Identification of novel inhibitors of the Co-Chaperone HOP in the context of KSHV infection

Molecular chaperones are an evolutionarily conserved family of proteins found across the
five kingdoms of life. Molecular chaperone function is essential for maintenance of the
proteome, ensuring proteins and protein complexes adopt the correct folding and
conformational states. Kaposi’s sarcoma-associated herpesvirus (KSHV), like many other
viruses, utilise host cell molecular chaperones, in particular the heat shock protein (HSP)
machinery, enhancing both its latent and lytic replication cycles. Therefore, targeting HSPs
may be an attractive antiviral therapeutic strategy. This is supported by findings that show
HSP70 and HSP90 specific ATPase inhibitors result in effective inhibition of the KSHV lytic
replication cycle. However, utilisation of these HSP inhibitors is not a clinically viable
approach, due to redundancy in the HSP network and toxic side effects. Thus, alternative
approaches to modulating the HSP70 and HSP90 system is an active area of research for
pharmaceutical development.
This thesis describes an alternative approach to inhibiting the host cell HSP machinery, by
targeting the molecular co-chaperone HOP, which facilitates the transfer of client proteins
from HSP70 to HSP90. The first aim was to determine whether HOP was essential for KSHV
lytic replication and a viable therapeutic target. Results in chapter 3 show that HOP is
redistributed to the nucleus during KSHV lytic replication with a proportion of HOP localising
to KSHV replication and transcription complexes (vRTCs). Moreover, depletion studies show
HOP is essential for efficient viral protein expression and infectious virion production. The
second aim was to develop and validate a high-throughput fluorescent polarisation assay to
screen potential inhibitors of HOP-HSP PPIs. Whilst no positive hit compounds were
detected, assay efficacy and effectiveness were demonstrated. Therefore, in chapter 5
alternative approaches to develop HOP-HSP70 PPI inhibitors were investigated, including
selective functional group and fragment screening, as well as peptide SAR development.
Results provided some interesting findings to be taken forward in the development of early
SAR relating to carboxylic acids. Moreover, peptide SAR identified a tryptophan containing
peptide with enhanced activity.
In conclusion, this work demonstrated that HOP is intrinsically involved in KSHV lytic
replication and may provide future pharmaceutical opportunities. However, targeting HOP
HSP interactions is a challenging medicinal chemistry problem.