells and solid tissues. Thus, CD123 is a promising target for AML. We have generated an anti-CD123 ADC that carries cyclopropylpyrroloindoline (CPI) payload that crosslinks DNA. A drug loading of 2 molecules of CPI per molecule of antibody was achieved by site-specific conjugation using our transglutaminase methodology. Upon binding to the CD123 antigen, CD123-ADC is internalized and delivered to the endosomal-lysosomal pathway whereupon the CPI payload is released from the antibody by proteolysis of the linker. The released CPI alkylates DNA, which activates ATR/ATM, CHK1, CHK2 and FANCD2, ultimately resulting in cell death. In vitro, CD123–CPI elicited cytotoxicity in a dose-dependent manner against several CD123-positive, but not against CD123-negative cell lines. Cell lines with higher CD123 expression level were more sensitive to the ADC. Long-Term Culture-Initiating Cells in vitro assay showed that AML patient bone marrow samples that naturally have high percentage of LSCs yielded substantially fewer colonies in CD123-ADC treated cells compared to control ADC. Importantly, CD123-ADC had no adverse effects in healthy donor bone marrow cells experimentally enriched in CD34+ primitive stem cells. This result suggests that CD123-ADC specifically inhibits the growth potential of leukemic blasts and progenitor cells. In vivo, robust antileukemic activity was observed in CD123-positive AML cell line-derived xenograft models. Low doses of CD123-ADC effectively regressed tumors whereas the tumor progressed in mice that received control ADC. Efficacy was also evaluated in disseminated AML PDX models (n≥7) established with patient samples of various cytogenetics and molecular abnormalities, and relapse/refractory. Flow cytometry analyses of leukemic load in peripheral blood and in bone marrow samples of mice showed that CD123-ADC was efficacious in reducing tumor burden even at the suboptimal doses. In summary, our data demonstrate that our CD123-ADC is highly active in a broad panel of primary AML samples. Currently, CD123-ADC in combination with other AML therapies is being tested in vivo. All these attributes of CD123-ADC make it an attractive agent to evaluate in clinical trials.

Citation Format: Yoon-Chi Han, Fan Jiang, Nicole Piche-Nicholas, Madan Katragadda, Nadira Prashad, Manoj Charati, Wendy Hu, Mauricio Leal, Nathan Tumey, Andreas Maderna, Russell Dushin, Kenny Kim, LuAnna Lemon, Marc Damelin, HP Gerber, Lioudmila Tchistiakova, Frank Loganza, Chris O'Donnell, Puja Sapra. Generation and preclinical characterization of CD123-CPI antibody-drug conjugate (ADC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 935.

Abstract 3095: The development of CPI as a novel, next-generation DNA-targeting payload for ADCs

DNA targeting drugs represent one of cornerstones of anti-cancer therapy for both hematologic and solid tumor indications. Low potency anti-DNA compounds (e.g. platins, anthracyclines) are included in many standard-of-care (SOC) regimens, however their modest activity and overall toxicity profiles limit their therapeutic potential. To increase the therapeutic window for DNA-damaging agents, high potency anti-DNA compounds with enhanced anti-tumor activity have been delivered to tumors as payloads of targeting modalities such as antibody-drug conjugates (ADCs). Herein, we describe the development of a novel DNA-damaging compound comprised of a dimeric structure of cyclopropylpyrrolo[e]indolones (CPIs) that was designed to alkylate DNA and generate toxic interstrand crosslinks (ICLs). In response to the CPI-induced formation of ICLs, CPI treatment of cells primarily activates the Fancomia anemia DNA damage response pathway, whereas other successful DNA-damaging ADC payloads such as calicheamicin activate double-strand break response pathways. CPI shows ~860-fold greater potency than calicheamicin in a panel of cell lines derived from a broad spectrum of tumor indications. Importantly, this new CPI payload retains potent activity in calicheamicin- and SOC-resistant tumor models (including overcoming overexpression of drug efflux pumps). When evaluated as payloads on anti-CD33 targeting ADCs, the CPI conjugate showed dramatically improved efficacy over the corresponding calicheamicin conjugates in MDR+ tumor models. As a site-specific conjugate, the CPI ADC shows enhanced in vivo stability and possesses a wider therapeutic window than the corresponding conventional calicheamicin conjugate and other leading DNA-damaging conjugates on the CD33 platform.

Citation Format: Jennifer Kahler, Maureen Dougher, Jane Xu, Matthew Doroski, Andreas Maderna, Russell Dushin, Stephane Thibault, Mauricio Leal, Madan Katragadda, Christopher J. O'Donnell, Matthew Sung, Puja Sapra. The development of CPI as a novel, next-generation DNA-targeting payload for ADCs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3095. doi:10.1158/1538-7445.AM2017-3095

Abstract 1697: Therapeutic targeting the NOTCH3 receptor with antibody drug conjugates

Activation and mutation of the NOTCH signaling pathway is oncogenic in many tissue types and the target of multiple anti-cancer therapies currently in clinical development. Initial therapeutic strategies designed to target the NOTCH pathway have focused on inhibition of aberrant signaling, but can have undesirable side-effects or insufficient anti-tumor activity. Antibody drug conjugates (ADCs) are an emerging therapeutic modality that equips antibodies with potent cytotoxic payloads that can be directly delivered to tumor cells. We have developed and compared anti-NOTCH3 ADCs using two different classes of therapeutic anti-NOTCH3 antibodies that target the juxtamembrane Negative Regulatory Region (NRR). The first class is unable to stabilize the NOTCH3-NRR in an auto-inhibitory conformation in the presence of ligand and does not block ADAM protease cleavage of the receptor. The second class contains an antibody that exhibits potent signaling inhibition by stabilizing the NRR in an inactive state. Despite antagonizing NOTCH3 signaling, the inhibitory anti-NOTCH3 antibody was unable to regress preclinical tumor xenografts with active NOTCH3 signaling. To enhance their potency, both classes of anti-NOTCH3 antibodies were conjugated to an auristatin-based microtubule inhibitor through a cleavable linker. Unexpectedly, the inhibitory anti-NOTCH3 antibody demonstrated more rapid trafficking to the lysosome than the non-inhibitory antibody suggesting that the two antibodies have distinct internalization routes with important implications for NOTCH3-ADC pharmacology. Pharmacodynamic biomarker analysis demonstrated anti-NOTCH3 ADCs disrupted the mitotic spindle apparatus, induced cell cycle arrest and triggered apoptosis. Anti-NOTCH3 ADCs exhibited robust anti-tumor activity and induce prolonged tumor regressions in preclinical models of breast, lung and ovarian cancer regardless of their ability to block signaling. Furthermore, anti-NOTCH3 ADC treatment was able to regress OVCAR3 ovarian tumor xenografts that were refractory to a platinum-based agent or relapsed anti-VEGF therapy. Our studies demonstrate that anti-NOTCH3 ADCs had enhanced efficacy compared to other NOTCH signaling inhibitors and also allowed targeting of tumors that over-expressed NOTCH3 but were not necessarily addicted to its signaling. The safety and efficacy of the non-inhibitory anti-NOTCH3 ADC, PF-06650808, is currently being examined in a Ph1 clinical trial (Protocol B7501001).

Citation Format: Kenneth G. Geles, Yijie Gao, Latha Sridharan, Andreas Giannakou, Ting-Ting Yamin, Jonathan Golas, Judy Lucas, Manoj Charati, Xiantang Li, Magali Guffroy, Tim Nichols, Kai Wang, Max Follettie, Andreas Maderna, Lioudmila Tchistiakova, Hans-Peter Gerber, Puja Sapra. Therapeutic targeting the NOTCH3 receptor with antibody drug conjugates. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1697. doi:10.1158/1538-7445.AM2015-1697

Novel Anti-TM4SF1 Antibody-Drug Conjugates with Activity against Tumor Cells and Tumor Vasculature

Antibody-drug conjugates (ADC) represent a promising therapeutic modality for managing cancer. Here, we report a novel humanized ADC that targets the tetraspanin-like protein TM4SF1. TM4SF1 is highly expressed on the plasma membranes of many human cancer cells and also on the endothelial cells lining tumor blood vessels. TM4SF1 is internalized upon interaction with antibodies. We hypothesized that an ADC against TM4SF1 would inhibit cancer growth directly by killing cancer cells and indirectly by attacking the tumor vasculature. We generated a humanized anti-human TM4SF1 monoclonal antibody, v1.10, and armed it with an auristatin cytotoxic agent LP2 (chemical name mc-3377). v1.10-LP2 selectively killed cultured human tumor cell lines and human endothelial cells that express TM4SF1. Acting as a single agent, v1.10-LP2 induced complete regression of several TM4SF1-expressing tumor xenografts in nude mice, including non-small cell lung cancer and pancreas, prostate, and colon cancers. As v1.10 did not react with mouse TM4SF1, it could not target the mouse tumor vasculature. Therefore, we generated a surrogate anti-mouse TM4SF1 antibody, 2A7A, and conjugated it to LP2. At 3 mpk, 2A7A-LP2 regressed several tumor xenografts without noticeable toxicity. Combination therapy with v1.10-LP2 and 2A7A-LP2 together was more effective than either ADC alone. These data provide proof-of-concept that TM4SF1-targeting ADCs have potential as anticancer agents with dual action against tumor cells and the tumor vasculature. Such agents could offer exceptional therapeutic value and warrant further investigation. Mol Cancer Ther; 14(8); 1868-76. ©2015 AACR.

Recent advances in the development of new auristatins: structural modifications and application in antibody drug conjugates

Dolastatin 10 is a powerful antineoplastic agent and microtubule inhibitor that was discovered by Pettit et al. and published in 1987. Since then, many research groups have engaged in SAR studies of synthetic analogues, termed "auristatins". It was eventually discovered that auristatins are of great value as payloads in antibody drug conjugates (ADCs), which led to the FDA-approved ADC brentuximab vedotin (Seattle Genetics). Currently, over 30 ADCs in clinical trials employ auristatins as payloads, and there is a great interest in the research community, both on academic and industrial sides, to further study these analogues. This review will provide an overview of the recent advancements in auristatin development spanning a time frame of about the past ten years. The main focus will be to describe structural changes made to the auristatin peptide and their resulting biological activities in tumor cell proliferation assays. Selected ADC examples will also be described.

Tumor cells chronically treated with a trastuzumab-maytansinoid antibody-drug conjugate develop varied resistance mechanisms but respond to alternate treatments

Antibody-drug conjugates (ADC) are emerging as clinically effective therapy. We hypothesized that cancers treated with ADCs would acquire resistance mechanisms unique to immunoconjugate therapy and that changing ADC components may overcome resistance. Breast cancer cell lines were exposed to multiple cycles of anti-Her2 trastuzumab-maytansinoid ADC (TM-ADC) at IC80 concentrations followed by recovery. The resistant cells, 361-TM and JIMT1-TM, were characterized by cytotoxicity, proteomic, transcriptional, and other profiling. Approximately 250-fold resistance to TM-ADC developed in 361-TM cells, and cross-resistance was observed to other non-cleavable-linked ADCs. Strikingly, these 361-TM cells retained sensitivity to ADCs containing cleavable mcValCitPABC-linked auristatins. In JIMT1-TM cells, 16-fold resistance to TM-ADC developed, with cross-resistance to other trastuzumab-ADCs. Both 361-TM and JIMT1-TM cells showed minimal resistance to unconjugated mertansine (DM1) and other chemotherapeutics. Proteomics and immunoblots detected increased ABCC1 (MRP1) drug efflux protein in 361-TM cells, and decreased Her2 (ErbB2) in JIMT1-TM cells. Proteomics also showed alterations in various pathways upon chronic exposure to the drug in both cell models. Tumors derived from 361-TM cells grew in mice and were refractory to TM-ADC compared with parental cells. Hence, acquired resistance to trastuzumab-maytansinoid ADC was generated in cultured cancer cells by chronic drug treatment, and either increased ABCC1 protein or reduced Her2 antigen were primary mediators of resistance. These ADC-resistant cell models retain sensitivity to other ADCs or standard-of-care chemotherapeutics, suggesting that alternate therapies may overcome acquired ADC resistance. Mol Cancer Ther; 14(4); 952-63. ©2015 AACR.

Discovery of cytotoxic dolastatin 10 analogues with N-terminal modifications

Auristatins, synthetic analogues of the antineoplastic natural product Dolastatin 10, are ultrapotent cytotoxic microtubule inhibitors that are clinically used as payloads in antibody-drug conjugates (ADCs). The design and synthesis of several new auristatin analogues with N-terminal modifications that include amino acids with α,α-disubstituted carbon atoms are described, including the discovery of our lead auristatin, PF-06380101. This modification of the peptide structure is unprecedented and led to analogues with excellent potencies in tumor cell proliferation assays and differential ADME properties when compared to other synthetic auristatin analogues that are used in the preparation of ADCs. In addition, auristatin cocrystal structures with tubulin are being presented that allow for the detailed examination of their binding modes. A surprising finding is that all analyzed analogues have a cis-configuration at the Val-Dil amide bond in their functionally relevant tubulin bound state, whereas in solution this bond is exclusively in the trans-configuration. This remarkable observation shines light onto the preferred binding mode of auristatins and serves as a valuable tool for structure-based drug design.

Abstract 2669: Targeting the tumor vasculature with antibody drug conjugates

Clinical use of vascular targeting antibody drug conjugates (VT-ADCs) has not yet been explored. Herein, we preclinically demonstrate utility, mechanisms and advantages of VT-ADCs as targeted cancer therapeutics. A monoclonal human IgG1 antibody selective for murine VEGFR2 (B3) is non-VEGF-A neutralizing and traffics to the lysosome. B3 was conjugated to a proprietary auristatin microtubule inhibitor with a non-cleavable maleimidocaproyl linker, resulting in the proof-of-concept VT-ADC, B3-mcMTI. In vitro, free-payload and anti-VEGFR2-mcMTI selectively inhibit proliferating endothelial cells (ECs) with pM and low nM IC50s - suggesting that even with a broadly expressed, low-level target, a VT-ADC should be potent and tumor specific. To test this in vivo, we treated three cell line xenografts (CLX, HT29, Ls174T, A498) and a colorectal carcinoma patient derived xenograft (CRC PDX) with B3-mcMTI at 3 mg/kg q4d, resulting in tumor stasis in four models. In the HT29 colon carcinoma CLX and the CRC PDX model, B3-mcMTI was superior to VEGF-neutralizing antibody G6-31 (anti-VEGF mAb). In standard-of-care (SOC) chemotherapy (irinotecan and 5-FU) combination studies in HT29, B3-mcMTI had improved anti-tumor activity over SOC alone, and, moreover, was as effective in inhibiting tumor growth as a single agent ADC as anti-VEGF mAb combined with SOC. In the 4T1 orthotopic anti-VEGF resistant breast carcinoma setting, B3-mcMTI outperformed anti-VEGF mAb, and when combined with SOC (paclitaxel) demonstrated improved activity over single agent without an increase in metastases. B3-mcMTI internalization in endothelial cells is VEGFR2-mediated, with antibody binding and active payload releasing in normal and tumor tissues at concentrations above the in vitro IC50s; however, payload activity as measured by quantitative image analysis of pharmacodynamic biomarkers such as phospho-Histone H3 and cleaved caspase 3 is overwhelmingly localized to tumor ECs. Targeted vessels are smooth muscle invested, suggesting that VT-ADCs may target vasculature that contributes to anti-VEGF resistance. In conclusion, VT-ADCs are effective both as single agents and when combined with SOC, and VT-ADCs may overcome resistance mechanisms to standard anti-angiogenics. Taken together, these data suggest that payloads selective for proliferating ECs enable ADC-mediated targeting of widely expressed EC surface proteins, supporting the clinical pursuit of VT-ADCs.

Citation Format: Andrea T. Hooper, Chao-Pei Betty Chang, Kimberly Marquette, Jonathon Golas, Justin Lucas, Timothy Nichols, Judy Lucas, Gavriil Maria, Edward Rosfjord, Anton Xavier, Nathan Scott, Sadhana Jain, Wei Cao, Mauricio Leal, Andreas Maderna, Magali Guffroy, Xiang Zheng, Lioudmila Tchistiakova, Frank Loganzo, Hans-Peter Gerber, Chad May. Targeting the tumor vasculature with antibody drug conjugates. [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 2669. doi:10.1158/1538-7445.AM2014-2669

New cytotoxic benzosuberene analogs. Synthesis, molecular modeling and biological evaluation

In this Letter we describe the synthesis and biological evaluation of new benzosuberene analogs with structural modifications on the B-ring. The focus was initially to probe the chemical space around the B-ring C-8 position. This position was readily available for derivatization chemistry using our recently developed new synthesis for this compound class. Furthermore, we describe two new B-ring analogs, one containing a diene and the other a cyclic ether group. Both new analogs show excellent potencies in tumor cell proliferation assays. In addition, we describe molecular modeling studies that provide a binding rationale for reference compound 8 in the colchicine binding site using the known colchicine crystal structure. We also examine whether the cell based potency data obtained with selected new analogs are supported by modeling results.

Abstract 5471: Notch-antibody drug conjugates have a different mechanism of action than Notch signaling inhibitors and induce tumor regression

There are four different Notch receptors in mammalian cells that have overlapping patterns of expression in embryonic and adult tissues, but fulfill non-redundant roles during hematopoietic stem cell specification, T cell development, intestinal crypt cell specification and vascular development. Notch receptors are over-expressed or amplified in certain human tumors and regulate cell proliferation, differentiation, and survival through an intracellular domain that functions as a transcriptional activator. Several strategies are in development to block Notch signaling for therapeutic purposes in cancer, including gamma-secretase inhibitors that block all Notch signaling and antibody-based targeting of individual receptors. However, blocking pathway activation with inhibitory antibodies has proven to be less efficacious than originally anticipated. Therefore, we have targeted Notch with antibody-drug conjugates (ADCs) that combine the specificity of high affinity anti-Notch antibodies with the cytotoxicity of microtubule inhibitors. These ADCs enhance efficacy and also allow targeting in tumors that overexpress Notch but are not driven by its signaling. Notch antibodies were conjugated though cleavable and non-cleavable linkers to novel tubulin inhibitor-based payloads. Notch-ADCs inhibited the in vitro growth of lung, breast and ovarian cancer cell lines in the low ng/ml range and in vivo regressed the growth of established human tumor xenografts. Our data demonstrate that Notch-ADCs are more potent than small molecule inhibitors and unconjugated antibodies, and induce sustained tumor regression in pre-clinical models.

Citation Format: Kenneth G. Geles, Yijie Gao, Latha Sridharan, Andreas Giannakou, Ting-Ting Yamin, Jonathan Golas, Manoj Charati, Kiran Khandke, Judy Lucas, Andreas Maderna, Christopher J. O'Donnell, Lioudmila Tchistiakova, Hans-Peter Gerber, Puja Sapra. Notch-antibody drug conjugates have a different mechanism of action than Notch signaling inhibitors and induce tumor regression. [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 5471. doi:10.1158/1538-7445.AM2013-5471

Abstract 2530: Long-term tumor regression induced by a novel antibody drug conjugate that targets 5T4, an oncofetal antigen expressed on tumor-initiating cells

Antibody-drug conjugates (ADCs) represent a promising therapeutic modality for the clinical management of cancer. We have developed a novel ADC that targets 5T4 (also known as TPBG), a tumor-associated antigen that rapidly internalizes. In preclinical models of NSCLC, 5T4 was identified as a marker of undifferentiated tumorigenic cells that express properties of tumor-initiating cells (TICs) and was associated with a highly proliferating (Ki67 positive) cell phenotype. Based on the biological properties of 5T4, we designed the ADC by conjugating an internalizing humanized anti-5T4 antibody (Ab), A1, to the tubulin inhibitor monomethylauristatin F via a maleimidocaproyl (mc) linker (A1mcMMAF) with a drug/antibody ratio of ∼ 4. The A1 Ab has a Kd of 0.9 nM against the 5T4 antigen, binds to a broad range of 5T4 expressing cell lines, and rapidly internalizes (66% internalized within 4h). As an ADC, A1mcMMAF retains similar properties to the unconjugated Ab. In vitro, A1mcMMAF exhibited potent and target-specific cytotoxic activity against a panel of 5T4+ cell lines with an IC50 of 5 ng Ab/ml against high 5T4 expressing cells. In vivo, A1mcMMAF exhibited potent anti-tumor activity in all five tumor models tested (with a broad range of 5T4 expression) and caused long-term regressions monitored up to 100 days after the last dose. Strikingly, animals were cured of disease in every model with doses as low as 3 mg Ab/kg Q4d x 4. In a lung cancer patient-derived xenograft in which 5T4 is not uniformly expressed, but instead is preferentially expressed on the less differentiated sub-population of tumor cells, A1mcMMAF treatment resulted in sustained tumor regression. This result highlights the clinical potential of ADCs that target aggressive cell subpopulations such as TICs. In exploratory safety studies, A1mcMMAF exhibited no overt toxicities when administered at 10 mg Ab/kg/cycle x 2 to cynomolgus monkeys and had a half-life of ∼5 days. The encouraging efficacy and safety data of the conjugate resulting in high therapeutic index in preclinical models warrants further clinical testing of this ADC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2530. doi:1538-7445.AM2012-2530

Abstract A215: Antitumor activity of an antibody-drug conjugate targeting 5T4, a putative tumor-initiating cell antigen

5T4 (also known as TPBG) is a transmembrane, tumor-associated protein that rapidly internalizes. In preclinical models of NSCLC, 5T4 was identified as a marker of undifferentiated tumorigenic cells that express properties of tumor-initiating cells (TICs) and was associated with a highly proliferating (Ki67 positive) cell phenotype. In addition, 5T4 has been associated with a worse clinical outcome in NSCLC (Damelin et al, Cancer Res, 2011). We constructed an ADC with a humanized anti-5T4 Ab (A1) linked to the tubulin inhibitor monomethylauristatin F through the noncleavable maleimidocaproyl (mc) linker attached to cysteine residues (A1mcMMAF) with a DAR of approximately 4 in order to target 5T4 expressing tumor cells. Anti-5T4 A1 Ab has a Kd of 0.9 nM against the 5T4 antigen, binds to a broad range of 5T4 expressing cell lines, and rapidly internalizes (66% internalized within 4h). As an ADC, A1mcMMAF retains similar properties to the unconjugated Ab. In vitro, A1mcMMAF exhibited receptor-density dependent cytotoxic activity against a panel of 5T4 + cell lines with an IC50 of 5 ng Ab/ml against high 5T4 expressing cells. A1mcMMAF exerts no inhibitory effect on 5T4 negative cells demonstrating it does not exert off-target activity in vitro. In vivo, A1mcMMAF causes long-term (100 days) tumor regressions at 10 mg Ab/kg in MDAMB435/5T4 tumor xenografts (Q4d×2, high 5T4 expression by IHC) and in the NSCLC patient-derived xenograft 37622A model (Q4d×4, high 5T4 expression by IHC though only a portion of the cells express 5T4). Significant anti-tumor activity was demonstrated at 1 mg/kg. Against the low 5T4 expressing H1975 tumor xenograft, A1mcMMAF causes potent tumor regression in spite of its lack of in vitro inhibitory activity against this cell line. Bioimaging of the H1975 tumor demonstrated good penetration of Alexa 750 labeled A1 Ab into the xenograft. A1mcMMAF exhibited no overt toxicities when administered at 10 mg Ab/kg/cycle × 2 to cynomolgus macques and possessed a half-life of 4 to 7 days. The observation that A1mcMMAF regresses H1975 tumor xenografts while demonstrating poor activity against H1975 in vitro demonstrates the attractiveness of targeting 5T4 in the tumor environment and may be explained by 5T4's principal association with proliferating cells in the tumor. It is also interesting that A1mcMMAF was able to completely regress 37622A xenografts since this patient-derived xenograft presents heterogeneous 5T4 expression, i.e. not all cells demonstrate detectable levels of 5T4.

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 A215.

RDEA119/BAY 869766: a potent, selective, allosteric inhibitor of MEK1/2 for the treatment of cancer

The RAS-RAF-mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)-ERK pathway provides numerous opportunities for targeted oncology therapeutics. In particular, the MEK enzyme is attractive due to high selectivity for its target ERK and the central role that activated ERK plays in driving cell proliferation. The structural, pharmacologic, and pharmacokinetic properties of RDEA119/BAY 869766, an allosteric MEK inhibitor, are presented. RDEA119/BAY 869766 is selectively bound directly to an allosteric pocket in the MEK1/2 enzymes. This compound is highly efficacious at inhibiting cell proliferation in several tumor cell lines in vitro. In vivo, RDEA119/BAY 869766 exhibits potent activity in xenograft models of melanoma, colon, and epidermal carcinoma. RDEA119/BAY 869766 exhibits complete suppression of ERK phosphorylation at fully efficacious doses in mice. RDEA119/BAY 869766 shows a tissue selectivity that reduces its potential for central nervous system-related side effects. Using pharmacokinetic and pharmacodynamic data, we show that maintaining adequate MEK inhibition throughout the dosing interval is likely more important than achieving high peak levels because greater efficacy was achieved with more frequent but lower dosing. Based on its longer half-life in humans than in mice, RDEA119/BAY 869766 has the potential for use as a once- or twice-daily oral treatment for cancer. RDEA119/BAY 869766, an exquisitely selective, orally available MEK inhibitor, has been selected for clinical development because of its potency and favorable pharmacokinetic profile.

Identification of isothiazole-4-carboxamidines derivatives as a novel class of allosteric MEK1 inhibitors

The development of potent, orally bioavailable, and selective series of 5-amino-3-hydroxy-N(1-hydroxypropane-2-yl)isothiazole-4-carboxamidine inhibitors of MEK1 and MEK-2 kinase is described. Optimization of the carboxamidine and the phenoxyaniline group led to the identification of 55 which gave good potency as in vitro MEK1 inhibitors, and good oral exposure in rat.

Organic Syntheses on an Icosahedral Borane Surface: Closomer Structures with Twelvefold Functionality

The syntheses of a series of novel ester-linked derivatives of the icosahedral [closo-B12(OH)12]2- boron cluster (closomer esters) are described using several synthetic methods. The reaction of bis(tetrabutylammonium)-closo-dodecahydroxy-dodecaborate, [NBu4]2 1, with carboxylic acid chlorides and anhydrides, vinyl esters with a Y5(OiPr)13O catalyst and 1,1'-carbonyldiimidazole-activated carboxylic acids yields the corresponding dianionic dodeca-ester closomers. The method using 1,1'-carbonyldiimidazole-activated carboxylic acids may be employed as a general synthetic strategy. The use of elevated reaction temperatures, achievable under pressure, to expedite syntheses is described. An attractive methodology using immobilized scavenger reagents for the expeditious purification of the closomer esters was employed. The developed methodology is compatible with a variety of peripheral functional groups attached to the termini of densely packed, carboxylate ester-linked radial arms bonded to the icosahedral borane surface. A closomer ester having twelve terminal amino groups was prepared, and without isolation, fully acetylated in good yield.

Microwave-Assisted Allylation of Acetals with Allyltrimethylsilane in the Presence of CuBr

We describe the first synthesis of homoallyl ethers from acetals and allyltrimethylsilane using microwave heating and CuBr as a promoter. This method works best for aromatic acetals, giving the corresponding homoallyl ethers in good to quantitative yield.

Synthesis of a porphyrin-labelled carboranyl phosphate diester: a potential new drug for boron neutron capture therapy of cancer

A boron-rich, water-soluble porphyrin conjugate was synthesized by coupling of two carboranyl alcohols with 2-chlorophenoxyphosphorus dichloride, followed by conjugation to an amine-functionalized tetraphenyl-porphyrin via an amide linkage.

Twelvefold Functionalization of an Icosahedral Surface by Total Esterification of [B12(OH)12]2-: 12(12)-Closomers

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