Phase II Study of Enzastaurin, a Protein Kinase C Beta Inhibitor, in Patients With Relapsed or Refractory Diffuse Large B-Cell Lymphoma

Purpose Protein kinase C beta (PKCβ) was identified by gene-expression profiling, preclinical evaluation, and independent immunohistochemical analysis as a rational therapeutic target in diffuse large B-cell lymphoma (DLBCL). We conducted a multicenter phase II study of a potent inhibitor of PKCβ, enzastaurin, in patients with relapsed or refractory DLBCL. Patients and Methods Enzastaurin was taken orally once daily until disease progression or unacceptable toxicity occurred. Study end points included freedom from progression (FFP) for ≥ two cycles (one cycle = 28 days), objective response, and toxicity. Results Fifty-five patients (median age, 68 years) were enrolled. Patients had received a median number of two prior therapies (range, one to five); six patients relapsed after high-dose therapy and autologous stem-cell transplantation. Only one grade 4 toxicity (hypomagnesemia) occurred. Grade 3 toxicities included fatigue (n = 2), edema (n = 1), headache (n = 1), motor neuropathy (n = 1), and thrombocytopenia (n = 1). No grade 3 or 4 neutropenia occurred. No deaths or discontinuations due to toxicity were reported. Fifteen patients completed less than one cycle of therapy. Twelve of 55 patients (22%; 95% CI, 13% to 46%) experienced FFP for ≥ two cycles, and eight patients remained free from progression for ≥ four cycles (15%; 95% CI, 6% to 27%). Four patients (7%; 95% CI, 2% to 18%), including three complete responders and one patient with stable disease, continue to experience FFP 20+ to 50+ months after study entry. Conclusion Treatment with enzastaurin was well-tolerated and associated with prolonged FFP in a small subset of patients with relapsed or refractory DLBCL. Further studies of enzastaurin in DLBCL are warranted.