Part C | 21.5
536 Part C Marine Genomics
generally harbor many such small molecules, which
can be screened well with induced gene expression.
However, the main hindrance in this method is that
only specific types of molecules can be screened out
(Fig. 21.4).
21.3.5 Sequence-Based Metagenomics
This method generally involves the design and use of
polymerase chain reaction (PCR) primers or hybridization probes for the gene being targeted, which for
enzymes is usually based on conserved regions of an
already well-characterized protein family (Fig. 21.5).
In brief, an environmental sample is collected and
then the total community DNA is extracted from the
sample. The isolated DNA is then embedded into the
suitable nitrocellulose membrane.
Preparation of the Probe
A list of the novel compounds reported to be present
in this environment should be made. A detailed search
for corresponding genes should be made through Basic Local Alignment Search Tool (BLAST) and the
probe can be designed either by PCR amplification or
by synthesis of part of these target genes. The targeted probe is labeled in vitro with [5’ c/ c32p]dCTP
(3753000 mCi mM
1 ) with a Nick translation kit following the recommended protocol supplied with the
kit.
32 P-labeled oligonucleotides are separated from the
32 P-labeled probe by elution through a 3 cm 3 Sephadex
G-50 column with a column buffer that contains 0:25 M
NaC1, 0:05 M Tris, 0:002 M EDTA, and 0:5 SDS (pH
8:0) [21.29].
Hybridization
Binding of the
32 P-labeled DNA probe with a complementary sequence of the DNA-bound nitrocellulose
membrane is a crucial and tricky step in this method.
In brief, the DNA-bound nitrocellulose membrane is
deeped in a prehybridization buffer for initial washing
of the membrane. Subsequently, the prehybridization
buffer is replaced by a hybridization buffer with the
addition of the required amount of DNA probe. After
completion of hybridization, a final washing is performed in a temperature fixed on the basis of the
required stringency condition.
21.4 The Hurdles of Drug Discovery
The prevention of different forms of cancer is the
biggest challenge to the medical scientist at present.
However, the development of new anticancer medicines
is an arduous task that requires the coordinated efforts
of a team of scientists from chemical and biological
sciences. Any potential cancer chemotherapeutic candidate must undergo a rigorous series of tests prior to
gaining FDA approval for commercialization. The process generally starts with in vitro tests against a panel
of 60 different types of cancer cells. Additionally,
xenograft models are also conducted on many occasions. Determination of the effective dose (ED 50 ) is the
next step. A molecule becomes a candidate for testing
in humans if it displays both toxicity against cancer
cells and tolerance by healthy cells and in the later
stage by whole animals. Human testing generally follows a three-phase protocol. Initially, Phase I involves
treatment of a small number of healthy (paid) volunteers with the drug candidate in order to ascertain
whether humans tolerate the compounds. If no adverse
effects are detected, then the drug is generally used on
a small number of patients with different cancers that
do not respond to conventional treatment (Phase II).
Drug candidates that continue to show therapeutic potential at this point then enter Phase III trials, in which
they are administered to a broad range of cancer patients. Eventually, if the drug candidate survives these
experimental challenges, FDA sanctions the approval
after analyzing all the data. It is reported that generally more than 99:9% preclinical drug candidates fail
this rigorous screening method [21.30]. Only a handful
of compounds was discovered in the last 10 years. In
fact, the National Cancer Institute (NCI) maintains an
ever-expanding repository of over 60 000 plant and marine samples available for testing, and about 700 new
marine samples are added each year.
21.5 Marine Pharmaceuticals Under Clinical Trials
The first reported structure of marine product was in
1880 by Vosmaer et al. [21.31]. The development of different chromatographic techniques increased the number of structurally-complex molecules obtained from
536 Part C Marine Genomics
generally harbor many such small molecules, which
can be screened well with induced gene expression.
However, the main hindrance in this method is that
only specific types of molecules can be screened out
(Fig. 21.4).
21.3.5 Sequence-Based Metagenomics
This method generally involves the design and use of
polymerase chain reaction (PCR) primers or hybridization probes for the gene being targeted, which for
enzymes is usually based on conserved regions of an
already well-characterized protein family (Fig. 21.5).
In brief, an environmental sample is collected and
then the total community DNA is extracted from the
sample. The isolated DNA is then embedded into the
suitable nitrocellulose membrane.
Preparation of the Probe
A list of the novel compounds reported to be present
in this environment should be made. A detailed search
for corresponding genes should be made through Basic Local Alignment Search Tool (BLAST) and the
probe can be designed either by PCR amplification or
by synthesis of part of these target genes. The targeted probe is labeled in vitro with [5’ c/ c32p]dCTP
(3753000 mCi mM
1 ) with a Nick translation kit following the recommended protocol supplied with the
kit.
32 P-labeled oligonucleotides are separated from the
32 P-labeled probe by elution through a 3 cm 3 Sephadex
G-50 column with a column buffer that contains 0:25 M
NaC1, 0:05 M Tris, 0:002 M EDTA, and 0:5 SDS (pH
8:0) [21.29].
Hybridization
Binding of the
32 P-labeled DNA probe with a complementary sequence of the DNA-bound nitrocellulose
membrane is a crucial and tricky step in this method.
In brief, the DNA-bound nitrocellulose membrane is
deeped in a prehybridization buffer for initial washing
of the membrane. Subsequently, the prehybridization
buffer is replaced by a hybridization buffer with the
addition of the required amount of DNA probe. After
completion of hybridization, a final washing is performed in a temperature fixed on the basis of the
required stringency condition.
21.4 The Hurdles of Drug Discovery
The prevention of different forms of cancer is the
biggest challenge to the medical scientist at present.
However, the development of new anticancer medicines
is an arduous task that requires the coordinated efforts
of a team of scientists from chemical and biological
sciences. Any potential cancer chemotherapeutic candidate must undergo a rigorous series of tests prior to
gaining FDA approval for commercialization. The process generally starts with in vitro tests against a panel
of 60 different types of cancer cells. Additionally,
xenograft models are also conducted on many occasions. Determination of the effective dose (ED 50 ) is the
next step. A molecule becomes a candidate for testing
in humans if it displays both toxicity against cancer
cells and tolerance by healthy cells and in the later
stage by whole animals. Human testing generally follows a three-phase protocol. Initially, Phase I involves
treatment of a small number of healthy (paid) volunteers with the drug candidate in order to ascertain
whether humans tolerate the compounds. If no adverse
effects are detected, then the drug is generally used on
a small number of patients with different cancers that
do not respond to conventional treatment (Phase II).
Drug candidates that continue to show therapeutic potential at this point then enter Phase III trials, in which
they are administered to a broad range of cancer patients. Eventually, if the drug candidate survives these
experimental challenges, FDA sanctions the approval
after analyzing all the data. It is reported that generally more than 99:9% preclinical drug candidates fail
this rigorous screening method [21.30]. Only a handful
of compounds was discovered in the last 10 years. In
fact, the National Cancer Institute (NCI) maintains an
ever-expanding repository of over 60 000 plant and marine samples available for testing, and about 700 new
marine samples are added each year.
21.5 Marine Pharmaceuticals Under Clinical Trials
The first reported structure of marine product was in
1880 by Vosmaer et al. [21.31]. The development of different chromatographic techniques increased the number of structurally-complex molecules obtained from