Selection of a novel anti-nicotine vaccine: influence of antigen design on antibody function in mice

Abstract

Anti-nicotine vaccines may aid smoking cessation via the induction of anti-nicotine antibodies (Ab) which reduce nicotine entering the brain, and hence the associated reward. Ab function depends on both the quantity (titer) and the quality (affinity) of the Ab. Anti-nicotine vaccines tested previously in clinical studies had poor efficacy despite high Ab titer, and this may be due to inadequate function if Ab of low affinity were induced. In this study, we designed and synthesized a series of novel nicotine-like haptens which were all linked to diphtheria toxoid (DT) as carrier, but which differed in the site of attachment of linker to nicotine, the nature of linker used, and the handle used to attach the hapten to DT. The resulting hapten conjugates were evaluated in a mouse model, using CpG (a TLR9 agonist) and aluminum hydroxide (Al(OH)3) as adjuvants, whereby Ab titers, affinity and function were evaluated using a radiolabeled nicotine challenge model. A series of additional linkers varying in length, rigidity and polarity were used with a single hapten to generate additional DT-conjugates, which were also tested in mice. Conjugates made with different haptens resulted in various titers of anti-nicotine Ab. Several haptens gave similarly high Ab titers, but among these, Ab affinity and hence function varied considerably. Linker also influenced Ab titer, affinity and function. These results demonstrate that immune responses induced in mice by nicotine-conjugate antigens are greatly influenced by hapten design including site of attachment of linker to nicotine, the nature of linker used, and the handle used to attach the hapten to DT. While both Ab titer and affinity contributed to function, affinity was more sensitive to antigen differences.

Figure 1. Nicotine and hapten structures.

The thioacetate of Hapten 8 was deprotected to the thiol for coupling with DT.

Figure 2. Synthesis of Haptens 1, 2, 3, 4, 6 and 7.

Figure 3. Synthesis of Hapten 8.

Figure 4. Synthesis of Hapten 5.

Figure 5. Synthesis of Hapten 9.

Figure 6. Synthesis of Hapten 10.

Figure 7. Structures of different linker-modified nicotine hapten.

Figure 8. General scheme for addition of different linkers to Hapten 7.

Figure 9. Anti-nicotine antibody titer and function in mice.

Panel A: BALB/c mice (n = 12/gp) were immunized by IM injection with 10 µg of different nicotine Hapten-DT conjugates adjuvanted with Al(OH)₃ (40 µg Al³⁺) + CpG 24555 (50 µg) on days 0, 28 and 42. Plasma was collected on day 54 and anti-nicotine antibody levels determined by ELISA (Panel A). On day 56 animals received an IV injection of ³H-nicotine (0.05 mg/kg) and plasma and brains collected. Panel B shows nicotine levels in plasma (ng-eq/mL), and Panel C shows nicotine levels in brain (ng-eq/g).

Figure 10. Anti-nicotine antibody titer and function in mice.

Panel A: BALB/c mice (n = 12/gp) were immunized by IM injection with 10 µg of different nicotine Hapten-DT conjugates adjuvanted with Al(OH)₃ (40 µg Al³⁺) + CpG 24555 (50 µg) on days 0, 28 and 42. Plasma was collected on day 54 and anti-nicotine antibody levels determined by ELISA (Panel A). On day 56 animals received an IV injection of ³H-nicotine (0.05 mg/kg) and plasma and brains collected. Panel B shows nicotine levels in plasma (ng-eq/mL), and Panel C shows nicotine levels in brain (ng-eq/g).