Antitumor activity of XR5944, a novel and potent topoisomerase poison.

Inhibitors of topoisomerases are widely used in the treatment of cancer, including inhibitors of topoisomerase I (camptothecin analogs such as irinotecan and topotecan) and topoisomerase II (etoposide and doxorubicin). The novel bis-phenazine, XR5944, is a joint inhibitor of topoisomerase I and II as shown by the stabilization of topoisomerase-dependent cleavable complexes. XR5944 demonstrated exceptional activity against human and murine tumor cells in vitro and in vivo.

In vitro and in vivo reversal of P-glycoprotein-mediated multidrug resistance by a novel potent modulator, XR9576.

The overexpression of P-glycoprotein (P-gp) on the surface of tumor cells causes multidrug resistance (MDR). This protein acts as an energy-dependent drug efflux pump reducing the intracellular concentration of structurally unrelated drugs. Modulators of P-gp function can restore the sensitivity of MDR cells to such drugs.

Role of lipoxygenase metabolites in platelet-activating factor- and antigen-induced bronchial hyperresponsiveness and eosinophil infiltration.

The effect of a novel leuktriene B4 receptor antagonist N-[5[[8-(1-hydroxy-2- phenyl)ethyl]dibenzofuran-2yl]5-hydroxypentanoyl]pyrrolidine (PF 10042) has been evaluated in comparison with 2-[3(1-hydroxyhexyl)phenoxymethyl]quinoline hydrochloride (PF 5901), a specific inhibitor of the 5-lipoxygenase pathway of arachidonic acid metabolism, against platelet activating factor (PAF) and allergen induced bronchial hyperresponsiveness and pulmonary eosinophil infiltration in the guinea pig. PF 10042 significantly displaced radiolabelled [3H]leukotriene B4 from binding sites on human neutrophils with an EC50 of 3 muM. PF 10042 (100 mg/kg, i.

Effect of PF 10040 on PAF-induced airway responses in neonatally immunized rabbits.

1. PF 10040 displaced [3H]-PAF from binding sites on rabbit platelets with an IC50 = 1.07 x 10(-5) M, which was approximately three orders of magnitude below that of a standard PAF antagonist WEB 2086 (IC50 = 4.