10.1002/anie.201806763
Angewandte Chemie International Edition
COMMUNICATION
respectively (Figure S18). The polymeric backbone was also
maintained during the alendronate grafting as shown in the GPC
chromatograms (Figure S19 and Table S1).
polymer can be cleaved for modulation of pH-responsive
degradation of the linkages. The grafted ROMP polymers with
different accessibility between acid and amide groups showed
distinct kinetics of pH-responsive degradation, especially in
mildly acidic conditions at pH 5-6. The ROMP polymers having
α,β-unsaturated anhydrides can provide a useful platform for
smart materials in the biomedical field where tunable pH-
responsiveness is needed in biologically tolerable conditions.
The pH-dependent cytotoxicity of the alendronate-grafted
polymers was compared on MDA-MB-231 cells (human breast
cancer cells). After incubation for 24 h, free alendronate exhibits
similar half maximal inhibitory concentration (IC50) values around
15 μM irrespective of pH conditions. However, the cytotoxicity of
the alendronate-grafted polymers was highly dependent upon
the incubation conditions. At pH 7.4, all three polymers exhibited
negligible toxicity up to 50 μM on the cancer cells (Figure 4c).
However, at pH 6.5, polymer 11 showed only 40% viability at 25
μM, whereas polymer 9 and 10 still showed almost no toxicity in
the experimental concentration range (Figure 4b). On the other
hand, at pH 5.8, all three polymers showed evident toxicity.
Among them, polymer 11 showed the highest toxicity similar to
free alendronate (Figure 4a). The comparison of IC50 values
clearly showed the induction of toxicity at acidic pH on the cells
treated with the alendronate-grafted polymers (Figure 4d).
Polymer 11 has faster degradability at mildly acidic pH
conditions than polymer 9 and 10 (Figure S21), while non-
grafted polymer 3, 4, and 5 showed no toxicity on the cells in the
concentration range of the treatment (Figure S24). In addition,
polymer 11 gave the toxic effect on the cells rather slowly than
free alendronate at pH 5.8 (Figure S25). Therefore, we inferred
that the cytotoxicity of the alendronate-grafted polymers was
originated from alendronate released from the polymers in pH-
dependent manners. Although further investigation should be
required for practical biomedical applications, it was clearly
shown that pH-responsive release and efficacy of amine-
containing drugs can be delicately controlled by the structure of
the cis-α,β-unsaturated acid amides in the ROMP polymers.
Acknowledgements
This work was supported by the National Research Foundation
of Korea Grant funded by the Korean Government (NRF-
2015R1C1A1A01052185).
Keywords: ROMP • pH-degradability• bicyclic α,β-unsaturated
anhydride • cis-α,β-unsaturated acid amide • reversible grafting
and release
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Figure 4. Relative viability of MDA-MB-231 cells treated by the alendronate-
grafted ROMP polymers (polymer 9; ● (dot and dashed), polymer 10; ■ (short
dashed), polymer 11; ▲ (long dashed)) and free alendronate (▼; line) at pH
5.8 (a), 6.5 (b) and 7.4 (c). Error bar means the standard deviation (n=5). (d)
IC50 values [μM] of the alendronate-grafted ROMP polymers and free
alendronate on MDA-MB-231 cells at each pH condition. The polymer
concentration indicated corresponding alendronate grafted on the polymer.
DPs of polymer 9, 10, and 11 were 42, 48, and 48, respectively.
In summary, ROMP polymers having α,β-unsaturated
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