An imidazo[1,2-a]pyridine-pyridine derivative potently inhibits FLT3-ITD and FLT3-ITD secondary mutants, including gilteritinib-resistant FLT3-ITD/F691L

FLT3 activating mutations are detected in approximately 30 % of newly diagnosed acute myeloid leukemia (AML) cases, most commonly consisting of internal tandem duplication (ITD) mutations in the juxtamembrane region. Recently, several FLT3 inhibitors have demonstrated clinical activity and three are currently approved - midostaurin, quizartinib, and gilteritinib. Midostaurin is a first-generation FLT3 inhibitor with minimal activity as monotherapy. Midostaurin lacks selectivity and is only approved by the USFDA for use in combination with other chemotherapy agents. The second-generation inhibitors quizartinib and gilteritinib display improved specificity and selectivity, and have been approved for use as monotherapy. However, their clinical efficacies are limited in part due to the emergence of drug-resistant FLT3 secondary mutations in the tyrosine kinase domain at positions D835 and F691. Therefore, in order to overcome drug resistance and further improve outcomes, new compounds targeting FLT3-ITD with secondary mutants are urgently needed. In this study, through the structural modification of a reported compound Ling-5e, we identified compound 24 as a FLT3 inhibitor that is equally potent against FLT3-ITD and the clinically relevant mutants FLT3-ITD/D835Y, and FLT3-ITD/F691L. Its inhibitory effects were demonstrated in both cell viability assays and western blots analyses. When tested against cell lines lacking activating mutations in FLT3, no non-specific cytotoxicity effect was observed. Interestingly, molecular docking results showed that compound 24 may adopt different binding conformations with FLT3-F691L compared to FLT3, which may explain its retained activity against FLT3-ITD/F691L. In summary, compound 24 has inhibition potency on FLT3 comparable to gilteritinib, but a more balanced inhibition on FLT3 secondary mutations, especially FLT3-ITD/F691L which is gilteritinib resistant. Compound 24 may serve as a promising lead for the drug development of either primary or relapsed AML with FLT3 secondary mutations.

Chemical Optimization of CBL0137 for Human African Trypanosomiasis Lead Drug Discovery

The carbazole CBL0137 (1) is a lead for drug development against human African trypanosomiasis (HAT), a disease caused by Trypanosoma brucei. To advance 1 as a candidate drug, we synthesized new analogs that were evaluated for the physicochemical properties, antitrypanosome potency, selectivity against human cells, metabolism in microsomes or hepatocytes, and efflux ratios. Structure-activity/property analyses of analogs revealed eight new compounds with higher or equivalent selectivity indices (5j, 5t, 5v, 5w, 5y, 8d, 13i, and 22e). Based on the overall compound profiles, compounds 5v and 5w were selected for assessment in a mouse model of HAT; while 5v demonstrated a lead-like profile for HAT drug development, 5w showed a lack of efficacy. Lessons from these studies will inform further optimization of carbazoles for HAT and other indications.

Pyrrolo[2,3-d]pyrimidine derivatives as inhibitors of RET: Design, synthesis and biological evaluation

Gene fusions and point mutations of RET kinase are crucial for driving thoracic cancers, including thyroid cancer and non-small cell lung cancer. Various scaffolds based on different heterocycles have been synthesized and evaluated as RET inhibitors. In this work, we investigate pyrrolo[2,3-d]pyrimidine derivatives for inhibition of RET-wt, drug resistant mutant RET V804M and RET gene fusion driven cell lines. Several compounds were synthesized and the structure activity relationship was extensively studied to optimize the scaffold. Thieno[2,3-d]pyrimidine, a bioisostere of pyrrolo[2,3-d]pyrimidine, was also explored for the effect on RET inhibition. We identified a lead compound, 59, which shows low nanomolar potency against RET-wt and RET V804M. Further 59 shows growth inhibition of LC-2/ad cells which RET-CCDC6 driven. We also determined that 59 is a type 2 inhibitor of RET and demonstrated its ability to inhibit migration of tumor cells. Based on computational studies, we proposed a binding pose of 59 in RET pocket and have quantified the contributions of individual residues for its binding. Together, 59 is an important lead compound which needs further evaluation in biological studies.

Abstract 5155: Orally bioavailable aurora-kinase B inhibitor (MK7) as a potential therapeutic approach in multiple myeloma

Multiple myeloma (MM) is a plasma cell malignancy diagnosed in approximately 30 thousand patients per year and accounts for nearly 12 thousand deaths in the US representing 2% of all cancer-related mortality. Novel agents have increased the survival of MM patients; however, patients with high-risk features and/or relapsed/refractory disease exhibit poor outcomes and remain an unmet, therapeutic challenge. Most patients develop refractory disease through a lack of successful mechanism-based therapies and progressive, genetic instability with copy number abnormalities. Aurora-kinase B (AURKB) is a key component of the chromosomal passenger complex (CPC), a key regulator of mitosis. The CPC ensures correct chromosome alignment and segregation and is required for chromatin-induced microtubule stabilization and spindle assembly as well as orderly cytokinesis. AURKB is a therapeutic target for many cancers but targeting attempts have been fraught with specificity and toxicity issues warranting further work to improve small molecule inhibitors. Thus, we sought to characterize the potential of MK7, a novel AURKB inhibitor, as a therapeutic approach in MM. MK7 is the first orally bioavailable AURKB inhibitor with favorable pharmacokinetic properties. Histone phosphorylation plays a direct role in major cell events, such as mitosis, cell death, repair, replication and recombination. MK7 activity can be assessed by a decrease in the levels of phosphorylation of histone H3(p-H3). First, we measured the expression of mRNA of AURKB in MM cell lines (i.e., MM1S, MM1R, U266, SKO-007, U266 lenalidomide resistant (U266-LR), AMO1, AMO1 bortezomib resistant (AMO1-BZ) and AMO1 carfilzomib resistant (AMO1-CZ) and primary CD138+ BM samples from patients with MM. In addition, we determined protein levels of AURKB and its substrate H3 (as phospho-H3) and found that all cell lines and primary samples showed detectable levels of AURKB and p-H3, including cell lines resistant to lenalidomide, bortezomib, and carfilzomib. Next, we evaluated the in vitro dose response to MK7 (5 to 0.015uM) and found a significant decrease in viability at concentrations below 125nM as early as 24 hours post-treatment in all cell lines tested (less than 50%). Furthermore, we observed dramatic changes in size and morphology as early as 6 hours post treatment. Response to MK7 was also assessed in vivo using U266-GFP/Luciferase xenografts. Mice were treated with 30 mg/kg P.O. MK7 three times a week (total 14 doses) and compared to vehicle. We observed an increase in overall survival in mice receiving MK7. Given the favorable results, additional in vivostudies are being performed and will be presented at the meeting. In summary, MK7 is a novel, orally bioavailable AURKB inhibitor with potent activity in MM. With this promising orally active chemical platform, we believe that AURKB inhibitors with favorable pharmacokinetics and a lower toxicity profile should be developed for the treatment of patients with MM.

Citation Format: Jorge Contreras, Eloisi Caldas Lopes, Jorge Monge, David Jayabalan, Naresh Gunaganti, Brendan Frett, Hong-yu Li, Morton Coleman, Ruben Niesvizky, Monica L. Guzman. Orally bioavailable aurora-kinase B inhibitor (MK7) as a potential therapeutic approach in multiple myeloma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5155.

Medicinal Chemistry Optimization of a Diaminopurine Chemotype: Toward a Lead for Trypanosoma brucei Inhibitors

Human African trypanosomiasis (HAT), or sleeping sickness, is caused by the protozoan parasite Trypanosoma brucei and transmitted through the bite of infected tsetse flies. The disease is considered fatal if left untreated. To identify new chemotypes against Trypanosoma brucei, previously we identified 797 potent kinase-targeting inhibitors grouped into 59 clusters plus 53 singleton compounds with at least 100-fold selectivity over HepG2 cells. From this set of hits, a cluster of diaminopurine-derived compounds was identified. Herein, we report our medicinal chemistry investigation involving the exploration of structure-activity and structure-property relationships around one of the high-throughput screening (HTS) hits, N²-(thiophen-3-yl)-N⁶-(2,2,2-trifluoroethyl)-9H-purine-2,6-diamine (1, NEU-1106). This work led to the identification of a potent lead compound (4aa, NEU-4854) with improved in vitro absorption, distribution, metabolism, and excretion (ADME) properties, which was progressed into proof-of-concept translation of in vitro antiparasitic activity to in vivo efficacy.

Discovery of SP-96, the first non-ATP-competitive Aurora Kinase B inhibitor, for reduced myelosuppression

Aurora Kinase B is a serine-threonine kinase known to be overexpressed in several cancers, with no inhibitors approved for clinical use. Herein, we present the discovery and optimization of a series of novel quinazoline-based Aurora Kinase B inhibitors. The lead inhibitor SP-96 shows sub-nanomolar potency in Aurora B enzymatic assays (IC₅₀ = 0.316 ± 0.031 nM). We identified the important pharmacophore features resulting in selectivity against receptor tyrosine kinases. Particularly, SP-96 shows >2000 fold selectivity against FLT3 and KIT which is important for normal hematopoiesis. This could diminish the adverse effect of neutropenia reported in the clinical trials of the Aurora B inhibitor Barasertib, which inhibits FLT3 and KIT in addition to Aurora B. Enzyme kinetics of SP-96 shows non-ATP-competitive inhibition which makes it a first-in-class inhibitor. Further, SP-96 shows selective growth inhibition in NCI60 screening, including inhibition of MDA-MD-468, a Triple Negative Breast Cancer cell line.

β-Amino acid derivatives as mitochondrial complex III inhibitors of L. donovani: A promising chemotype targeting visceral leishmaniasis

β-amino acids and their analogues are gathering increased attention not only because of their antibacterial and antifungal activity, but also for their use in designing peptidomimetics with increased oral bioavailability and resistance to metabolic degradation. In this study, a series of α-phenyl substituted chalcones, α-phenyl, β-amino substituted dihydrochalcones and β-amino acid derivatives were synthesized and evaluated for their antileishmanial efficacy against experimental visceral leishmaniasis (VL). Among all synthesized derivatives, 10c showed promising antileishmanial efficacy against both extracellular promastigote and intracellular amastigote (IC₅₀ 8.2 μM and 20.5 μM respectively) of L. donovani with negligible cytotoxic effect towards J774 macrophages and Vero cells. 10c effectively reduced spleen and liver parasite burden (>90%) in both hamster and Balb/c model of VL without any hepatotoxicity. In vitro pharmacokinetic analysis showed that 10c was stable in gastric fluid and plasma of Balb/c mice at 10 μg/ml. Further analysis of the molecular mechanism revealed that 10c entered into the parasite by depolarizing the plasma membrane rather than forming nonspecific pores and induced molecular events like loss in mitochondrial membrane potential with a gradual decline in ATP production. This, in turn, did not induce programmed cell death of the parasite; rather 10c induced bioenergetic collapse of the parasite by decreasing ATP synthesis through specific inhibition of mitochondrial complex III activity. Altogether, our results allude to the therapeutic potential of β-amino acid derivatives as novel antileishmanials, identifying them as lead compounds for further exploration in the design of potent candidates for the treatment of visceral leishmaniasis.

Catalyst free, C-3 functionalization of imidazo[1,2-a]pyridines to rapidly access new chemical space for drug discovery efforts

Multicomponent reactions (MCRs) are robust tools for the rapid synthesis of complex, small molecule libraries for use in drug discovery and development. By utilizing MCR chemistry, we developed a protocol to functionalize the C-3 position of imidazo[1,2-a]pyridine through a three component, decarboxylation reaction involving imidazo[1,2-a]pyridine, glyoxalic acid, and boronic acid.

Insights into Current Tropomyosin Receptor Kinase (TRK) Inhibitors: Development and Clinical Application

The use of kinase-directed precision medicine has been heavily pursued since the discovery and development of imatinib. Annually, it is estimated that around ∼20 000 new cases of tropomyosin receptor kinase (TRK) cancers are diagnosed, with the majority of cases exhibiting a TRK genomic rearrangement. In this Perspective, we discuss current development and clinical applications for TRK precision medicine by providing the following: (1) the biological background and significance of the TRK kinase family, (2) a compilation of known TRK inhibitors and analysis of their cocrystal structures, (3) an overview of TRK clinical trials, and (4) future perspectives for drug discovery and development of TRK inhibitors.