Abstract 127: Targeting of dr5/trail-r2 in combination with irinotecan triggers p53- and chk2-dependent gastrointestinal toxicity in mice in vivo and synergistic cell death in human gastrointestinal epithelial cells in vitro
Authors: Finnberg Niklas K. , Arunasalam Navaraj , Lang Krystle , Cerniglia George , Motoyama Noboru , Zhou Bin-Bing , El-Deiry Wafik 
Published: February 2011

Abstract
Targeting the TRAIL-death receptor DR5/TRAIL-R2 with agonistic antibodies in combination with chemotherapy may offer more efficient killing of cancer cells compared to either therapy alone. Clinical trials indicate that antibodies targeting TRAIL-death receptors as monotherapy appears safe, the safety of combination therapy is less well investigated. Expression of DR5/TRAIL-R2 is increased in several normal tissues following radiation and chemotherapy in a p53-dependent manner and may subsequently be increasingly sensitized to cell death following co-treatment with DR5/TRAIL-R2-agonists. Wild-type, trail-r-/- (mice lacking the mouse orthologue to human DR5/TRAIL-R2), chk2-/- and Trp53-/- mice were subjected to treatment with a TRAIL-R-agonistic antibody; MD5-1 (1.2 mg/kg bw) alone or in combination with either Irinotecan (280 mg/kg bw) or 5-fluorouracil (5-FU; 150 mg/kg). No toxicity was observed up to a minimum of 1 month following monotherapy with either MD5-1, 5-FU or Irinotecan. However, when MD5-1 was combined with Irinotecan, wild-type but not trail-r-/-, chk2-/- nor Trp53-/- mice showed significant weight loss and increased lethality within 7 days following treatment. Weight loss and lethality was associated with increased acute (24 hrs) epithelial crypt apoptosis and subsequent (4 days) epithelial atrophy and inflammation in the gastrointestinal (GI) tract. Interestingly, although loss of trail-r and p53 did provide complete protection from GI-toxicity when 5-FU was combined with MD5-1, loss of chk2 did not, suggesting that loss of chk2 confer chemotherapeutic-specific protection to the GI-tract when combined with TRAIL-R-targeting antibodies. Co-treatment of animals with the p53-inhibitior cyclic alpha-Pifithrin inhibited the manifestation of GI-toxicity following MD5-1 in combination with chemotherapy and improved weight loss-recovery of surviving animals suggesting that the observed GI-toxicity can be pharmacologically modulated. In order to address the relevance of our findings to normal human cells, we also treated the GI-epithelial cell line FHs 74-Int with Irinotecan in combination with a DR5/TRAIL-R2 agonistic antibody (mAb631). A small increase of cell death (sub-G1 content) relative to untreated control was detected following treatment with mAb631 alone (2.0 ± 0.5 and 4.5 ± 0.6 % respectively). However, when mAb631 was combined with Irinotecan a clear synergistic increase in sub-G1 content was observed (16.4 ± 0.5 and 44 ± 3.9 % respectively). Data suggest that Irinotecan sensitizes the GI-epithelium to TRAIL-R-mediated apoptosis and GI-toxicity in a chk2- and p53-dependent manner. Combined pharmacologic inhibition of p53 may reduce GI-toxicity and subsequently improve the therapeutic window of TRAIL-R2/DR5-agonists and chemotherapy.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 127.