Physalis Mottle Virus-Like Nanocarriers with Expanded Internal Loading Capacity.

An ongoing challenge in precision medicine is the efficient delivery of therapeutics to tissues/organs of interest. Nanoparticle delivery systems have the potential to overcome traditional limitations of drug and gene delivery through improved pharmacokinetics, tissue targeting, and stability of encapsulated cargo. Physalis mottle virus (PhMV)-like nanoparticles are a promising nanocarrier platform which can be chemically targeted on the exterior and interior surfaces through reactive amino acids. Cargo-loading to the internal cavity is achieved with thiol-reactive small molecules. However, the internal loading capacity of these nanoparticles is limited by the presence of a single reactive cysteine (C75) per coat protein with low inherent reactivity. Here, we use structure-based design to engineer cysteine-added mutants of PhMV VLPs that display increased reactivity toward thiol-reactive small molecules. Specifically, the A31C and S137C mutants show a greater than 10-fold increased rate of reactivity towards thiol-reactive small molecules, and PhMV Cys1 (A31C), PhMV Cys2 (S137C), and PhMV Cys1+2 (double mutant) VLPs display up to three-fold increased internal loading of the small molecule chemotherapeutics aldoxorubicin and vcMMAE and up to four-fold increased internal loading of the MRI imaging reagent DOTA(Gd). These results further improve upon a promising plant virus-based nanocarrier system for use in targeted delivery of small-molecule drugs and imaging reagents in vivo.

A co-formulated vaccine of irradiated cancer cells and cowpea mosaic virus improves ovarian cancer rejection.

Ovarian cancer ranks fifth in cancer deaths amongst women, and most patients are diagnosed with late-stage and disseminated diseases. Surgical debulking and chemotherapy remove most of the tumor burden and provide a short period of remission; however, most patients experience cancer relapse and eventually succumb to the disease. Therefore, there is an urgent need for the development of vaccines to prime anti-tumor immunity and prevent its recurrence. Here we developed vaccine formulations composed of a mixture of irradiated cancer cells (ICCs, providing the antigen) and cowpea mosaic virus (CPMV) adjuvants. More specifically we compared the efficacy of co-formulated vs. mixtures of ICCs and CPMV. Specifically, we compared co-formulations where the ICCs and CPMV are bonded through natural CPMV-cell interactions or chemical coupling vs. mixtures of PEGylated CPMV and ICCs, where PEGylation of CPMV prevents ICC interactions. Flow cytometry and confocal imaging provided insights into the composition of the vaccines and their efficacy was tested using a mouse model of disseminated ovarian cancer. 67% of the mice receiving the co-formulated CPMV-ICCs survived the initial tumor challenge, and 60% of the surviving mice rejected tumors in a re-challenge experiment. In stark contrast, simple mixtures of the ICCs and (PEGylated) CPMV adjuvants were ineffective. Overall, this study highlights the importance of the co-delivery of cancer antigens and adjuvants in ovarian cancer vaccine development.

Cisplatin-Loaded Tobacco Mosaic Virus for Ovarian Cancer Treatment.

Ovarian cancer is the foremost cause of gynecological cancer and a major cause of cancer death in women. Treatment for advanced stage is surgical debulking followed by chemotherapy; however, most patients relapse with more aggressive and therapy-resistant tumors. There is a need to develop drug delivery approaches to deliver platinum therapies to tumors to increase efficacy while maintaining safety. Toward this goal, we utilized the protein nanotubes from the plant virus, tobacco mosaic virus (TMV), as a drug carrier. Specifically, the nanochannel of TMV was loaded with the active dication form of cisplatin (cisPt2+), making use of the negatively charged Glu acid side chains that line the interior channel of TMV. We achieved a loading efficiency with ∼2700 cisPt2+ per TMV; formulation stability was established with drug complexes stably loaded into the carrier for 2 months under refrigerated storage. TMV-cisPt maintained its efficacy against ovarian tumor cells with an IC50 of ∼40 µM. TMV-cisPt exhibited superior efficacy vs free cisPt in ovarian tumor mouse models using intraperitoneal ID8-Defb29/Vegf-a-Luc (mouse) tumors and subcutaneous A2780 (human) xenografts. TMV-cisPt treatment led to reduced tumor burden and increased survival. Using ID8-Defb29/Vegf-a-Luc-bearing C57BL/6 mice, we also noted reduced tumor growth when animals were treated with TMV alone, which may indicate antitumor immunity induced by the immunomodulatory nature of the plant virus nanoparticle. Biodistribution studies supported the efficacy data, showing increased cisPt accumulation within tumors when delivered via the TMV carrier vs free cisPt administration. Finally, good safety profiles were noted. The study highlights the potential of TMV as a drug carrier against cancer and points to the opportunity to explore plant viruses as chemo-immuno combination cancer therapeutics.