In vitro and in vivo preclinical evaluation of a minisphere emulsion-based formulation (SmPill®) of salmon calcitonin

Salmon calcitonin (sCT, MW 3432 Da) is a benchmark molecule for an oral peptide delivery system because it is degraded and has low intestinal epithelial permeability. Four dry emulsion minisphere prototypes (SmPill®) containing sCT were co-formulated with permeation enhancers (PEs): sodium taurodeoxycholate (NaTDC), sodium caprate (C10) or coco-glucoside (CG), or with a pH acidifier, citric acid (CA). Minispheres protected sCT from thermal degradation and the released sCT retained high bioactivity, as determined by cyclic AMP generation in T47D cells. Pre-minisphere emulsions of PEs combined with sCT increased absolute bioavailability (F) compared to native sCT following rat intra-jejunal (i.j.) and intra-colonic (i.c.) loop instillations, an effect that was more pronounced in colon. Minispheres corresponding to ~ 2000 I.U. (~ 390 μg) sCT/kg were instilled by i.j. or i.c. instillations and hypocalcaemia resulted from all prototypes. The absolute F (i.j.) of sCT was 11.0, 4.8, and 1.4% for minispheres containing NaTDC (10 μmol/kg), CG (12 μmol/kg) or CA (32 μmol/kg) respectively. For i.c. instillations, the largest absolute F (22% in each case) was achieved for minispheres containing either C10 (284 μmol/kg) or CG (12 μmol/kg), whilst the absolute F was 8.2% for minispheres loaded with CA (32 μmol/kg). In terms of relative F, the best data were obtained for minispheres containing NaTDC (i.j.), a 4-fold increase over sCT solution, and also for either C10 or CG (i.c.), where there was a 3-fold increase over sCT solution. Histology of instilled intestinal loops indicated that neither the minispheres nor components thereof caused major perturbation. In conclusion, selected SmPill® minisphere formulations may have the potential to be used as oral peptide delivery systems when delivered to jejunum or colon.

Left: SmPill® minispheres entrapped with salmon-calcitonin designed for in situ intestinal instillations to rats (bar = 3 mm). Right: Scanning EM of a single minisphere (bar = 500 μm).117