Drug Design Concepts for LSD1-Selective Inhibitors

Strategies that regulate LSD1 for novel therapeutics

Histone methylation plays crucial roles in regulating chromatin structure and gene transcription in epigenetic modifications. Lysine-specific demethylase 1 (LSD1), the first identified histone demethylase, is universally overexpressed in various diseases. LSD1 dysregulation is closely associated with cancer, viral infections, and neurodegenerative diseases, etc., making it a promising therapeutic target. Several LSD1 inhibitors and two small-molecule degraders (UM171 and BEA-17) have entered the clinical stage. LSD1 can remove methyl groups from histone 3 at lysine 4 or lysine 9 (H3K4 or H3K9), resulting in either transcription repression or activation. While the roles of LSD1 in transcriptional regulation are well-established, studies have revealed that LSD1 can also be dynamically regulated by other factors. For example, the expression or activity of LSD1 can be regulated by many proteins that form transcriptional corepressor complexes with LSD1. Moreover, some post-transcriptional modifications and cellular metabolites can also regulate LSD1 expression or its demethylase activity. Therefore, in this review, we will systematically summarize how proteins involved in the transcriptional corepressor complex, various post-translational modifications, and metabolites act as regulatory factors for LSD1 activity.

Design, synthesis, and biological evaluation of phenylcyclopropylamine-entinostat conjugates that selectively target cancer cells

Small molecule-based selective cancer cell-targeting can be a desirable anticancer therapeutic strategy. Aiming to discover such small molecules, we previously developed phenylcyclopropylamine (PCPA)-drug conjugates (PDCs) that selectively release anticancer agents in cancer cells where lysine-specific demethylase 1 (LSD1) is overexpressed. In this work, we designed PCPA-entinostat conjugates for selective cancer cell targeting. PCPA-entinostat conjugate 12 with a 4-oxybenzyl group linker released entinostat in the presence of LSD1 in in vitro assays and selectively inhibited the growth of cancer cells in preference to normal cells, suggesting the potential of PCPA-entinostat conjugates as novel anticancer drug delivery small molecules.

Viscosalactone B, a natural LSD1 inhibitor, inhibits proliferation in vitro and in vivo against prostate cancer cells

Lysine-specific demethylase 1 (LSD1) has been a promising target to treat prostate cancer, and discovery of novel LSD1 inhibitors would have great clinical significance. In this work, viscosalactone B was first identified as a novel LSD1 inhibitor. Viscosalactone B isolated from Withania Somnifera displayed antiproliferative activity against PC3, DU145, C42B, PC3/MDVR, DU145/MDVR, and C42B/MDVR cells with IC₅₀ values of 1.17, 0.72, 3.86, 2.06, 0.96 and 1.15 μM, respectively. In comparison, it was a selective LSD1 inhibitor with an IC₅₀ value of 970.27 nM and could induce a significant accumulation of LSD1 substrates H3K9me1, H3K9me2, and H3K4me1 in a concentration-dependent manner in DU145 cells. According to docking studies, it formed hydrogen bonds with the Thr11, Lys14, and Arg8 residues of LSD1. Importantly, while it displayed potent antitumor efficacy in vivo, it did not show obvious cytotoxicity on the major organs of nude mice. Therefore, viscosalactone B, as a novel LSD1 inhibitor, is a potential candidate that can be used for the treatment of prostate cancer in clinics.

Cancer-Cell-Selective Targeting by Arylcyclopropylamine-Vorinostat Conjugates

Anticancer drug delivery by small molecules offers a number of advantages over conventional macromolecular drug delivery systems. We previously developed phenylcyclopropylamine (PCPA)-drug conjugates (PDCs) as small-molecule-based drug delivery vehicles for targeting lysine-specific demethylase 1 (LSD1)-overexpressing cancers. In this study, we applied this PDC strategy to the HDAC-inhibitory anticancer agent vorinostat. Among three synthesized PCPA or arylcyclopropylamine (ACPA)-vorinostat conjugates 1, 9, and 32, conjugate 32 with a 4-oxybenzyl linker showed sufficient stability in buffer solutions, potent LSD1 inhibition, efficient LSD1-dependent vorinostat release, and potent and selective antiproliferative activity toward LSD1-expressing human breast cancer and small-cell lung cancer cell lines. These results indicate that the conjugate selectively releases vorinostat in cancer cells. A similar strategy may be applicable to other anticancer drugs.

Roles of lysine-specific demethylase 1 (LSD1) in homeostasis and diseases

Lysine-specific demethylase 1 (LSD1) targets mono- or di-methylated histone H3K4 and H3K9 as well as non-histone substrates and functions in the regulation of gene expression as a transcriptional repressor or activator. This enzyme plays a pivotal role in various physiological processes, including development, differentiation, inflammation, thermogenesis, neuronal and cerebral physiology, and the maintenance of stemness in stem cells. LSD1 also participates in pathological processes, including cancer as the most representative disease. It promotes oncogenesis by facilitating the survival of cancer cells and by generating a pro-cancer microenvironment. In this review, we discuss the role of LSD1 in several aspects of cancer, such as hypoxia, epithelial-to-mesenchymal transition, stemness versus differentiation of cancer stem cells, as well as anti-tumor immunity. Additionally, the current understanding of the involvement of LSD1 in various other pathological processes is discussed.

Reversible Lysine Specific Demethylase 1 (LSD1) Inhibitors: A Promising Wrench to Impair LSD1

As a flavin adenine dinucleotide (FAD)-dependent monoamine oxidase, lysine specific demethylase 1 (LSD1/KDM1A) functions as a transcription coactivator or corepressor to regulate the methylation of histone 3 lysine 4 and 9 (H3K4/9), and it has emerged as a promising epigenetic target for anticancer treatment. To date, numerous inhibitors targeting LSD1 have been developed, some of which are undergoing clinical trials for cancer therapy. Although only two reversible LSD1 inhibitors CC-90011 and SP-2577 are in the clinical stage, the past decade has seen remarkable advances in the development of reversible LSD1 inhibitors. Herein, we provide a comprehensive review about structures, biological evaluation, and structure-activity relationship (SAR) of reversible LSD1 inhibitors.

4-Hydroxy-3-methylbenzofuran-2-carbohydrazones as novel LSD1 inhibitors

Histone lysine specific demethylase 1 (LSD1 or KDM1A) is a potential therapeutic target in oncology due to its overexpression in various human tumors. We report herein a new class of benzofuran acylhydrazones as potent LSD1 inhibitors. Among the 31 compounds prepared, 14 compounds exhibited excellent LSD1 inhibitory activity with IC₅₀ values ranging from 7.2 to 68.8 nM. In cellular assays, several compounds inhibited the proliferations of various cancer cell lines, including PC-3, MCG-803, U87 MG, PANC-1, HT-29 and MCF-7. This opens up the opportunity for further optimization and investigation of this class compounds for potential cancer treatment.

Epigenetic treatment combinations to effectively target cisplatin-resistant germ cell tumors: past, present, and future considerations

BACKGROUND

Type II germ cell tumors represent the most common solid malignancy in men aged 15-45 years. Despite high cure rates of >90% over all stages, 10-15% of advanced patients develop treatment resistance and potentially succumb to their disease. Treatment of refractory germ cell tumors remains unsatisfactory, and new approaches are needed to further improve outcomes.

OBJECTIVES

With this narrative review, we highlight epigenetic mechanisms related to resistance to standard systemic treatment, which may act as promising targets for novel combined epigenetic treatment approaches.

MATERIALS AND METHODS

A comprehensive literature search of PubMed and MEDLINE was conducted to identify original and review articles on resistance mechanisms and/or epigenetic treatment of germ cell tumors in vitro and in vivo. Review articles were hand-searched to identify additional articles.

RESULTS

Distinct epigenetic phenomena have been linked to chemotherapy resistance in germ cell tumors, among which DNA hypermethylation, histone acetylation, and bromodomain proteins appear as promising targets for therapeutic exploitation. Inhibitors of key regulators, for example DNA methyltransferases (e.g. decitabine, guadecitabine), histone deacetylases (e.g. romidepsin), and bromodomain proteins (e.g. JQ1) decreased cell viability, triggered apoptosis, and growth arrest. Additionally, these epigenetic drugs induced differentiation and led to loss of pluripotency and re-sensitization towards cisplatin in cell lines and animal models.

DISCUSSION

Epigenetic treatments hold promise to (i) reduce the treatment burden of and (ii) overcome resistance to standard cisplatin-based chemotherapy. Combined approaches may enhance activity, while the ideal target and treatment combination of epigenetic drugs, either with another epigenetic agent or conventional cytotoxic agents need to be defined.

CONCLUSION

Epigenetic (combination) treatment for germ cell tumors should be further explored in pre-clinical and clinical research for its potential to further improve germ cell tumor treatment.

Suppression of LSD1 enhances the cytotoxic and apoptotic effects of regorafenib in hepatocellular carcinoma cells

Regorafenib has been approved to treat patients who have HCC progression after sorafenib failure, however, regorafenib also faces the risk of drug resistance and subsequent progression of HCC patients. As LSD1 inhibitors can alleviate acquired resistance to sorafenib, in this context, we are interested to investigate the role of LSD1 in regorafenib treatment. Firstly, over-expressed LSD1 was observed in HCC patients and predicted poor prognosis. However, regorafenib failed to suppress the expression of LSD1 in HCC cells. Thus, we hypothesized that LSD1 inhibition could enhance the anti-HCC activity of regorafenib. As expected, LSD1 knockdown could enhance anti-proliferation effect of regorafenib in HCC cells. LSD1 inhibitor SP2509 could enhance the cytotoxic and apoptotic effects of regorafenib in HCC cells. In addition, clinically used LSD1 inhibitor tranylcypromine also enhanced anti-HCC effect of regorafenib. Furthermore, LSD1 suppressed by SP2590 or tranylcypromine could alleviate the activated p-AKT (ser473) induced by regorafenib in HCC cells. Thus, inhibiting LSD1 might be an attractive target for regorafenib sensitization and clinical HCC therapy, our findings could help to elucidate more effective therapeutic options for HCC patients.

Pharmacological Inhibition of LSD1 for Cancer Treatment

Lysine-specific demethylase 1A (LSD1, also named KDM1A) is a demethylase that can remove methyl groups from histones H3K4me1/2 and H3K9me1/2. It is aberrantly expressed in many cancers, where it impedes differentiation and contributes to cancer cell proliferation, cell metastasis and invasiveness, and is associated with inferior prognosis. Pharmacological inhibition of LSD1 has been reported to significantly attenuate tumor progression in vitro and in vivo in a range of solid tumors and acute myeloid leukemia. This review will present the structural aspects of LSD1, its role in carcinogenesis, a comparison of currently available approaches for screening LSD1 inhibitors, a classification of LSD1 inhibitors, and its potential as a drug target in cancer therapy.