Stromal cell protein kinase C-β inhibition enhances chemosensitivity in B cell malignancies and overcomes drug resistance.

Overcoming drug resistance remains a key challenge to cure patients with acute and chronic B cell malignancies. Here, we describe a stromal cell-autonomous signaling pathway, which contributes to drug resistance of malignant B cells. We show that protein kinase C (PKC)-beta-dependent signals from bone marrow-derived stromal cells markedly decrease the efficacy of cytotoxic therapies. Conversely, small-molecule PKC-beta inhibitors antagonize prosurvival signals from stromal cells and sensitize tumor cells to targeted and nontargeted chemotherapy, resulting in enhanced cytotoxicity and prolonged survival in vivo. Mechanistically, stromal PKC-beta controls the expression of adhesion and matrix proteins, required for activation of phosphoinositide 3-kinases (PI3Ks) and the extracellular signal-regulated kinase (ERK)-mediated stabilization of B cell lymphoma-extra large (BCL-X-L) in tumor cells. Central to the stroma-mediated drug resistance is the PKC-beta-dependent activation of transcription factor EB, regulating lysosome biogenesis and plasma membrane integrity. Stroma-directed therapies, enabled by direct inhibition of PKC-beta, enhance the effectiveness of many antileukemic therapies.