Cell death ELISAs in the phase I clinical evaluation of AEG35156 (XIAP antisense) administered as an intravenous infusion over 7-days, 3-days, and 2-hours.

C163 The X-linked inhibitor of apoptosis protein (XIAP) is a potent anti-apoptotic protein and is widely up-regulated in a variety of cancer cell lines. AEG35156 (Aegera Therapeutics Inc) is a second generation antisense oligonucleotide targeting human XIAP and pre-clinical studies indicate that AEG35156 will induce tumour cell death both as a single agent and in combination with radiotherapy or chemotherapy. AEG35156 has been administered as a 7-day or 3-day continuous infusion every 3 weeks, and as a weekly 2-hour infusion (ongoing). The primary objectives of these Phase I trials were to establish the Maximum Tolerated Dose (MTD) and toxicity profile. Secondary objectives included the evaluation of three potential plasma pharmacodynamic biomarkers of apoptosis, which may be used in conjuction with measurements of the direct impact of AEG35156 on XIAP mRNA and protein, to identify optimal biological doses and schedules of AEG35156 for future studies. 1) An M30 ELISA detects a caspase-cleaved fragment of the epithelial cell protein cytokeratin 18 (CK18) as a selective marker of apoptosis 2) An M65 ELISA detects both intact and caspase-cleaved CK18 as markers of apoptotic and non-apoptotic cell death; and 3) An ELISA assay for the quantification of circulating nucleosomal DNA (nDNA).
 Plasma samples were collected from treated patients, initially with epithelial tumours and subsequently from all types of advanced refractory cancer, at multiple time points during treatment. Samples have been analysed from 24 patients in the 7-day infusion protocol, 16 patients in the 3-day protocol, and 20 patients in the 2-hour protocol. The biomarker profiles showed a temporal association with drug infusion; a significant rise in biomarker value from baseline typically occurred before day 4 of treatment. Generally there was a good correlation between M30, M65 and nDNA results, with the best agreement between M65 & nDNA. Some patients have a biomarker signature suggestive of disease progression. The most commonly occurring drug-related toxicities were reversible transaminitis and thrombocytopenia. . Longitudinal plots of liver transaminases and M65 antigen levels revealed that patients who had an elevation in liver transaminases also had a significant temporally associated rise in M65 antigen levels. Such increases in circulating M65 antigen levels during or following treatment in patients with non-epithelial, non-CK18 expressing tissues suggest that ELISAs may also detect non-tumour tissue toxicity. In conclusion, these emerging results from the XIAP trials suggest three pharmacodynamic biomarkers of apoptosis may have clinical potential as indicators of pathological progression, and can also yield information on both tumour and non-tumour response to AEG35156. Further studies are required to assess the correlation with clinical outcome.