A superior drug carrier – aponeocarzinostatin in partially unfolded state fully protects the labile antitumor enediyne

Table 1 Protection of NCS-Chr against degradation by binding with MG-like state of apoNCS

Sample contents	Remaining % of NCS-Chr^a
NCS-Chr	0%
NCS-Chr + 1.2 M GdnHCl	13 ± 4%^b
holoNCS (NCS-Chr + 1:1 folded state of apoNCS)	100 ± 4%
NCS-Chr + 1:1 MG-like state of apoNCS (in 1.2 M GdnHCl)	101 ± 4%^c

^aSamples containing 20 μM NCS-Chr were incubated with folded or MG-like state of apoNCS in 10 mM phosphate aqueous buffer at pH 3 and 25°C for 30 min. Remaining amount of intact NCS-Chr was analyzed by HPLC.
^bMost NCS-Chr was degraded in acidic aqueous condition in the presence of 1.2 M GdnHCl. The small remaining amount of the NCS-Chr exhibited additional forms. About 35 ± 10% of the remaining NCS-Chr was converted into chlorohydrin form of the chromophore. It is known that the chlorohydrin derivative of NCS-Chr can be obtained by treatment of HCl [2]. Presumably, excess amount of GdnHCl triggers the conversion process.
^cNo chlorohydrin conversion could be found in the remaining NCS-Chr in the presence of MG-like state of apoNCS. Presumably, binding of apoNCS prevents the chromophore conversion reaction triggered by excess amount of GdnHCl.

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