PM-DTPA/PTX Case Study

PM-DTPA/PTX was developed to passively target solid tumors, however, instability of micellar carriers in an aqueous medium are often reported problems.
Thus lyophilization is a potential alternative to prevent instability in these cases[23,24,30]. Given that freeze-dried kits for radiodiagnosis are reported as an easy, fast, safe and reproducible way to obtain radiopharmaceuticals, it has been seen as a safe and effective alternative to prepare the PM-DTPA/PTX formulation[22,31,32]. However, considering that a lyophilization process involves conditions of stress, such as freezing and removal of water[33,34], and freeze-dried kits should be stable for long period of storage, a detailed study of the lyophilized kit is indispensable.
Our kit
As expected, biodistribution and imaging studies showed high uptake in liver and spleen, which might be attributed to the activation of the MPS[39,40]. The reduction in thyroid uptake (p = 0.007) and stomach (p = 0.028) observed may be due to the lower level of 99mTcO4- in freeze-dryed PM-DTPA-99mTc/PTX, which can be explained by the greater amount of stannous chloride used in the kit when compared to the system freshly prepared. Despite a lower uptake in tumor observed for micelles from kit, no significant change (p>0.05) in tumor-to-muscle ratio was observed when compared to non-lyophilized micelles. Importantly, micelles, lyophilized or not, showed signal-to-noise ratios over than 4.0. It has been established that radiotracers showing tumor-to-muscle ratio higher than 1.5 (50% more uptake in the targeting tissue) can be considered as promising imaging probes for tumor identification[41,42]. These results indicate that the freeze-dryed system, after 180 days of storage, maintains similar properties than those found in the freshly prepared micelles, indicating that kit are feasible for application in tumor