13005 Background: TRC102 (methoxyamine) reverses resistance to alkylating agents by inhibiting base excision repair (BER; a mechanism of DNA repair), thereby increasing DNA strand breaks and potentiating the anti-tumor activity of alkylating agents without additional toxicity, Based on these data, TRC102 is currently being studied in combination with temozolomide in a phase 1 trial. We hypothesized that inhibition of BER by TRC102 would also increase DNA strand breaks and improve the anti-tumor activity of anti-metabolite chemotherapeutics, including pemetrexed, because these agents also produce AP sites that are recognized and repaired by BER. Methods: Pemetrexed- induced AP sites and BER inhibition was quantified using an apurinic/apyrimidinic (AP) site assay in vitro. Single and double DNA strand breaks were quantified by the Comet assay in vitro and anti-tumor activity was assessed in an in vivo xenograft study of subcutaneously implanted H460 human lung cancer cells. Results: Pemetrexed induced and TRC102 reduced the number of available AP sites in pemetrexed- treated H460 cells (by 60–80%), indicating successful inhibition of BER. TRC102 treatment increased DNA strand breaks in pemetrexed-treated H460 cells (2 fold increase versus treatment with pemetrexed alone). Premetrexed treatment alone and in combination with TRC 102 delayed tumor growth in vivo (tumor growth delay of 4.7 days in the 150 mg/m2 pemetrexed alone group, 5.7 days in the 150 mg/m2 pemetrexed + 2 mg/m2 TRC102 group and 6.9 days in the 150 mg/m2 pemetrexed + 4 mg/m2 TRC102 group); in vivo systemic toxicity was not increased. TRC102 alone had no effect in vitro or in vivo. Conclusions: TRC102 effectively inhibits BER in lung cancer cells treated with pemetrexed. Inhibition of DNA repair by TRC102 results in an increase in DNA strand breaks and improved anti-tumor activity versus treatment with pemetrexed alone. Given its preclinical efficacy and safety profile, study of TRC102 combined with pemetrexed in a phase 1 trial is warranted. No significant financial relationships to disclose.
Geochemical compositional controls on DNA strand breaks induced in in vitro cell-free assays by crushed rock powders from the Panasqueira mine area, Portugal
