br a requirement to establish the appropriate
a requirement to establish the appropriate concentration of rapa-mycin and sequence of administration that is capable of activating autophagy, inducing mitophagy or promoting tumor cell apoptosis, so as to provide a new approach to treating malignant tumor.
3.5. Targeted delivery of nanomedicines to MCF-7 tumor-bearing nu/nu mice
To further investigate the tumor targeting efficacy of 7pep-modified (-)-Bicuculline methiodide and optimize the dosage regimen, we applied in vivo fluo-rescence imaging on MCF-7 tumor-bearing mice models. Fig. 7A displays the fluorescence distribution of tumor-bearing nude mice at different time points after the administration of M-DiR or 7pep-M-DiR. For all groups, the fluorescence intensity in the tumor sites increased with time. The DiR accumulation of 7pep-M-DiR at the tumor site was higher than that of M-DiR at all time points. Compared with 7pep-M-DiR group, the fluorescence intensity of 7pep block group at the tumor site was significantly lower at all time points, suggesting that 7pep in blank active micelles could competitively inhibit the distribution in tumors after specifically binding to TfR. This finding indicated that the in vivo targeting effect of 7pep-modified micelles was still a receptor-mediated process. From Fig. 7B, the 7pep-M-DiR group showed higher fluorescent intensity in excised tumor than M-DiR group, while no distinct difference was detected in the other main organs.
The bio-distribution of 7pep-M-DiD and 7pep-M-DiR used in combination was further performed to investigate the effect of different dosing regimens on the drug distribution in tumor sites. DiD was employed as the indicator for RAP loaded in 7pep-M-RAP and DiR was applied as the indicator for PTX loaded in 7pep-M-PTX. It has been reported that the two fluorescence probes did not interfere with each other under their respective excitation/emission conditions and could be used simultaneously for tissue distribution studies in combination administration48. As the appropriate administration sequencing is very crucial for the therapeutic outcome of combination therapy48, two different dosing regimens were compared to achieve better distribution characteristics with dual-nanomedicines (Fig. 7C). As shown in Fig. 7D and F, when two nanocarriers were administrated simultaneously (referred to as Combi-simu group), the fluorescence intensity of either DiR or DiD increased over time until the peak at 24e36 h, then decreased till the end of experiment. This tendency of signal intense was similar to sleep movement of monotherapy group, indicating that the co-administration had no effect on the peak time and elimination rates of nanomedicines compared with single drug treatments. However, the fluorescence intensity of either DiR or DiD was lower than that of the monotherapy group at the same time point, respectively. This phenomenon in Combi-simu group was particu-larly pronounced. It could be speculated that the two micellar for-mulations exhibited the similar peak times and the accumulation process after simultaneous administration, which might lead to competitive penetration into the tumor tissues. In addition, the 7pep modified on 7pep-M-DiD and 7pep-M-DiR competitively binds to TfR in tumor cells, resulting in a competitive uptake of nano-carriers, which were consistent with the observations of in vitro cellular uptake. In view of this, we proposed a cross-over design in which DiD-loaded nanocarriers were injected 24 h prior to the in-jection of DiR-loaded nanocarriers (referred to as Combi-cros group), aiming to avoid the competitive inhibition effect. As seen in Fig. 7DeG, the accumulation of either DiR or DiD at the tumor sites in Combi-cros group was similar to that of the single drug administration group, which was in line with our expectation. r>