108
D.C. Hill etal.
the discovery of compounds with new biological activities. They represent
a wide range of structural types including simple and complex peptides, nitrogen
and oxygen-based heterocyclic compounds, terpenoids, quinones, simple and
complex aromatic systems, macrocyclic lactones and simple sugar analogues.
Their producing organisms ranged from various Streptomyces spp. and representatives of some of the rarer antinomycete genera through a wide variety of
fungi from simple Aspergillus and Penicillium spp. to some higher fungal species,
highlighting the value of a broad microbial collection for screening.
None of the compounds described have yet progressed into a full development programme. Some, such as the myriocins (Sect. 2.1.2), FR-111142
(Sect. 2.3.2), the pyripyropenes (Sect. 4.3.1) and the squalestatins/zaragozic acids
(Sect.4.3.1), have been the subjects of preclinical research efforts which have
resulted in analogue synthesis projects. At Xenova we have worked with great
success on the lead optimisation of the diketopiperazine PAI-I inhibitors
(Sect. 4.3.3), which are very amenable to synthetic modification. We have also
embarked on a programme of semi-synthetic modification of xenovulene A as
a selective benzodiazepine GABAA receptor antagonist (Sect. 3.4.1). It is difficult
to gauge the extent of preclinical research projects based on microbial products
in other companies as such information tends to be very closely guarded.
5.2 Review of Screen Methodologies
A wide range of assays yielded the compounds described in Sects. 2-4. For the
cell based screens, a common assay choice was to monitor cell growth and
morphology. Measurement of the behaviour of cells was commonly by microscopic observation. Although this approach can yield valuable information,
throughput may be limited due to the need for rigorous manual scoring of the
results. Other screens, such as those used to search for inhibitors of cell adhesion
(Sect. 2.1.3), and myeloperoxidase release (Sect. 2.1.5), for example, have the
advantage that results can be obtained directly from plate readers and analyzed
using a suitable data management system. This allows increased sample
throughput thereby broadening the opportunity for new drug discovery by
accessing greater molecular diversity.
In the case of the receptor binding assays, all of the published compounds,
except the CD4 binding inhibitors (Sect. 3.1.2), were discovered using assays to
detect inhibition of binding of radiolabelled Iigands to various cell membranes.
Whilst this technique remains a popular choice for screening, there are increasing concerns over the use of radioactivity in large scale screening programmes
and alternative technology for exploitation of recombinant receptors, as well as
membranes and whole cells, is now being used more widely.
Finally, for the enzyme targets the screens used for discovery of new inhibitors included simple colorimetric assays with end-point read-outs, radiometric
assays where the product was measured after a separation step, and electrophoretic assays for determination of enzyme activity on DNA conformation.
D.C. Hill etal.
the discovery of compounds with new biological activities. They represent
a wide range of structural types including simple and complex peptides, nitrogen
and oxygen-based heterocyclic compounds, terpenoids, quinones, simple and
complex aromatic systems, macrocyclic lactones and simple sugar analogues.
Their producing organisms ranged from various Streptomyces spp. and representatives of some of the rarer antinomycete genera through a wide variety of
fungi from simple Aspergillus and Penicillium spp. to some higher fungal species,
highlighting the value of a broad microbial collection for screening.
None of the compounds described have yet progressed into a full development programme. Some, such as the myriocins (Sect. 2.1.2), FR-111142
(Sect. 2.3.2), the pyripyropenes (Sect. 4.3.1) and the squalestatins/zaragozic acids
(Sect.4.3.1), have been the subjects of preclinical research efforts which have
resulted in analogue synthesis projects. At Xenova we have worked with great
success on the lead optimisation of the diketopiperazine PAI-I inhibitors
(Sect. 4.3.3), which are very amenable to synthetic modification. We have also
embarked on a programme of semi-synthetic modification of xenovulene A as
a selective benzodiazepine GABAA receptor antagonist (Sect. 3.4.1). It is difficult
to gauge the extent of preclinical research projects based on microbial products
in other companies as such information tends to be very closely guarded.
5.2 Review of Screen Methodologies
A wide range of assays yielded the compounds described in Sects. 2-4. For the
cell based screens, a common assay choice was to monitor cell growth and
morphology. Measurement of the behaviour of cells was commonly by microscopic observation. Although this approach can yield valuable information,
throughput may be limited due to the need for rigorous manual scoring of the
results. Other screens, such as those used to search for inhibitors of cell adhesion
(Sect. 2.1.3), and myeloperoxidase release (Sect. 2.1.5), for example, have the
advantage that results can be obtained directly from plate readers and analyzed
using a suitable data management system. This allows increased sample
throughput thereby broadening the opportunity for new drug discovery by
accessing greater molecular diversity.
In the case of the receptor binding assays, all of the published compounds,
except the CD4 binding inhibitors (Sect. 3.1.2), were discovered using assays to
detect inhibition of binding of radiolabelled Iigands to various cell membranes.
Whilst this technique remains a popular choice for screening, there are increasing concerns over the use of radioactivity in large scale screening programmes
and alternative technology for exploitation of recombinant receptors, as well as
membranes and whole cells, is now being used more widely.
Finally, for the enzyme targets the screens used for discovery of new inhibitors included simple colorimetric assays with end-point read-outs, radiometric
assays where the product was measured after a separation step, and electrophoretic assays for determination of enzyme activity on DNA conformation.