Study on the interactions between anti-cancer drug oxaliplatin and DNA by atomic force microscopy

Study on the Interactions Between Cisplatin and Cadherin by Fluorescence Spectrometry and Atomic Force Microscopy

Cisplatin is an important platinum drug in cancer chemotherapy in clinical practice. It is well established that the main target of cisplatin is nuclear DNA. However, recent studies have demonstrated that platinum drugs may act on some important functional proteins in the human body. E-cadherin is a newly discovered glycoprotein that has been regarded as an important sign of the occurrence and development of some tumors. This study examines the interactions between cisplatin and E-cadherin by fluorescence spectrometry and atomic force microscopy (AFM). The fluorescence spectrometry results indicated that cisplatin can efficiently quench the fluorescence of E-cadherin. The calculated binding constant Kb was 3.20 × 106 (25 ℃), 1.36 × 106(31 ℃), and 8.22 × 105 L mol-1 (37 ℃). These results reveal that the fluorescence quenching effect of cisplatin on E-cadherin is static quenching. The obtained thermodynamic parameters ΔH < 0, ΔS < 0, and ΔG < 0, indicate that the binding of cisplatin on E-cadherin is a spontaneous process dominated by hydrogen bonds and Van der Waals forces. The AFM results revealed that E-cadherins are interlaced with each other to form a spherical-chain structure. The addition of cisplatin can significantly disrupt the interlaced structure of the E-cadherin molecules.

Oxaliplatin derived monofunctional triazole-containing platinum(II) complex counteracts oxaliplatin-induced drug resistance in colorectal cancer

Oxaliplatin-based chemotherapy is the current standard of care in adjuvant therapy for advanced colorectal cancer (CRC). But acquired resistance to oxaliplatin eventually occurs and becoming a major cause of treatment failure. Thus, there is an unmet need for developing new chemical entities (NCE) as new therapeutic candidates to target chemotherapy-resistant CRC. Novel Pt(II) complexes were designed and synthesized as cationic monofunctional oxaliplatin derivatives for DNA platination-mediated tumor targeting. The complex Ph-glu-Oxa sharing the same chelating ligand of diaminocyclohexane (DACH) with oxaliplatin but is equally potent in inhibiting the proliferation of HT29 colon cancer cells and its oxaliplatin-resistant phenotype of HT29/Oxa. The in vivo therapeutic potential of Ph-glu-Oxa was confirmed in oxaliplatin-resistant xenograft model demonstrating the reversibility of the drug resistance by the new complex and the efficacy was associated with the unimpaired high intracellular drug accumulation in HT29/Oxa. Guanosine-5'-monophosphate (5'-GMP) reactivity, double-strand plasmid DNA cleavage, DNA-intercalated ethidium bromide (EB) fluorescence quenching and atomic force microscopy (AFM)-mediated DNA denaturing studies revealed that Ph-glu-Oxa was intrinsically active as DNA-targeting agent. The diminished susceptibility of the complex to glutathione (GSH)-mediated detoxification, which confers high intracellular accumulation of the drug molecule may play a key role in maintaining cytotoxicity and counteracting oxaliplatin drug resistance.

Structural study on the interactions of oxaliplatin and linear DNA

Damage to cellular DNA is believed to determine the cytotoxicity of oxaliplatin. However, high resolution structures formed by oxaliplatin and different linear DNA remain unclear. This study characterized, the key structures of different linear DNA in the platination process by UV absorption spectra and atomic force microscopy (AFM). Bathochromic shift and hyperchromicity in UV spectra after addition of oxaliplatin revealed that it can disrupt base stacking of DNA in the platination process. AFM results of different linear DNA indicated that, the platination process can induce DNA change from an extended conformation to the network structure with many kinks and finally to the compact particles, or toroids with increasing the incubation time. All AFM results confirmed that, platination of different linear DNA by oxaliplatin is a time depended process. The present AFM results provide, structural evidence about the interactions between oxaliplatin and different linear DNA containing multiple targets. SCANNING 38:880-888, 2016. © 2016 Wiley Periodicals, Inc.