Tu1898 Therapeutic Potential of a Novel Poly(ADP-ribose) Polymerase Inhibitor, Hydamtiq, in Human Pancreatic and Colon Cancers

Many cancer cells are resistant to TRAIL or FASL through overexpression of c-FLIP, a potent inhibitor of death receptor mediated apoptosis.We previously published that inhibition of c-FLIP by RNAi or treatment with 5μM BAY 11-7085 restored TRAIL and FASL sensitivity in colon and pancreatic cancer cells.However, the pharmacologic regulation of c-FLIP protein in cancer cells is poorly understood.AIMS: To define signaling pathways that regulate c-FLIP in colon and pancreatic cancer cells in order to find potential treatments for PC.METHODS: HT-29 colon and SU.86.86 pancreatic cancer cells were were stably transfected with Firefly luciferase to allow their detection in athymic mice.An immunoblot-based kinome analysis of HT-29 cells treated with BAY 11-7085 was performed by Kinexus.1-5 million cancer cells were injected intraperitoneally (IP) in mice to generate PC.RESULTS: Inhibition of c-FLIP with BAY 11-7085 or c-FLIP RNAi significantly inhibited peritoneal tumors in athymic mice injected with HT-29 colon cancer cells.This was shown to be due to juxtacrine activation of death receptors expressed on the cancer cells by the cognate ligands (TRAIL, FASL) expressed on the mesothelial cells which line the peritoneum.-Kinome analysis revealed activation of ASK, MEKK4 and JNK by BAY 11-7085 in HT-29 cells.-Inhibition of JNK with soluble inhibitors (CC-401, SP600125) or DN-JNK1 construct reversed BAY 11-7085-induced c-FLIP degradation and death receptor-mediated apoptosis in the cancer cell lines.DN-JNK1 expression in HT-29 cells increased PC in mice while DA-JNK1 expression greatly decreased PC in mice compared with control cells.-ROCK is known to activate ASK and JNK.ROCK inhibition (Y27362) diminished BAY 11-7085 induced JNK activation in the cancer cell lines and increased PC in mice.Treatment of the cancer cells with BAY 11-7085 and Y27362 significantly diminished BAY 11-7085-mediated inhibition of PC in mice.Expression of a constitutively active ROCK-1 mutant in the cancer cells greatly decreased PC in mice, and, activated JNK signaling and inhibited c-FLIP expression in the cancer cells.-NMIIA is known to interact with ROCK and NMIIA inhibition (blebbistatin) greatly increased PC in mice.Overexpression of NMIIA in the cancer cells greatly decreased PC in mice and increased ROCK activation (p-Ser19 of MLC), p-JNK levels and inhibited c-FLIP expression in the cancer cells.CONCLUSIONS: Our results define the role of an NMIIA-ROCK-JNK pathway in peritoneal carcinomatosis.Activation of this signaling pathway culminates in inhibition of c-FLIP expression, which restores death receptor-mediated apoptosis in TRAIL-resistant colon and pancreatic cancer cells.These studies reveal the novel combinatorial potential of BAY 11-7085 and TRAIL in treating PC, but add caution the proposed use of JNK inhibitors in cancer.