Amino Acids (2017) 49:1469–1485 DOI 10.1007/s00726-017-2454-x REVIEW ARTICLE Isoprenyl carboxyl methyltransferase inhibitors: a brief review including recent patents Woo Seok Yang1 · Seung‑Gu Yeo2 · Sungjae Yang1 · Kyung‑Hee Kim3 · Byong Chul Yoo3 · Jae Youl Cho1 Received: 10 June 2017 / Accepted: 14 June 2017 / Published online: 19 June 2017 © The Author(s) 2017. This article is an open access publication Abstract Among the enzymes involved in the post-transla- based on formulas other than the indole base. However, fur- tional modifcation of Ras, isoprenyl carboxyl methyltrans- ther optimization of chemicals targeted to functional groups ferase (ICMT) has been explored by a number of research- is needed to improve the characteristics of ICMT inhibi- ers as a signifcant enzyme controlling the activation of Ras. tors related to their application as drugs, such as solubility, Indeed, inhibition of ICMT exhibited promising anti-cancer effectiveness, and safety, to facilitate clinical use. activity against various cancer cell lines. This paper reviews patents and research articles published between 2009 and Keywords ICMT inhibitor · Cancer · Methylation · 2016 that reported inhibitors of ICMT as potential chemo- Cysmethynil · Ras therapeutic agents targeting Ras-induced growth factor signaling. Since ICMT inhibitors can modulate Ras signal- ing pathway, it might be possible to develop a new class of Introduction anti-cancer drugs targeting Ras-related cancers. Research- ers have discovered indole-based small-molecular ICMT The post-translational modifcation of Ras family members inhibitors through high-throughput screening. Researchers is a crucial step in inducing translocation of Ras proteins at Duke University identifed a prototypical inhibitor, cys- from the endoplasmic reticulum to the plasma membrane methynil. At Singapore University, Ramanujulu and his for management of cell proliferation triggered by growth colleagues patented more potent compounds by optimizing factor signaling. Mutations in Ras family proteins (e.g., cysmethynil. In addition, Rodriguez and Stevenson at Uni- K-RAS) are also closely related to the incidence of vari- versidad Complutense De Madrid and Cancer Therapeu- ous types of cancers in humans, such as pancreatic cancer tics CRC PTY Ltd., respectively, have developed inhibitors (Downward 2003; Pylayeva-Gupta et al. 2011). Normally, a series of post-translational modifcations of Ras proteins are a prerequisite for localization of Ras in the plasma Woo Seok Yang and Seung-Gu Yeo were contributed equally. membrane; however, mutations in Ras proteins can induce * Byong Chul Yoo uncontrolled activation of Ras signaling pathways and [email protected] Ras-mediated oncogenesis in the cell membrane. The post- * Jae Youl Cho translational modifcation of Ras frst requires farnesylation [email protected] or geranylgeranylation of the C-terminal CAAX motif, in which covalent bonding of farnesyl or geranylgeranyl iso- 1 Department of Genetic Engineering, Sungkyunkwan prenoid lipids to the cysteine residue of CAAX is mediated University, 2066 Seobu‑ro, Jang‑gu, Suwon 16419, Republic of Korea by farnesyl transferase (FTase) or geranylgeranyl trans- ferase (GGTase I), respectively, as summarized in Fig. 1 2 Department of Radiation Oncology, Soonchunhyang University College of Medicine, Soonchunhyang University (Winter-Vann and Casey 2005; Clarke 1988). During this Hospital, Cheonan 31151, Republic of Korea step, the CAAX endoprotease RCE1 cleaves the three C-ter- 3 Biomarker Branch, Research Institute, National Cancer minal amino acids (–AAX) (Ashby 1998), and isoprenyl Center, Goyang 10408, Republic of Korea carboxyl methyltransferase (ICMT) methylates a prenylated 1 3 1470 W. S. Yang et al. Fig. 1 Schematic diagram of the RAS/ICMT regulatory pro- cess in a growth factor-inducing Farnesyl group Farnesyl group signaling cascade. FTase S S GF farnesyltransferase, RCE1 Ras- converting CAAX endopepti- Ras-CAAX-COOH Ras-C-COOH dase 1, ICMT isoprenylcysteine RCE1 methyltransferase, AdoMet CH3 Farnesyl group FTase AdoMet S-adenosyl-L-methionine, ICMT AdoHcy S-adenosyl-L-homo- SH S cysteine, GF growth factor Ras-CAAX-COOH AdoHcy Ras-C-COOCH3 Ras-mediated proliferation-regulatory signaling cysteine (Bergo et al. 2000). Isoprenyl carboxyl methylated frst class of these inhibitors includes S-adenosyl-L-ho- proteins anchor to the cell membrane (Eisenberg et al. 2013) mocysteine (AdoHcy) and its precursors. During meth- and infuence cell signaling pathways. (Bergo et al. 2004; ylation, S-adenosyl-L-methionine (AdoMet) donates a Goodman et al. 1990). ICMT (MW 32 kDa) is essential for methyl group to the substrate proteins and is converted post-translational modifcation of Ras proteins and is local- to AdoHcy (Pylayeva-Gupta et al. 2011; Anderson et al. ized in the endoplasmic reticulum (Zhang and Casey 1996). 2005; Kim et al. 2013; Perez-Sala et al. 1992), a by-prod- Since Ras plays an important role in cancerous signaling uct that acts in a negative feedback reaction and leads pathways, ICMT is also a substantial focus of studies on to reduced enzyme activity of methyltransferase until it anti-cancer agents (Wahlstrom et al. 2008). Suppression of is cleaved by AdoHcy hydrolase (Shi and Rando 1992; the carcinogenic transformation of RAS by inhibition of the Kramer et al. 2003). Therefore, AdoHcy suppresses the enzymes involved in farnesylation or geranylgeranylation activity of ICMT by acting as a non-selective inhibitor of has been studied for treatment of cancer. There are several other methyltransferases (Winter-Vann et al. 2003), and inhibitors of FTase, including lonafarnib (IC 1.9 nM) specifc inhibitors of ICMT are still needed for treatment. 50 = and tipifarnib (IC 7.9 nM) (Basso et al. 2006). Although N-Acetyl-S-farnesyl-L-cysteine (AFC) and N-acetyl- 50 = some inhibitors of FTase have shown inhibitory activities S-geranylgeranyl-L-cysteine (AGGC) can competitively in mouse models, they had no notable effect on the clinical bind to the same substrate tunnel of farnesylated proteins. score in cancer patients. Moreover, the geranylgeranylated These structural analogs of prenylcysteine represent the Ras proteins maintain biological activities when FTase is second class of ICMT inhibitors by acting as actual sub- blocked by inhibitors, limiting the effects of those inhibitors strates that can compete with Ras (Henriksen et al. 2005). (Anderson et al. 2005; Doll et al. 2004; Mazieres et al. 2004; In fact, there are three structural mimics of AFC. The Lene 2009). Numerous reports have also demonstrated that frst analog of AFC, which has a sulphonamide linkage inhibition of ICMT leads to an anti-proliferative effect in in place of an amide bond, had an IC 50 value of 8.8 μM cancer (Clarke 1988; Bos 1989; Bishop et al. 2003; Gibbs in a vapor diffusion assay (Hrycyna and Clarke 1990). et al. 1994). Pharmacologic or genetic inactivation of ICMT The other analog of AFC has a triazole moiety in place resulted in cell cycle arrest and apoptosis (Bergo et al. of an allylic thioether, which can be easily degraded by 2000, 2004). Therefore, the strategy of suppressing ICMT enzymatic and chemical processes. This analog has an with chemical inhibitors could be considered an alternative IC50 value of 19.4 μM. The third structural mimic pos- therapeutic approach targeting Ras-mediated tumorigenic sesses an aryl alkyl moiety in the farnesyl side chain responses (Teh et al. 2014). of AFC instead of two isoprenoid units and has an IC 50 value of 34.6 μM (Ramanujulu et al. 2013; Buchanan et al. 2007, 2008a, b). The third class of ICMT inhibi- ICMT inhibitor classes tors includes molecules that have a low molecular weight (<900 Da) and are utilized as drugs due to their rapid dif- Isoprenyl carboxyl methyltransferase inhibitors are fusion through the cell membrane (Macielag 2012). Cys- divided into three classes based on their properties. The methynil (2-[5-(3-methylphenyl)-l-octyl-lH-indolo-3-yl] 1 3 Isoprenyl carboxyl methyltransferase inhibitors: a brief review including recent patents 1471 acetamide), which was identifed from 10,000 compounds The subsections are organized in chronological order by in the chemical library, is a representative small-molecu- patent applicant. lar inhibitor that competes with isoprenylated cysteine of other CAAX-containing proteins, but not AdoMet (Lene Purdue research foundation 2009). Cysmethynil induces incorrect localization of Ras and interrupts the signaling pathway of cancer cells. Despite fndings that FTase is a key enzyme in the post- Consequently, cysmethynil causes autophagic cell death translational modifcation of Ras proteins and other major through pharmacological inhibition of ICMT (Winter- causative enzymes involved in 30% of human cancers, Vann et al. 2003; Henriksen et al. 2005; Wang et al. 2008; numerous human tumors associated with mutation of K-Ras Clarke and Tamanoi 2004; Baron et al. 2007). Because are resistant to FTase inhibitors. In the presence of FTase the desired concentration of a drug in circulation is deter- inhibitors, the decreased biological activity of farnesylated mined by its solubility, this measure is a very important K-Ras is compensated for by another form of K-Ras post- aspect of drug development (Savjani et al. 2012). Cys- translational modifcation: geranylgeranylation by GGTase methynil is insoluble in water and has high lipophilicity I. Therefore, many research centers and institutes have and structural fexibility and is, therefore, considered to focused on the identifcation