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Arginine-Rich Molecular Transporters for Drugs 149
Mean Fluorescence
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r9
N-hxg9
N-btg9
N-arg9
N-etg9
0
0.1 1.0 10.0 100.0
FIGURE 7.2 Relative cellular uptake of a set of guanidino peptoids with side chains of
varying length. The mean fluorescence from 5000 cells of a human T cell line, Jurkat, is
shown after incubation with each of the peptoids for 5 min. Uptake was measured in triplicate
at concentrations varying from 80 nM to 50 µM.
d-arginine (r9>r7>>r5). Importantly, the N-arg5, 7, and 9 peptoids showed only a
slightly lower amount of cellular entry when compared to the corresponding
homopolymers of arginine.
These results demonstrate that hydrogen bonding along the peptide backbone
of arginine oligomers is not a required structural element for cellular uptake, oligomeric
guanidine-substituted peptoids and other backbone systems (hydrocarbons,
PEG, polyamines, etc.) can be utilized in place of arginine-rich peptides as molecular
transporters. The addition of sodium azide inhibited internalization, suggesting that
cellular uptake of peptoids was also energy dependent.
7.3.2 ROLE OF THE SIDE CHAIN CONFORMATIONAL FREEDOM OF GUANIDINO
PEPTOIDS IN CELLULAR UPTAKE
Concentration (µM)
Following the demonstration that N-arg peptoids efficiently crossed cellular membranes,
the effect of side chain length on cellular uptake was investigated by synthesizing
guanidino peptoids with monomers of side chains containing two, three,
four, or six methylenes between the backbone and the headgroup. Each of the
monomers was used to prepare a set of peptoid pentamers, heptamers, and nonamers.
The differential ability of each compound to enter T cells was assayed by flow
cytometry as described in Section 7.2. Within each set of peptoids of the same length
a similar pattern is observed (Figure 7.2 and data not shown): cellular uptake is
enhanced as the number of methylenes in the side chain increases. In the case of