6), even though this ITC dose cured oral candidiasis caused by an azole-susceptible C. albicans strain (Ishibashi et al., 2007). ITC treatment did not reduce the number of viable C. albicans MML611 cells in the oral cavity significantly (Fig. 6b). In contrast, co-administration of RC21v3 with ITC significantly reduced the lesion score and the viable cell number. These results indicate
that RC21v3 acts synergistically with ITC for oral candidiasis caused by azole-resistant C. albicans. The d-octapeptide RC21 was previously shown to chemosensitize azole-resistant C. albicans strains to azole drugs in vitro (Holmes et al., 2008). We have now demonstrated that the d-octapeptide derivative RC21v3, the
active principal of RC21, functions as a chemosensitizing agent in experimental Gemcitabine cell line oral candidiasis in mice. Treatment of oral infections MG-132 in vivo caused by the azole-resistant C. albicans clinical isolate MML611 with usual therapeutic doses of FLC (0.3 and 0.5 mg kg−1 of body weight per dose) or ITC (0.16 mg kg−1 of body weight per dose) (Graybill et al., 1998; Kamai et al., 2003) was only partial effective. However, the combination treatment with 0.02 μmol per dose of RC21v3 potentiated the therapeutic performance of both FLC and ITC, despite RC21v3 having no effect by itself. The drug combinations reduced the CFU of C. albicans in the oral cavity of the infected mice and reduced their oral lesions. Acetophenone Although the reductions in cfu were statistically significant,
there was only an approximately 10-fold reduction in cfu. In this regard, it is important to note that quantification of oral cfu by swabbing will measure only the loosely associated C. albicans cells and not those penetrating the tissue. Histological examination of the tongues revealed that the thickness of the oral candidiasis lesions was greatly reduced by combination therapy. Critically, the combination of RC21v3 with azole reduced the lesion scores to near zero. Although several studies have shown that fungal drug efflux pump inhibitors can chemosensitize azole-resistant C. albicans strains to azoles in vitro (Niimi et al., 2004; Tanabe et al., 2007; Ricardo et al., 2009), this is the first demonstration that pump inhibitors are effective in an in vivo infection model. It is known that the bioavailability of peptides can be attenuated or affected by the physicochemical environment with rapid degradation by proteinases, nonspecific binding with serum proteins, and interference by high salt concentrations. Because RC21v3 performed well in the oral cavity, we believe that RC21 is well suited to oral delivery for oral candidiasis. Applied locally rather than systemically, it will be less subject to serum-binding or interactions with salts and, as a D-peptide, it will not be susceptible to degradation by the proteinases present in the oral cavity.