Submitted May 17, 2006
Accepted September 19, 2006
PKC412 demonstrates JNK-dependent activity against human multiple myeloma cells
Janelle Sharkey, Tiffany Khong, and Andrew Spencer*
The Alfred Hospital, Australia
* Corresponding author; email: aspencer{at}netspace.net.au.
The effect and mode of action of the protein kinase C (PKC) inhibitor PKC412 on human multiple myeloma (MM) cell lines (HMCL) and primary MM cells was explored. We found that PKC412 induced apoptosis of HMCLs and primary MM cells with variable efficacy, however, some activity was seen against all HMCLs and primary MM cells with 
0.5µM PKC412. PARP cleavage and decreased PKC activity was observed in all HMCLs tested. Furthermore, PKC412 inhibited c-Fos transcription and nuclear protein expression, induced reactive oxygen species (ROS) production and induced both c-Jun expression and phosphorylation. The latter was inhibited by co-treatment with the JNK inhibitor SP600125, which similarly abrogated PKC412-induced apoptosis, suggesting that PKC412 induced apoptosis is a JNK dependent event. PKC412 treatment secondarily induced pro-survival stress responses as evidenced by activation of NF
B and increased expression of the heat shock proteins HSP 70 and HSP 90. Consistent with the former, sequential inhibition of NFB activation with bortezomib or SN50 synergistically enhanced cell killing. Our results demonstrate that PKC412 induces partially JNK dependent apoptosis of HMCL and primary MM cells and that this effect is enhanced by NFB inhibition. The further evaluation of PKC412 in the treatment of MM is justified.
