Vol. 58, Issue 4, 729-737, October 2000

Photo-Induced Inactivation of Protein Kinase C by Dequalinium Inhibits Motility of Murine Melanoma Cells

Regina M. Sullivan, Michael Stone, John F. Marshall, Florian Uberall, and Susan A. Rotenberg

Department of Chemistry and Biochemistry, Queens College-City University of New York, Flushing, New York (R.M.S., S.A.R.), Richard Dimbleby Department of Cancer Research, Imperial Cancer Research Fund Laboratory, St. Thomas' Hospital, London, United Kingdom (M.S., J.F.M.), and Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Innsbruck, Austria (F.U.)

Dequalinium (DECA) is a potent antitumor agent and inhibitor of protein kinase C (PKC). Previously it was shown that PKC activity in vitro could be irreversibly inhibited when treated with DECA at low micromolar concentrations and irradiated with 366 nm of light. This approach was used to probe the role of intracellular PKC activity in the motility of metastatic murine melanoma B16 F10 cells and as a target for DECA analogs with increasing PKC inhibitory potencies. Pretreatment of a monolayer of B16 F10 cells with 250 nM of a DECA analog in the presence of UV irradiation for 5 min resulted in 1) complete inhibition of cell motility for up to 4 h in a time-lapse motility assay and 40 to 60% inhibition of cell migration in a Boyden chamber, and 2) inhibition by 40 to 60% of intracellular phosphatidylserine/Ca²⁺-dependent PKC catalytic activity, signifying inactivation of a conventional PKC isoform. Because PKC is the only conventional PKC isoform detected in B16 F10 cells, a stably transfected clone expressing a kinase-defective mutant of PKC was developed that exhibited a substantial loss of adhesion and motility and was refractory to further inhibition by DECA. These findings identify PKC catalytic activity both as a mechanistic component of cell motility and adhesion and as a critical intracellular target of DECA. These studies further suggest that the combined use of UV with nanomolar concentrations of DECA offers an effective chemotherapeutic approach to inhibit metastatic behavior of melanoma cells.