Fungal vincristine from Eutypella spp - CrP14 isolated from Catharanthus roseus induces apoptosis in human squamous carcinoma cell line -A431

BACKGROUND

Catharanthus roseus, a medicinal plant, is known to produce secondary metabolites, vincristine and vinblastine, which are terpenoid indole alkaloids. Previously we have reported that Eutypella spp - CrP14 isolated from stem cutting of this plant had shown significant antiproliferative activity when tested in vitro against HeLa cell line. The present study was conducted to identify the anticancer compound responsible for the anti-proliferative activity of the fungal extract and to evaluate its in vitro anticancer and apoptotic effects.

METHODS

The anti-proliferative activity of the fungal anticancer compound, vincristine was analyzed by MTT assay against different cancer cell lines. We examined its efficacy of apoptotic induction on A431 cells. The parameters examined included cell cycle distribution, loss of mitochondrial membrane potential (MMP), DNA fragmentation and reactive oxygen species (ROS) generation.

RESULTS

The presence of vincristine in fungal culture filtrate was confirmed through chromatographic and spectroscopic analyses, and the amount was estimated to be 53 ± 5.0 μg/l. The partially purified fungal vincristine had strong cytotoxic activity towards human squamous carcinoma cells - A431 in the MTT assay. Furthermore, we showed that the fungal vincristine was capable of inducing apoptosis in A431 cells through generation of reactive oxygen species and activation of the intrinsic pathway leading to loss of MMP.

CONCLUSIONS

We have demonstrated for the first time that the vincristine from Eutypella spp - CrP14 is an efficient inducer of apoptosis in A431 cells, meriting its further evaluation in vivo.

An Endophytic Fungus, Talaromyces radicus, Isolated from Catharanthus roseus, Produces Vincristine and Vinblastine, Which Induce Apoptotic Cell Death

Endophytic fungi isolated from Catharanthus roseus were screened for the production of vincristine and vinblastine. Twenty-two endophytic fungi isolated from various tissues of C. roseus were characterized taxonomically by sequence analysis of the internal transcribed spacer (ITS) region of rDNA and grouped into 10 genera: Alternaria, Aspergillus, Chaetomium, Colletotrichum, Dothideomycetes, Eutypella, Eutypa, Flavodon, Fusarium and Talaromyces. The antiproliferative activity of these fungi was assayed in HeLa cells using the MTT assay. The fungal isolates Eutypella sp—CrP14, obtained from stem tissues, and Talaromyces radicus—CrP20, obtained from leaf tissues, showed the strongest antiproliferative activity, with IC₅₀ values of 13.5 μg/ml and 20 μg/ml, respectively. All 22 endophytic fungi were screened for the presence of the gene encoding tryptophan decarboxylase (TDC), the key enzyme in the terpenoid indole alkaloid biosynthetic pathway, though this gene could only be amplified from T. radicus—CrP20 (NCBI GenBank accession number KC920846). The production of vincristine and vinblastine by T. radicus—CrP20 was confirmed and optimized in nine different liquid media. Good yields of vincristine (670 μg/l) in modified M2 medium and of vinblastine (70 μg/l) in potato dextrose broth medium were obtained. The cytotoxic activity of partially purified fungal vincristine was evaluated in different human cancer cell lines, with HeLa cells showing maximum susceptibility. The apoptosis-inducing activity of vincristine derived from this fungus was established through cell cycle analysis, loss of mitochondrial membrane potential and DNA fragmentation patterns.