ANTITUMOR-ACTIVITY OF A MONOCLONAL-ANTIBODY DIRECTED AGAINST GASTRIN-RELEASING PEPTIDE IN PATIENTS WITH SMALL-CELL LUNG-CANCER

Background: Small cell lung cancer (SCLC) cells express and secrete ga strin-releasing peptide (GRP) which binds to receptors and stimulates growth of these cells. A murine monoclonal antibody, 2A11, which binds GRP with high affinity, decreased growth of SCLC cells in vitro and i n athymic nude mice. A phase 1 trial and pharmacokinetic modeling in p atients with lung cancer has defined the phase 2 dose of 2A11 but the antitumor activity in patients is unknown. Methods: Thirteen patients with previously treated SCLC received 2A11 at 250 mg/m(2) over 1 h thr ee times per week for 4 weeks. Serum GRP, urine GRP, serum levels of 2 A11, and human antimouse antibodies (HAMA) were determined. Results: O ne of 12 (8%; 95% confidence interval, 0 to 38%) evaluable patients ha d complete resolution of radiographically detectable tumor lasting 4 m onths. Four patients (33%) had stable disease. No toxic reactions were observed. The pretreatment serum GRP level of the responding patient was 3.1 fmol/mL and the median of nine nine nonresponding patients was 7.,3 fmol/mL (range, <1.0 to 29.0). The mean trough serum 2A11 leved was 49+/-18 mu g/mL in the responding patient and 32 to 487 mg/mL (med ian, 117) in 10 nonresponding patients, HAMA did not increase during 2 A11 administration in any patient. Conclusions: Interruption of the GR P autocrine growth factor loop with 2A11 results in clinical antitumor activity in a minority of patients with previously treated SCLC. Furt her evaluation of the antitumor effects of 2A11 is the warranted to de fine characteristics associated with response to 2A11.