Laura Scolaro

Leptin and its receptor are overexpressed in brain tumors and correlate with the degree of malignancy.

Although leptin and its receptor (ObR) have emerged as important cancer biomarkers, the role of the leptin system in brain tumor development remains unknown. We screened 87 human brain tumor biopsies using immunohistochemistry and detected leptin and ObR in 55.2% and 60.9% cases, respectively. In contrast, leptin and ObR were absent in 14 samples of normal brain tissue. The presence of leptin correlated with ObR with overall concordance 80.5%. The leptin/ObR system was highly expressed in glioblastomas and anaplastic astrocytomas, while lower expression of both markers was noted in low‐grade astrocytomas and gangliogliomas. The association between leptin/ObR and the degree of tumor malignancy was highly significant (P < 0.001). Using double immunofluorescence of glioblastoma tissues, we found co‐expression of leptin with ObR and with the proliferation marker Ki‐67 in 87% and 64% of cells, respectively. The leptin/ObR‐positive tissues also expressed activated forms of STAT3 and Akt. In line with this finding, ObR‐positive glioblastoma cells responded to leptin with cell growth and induction of the STAT3 and Akt pathways as well as inactivation of the cell cycle suppressor Rb. In summary, our data demonstrate that the leptin/ObR system is expressed in malignant brain tumors and might be involved in tumor progression.

Peptide-based leptin receptor antagonists for cancer treatment and appetite regulation

Leptin, a multifunctional hormone, controls various processes in both the central nervous system and in peripheral tissues. Because of the presence of multiple leptin/receptor (ObR) interaction sites and diverse leptin activities, the literature lacks truly monofunctional leptin protein derivatives or fragments. To date, selective ObR antagonists have not been reported. We developed short, pharmacologically advantageous peptide analogs of ObR‐binding site III of leptin that acted as selective ObR inhibitors without any partial agonistic activity. These reduced leptin‐dependent growth and signaling in cancer cell lines at picomolar and low nanomolar concentrations. In immunocompromised mice the peptides suppressed the growth of rapidly proliferating orthotopic human breast cancer xenografts by 50% when administered either intraperitoneally (i.p.) or subcutaneously (s.c.) for 38 days at a 0.1 mg/kg/day dose. The peptides were distributed to the brain, and when added to growing C57BL/6 normal mice i.p., s.c., or orally, the lead antagonist accelerated normal weight increase without producing any toxic effects. Weight gain increases could not be observed after 10–12 days of treatment indicating that the mice became resistant to the central nervous system activity of leptin antagonists. However, in normal growing rats the intranasal administration at 0.1 mg/kg/day for 20 days resulted in a 2% net total body weight gain without signs of resistance induction. In addition to the potential of these peptides in drug development against primary and metastatic tumors and cachexia, our data confirm that resistance to leptin resides at the blood‐brain barrier.

Leptin-based glycopeptide induces weight loss and simultaneously restores fertility in animal models

Aim: To design, manufacture and test a second generation leptin receptor (ObR) agonist glycopeptide derivative. The major drawback to current experimental therapies involving leptin protein is the appearance of treatment resistance. Our novel peptidomimetic was tested for efficacy and lack of resistance induction in rodent models of obesity and appetite reduction.

Leptin-based therapeutics

Leptin, a pluripotent adipokine, has been discovered as a hormone controlling energy balance in hypothalamic neuroendocrine centers. In addition, recent studies provided ample evidence that leptin can be produced by cells other than adipocytes, and that the hormone can regulate many physiological processes other than energy balance and appetite. In this context, it is not surprising that both leptin excess as well as leptin insufficiency have been implicated in various pathologies. Consequently, despite initially disappointing results with recombinant leptin as the drug for obesity management, new leptin receptor modifiers have been developed and emerged as potential treatment modalities for numerous metabolic, immunological and neoplastic diseases. The major focus of this paper is a systematic review of current experimental leptin-based therapies, including pharmacological advantages and limitations of each prodrug category.

Exploring leptin antagonism in ophthalmic cell models.

Background Emerging evidence suggests that angiogenic and pro-inflammatory cytokine leptin might be implicated in ocular neovascularization. However, the potential of inhibiting leptin function in ophthalmic cells has never been explored. Here we assessed mitogenic, angiogenic, and signaling leptin activities in retinal and corneal endothelial cells and examined the capability of a specific leptin receptor (ObR) antagonist, Allo-aca, to inhibit these functions. Methods and Results The experiments were carried out in monkey retinal (RF/6A) and bovine corneal (BCE) endothelial cells. Leptin at 50-250 ng/mL stimulated the growth of both cell lines in a dose-dependent manner. The maximal mitogenic response (35±7 and 27±3% in RF6A and BCE cells, respectively) was noted at 24 h of 250 ng/mL leptin treatments. Leptin-dependent proliferation was reduced to base levels with 10 and 100 nM Allo-aca in BCE and RF6A cells, respectively. In both cell lines, leptin promoted angiogenic responses, with the maximal increase in tube formation (163±10 and 133±8% in RF6A and BCE cultures, respectively) observed under a 250 ng/mL leptin treatment for 3 h. Furthermore, in both cell lines 250 ng/mL leptin modulated the activity or expression of several signaling molecules involved in proliferation, inflammatory activity and angiogenesis, such as STAT3, Akt, and ERK1/2, COX2, and NFκB. In both cell lines, leptin-induced angiogenic and signaling responses were significantly inhibited with 100 nM Allo-aca. We also found that leptin increased its own mRNA and protein expression in both cell lines, and this autocrine effect was abolished by 100-250 nM Allo-aca. Conclusions Our data provide new insights into the role of leptin in ocular endothelial cells and represent the first original report on targeting ObR in ophthalmic cell models.

Corrigendum: Designer Leptin Receptor Antagonist Allo-aca Inhibits VEGF Effects in Ophthalmic Neoangiogenesis Models

[This corrects the article on p. 67 in vol. 3, PMID: 27790618.].

Designer Leptin Receptor Antagonist Allo-aca Inhibits VEGF Effects in Ophthalmic Neoangiogenesis Models

Experimental and clinical data suggest that pro-angiogenic, pro-inflammatory and mitogenic cytokine leptin can be implicated in ocular neovascularization and other eye pathologies. At least in part, leptin action appears to be mediated through functional interplay with vascular endothelial growth factor (VEGF). VEGF is a potent regulator of neoangiogenesis and vascular leakage with a proven role in conditions such as proliferative diabetic retinopathy, age-related macular degeneration and diabetic macular edema. Accordingly, drugs targeting VEGF are becoming mainstream treatments for these diseases. The crosstalk between leptin and VEGF has been noted in different tissues, but its involvement in the development of eye pathologies is unclear. Leptin is coexpressed with VEGF during ocular neovascularization and can potentiate VEGF synthesis and angiogenic function. However, whether or not VEGF regulates leptin expression or signaling has never been studied. Consequently, we addressed this aspect of leptin/VEGF crosstalk in ocular models, focusing on therapeutic exploration of underlying mechanisms. Here we show, for the first time, that in retinal (RF/6A) and corneal (BCE) endothelial cells, VEGF (100 ng/mL, 24 h) stimulated leptin mRNA synthesis by 70 and 30%, respectively, and protein expression by 56 and 28%, respectively. In parallel, VEGF induced RF/6A and BCE cell growth by 33 and 20%, respectively. In addition, VEGF upregulated chemotaxis and chemokinesis in retinal cells by ~40%. VEGF-dependent proliferation and migration were significantly reduced in the presence of the leptin receptor antagonist, Allo-aca, at 100–250 nmol/L concentrations. Furthermore, Allo-aca suppressed VEGF-dependent long-term (24 h), but not acute (15 min) stimulation of the Akt and ERK1/2 signaling pathways. The efficacy of Allo-aca was validated in the rat laser-induced choroidal neovascularization model where the compound (5 μg/eye) significantly reduced pathological vascularization with the efficacy similar to that of a standard treatment (anti-VEGF antibody, 1 μg/eye). Cumulatively, our results suggest that chronic exposure to VEGF upregulates leptin expression and function. As leptin can in turn activate VEGF, the increased abundance of both cytokines could amplify pro-angiogenic and pro-inflammatory environement in the eye. Thus, combined therapies targeting ObR and VEGF should be considered in the treatment of ocular diseases.