Two monoclonal antibodies against small-cell lung cancer show existence of synergism in binding

Summary Murine IgG1 monoclonal antibodies (mAbs), ITK-2 and ITK-3, were generated against a small-cell lung cancer (SCLC) cell line. Enzyme-linked immunosorbent assay using a variety of established cell lines as substrates, immunoperoxidase staining of freshly frozen tissue sections, and fluorescence-activated cell sorter analysis of peripheral blood leukocytes showed that these mAbs recognize a part of the SCLC-associated cluster 1 antigen. In immunoprecipitation studies, both ITK-2 and ITK-3 bound to a 145-kDa glycoprotein of SCLC cell membrane extracts, as did MOC-1 and NKH-1, which both recognize the cluster 1 antigen. However, because the binding of¹²⁵I-labeled ITK-2 to SCLC cells was not inhibited by MOC-1 or NKH-1, the binding site of ITK-2 on SCLC cells appeared to be different from that of either MOC-1 or NKH-1. Unexpectedly, binding of¹²⁵I-labeled ITK-2 to SCLC cells increased in the presence of ITK-3. This ITK-3-induced increase in ITK-2 binding was due partly to an increase in the number of binding sites for ITK-2 on SCLC cells. Addition of ITK-3 may, therefore, improve the effectiveness of ITK-2-based tumor detection or therapy.     

2-Mercaptoethylamine, a competitive inhibitor of spermidine synthase in mammalian cells

Spermidine synthase from rat ventral prostate was inhibited by 2-mercaptoethylamine (MEA). Inhibition of spermidine synthase by MEA was competitive with respect to one of the substrates putrescine, but not competitive with respect to the other substrate decarboxylated S-adenosylmethionine. MEA markedly depressed spermidine and spermine contents in human erythroid leukemia K562 cells, suggesting that these changes resulted from the inhibitory effect of MEA on spermidine synthase in situ.     

Use of a copper-phthalocyanine membrane electrode for rapid preliminary detection of polycyclic mutagens

Preliminary screening of polycyclic mutagens is achieved within 20 min by using a biomimetic electrode composed of an oxygen electrode and a copper-phthalocyanine membrane. When benzo[alpha]pyrene (0.05 mM) was added to the buffer solution in the presence of 0.98 M hydrogen peroxide, the current of the phthalocyanine electrode decreased. A linear relationship was obtained between the current decrease and the benzo[alpha]pyrene concentration over the range 0.19-0.60 mM. The minimum measurable concentration for benzo[alpha]pyrene was 0.01 mM. Such responses were not obtained for other organic compounds such as alcohol, ether, n-hexane and cyclohexane. The copper-phthalocyanine membrane electrode has selectively detected polycyclic mutagens such as amino acid pyrolysis products. The current decrease was 1.18-1.46 microA when 0.05 mM amino acid pyrolysis products were employed.     

The structure of hemocyanin II from the horseshoe crab, Limulus polyphemus. The amino acid sequence of the second largest cyanogen bromide fragment

Fourteen fragments have been isolated from hemocyanin component II of Limulus polyphemus by cleavage with CNBr. The amino acid sequence of the largest fragment, CNBr Ia has been reported (Yokota, E., and Riggs, A. F. (1984) J. Biol. Chem. 259, 4739-4749). The amino acid sequence of the 12 smaller fragments is reported in an accompanying paper (Moore, M. D., Behrens, P. Q., and Riggs, A. F. (1985) J. Biol. Chem. 261, 10511-10519). We have determined the amino acid sequence of the second largest fragment, CNBr Ib. The fragment contains 142 residues and has a molecular weight of 16,095.     

A wasp venom mastoparan-induced polyphosphoinositide breakdown in rat peritoneal mast cells

The phospholipid metabolism of rat peritoneal mast cells stimulated with mastoparan, a secretagogue purified from wasp venom, was investigated. Mastoparan at 20 micrograms/ml caused a rapid secretion of histamine. Mastoparan induced a transient decrease of phosphatidylinositol 4,5-biphosphate on 32P labeling and generation of a water-soluble degradation product, inositol trisphosphate on [3H]inositol labeling, suggesting the activation of phospholipase C upon stimulation.     

Stimulatory effect of epidermal growth factor on prostaglandin E2 production in mouse fibrosarcoma cell line (HSDM1 C1)

Using HSDM1 C1 cell line derived from the mouse fibrosarcoma which synthesizes and secretes prostaglandin (PG) E2, specific binding sites for epidermal growth factor (EGF), a potent growth stimulator of many tissues, and its effect on PGE2 production by cultured tumor cells were studied. HSDM1 C1 cell line possessed specific, high-affinity receptors for EGF: Kd (5.5 X 10(-10 M) and binding capacity (17,650 sites/cell). EGF significantly stimulated PGE2 production in HSDM1 C1 line cultured in serum-free medium for 24 h in a dose-dependent manner; a 2.5-fold increase over control was induced by as little as 0.1 ng/ml and the maximal effect (3.5-fold increase) by 1 ng/ml. Its stimulatory effect on PGE2 production was completely blocked by indomethacin, an inhibitor of PG biosynthesis. These data suggest that EGF may be involved in modulation of synthesis and/or secretion of PGE2, a potent bone-resorbing factor, by the tumors which may partly contribute to hypercalcemia in certain types of neoplasms.     

Concomitant suppression of plasma ACTH- and beta-endorphin-like immunoreactivity by cyproheptadine, naloxone, and somatostatin in the ectopic ACTH syndrome

Release of plasma ACTH- and beta-endorphin (beta-EP)-like immunoreactivity (LI) was studied in vivo in a patient with an ectopic ACTH-producing malignant thymoma. Administration of lysin vasopressin stimulated concomitant release of plasma ACTH- and beta-EP-LI. Administration of cyproheptadine, naloxone, and somatostatin significantly suppressed plasma levels of ACTH- and beta-EP-LI, while saline infusion did not. Gel exclusion chromatography of the plasma extracts revealed that ACTH-LI consisted of two components, large and small molecular weight form, while beta-EP-LI consisted of three components, large molecular weight, beta-lipotropin-, and beta-EP-sized form; each of these components was incompletely suppressed by somatostatin infusion. It is suggested that certain tumors may have acquired aberrant multiple receptors during malignant transformation which may lead to the paradoxical hormone response as demonstrated in this case.     

The rapid polyphosphoinositide metabolism may be a triggering event for thrombin-mediated stimulation of human platelets

The metabolism of polyphosphoinositides was examined in human platelets activated by thrombin. The addition of thrombin to [3H]glycerol-labeled platelets induced an initial loss and a subsequent increase of the radioactivity in phosphatidylinositol-4,5-bisphosphate (TPI) without any significant change in phosphatidylinositol-4-phosphate (DPI). A marked enhancement of [32P]Pi incorporation into TPI occurred in parallel with an increase in this lipid content, which was accompanied with a conccurent decrease in phosphatidylinositol (PI). The rate of this subsequent increase in TPI was smaller than that observed in [3H]arachidonic acid-labeled platelets, suggesting that formed TPI in activated platelets may contain much greater amount of arachidonate than preexisting TPI in resting platelets. These data indicate that thrombin causes a rapid change in TPI metabolism (initial degradation of preexisting TPI and subsequent production of arachidonate-rich TPI), which might be a primary candidate to modulate thrombin-induced function in human platelets.     

Plasmodium falciparum: Attenuation by irradiation

The effect of irradiation on the in vitro growth of Plasmodium falciparum was investigated. The cultured malarial parasites at selected stages of development were exposed to gamma rays and the sensitivity of each stage was determined. The stages most sensitive to irradiation were the ring forms and the early trophozoites; late trophozoites were relatively insensitive. The greatest resistance was shown when parasites were irradiated at a time of transition from the late trophozoite and schizont stages to young ring forms. The characteristics of radiosensitive variation in the parasite cycle resembled that of mammalian cells. Growth curves of parasites exposed to doses of irradiation upto 150 gray had the same slope as nonirradiated controls but parasites which were exposed to 200 gray exhibited a growth curve which was less steep than that for parasites in other groups. Less than 10 organisms survived from the 10⁶ parasites exposed to this high dose of irradiation; the possibility exists of obtaining radiation-attenuated P. falciparum.