Cedric W. Long

Immunomodulatory and therapeutic properties of alkyl lysophospholipids in mice

This paper describes the immunomodulatory and therapeutic properties of the alkyl lysophospholipids [ALP; 1-O-octadecyl-2-O-rac-glycero-3-phosphocholine (ET-18-OCH3)]. ALP was able to activate macrophages both in vitro and in vivo as well as to act as an immunoadjuvant for syngeneic tumor vaccines. However, ALP appeared to be transferred, at least in part, to the macrophage membrane, and some of the tumoricidal macrophage-activating properties seem to be associated with the direct cytotoxic effect of membrane-released ALP. ALP also had some therapeutic activity for experimental and spontaneous metastases, requiring administration three but not two times weekly at near-toxic doses; this suggests that at least some of its therapeutic activity is due to direct cytotoxicity.

Immunomodulatory and therapeutic properties of FK-565 in mice*

SummaryThe heptanoyl tripeptide, FK-565 is a biological response modifier with potent therapeutic properties for the treatment of experimental and spontaneous metastases. Doses of FK-565 greater than 5 mg/kg are required for in vivo augmentation of natural killer cells, macrophages, and for therapeutic activity, presumably because FK-565 is a peptide small molecular mass which is rapidly degraded and excreted. Optimal therapeutic activity is observed at approximately 25–50 mg/kg FK-565, administered i.v. three times per week for 4 weeks. In addition to its therapeutic properties, which were consistently greater than the positive control at optimal doses, FK-565 had significant immunoaugmentary properties for natural killer cells, macrophages, and T cells both in vitro and in vivo, suggesting that its therapeutic activity is due to immune augmentation.

Induction of endogenous murine type C virus by an arginine analog: l-Canavanine

Abstract l -Canavanine, a naturally occurring analog of arginine, induced endogenous xenotropic type C virus from Kirsten sarcoma transformed BALB/c cells at a frequency approaching induction by cycloheximide. Several other amino acid analogs including another arginine analog, l -homoarginine, did not induce virus, suggesting that inhibition of protein synthesis alone cannot account for the induction effect of l -Canavanine.

Characterization of type C virus induction by amino acid analogs.

Several amino acid analogs were tested for their ability to induce type C virus from a cloned Balb/c mouse cell line transformed by Kirsten sarcoma virus. O-Methylthreonine and hydroxynorvaline, analogs of isoleucine and threonine, respectively, were found to induce type C virus with the host range of Balb:virus-2. Type C virus was also activated by lysine deprivation. When either O-methylthreonine or hydroxynorvaline was used in conjunction with the arginine analog canavanine, the induction equalled or surpassed the maximum induction by cycloheximide. Using synchronized cells, induction of virus by canavanine was found to be cell-cycle dependent. Depriving cells of certain single amino acids alone or in combination with specific analogs markedly reduced protein synthesis without inducing virus. The results suggest that a general reduction in protein synthesis cannot account for the induction and imply that the inducing analogs may affect the functionality or degradation of proteins involved in the regulation of virus expression.

Increased Expression of Endogenous Xenotropic Murine Retrovirus by Treatment with the Tetrapeptides, Tuftsin and Kentsin

Enhancement of endogenous xenotropic virus expression has been found upon treatment with tetrapeptides of a high-passage clone of Balb/c (K-Balb) mouse cells transformed with Kirsten sarcoma virus. Tuftsin (Thr-Lys-Pro-Arg) and kentsin (Thr-Pro-Arg-Lys) increased the expression of virus that was infectious for rat, but not mouse, cells in a concentration-dependent fashion. The enhancement of virus expression by the tetrapeptides was proportional to the spontaneous release of virus. The infectivity of the enhanced virus was neutralized by goat anti-RLV gp70 serum. Actinomycin D inhibited the induction of virus, suggesting that enhanced expression required de novo RNA synthesis. The effects observed using K-Balb cells offer an opportunity to study the many biological effects of these peptides in a fibroblast culture system.

Activation of endogenous type c virus by amino acid alcohols

Abstract Amino acid alcohols were examined for their ability to inhibit protein synthesis and induce endogenous type C virus from Kirsten sarcoma virus (KiSV)-transformed Balb/c mouse cells. Histidinol and tyrosinol, amino alcohols of histidine and tyrosine, were very effective short-term activators of virus. Both inducers were very efficient inhibitors of protein synthesis reducing [ 3 H]leucine incorporation by more than 90% in 1 hr. Two other alcohols, valinol and methioninol, also reduced protein synthesis but gave low activation. The activated virus had the host range of the xenotropic Balb virus:2, and following removal of inducer, the activated state decayed rapidly.

Isolation of a murine type-C virus p30 precursor protein by DNA-cellulose chromatography

Abstract Mouse L929 cells, a cell line shedding type-C virus at a slow rate, contain a viral-specific polyprotein of approximately 70,000 daltons (Pr 70), which is a precursor to the major internal structural protein, p30, of the virus. Pr 70, but not p30, specifically binds to single-stranded (ss) DNA and can be isolated by chromatography on ssDNA-cellulose.

Fusion inhibition: Bioassay of a Type C viral protein

Abstract Based on the observation that concentrated RD-114 virus directly induces fusion in a Rous sarcoma virus-transformed human glioma cell line, KC, an RD-114 virus protein was identified which had the property of inhibiting this fusion. The protein was irreversibly denatured by 2-mercaptoethanol, reacted with neutralizing sera to RD-114 virus, and eluted from guanidine agarose columns in a single peak in the 60 to 80,000 molecular-weight range. It does not prevent the fusion of KC cells by B-propiolactone-inactivated Sendai virus, and remained bound to KC cells even after extensive washing. It is suggested that the RD-114 fusion-inhibition factor is a viral surface protein which normally plays a role in virus attachment and is analogous to the 70,000-dalton glycoproteins (gp70) described for the murine Type C viruses.

Juvenile hormones inhibit murine cell cycle progression and expression of type c viruses

SummaryJuvenile hormones (JH), congeners of retinoic acid, were examined for their capacity to inhibit cell cycle progression and chemically induced expression of endogenous xenotropic retrovirus in Kirsten sarcoma virus-transformed BALB (K-BALB) mouse cells. JHI, II, and III were found to inhibit induction of virus by 5-iododeoxyuridine (IUdR) and histidinol (Hdl) in a concentration-dependent fashion. Some inhibition of macromolecular synthesis was observed upon culture of the cells with JH; the most affected was RNA synthesis, which was reduced 27 to 40% within 4 h by the juvenoids. Epoxide hydrase (EH) activity, as determined by high-pressure liquid chromatography (HPLC), was present in amounts sufficient for the cells to convert the hormones metabolically to an ultimate form. A contact-inhibited K-BALB variant was synchronized by mitotic arrest and the cell cyclespecific effect of JHIII on virus induction during S phase was studied. JHIII added during G1 phase, and followed by induction, inhibited virus expression 95 and 76% by IUdR and Hdl, respectively. Induction was inhibited only 35% when JHIII was added during S phase concomitantly with the inducers and no inhibition was observed when JHIII was added during G2 phase followed by the inducers. JHIII added to synchronous cells in G1 phase inhibited progression of cells into S phase and the onset of DNa synthesis. The results indicate that mouse fibroblasts have a juvenile hormone-sensitive restriction point in G1 phase that might relate to the effects these hormones have on cell replication and differentiation.

Enhancement of Endogenous Xenotropic Murine Retrovirus Expression by Tuftsin

The exposure of a high-passage clone of Kirsten sarcoma virus transformed Balb/c (K-Balb) mouse cells to tuftsin (Thr-Lys-Pro-Arg) enhanced the expression of endogenous xenotropic retrovirus. The tetrapeptide increased the expression of virus that was infectious for rat, but not mouse, cells in a concentration-dependent fashion (0.001-1000 micrograms/ml). Increased virus expression could be achieved during short-term incubations (3-4 hr), with maximum enhancement occurring over longer time periods (16-18 hr). The enhancement of virus expression by tuftsin was proportional to the spontaneous release of virus. The infectivity of the enhanced virus was neutralized by goat anti-RLV gp 70 serum. Actinomycin D inhibited the induction of virus, suggesting that enhanced expression required de novo RNA synthesis. Tuftsin stimulated DNA, RNA, and protein synthesis in K-Balb cells during 16-hr incubations. Increased cellular proliferation was also seen at various time periods. The effects observed using K-Balb cells offer an opportunity to study the modulation of gene expression by tuftsin in a fibroblast culture system.