Nanoparticles engineered with rituximab and loaded with nutlin-3 show promising therapeutic activity in B-leukemic xenografts

Purpose: Because the nongenotoxic inhibitor of the p53/MDM2 interactions Nutlin-3 has shown promising in vitro therapeutic activity against a variety of p53^wild-type cancer cells, in this study we evaluated an innovative strategy able to specifically target Nutlin-3 toward CD20⁺ malignant cells. Experimental Design: The cytotoxic effects of Nutlin-3 encapsulated into poly(lactide-co-glycolide) nanoparticles (NP-Nut) and into rituximab (anti-CD20 antibody)-engineered NP (NP-Rt-Nut) as well as of NPs engineered with rituximab alone (NP-Rt) were initially analyzed in vitro in JVM-2 B-leukemic cells, by assessing both the functional activation of the p53 pathway (by Nutlin-3) and/or the activation of the complement cascade (by rituximab). Moreover, the potential therapeutic efficacy of NP-Nut, NP-Rt, and NPRt- Nut were comparatively assessed in vivo in CD20 ⁺ JVM-2 leukemic xenograft SCID mice. Results: Functional in vitro assays showed that NP-Nut and NP-Rt-Nut exhibited a comparable ability to activate the p53 pathway in the p53 ^wild-type JVM-2 leukemic cells. On the other hand, NP-Rt and NPRt- Nut, but not NP nor NP-Nut, were able to promote activation of the complement cascade. Of note, the in vivo intratumoral injection in JVM-2 B-leukemic/xenograft mice showed that NP-Rt-Nut displayed the maximal therapeutic activity promoting a survival rate significantly higher not only with respect to control animals, treated either with vehicle or with empty NP, but also with respect to animals treated with NP-Nut or NP-Rt. Conclusions: Our data show for the first time the potential antileukemic activity of rituximabengineered Nutlin-3-loaded NPs in xenograft SCID mice.