Dapson in heterocyclic chemistry, part VIII: synthesis, molecular docking and anticancer activity of some novel sulfonylbiscompounds carrying biologically active 1,3-dihydropyridine, chromene and chromenopyridine moieties

Several new sulfonebiscompounds having a biologically active 1,2-dihydropyridine-2-one 3–19, acrylamide 20, chromene 21, 22 and chromenopyridine 23, 24 moieties were synthesized and evaluated as potential anticancer agents. The structures of the products were confirmed via elemental analyses and spectral data. The screening tests showed that many of the biscompounds obtained exhibited good anticancer activity against human breast cell line (MCF7) comparable to doxorubicin which was used as reference drug. Compounds 11, 17 and 24 showed IC50 values 35.40 μM, 29.86 μM and 30.99 μM, respectively. In order to elucidate the mechanism of action of the synthesized compounds as anticancer agents, docking on the active site of farnesyltransferase and arginine methyltransferase was also performed and good results were obtained.

Recent studies have proved the remarkable effect of Dapson on inhibiting cell growth in glioblastoma by acting as anti-VEGF and anti-angiogenic agent via depriving glioblastoma of neutrophil-mediated growth promoting effects [36]. Allantodapson V, a Dapson derivative showed high activity as anticancer through inhibition of arginine methyltranseferase (PRMT1) an enzyme which plays an important role in hormone dependent cancers. A series of acylated diarylsulfone derivatives were evaluated for the same activity and compound VI exihibited good activity as (PRMT1) inhibitor [37].
In view of these findings, and in continuation to our work in the synthesis of novel anticancer agents [38][39][40][41][42] we undertook the synthesis of bisheterocyclicsulfone compounds analogues for 2-pyridones incorporating biologically active 1,2-dihydropyridine-2-one, chromene, and chromenopyridone in one molecule to explore the promising anticancer compounds. Furthermore, Perkin reaction was carried out by reacting compound 2 with salicylaldehyde in acetic anhydride containing catalytic amount of anhydrous sodium acetate to give the corresponding chromene derivative 21, while reaction of 2 with salicylaldehyde in ammonium acetate afforded 2-iminochromene derivative 22 (Scheme 3).

Molecular docking
The zinc-metalloenzyme farnesyl transferase (FTase) catalyzes the transfer of a farnesyl group to a cysteine thiol group contained in the C-terminal tetra peptide signal sequence of Ras, frequently referred to as aCAAX motif. Farnesylation causes membrane localization of Ras which, in turn, determines the switch from an inactive to an active Ras-GTP-bound form [43][44][45]. Among the Ras isoforms H-ras, N-ras, and K-ras, mutations in the K-ras isoform are most relevant to human cancers in particular pancreatic, colon, and lung cancers, which exhibit approximately 90, 40, and 25% incidence of Kras mutations, respectively. Inhibitors of FTase prevent membrane localization of the Ras oncogene and have the ability to revert the transformed phenotype, providing the rationale for the development of farnesyl transferase inhibitors (FTIs) as anticancer drugs [46][47][48][49].
On the other hand, the relative levels of arginine methyltransferase (PRMT1) isoforms are altered between normal and cancerous breast issue, with two of the isoforms down-regulated [50]. Therefore, it appears that PRMT1expression in cancer cells may be altered depending on the tumor type. Studies are beginning to examine the specific role of PRMT1in cancer. PRMT1 is an essential component of a Mixed Line age Leukaemia (MLL) transcriptional complex that modifies histones by methylation, at H4R3, and acetylation [51]. This serves as the first demonstration of a direct role for PRMT1-mediated transcriptional up regulation during cancer progression.
Thus, the present investigation is concerned with the synthesis of novel anticancer agents and trying to understand their mechanism of action. In order to perform the aim of the present investigations the authors have performed molecular docking of the synthesized compounds on the active sites of both farnesyl transferase and arginine methyltransferase (PRMT1) which may lead to understanding of their effect as antitumor agents.

Molecular docking on the active site of farnesyl transferase
The protein data bank file (PDB:3E30) was selected for this purpose. The file contains farnesyl transferase enzyme co-crystallized with a sulfone ligand. All docking procedures were achieved by MOE (Molecular Operating Environment) software 10.2008 provided by chemical computing group, Canada. Docking on the active site of farnesyl transferase enzyme was performed for all synthesized compounds 2-24.
Docking protocol was verified by redocking of the cocrystallized ligand in the vicinity of the active site of the enzyme with energy score (S) = −25.6345 Kcal/ mol and root mean standard deviation (RMSD) = 2.8268 ( Figure 1).
The sulfone ligand interacts with the active site of farnesyl transferase by four interactions: Try B361 with a hydrogen bond of 2.95 A o and arene-arene interaction, Trp 102 with a hydrogen bond of 2.83 and with Zn by the lone pair of imidazole nitrogen. All synthesized compounds were fit to the active site of farnesyl transferase enzyme with good energy scores (S) suggesting activity as farnesyl transferase inhibitors. Energy scores (S) and amino acid interactions for synthesized compounds were listed in (Table 1) All synthesized compounds were fit to the active site of arginine methyltransferase enzyme with good energy scores (S) except compounds 7, 18 and 19 suggesting good activity as arginine methyltransferase inhibitors for most of the synthesized compounds. Energy scores (S) and amino acid interactions for the synthesized compounds were listed in (Table 2).

In vitro antitumor activity
The newly synthesized compounds were evaluated for their in vitro cytotoxic activity against human breast cancer cell line; MCF7. Doxorubicin which is one of the most effective anticancer agents was used as the reference drug in this study. The relationship between surviving fraction and drug concentration was plotted to obtain the survival curve of breast cancer cell line (MCF7).The response parameter calculated was the IC 50 value, which corresponds to the concentration required for 50% inhibition of cell viability. Table 3 shows the in vitro cytotoxic activity of the synthesized compounds where all compounds exhibited significant activity compared to the reference drug. All the synthesized compounds showed better cytotoxic activity than Doxorubicin except compound 5 which showed IC 50   Compound 24 also showed the best scoring energy S = −45.9317 kcal/Mol. and the best amino acid interactions upon docking on the active site of farnesyl transferase enzyme. It also showed the best energy score S = −23.0582 kcal/Mol. and the best amino acid interactions upon docking on the active site of arginine methyl transferase enzyme.
The promising results of cytotoxic activity of the synthesized compounds especially compounds 17, 24 urge more investigations for their mechanism of action. The trial in the present investigation to predict an assumption of the mechanism of action of the synthesized compounds was conducted through molecular docking on the active site of two enzymes based on the similarities between the synthesized compounds and the enzyme inhibitors of these enzymes.

Experimental Chemistry
Melting points (°C, uncorrected) were determined in open capillaries on a Gallenkemp melting point apparatus (Sanyo Gallenkemp, Southborough, UK) and were uncorrected. Precoated silica gel plates (silica gel 0.25 mm, 60 G F254; Merck, Germany) were used for thin layer chromatography, dichloromethane/methanol (9.5:0.5) mixture was used as a developing solvent system and the spots were visualized by ultraviolet light and/or iodine. Infra-red spectra were recorded in KBr discs using IR-470 Shimadzu spectrometer (Shimadzu, Tokyo, Japan). NMR spectra (in DMSO-d6) were recorded on Bruker AC-300 Ultra Shield NMR spectrometer (Bruker, Flawil, Switzerland, δ ppm) at 300 MHz using TMS as internal Standard and peak multiplicities are designed as follows: s, singlet; d, doublet; t, triplet; m, multiplet. Elemental analyses were performed on Carlo Erba 1108 Elemental Analyzer (Heraeus, Hanau, Germany).