Results of a Phase I Trial of SGN-40 (Anti-huCD40 mAb) in Patients with Relapsed Multiple Myeloma.

SGN-40 is a humanized anti-CD40 monoclonal antibody that has demonstrated potent in vitro and in vivo efficacy against cell lines expressing CD40, a member of the tumor necrosis factor receptor family. CD40 is widely expressed on tumors of B-cell origin, including myeloma, non-Hodgkin’s lymphoma, Hodgkin’s disease, and chronic lymphocytic leukemia. SGN-40 has been evaluated in a phase I, multi-dose, single-agent, dose escalation study for patients with relapsed or refractory multiple myeloma. This single-arm trial was designed to evaluate safety, pharmacokinetics, immunogenicity, and antitumor activity. Thirty-two patients were treated at five clinical sites. Patients had been heavily pretreated with a median of four prior regimens and 4.8 years since diagnosis. Initially, patients were treated with four weekly infusions at a cohort-specific dose. This schedule was well-tolerated at 0.5, 1.0 and 2.0 mg/kg/wk; however, two of three patients experienced dose-limiting toxicities following the first dose at 4 mg/kg. One patient had aseptic meningitis (grade 3) and another had headache (grade 3) and aseptic meningitis (grade 4); both patients fully recovered after several days of symptom management. Subsequently, the protocol was amended to allow intra-patient dose-loading, which resulted in successful dose escalation to 8 mg/kg, the highest dose tested. There was neither recurrence of grade 3 neurotoxicity nor evidence of cumulative toxicity. Drug-related adverse events were mostly grade 1 or 2 and included: fatigue (38%), headache (34%), nausea (16%), conjunctivitis (13%), diarrhea (13%), vomiting (13%), anemia (9%), anorexia (9%), chills (9%), and pyrexia (9%). Transient grade 3 elevation of hepatic transaminases (1) and grade 3 neutropenia (1) were observed. Overall, toxicity did not appear to increase in incidence or severity at higher doses. Patients were evaluated at baseline and end of treatment for development of anti-SGN-40 antibodies. Of 30 patients for whom appropriate samples were available for testing, only one low-titer immune response (16 ng/mL) was detected, suggesting that immunogenicity does not appear to be a significant problem in this patient population. Pharmacokinetic analysis demonstrates dose-proportional changes in Cmax and AUC with a relatively short terminal half-life, similar to that seen in non-human primates. Final analysis of SGN-40 serum levels is ongoing. Although several patients demonstrated decreased M-protein and improvement in subjective symptoms, no patients met criteria for objective response. Five patients (16%) had stable disease at the time of restaging. In summary, dose-dependent toxicity was established only in relation to the first dose of SGN-40, which may be due to partial agonistic signal transduction. Using a dose-loading schedule, SGN-40 was administered up to 8 mg/kg without reaching a maximum tolerated dose. Some patients with advanced myeloma appeared to derive clinical benefit from therapy, and further development of this antibody, either as monotherapy or in combination with other anti-myeloma therapies, is indicated.