mp5b00803_si_001.pdf (296.56 kB)
The pH of Piperazine Derivative Solutions Predicts Their Utility as Transepithelial Permeation Enhancers
journal contribution
posted on 2016-02-01, 00:00 authored by Nicholas
G. Lamson, Gabrielle Cusimano, Kanika Suri, Anna Zhang, Kathryn A. WhiteheadThe
oral delivery of macromolecular drugs, including proteins and
nucleic acids, is one of the greatest unmet needs in modern biomedicine.
Although engineering solutions have been used to overcome enzymatic
degradation and the low pH in the stomach, poor absorption across
the intestinal epithelium into the bloodstream continues to pose the
most significant challenge to clinical translation. One common approach
to increase the flux of macromolecules across the intestinal epithelium
is the use of chemical permeation enhancers. Unfortunately, the vast
majority of effective enhancers have been thwarted by toxicity, and
the structural and molecular parameters that contribute to this behavior
are poorly understood. Previous work has shown that select piperazine-derived
molecules favorably affect transepithelial and intracellular delivery
outcomes, suggesting that piperazine-derived molecules interface uniquely
with cellular barriers. To gain a better understanding of piperazine-mediated
permeation enhancement, this work examined piperazine and 13 of its
simple, hydrocarbon-substituted derivatives using Caco-2 monolayers
as a model of the intestinal epithelium. After evaluating each piperazine
for permeation enhancement efficacy and cytotoxicity at three concentrations,
it became clear that piperazine derivatives consistently enhance permeability
with each derivative resulting in noncytotoxic permeation enhancement
at one or more concentrations. In attempting to identify structure–function
relationships for the piperazine derivatives, it was found that treatment
concentration, structural characteristics, and molecular pKa were not reliable indicators of permeation
potential. Interestingly, the pH of the enhancer solution was identified
as a controlling parameter even when accounting for the effects from
pH change alone. Specifically, piperazine treatments with a pH between
9.2 and 9.6 guaranteed noncytotoxic efficacy. Furthermore, all effective
treatments resulted in pH values between 8.7 and 9.6, behavior that
was not shared by the other small, noncyclic amines studied. These
data have important implications in the design of oral biologic delivery
systems that employ permeation enhancers and underscore the need to
carefully control the final treatment pH of the local intestinal epithelial
environment.