Novel orally bioavailable piperidine derivatives as extracellular arginase inhibitors developed by a ring expansion

Arginase is a multifaced enzyme that plays an important role in health and disease being regarded as a therapeutic target for the treatment of various pathological states such as malignancies, asthma, and cardiovascular disease. The discovery of boronic acid-based arginase inhibitors in 1997 revolutionized attempts of medicinal chemistry focused on development of drugs targeting arginase. Unfortunately, these very polar compounds had limitations such as analysis and purification without chromophores, synthetically challenging space, and poor oral bioavailability. Herein, we present a novel class of boronic acid-based arginase inhibitors which are piperidine derivatives exhibiting a different pharmacological profile compared to our drug candidate in cancer immunotherapy -OATD-02 - dual ARG1/2 inhibitor with high intracellular activity. Compounds from this new series show low intracellular activity, hence they can inhibit mainly extracellular arginase, providing different therapeutic space compared to a dual intracellular ARG1/2 inhibitor. The disclosed series showed good inhibitory potential towards arginase enzyme in vitro (IC50 up to 160 nM), favorable pharmacokinetics in animal models, and encouraging preliminary in vitro and in vivo tolerability. Compounds from the new series have moderate-to-high oral bioavailability (up to 66 %) and moderate clearance in vivo. Herein we describe the development and optimization of the synthesis of the new class of boronic acid-based arginase inhibitors via a ring expansion approach starting from the inexpensive chirality source (d-hydroxyproline). This upgraded methodology facilitated a gram-scale delivery of the final compound and eliminated the need for costly and time-consuming chiral resolution.

Arginase 1/2 inhibitor OATD-02: from discovery to first-in-man setup in cancer immunotherapy

Pharmacological inhibition of the controlling immunity pathway enzymes arginases 1 and 2 (ARG1 and ARG2) is a promising strategy for cancer immunotherapy. Here, we report the discovery and development of OATD-02, an orally bioavailable, potent arginases inhibitor. The unique pharmacological properties of OATD-02 are evidenced by targeting intracellular ARG1 and ARG2, as well as long drug-target residence time, moderate to high volume of distribution, and low clearance which may jointly provide a weapon against arginase-related tumor immunosuppression and ARG2-dependent tumor cell growth. OATD-02 monotherapy had an antitumor effect in multiple tumor models and enhanced an efficacy of the other immunomodulators. Completed non-clinical studies and human pharmacokinetic predictions indicate a feasible therapeutic window and allow for proposing a dose range for the first-in-human clinical study in cancer patients.

Abstract B003: Development of OAT-1746, a novel arginase 1 and 2 inhibitor for cancer immunotherapy

Depletion of arginine represents an important mechanism of immunosuppression, and high plasma and tumor arginase (ARG) activity has been demonstrated in patients with a wide spectrum of cancers and correlated with a poor prognosis. Low arginine levels inhibit proliferation and activation of cytotoxic T and NK cells. Preclinical and clinical studies show that simultaneous interference with multiple mechanisms of immunosuppression results in a strongly improved antitumor efficacy. In this context, we have developed OAT-1746, a novel, potent, and selective small-molecule inhibitor of ARG1 and ARG2 with profound antitumor efficacy as a monotherapy and in combinations with gemcitabine and PD-L1 inhibitor.

The IC50 of OAT-1746 was determined against the recombinant human and murine ARG1 and ARG2. Cellular activity was evaluated in M2-polarized, bone marrow-derived murine macrophages, and CHO cells transfected with human ARG1 or ARG2. The in vivo antitumor efficacy of OAT-1746 was evaluated in syngeneic mouse models and in an orthotopic C6 rat glioma model after oral administration. In the rat model, C6 glioma cells were implanted by stereotactic intracranial inoculation and the tumor size was measured by bioluminescence in vivo imaging or immunohistochemistry. Quantitative real-time PCR was used to determine inflammatory markers. The tumor arginase activity was assessed using the urea detection assay. L-Arginine and drug levels in plasma and tumor were evaluated by LC/MS method. We have developed potent, selective, orally active inhibitors of ARG1 and ARG2. The clinical candidate, OAT-1746, has IC50=32 nM and 50 nM against human ARG1 and ARG2, respectively, and a potent cellular activity (M2 macrophages IC50=32 nM, CHO-K1 hARG1 IC50=55 nM). In vivo, OAT-1746 showed good pharmacologic properties and demonstrated significant antitumor efficacy as a monotherapy in 4 tumor models: B16 (melanoma), LLC (lung carcinoma), CT26 (CRC), and C6 glioma with TGI=34-53%. The antitumor efficacy correlated with sustained pharmacodynamic (PD) effects: suppression of tumor arginase activity and 3-6 fold increases in plasma and tumor arginine concentrations. Induction of inflammatory markers in tumors confirmed reversal of immunosuppression. Combinations of OAT-1746 with PD-L1 checkpoint inhibitor and gemcitabine showed increased efficacy. Administration of OAT-1746 with anti-PD-L1 antibody resulted in a “controlled” tumor growth with 55% of tumors remaining under 500 mm3 at day 24 versus 36% for PD-L1 monotherapy. Full regression was observed in 20% of the animals treated in combination with gemcitabine in comparison to 0% for monotherapy. OAT-1746 also demonstrated efficacy and PD effects in the orthotopic model of GBM, confirming its ability to cross the blood-brain barrier. Together these results support the clinical development of OAT-1746 for cancer therapy.

Citation Format: Paulina Seweryna Stanczak, Marcin Mikolaj Grzybowski, Paulina Wolska, Anna Maria Zdziarska, Marcin Mazurkiewicz, Paulina Pilanc, Anna Gieryng, Bozena Kaminska, Anna Gzik, Marek Dziegielewski, Karol Jedrzejczak, Bartlomiej Borek, Roman Blaszczyk, Adam Golebiowski, Pawel Dobrzanski, Karolina Dzwonek. Development of OAT-1746, a novel arginase 1 and 2 inhibitor for cancer immunotherapy [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B003.

Synthesis of chiral triazine coupling reagents based on esters of N-alkylproline and their application in the enantioselective incorporation of D or L amino acid residue directly from racemic substrate

Esters of N-methylproline and N-allylproline were prepared and used as component for synthesis of chiral triazine based coupling reagents. N-Triazinylammonium tetrafluoroborate obtained from methylester of L-N-methylproline, 2-chloro-4,6-dimethozxy-1,3,5-triazine and tetrafluoroboric acid in the coupling of rac-Z- A1a-OH with glycine methylester preferred formation of D-Z-AlaGly-OMe with L/D ratio 21/79. Coupling reagent prepared from D enantiomer of N-methylproline gave L-Z-AlaGly-OMe with L/D ratio 75/25.