Biomedical subjects

M J Towle

Publications and source records attributed to M J Towle.

4 recordsLinked to original sources

PubMed2001

In vitro and in vivo anticancer activities of synthetic macrocyclic ketone analogues of halichondrin B.

Halichondrin B is a highly potent anticancer agent originally found in marine sponges. Although scarcity of the natural product has hampered efforts to develop halichondrin B as a new anticancer drug, the existence of a complete synthetic route has allowed synthesis of structurally simpler analogues that retain the remarkable potency of the parent compound. In this study, we show that two macrocyclic ketone analogues of halichondrir B, ER-076349 and ER-086526, have sub-nM growth inhibitory activities in vitro against numerous human cancer cell lines as well as marked in vivo activities at 0.1-1 mg/kg against four human xenografts: MDA-MB-435 breast cancer, COLO 205 colon cancer, LOX melanoma, and NIH: OVCAR-3 ovarian cancer. ER-076349 and ER-086526 induce G2-M cell cycle arrest and disruption of mitotic spindles, consistent with the tubulin-based antimitotic mechanism of halichondrin B. This is supported further by direct binding of the biotinylated analogue ER-040798 to tubulin and inhibition of tubulin polymerization in vitro by ER-076349 and ER-086526. Retention of the extraordinary in vitro and in vivo activity off halichondrin B in structurally simplified, fully synthetic analogues establishes the feasibility of developing halichondrin B-based agents as highly effective, novel anticancer drugs.

Animals↗

PubMed1993

Inhibition of urokinase by 4-substituted benzo[b]thiophene-2-carboxamidines: an important new class of selective synthetic urokinase inhibitor.

Urokinase-type plasminogen activator (uPA) is an important mediator of cellular invasiveness. Specifically, cell surface receptor-bound uPA activates plasminogen to the potent general protease plasmin, which then degrades extracellular matrix or basement membrane either directly or via proteolytic activation of latent collagenases. Thus, cell surface uPA initiates an extracellular proteolytic cascade with which invasive cells eliminate barriers to movement. Since cellular invasiveness plays important roles in several disease states, including cancer metastasis and invasion, arthritis and inflammation, and diabetic retinal neovascularization, the development of synthetic uPA inhibitors is an attractive therapeutic goal. Here we show that 4-substituted benzo[b]thiophene-2-carboxamidines represent an important new class of potent and selective synthetic uPA inhibitor. Two compounds in this class, B428 and B623, inhibit human uPA in plasminogen-linked assays with median inhibition concentration (IC50) values of 0.32 and 0.07 microM, respectively. This level of inhibition represents 20- and 100-fold increases in potency, respectively, relative to the 6-7 microM potencies reported for amiloride and 4-chlorophenylguanidine, the two most potent selective synthetic uPA inhibitors previously described. Importantly, both compounds show > 300-fold selectivity for uPA relative to tissue-type plasminogen activator and > 1000-fold selectivity relative to plasmin. Lineweaver-Burk analyses show uPA inhibition by B428 and B623 to be competitive in nature with inhibition constants (Ki) of 0.53 and 0.16 microM, respectively. Since it is cell surface uPA and not free or secreted uPA that is primarily responsible for cellular invasiveness, biologically effective uPA inhibitors must be capable of inhibiting cell surface uPA. B428 and B623 meet this criterion by inhibiting cell surface uPA on HT1080 human fibrosarcoma cells with IC50 values of 0.54 and 0.20 microM, respectively. Moreover, degradation of [3H]fibronectin by HT1080 cells via cell surface uPA-mediated, plasminogen-dependent mechanisms is inhibited by B428 and B623, with IC50 values of 1.5 and 0.39 microM, respectively. In summary, 4-substituted benzo[b]thiophene-2-carboxamidines such as B428 and B623 represent the most potent class of competitive synthetic uPA inhibitors currently known. Their ability to selectively inhibit both free and cell surface uPA as well as cell surface uPA-mediated cellular degradative functions suggests that this class of compounds may hold significant promise for further development as antiinvasiveness drugs.

Amidines↗

PubMed1993

The synthesis of three 4-substituted benzo[b]thiophene-2-carboxamidines as potent and selective inhibitors of urokinase.

Efficient synthesis of structurally novel 4-substituted benzo[b]thiophene-2-carboxamidines 1-3, which selectively inhibit urokinase-type plasminogen activator (uPA) with IC50 values of 70-320 nM, are described. The key intermediate, methyl 4-iodobenzo[b]thiophene-2-carboxylate (7), is prepared from 3-fluoroiodobenzene in two steps in 70% overall yield via fluorine-directed metalation/formylation and subsequent thiophene annulation. Amidination of ester 7 gives the 320 nM inhibitor 1. Palladium-catalyzed arylacetylene and vinyl stannane couplings with ester 7 or 4-iodobenzo[b]thiophene-2-carbonitrile (16, derived from 7), respectively, followed by amidination leads to the more potent inhibitors 2 (IC50 = 133 nM) and 3 (IC50 = 70 nM). These compounds represent an important new class of synthetic uPA inhibitors, with carboxamidine 3 being the most potent selective inhibitor currently described in the literature.

Amidines↗

PubMed1988

Recombinant retroviruses encoding cell surface antigens as selectable markers.

Recombinant retroviruses are frequently used in the transfer and analysis of genes. This report describes new retrovirus vectors that incorporate a cDNA copy of a cell surface antigen to function as a selectable marker. By using techniques based on quantitative cell surface immunofluorescence, these vectors allow the rapid detection and isolation of infected cells. These vectors also allow the rapid detection of packaging cell lines producing large amounts of recombinant retroviruses. Potential applications of these vectors are demonstrated.

Antigens, Surface↗