Abstract
Inhibitors of the M1 and M17 class of aminopeptidases such as CHR-2797 (tosedostat) and bestatin are anti-proliferative agents which induce apoptosis in leukemic cells in vitro. Previously, in leukemic cell lines (Krige et al (2008) Cancer Research 68:6669-79), we have shown that aminopeptidase inhibitors increase the intracellular concentration of small peptides (the substrates of aminopeptidases for the generation of amino acids), leading to amino acid deprivation via inhibition of intracellular protein recycling. In addition, CHR-2797 induced a well defined transcriptional response indicative of amino acid depletion, the amino acid deprivation response (AADR), including upregulation of tRNA synthetases, amino acid transporters and amino acid biosynthetic enzymes. To confirm that the transcriptional response to aminopeptidase inhibition in leukemic cells is an AADR, we have used siRNA to knockdown the expression of ATF4, the transcription factor controlling the response. In these cells AADR gene expression in response to CHR-2797 treatment is ablated. We have now extended our studies with CHR-2797 to non-small cell lung cancer (NSCLC). Microarray analysis of the sensitive tumor cell line H23 treated with CHR-2797 showed the expression of a number of genes, not identified to date as typical AADR genes, were increased. Similar changes were induced by removal of extracellular amino acids and by the threonine tRNA synthetase inhibitor borrelidin, confirming that although the response is different to that seen in leukemic cells it is indeed a novel response to amino acid deprivation. Furthermore, we have demonstrated a correlation between the transcriptional response and sensitivity to the anti-proliferative effects of aminopeptidase inhibition. Other NSCLC cell lines sensitive to the anti-proliferative effects of the compound showed similar transcriptional changes when treated with CHR-2797, whereas cells that were insensitive did not exhibit an AADR, even though it could be induced in these cells by the removal of extracellular amino acids or borrelidin treatment. These data are consistent with the notion that, despite the ready availability of amino acids outside the cell, NSCLC, as well as leukemic cells, are dependent for their survival upon amino acid provision through intracellular protein recycling, a process known to be sensitive to aminopeptidase inhibition. CHR-2797 is currently undergoing late stage clinical development in acute myeloid leukemia. These results highlight CHR-2797 as a promising new anti-cancer agent in solid cancer types as well as leukemia.
Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 1821.
100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO