Novel chloroquinoline derivatives incorporating biologically active benzenesulfonamide moiety: synthesis, cytotoxic activity and molecular docking

Background Quinoline derivatives have diverse biological activities including anticancer activity. On the other hand, many sulfonamide derivatives exhibited good cytotoxic activity. Hybrids of both moieties may present novel anticancer agents. Results Chloroquinoline incorporating a biologically active benzene-sulfonamide moieties 5–21 and diarylsulfone derivatives 22 and 23 were prepared using (E)-1-(4-((E)-7-chloro-1-methylquinolin-4(1H)-ylideneamino)phenyl)-3-(dimethyl-amino)prop-2-en-1-one 4 as strategic starting material. The structure of the newly synthesized compounds were confirmed by elemental analyses and spectral data. Compound 4 was confirmed by X-ray crystallographic analysis. The prepared compounds were evaluated for their anticancer activity against Lung, HeLa, Colorectal and breast cancer cell lines. Compounds 2, 4, 7, 11, 14 and 17 showed better or comparable activity to 2′, 7′-dichlorofluorescein (DCF) as reference drug. Molecular docking of the active compounds on the active site of PI3K enzyme was performed in order to explore the binding mode of the newly synthesized compounds. Conclusion Compounds 2, 4, 7, 11, 14 and 17 are novel quinoline derivatives that may represent good candidates for further evaluations as anticancer agents. The mechanism of action of these compounds could be through inhibition of PI3K enzyme.Graphical abstract Compound 17 on the active site of PI3K

Numerous mechanisms of action were optional for such action among them was the strong suppression of E2F1 that inhibits growth by thwarting cell cycle progression and fasters differentiation by creating a permissive environment for cell distinction [11]. Chloroquinolines were valuable in sundry cancer sorts remarkably, breast cancer with high aptitude to induce apoptosis [12]. Heterocyclic sulfonamides have publicized good anticancer bustle with diversity of mechanisms embracing cell cycle perturbation at G1 phase, disruption of microtubules assembly and the eminent carbonic anhydrase inhibition activity with selectivity to the tumor allied isoforms hCA IX and hCA XII [13][14][15][16][17]. Merging quinoline scaffold with the biologically active benzene-sulfonamide moiety has received immense attention as PI3K inhibitor which is an vital enzyme regulatory signal transduction [16,[18][19][20]. Freshly, diaryl sulfones that were prepared from Dapson have shown respectable cytotoxic activity on breast cancer cell line [21]. Based on the aforementioned and as a continuation for our effort to synthesize a novel anticancer agents [18][19][20][21][22][23][24][25], we have prepared novel quinolonesulfonamide and diarylsulfone derivatives. Prepared compounds were subjected to cytotoxic assay on lung, hela, colorectal and breast cancer cell lines. Likewise, "the highest active compounds were docked on the active site of PI3K enzyme" to recommend their binding mode in a trial to explore their mechanism of action expecting to reach innovative anticancer agents.

Chemistry
The ambition of this effort was to prepare a new series of chloroquinolines carrying biologically active benzenesulfonamide moieties and to assess their anticancer activity. Thus, interaction of 2 [26] with dimethylformamide-dimethylacetal (DMF-DMA) in dry xylene yielded the unexpected 4 instead of expected 3. "The structural assignments to synthesized compounds were based on their physico-chemical characteristics and spectroscopic (FT-IR, 1 H-NMR, 13 C-NMR, and mass spectroscopy) investigations". Structure of 4 was confirmed by X-ray crystallographic analysis [27] (Figs. 1, 2). IR of 4 revealed the disappearance of NH band and presence of absorption bands for (aromatic), (aliphatic), (CO), (CN), (CCl). 1 H-NMR showed the presence of a singlet at 2.4 ppm attributed to N-(CH 3 ) 2 , singlet at 3.4 ppm assigned to N-CH 3 , two doublet at 5.4, 6.5 ppm for CH = CH of quinolone ring, two doublet at 6.1,7.4 ppm assigned to CH = CH group. Enaminones are highly reactive intermediates extensively used for the preparation of heterocyclic derivatives. Thus, treatment of 4-(7-chloro-1-methylquinolin-4-(1H)-ylideneamino) phenyl-3-(dimethyl-amino)-prop-2-en-1-one 4 with sulfonamide derivatives in refluxing ethanol/acetic acid mixture (2:1) afforded the sulfonamide derivatives 5-21 (Scheme 1). "Structures of the latter products were assigned on the basis of their analytical and spectral data". 1 H NMR of 5-21 support the assumption that these structures were in E-form and not in Z form, while the coupling constant of doublet signals for olefinic protons was equal to 6.1-7.7 Hz. IR of the reaction products showed in each case three absorption bands for 2NH functions in the 3446-3143 cm −1 region, in addition to carbonyl functions 1654-1635 cm −1 region and CCl functions 883-763 cm −1 (Scheme 1). 1 H-NMR of 5 showed singlet at 12.0 ppm assigned to NH group, while 13

In vitro cytotoxic screening
The newly synthesized compounds were evaluated for their in vitro cytotoxic activity against human lung (A549-Raw), hela, colorectal (lovo) and breast (MDA-MB231) cancer cell lines and 2′,7′-dichlorofluorescein (DCF) 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 cancer cell lines. The response parameter calculated was the IC 50 value, which corresponds to the concentration required for 50 % inhibition of cell viability. Table 1 shows the in vitro cytotoxic activity of the newly synthesized compounds. In a closer look to  again was the most active compound with IC 50 value of 26.54 μg/ml. In the light of biological results, we can see that the 4,7-dichloroquinoline 1 showed moderate anticancer activity that were enhanced upon converting it to 1-(4-(7-chloloquinoline-4-ylamino) phenyl)ethanone 2. The activity still exists upon preparation of (E)-1-(4- Further preparation of the sulfonamide derivatives 5-21 using various sulfa drugs only succeeded to obtain active derivatives with the guanidine derivative 7, the thiazole derivative 11, the pyrimidine derivative 14 and the 5-methoxypyrimidine derivative 17. Combination with diaryl sulfone moieties as in compounds 22 and 23 did not yield active compounds.

Molecular docking
Phosphoinositide 3-kinases (PI3K) comprises an important class of enzymes that phosphorylates the 3 hydroxyl group of inisitol and play a major role in signal transduction through the cell cycle. Targeting PI3K by inhibitors has become a well-known strategy in seeking for new anticancer agents [28]. Quinolinesulfonamide derivatives were reported to express good inhibitory activity on PI3K enzyme [16]. In our present investigation and in a trial to suggest the mechanism of action of the active compounds, molecular docking of compounds 1, 2, 4, 7, 11, 14 and 17 was performed on the active site of PI3K to explore their binding modes to amino acids of the active site of the enzyme. The protein data bank file (PDB: 3S2A) was selected for this purpose. The file contains PI3K enzyme co-crystallized with a quinoline 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 PI3K enzyme was performed for all synthesized compounds. Docking protocol was verified by redocking of the cocrystallized ligand in the vicinity of the active site of the enzyme with energy score (S) = −29.8249 kcal/mol and root mean standard deviation (RMSD) = 1.9094 (Fig. 3) C. Chemical shifts are expressed in δ-values (ppm) relative to TMS as an internal standard, using DMSO-d 6 as a solvent. Elemental analyses were done on a model 2400 CHNSO analyser (Perkin Elmer, USA). All the values were within ±0.4 % of the theoretical values. All reagents used were of AR grads.

Molecular docking
"All the molecular modeling studies were carried out on an Intel Pentium 1.6 GHz processor, 512 MB memory with Windows XP operating system using Molecular Operating Environment (MOE, 10.2008) software. All the minimizations were performed with MOE until a RMSD gradient of 0.05 kcal mol −1 Å −1 with MMFF94X force field and the partial charges were automatically calculated. The protein data bank file (PDB: 3S2A) was selected for this purpose. The file contains PI3K enzyme co-crystallized with a quinoline ligand obtained from protein data bank. The enzyme was prepared for docking studies where: (i) Ligand molecule was removed from the enzyme active site. (ii) Hydrogen atoms were added to the structure with their standard geometry. (iii) MOE Alpha Site Finder was used for the active sites search in the enzyme structure and dummy atoms were created from the obtained alpha spheres. (iv) The obtained model was then used in predicting the ligand enzymes interactions at the active site".

Conclusion
In summary, we had synthesized a novel series of benzene-sulfonamide derivatives. Seven products 1, 2, 4, 7, 11, 14 and 17 presented sound anticancer activity hostile to lung (A594 Raw), hela, and colorectal (lovo) cancer cell lines with better or comparable activity to DCF. Moreover, molecular docking for these active compounds showed proper fitting on the active site of PI3K enzyme suggesting their action as inhibitors for this enzyme but more investigation should be carried out in the future to explore precisely the mechanism of the action of the synthesized derivatives.