Writing and erasing of posttranslational modifications are crucial to phenotypic plasticity and antigenic variation of eukaryotic pathogens. Targeting pathogens' modification machineries, thus, represents a valid approach to fighting parasitic diseases. However, identification of parasitic targets and the development of selective anti-parasitic drugs still represent major bottlenecks. Here, we show that the zinc-dependent histone deacetylases (HDACs) of the protozoan parasite Trypanosoma cruzi are key regulators that have significantly diverged from their human counterparts. Depletion of T. cruzi class I HDACs tcDAC1 and tcDAC2 compromises cell-cycle progression and division, leading to cell death. Notably, tcDAC2 displays a deacetylase activity essential to the parasite and shows major structural differences with human HDACs. Specifically, tcDAC2 harbors a modular active site with a unique subpocket targeted by inhibitors showing substantial anti-parasitic effects in cellulo and in vivo. Thus, the targeting of the many atypical HDACs in pathogens can enable anti-parasitic selective chemical impairment.

Epigenetic modifiers of the histone deacetylase (HDAC) family are often dysregulated in cancer cells. Experiments with small molecule HDAC inhibitors (HDACi) have proven that HDACs are a vulnerability of transformed cells. We evaluated a novel hydroxamic acid-based HDACi (KH16; termed yanostat) in human pancreatic ductal adenocarcinoma (PDAC) cells, short- and long-term cultured colorectal cancer (CRC) cells, and retinal pigment epithelial cells. We show that KH16 induces cell cycle arrest and apoptosis, both time and dose dependently in PDAC and CRC cells. This is associated with altered expression of BCL2 family members controlling intrinsic apoptosis. Recent data illustrate that PDAC cells frequently have an altered expression of the pro-apoptotic BH3-only protein NOXA and that HDACi induce an accumulation of NOXA. Using PDAC cells with a deletion of NOXA by CRISPR-Cas9, we found that a lack of NOXA delayed apoptosis induction by KH16. These results suggest that KH16 is a new chemotype of hydroxamic acid HDACi with superior activity against solid tumor-derived cells. Thus, KH16 is a scaffold for future research on compounds with nanomolar activity against HDACs.

The FMS-like tyrosine kinase-3 (FLT3) is mutated in ~30% of acute myeloid leukemia (AML) patients. Common FLT3 mutations are internal tandem duplications (FLT3-ITD) and point mutations in its c-terminal tyrosine kinase domain (FLT3-TKD). The resulting active FLT3 receptors promote cell proliferation and resistance to programmed cell death (apoptosis) [1]. The poor prognosis of patients with FLT3-ITD has spurred an intensive search for FLT3 inhibitors (FLT3i) [2]. These include the nanomolar FLT3i quizartinib, which has produced promising benefits in AML patients with FLT3-ITD [3]. TKD mutations in FLT3-ITD arise during the therapy of patients with quizartinib and confer drug resistance. The broad-range tyrosine kinase inhibitors midostaurin and gilteritinib are used with standard chemotherapy to treat AML. Their pleiotropic actions frequently evoke hematological toxicity [1, 2]. Marbotinib is a hybrid FLT3i containing elements of quizartinib and bis(1H-indol-2-yl)methanone. Marbotinib specifically inhibits FLT3-ITD and FLT3-TKD [4, 5]. Epigenetic modifiers of the histone deacetylase (HDAC) family control the development and survival of blood cells. Compared to normal cells, certain leukemic cell types frequently have aberrant expression levels and activities of epigenetic modifiers that belong to the histone deacetylase (HDAC) family. Accordingly, inhibitors of zinc-dependent HDACs (HDACi) are approved drugs for the treatment of subtypes of leukemia and lymphoma. These agents are vorinostat, romidepsin, belinostat, and chidamide. Further HDACi are tested clinically (www.clinicaltrials.org), such as the benzamide entinostat (MS-275) [6, 7]. HDACi decrease FLT3-ITD through ubiquitin-dependent proteasomal degradation and apoptosis-associated caspase activation. Combinations of HDACi and FLT3i synergistically kill FLT3-ITD-positive cells through accelerated elimination of FLT3-ITD and DNA replication stress/ DNA damage induction. HDAC1, HDAC2, and particularly HDAC3 maintain the stability of FLT3-ITD [8]. A cellular self-digestion process termed autophagy also eliminates FLT3-ITD [9]. Nonetheless, autophagy can promote FLT3i resistance [10, 11]. HDACs