Taipan Natriuretic Peptides Are Potent and Selective Agonists for the Natriuretic Peptide Receptor A.

Cardiovascular ailments are a major cause of mortality where over 1.3 billion people suffer from hypertension leading to heart-disease related deaths. Snake venoms possess a broad repertoire of natriuretic peptides with therapeutic potential for treating hypertension, congestive heart failure, and related cardiovascular disease. We now describe several taipan (Oxyuranus microlepidotus) natriuretic peptides TNPa-e which stimulated cGMP production through the natriuretic peptide receptor A (NPR-A) with higher potencies for the rat NPR-A (rNPR-A) over human NPR-A (hNPR-A). TNPc and TNPd were the most potent, demonstrating 100- and 560-fold selectivity for rNPR-A over hNPR-A. In vivo studies found that TNPc decreased diastolic and systolic blood pressure (BP) and increased heart rate (HR) in conscious normotensive rabbits, to a level that was similar to that of human atrial natriuretic peptide (hANP). TNPc also enhanced the bradycardia due to cardiac afferent stimulation (Bezold-Jarisch reflex). This indicated that TNPc possesses the ability to lower blood pressure and facilitate cardiac vagal afferent reflexes but unlike hANP does not produce tachycardia. The 3-dimensional structure of TNPc was well defined within the pharmacophoric disulfide ring, displaying two turn-like regions (RMSD = 1.15 Å). Further, its much greater biological stability together with its selectivity and potency will enhance its usefulness as a biological tool.

Cisplatin treatment induces a transient increase in tumorigenic potential associated with high interleukin-6 expression in head and neck squamous cell carcinoma.

Head and neck squamous cell carcinoma (HNSCC) is characterized by the 5-year survival rate of approximately 50%. Despite aggressive surgical, radiation, and chemotherapeutic interventions, 30% to 40% of patients die from the development of recurrent or disseminated disease that is resistant to chemotherapy. As a model of recurrence, we examined the effects of cisplatin on the ability of head and neck cancer cells to initiate tumors in a xenotransplant model. HNSCC cells were treated in vitro with cisplatin at a concentration that elicited >99% cytotoxicity and assessed for tumorigenic potential in nonobese diabetic/severe combined immunodeficient mice. HNSCC cells that survived cisplatin treatment formed tumors in nonobese diabetic/severe combined immunodeficient mice more efficiently than nontreated cells. Cisplatin-resistant cells were characterized using clonal analysis, in vivo imaging, and transcriptomic profiling. Preliminary functional assessment of a gene, interleukin-6 (IL-6), highly upregulated in cisplatin-treated cells was carried out using clonogenicity and tumorigenicity assays. We show that cisplatin-induced IL-6 expression can contribute to the increase in tumorigenic potential of head and neck cancer cells but does not contribute to cisplatin resistance. Finally, through clonal analysis, we show that cisplatin-induced IL-6 expression and cisplatin-induced tumorigenicity are stochastically derived. We report that cisplatin treatment of head and neck cancer cells results in a transient accumulation of cisplatin-resistant, small, and IL-6-positive cells that are highly tumorigenic. These data also suggest that therapies that reduce IL-6 action may reduce recurrence rates and/or increase disease-free survival times in head and neck cancer patients, and thus, IL-6 represents a promising new target in HNSCC treatment.

Tumor-initiating activity and tumor morphology of HNSCC is modulated by interactions between clonal variants within the tumor.

Tumor initiation (TI) in xenotransplantation models of head and neck squamous cell carcinoma (HNSCC) is an inefficient process. Poor TI could be due to (1) posttransplant cell loss, (2) a rare sub-population of cancer stem cells or (3) a requirement for specific cellular interactions, which rely on cell number. By tracking GFP-expressing HNSCC cells, we conclude that the posttransplant loss of cancer cells is minimal in the xenotransplant model. Furthermore, an examination of putative cancer stem cell markers (such as CD133, CD44, SP and label retention) in HNSCC cell lines revealed no correlation between marker expression and tumorigenicity. In addition, single-cell clones randomly isolated from HNSCC cell lines and then transplanted into mice were all capable of initiating tumors with efficiencies varying almost 34-fold. As the observed variation in the clones was both more and less tumorigenic than the parental cells, a combination of two clones, at suboptimal cell numbers for TI, was implanted into mice and was found to modulate the tumor-initiating activity, thus indicating that TI is dependent on a 'critical' number of cells and, for the first time, that interactions between clonal variants within tumors can modulate the overall tumor-initiating activity. Put in context with previous literature on tumorigenic activity, we believe that interactions between clonal variants within a tumor as well as (1) stromal interactions, (2) angiogenic activity, (3) immunocompetence and (4) cancer stem cells may all contribute to tumorigenic potential and the propensity for tumor growth and recurrence.