Structure-Cytotoxicity Relationships of Analogues of N14-Desacetoxytubulysin H

Herein we report structure-cytotoxicity relationships for analogues of N¹⁴-desacetoxytubulyisn H 1. A novel synthetic approach toward 1 enabled the discovery of compounds with a range of activity. Calculated basicity of the N-terminus of tubulysins was shown to be a good predictor of cytotoxicity. The impact of structural modifications at the C-terminus of 1 upon cytotoxicity is also described. These findings will facilitate the development of new tubulysin analogues for the treatment of cancer.

Straightforward Glycoengineering Approach to Site-Specific Antibody-Pyrrolobenzodiazepine Conjugates

Antibody-drug conjugates (ADCs) have become a powerful platform to deliver cytotoxic agents selectively to cancer cells. ADCs have traditionally been prepared by stochastic conjugation of a cytotoxic drug using an antibody's native cysteine or lysine residues. Through strategic selection of the mammalian expression host, we were able to introduce azide-functionalized glycans onto a homogeneously glycosylated anti-EphA2 monoclonal antibody in one step. Conjugation with an alkyne-bearing pyrrolobenzodiazepine dimer payload (SG3364) using copper-catalyzed click chemistry yielded a site-specific ADC with a drug-to-antibody ratio (DAR) of four. This ADC was compared with a glycoengineered DAR two site-specific ADC, and both were found to be highly potent against EphA2-positive human prostate cancer cells in both an in vitro cytotoxicity assay and a murine tumor xenograft model.

A Biparatopic HER2-Targeting Antibody-Drug Conjugate Induces Tumor Regression in Primary Models Refractory to or Ineligible for HER2-Targeted Therapy

Antibody-drug conjugate (ADC) which delivers cytotoxic drugs specifically into targeted cells through internalization and lysosomal trafficking has emerged as an effective cancer therapy. We show that a bivalent biparatopic antibody targeting two non-overlapping epitopes on HER2 can induce HER2 receptor clustering, which in turn promotes robust internalization, lysosomal trafficking, and degradation. When conjugated with a tubulysin-based microtubule inhibitor, the biparatopic ADC demonstrates superior anti-tumor activity over ado-trastuzumab emtansine (T-DM1) in tumor models representing various patient subpopulations, including T-DM1 eligible, T-DM1 ineligible, and T-DM1 relapsed/refractory. Our findings indicate that this biparatopic ADC has promising potential as an effective therapy for metastatic breast cancer and a broader patient population may benefit from this unique HER2-targeting ADC.

Abstract B170: Discovery of tubulysin payloads for antibody drug conjugates with potent in vitro activity and in vivo efficacy in solid tumor models

Antibody drug conjugates (ADCs) combine the specificity of antibodies with the potency of small molecule cytotoxic drugs and have the potential to provide significant efficacy as a treatment for cancer. The objective of this work was to identify potent new cytotoxic ADC payloads that can be used to target diverse tumor types. Here we report for the first time the discovery of fully synthetic tubulysin payloads which belong to a class of highly cytotoxic natural products that disrupt the cellular microtubule network leading to apoptosis of tumor cells. Our fully synthetic tubulysin payloads are comprised of: (i) a tubulysin warhead that displays pM potency, (ii) a protease cleavable amino-acid sequence and (iii) a tether bearing a reactive maleimide group. Tubulysin-based ADCs were generated via site-specific conjugation of these payloads to cysteines engineered into antibodies against cancer antigen target oncofetal protein 5T4. The resulting ADCs showed potent in vitro cell killing and in vivo efficacy in multiple solid tumor xenograft models including prostate cancer, non-small cell lung adenocarcinoma, breast cancer and gastric carcinoma. Furthermore, specific structural features of the tubulysin warhead, linker design and antibody engineering were shown to impact the overall in vitro and in vivo properties of the ADCs. Thus, these synthetic tubulysin payloads represent novel microtubule network disrupting compounds that display potent preclinical anti-tumor activity as an ADC that could be advanced to the clinic.

Citation Format: Dorin Toader, Jay Harper, Chris Lloyd, Rose Marwood, David Bannister, Shenlan Mao, Cui (Tracy) Chen, Haihon (Helen) Zhong, Vahe Bedian, Fengjiang Wang, Lakshmaiah Gingipalli, Melisa Vasbinder, Pamela Thompson, Ryan Fleming, Byniam Bezabeh, Nazzareno Dimasi, Changshou Gao, Adeela Kamal. Discovery of tubulysin payloads for antibody drug conjugates with potent in vitro activity and in vivo efficacy in solid tumor models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B170.

Identification of azabenzimidazoles as potent JAK1 selective inhibitors

We have identified a class of azabenzimidazoles as potent and selective JAK1 inhibitors. Investigations into the SAR are presented along with the structural features required to achieve selectivity for JAK1 versus other JAK family members. An example from the series demonstrated highly selective inhibition of JAK1 versus JAK2 and JAK3, along with inhibition of pSTAT3 in vivo, enabling it to serve as a JAK1 selective tool compound to further probe the biology of JAK1 selective inhibitors.

Abstract 3601: Antibody-drug conjugates (ADCs) with tubulysin and PBD warheads, maintain potent in vitro cytotoxicity against multidrug-resistant tumor cells expressing P-glycoprotein (P-gp)

Development of resistance to initially-effective therapies remains a major challenge in the treatment of cancer. Resistance to antibody-drug conjugates (ADCs) can arise due to many factors including down-regulation of the target, modified internalization or trafficking of the internalized ADC/antigen complexes, decreased sensitivity to the warhead conjugated to the ADC, or combinations of these. One of the common mechanisms of resistance to ADCs is increased expression of efflux drug pumps such as P-glycoprotein (P-gp) which can then transport small molecule warheads out of the cell leading to multi-drug resistance (MDR). In fact, the warheads used in the two clinically-approved ADCs, Adcetris® and Kadcyla™, have been reported to be P-gp substrates and P-gp overexpression can lead to acquired resistance against these ADCs. Studies were conducted to determine if pyrrolobenzodiazepine (PBD) dimer or tubulysin warheads, and/or ADCs conjugated with these warheads were susceptible to P-gp-mediated resistance. The P-gp susceptibility of these warheads and associated ADCs was evaluated by comparing the relative cytotoxicity of warheads/ADCs in parental tumor cell lines compared to the same cell lines that have been manipulated to overexpress P-gp. Verapamil, an inhibitor of P-gp-mediated efflux, was used to confirm whether decreased sensitivity was due to P-gp activity. Unlike known P-gp substrates MMAE, paclitaxel, and vinblastine, the majority of PBD and tubulysin warheads tested were not significant P-gp substrates. These warheads and ADC's conjugated with these warheads potently induced cytotoxicity of the parental cancer cell lines, and maintained this potency in the same cell lines overexpressing P-gp. Interestingly, certain tubulysins had differential susceptibility to P-gp depending on whether they were conjugated or depending on the linker that was used. For example, one tubulysin warhead showed moderate susceptibility to P-gp-mediated efflux as a naked warhead, but ADCs conjugated with this warhead had equivocal efficacy in parental and P-gp-overexpressing cell lines. An alternative tubulysin warhead was equipotent as an unconjugated small molecule in either parental or P-gp-overexpressing cell lines, however an ADC conjugated with this warhead using a cleavable linker had no activity in the resistant cells; an effect that was reversible with verapamil treatment, confirming the role of P-gp. These data suggest that ADCs conjugated with either PBD or tubulysin warheads may be active in MDR settings where resistance is mediated by P-gp expression, however activity against MDR cancers may be dependent on the particular warhead that was used and/or the particular linker that is used to conjugate the warhead to the antibody.

Citation Format: Shenlan Mao, Ryan Fleming, Binyam Bezabeh, Nazzareno Dimasi, Dorin Toader, Thais Cailleau, Philip Howard, Changshou Gao, Bob Hollingsworth, Adeela Kamal, Jay Harper. Antibody-drug conjugates (ADCs) with tubulysin and PBD warheads, maintain potent in vitro cytotoxicity against multidrug-resistant tumor cells expressing P-glycoprotein (P-gp). [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 3601. doi:10.1158/1538-7445.AM2015-3601

Experimental demonstration of Martian soil simulant removal from a surface using a pulsed plasma jet

A plasma jet produced in a small coaxial plasma gun operated at voltages up to 2 kV and working in pure carbon dioxide (CO2) at a few Torr is used to remove Martian soil simulant from a surface. A capacitor with 0.5 mF is charged up from a high voltage source and supplies the power to the coaxial electrodes. The muzzle of the coaxial plasma gun is placed at a few millimeters near the dusty surface and the jet is fired parallel with the surface. Removal of dust is imaged in real time with a high speed camera. Mars regolith simulant JSC-Mars-1A with particle sizes up to 5 mm is used on different types of surfaces made of aluminium, cotton fabric, polyethylene, cardboard, and phenolic.

Collimated electron beam accelerated at 12 kV from a Penning discharge

A pulsed electron beam accelerated at 12 kV with a duration of 40 μs per pulse is obtained from a Penning discharge with a hollow anode and two cathodes. The electrons are extracted through a hole in one of the cathodes and focused by a pair of coils. The electron beam has a diameter of a few mm in the cross section, while the beam current reaches peak values of 400 mA, depending on the magnetic field inside the focussing coils. This relatively inexpensive and compact device is suitable for the irradiation of small material samples placed in high vacuum.

Abstract 2659: The MedImmune ADC platform: Building highly potent and specific cancer drugs

MedImmune has made a major commitment to developing antibody-drug conjugates for cancer. Our ADC initiative builds on our previous experience with this area and with other armed antibody technologies, which have generated several drugs currently undergoing clinical development. We have leveraged our expertise in antibody engineering to develop new antibody constructs for ADC development, including variants that facilitate site-specific conjugation of the payload to the antibody. This technology circumvents problems associated with random payload conjugation, resulting in a more homogeneous drug product as well as improving the stability and potency of the ADC. We have developed new, potent payloads, teaming up with Spirogen to apply their expertise in the pyrrolobenzodiazapine (PBD) dimer payload technology. The PBD payloads are versatile and potent, allowing use of multiple types of linkers and adjustment of potency to very high levels (picomolar IC50 range). The mechanism of action of the PBDs is different from other commonly used ADC payloads, inducing DNA damage that may evade DNA repair mechanisms and killing both bulk cancer cells and cancer stem cells. We have also developed other, novel ADC payloads. Our ADC target discovery approach permits rapid identification and validation of targets specifically suited for this technology. This includes the early generation and use of tool ADCs for target evaluation. We are applying this state-of-the-art ADC platform to advancing multiple projects as a major component of our oncology drug development strategy.

Citation Format: Robert E. Hollingsworth, Adeela Kamal, Philip W. Howard, John A. Hartley, David Tice, Changshou Gao, Nazzareno Dimasi, Haihong Zhong, Jay Harper, Zhan Xiao, Dorin Toader, Chris Martin, Herren Wu, Norman Greenberg, Bahija Jallal. The MedImmune ADC platform: Building highly potent and specific cancer drugs. [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 2659. doi:10.1158/1538-7445.AM2014-2659

Abstract 2459: Discovery of small molecule TAK1 inhibitors with antiproliferative activity in cell lines derived from hematological malignancies

Transforming growth factor β-activated kinase 1 (TAK1), a member of the MAPKKK family, is a key mediator of proinflammatory and stress signaling. It was shown previously that inhibition of TAK1 via the use of siRNA or small-molecule kinase inhibitors can inactivate NF-κB, down-regulate p38, and activate the intrinsic caspase pathway, resulting in profound induction of apoptosis. Herein we report the discovery of 5-fluoro-4-(imidazo[1,2-b]pyridazin-3-yl)-N-phenylpyrimidin-2-amines as TAK1 ATP competitive small molecule inhibitors. These compounds inhibit the kinase activity of TAK1 in vitro with low nanomolar potency. Evidence is presented that supports a mechanism of action consistent with inhibition of TAK1 kinase activity within the NF-κB pathway. Optimization of potency and selectivity for this series from hit to lead will be discussed, including the structure-based design and crystallographic determination of the binding mode. The outcome of efforts aimed at improving the in vivo pharmacokinetics of compounds is described. Results of kinase selectivity profiling for both an in vitro probe compound - AZ TAK1 - and an in vivo probe compound will be presented. Furthermore, we report low nanomolar antiproliferative activities in cell lines derived from Haematological Malignancies for these compounds. This cellular activity profile is suggesting that TAK1 inhibition presents therapeutic potential in Haematological Cancers.

Citation Format: Dorin Toader, Jamal C. Saeh, Nin Guan, Francoise Powell, Raymond Chen, Corinne Reimer, Kate Byth. Discovery of small molecule TAK1 inhibitors with antiproliferative activity in cell lines derived from hematological malignancies. [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 2459. doi:10.1158/1538-7445.AM2013-2459

Mechanism and in vitro pharmacology of TAK1 inhibition by (5Z)-7-Oxozeaenol

Transforming growth factor-β activated kinase-1 (TAK1) is a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family that regulates several signaling pathways including NF-κB signal transduction and p38 activation. TAK1 deregulation has been implicated in human diseases including cancer and inflammation. Here, we show that, in addition to its kinase activity, TAK1 has intrinsic ATPase activity, that (5Z)-7-Oxozeaenol irreversibly inhibits TAK1, and that sensitivity to (5Z)-7-Oxozeaenol inhibition in hematological cancer cell lines is NRAS mutation status and TAK1 pathway dependent. X-ray crystallographic and mass spectrometric studies showed that (5Z)-7-Oxozeaenol forms a covalent complex with TAK1. Detailed biochemical characterization revealed that (5Z)-7-Oxozeaenol inhibited both the kinase and the ATPase activity of TAK1 following a bi-phase kinetics, consistent with the irreversible inhibition mechanism. In DoHH2 cells, (5Z)-7-Oxozeaenol potently inhibited the p38 phosphorylation driven by TAK1, and the inhibition lasted over 6 h after withdrawal of (5Z)-7-Oxozeaenol. Profiling (5Z)-7-Oxozeaenol in a panel of hematological cancer cells showed that sensitive cell lines tended to carry NRAS mutations and that genes in TAK1 regulated pathways were enriched in sensitive cell lines. Taken together, we have elucidated the molecular mechanism of a TAK1 irreversible inhibitor and laid the foundation for designing next generation TAK1 irreversible inhibitors. The NRAS-TAK1-Wnt signaling network discerned in our study may prove to be useful in patient selection for TAK1 targeted agents in hematological cancers.

Discovery of checkpoint kinase inhibitor (S)-5-(3-fluorophenyl)-N-(piperidin-3-yl)-3-ureidothiophene-2-carboxamide (AZD7762) by structure-based design and optimization of thiophenecarboxamide ureas

Checkpoint kinases CHK1 and CHK2 are activated in response to DNA damage that results in cell cycle arrest, allowing sufficient time for DNA repair. Agents that lead to abrogation of such checkpoints have potential to increase the efficacy of such compounds as chemo- and radiotherapies. Thiophenecarboxamide ureas (TCUs) were identified as inhibitors of CHK1 by high throughput screening. A structure-based approach is described using crystal structures of JNK1 and CHK1 in complex with 1 and 2 and of the CHK1-3b complex. The ribose binding pocket of CHK1 was targeted to generate inhibitors with excellent cellular potency and selectivity over CDK1and IKKβ, key features lacking from the initial compounds. Optimization of 3b resulted in the identification of a regioisomeric 3-TCU lead 12a. Optimization of 12a led to the discovery of the clinical candidate 4 (AZD7762), which strongly potentiates the efficacy of a variety of DNA-damaging agents in preclinical models.

Structural approaches to obtain kinase selectivity

One of the grand challenges in kinase drug discovery is the design of small-molecule inhibitors with selectivity profiles that will ultimately be efficacious in the clinic. Current medicinal chemistry strategies make heavy use of structural, biophysical and computational approaches to achieve this multi-faceted goal. Here we review structure-based approaches underlying the development of several molecules that are currently in clinical trials, including the cMet inhibitor ARQ197 and the Bcr-Abl inhibitor ponatinib. We highlight the challenge posed by the emergence of resistance mutants and discuss promising lead generation strategies to obtain selective inhibitors of protein and lipid kinases such as targeting of specific sites, the use of fragment-based approaches and new chemical probes based on metal complexes.

Discovery of a novel class of 2-ureido thiophene carboxamide checkpoint kinase inhibitors

Checkpoint kinase-1 (Chk1, CHEK1) is a Ser/Thr protein kinase that mediates the cellular response to DNA-damage. A novel class of 2-ureido thiophene carboxamide urea (TCU) Chk1 inhibitors is described. Inhibitors in this chemotype were optimized for cellular potency and selectivity over Cdk1.

Structure-based design of protein tyrosine phosphatase-1B inhibitors

Using structure-based design, a new class of inhibitors of protein tyrosine phosphatase-1B (PTP1B) has been identified, which incorporate the 1,2,5-thiadiazolidin-3-one-1,1-dioxide template.

Syntheses of 2-alkylamino- and 2-dialkylamino-4,6-diarylpyridines and 2,4,6-trisubstituted pyrimidines using solid-phase-bound chalcones

Several substituted 2- and 4-hydroxyacetophenones are linked to Wang resin via a modified Mitsunobu protocol. These resin-bound acetophenones are condensed with aromatic aldehydes, and the resulting chalcones 5 are used for the synthesis of 2-dialkylamino- (9a-d) and 2-alkylamino-4,6-diarylpyridines (11a-f), and 2-alkyl-4,6-diaryl- (14a) and 2,4,6-triarylpyrimidines (14b,c) in a manner suitable for combinatorial applications.

Reactions of 1-(Benzotriazol-1-yl)-1-phenoxyalkane and (Benzotriazol-1-yl)ethoxy-phenylmethane Anions with Nitroarenes: A New Approach to Alkyl and Aryl p-Nitroaryl Ketones

p-Nitroaryl alkyl ketones and p-nitroaryl aryl ketones are prepared regioselectively by reactions of non-functionalized nitroarenes and benzotriazole stabilized carbanions.