Cancer's increasing mortality necessitates more effective therapeutic strategies. Current antitumor drugs lack selective targeting, leading to the need for efficient drug delivery systems. Nanotechnology offers a promising solution, with nanoparticles enabling controlled release and targeted delivery of various therapeutic molecules. Protein nanoparticles are particularly attractive due to their biodegradability and biocompatibility. Genetic engineering and chemical conjugation allow for precise control over nanoparticle properties, including surface charge, environmental responsiveness, drug encapsulation, stability, and ligand display, surpassing the capabilities of naturally occurring or synthetic nanoparticles. This review focuses on the design, construction, and application of protein nanoparticles for effective therapeutic drug delivery in cancer treatment.

The review extensively cites existing literature on nanoparticle drug delivery systems for cancer, including metallic nanoparticles, liposomes, and protein nanoparticles. It emphasizes the importance of controlling particle size, surface properties, and drug release rates for site-specific effects. The literature reviewed highlights the advantages of genetically encoded nanoparticle synthesis over natural or chemically synthesized approaches, providing near-complete control over stereochemistry, structure, and self-assembly. Existing challenges in drug encapsulation and protein aggregation are also discussed, setting the stage for the review's focus on advanced protein nanoparticle designs and functionalization techniques.

The review method is a comprehensive literature survey of published research articles on protein nanoparticles for cancer therapy. The authors systematically analyze existing studies on the engineering, functionalization, and therapeutic application of various protein nanocarriers. The focus is on the design and modification of naturally occurring self-assembled protein nanoparticles (ferritins, vaults, encapsulins, small heat shock proteins, and elastin-like polypeptides) for improved drug delivery. The review describes different genetic engineering and chemical conjugation strategies used to tailor the properties of these nanocarriers. Specific examples are provided to illustrate the successful application of these engineered nanoparticles for targeted drug delivery, controlled release, and enhanced therapeutic efficacy. Additionally, the review explores de novo design of protein nanoparticles using computational techniques and directed evolution, highlighting recent advancements in the rational design of self-assembling protein architectures.

The review details several key advancements in protein nanoparticle-based cancer therapy: **Ferritin Nanoparticles:** Engineered ferritins, produced recombinantly in E. coli, exhibit superior tumor-targeting capabilities. One-step drug loading methods have been developed to achieve high drug loading capacity and encapsulation efficiency. Biosilica coating enhances stability and enables dual-drug delivery systems with pH-responsive release profiles. **Vault Nanoparticles:** Recombinant major vault protein (MVP) self-assembles into nanoparticles suitable for drug encapsulation. Genetic engineering allows for functionalization with targeting peptides or antibodies, enhancing tumor cell specificity. The ability of vaults to dissociate at low pH improves cytoplasmic drug delivery. Improved production and purification methods are discussed. **Encapsulin Nanoparticles:** Engineered encapsulins from Thermotoga maritima allow simultaneous incorporation of targeting ligands, therapeutic reagents, and diagnostic probes. Genetic modifications enable specific targeting of cancer cells. Split intein and SpyTag/SpyCatcher systems enable precise functionalization of both the interior and exterior surfaces. **Small Heat Shock Protein (sHSP) Nanoparticles:** sHSPs from Methanococcus jannaschii have been engineered for targeted drug delivery. Genetic modifications introduce cysteine residues for pH-sensitive drug conjugation and surface display of targeting peptides. These nanoparticles demonstrate selective targeting of cancer cells while minimizing cytotoxicity to normal cells. **Elastin-Like Polypeptide (ELP) Nanoparticles:** ELPs are genetically engineered to form nanoparticles with tunable properties. Biomineralization enhances drug loading and controlled release. Fusion with targeting peptides, antibodies, and cell-penetrating peptides allows for targeted drug delivery and improved cell penetration, overcoming multidrug resistance. **De Novo Designed Protein Nanoparticles:** Computational design enables the creation of highly homogenous self-assembling protein nanoparticles with precise control over structure and function. Examples include computationally designed nanocages and self-assembled peptide cages (SAGE), which can be functionalized with targeting moieties and antigens for drug delivery and vaccine development. Modular protein assembly methods utilizing SpyTag/SpyCatcher and SnoopTag/SnoopCatcher systems allow for the creation of complex, multivalent protein structures with enhanced therapeutic potential. Coiled-coil protein origami (CCPO) structures are also highlighted, demonstrating in vivo self-assembly and potential for drug and vaccine delivery.

The review demonstrates that protein nanoparticles offer significant advantages over other nanocarriers for cancer therapy due to their biocompatibility, biodegradability, and amenability to precise genetic engineering. The diverse range of naturally occurring and de novo designed protein nanocarriers, coupled with advanced functionalization strategies, provides a wealth of opportunities for developing highly targeted and effective cancer therapies. The ability to control drug loading, release profiles, and cellular targeting represents significant progress towards overcoming challenges such as multidrug resistance and poor drug delivery efficacy. The success of these approaches in preclinical studies suggests a promising future for protein nanoparticle-based cancer therapeutics.

This review highlights significant advancements in the development of tailored functionalized protein nanocarriers for cancer therapy. Genetic engineering offers precise control over nanoparticle properties, leading to enhanced tumor targeting, controlled drug release, and the potential to overcome multidrug resistance. Both naturally occurring and de novo designed protein nanoparticles provide versatile platforms for drug delivery and vaccine development. Future research should focus on addressing challenges such as immunogenicity and scaling up production for clinical translation. Continued advances in computational protein design and molecular biology techniques will further expand the potential of protein nanoparticles in nanomedicine.

While the review provides a comprehensive overview of current advancements, the field is rapidly evolving. The long-term in vivo effects and potential toxicity of some of the described nanocarriers require further investigation. Furthermore, the translation of these promising preclinical findings to clinical applications requires careful consideration of manufacturing scalability, regulatory hurdles, and potential off-target effects. The focus on cancer therapy may not fully reflect the broader applicability of protein nanocarriers for other therapeutic applications.