This study evaluated pembrolizumab-conjugated, doxorubicin (DOX)-loaded microbubbles (PDMs) in combination with ultrasound (US) as molecular imaging agents for early diagnosis of B cell lymphomas, and as a targeted drug delivery system. Pembrolizumab, a monoclonal CD20 antibody, was attached to the surfaces of DOX-loaded microbubbles. PDM binding to B cell lymphoma cells was assessed using immunofluorescence. The cytotoxic effects of PDMs in combination with ultrasound (PDMs þ US) were evaluated in vitro in CD20þ and CD20-cell lines, and its antitumor activities were assessed in Raji (CD20þ) and Jurkat (CD20-) lymphoma cell-grafted mice. PDMs specifically bound to CD20þ cells in vitro and in vivo. Contrast enhancement was monitored in vivo via US. PDM peak intensities and contrast enhancement durations were higher in Raji than in Jurkat cell-grafted mice (p < 0.05). PDMs þ US treatment resulted in improved antitumor effects and reduced systemic toxicity in Raji cell-grafted mice compared with other treatments (p < .05). Our results showed that PDMs þ US enhanced tumor targeting, reduced systemic toxicity, and inhibited CD20þ B cell lymphoma growth in vivo. Targeted PDMs could be employed as US molecular imaging agents for early diagnosis, and are an effective targeted drug delivery system in combination with US for CD20þ B cell malignancy treatment.

Celastrol (CST) has positive pharmacological effects on various cancers, but clinical application is limited because of poor water solubility and systemic toxicity. Ferric oxide (Fe3O4) has a large specific surface area and can be functionalized by inorganic modification to form complex magnetic drug delivery systems. Herein, Fe3O4 was surface-modified with citric acid and polyethylene glycol (PEG) (via) the Mitsunobu reaction and then covalently bound to CST. Finally, magnetic microbubbles (MMBs) containing perfluoropropane (C3F8) and Fe3O4-PEG2K-CST particles were constructed with poly(lactic-co-glycolic acid) (PLGA) as the shell membrane. In vitro studies showed that ultrasound-mediated MMBs exhibited improved inhibition of VX2 cell proliferation compared to inhibition achieved using MMBs without ultrasound mediation, blank MBs, or free CST. In ultrasound mode, MMBs have favorable imaging properties. After the application of a high mechanical index, MMBs collapse through the cavitation effect, releasing their internal Fe3O4-PEG2K-CST. The CST is then delivered to the tumor microenvironment under acidic conditions. In magnetic resonance imaging T2 mode, a specific hypointense signal was observed in the tumor area compared with that before treatment, whereas no significant change occurred in the signal intensity of the surrounding organs. After treatment, pathological examination of tumor-bearing rabbit tissues showed that iron elements accumulated in several apoptosis cells in the tumor area, with no apparent abnormalities found in other areas. Thus, ultrasound-mediated MMBs could significantly improve the drug uptake of solid tumors and inhibit tumor growth with favorable biological safety.

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