Bala Krishnan

Targeting acute ischemic stroke with a calcium-sensitive opener of maxi-K potassium channels

During ischemic stroke, neurons at risk are exposed to pathologically high levels of intracellular calcium (Ca++), initiating a fatal biochemical cascade. To protect these neurons, we have developed openers of large-conductance, Ca++-activated (maxi-K or BK) potassium channels, thereby augmenting an endogenous mechanism for regulating Ca++ entry and membrane potential. The novel fluoro-oxindoles BMS-204352 and racemic compound 1 are potent, effective and uniquely Ca++-sensitive openers of maxi-K channels. In rat models of permanent large-vessel stroke, BMS-204352 provided significant levels of cortical neuroprotection when administered two hours after the onset of occlusion, but had no effects on blood pressure or cerebral blood flow. This novel approach may restrict Ca++ entry in neurons at risk while having minimal side effects.

Isolation and structure of rebeccamycin ― a new antitumor antibiotic from Nocardia aerocoligenes

The isolation and structure elucidation of rebeccamycin 1, a new antitumor agent from , is described. The NMR spectra of 1 and its peracetate 2 are discussed.

The Antiangiogenic Activity in Xenograft Models of Brivanib, a Dual Inhibitor of Vascular Endothelial Growth Factor Receptor-2 and Fibroblast Growth Factor Receptor-1 Kinases

Tumor angiogenesis is a complex and tightly regulated network mediated by various proangiogenic factors. The fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) family of growth factors, and associated tyrosine kinase receptors have a major influence in tumor growth and dissemination and may work synergistically to promote angiogenesis. Brivanib alaninate is the orally active prodrug of brivanib, a selective dual inhibitor of FGF and VEGF signaling. Here, we show that brivanib demonstrates antitumor activity in a broad range of xenograft models over multiple dose levels and that brivanib alaninate shows dose-dependent efficacy equivalent to brivanib in L2987 human tumor xenografts. Brivanib alaninate (107 mg/kg) reduced tumor cell proliferation as determined by a 76% reduction in Ki-67 staining and reduced tumor vascular density as determined by a 76% reduction in anti-CD34 endothelial cell staining. Furthermore, Matrigel plug assays in athymic mice showed that brivanib alaninate inhibited angiogenesis driven by VEGF or basic FGF alone, or combined. Dynamic contrast-enhanced magnetic resonance imaging, used to assess the effects of brivanib alaninate on tumor microcirculation, showed a marked decrease in gadopentetate dimeglumine contrast agent uptake at 107 mg/kg dose, with a reduction in area under the plasma concentration-time curve from time 0 to 60 minutes at 24 and 48 hours of 54% and 64%, respectively. These results show that brivanib alaninate is an effective antitumor agent in preclinical models across a range of doses, and that efficacy is accompanied by changes in cellular and vascular activities. Mol Cancer Ther; 9(2); 369–78

Stereochemical studies on esperamicins: Determination of the absolute configuration of hydroxyamino sugar fragment.

Abstract The β-D-gluco-hexopyranose configuration has been assigned for the hydroxyamino sugar fragment of esperamicin A 1 . This determination concluded our study on the absolute configuration of the carbohydrate portion of esperamicins.

Protein damage caused by a synthetic enediyne core

The simple enediyne core molecule 1 is shown to cause protein damage to several cellular protein isolates in vitro. The aromatization of 1 to generate a benzene diradical under simulated physiological conditions is also described.

Antitumor and Antiangiogenic Activities of BMS-690514, an Inhibitor of Human EGF and VEGF Receptor Kinase Families

Purpose: The extensive involvement of the HER kinases in epithelial cancer suggests that kinase inhibitors targeting this receptor family have the potential for broad spectrum antitumor activity. BMS-690514 potently inhibits all three HER kinases, and the VEGF receptor kinases. This report summarizes data from biochemical and cellular pharmacology studies, as well as antitumor activity of BMS-690514. Experimental Design: The potency and selectivity of BMS-690514 was evaluated by using an extensive array of enzymatic and binding assays, as well as cellular assays that measure proliferation and receptor signaling. Antitumor activity was evaluated by using multiple xenograft models that depend on HER kinase signaling. The antiangiogenic properties of BMS-690514 were assessed in a matrigel plug assay, and effect on tumor blood flow was measured by dynamic contrast-enhanced MRI. Results: BMS-690514 is a potent and selective inhibitor of epidermal growth factor receptor (EGFR), HER2, and HER4, as well as the VEGF receptor kinases. It inhibits proliferation of tumor cells with potency that correlates with inhibition of receptor signaling, and induces apoptosis in lung tumor cells that have an activating mutation in EGFR. Antitumor activity was observed with BMS-690514 at multiple doses that are well tolerated in mice. There was evidence of suppression of tumor angiogenesis and endothelial function by BMS-690514, which may contribute to its efficacy. Conclusions: By combining inhibition of two receptor kinase families, BMS-690524 is a novel targeted agent that disrupts signaling in the tumor and its vasculature. Clin Cancer Res; 17(12); 4031–41. ©2011 AACR.

The synthesis and characterization of 1,1-bis(aminomethyl)cyclohexaneplatinum(II) compounds and the crystal structure determination of 1,1-bis(aminomethyl)cyclohexaneaquosulphatoplatinum(II) monohydrate

Abstract The synthesis and characterization of a number of 1,1-bis(aminomethylcyclohexane)platinum(II) complexes is described. Reaction of 1,1-bis(aminomethyl- cyclohexane)dichloroplatinum(II) (LPtCl 2 ) with silver sulphate and silver nitrate in water results in the isolation of the corresponding aquosulphato·monohydrate, LPt(H 2 O)SO 4 ·H 2 O and dinitratoplatinum- (II), LPt(NO 3 ) 2 , complexes. Treatment of aqueous solutions of these compounds with an equimolar amount of sodium hydroxide results in the formation of mixtures of hydroxo-bridged dimers and trimers. The less soluble cyclic trimeric species [LPt(μ-OH)] 3 (NO 3 ) 3 ·2H 2 O and {[LPt(μ-OH)] 3 } 2 (SO 4 ) 3 ṡ8H 2 O have been isolated. The 1 H, 13 C and 195 Pt NMR spectra of the various compounds have been studied in D 2 O. In particular, 195 Pt NMR is a valuable tool for identification of the various platinum complexes present in aqueous solution. IR spectral data are reported. The IR spectra of LPt(SO 4 )ṡxH 2 O containing varying amounts of water of crystallization and/or coordination are discussed. In LPt(H 2 O)SO 4 ṡH 2 O the symmetry of the monodentate SO 4 ligand appears to be lowered as a result of strong hydrogen bonding to the water molecules. The crystal structure of this compound has been determined by single-crystal X-ray diffraction. The monoclinic crystal, space group P 2 1 / c , has cell dimensions a = 13.615(9), b = 7.372(1), c = 14.702(2) A, β = 109.26(4)° and has four formula units in the unit cell. The structure was solved by standard methods and refined to R = 0.0337 based on 2671 reflections. The coordination of the metal atom is square planar with two nitrogen atoms, one oxygen of a water molecule and one oxygen of the sulfate anion being bound to platinum(II). There is extensive inter- and intramolecular hydrogen bonding.

Fluorescence polarization studies of the binding of BMS 181176 to DNA.

The DNA binding of BMS 181176, an antitumor antibiotic derivative of rebeccamycin was characterized by DNA unwinding assays, as well as by fluorescence emission and polarization spectroscopic techniques. Unwinding and rewinding of supercoiled DNA was interpreted in terms of intercalation of BMS 181176 into DNA. BMS 181176 shows an enhanced fluorescence emission upon binding to the AT sequence and no enhancement upon binding to the GC sequence. BMS 181176 appears to be a weaker binder to poly(dAdT).poly(dAdT) compared to doxorubicin and ethidium bromide. When bound to DNA, the rotational motion of BMS 181176 is substantially decreased as evident from the increase in fluorescence polarization. BMS 181176 exhibits a range of binding strengths depending on the DNA. This is demonstrated by the Acridine Orange displacement assay using fluorescence polarization.

Stereochemical studies on esperamicins : the absolute configuration of their bicyclic aglycone

Abstract Single crystal x-ray diffraction analyses revealed the relative configuration of esperamicin X and the absolute configuration of 2-deoxy fucose, a fragment present in all known esperamicins. Comparison of the CD curves for esperamicins X and Z gave evidence for their identical chirality. Based on these data the absolute stereochemistry of [7,3,1] bicyclic aglycone of esperamicins has been assigned as C-1 ( S ), C-8 ( S ). and C-12 ( S ).

Determination of DNA Cleavage Specificity by Esperamicins

The esperamicins are members of a class of potent antitumor antibiotics that contain stained diacetylenic ring systems capable of forming DNA-cleaving diradicals upon reaction with thiols. Here we show that the diacetylenic ring core itself determines the sequence specificity for scission of duplex DNA): esperamicin A1, and three products of hydrolysis of the glycon, esperamicins C, D, and E, are found to retain a common sequence preference. The sugar residues exert a strong influence on the cleavage efficiency, presumably by interacting nonspecifically with DNA. The presence of a branch in the DNA is found locally to inhibit scission by esperamicins, and this effect is shown to be due to the core also.