Abstract 5557: Steady DNA adduct accumulation by dibenzo[a,l]pyrene implants

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL The past and current trends in determining the DNA-damaging and carcinogenicity potential of environmental toxicants rely largely on treatment of rodents with single or multiple bolus doses. To simulate the human scenario where the exposure is generally continuous to low doses, we have developed polymeric implants embedded with carcinogens. When grafted subcutaneously, polymeric implants provide continuous (“24/7”) low dose exposure. In this study we report the effects of sustained low doses of a highly potent environmental carcinogen, dibenzo[a,l]pyrene (DBP) on DNA adduct accumulation. Different size DBP implants (10 – 20 mm long, 1.4 – 2.4 mm dia; 5% DBP load) were tested first in a pilot study using female A/J mice to optimize the implant surface area. Two 20-mm implants (1.4 mm dia), which produced maximal lung DNA adducts, were used subsequently. Groups of female A/J mice (n = 4 – 6) were grafted with sham or DBP implants. For comparison, animals were also treated in parallel with a bolus carcinogenic dose of DBP intraperitoneally (6 mg/kg) or vehicle alone. Animals from both the treatment groups were euthanized at different time intervals and selected tissues were collected. Analysis of the target (lung) DNA adducts by 32P-postlabeling showed qualitative identical adduct patterns by the two routes of administration; the sham treatments showed no detectable adducts. As expected, the bolus dose treatment resulted in higher DNA adducts (in adducts /109 nucleotides) (72 ± 18) compared with the implant group (33 ± 17) one week post-treatment. However, 3 weeks later, adduct levels in the implant group increased (54 ± 17) but a significant declined occurred in the i.p treatment group (19 ± 13). The adduct levels after 4 weeks in the implant group (66 ± 19) were somewhat higher than the 3 week group, suggesting that the adduct levels plateaued. The steady accumulation of DNA adducts was consistent with continuous release of DBP from the implant (about 10 µg/day based on in vitro release). The study is ongoing to determine if the low-dose continuous exposure which provides steady accumulation of DNA adducts in the target tissue will be tumorigenic. In summary, the steady-state adduct level reflect human exposure scenario and this approach will be ideal to determine both carcinogenicity and biological/pathological changes due to low-dose exposure as well as for screening potential chemopreventive agents. This exposure system has been used to determine efficacy of chemopreventive agents (accompanying abstracts by Aqil et al.; Gupta et al.) (Supported from CA-118114, KLCRP and Agnes Brown Duggan Endowment). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5557. doi:10.1158/1538-7445.AM2011-5557