Abstract A143: Novel temozolomide analog may overcome MGMT and MMR

Abstract

Abstract Glioblastoma multiforme (GBM) is the most common and lethal type of brain cancer. The current standard of care for GBM patients includes surgery, radiotherapy and oral alkylating agent temozolomide (TMZ) chemotherapy. The cytotoxic activity of TMZ is dependent on DNA repair pathways, being inversely related to O6-methylguanine methyltransferase (MGMT) levels and dependent on functional mismatch repair (MMR). Intrinsic or emergent acquired resistance to TMZ presents severe obstacles to successful treatment. Therefore, TMZ analogs have been designed to overcome TMZ resistance, potentially possessing a broader spectrum of anti-cancer activity. Activities of TMZ and novel analogs were tested against 2 isogenic glioma cell line pairs: SNB19V and U373V (vector control cell lines, low MGMT) and SNB19M and U373M (MGMT overexpressing counterparts). TMZ and the corresponding triazene MTIC demonstrated 13.2- and 9.3-fold resistance in SNB19M cells; 5.4- and 4.25-fold resistance in U373M cells (compared to each vector transfected isogenic pair). Analog DC-010-116, where methoxycarbonylmethylene (CH2CO2CH3) replaces the methyl group of TMZ, and its corresponding triazene exerted growth inhibitory activity in TMZ sensitive (V) and TMZ resistant (M) cells, with GI50 values < 50 µM in all 4 cell lines. In addition, MMR deficient HCT 116 colon carcinoma cells, resistant to TMZ (GI50 590.6 µM) responded to DC-010-116 treatment (GI50 44.6 µM). Therefore, DC-010-116 exerts anticancer activity irrespective of MGMT and MMR status in glioma and colon carcinoma cells. Moreover, cross-resistance to DC-010-116 was not observed in glioma cell lines with acquired TMZ resistance (SNB19VR; U373VR). DC-010-116 blocked SNB19V, SNB19M and SNB19VR cells in G2/M and caused apoptosis in a time and dose dependent manner. Cellular DNA damage was detected by Alkaline Comet Assay, and H2AX phosphorylation indicated formation of lethal DNA double strand breaks following DC-010-116 treatment. DC-010-116 showed 3.7- fold difference in activity in paired base excision repair (BER) deficient/proficient CHO cell lines; furthermore, PARP inhibition potentiated sensitivity of HCT 116 cells to DC-010-116 (3-fold). However, DC-010-116, a likely substrate for plasma esterase activity, was devoid of activity in vivo. Accordingly the hydrolyzed carboxylic acid product (CH2CO2H) was inactive in vitro. In conclusion, we demonstrate that the anticancer activity of DC-010-116 escapes MGMT and MMR, blocks glioma cells in G2/M and induces apoptosis. DNA damage, recruiting BER, was detected. However, in vivo activity was compromized by plasma esterase activity. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A143.