The molecular electrostatic potential of the B-DNA helix

Potent antitumor 9-anilinoacridines bearing an alkylating N-mustard residue on the anilino ring: synthesis and biological activity

A series of N-mustard derivatives of 9-anilinoacridine was synthesized for antitumor and structure-activity relationship studies. The alkylating N-mustard residue was linked to the C-3' or C-4' position of the anilino ring with an O-ethylene (O-C(2)), O-butylene (O-C(4)), and methylene (C(1)) spacer. All of the new N-mustard derivatives exhibited significant cytotoxicity in inhibiting human lymphoblastic leukemic cells (CCRF-CEM) in culture. Of these agents, (3-(acridin-9-ylamino)-5-{2-[bis (2-chloroethyl)amino]ethoxy}phenyl)methanol (10) was subjected to antitumor studies, resulting in an approximately 100-fold more potent effect than its parent analogue 3-(9-acridinylamino)-5-hydroxymethylaniline (AHMA) in inhibiting the growth of human lymphoblastic leukemic cells (CCRF-CEM) in vitro. This agent did not exhibit cross-resistance against vinblastine-resistant (CCRF-CEM/VBL) or Taxol-resistant (CCRF-CEM/Taxol) cells. Remarkably, the therapeutic effect of 10 at a dose as low as one tenth of the Taxol therapeutic dose [i.e., 1-2mg/kg (Q3Dx7) or 3mg/kg (Q4Dx5); intravenous injection] on nude mice bearing human breast carcinoma MX-1 xenografts resulted in complete tumor remission in two out of three mice. Furthermore, 10 yielded xenograft tumor suppression of 81-96% using human T-cell acute lymphoblastic leukemia CCRF-CEM, colon carcinoma HCT-116, and ovarian adenocarcinoma SK-OV-3 tumor models.

Drug-receptor recognition: molecular orientation and dielectric effects

1 The orientation of ethidium and its carboxyphenyl derivative was computed at various positions around one turn of the B-DNA helical receptor. 2 Dielectric effects of solvent were included using values for the bulk constant and a dielectric vector to simulate dielectric inhomogeneities. 3 From the electrostatic energy values for the orientations, the corresponding Boltzmann distributions were obtained to assess the orientation restriction to the drug imposed by the receptor. 4 A correlation was observed between the direction of the drug molecular dipole and the local line of force generated by the receptor vector field. 5 These findings are discussed with respect to the phenomenon of drug-receptor recognition.

Drug-receptor recognition: electrostatic field lines at the receptor and dielectric effects

1. In this paper the directional component of the vector electrostatic field emanating from a drug receptor is analysed in the three orthogonal planes. 2. B-DNA with an alternating guanine-cytosine sequence was chosen for a receptor model and the lines of force constructed for two dielectric conditions, namely the cases where firstly the dielectric is homogeneous and a constant throughout the space surrounding the receptor, and secondly where the dielectric is inhomogeneous and is treated as a vector quantity. 3. Electric field line maps indicate marked differences in the local fields situated in the helical wide and narrow grooves for the different sequences of cytosine and guanine; these variations are enhanced when the dielectric is handled as a vector. 4. The significance of electric field lines in interpreting receptor-induced ligand orientation effects is discussed since the direction of the lines is related to the torque that a receptor would impose on an attacking drug molecule.

Molecular electrostatic potential of the nucleic acids

It is generally acknowledged that geometrical and conformational properties of biopolymers have an important effect on their biochemical behaviour. It is less easily recognized that these properties depend also on their macromolecular electronic characteristics.

The aim of this review is to demonstrate the significance of such macromolecular electronic effects. Particularly useful for this sake is the recently much developed concept of ‘molecular electrostatic potential’ (MEP) (Scrocco & Tomasi, 1973, 1978) by which is defined the electrostatic (Coulomb) potential created in the neighbouring space by the nuclear charges and the eletronic distribution of a molecule.

Electrostatic components of drug-receptor recognition. I. Structural and sequence analogues of DNA polynucleotides

The electrostatic fields associated with the important biological receptor DNA have been studied by means of stereoscopic displays to investigate drug-receptor recognition processes. This revealed great differences between A- and B-type structures and enabled significant nucleotide sequence effects to be detected for the latter helix. These variations were further investigated by topological analysis of the surface potential in the two grooves of the B-DNA duplex at different radii from the helix axis. This made it possible to characterize the potential surface and to allocate curvature changes to specific atomic groupings. A general finding was that larger potential fields were found in the space encompassed by the narrow groove with strong potential gradients from the ends of the helix to the centre in both grooves. This gradient may provide a motive force for translating small molecules on the surface of a polynucleotide.