First in human phase I trial of 852A, a novel systemic toll-like receptor 7 agonist, to activate innate immune responses in patients with advanced cancer.

PURPOSE

Recent advances in the understanding of innate immunity suggest that an orchestrated sequence of events is required to elicit a productive immune response against cancer. We studied the systemic administration of the Toll-like receptor 7 agonist 852A, a small-molecule imidazoquinoline, in patients with advanced cancer. Preclinical studies showed that 852A stimulates plasmacytoid dendritic cells to produce multiple cytokines, such as IFN-alpha, interleukin-1 receptor antagonist, and IFN-inducible protein-10. Our goal was to define the tolerated dose, pharmacokinetics, pharmacodynamics, and immunologic effects of 852A in humans.

EXPERIMENTAL DESIGN

Eligible adult patients with refractory solid organ tumors received i.v. 852A thrice weekly for 2 weeks. Patients who had responses or stable disease were eligible for additional cycles.

RESULTS

Twenty-five patients (median age, 55.0 years; 72% male) were enrolled in six cohorts at dose levels of 0.15 to 2.0 mg/m(2). Serum drug levels showed dose proportionality and no evidence of drug accumulation. The maximum tolerated dose was 1.2 mg/m(2); higher doses were limited by fatigue and constitutional symptoms. Increases in IFN-alpha, interleukin-1 receptor antagonist, and IFN-inducible protein-10, immunologic activity, and clinical symptoms were observed in all patients receiving dose levels > or =0.6 mg/m(2). Significant correlations were found between pharmacodynamic biomarkers and pharmacokinetic variables, and an objective clinical response was seen.

CONCLUSIONS

852A was safely administered i.v. at doses up to 1.2 mg/m(2) thrice weekly for 2 weeks with transient or reversible adverse effects. This novel Toll-like receptor 7 agonist is biologically active and holds promise for stimulating innate immune responses. Future trials are warranted to assess its therapeutic role in patients with cancer.