Safety is always a consideration when
evaluating a drug to treat a disease with
no immediate danger to the patient. In
testing the hypothesis that HDAC inhibition
will purge the latent pool of HIV-1,
VPA falls short because of a low level of
induced expression compared with
ITF2357. Givostat is safe and effective in
humans. In healthy human subjects in a
phase I trial, a single dose of givinostat
of 1.5 mg/kg resulted in a peak plasma
level of 200 nmol/L (43). In a phase II
trial in children with active systemiconset
juvenile idiopathic arthritis, a daily
oral dose of givinostat at 1.5 mg/kg for
12 weeks exhibited no organ toxicity and
achieved significant (P < 0.01) reduction
in parameters of systemic disease as well
as the number of painful joints (44). Doses
of VPA, on the other hand, when used to
reach concentrations >110 μg/mL in females
or >135 μg/mL in males, carries
significant side effects and especially severe
thrombocytopenia (50). Thus, higher
concentrations of VPA would be impractical
to induce more viral expression.
In light of the in vitro data suggesting
its potency in inducing HIV-1 expression
as well as the clinical data suggesting
that givinostat is safe, a phase II clinical
trial of givinostat would be worthwhile.
Administration of givinostat at 1.5 mg/kg
or possibly 1.0 mg/kg in two divided
doses may induce a limited number of
CD4+ T cells to express HIV-1. One end
point of such a study is whether after a
12-week course there is a reduction in
the inducible pool of latent virus. In addition,
it would also be important to determine
whether anti–HIV-1 cytotoxic
T cells increased after these courses of
givinostat. Although some patients may
be reluctant to stop antiretroviral therapy
after courses of HDAC inhibitors, the ex
vivo testing of the reservoir would provide
evidence that there has been an objective objective
reduction in the latent pool.
Surely, the test of the hypothesis that
HDAC inhibitor can reduce the reservoir
comes with cessation of antiretroviral
therapy and the duration of time before
circulating mRNA levels reappear. Ideally,
there would be no return of viral
load. Nevertheless, a significant delay in
the return of viral load would provide
encouragement for the development of
specific targeting of HDACs that assist in
maintaining HIV-1 latency.