Structural, conformational and thermodynamic aspects of groove-directed-intercalation of flavopiridol into DNA

In vitro interaction of nucleoside reverse transcriptase inhibitor, didanosine with calf-thymus DNA: Insights from spectroscopic studies

Many antivirals interact with DNA and alter their expression profile. Thus, it is necessary to understand the binding mode. Didanosine, a nucleoside reverse transcriptase inhibitor, is used to treat HIV infection in patients with or without acquired immunodeficiency syndrome. Understanding the mechanism of interaction of this nucleoside reverse transcriptase inhibitor with DNA can prove useful in the development of a rational drug designing system. In vitro studies (UV-vis, fluorescence, and viscometry techniques) under physiological conditions (Tris-HCl buffer solutions, pH 7.4) show that didanosine drug interacts with calf-thymus DNA (ct-DNA) via partial intercalative binding mode. UV-visible spectroscopy confirmed the formation didanosine-DNA complex with a binding strength of about 1.5 × 10⁵ M^-1 thus indicating their biological worth. Dye displace experiments and viscometry confirmed that didanosine partially intercalates toward DNA molecules. Negative value of Gibb's-free energy change revealed that the process is spontaneous. The thermodynamic parameters such as enthalpy change (ΔH) and entropy change (ΔS) showed that the acting forces between didanosine and ct-DNA mainly included hydrophobic interactions.

RNA targeting by an anthracycline drug: spectroscopic and in silico evaluation of epirubicin interaction with tRNA

Anthracyclines are putative anticancer agents used to treat a wide range of cancers. Among these anthracyclines, epirubicin is derived from the doxorubicin by the subtle difference in the orientation of C4-hydroxyl group at sugar molecule. Epirubicin has great significance as it has propitious anticancer potential with lesser cardiotoxicity and faster elimination from the body. The present study is done to understand the molecular aspect of epirubicin binding to tRNA. We have used various spectroscopic techniques like Fourier transform infrared spectroscopy (FTIR), absorption spectroscopy and circular dichroism to illustrate the binding sites, the extent of binding and conformational changes associated with tRNA after interacting with epirubicin. From infrared studies, we infer that epirubicin interacts with guanine and uracil bases of tRNA. Results obtained from infrared and CD studies suggest that epirubicin complexation with tRNA does not result in any conformational change in tRNA structure. Binding constant (2.1 × 10³ M^-1) calculated from the absorbance data illustrates that epirubicin has a weak interaction with tRNA molecule. These spectroscopic results like the binding site of epirubicin and binding energy of epirubicin-tRNA complex were also verified by the molecular docking. Results of the present study provide information that aids in the development of efficient RNA targeted drugs from the existing drugs by certain chemical modification in their structure resulting in lesser side effects and better efficacy.Communicated by Ramaswamy H. Sarma.

Binding of platinum derivative, oxaliplatin to deoxyribonucleic acid: structural insight into antitumor action

Platinum-derived chemodrugs constitute an active class in cancer therapeutics. Besides being potent against various solid tumors, oxaliplatin has been recognized as the first platinum compound to be approved for the treatment of colorectal cancer. Structurally, oxaliplatin consists of a platinum metal complexed to oxalate and diaminocyclohexane (DACH) and exert its anticancer action by inhibiting DNA replication and transcription. The present study highlights the binding properties of oxaliplatin with calf thymus DNA using spectroscopic methods to comprehend its binding mechanism at molecular level to overcome associated cellular resistance and side effects. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopic outcomes confirm that oxaliplatin is a covalent binding agent and also provide sequence specificity in DNA molecule. Infrared spectral results further indicate that oxaliplatin alkylates purine nitrogenous bases majorly guanine residues (G) in the major groove via formation of either interstrand or intrastrand guanine-guanine d(GpG) and guanine-adenine d(GpA) (N7 position) crosslinks accompanied with a slight external binding to sugar-phosphate backbone. Again, circular dichroism (CD) spectroscopic results suggest subtle conformational changes in DNA molecule due to its complexation with oxaliplatin and duplex attains an intermediate conformational state, having characteristics of both B- and C-forms. Further, a moderate binding strength of 4.12 ± 0.2 × 10⁴ M^-1 for the interaction has been estimated via ultraviolet-visible spectroscopy. The inferences obtained from these investigations are encouraging and can form the basis for further exploration in the field of rational drug development based on platinum compounds possessing preferential binding for nucleic acid with improved competence. Communicated by Ramaswamy H. Sarma.

Alvocidib (flavopiridol) for the treatment of chronic lymphocytic leukemia

INTRODUCTION

Alvocidib, which has orphan drug designation in chronic lymphocytic leukemia (CLL) from the FDA and the EMA, is a plant-derived semisynthetic flavone that acts as a cyclin-dependent kinase inhibitor. It induces apoptosis in CLL cells in vitro and was introduced into clinical trials in CLL as an intravenous infusion in 1997, which proved disappointing. Since the drug avidly binds to plasma proteins, higher serum concentrations were required for clinical antileukemia activity than those suggested by in vitro studies. Subsequent studies utilizing bolus plus infusional doses revealed significant activity against CLL, even in patients with unfavorable characteristics. However, significant toxicity including high rates of major tumor lysis syndrome, cytokine release syndrome and secretory diarrhea were also observed.

AREAS COVERED

The chemistry, pharmacodynamics, pharmacokinetics and metabolism of alvocidib are briefly discussed and phase I-II studies in CLL are discussed in detail. To date, no phase III studies in CLL have been reported.

EXPERT OPINION

A number of much less toxic drugs with similar efficacy against CLL both with and without unfavorable cytogenetics have come to market. Furthermore, enthusiasm for the development of alvocidib as a single agent for the treatment of CLL has waned, primarily due to its toxicity.