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Res Commun Mol Pathol Pharmacol. 1996 Feb;91(2):131-47.

The activation of murine macrophages and natural killer cells by the partially thiolated double stranded RNA poly(I)-mercapto poly(C).

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Department of Biochemical Pharmacology, School of Pharmacy, State University of New York at Buffalo, 14260, USA.


Partially thiolated analogs of the biological response modifier poly I.poly C (pI.pC) were synthesized. Each of these analogs (pI.MPC) contained a partially thiolated polycytidylate (MPC) strand containing either 1.2%, 4.6%, or 17% 5-mercaptocytosine (%SH) randomly introduced throughout the polynucleotide. The ability of these double stranded RNAs (dsRNAs) to activate murine peritoneal macrophages in vitro and augment natural killer (NK) cell activity in mice following intraperitoneal (i.p.) administration was determined. Macrophages were treated in vitro for 24 hours with pI.pC, or pI.MPC, washed, and then overlayed with exponentially growing L1210 leukemia cells at an effector to target (E:T) ratio of 25:1. The cytostatic effect of the macrophages on the L1210 cells was determined by 3H.thymidine pulse labelling. The rank order of potency for macrophage activation was determined to be: pI.pC>pI.MPC(1.2% SH)>pI.MPC(4.6% SH)pI.MPC(17% SH). Twenty hours following i.p. administration of 5 mg/kg of each pI.MPC analog, splenic NK cell activity was assessed in a standard 51Cr release assay using the murine tumor target cell line YAC- 1. The rank order of potency observed for NK cell activation was determined to be; pI.pCpI MPC(1.2% SH)>pI.MPC(4.6% SH)>pI.MPC(17% SH). These dsRNAs activated NK cells in a dose dependent manner. The efficacy and time course for NK cell activation following i.p. administration of pI.MPC (1.2% SH) at a dose of 10 mg/kg was directly compared to an equivalent 10 mg/kg i.p. dose of pI.pC. NK cell activation took place within three hours following treatment with pI-pC whereas the onset of NK cell activation by pI.MPC (1.2%) occurred between 8 and 20 hours post treatment. NK cell activity steadily declined from 24 to 50 hours post treatment at which time the NK activity in both treatment groups was similar. There was a significant correlation between the immunostimulatory potency of these dsRNAs and their experimentally determined melting temperatures (r2 = 0.88) and percent hyperchromicity upon thermal denaturation (r2 = 0.99). At the lower %SH, pI.MPC retains most of the immunostimulatory activities of p1.pC and may serve as a useful and potent biological response modifier.

[Indexed for MEDLINE]

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