ABSTRACT:Although approaches to the prediction of drug-drug interactions (DDIs) arising via time-dependent inactivation have recently been developed, such approaches do not account for simple competitive inhibition or induction. Accordingly, these approaches do not provide accurate predictions of DDIs arising from simple competitive inhibition (e.g., ketoconazole) or induction of cytochromes P450 (e.g., phenytoin). In addition, methods that focus upon a single interaction mechanism are likely to yield misleading predictions in the face of mixed mechanisms (e.g., ritonavir). As such, we have developed a more comprehensive mathematical model that accounts for the simultaneous influences of competitive inhibition, time-dependent inactivation, and induction of CYP3A in both the liver and intestine to provide a net drug-drug interaction prediction in terms of area under the concentration-time curve ratio. This model provides a framework by which readily obtained in vitro values for competitive inhibition, time-dependent inactivation and induction for the precipitant compound as well as literature values for f m and F G for the object drug can be used to provide quantitative predictions of DDIs. Using this model, DDIs arising via inactivation (e.g., erythromycin) continue to be well predicted, whereas those arising via competitive inhibition (e.g., ketoconazole), induction (e.g., phenytoin), and mixed mechanisms (e.g., ritonavir) are also predicted within the ranges reported in the clinic. This comprehensive model quantitatively predicts clinical observations with reasonable accuracy and can be a valuable tool to evaluate candidate drugs and rationalize clinical DDIs.

Epitopes of the circumsporozoite (CS) protein of Plasmodium falciparum, the most pathogenic species of the malaria parasite, have been shown to elicit protective immunity in experimental animals and human volunteers. The mechanisms of immunity include parasite-neutralizing antibodies that can inhibit parasite motility in the skin at the site of infection and in the bloodstream during transit to the hepatocyte host cell and also block interaction with host cell receptors on hepatocytes. In addition, specific CD4+ and CD8+ cellular mechanisms target the intracellular hepatic forms, thus preventing release of erythrocytic stage parasites from the infected hepatocyte and the ensuing blood stage cycle responsible for clinical disease. An innovative method for producing particle vaccines, layer-by-layer (LbL) fabrication of polypeptide films on solid CaCO3 cores, was used to produce synthetic malaria vaccines containing a tri-epitope CS peptide T1BT* comprising the antibody epitope of the CS repeat region (B) and two T-cell epitopes, the highly conserved T1 epitope and the universal epitope T*. Mice immunized with microparticles loaded with T1BT* peptide developed parasite-neutralizing antibodies and malaria-specific T-cell responses including cytotoxic effector T-cells. Protection from liver stage infection following challenge with live sporozoites from infected mosquitoes correlated with neutralizing antibody levels. Although some immunized mice with low or undetectable neutralizing antibodies were also protected, depletion of T-cells prior to challenge resulted in the majority of mice remaining resistant to challenge. In addition, mice immunized with microparticles bearing only T-cell epitopes were not protected, demonstrating that cellular immunity alone was not sufficient for protective immunity. Although the microparticles without adjuvant were immunogenic and protective, a simple modification with the lipopeptide TLR2 agonist Pam3Cys increased the potency and efficacy of the LbL vaccine candidate. This study demonstrates the potential of LbL particles as promising malaria vaccine candidates using the T1BT* epitopes from the P. falciparum CS protein.

Layer-by-layer microparticle (LbL-MP) fabrication was used to produce synthetic vaccines presenting a fusion peptide containing RSV G protein CX3C chemokine motif and a CD8 epitope of the RSV matrix protein 2 (GM2) with or without a covalently linked TLR2 agonist (Pam3.GM2). Immunization of BALB/c mice with either GM2 or Pam3.GM2 LbL-MP in the absence of adjuvant elicited G-specific antibody responses and M2-specific CD8+ T-cell responses. Following challenge with RSV, mice immunized with the GM2 LbL-MP vaccine developed a Th2-biased immune response in the lungs with elevated levels of IL-4, IL-5, IL-13, and eotaxin in the bronchoalveolar lavage (BAL) fluid and a pulmonary influx of eosinophils. By comparison, mice immunized with the Pam3.GM2 LbL-MP vaccine had considerably lower to non-detectable levels of the Th2 cytokines and chemokines and very low numbers of eosinophils in the BAL fluid post-RSV challenge. In addition, mice immunized with the Pam3.GM2 LbL-MP also had higher levels of RSV G-specific IgG2a and IgG2b in the post-challenge BAL fluid compared to those immunized with the GM2 LbL-MP vaccine. While both candidates protected mice from infection following challenge, as evidenced by the reduction or elimination of RSV plaques, the inclusion of the TLR2 agonist yielded a more potent antibody response, greater protection, and a clear shift away from Th2/eosinophil responses. Since the failure of formalin-inactivated RSV (FI-RSV) vaccines tested in the 1960s has been hypothesized to be partly due to the ablation of host TLR engagement by the vaccine and inappropriate Th2 responses upon subsequent viral infection, these findings stress the importance of appropriate engagement of the innate immune response during initial exposure to RSV G CX3C.

Microparticle vaccines containing the conserved T1B repeat and T* epitopes from the P. falciparum CS protein were synthesized via layer-by-layer (LbL) fabrication on a solid core; microcapsules were prepared by dissolution of the particle core. Mice immunized with microparticles or microcapsules yielded T1B-specific antibody responses that neutralized Plasmodium parasite in vitro. The mice also developed T1BT*-specific cellular responses, including Th1, Th2, and CD4+ cytotoxic effector cells. When challenged with PfPb, a recombinant P. bergheii expressing the T1B repeats from P. falciparum, 70-80% of the mice immunized with microparticle, and 40-50% immunized with microcapsule, showed >90% reduction in liver parasite burden compared to naïve challenged mice. A minority of mice with reduced parasite burden did not have potent PfPb-neutralizing antibody activity. Since depletion of either CD4+ or CD8+ cells prior to challenge did not ablate protection, the vaccine-induced protection appears to be primarily associated with antibody responses but may also involve other mechanisms not yet defined. An examination of cytokine and chemokine gene expression in the liver post-challenge did not reveal any evidence of inflammatory responses following LbL vaccination and PfPb challenge. These results demonstrate that synthetic LbL vaccines bearing the conserved T1BT* epitopes can elicit protective immunity against Plasmodium without triggering unwanted inflammatory responses.

Nanoparticle vaccines synthesized via layer-by-layer (LbL) fabrication were loaded with designed peptides representing epitopes of the attachment (G) and matrix (M2) proteins of respiratory syncytial virus. The CX3C chemokine mimic epitope of RSV-G has been proposed to contribute to inflammatory responses post-challenge while CD8+ T-cell responses against RSV M2 have been shown to limit the severity of infection and inflammatory pathology. Both monovalent designs (G or M2) and multivalent designs (G+M2) were tested. Mice immunized with RSV-G nanoparticles produced antibody responses that recognized the CX3C epitope only in its folded conformation and not in a linearized state. The same sera also bound native RSV-G protein, inhibited binding of RSV-G protein to the CX3CR1 chemokine receptor, and inhibited migration of human leukocytes toward RSV-G protein. Mice immunized with RSV M2 nanoparticles generated CD8+ T-cell responses and in vitro CTL activity against M2-labeled target cells. The multivalent vaccines containing both G and M2 elicited higher antibody responses to RSV-G and, surprisingly, more potent cellular responses against RSV-M2. These novel nanoparticle vaccines are currently being tested for the induction of neutralizing antibody responses and protection from viral challenge. If successful, the LbL nanoparticle fabrication strategy will provide an innovative approach to formulating safe and effective subunit vaccines for respiratory pathogens including RSV.