Preclinical evaluation of an anti-autocrine growth factor monoclonal antibody for treatment of patients with small-cell lung cancer.

We have evaluated an anti-autocrine growth factor monoclonal antibody for potential use in the treatment of patients with small-cell lung cancer. The monoclonal antibody, designated 2A11, binds to the C-terminal region of the autocrine growth factor gastrin-releasing peptide and neutralizes its growth-promoting effects in vitro and in vivo. Equilibrium-binding analysis demonstrated that the peptide binds to the antibody (dissociation constant = 1.5 x 10(-10) at least as avidly as it binds to the tumor peptide receptor. Pharmacokinetic studies in normal BALB/c mice demonstrated an initial clearance half-life (alpha t1/2) of 24.3 +/- 4 hours and a secondary clearance half-life (beta t1/2) of 1039.6 +/- 309 hours, and biodistribution studies revealed a distribution pattern which generally reflected blood flow. Single intravenous infusions of 2A11 (20 mg/20-25-kg dogs) into normal mongrel dogs with surgically created gastric fistulas antagonized the stimulatory effects of exogenously infused gastrin-releasing peptide or bombesin on plasma gastrin release and gastric acid secretion. Toxicology studies in normal dogs (with gastric fistulas) infused with 50 mg 2A11 intravenously three times a week for 4 weeks failed to reveal any adverse behavioral, clinical, or pathological effects. Four of six dogs developed an immune response to 2A11. Anti-idiotypic antibodies elicited in two cases did not mimic the functional effects of the peptide. We conclude that the concept of immunoblockade of an autocrine growth factor appears feasible in vivo.