Effects of the interferon-inducer ABPP on colon cancer in rats; importance of tumor load and tumor site

Summary ABPP (2-amino-5-bromo-6-phenyl-4-pyrimidinone) is a pyrimidinone with known interferon-inducing, natural killer (NK) cell activity enhancing, antiviral and antitumor properties in several animal species. Its effect on CC531, a dimethylhydrazine-induced, transplantable, weakly immunogenic adenocarcinoma of the colon in WAG rats, was studied. ABPP was found to have no direct cytotoxic effect on CC531 cells in vitro. When small cubes of tumor of equal weight were implanted under the renal capsule, administration of 250 mg/kg of ABPP i. p. on day 0 and +1 led repeatedly to significant (p<0.02 up to p<0.001) inhibition of tumor growth, when measured on day +7. Lower doses or a single dose of ABPP did not achieve this effect. Late administration (on day +6 and +7) of 250 mg/kg of ABPP in this model was found to have no effect on tumor growth when measured on day +13. When 5×10⁵ tumor cells were injected in the portal vein, administration of 250 mg/kg of ABPP i.p. on day 0 and +1 reduced significantly (p=0.002) the number of liver metastases, when counted on day +30. Survival in this group was significantly prolonged (p<0.01). However when ABPP was given on day +6 and +7, significantly more (p<0.02) metastases in the liver were counted on day +30. The results show a significant antitumor effect of ABPP against tumor CC531 in the subrenal capsule assay (SRCA) model as well as in the liver metastasis model when administered at the time of tumor inoculation. Late administration of ABPP did not inhibit tumor growth in the SRCA and significantly enhanced the development of liver metastases. The role of timing, tumor site, and the mechanisms by which this dual outcome of immunotherapy with ABPP is mediated are discussed. The results of these experiments may have important implications for the design of clinical studies with ABPP.This study was supported in part by a grant from The Upjohn Company, Kalamazoo, Michigan, USA     

Functional effects of expression of hslo Ca activated K channels in cultured macrovascular endothelial cells

The aim of the present study is to elucidate the effects of the expression of large conductance Ca²⁺ activated K⁺ channels (BK_Ca) in an endothelial cell type normally lacking this channel. The human homologue hslo of BK_Ca was expressed in cultured bovine pulmonary artery endothelial (CPAE) cells, which have no endogenous BK_Ca. Membrane potential, ionic currents and Ca²⁺ signals were investigated in non-transfected and transfected cells using a combined patch clamp and Fura-2 fluorescence technique. In non-transfected control CPAE cells, ATP evoked a Ca²⁺ activated CI⁻ current (I_cl,ca). The most prominent current component during ATP stimulation in hslo expressing cells was conducted 13K Ca which resulted in a pronounced transient hyperpolarization. This hyperpolarization, which was absent in non-transfected cells, was enhanced if I_Cl,Ca was blocked with niflumic acid. The sustained component of the Ca²⁺ response during ATP stimulation was significantly larger in hslo transfected cells than in non-transfected cells. This plateau level correlated well with the corresponding effects of ATP on the membrane potential, indicating that the expression of cloned BK_Ca exerts a positive feedback on Ca²⁺ signals in endothelial cells by counteracting the negative (depolarizing)effect of stimulation of Ca²⁺-activated CI⁻ channels.     

Do voltage-gated Kv1.1 and inward rectifier Kir2.1 potassium channels form heteromultimers?

Possible heteromultimer formation between Kv- and Kir-type K⁺ channels was investigated, in connection with the known functional diversity of K⁺ channels in vivo. Voltage-clamp experiments were performed on Xenopus oocytes, either injected with concatenated Kir2.1-Kv1.1 mRNA, or co-injected with Kv1.1 and Kir2.1 mRNA. K⁺ currents could be approximated by the algebraic sum of the 2 K⁺ current types alone. The tandem construct did not show functional expression, although it could be detected by Western blotting. We conclude that Kv1.1 and Kir2.1 α-subunit proteins fail to assemble and do not contribute functional diversity to K⁺ channels.