The advent of trastuzumab has significantly improved the prognosis of HER2-positive (HER2+) breast cancer patients; nevertheless, drug resistance limits its clinical benefit. Anti-HER2 active immunotherapy represents an attractive alternative strategy, but effective immunization needs to overcome the patient’s immune tolerance against the self-HER2. Phage display technology, taking advantage of phage intrinsic immunogenicity, permits one to generate effective cancer vaccines able to break immune tolerance to self-antigens. In this study, we demonstrate that both preventive and therapeutic vaccination with M13 bacteriophages, displaying the extracellular (EC) and transmembrane (TM) domains of human HER2 or its Δ16HER2 splice variant on their surface (ECTM and Δ16ECTM phages), delayed mammary tumor onset and reduced tumor growth rate and multiplicity in ∆16HER2 transgenic mice, which are tolerant to human ∆16HER2. This antitumor protection correlated with anti-HER2 antibody production. The molecular mechanisms underlying the anticancer effect of vaccine-elicited anti-HER2 antibodies were analyzed in vitro against BT-474 human breast cancer cells, sensitive or resistant to trastuzumab. Immunoglobulins (IgG) purified from immune sera reduced cell viability mainly by impairing ERK phosphorylation and reactivating retinoblastoma protein function in both trastuzumab-sensitive and -resistant BT-474 cells. In conclusion, we demonstrated that phage-based HER2 vaccines impair mammary cancer onset and progression, opening new perspectives for HER2+ breast cancer treatment.

Second messenger nucleotides, such as guanosine penta- or tetra-phosphate, commonly referred to as (p)ppGpp, are powerful signaling molecules, used by all bacteria to fine-tune cellular metabolism in response to nutrient availability. Indeed, under nutritional starvation, accumulation of (p)ppGpp reduces cell growth, inhibits stable RNAs synthesis, and selectively up- or down- regulates the expression of a large number of genes. Here, we show that the E. colihns promoter responds to intracellular level of (p)ppGpp. hns encodes the DNA binding protein H-NS, one of the major components of bacterial nucleoid. Currently, H-NS is viewed as a global regulator of transcription in an environment-dependent mode. Combining results from relA (ppGpp synthetase) and spoT (ppGpp synthetase/hydrolase) null mutants with those from an inducible plasmid encoded RelA system, we have found that hns expression is inversely correlated with the intracellular concentration of (p)ppGpp, particularly in exponential phase of growth. Furthermore, we have reproduced in an in vitro system the observed in vivo (p)ppGpp-mediated transcriptional repression of hns promoter. Electrophoretic mobility shift assays clearly demonstrated that this unusual nucleotide negatively affects the stability of RNA polymerase-hns promoter complex. Hence, these findings demonstrate that the hns promoter is subjected to an RNA polymerase-mediated down-regulation by increased intracellular levels of (p)ppGpp.

Nucleolin (NCL), an RNA-binding protein which regulates critical cellular processes, is frequently dysregulated in human cancers, including breast cancer, making it an attrac-tive therapeutic target. However, molecular details of the RNA-NCL interaction have not been investigated yet. A tRNA fragment named tRF3E, displaying tumor suppressor roles in breast cancer, was found to bind NCL with high affinity displacing NCL-controlled transcripts. Here, we investigated the determinants and cooperativity of tRF3E-NCL in-teraction by Electrophoretic Mobility Shift Assays and in silico docking analysis, using wild-type or mutated tRF3E. We found that NCL, through its RNA-binding domains (RBD1-2 and RBD3-4), binds simultaneously two tRF3E molecules, giving rise to an en-ergetically favored complex. Instead, a mutant form of tRF3E (M19-24), in which the NCL recognition element in position 19-24 has been disrupted, contacts NCL exclusively at RBD3-4, causing the loss of cooperativity among RBDs. Importantly, when expressed in MCF7 breast cancer cells, tRF3E significantly reduced cell proliferation and colony for-mation, confirming its role as tumor suppressor, but tRF3E functional properties were lost when the 19-24 motif was mutated, suggesting that cooperativity among multiple domains is required for the NCL-mediated tRF3E antitumor function. This study sheds light on the dynamic of RNA-NCL interaction and lays the foundations for using tRF3E as promising NCL-targeted biodrug candidate.

Nucleolin (NCL), an RNA-binding protein which regulates critical cellular processes, is frequently dysregulated in human cancers, including breast cancer, making it an attractive therapeutic target. However, molecular details of the RNA-NCL interaction have not been investigated yet. A tRNA fragment named tRF3E, displaying tumor suppressor roles in breast cancer, was found to bind NCL with high affinity displacing NCL-controlled transcripts. Here, we investigated the determinants and cooperativity of tRF3E-NCL interaction by Electrophoretic Mobility Shift Assays and in silico docking analysis, using wild-type or mutated tRF3E. We found that NCL, through its RNA-binding domains (RBD1–2 and RBD3–4), binds simultaneously two tRF3E molecules, giving rise to an energetically favored complex. Instead, a mutant form of tRF3E (M19–24), in which the NCL recognition element in position 19–24 has been disrupted, contacts NCL exclusively at RBD3–4, causing the loss of cooperativity among RBDs. Importantly, when expressed in MCF7 breast cancer cells, tRF3E significantly reduced cell proliferation and colony formation, confirming its role as tumor suppressor, but tRF3E functional properties were lost when the 19–24 motif was mutated, suggesting that cooperativity among multiple domains is required for the NCL-mediated tRF3E antitumor function. This study sheds light on the dynamic of RNA-NCL interaction and lays the foundations for using tRF3E as a promising NCL-targeted biodrug candidate.

Background/Objectives: Cancer vaccines represent the next frontier in immunotherapy, aiming to elicit long-lasting protective anti-tumor protective immune responses. Human epidermal growth factor receptor 2 (HER2) is a well-established therapeutic target in breast cancer. Active immunization with HER2-displaying M13 bacteriophages can induce a therapeutic immune response against HER2-positive breast cancer, offering a promising alternative to trastuzumab. However, the duration of anticancer immune protection triggered by anti-HER2 phage-based vaccines is limited by tumor-immune suppressive mechanisms. Methods: In this study, two vaccination cycles with ECTM phages displaying the extracellular (EC) and transmembrane (TM) domains of human HER2 were combined with palbociclib, a CDK4/6 inhibitor, to enhance antitumor im-munity in the clinically relevant Δ16HER2 transgenic preclinical model of breast cancer. Results: The proposed combination treatment resulted in a better and long-lasting control of tumor growth rate and multiplicity than either palbociclib or phage vaccination alone, correlating with a significantly stronger anti-HER2 humoral response (IgG2a isotype). Analysis of the tumor immune infiltrate revealed an increased presence of CD8⁺ T cells concomitant with a reduction in FoxP3⁺ regulatory T cells (Tregs) in tumors explanted from mice receiving the combination therapy. Conclusions: These preclinical results provide a rationale for the clinical translation of CDK4/6 inhibitors combined with anti-HER2 active immunotherapies in breast cancer, as they may yield sustained antitumor responses by reverting the immunosuppressive tumor environment.

Background/Objectives: Cancer vaccines represent the next frontier in immunotherapy, aiming to elicit long-lasting protective anti-tumor immune responses. Human epidermal growth factor receptor 2 (HER2) is a well-established therapeutic target in breast cancer. Active immunization with HER2-displaying M13 bacteriophages can induce a therapeutic immune response against HER2-positive breast cancer, offering a promising alternative to trastuzumab. However, the duration of anticancer immune protection triggered by anti-HER2 phage-based vaccines is limited by tumor-immune suppressive mechanisms. Methods: In this study, two vaccination cycles with ECTM phages displaying the extracellular (EC) and transmembrane (TM) domains of human HER2 were combined with palbociclib, a CDK4/6 inhibitor, to enhance antitumor immunity in the clinically relevant Δ16HER2 transgenic preclinical model of breast cancer. Results: The proposed combination treatment resulted in a better and long-lasting control of tumor growth rate and multiplicity than either palbociclib or phage vaccination alone, correlating with a significantly stronger anti-HER2 humoral response (IgG2a isotype). Analysis of the tumor immune infiltrate revealed an increased presence of CD8⁺ T cells concomitant with a reduction in FoxP3⁺ regulatory T cells (Tregs) in tumors explanted from mice receiving the combination therapy. Conclusions: These preclinical results provide a rationale for the clinical translation of CDK4/6 inhibitors combined with anti-HER2 active immunotherapies in breast cancer, as they may yield sustained antitumor responses by reverting the immunosuppressive tumor environment.