Design and Synthesis of Acridine Derivative as Telomerase Inhibitors for The Treatment of Lung Cancer

Abstract

The current study was initiated with a thorough assessment of the cancer literature by which lung cancer has been identified as one of the deadliest cancers, among all types of cancer. It has been observed that 80-90% of malignant tumours, including lung cancer, utilize telomerase activity for achieving immortality. Numerous anti-telomerase approaches were intended for anti-cancer activity till date. However, none of the approaches has been successful in getting the FDA approval, either due to lower potency, lower selectivity or toxicity constraints. The present research emphasizes on finding novel anti-cancer agents for targeting telomerase enzyme that can provide a broad-spectrum activity with a significant reduction of toxicity. During the designing process, the biologically active scaffold was identified through pharmacophore modelling with the aid of DISCOtech refined by the GASP module in Sybyl X. Resultant of the study gave nine feature pharmacophore unit, consisted of one hydrophobic feature, one acceptor atom, one donor atom, three donor site and three acceptor sites of the receptor protein. Further, the model was validated by ROC curve and GH score analysis followed by virtual screening through the NCI database. Virtual screening helped to enrich active molecules from the randomly selected molecules. Bio-isosteric replacement was sought to replacement of functional groups or scaffolds for acquiring novel and better intellectual properties of the parent compound. Simultaneously 3D-QSAR (CoMFA and CoMSIA) provided a guideline regarding the favourable and unfavourable fields of the compound responsible for telomerase inhibition. Based upon these knowledge-based approaches, hundreds of thiadiazole bearing acridine derivatives were designed and docked with telomerase protein (5CQG) which gave the idea about the essential molecular interactions with the receptor protein. In-silico ADMET explained the designed acridine-thiadiazole compounds were non-toxic and showed drug-likeness properties. From all this data, 32 compounds were selected for synthesis and biological activities. For the synthesis of desired compounds, a halo-amine coupling reaction between o-chloro-benzoic acid and substituted anilines were performed, which led to the formation of anthranilic acid. Further, the cyclization of anthranilic acid gave 9-chloroacridine derivatives. Simultaneously the substituted thiadiazole derivatives were synthesised by the cyclisation of thiosemicarbazide and benzaldehydes. In the last step of the synthesis, halo-amine coupling between 4-substituted-9-chloro-acridine derivatives with 2-amino-1,3,4-thiadiazole gave the desired compounds. All the synthesised compounds were characterised by FTIR, Mass and 1H, 13C NMR spectroscopy and the purity of the compounds were analysed by HPLC. The anti-proliferative activity of the compounds was screened against the various cancerous cell lines viz small cell lung cancer (A-549), non-small cell lung cancer (NCIH-460), colon cancer (HT-29), breast cancer (MDA-MB-231) and Vero cells. The potential anti-proliferative compounds were further analysed by colony-forming assay and flow cytometric analysis. Based on all these studies, compounds HB-KV-A1-102 (114), HB-KV A2-101(121), HB-KV-A2-102 (122), and HB-KV-A3-101 (132) were found to be the potent against lung cancer. Further, the telomerase inhibitory potential of these compounds over the A549 cell line was determined by TRAP assay, where all these compounds were found to be significantly potent with compared to control and standard drug (BIBR 1532). In the control group, highest telomerase activity with maximum telomere amplification as highest fold change value of 1.0 was observed, while in the presence of BIBR 1532 the minimum amplification with fold change value of 0.148 was observed. In the case of cells treated with compounds 114, 121, 122, and 132 the amplification or the fold change value of 0.176, 0.214, 0.535 and 0.189 were observed, respectively. After completion of in-vitro analysis, the compounds were assessed for the in-vivo biological evaluation by benzo (a)pyrene induced lung cancer animal model, and the efficacy of these compounds were measured by the biochemical parameters and histological assessment of lung tissue. Among all four selected compound 121 got special attention during in-vitro and in-vivo analysis. It showed better telomerase inhibition effect with fold change value of 0.214. Also, it showed high anti-proliferative effect, with a decrease in the colony formation efficacy of the cancer cell and had equivalent potency as standard compound BIBR 1532 during apoptosis analysis. This compound also gave highly prominent results during the in-vivo analysis and treated lung cancer similar to standard drug everolimus. The key findings of the study paw the way for identifying the novel potential compounds for the treatment of lung cancer, that predominantly target telomerase in future.