Heterocyclic organobismuth (III) compounds containing an eight-membered ring: Inhibitory effects on cell cycle progression

Coordination environment dependence of anticancer activity in cyclometalated bismuth(III) complexes with C,O-chelating ligands

In this paper, a series of cyclometalated bismuth(III) complexes bearing C,O-bidentate ligands were synthesized and characterized by techniques such as UV-vis, NMR, HRMS, and single crystal X-ray diffraction. Meanwhile, their cytotoxicities against various human cell lines, including colon cancer cells (HCT-116), breast cancer cells (MDA-MB-231), lung cancer cells (A549), gastric cancer cells (SGC-7901), and normal embryonic kidney cells (HEK-293) were assessed in vitro. Compared with the clinical cisplatin, most of the synthesized complexes possessed significantly higher degrees of anticancer activity and selectivity, giving a selectivity index of up to 71.3. The structure-activity relationship study revealed that the anticancer performance of these bismuth(III) species depends on the factors of coordination environment surrounding the metal center, such as coordination number, coordination bonding strength, lone 6s2 electron pair stereoactivity. The Annexin V-FITC/PI double staining assay results suggested that the coordination environment-dependent cytotoxicity is ascribable to apoptosis. Western blot analysis confirmed the proposal, as evidenced by the down-regulating level of Bcl-2 and the activation of caspase-3. Furthermore, the representative complexes Bi1, Bi4, Bi6, and Bi8 exhibited relatively lower inhibitory efficiency on human ovarian cancer cells (A2780) than on its cisplatin-resistant daughter cells (A2780/cis), thus demonstrating that such compounds are capable of circumventing the cisplatin-induced resistance. This investigation elucidated the excellent anticancer performance of C,O-coordinated bismuth(III) complexes and established the correlation between cytotoxic activity and coordination chemistry, which provides a practical basis for in-depth designing and developing bismuth-based chemotherapeutics.

Biological Activities of Bismuth Compounds: An Overview of the New Findings and the Old Challenges Not Yet Overcome

Bismuth-based drugs have been used primarily to treat ulcers caused by Helicobacter pylori and other gastrointestinal ailments. Combined with antibiotics, these drugs also possess synergistic activity, making them ideal for multiple therapy regimens and overcoming bacterial resistance. Compounds based on bismuth have a low cost, are safe for human use, and some of them are also effective against tumoral cells, leishmaniasis, fungi, and viruses. However, these compounds have limited bioavailability in physiological environments. As a result, there is a growing interest in developing new bismuth compounds and approaches to overcome this challenge. Considering the beneficial properties of bismuth and the importance of discovering new drugs, this review focused on the last decade's updates involving bismuth compounds, especially those with potent activity and low toxicity, desirable characteristics for developing new drugs. In addition, bismuth-based compounds with dual activity were also highlighted, as well as their modes of action and structure-activity relationship, among other relevant discoveries. In this way, we hope this review provides a fertile ground for rationalizing new bismuth-based drugs.

Medicinal chemistry and biomedical applications of bismuth-based compounds and nanoparticles

Bismuth as a relatively non-toxic and inexpensive metal with exceptional properties has numerous biomedical applications. Bismuth-based compounds are used extensively as medicines for the treatment of gastrointestinal disorders including dyspepsia, gastric ulcers and H. pylori infections. Recently, its medicinal application was further extended to potential treatments of viral infection, multidrug resistant microbial infections, cancer and also imaging, drug delivery and biosensing. In this review we have highlighted the unique chemistry and biological chemistry of bismuth-209 as a prelude to sections covering the unique antibacterial activity of bismuth including a description of research undertaken to date to elucidate key molecular mechanisms of action against H. pylori, the development of novel compounds to treat infection from microbes beyond H. pylori and the significant role bismuth compounds can play as resistance breakers. Furthermore we have provided an account of the potential therapeutic application of bismuth-213 in targeted alpha therapy as well as a summary of the biomedical applications of bismuth-based nanoparticles and composites. Ultimately this review aims to provide the state of the art, highlight the untapped biomedical potential of bismuth and encourage original contributions to this exciting and important field.

Heterocyclic organobismuth(III) compound induces nonapoptotic cell death via lipid peroxidation

Heterocyclic organobismuth compounds, such as N-tert-butyl-bi-chlorodibenzo[c,f][1,5]azabismocine (compound 1) and bi-chlorodibenzo[c,f ][1,5]thiabismocine (compound 3), exert potent antiproliferative activities in vitro in human cancer cell lines. We showed that compound 3 induced both apoptotic and nonapoptotic cell death via reactive oxygen species production and mitotic arrest in a dose-dependent manner. The mechanisms underlying the dose-dependent effect of these organobismuth compounds were not clear. In the present study, we examined the dose-dependent mechanism underlying cell death induced by compound 1 in a human pancreatic cancer cell line, SUIT-2, and a human colorectal cancer cell line, DLD-1. Compound 1 inhibited cell growth in a dose-dependent manner and induced cell death. Treatment with the pan-caspase inhibitor zVAD-fmk reduced cell death induced by compound 1, whereas the inhibitory effect of zVAD-fmk was limited. Moreover, compound 1 significantly induced lipid peroxidation with concomitant induction of caspase-independent cell death. Our results suggested that eight-membered ring organobismuth compounds induce nonapoptotic cell death via lipid peroxidation.

Upregulation of nuclear factor (erythroid-derived 2)-like 2 protein level in the human colorectal adenocarcinoma cell line DLD-1 by a heterocyclic organobismuth(III) compound: Effect of organobismuth(III) compound on NRF2 signaling

An increasing number of metal-based compounds, including arsenic trioxide, auranofin, and cisplatin, have been reported to have antitumor activity. Their beneficial effects are controlled by a transcription factor, nuclear factor (erythroid-derived 2)-like 2 (NRF2). In response to oxidative stress, NRF2 induces the expression of cytoprotective genes. NRF2 protein levels are regulated by Kelch-like ECH-associated protein 1 (KEAP1) via ubiquitination. Bi-chlorodibenzo[c,f][1,5]thiabismocine (compound 3), a bismuth compound, is known for its potent anti-proliferative activity against various cancer cell lines. In the present study, we investigated the effect of compound 3 on NRF2 signaling in the human colorectal adenocarcinoma cell line DLD-1 in terms of cell viability as well as mRNA and protein expression levels of NRF2. Compound 3 upregulated NRF2 protein levels in a time- and concentration-dependent manner, accompanied by a marked increase in heme-oxygenase-1 (HO-1) mRNA and protein levels. We observed that brusatol, an NRF2 inhibitor, as well as small interfering RNA (siRNA)-mediated knockdown of NRF2 in DLD-1 cells suppressed compound 3-induced HO-1 expression. The anticancer activity of compound 3 was enhanced by compounds that downregulate NRF2. These results suggest that compound 3 upregulates HO-1 via NRF2 activation and that the NRF2-HO-1 pathway is the cellular response to compound 3. We also discovered that compound 3 slightly downregulated KEAP1; thus, NRF2 activation may be associated with KEAP1 modification. Collectively, our results indicate that compound 3 simultaneously activates an anti-oxidative stress pathway, such as NRF2 and HO-1, and a pro-cell death signal in DLD-1 cells. Our findings may provide useful information for the development of a potent anticancer organobismuth(III) compound.

Platelet-membrane-camouflaged bismuth sulfide nanorods for synergistic radio-photothermal therapy against cancer

Bismuth-containing nanoparticles (BNPs) are potential enhancers for tumor radiotherapy. Improving the bioavailability and developing synergistic therapeutic regimens benefit the drug transformation of BNPs. In the present study, we prepare a mesoporous silica-coated bismuth nanorod (BMSNR) camouflaged by a platelet membrane (PM). This biomimetic material is termed BMSNR@PM. The PM camouflage enhances the immune escape of the BMSNRs by lowering endocytosis by macrophages in the reticuloendothelial system. Additionally, the PM camouflage strengthens the material tumor-targeting capacity and leads to better radiotherapeutic efficacy compared with bare BMSNRs. Owing to the photothermal effect, BMSNR@PMs alters the cell cycle of 4T1 cancer cells post-treatment with 808 nm near-infrared irradiation (NIR). The proportions of S phase and G2/M phase cells decrease and increase, respectively, which explains the synergistic effect of NIR on BMSNR@PM-based radiotherapy. BMSNR@PMs efficiently eradicates cancer cells by the combined action of photothermal therapy (PTT) and radiotherapy in vivo and markedly improves the survival of 4T1-tumor-bearing mice. The synergistic therapeutic effect is superior to the outcomes of PTT and radiotherapy performed alone. Our study demonstrates a versatile bismuth-containing nanoplatform with tumor-targeting, immune escape, and radiosensitizing functionalities using an autologous cell membrane biomimetic concept that may promote the development of radiotherapy enhancers.