Anticancer activity of a cis-dichloridoplatinum(ii) complex of a chelating nitrogen mustard: insight into unusual guanine binding mode and low deactivation by glutathione

Abstract

A pyridine ring containing a chelating nitrogen mustard ligand bis(2-chloroethyl)pyridylmethylamine hydrochloride (L2·HCl) was synthesized from bis(2-hydroxyethyl)pyridylmethylamine (L1) on reaction with thionyl chloride. Both the ligands upon reaction with cis-[PtCl2(DMSO)2] afforded square planar complexes cis-[PtCl2(L1)] (1) and cis-[PtCl2(L2)] (2) respectively. Both the complexes were characterized by NMR, IR, UV and elemental analysis. 2 crystallized in the P21/c space group. 2 shows greater solution stability than 1 in kinetic studies by 1H NMR. Both 1 and 2 bind the model nucleobase 9-ethylguanine (9-EtG) and form multiple mono-adducts. Existence of unusual N7,O6 chelated guanine bound 2 (2e) was traced. Binding studies of 2 with glutathione (GSH) show formation of a mono-adduct cis-[PtCl(L2)SG] (2c), which transformed within a day to give an aziridinium ion of L2 (2b) after loss of L2. In vitro cytotoxicity of ligands, complexes and the clinical anticancer drug cisplatin show that 2 is the most potent against MCF-7, A549 and MIA PaCa2 exhibiting IC50 values of 12.6 ± 0.8, 18.2 ± 1.8 and 4.2 ± 1.0 μM respectively. The in vitro cytotoxicity of 2 against MCF-7, A549 and MIA PaCa2 was also probed in hypoxia and in the presence and absence of added GSH. Even in the presence of excess GSH in hypoxia, 2 exhibits significant cytotoxicity against MIA PaCa2 and MCF-7 with IC50 of 4.4 ± 0.8 and 12.5 ± 1.1 μM respectively. Metal accumulation studies by ICP-MS display greater cellular internalization of 2, than 1 and cisplatin in MCF-7 cells. 2 arrests the cell cycle at sub G1 and G2/M phases in MCF-7 whereas cisplatin exhibits S phase arrest to be dominant with increase in concentration. Complex 2 exhibits a change in mitochondrial membrane potential, caspase activity and suggests apoptotic cell death through the intrinsic pathway. Moreover it is encouraging to find that 2 also restricts angiogenesis in chick embryo.

Anticancer activity of a chelating nitrogen mustard bearing tetrachloridoplatinum(iv) complex: better stability yet equipotent to the Pt(ii) analogue

“…One important point to note here is that the chemical shifts corresponding to the free aziridinium ion (of equatorial ligand L1, 3b, Scheme 3) were found to be distinctly visible during our earlier work with 3 alone as the starting complex. 32 However in this case where 3 is generated in situ from 1a, we could see new peaks which may be due to aziridinium ion formation, but they did not appear distinctively and hence they cannot be assigned with certainty.…”

“…It is also possible that the formation of the 9-EtG adduct is very quick after the aquation step hence the aquated species could not be observed. It should be borne in mind however, that the chemistry of the Pt(II) complex (3) presented earlier 32 does not support such a fast 9-EtG binding upon aquation hence the above prediction about the difference in the reaction pathway is made.…”

“…In our ligand design we have used the pyridine containing nitrogen mustard (L1) which gave us valuable information during our work on the Pt(II) complex (3, Scheme 2). 32 We have synthesized the Pt(IV) mustard complex 1a in a single step from the Pt(II) complex of the ligand bis(2-hydroxyethyl)-pyridylmethylamine with SOCl 2 in good yield (Scheme 2). For the sake of comparison of activity we also synthesized a Pt(IV) complex (2a) bearing a -NHCH 2 CH 2 Cl group in the ligand (L2) instead of the mustard group, -N(CH 2 CH 2 Cl) 2 (Scheme 2).…”

Injectable Click Polypeptide Hydrogels via Tetrazine-Norbornene Chemistry for Localized Cisplatin Release

“…In addition, the effect of CDDP-loaded hydrogels on the cell cycle of MCF-7 cells was investigated by detecting DNA content after staining with PI. As illustrated in Figure 4B, CDDP-loaded hydrogels induced predominant S phase arrest of MCF-7 cells (50.10%) as compared with the PBS group (38.35%) [32][33][34], while the percentages of MCF-7 cells incubated with blank hydrogels in various phases were comparable to those of the PBS group. This further manifested the cytocompatibility of the iEDDA-based polypeptide hydrogels.…”

Hybrid inhibitors of DNA and HDACs remarkably enhance cytotoxicity in leukaemia cells

“…After exposed to the indicated concentrations of chlorambucil and chloram-HDi for 24 h, the cell cycle distribution of HL-60 cells was measured. As shown in Figure 6, the exposure of HL-60 cells with chloram-HDi remarkably promoted the cell cycle arrest in the G 2 /M phases, compared with the DMSO control and the reference drug chlorambucil in that the prominence of G 2 /M cell cycle arrest is a reported feature of the nitrogen mustards 48,49 . The result indicated that chloram-HDi caused the DNA double-strand breaks of HL-60 cells, leading to the activation of the homologous recombination repair (HRR) pathway through G 2 /M cell cycle arrest.…”