(TSS), total dissolved solids (TDS), and total protein content of whey effluent.
Hence, this simple solid-state fermentation approach, employing the endophytic
fungus and cheaper substrates, such as whey and soybean meal may be useful in
producing valued anticancer pro-drug, CPT.
Lately, Clarance et al. (2019), reported the endophyte, F. solani strain ATLOY-8
from Chonemorpha fragrans (Moon) Alston., and it was capable of producing
CPT. The optimized process to yield camptothecin was designed using the conventional approaches and analytical methods. For improved biomass and yield of
CPT, the Box–Behnken design matrix (n = 17) and one factor at a time method was
used to identify and select optimized variables. According to them, the Box–
Behnken design matrix method in the basal media with 1% glucose, 5% absolute
ethanol, and 0.03% precursors (a mixture of geraniol, tryptophan, and tryptamine)
could increase the CPT production up to 1.4 fold increase and biomass up to 1.2
fold in comparison to one factor at a time method.
9.4 Mode of Action of Camptothecin
Early researchers have stated the antineoplastic activity of CPT mainly mediated by
inhibiting nucleic acids synthesis in both tumor (L1210) and normal cells (HeLa)
(Kessel 1971a,b; Horwitz et al. 1971). This inhibitory effect of CPT over macromolecules synthesis was observed to be transient with the removal of the drug.
However, its prolonged treatment period may completely suppress nucleic acids
synthesis leading to cell death. Also, CPT-induced rapid fragmentation of nucleic
acids at concentrations that do not primarily impact on the synthesis of protein
(Horwitz et al. 1971). In intact cells, the suppression of RNA synthesis can be fully
reversed by removing CPT. Nevertheless, CPT failed to block the activities of
purified enzymes (DNA and RNA polymerases). CPT exerts its cytotoxicity by
inhibiting topoisomerase enzymes that relieve the topological strains created during
the process of chromosomal recombination, replication, and transcription
(Champoux 2001; Das et al. 2016). Topoisomerases are of two types (topoisomerase 1 and topoisomerase (2) classified based on their mode of action, i.e.,
whether they cleave either a single or double DNA strands (Raveendran 2015).
Typically, Topoisomerase 1 (Top 1) enzyme relaxes the DNA supercoiling that
involves the following steps: (a) cleavage of one of the two strands of DNA after
the attachment, (b) relaxation of the strand, and (c) re-annealing of the strand. The
incubation of CPT together with isolated DNA results in intact binding and cause
fragmentation of DNA. Further, molecular interaction studies using X-ray crystallography has witnessed the establishment of a Topo1-DNA complex with
numerous interactions (Redinbo et al. 1998; Liu et al. 2000). This forms the target
for many anticancer drugs to induce cell death by trapping this covalent complex
formed by Top-I and II enzymes (Zhang et al. 2011). As stated earlier, the
obstruction of DNA synthesis and DNA cleavage is because of the suppression of
DNA Top 1 enzyme (Hsiang et al. 1985). Top 1 inhibition is mainly mediated by
320
M. K. Swamy et al.
Hence, this simple solid-state fermentation approach, employing the endophytic
fungus and cheaper substrates, such as whey and soybean meal may be useful in
producing valued anticancer pro-drug, CPT.
Lately, Clarance et al. (2019), reported the endophyte, F. solani strain ATLOY-8
from Chonemorpha fragrans (Moon) Alston., and it was capable of producing
CPT. The optimized process to yield camptothecin was designed using the conventional approaches and analytical methods. For improved biomass and yield of
CPT, the Box–Behnken design matrix (n = 17) and one factor at a time method was
used to identify and select optimized variables. According to them, the Box–
Behnken design matrix method in the basal media with 1% glucose, 5% absolute
ethanol, and 0.03% precursors (a mixture of geraniol, tryptophan, and tryptamine)
could increase the CPT production up to 1.4 fold increase and biomass up to 1.2
fold in comparison to one factor at a time method.
9.4 Mode of Action of Camptothecin
Early researchers have stated the antineoplastic activity of CPT mainly mediated by
inhibiting nucleic acids synthesis in both tumor (L1210) and normal cells (HeLa)
(Kessel 1971a,b; Horwitz et al. 1971). This inhibitory effect of CPT over macromolecules synthesis was observed to be transient with the removal of the drug.
However, its prolonged treatment period may completely suppress nucleic acids
synthesis leading to cell death. Also, CPT-induced rapid fragmentation of nucleic
acids at concentrations that do not primarily impact on the synthesis of protein
(Horwitz et al. 1971). In intact cells, the suppression of RNA synthesis can be fully
reversed by removing CPT. Nevertheless, CPT failed to block the activities of
purified enzymes (DNA and RNA polymerases). CPT exerts its cytotoxicity by
inhibiting topoisomerase enzymes that relieve the topological strains created during
the process of chromosomal recombination, replication, and transcription
(Champoux 2001; Das et al. 2016). Topoisomerases are of two types (topoisomerase 1 and topoisomerase (2) classified based on their mode of action, i.e.,
whether they cleave either a single or double DNA strands (Raveendran 2015).
Typically, Topoisomerase 1 (Top 1) enzyme relaxes the DNA supercoiling that
involves the following steps: (a) cleavage of one of the two strands of DNA after
the attachment, (b) relaxation of the strand, and (c) re-annealing of the strand. The
incubation of CPT together with isolated DNA results in intact binding and cause
fragmentation of DNA. Further, molecular interaction studies using X-ray crystallography has witnessed the establishment of a Topo1-DNA complex with
numerous interactions (Redinbo et al. 1998; Liu et al. 2000). This forms the target
for many anticancer drugs to induce cell death by trapping this covalent complex
formed by Top-I and II enzymes (Zhang et al. 2011). As stated earlier, the
obstruction of DNA synthesis and DNA cleavage is because of the suppression of
DNA Top 1 enzyme (Hsiang et al. 1985). Top 1 inhibition is mainly mediated by
320
M. K. Swamy et al.