Metabolism-driven in vitro/in vivo disconnect of an oral ERɑ VHL-PROTAC.

Targeting the estrogen receptor alpha (ERα) pathway is validated in the clinic as an effective means to treat ER+ breast cancers. Here we present the development of a VHL-targeting and orally bioavailable proteolysis-targeting chimera (PROTAC) degrader of ERα. In vitro studies with this PROTAC demonstrate excellent ERα degradation and ER antagonism in ER+ breast cancer cell lines. However, upon dosing the compound in vivo we observe an in vitro-in vivo disconnect. ERα degradation is lower in vivo than expected based on the in vitro data. Investigation into potential causes for the reduced maximal degradation reveals that metabolic instability of the PROTAC linker generates metabolites that compete for binding to ERα with the full PROTAC, limiting degradation. This observation highlights the requirement for metabolically stable PROTACs to ensure maximal efficacy and thus optimisation of the linker should be a key consideration when designing PROTACs.

Discovery of AZD4747, a Potent and Selective Inhibitor of Mutant GTPase KRASG12C with Demonstrable CNS Penetration.

The glycine to cysteine mutation at codon 12 of Kirsten rat sarcoma (KRAS) represents an Achilles heel that has now rendered this important GTPase druggable. Herein, we report our structure-based drug design approach that led to the identification of 14, AZD4747, a clinical development candidate for the treatment of KRASG12C-positive tumors, including the treatment of central nervous system (CNS) metastases. Building on our earlier discovery of C5-tethered quinazoline AZD4625, excision of a usually critical pyrimidine ring yielded a weak but brain-penetrant start point which was optimized for potency and DMPK. Key design principles and measured parameters that give high confidence in CNS exposure are discussed. During optimization, divergence between rodent and non-rodent species was observed in CNS exposure, with primate PET studies ultimately giving high confidence in the expected translation to patients. AZD4747 is a highly potent and selective inhibitor of KRASG12C with an anticipated low clearance and high oral bioavailability profile in humans.

Chemical Biology Approaches Confirm MCT4 as the Therapeutic Target of a Cellular Optimized Hit.

Lactic acid transport is a key process maintaining glycolytic flux in tumors. Inhibition of this process will result in glycolytic shutdown, impacting on cell growth and survival and thus has been pursued as a therapeutic approach for cancers. Using a cell-based screen in a MCT4-dependent cell line, we identified and optimized compounds for their ability to inhibit the efflux of intracellular lactic acid with good physical and pharmacokinetic properties. To deconvolute the mechanism of lactic acid efflux inhibition, we have developed three assays to measure cellular target engagement. Specifically, we synthesized a biologically active photoaffinity probe (IC50 < 10 nM), and using this probe, we demonstrated selective engagement of MCT4 of our parent molecule through a combination of confocal microscopy and in-cell chemoproteomics. As an orthogonal assay, the cellular thermal shift assay (CETSA) confirmed binding to MCT4 in the cellular system. Comparisons of lactic acid efflux potencies in cells with differential expression of MCT family members further confirmed that the optimized compounds inhibit the efflux of lactic acid through the inhibition of MCT4. Taken together, these data demonstrate the power of orthogonal chemical biology methods to determine cellular target engagement, particularly for proteins not readily amenable to traditional biophysical methods.

Discovery of Clinical Candidate AZD0095, a Selective Inhibitor of Monocarboxylate Transporter 4 (MCT4) for Oncology.

Due to increased reliance on glycolysis, which produces lactate, monocarboxylate transporters (MCTs) are often upregulated in cancer. MCT4 is associated with the export of lactic acid from cancer cells under hypoxia, so inhibition of MCT4 may lead to cytotoxic levels of intracellular lactate. In addition, tumor-derived lactate is known to be immunosuppressive, so MCT4 inhibition may be of interest for immuno-oncology. At the outset, no potent and selective MCT4 inhibitors had been reported, but a screen identified a triazolopyrimidine hit, with no close structural analogues. Minor modifications to the triazolopyrimidine were made, alongside design of a constrained linker and broad SAR exploration of the biaryl tail to improve potency, physical properties, PK, and hERG. The resulting clinical candidate 15 (AZD0095) has excellent potency (1.3 nM), MCT1 selectivity (>1000×), secondary pharmacology, clean mechanism of action, suitable properties for oral administration in the clinic, and good preclinical efficacy in combination with cediranib.

Optimization of hERG and Pharmacokinetic Properties for Basic Dihydro-8H-purin-8-one Inhibitors of DNA-PK.

The DNA-PK complex is activated by double-strand DNA breaks and regulates the non-homologous end-joining repair pathway; thus, targeting DNA-PK by inhibiting the DNA-PK catalytic subunit (DNA-PKcs) is potentially a useful therapeutic approach for oncology. A previously reported series of neutral DNA-PKcs inhibitors were modified to incorporate a basic group, with the rationale that increasing the volume of distribution while maintaining good metabolic stability should increase the half-life. However, adding a basic group introduced hERG activity, and basic compounds with modest hERG activity (IC50 = 10-15 µM) prolonged QTc (time from the start of the Q wave to the end of the T wave, corrected by heart rate) in an anaesthetized guinea pig cardiovascular model. Further optimization was necessary, including modulation of pK a, to identify compound 18, which combines low hERG activity (IC50 = 75 µM) with excellent kinome selectivity and favorable pharmacokinetic properties.

Discovery of AZD4625, a Covalent Allosteric Inhibitor of the Mutant GTPase KRASG12C.

KRAS is an archetypal high-value intractable oncology drug target. The glycine to cysteine mutation at codon 12 represents an Achilles heel that has now rendered this important GTPase druggable. Herein, we report our structure-based drug design approach that led to the identification of 21, AZD4625, a clinical development candidate for the treatment of KRASG12C positive tumors. Highlights include a quinazoline tethering strategy to lock out a bio-relevant binding conformation and an optimization strategy focused on the reduction of extrahepatic clearance mechanisms seen in preclinical species. Crystallographic analysis was also key in helping to rationalize unusual structure-activity relationship in terms of ring size and enantio-preference. AZD4625 is a highly potent and selective inhibitor of KRASG12C with an anticipated low clearance and high oral bioavailability profile in humans.

Direct targeting of FOXP3 in Tregs with AZD8701, a novel antisense oligonucleotide to relieve immunosuppression in cancer.

BACKGROUND: The Regulatory T cell (Treg) lineage is defined by the transcription factor FOXP3, which controls immune-suppressive gene expression profiles. Tregs are often recruited in high frequencies to the tumor microenvironment where they can suppress antitumor immunity. We hypothesized that pharmacological inhibition of FOXP3 by systemically delivered, unformulated constrained ethyl-modified antisense oligonucleotides could modulate the activity of Tregs and augment antitumor immunity providing therapeutic benefit in cancer models and potentially in man. METHODS: We have identified murine Foxp3 antisense oligonucleotides (ASOs) and clinical candidate human FOXP3 ASO AZD8701. Pharmacology and biological effects of FOXP3 inhibitors on Treg function and antitumor immunity were tested in cultured Tregs and mouse syngeneic tumor models. Experiments were controlled by vehicle and non-targeting control ASO groups as well as by use of multiple independent FOXP3 ASOs. Statistical significance of biological effects was evaluated by one or two-way analysis of variance with multiple comparisons. RESULTS: AZD8701 demonstrated a dose-dependent knockdown of FOXP3 in primary Tregs, reduction of suppressive function and efficient target downregulation in humanized mice at clinically relevant doses. Surrogate murine FOXP3 ASO, which efficiently downregulated Foxp3 messenger RNA and protein levels in primary Tregs, reduced Treg suppressive function in immune suppression assays in vitro. FOXP3 ASO promoted more than 70% reduction in FOXP3 levels in Tregs in vitro and in vivo, strongly modulated Treg effector molecules (eg, ICOS, CTLA-4, CD25 and 4-1BB), and augmented CD8+ T cell activation and produced antitumor activity in syngeneic tumor models. The combination of FOXP3 ASOs with immune checkpoint blockade further enhanced antitumor efficacy. CONCLUSIONS: Antisense inhibitors of FOXP3 offer a promising novel cancer immunotherapy approach. AZD8701 is being developed clinically as a first-in-class FOXP3 inhibitor for the treatment of cancer currently in Ph1a/b clinical trial (NCT04504669).

Structure-Based Design and Pharmacokinetic Optimization of Covalent Allosteric Inhibitors of the Mutant GTPase KRASG12C.

Attempts to directly drug the important oncogene KRAS have met with limited success despite numerous efforts across industry and academia. The KRASG12C mutant represents an "Achilles heel" and has recently yielded to covalent targeting with small molecules that bind the mutant cysteine and create an allosteric pocket on GDP-bound RAS, locking it in an inactive state. A weak inhibitor at this site was optimized through conformational locking of a piperazine-quinazoline motif and linker modification. Subsequent introduction of a key methyl group to the piperazine resulted in enhancements in potency, permeability, clearance, and reactivity, leading to identification of a potent KRASG12C inhibitor with high selectivity and excellent cross-species pharmacokinetic parameters and in vivo efficacy.

The Discovery of 7-Methyl-2-[(7-methyl[1,2,4]triazolo[1,5-a]pyridin-6-yl)amino]-9-(tetrahydro-2H-pyran-4-yl)-7,9-dihydro-8H-purin-8-one (AZD7648), a Potent and Selective DNA-Dependent Protein Kinase (DNA-PK) Inhibitor.

DNA-PK is a key component within the DNA damage response, as it is responsible for recognizing and repairing double-strand DNA breaks (DSBs) via non-homologous end joining. Historically it has been challenging to identify inhibitors of the DNA-PK catalytic subunit (DNA-PKcs) with good selectivity versus the structurally related PI3 (lipid) and PI3K-related protein kinases. We screened our corporate collection for DNA-PKcs inhibitors with good PI3 kinase selectivity, identifying compound 1. Optimization focused on further improving selectivity while improving physical and pharmacokinetic properties, notably co-optimization of permeability and metabolic stability, to identify compound 16 (AZD7648). Compound 16 had no significant off-target activity in the protein kinome and only weak activity versus PI3Kα/γ lipid kinases. Monotherapy activity in murine xenograft models was observed, and regressions were observed when combined with inducers of DSBs (doxorubicin or irradiation) or PARP inhibition (olaparib). These data support progression into clinical studies (NCT03907969).

AZD7648 is a potent and selective DNA-PK inhibitor that enhances radiation, chemotherapy and olaparib activity.

DNA-dependent protein kinase (DNA-PK) is a critical player in the DNA damage response (DDR) and instrumental in the non-homologous end-joining pathway (NHEJ) used to detect and repair DNA double-strand breaks (DSBs). We demonstrate that the potent and highly selective DNA-PK inhibitor, AZD7648, is an efficient sensitizer of radiation- and doxorubicin-induced DNA damage, with combinations in xenograft and patient-derived xenograft (PDX) models inducing sustained regressions. Using ATM-deficient cells, we demonstrate that AZD7648, in combination with the PARP inhibitor olaparib, increases genomic instability, resulting in cell growth inhibition and apoptosis. AZD7648 enhanced olaparib efficacy across a range of doses and schedules in xenograft and PDX models, enabling sustained tumour regression and providing a clear rationale for its clinical investigation. Through its differentiated mechanism of action as an NHEJ inhibitor, AZD7648 complements the current armamentarium of DDR-targeted agents and has potential in combination with these agents to achieve deeper responses to current therapies.

Evolution of Small Molecule Kinase Drugs.

The development of small molecule kinase drugs is a rapidly evolving field and represents one of the most important research areas within oncology. This innovation letter provides an overview and analysis of approved kinase drugs according to their WHO registration (INN) dates, primary biological targets, and selectivity and structural similarities, which are also depicted in an associated poster. It also discusses new trends in kinase drug discovery programs such as new kinase targets, novel mechanisms of action, and diverse indications.

Preclinical Evaluation of AZ12601011 and AZ12799734, Inhibitors of Transforming Growth Factor ß Superfamily Type 1 Receptors.

The transforming growth factor ß (TGFß) superfamily includes TGFß, activins, inhibins, and bone morphogenetic proteins (BMPs). These extracellular ligands have essential roles in normal tissue homeostasis by coordinately regulating cell proliferation, differentiation, and migration. Aberrant signaling of superfamily members, however, is associated with fibrosis as well as tumorigenesis, cancer progression, metastasis, and drug-resistance mechanisms in a variety of cancer subtypes. Given their involvement in human disease, the identification of novel selective inhibitors of TGFß superfamily receptors is an attractive therapeutic approach. Seven mammalian type 1 receptors have been identified that have context-specific roles depending on the ligand and the complex formation with the type 2 receptor. Here, we characterize the biologic effects of two transforming growth factor ß receptor 1 (TGFBR1) kinase inhibitors designed to target TGFß signaling. AZ12601011 [2-(2-pyridinyl)-4-(1H-pyrrolo[3,2-c]pyridin-1-yl)-6,7-dihydro-5H-cyclopenta[d]pyrimidine]; structure previously undisclosed] and AZ12799734 [4-({4-[(2,6-dimethyl-3-pyridinyl)oxy]-2-pyridinyl}amino)benzenesulfonamide] (IC50 = 18 and 47 nM, respectively) were more effective inhibitors of TGFß-induced reporter activity than SB-431542 [4-[4-(1,3-benzodioxol-5-yl)-5-(2-pyridinyl)-1H-imidazol-2-yl]benzamide] (IC50 = 84 nM) and LY2157299 [4-[2-(6-methylpyridin-2-yl)-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazol-3-yl]quinoline-6-carboxamide monohydrate]] (galunisertib) (IC50 = 380 nM). AZ12601011 inhibited phosphorylation of SMAD2 via the type 1 receptors activin A receptor type 1B (ALK4), TGFBR1, and activin A receptor type 1C (ALK7). AZ12799734, however, is a pan TGF/BMP inhibitor, inhibiting receptor-mediated phosphorylation of SMAD1 by activin A receptor type 1L, bone morphogenetic protein receptor type 1A, and bone morphogenetic protein receptor type 1B and phosphorylation of SMAD2 by ALK4, TGFBR1, and ALK7. AZ12601011 was highly effective at inhibiting basal and TGFß-induced migration of HaCaT keratinocytes and, furthermore, inhibited tumor growth and metastasis to the lungs in a 4T1 syngeneic orthotopic mammary tumor model. These inhibitors provide new reagents for investigating in vitro and in vivo pathogenic processes and the contribution of TGFß- and BMP-regulated signaling pathways to disease states.

Optimization of Highly Kinase Selective Bis-anilino Pyrimidine PAK1 Inhibitors.

Group I p21-activated kinase (PAK) inhibitors are indicated as important in cancer progression, but achieving high kinase selectivity has been challenging. A bis-anilino pyrimidine PAK1 inhibitor was identified and optimized through structure-based drug design to improve PAK1 potency and achieve high kinase selectivity, giving in vitro probe compound AZ13705339 (18). Reduction of lipophilicity to lower clearance afforded AZ13711265 (14) as an in vivo probe compound with oral exposure in mouse. Such probes will allow further investigation of PAK1 biology.

Rapid generation of a high quality lead for transforming growth factor-beta (TGF-beta) type I receptor (ALK5).

A novel class of 4-pyridinoxy-2-anilinopyridine-based TGF-beta type I receptor (also known as activin-like kinase 5 or ALK5) inhibitors is reported. The binding mode of this scaffold was successfully predicted by analyzing possible docked binding modes of literature inhibitors and novel synthetic ideas. Compounds such as 19 are potent ALK5 inhibitors with good physicochemical and pharmacokinetic properties and thus represent high quality leads for further optimization.

The changing landscape of cancer drug discovery: a challenge to the medicinal chemist of tomorrow.

Since the development of the first cytotoxic agents, synthetic organic chemistry has advanced enormously. The synthetic and medicinal chemists of today are at the centre of drug development and are involved in most, if not all, processes of drug discovery. Recent decreases in government funding and reformed educational policies could, however, seriously impact on drug discovery initiatives worldwide. Not only could these changes result in fewer scientific breakthroughs, but they could also negatively affect the training of our next generation of medicinal chemists.