Targeting PKC in multiple myeloma: in vitro and in vivo effects of the novel, orally available small-molecule inhibitor enzastaurin (LY317615.HCl).
In multiple myeloma (MM) protein kinase C (PKC) signaling pathways have been implicated in cell proliferation, survival, and migration. Here we investigated the novel, orally available PKC-inhibitor enzastaurin for its anti-MM activity. Enzastaurin specifically inhibits phorbol ester-induced activation of PKC isoforms, as well as phosphorylation of downstream signaling molecules MARCKS and PKCmu. Importantly, it also inhibits PKC activation triggered by growth factors and cytokines secreted by bone marrow stromal cells (BMSCs), costimulation with fibronectin, vascular endothelial growth factor (VEGF), or interleukin-6 (IL-6), as well as MM patient serum. Consequently, enzastaurin inhibits proliferation, survival, and migration of MM cell lines and MM cells isolated from multidrug-resistant patients and overcomes MM-cell growth triggered by binding to BMSCs and endothelial cells. Importantly, strong synergistic cytotoxicity is observed when enzastaurin is combined with bortezomib and moderate synergistic or additive effects when combined with melphalan or lenalidomide. Finally, tumor growth, survival, and angiogenesis are abrogated by enzastaurin in an in vivo xenograft model of human MM. Our results therefore demonstrate in vitro and in vivo efficacy of the orally available PKC inhibitor enzastaurin in MM and strongly support its clinical evaluation, alone or in combination therapies, to improve outcome in patients with MM.
Podar
Klaus
K
Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA. klaus_podar@dfci.harvard.edu
Raab
Marc S
MS
Zhang
Jing
J
McMillin
Douglas
D
Breitkreutz
Iris
I
Tai
Yu-Tzu
YT
Lin
Boris K
BK
Munshi
Nikhil
N
Hideshima
Teru
T
Chauhan
Dharminder
D
Anderson
Kenneth C
KC
D000284:Administration, Oral; D000818:Animals; D002450:Cell Communication; D018920:Coculture Techniques; D016207:Cytokines / Q000378:metabolism / Q000494:pharmacology; D016503:Drug Delivery Systems; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D051379:Mice; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000473:pathology; D009389:Neovascularization, Pathologic / Q000188:drug therapy; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation; D020033:Protein Isoforms; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D017154:Stromal Cells / Q000166:cytology; D014183:Transplantation, Heterologous; D047368:Tumor Burden / Q000187:drug effects; D014407:Tumor Cells, Cultured
D016207:Cytokines; D007211:Indoles; D010703:Phorbol Esters; D020033:Protein Isoforms; D011493:Protein Kinase C; C504878:enzastaurin