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The response of cultured normal and DNA repair deficient human cells to Adenovirus type 12 : UV-impaired virus or the combined effect of virus and chemical carcinogens Lam, Paul Pong-Shing

Abstract

The action of UV and chemical carcinogens, on the replication of Adenovirus type 12 (Ad 12) in cultured normal and DNA repair deficient human cultures was examined Fibroblasts obtained from skin biopsies of a normal person and 3 patients with Xeroderma pigmentosum (XP-E, XP-C, XP-K) were grown in monolayer cultures fed with Eagle's Minimum Essential Medium (MEM) supplemented with fetal calf serum. Cells were exposed to UV-irradiated Ad 12 or the combined treatment with Ad 12 and chemical carcinogens. The chemicals which have been examined include 4-nitroquinollne-N-oxide (4NQO) and its derivatives, N-methyl-N¹nitro-N-nitroso-guanidine (MNNG), aflatoxin Bl, and sterigmatocystin. The cells were sampled at 72 hours post-infection and cells with replicating virus were identified by the presence of intranuclear inclusion bodies (IB). When normal and XP cultures were exposed to UV-irradiated Ad 12, the DNA repair deficient XP cultures showed a reduced capacity to form IB. The ability to reactivate the irradiated virus appeared to-depend on the repair capacity of the cells. For example, XP-K which has a higher repair than XP-C and XP-E reactivated UV-impaired Ad 12 more efficiently. A lower frequency of cells with IB in XP cultures was also observed following the combined treatment with Ad 12 and certain chemical carcinogens. For example, there was a marked difference between XP and control cells following exposure to Ad 12 and 4NQO. The capacity to form IB was abolished faster in XP cells than in control cells. It is postulated that 4NQO interacted with viral DNA and the damage was unrepaired or only partially repaired in XP cells resulting in an abortive infection. On the other hand in control cells, the damaged viral DNA was repaired more efficiently resulting in a. successful viral replication. Exposure of cells infected with Ad 12 to MNNG, however, showed no difference in the capacity to form IB between control and XP cells. It is postulated that MNNG interacted with the viral DNA but the damage was repaired efficiently in control and XP cells thereby resulting in a successful viral replication in both cell types. This agrees with previous reports that DNA repair synthesis as shown by unscheduled ³HTdR uptake was observed in both normal and XP cells following MNNG treatment. An in vitro technique to simulate in vivo metabolism of pre-carcinogens was used to "activate" aflatoxin Bl and sterigmato-cystin. It was reported that when aflatoxin Bl or sterigmatocystin was combined with NADP-dependent activation systems containing the post-mitochondria I supernatant (9S) fraction of mouse liver homogenate, levels of DNA repair synthesis, chromosome aberrations and cell lethality was increased. In the present study, cells infected with Ad 12 were exposed to "activated" aflatoxin Bl or sterigmato-cystin. Without any "activation", aflatoxin Bl and sterigmatocystin showed little effects on IB formation. However, XP cells exposed to "activated" aflatoxin Bl or sterigmatocystin showed a marked. decrease in IB formation as compared to control cells. It is postulated that "activated" aflatoxin Bl and sterigmatocystin also interacted with viral DNA as in the case of 4NQO and the damage was unrepaired or partially repaired in XP cells resulting in an abortive infection. The consequences of an abortively infected cell to become a neoplastic cell and the possible use of this Ad 12 and carcinogen combined treatment as a cheap and efficient way of screening environmental chemical carcinogens and DNA-repair deficient human populations are also discussed.

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