MtDef4 is a 47-amino acid cysteine-rich evolutionary conserved defensin from a model legume Medicago truncatula. It is an apoplast-localized plant defense protein that inhibits the growth of the ascomycetous fungal pathogen Fusarium graminearum in vitro at micromolar concentrations. Little is known about the mechanisms by which MtDef4 mediates its antifungal activity. In this study, we show that MtDef4 rapidly permeabilizes fungal plasma membrane and is internalized by the fungal cells where it accumulates in the cytoplasm. Furthermore, analysis of the structure of MtDef4 reveals the presence of a positively charged γ-core motif composed of β2 and β3 strands connected by a positively charged RGFRRR loop. Replacement of the RGFRRR sequence with AAAARR or RGFRAA abolishes the ability of MtDef4 to enter fungal cells, suggesting that the RGFRRR loop is a translocation signal required for the internalization of the protein. MtDef4 binds to phosphatidic acid (PA), a precursor for the biosynthesis of membrane phospholipids and a signaling lipid known to recruit cytosolic proteins to membranes. Amino acid substitutions in the RGFRRR sequence which abolish the ability of MtDef4 to enter fungal cells also impair its ability to bind PA. These findings suggest that MtDef4 is a novel antifungal plant defensin capable of entering into fungal cells and affecting intracellular targets and that these processes are mediated by the highly conserved cationic RGFRRR loop via its interaction with PA.

Cancer cells develop tactics to circumvent the interventions by desensitizing themselves to interventions. Amongst many, the principle routes of desensitization include a) activation of survival pathways (e.g. NF-kB, PARP) and b) downregulation of cell death pathways (e.g. CD95/CD95L). As a result, it requires high therapeutic dose to achieve tumor regression which, in turn damages normal cells through the collateral effects. Methods are needed to sensitize the low and non-responsive resistant tumor cells including cancer stem cells (CSCs) in order to evoke a better response from the current treatments. Current treatments including chemotherapy can induce cell death only in bulk cancer cells sparing CSCs and cancer resistant cells (CRCs) which are shown to be responsible for high recurrence of disease and low patient survival. Here, we report several novel tumor targeted sensitizers derived from the natural Vitamin E analogue (AMP-001-003). The drug design is based on a novel concept “A priori activation of apoptosis pathways of tumor technology (AAAPT) which is designed to activate specific cell death pathways and inhibit survival pathways simultaneously and selectively in cancer cells sparing normal cells. Our results indicate that AMP-001-003 sensitize various types of cancer cells including MDA-MB-231 (triple negative breast cancer), PC3 (prostate cancer) and A543 (lung cancer) cells resulting in reducing the IC-50 of doxorubicin in vitro when used as a combination. At higher doses, AMP-001 acts as an anti-tumor agent on its own. The synergy between AMP-001 and doxorubicin could pave a new pathway to use AAAPT leading molecules as neoadjuvant to chemotherapy to achieve better efficacy and reduced off-target toxicity compared to the current treatments.

Introduction: MsDef1, a 45-amino acid cysteine-rich peptide from the seed of Medicago sativa is an antifungal defensin small protein. It exhibits broad-spectrum antifungal activity against fungal pathogens of plants at low micromolar concentrations. The common vulnerability of fungal and cancer cells determines the utility of MsDef1 as a potential anti-tumor agent. Results: The solution dynamics of 15N-labeled MsDef1, 15N longitudinal relaxation (T1) and 15N-1H Nuclear Overhauser Effect (NOE) shows that GlcCer binds at two sites on the peptide molecule, i.e., Asp36-Cys39 and amino acids between 12-20 and 33-40. MsDef1 interacts with drug resistant breast cancer MCF-7R cells, permeates GlcCer-rich plasma membrane and releases apoptotic ceramide. This results in the activation of ceramide pathway involving interaction of the peptide with intracellular thioredoxin (Trx), another tumor specific biomarker. MsDef1 oxidizes Trx through four S-S bonds and in the process, gets reduced to thiols. Oxidation of Trx is correlated with the activation of Apoptosis Stimulating Kinase 1 (ASK1) which is known to sensitize cancer cells to chemotherapeutics including front-line drug Doxorubicin. A combination of MsDef1 and Doxorubicin exhibits 5-10-fold greater apoptosis in vitro in MDR triple negative breast cancer (TNBC) cells compared to either MsDef1 or Doxorubicin alone. Conclusion: An antifungal plant defensin MsDef1 is shown to be a cell permeating peptide (CPP) for MDR cancer cells targeted to two tumor specific targets activating two cell death pathways. That makes MsDef1, potentially a tumor targeted sensitizer neoadjuvant to cancer therapy.

Traditional drug design focuses on specific biological targets where specific receptors or biomarkers are overexpressed by cancer cells. Cancer cells circumvent the interventions by activating survival pathways and/or downregulating cell death pathways for their survival. A priori activation of apoptosis pathways of tumor (AAAPT) is a novel tumor-sensitizing technology that sensitizes tumor cells that are not responding well to the current treatments by targeting specific survival pathways involved in the desensitization of tumor cells and tries to revive them selectively in cancer cells, sparing normal cells. Several vitamin E derivatives (AMP-001, AMP-002, AMP-003, and AMP-004) were synthesized, characterized, and studied for their anti-tumorigenic properties and their synergistic potential with the standard chemotherapy doxorubicin in various cancer cells including brain cancer stem cells in vitro. Preliminary studies revealed that AAAPT drugs (a) reduced the invasive potential of brain tumor stem cells, (b) synergized with Federal Drug Application-approved doxorubicin, and (c) enhanced the therapeutic index of doxorubicin in the triple-negative breast cancer tumor rat model, preserving the ventricular function compared to cardiotoxic doxorubicin alone at therapeutic dose.The AAAPT approach has the advantage of inhibiting survival pathways and activating cell death pathways selectively in cancer cells by using targeting, linkers cleavable by tumor-specific Cathepsin B, and PEGylation technology to enhance the bioavailability. We propose AAAPT drugs as a neoadjuvant to chemotherapy and not as stand-alone therapy, which is shown to be effective in expanding the therapeutic index of doxorubicin and making it work at lower doses.

Both innate and adaptive immunity are the important components of the human defense system against various diseases including cancer. Human Beta Defensin (hBD-1) is one such immunomodulatory peptide which is lost at high frequencies in malignant cancers, while high levels of expression are maintained in benign regions making it a potential biomarker for the onset and metastasis of the disease. Loss of putative function of hBD-1 as a tumor suppressor gene combined with the defects in apoptosis pathways (CD95, ASK1) make tumor cells insensitive to chemotherapy and render it ineffective. Triple negative breast cancer (TNBC) is an aggressive form of breast cancer for which no targeted therapy works due to lack of biomarkers (ER, PR and HER2 negative). That makes chemotherapy as a first line of treatment despite high side effects. TNBC is known for avoiding immunosurveillance and desensitizing themselves to intervention by dysregulating cell death pathways (CD95 & ASK1) and developing resistance to chemotherapy A priori Activation of Apoptosis Pathways of Tumor often referred to as AAAPT is a novel targeted tumor sensitizing technology which sensitizes low responsive and resistant tumor cells to evoke a better response from the current treatments for TNBC. Here, we show that hBD-1 is shown to target tumor specific biomarker Trx, activates dual cell death pathways CD95 and ASK1 (apoptosis stimulating kinase) to sensitize TNBC cells to chemotherapy drug Doxorubicin. As far as we know, this is the first-time injection of hBD-1 in TNBC mouse model to prove the restoration of hBD-1 back to the basal level can sensitize cancer cells which resulted in significant reduction of tumor volume in TNBC mouse model' in vivo. Sensitizing the low or non-responsive tumor cells by AAAPT and making chemotherapy work at lower doses may lead to the significant reduction of dose related side effects and may expand the therapeutic index of the current treatments.