LSD1 Inhibitors
Lysine-specific demethylase 1 (LSD1), also known as KDM1A, was the first histone demethylase discovered and has since become a focal point in epigenetic research. LSD1 is a flavin adenine dinucleotide (FAD)-dependent amine oxidase that specifically removes mono- and di-methyl groups from lysine 4 and lysine 9 of histone H3 (H3K4 and H3K9). By modulating these marks, LSD1 acts as a key regulator of gene expression, often functioning within large multi-protein complexes such as CoREST (REST corepressor 1) or NuRD (nucleosome remodeling and deacetylase). While its primary role is in histone modification, LSD1 also demethylates non-histone proteins like p53, DNMT1, and E2F1, further expanding its regulatory influence. LSD1 is highly expressed in a variety of malignancies, including acute myeloid leukemia (AML), small cell lung cancer (SCLC), and prostate cancer. In AML, LSD1 is essential for maintaining the "leukemic stem cell" program and preventing the differentiation of myeloid blasts. In solid tumors, it is often associated with epithelial-mesenchymal transition (EMT), metastasis, and poor prognosis.
These findings have spurred the development of a diverse array of LSD1 inhibitors, which are currently at various stages of clinical and preclinical development. LSD1 inhibitors are generally classified into two main groups based on their mechanism of action: irreversible and reversible inhibitors. Irreversible inhibitors are typically derivatives of the antidepressant tranylcypromine (TCP). These compounds form a covalent adduct with the FAD cofactor in the LSD1 active site, permanently inactivating the enzyme. Several TCP-based inhibitors, such as iadademstat (ORY-1001) and vafidemstat (ORY-2001), have entered clinical trials for AML and SCLC, showing promising results in inducing cell differentiation. Reversible inhibitors, on the other hand, do not form covalent bonds and often target the substrate-binding pocket or the interaction interface between LSD1 and CoREST. Examples include SP-2509 and pulvomycin.
These reversible agents may offer a different toxicity profile and are being explored for their ability to disrupt the scaffolding functions of LSD1. One of the most significant challenges in LSD1 therapy is the potential for hematological toxicity, particularly thrombocytopenia, as LSD1 is involved in megakaryocyte differentiation. To mitigate this, researchers are investigating intermittent dosing schedules and combination strategies. A particularly promising approach is the combination of LSD1 inhibitors with all-trans retinoic acid (ATRA) in AML, which synergistically promotes the differentiation of leukemia cells. Additionally, LSD1 inhibition has been shown to enhance the immunogenicity of "cold" tumors by inducing a state of viral mimicry through the activation of endogenous retroelements, making them more responsive to immune checkpoint inhibitors like anti-PD-1/PD-L1. This has opened a new frontier for using LSD1 inhibitors in immuno-oncology. As the field progresses, the focus is shifting toward developing more selective inhibitors that can distinguish between LSD1 and its homolog LSD2, as well as exploring the potential of LSD1-targeting PROTACs to achieve more complete and sustained inhibition of its oncogenic functions.
