Recent News 9 : Exploiting Bacteriophages in Cancer: From Targeted Delivery to Immunomodulation

Exploiting Bacteriophages in Cancer: From Targeted Delivery to Immunomodulation

Over the past two decades, bacteriophages (phages), viruses that infect and replicate within bacteria, have emerged as versatile tools in biomedical research. While their most prominent medical application has been in combating antibiotic-resistant infections, a growing body of evidence suggests that phages may also have a significant role to play in oncology. From functioning as vectors for gene or drug delivery to modulating immune responses and serving as platforms for tumor vaccines, phages offer multiple avenues to support cancer diagnosis and therapy. These applications leverage both their biological specificity and their capacity for genetic engineering, often intersecting with synthetic biology and immunotherapy.

Phage Display and Tumor Targeting

One of the earliest and most developed oncological applications of phages is phage display, a technique that allows for the presentation of peptides or proteins on the surface of phage capsids. This method, pioneered by George P. Smith and later expanded by Sir Gregory Winter (Nobel Prize in Chemistry, 2018), enables the identification of ligands that bind specifically to tumor-associated antigens (TAAs).

Libraries of phages displaying random peptides have been screened against tumor cell lines and biopsies to isolate high-affinity binders. For instance, peptides identified through phage display have shown strong binding affinity to markers like HER2 in breast cancer or αvβ3 integrin in glioblastoma. These ligands can then be used to direct nanocarriers, including liposomes or nanoparticles, to tumor tissues, thereby enhancing the specificity and reducing systemic toxicity of chemotherapeutic agents.

In one study, Pasqualini and Ruoslahti (Nature Biotechnology, 1996) demonstrated the use of a phage-displayed peptide targeting tumor vasculature in vivo in a mouse model. More recently, targeted delivery of doxorubicin-conjugated liposomes using phage-derived peptides has improved drug accumulation in tumors by over 300% compared to untargeted controls (Liu et al., ACS Nano, 2019).

Phages as Drug Delivery Vehicles in Solid Tumors

Filamentous phages such as M13 can be genetically modified to carry payloads of small molecules, nucleic acids, or proteins. Due to their nanoscale size (6.5 nm in diameter and ~900 nm in length) and modifiable surfaces, they exhibit favorable biodistribution profiles. Phage particles can penetrate the leaky vasculature of tumors through the enhanced permeability and retention (EPR) effect, and engineered surface peptides enhance cell-specific internalization.

Hybrid constructs have been created in which phages encapsulate chemotherapy drugs or RNA therapeutics, increasing both bioavailability and precision. For example, in a 2021 study published in Advanced Drug Delivery Reviews, bacteriophage MS2 was engineered to carry siRNA targeting oncogenic KRAS in pancreatic cancer models. The results showed significant tumor volume reduction with minimal toxicity, underlining the promise of phage-based delivery in difficult-to-treat cancers.

Figure 1 Identification of phage-displayed antibodies/peptides that specifically target cancer cells, aiming to utilize them for cancer therapy.

(https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2023.1290296/full (c))

Phages as Tumor-Associated Antigen Carriers for Vaccination

Phages are potent immunogenic platforms. They can carry and present tumor-associated antigens to the immune system, thereby functioning as prophylactic or therapeutic cancer vaccines. The immunostimulatory nature of phage capsids, especially the single-stranded DNA and CpG motifs in their genome, can stimulate dendritic cells and promote antigen presentation via MHC class I and II pathways.

Studies using λ phage displaying the human papillomavirus (HPV) E7 antigen have demonstrated the generation of robust cytotoxic T lymphocyte (CTL) responses and tumor regression in mouse models of cervical cancer (Sørensen et al., Cancer Immunology Research, 2015). Another notable example involves T7 phage displaying epitopes from melanoma-associated antigen A3 (MAGE-A3), showing elevated interferon-γ production and tumor suppression in B16 melanoma mouse models (Zhou et al., Vaccine, 2020).

Phages as Oncolytic Agents

Although phages do not infect eukaryotic cells, they can have indirect oncolytic effects. Certain phages have been observed to penetrate tumors and influence the tumor microenvironment. For instance, phage administration can induce the production of cytokines and chemokines such as IL-12 and TNF-α, leading to macrophage polarization toward an anti-tumoral M1 phenotype.

Moreover, phage therapy in cancer-bearing hosts has been associated with increased infiltration of CD8+ T cells in tumors, as reported by Górski et al. (Frontiers in Immunology, 2021). These immune-modulatory effects may synergize with existing immunotherapies, such as checkpoint inhibitors, potentially enhancing their efficacy and overcoming resistance.

Table 2 The phages for cancer therapy.

(https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2023.1290296/full (c))

Phages and the Microbiome–Cancer Axis

Emerging research suggests a complex interplay between gut microbiota and cancer progression or treatment response. Phages, as modulators of bacterial populations, can influence this axis. For example, phage therapy targeting Fusobacterium nucleatum—a bacterium implicated in colorectal cancer—has demonstrated reduced tumor progression in murine models (Hannigan et al., Cell Host & Microbe, 2020).

Additionally, phage modulation of the microbiota may alter the efficacy of immune checkpoint blockade therapy. A study in Science (Matson et al., 2018) reported that gut microbial composition correlated with response to PD-1 inhibition in melanoma patients. Thus, targeted phage modulation of the gut ecosystem may one day be integrated into oncological precision medicine.

Phage Engineering and Synthetic Biology in Cancer Applications

The convergence of synthetic biology and phage engineering has opened new dimensions for their use in oncology. Techniques such as CRISPR-Cas systems, recombineering, and directed evolution allow for the rational design of phages with enhanced properties.

A groundbreaking example involves the use of synthetic T4 phages engineered to encode tumor-killing bacterial toxins under cancer-specific promoters. Once delivered to a tumor-colonizing bacterium like Salmonella, these phages induce in situ toxin production, leading to localized tumor necrosis. This concept, termed “bacterium-phage synergism,” was highlighted in a 2022 Nature Biomedical Engineering article and offers a novel strategy for intra-tumoral therapy.

Furthermore, researchers are developing chimeric phages capable of simultaneously delivering immunostimulatory molecules and imaging agents, thereby bridging therapy and diagnostics—so-called theranostic phages.

Figure 3 A diagram illustrating the mechanism by which phage vaccines trigger immune responses.

(https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2023.1290296/full (c))

Challenges and Future Perspectives

Despite promising advances, several challenges must be addressed before phages can become mainstream cancer therapeutics. Immunogenicity, while beneficial for vaccine applications, may hinder repeated systemic administration. Phage pharmacokinetics, biodistribution, and clearance mechanisms require optimization. Regulatory frameworks are also underdeveloped, and manufacturing at clinical grade and scale remains complex.

Nevertheless, the field is advancing rapidly. As of 2024, over 25 clinical trials involving phage-based constructs in oncology were registered on ClinicalTrials.gov. These span a range of indications from glioblastoma to metastatic melanoma.

The integration of phages into multi-modal cancer therapy regimes—alongside chemotherapy, immunotherapy, and microbial interventions—holds substantial potential. Their modularity, safety profile, and tunability make them uniquely adaptable to the evolving landscape of personalized oncology.

References :

1. Pasqualini R, Ruoslahti E. "Organ targeting in vivo using phage display peptide libraries." Nature Biotechnology. 1996;14(6): 777–782.

2. Liu Y, et al. "Phage display identified peptide functionalized liposomes for tumor-targeted drug delivery." ACS Nano. 2019;13(9): 10645–10654.

3. Sørensen M, et al. "Tumor regression by DNA vaccination using lambda phage particles encoding HPV16 E7." Cancer Immunology Research. 2015;3(4): 348–357.

4. Górski A, et al. "Perspectives of phage therapy in oncology." Frontiers in Immunology. 2021;12: 638940.

5. Zhou Y, et al. "T7 phage-based vaccines for cancer immunotherapy." Vaccine. 2020;38(21): 3747–3755.

6. Hannigan GD, et al. "Bacteriophages targeting Fusobacterium nucleatum attenuate colorectal cancer in preclinical models." Cell Host & Microbe. 2020;28(6): 1–13.

7. Matson V, et al. "The commensal microbiome is associated with anti–PD-1 efficacy in metastatic melanoma patients." Science. 2018;359(6371): 104–108.

8. Luo Y, et al. "Engineered bacteriophage for combined anti-tumor therapy via the modulation of tumor-associated bacteria." Nature Biomedical Engineering. 2022;6(5): 486–497.

9. https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2023.1290296/full (c)