squalene epoxidase, which is part of the ergosterol synthesis pathway (Favre &
Ryder, 1996). T. rubrum, which is less sensitive to terbinafine, was first found in
Japan (Suzuki et al., 2018a, 2018b). Allylamine and benzylamine antifungal agents
specifically inhibit squalene epoxidase, which is part of the ergosterol synthesis
pathway (Favre & Ryder, 1996), and block the synthesis of squalene epoxide from
squalene, resulting in accumulation of toxic levels of squalene and decreased levels
of ergosterol production, finally leading to rapid fungicidal activity (Leyden, 1998).
Like terbinafine, itraconazole, an azole, inhibits the growth of fungi by interfering
with the synthesis of ergosterol in the cell wall, but works at a later step than
terbinafine and blocks the formation of ergosterol from lanosterol (Leyden, 1998).
Thus, the mechanism of action between terbinafine and itraconazole differs, and
unsurprisingly, cross-resistance to itraconazole was not observed in terbinafine
low-susceptibility isolates. Based on the results of these studies, we suggested that
the mechanism of resistance in terbinafine low-susceptibility strains may be due to
the loss of sensitivity to squalene epoxidase inhibitors meaning that antifungal drugs
with different mechanisms of action may still be effective.
2.3 Purpose of Basic Medical Research
To explore the mechanism for developing antifungal agents against these resistant
fungi, application of cloning technology using genetic analysis is the key. For these
ringworms, many therapeutic drugs and symptom-relieving methods have been
proposed, but eradicating ringworm fungi that have parasitized the skin stratum
corneum is difficult, and fundamental treatment methods have not yet been
established. The most important issues are the cloning and transformation of genes
involved in the invasion factor (pathogenic factor), the regulatory factor of ringworm, and the establishment of gene disruption. In other words, to develop a tool for
the creation of animal models of ringworm, pathological and ultrastructural analysis
of ringworm can be used to elucidate the pathophysiology and the invasion factors
that are possibly involved in the pathogenesis of ringworm and the mechanisms of
infection (Yamada et al., 2017).
3 New Technologies
3.1 Challenges and Solutions
Gene disruption is difficult in ringworm because (1) the transformation efficiency of
the gene disruption vector is low and (2) the frequency of homologous recombination occurring between the target gene and the vector is low (Yamada, Makimura,
et al., 2009). In ringworm, gene destruction and introduction are difficult, and gene
function analysis is nearly impossible. In many pathogenic fungi other than
142
K. Fujitani et al.
Ryder, 1996). T. rubrum, which is less sensitive to terbinafine, was first found in
Japan (Suzuki et al., 2018a, 2018b). Allylamine and benzylamine antifungal agents
specifically inhibit squalene epoxidase, which is part of the ergosterol synthesis
pathway (Favre & Ryder, 1996), and block the synthesis of squalene epoxide from
squalene, resulting in accumulation of toxic levels of squalene and decreased levels
of ergosterol production, finally leading to rapid fungicidal activity (Leyden, 1998).
Like terbinafine, itraconazole, an azole, inhibits the growth of fungi by interfering
with the synthesis of ergosterol in the cell wall, but works at a later step than
terbinafine and blocks the formation of ergosterol from lanosterol (Leyden, 1998).
Thus, the mechanism of action between terbinafine and itraconazole differs, and
unsurprisingly, cross-resistance to itraconazole was not observed in terbinafine
low-susceptibility isolates. Based on the results of these studies, we suggested that
the mechanism of resistance in terbinafine low-susceptibility strains may be due to
the loss of sensitivity to squalene epoxidase inhibitors meaning that antifungal drugs
with different mechanisms of action may still be effective.
2.3 Purpose of Basic Medical Research
To explore the mechanism for developing antifungal agents against these resistant
fungi, application of cloning technology using genetic analysis is the key. For these
ringworms, many therapeutic drugs and symptom-relieving methods have been
proposed, but eradicating ringworm fungi that have parasitized the skin stratum
corneum is difficult, and fundamental treatment methods have not yet been
established. The most important issues are the cloning and transformation of genes
involved in the invasion factor (pathogenic factor), the regulatory factor of ringworm, and the establishment of gene disruption. In other words, to develop a tool for
the creation of animal models of ringworm, pathological and ultrastructural analysis
of ringworm can be used to elucidate the pathophysiology and the invasion factors
that are possibly involved in the pathogenesis of ringworm and the mechanisms of
infection (Yamada et al., 2017).
3 New Technologies
3.1 Challenges and Solutions
Gene disruption is difficult in ringworm because (1) the transformation efficiency of
the gene disruption vector is low and (2) the frequency of homologous recombination occurring between the target gene and the vector is low (Yamada, Makimura,
et al., 2009). In ringworm, gene destruction and introduction are difficult, and gene
function analysis is nearly impossible. In many pathogenic fungi other than
142
K. Fujitani et al.