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Antitumor Activity of Silica Gel PF 254 Eluate¹

Rega Institute for Medical Research, University of Leuven, Leuven, 3000 Belgium

Tumor growth in NMRI mice infected neonatally with the Moloney murine sarcoma virus was effectively inhibited by an aqueous eluate from the silica gel "Kieselgel PF 254." This inhibitory effect was observed whether the silica gel eluate was injected 12 hr before virus inoculation or mixed directly with the virus inoculum. Upon mixing with the Moloney murine sarcoma virus, the silica gel eluate was barely effective if the virus-eluate mixture was incubated for only 1 min (at 25°) but significantly more effective if the mixture was incubated for 5 min (or more) (at 25°), suggesting that the antitumor activity of the eluate was due to a direct inactivating effect on the virus. This virus-inactivating effect was equally well expressed in immunocompetent (NMRI) as in immunoincompetent (genetically thymusless nude) mice. The postulated virucidal effect of silica gel eluate appeared to be limited to oncogenic RNA viruses; the eluate did not alter the infectivity of other viruses such as vaccinia, herpes simplex, Newcastle disease, vesicular stomatitis, and polio. The Moloney murine sarcoma virus-inhibiting effect of the silica gel eluate might have been related to a stimulatory effect on the RNA-dependent DNA polymerase activity of oncogenic RNA viruses, as a markedly increased DNA synthesis was noted in an in vitro DNA polymerase assay with the Moloney murine leukemia virus. However, the silica gel eluate did not affect the integrity of the Moloney murine leukemia virus, as assayed by isopycnic centrifugation of treated and untreated virus particles in a sucrose density gradient.

¹ This study was supported by the Ligue pour la Prévention du Cancer, Prix Docteur René Reding.

Received 2/20/73. Accepted 5/24/73.