The Conjugates of Indolo[2,3- b]quinoline as Anti-Pancreatic Cancer Agents: Design, Synthesis, Molecular Docking and Biological Evaluations

Abstract

New amide conjugates of hydroxycinnamic acids (HCAs) and the known antineoplastic 5,11-dimethyl-5H-indolo[2,3-b]quinoline (DiMIQ), an analog of the natural alkaloid neocryptolepine, were synthesized and tested in vitro for anticancer activity. The compound 9-[((2-hydroxy)cinnamoyl)amino]-5,11-dimethyl-5H-indolo[2,3-b]quinoline (2), which contains the ortho-coumaric acid fragment, demonstrated dose-dependent effectiveness against both normal BxPC-3 and metastatic AsPC-1 pancreatic cancer cells. The IC₅₀ values for AsPC-1 and BxPC-3 were 336.5 nM and 347.5 nM, respectively, with a selectivity index of approximately 5 for both pancreatic cancer cells compared to normal dermal fibroblasts. Conjugate 2 did not exhibit any hemolytic activity against human erythrocytes at the tested concentration. Computational studies were performed to predict the pharmacokinetic profile and potential mechanism of action of the synthesized conjugates. These studies focused on the ADME properties of the conjugates and their interactions with DNA, as well as DNA-topoisomerase alpha and beta complexes. All of the conjugates studied showed approximately one order of magnitude stronger binding to DNA compared to the reference DiMIQ, and approximately two orders of magnitude stronger binding to the topoisomerase II-DNA complex compared to DiMIQ. Conjugate 2 was predicted to have the strongest binding to the enzyme-DNA complex, with a Ki value of 2.8 nM.

Keywords: biological activity; heterocyclic moieties; molecular modeling; nature-derived molecules; organic synthesis.

Figure 1

The structure of drugs included in FOLFIRINOX combination therapy against metastatic pancreatic cancer (also called FOLFOXIRI).

Figure 2

Schematic structure of registered drug Adcertis—the conjugate of brentuximab monoclonal antibody and monomethyl auristatin E antineoplastic agent [19].

Figure 3

The examples of anticancer drug–sugar conjugates designed to enhance cancer targeting through GLUT transporter mechanism: glufosfamide, doxorubicin derivative, 2-D-glucose conjugated paclitaxel.

Figure 4

Examples of anticancer hybrid molecules: indenoisoquinoline–camptothecin, chalcone-coumarin, coumarin–artemisinin.

Figure 5

Chemical structures of DIMIQ (6), 9-amino-DiMIQ and HCA conjugates 1–5.

Scheme 1

Synthesis of 1–5 conjugates. Reagents and reaction conditions: (i) CH₃OH, CH₃COCl, r.t.; (ii) allyl bromide, K₂CO₃, acetone, r.t.; (iii) NaOH, H₂O/MeOH; (iv) TBTU, DIPEA, DMF, r.t.; (v) Et₃SiH, Pd(PPh₃)₄, DMF, r.t.; (vi) pyridine, DMAP, (CH₃CO)₂O; (vii) SOCl₂, DCM; (viii) pyridine, DCM, −20–−5 °C then r.t; (ix) K₂CO₃, DMF, r.t.; (x) DCC, DMAP, DMF, 0 °C, then r.t.

Figure 6

Cytotoxic effect of newly synthesized conjugates 1–5 and control DiMIQ (6), determined by the MTT assay, after a 72 h incubation period for BxPC-3 (A) and AsPC-1 (B) cell lines. The results were expressed as % of viability compared to the untreated control.

Figure 7

Cytotoxic effects of conjugates 1–5 and reference compound DiMIQ (6) on HeLa (A) and MCF-7 cells (B) after a 72 h incubation period. The results were expressed as a % of viability compared to the untreated control.

Figure 8

Cytotoxic effects of selected conjugates (1 and 2) and 5,11-dimethyl-5H-indolo[2,3-b]quinoline (6) on NHDF cells, determined by the MTT assay after 72 h of incubation. The results were expressed as % of viability compared to the untreated control.

Figure 9

Cytotoxic effects of conjugates 1 and 2, reference DiMIQ (6), HCA derivatives 12 and 13, 6 plus 12, 6 plus 13 on BxPC-3 cells after 72 h of incubation at 500 nM concentrations. The results were expressed as the % of viability compared to the untreated control.

Figure 10

Structures of ligands used in the computational part of this study.

Figure 11

Predicted binding sites and hydrogen bonds between ligands (in green) and DNA (in orange/yellow): (a) for compound 4, (b) for compound 2 and its predicted binding sites, as well as the most important interactions in the complex formed by conjugate 2 with DNA, (c) for topoisomerase II alpha, and (d) for topoisomerase II beta.