Binuclear palladacycles with ionisable and non-ionisable tethers as anticancer agents

The search for novel anticancer agents to replace the current platinum-based treatments remains an ongoing process. Palladacycles have shown excellent promise as demonstrated by our previous work which yielded BTC2, a binuclear palladadycle with a non-ionisable polyethylene glycol (PEG) tether. Here, we explore the importance of the PEG-tether length on the anticancer activity of the binuclear palladacycles by comparing three analogous binuclear palladacycles, BTC2, BTC5 and BTC6, in the oestrogen receptor positive MCF7 and triple-negative MDA-MB-231 breast cancer cell lines. In addition, these are compared to another analogue with an ionisable morpholine tether, BTC7. Potent anticancer activity was revealed through cell viability studies (MTT assays) revealed that while BTC6 showed similar potent anticancer activity as BTC2, it was less toxic towards non-cancerous cell lines. Interestingly, BTC7 and BTCF were less potent than the PEGylated palladacycles but showed significantly improved selectivity towards the triple-negative breast cancer cells. Cell death analysis showed that BTC7 and BTCF significantly induced apoptosis in both the cancer cell lines while the PEGylated complexes induced both apoptosis and secondary necrosis. Furthermore, experimental and computational DNA binding studies indicated partial intercalation and groove binding as the modes of action for the PEGylated palladacycles. Similarly, experimental and computational BSA binding studies indicated and specific binding sites in BSA dependent on the nature of the tethers on the complexes.

Synthesis, Characterization, Thermal Analysis, DFT, and Cytotoxicity of Palladium Complexes with Nitrogen-Donor Ligands

Three new palladium complexes ([Pd(DABA)Cl₂], [Pd(CPDA)Cl₂], and [Pd(HZPY)Cl₂]) bearing dinitrogen ligands (DABA: 3,4-diaminobenzoic acid; CPDA: 4-chloro-o-phenylenediamine; HZPY: 2-hydraziniopyridine) were synthesized, characterized, and tested against breast cancer (MCF-7), prostate carcinoma cell line (PC3) and liver carcinoma cell line (HEPG2). [Pd(DABA)Cl₂] complex exhibited the highest inhibition percentage, lying between 68-71%. The hydrolysis mechanism of each palladium complex, the key step preceding the binding to the biological target, as well as their photophysical properties were explored by means of DFT and TDDFT computations. Results indicate a faster hydrolysis process for the Pd(DABA)Cl₂ complex. The computed activation energies for the first and second hydrolysis processes suggest that all the compounds could reach DNA in their monohydrated form.

Design and Synthesis of Biotinylated Bivalent Carboline Derivatives as Potent Antitumor Agents

Compound 6, a novel β-carboline comprising two 1-methyl-9H-β-carboline-3-carboxylic acids and a biotin moiety conjugated together using tris(2-aminoethyl)amine, was synthesized and tested for its cytotoxicity toward MCF-7 and HepG2 cell lines and antitumor potency in an S180 tumor-bearing mouse model. Compound 6 was delivered via biotin receptor-mediated endocytosis and exerted its therapeutic effects by intercalation binding with DNA. In vivo antitumor evaluations of 6 revealed that it is efficacious and exhibits low systemic toxicity.

An insight into DNA binding properties of newly designed cationic δ,δ'‑diazacarbazoles: Spectroscopy, AFM imaging and living cells staining studies

Two cationic δ,δ'‑diazacarbazoles, 1‑Methyl‑5H‑pyrrolo[3,2‑b:4,5‑b']dipyridinium iodide (MPDPI) and 1,5‑Dimethyl‑5H‑pyrrolo[3,2‑b:4,5‑b']dipyridinium iodide (DPDPI), were devised and synthesized. Through characterizations of the interactions between DNA and the two δ,δ'‑diazacarbazoles by various spectroscopy means, the strong interactions between the two compounds and double-strand DNA have been observed and the interaction types and mechanisms were explored. UV-Vis and fluorescent data have shown the big changes of DNA in the presence of either of the two compounds, demonstrating that both of the δ,δ'‑diazacarbazoles can bind to DNA tightly, and high ionic strength decreased the intercalative interactions. The UV-Vis and fluorescence of dsDNA in the presence of DPDPI showed more profound changes than those in the presence of MPDPI, due to CH₃ (in the structure of DPDPI) taking place of H (in the structure of MPDPI) at the position of 5‑NH. And the circular dichroism (CD) spectra of CT-DNA and atomic force microscopy (AFM) results indicated more compacted conformation of DNA in the presence of DPDPI than MPDPI, implying that DPDPI has a more significant effect on DNA conformations than MPDPI. Most interestingly, fluorescence enhancement of cationic δ,δ'‑diazacarbazoles occurred in the presence of DNA. With ionic strength increasing, the intercalative interactions between δ,δ'‑diazacarbazoles and DNA were weakened, but δ,δ'‑diazacarbazoles-DNA complexes showed enhanced fluorescence, which indicated that there are other interactions present at high ionic strength. Furthermore, laser confocal fluorescence microscopy results proved that DPDPI was membrane-permeable and stained living cells.

α-Diimine homologues of cisplatin: synthesis, speciation in DMSO/water and cytotoxicity

α-Diimine Pt(ii) complexes display variable stability in DMSO and DMSO/water mixtures, depending on the nature of the N-substituents. The most stable compounds are moderately cytotoxic, or are essentially inactive, against A2780 and A2780cisR cancer cell lines.

PdII and PtII complexes with a thio-aza macrocycle ligand containing an intercalating fragment: Structural and antitumor activity studies

Two new Pt^II and Pd^II complexes of formula [LMCl₂] (M=Pt, Pd) were synthesized and characterized both in solution and solid state. They were obtained using the thio-aza macrocycle 9,18-dimethyl-12,17dithia-9,18,27,28-tetraaaza-29-oxatetracyclo[24.2.1.0^2,7.0^20,25]enneicosa-2,4,6,20,22,24,26,28¹-octaene (L) containing the 2,5-diphenyl [1, 3, 4]oxadiazole as intercalating fragment. M^II is coordinated in cis-position by the two S atoms of L. The two crystal structures of [LPtCl₂] and [LPdCl₂] complexes showed that the M^II ion is located outside the macrocyclic cavity. The square planar coordination sphere is fulfilled by two chloride anions in a cisplatin-like arrangement with the chloride leaving groups exposed to the environment. The biological activity of both [LPtCl₂] and [LPdCl₂], monitored towards a leukemic cellular model (U937), is coherent with their ability to interfere, at different levels, with the DNA structure.

The synergistic effect of cobalt on a Pd/Co catalyzed Suzuki–Miyaura cross-coupling in water

We report on the first Suzuki–Miyaura reaction promoted by a phosphine-free trimetallic Pd₂/Co catalyst proceeding in water, under aerobic conditions. Results reveal a synergistic Co–Pd cooperation.

Characterizations of cationic γ-carbolines binding with double-stranded DNA by spectroscopic methods and AFM imaging

Two cationic γ-carbolines, 2-methyl-5H-pyrido[4,3-b]indolium iodide (MPII) and 2,5-dimethyl-5H-pyrido[4,3-b]indolium iodide (DPII), were synthesized, and the DNA-binding properties of the cationic γ-carbolines were elucidated. Through a series of experiments, we proved that the two cationic γ-carbolines could strongly interact with DNA by intercalative binding. However, DPII, with a methyl group substituting H atom of 5-NH, has shown a stronger intercalative interaction with DNA compared to MPII. The dissociation of H from the 5-NH of MPII resulted in better water solubility and less binding affinity to DNA. Atomic force microscopy (AFM) images of pBR322 showed that both MPII and DPII strongly interacted with DNA and induced conformational changes in DNA. Moreover, the CT-DNA circular dichroism (CD) spectra changes and the statistics of the node numbers of pBR322 in AFM images indicated that MPII had more profound effects on DNA conformations compared to DPII. Furthermore, our studies have shown that the interactions between cationic γ-carbolines and DNA were sensitive to ionic strength. Increased ionic strength in the buffer caused the DNA helix to shrink, and the base stacking would be more compact, which resulted in minimal intercalation of cationic γ-carbolines into DNA.