Background: Obesity is a recognized risk factor for endometrial cancer (EmCa) and other cancer types. Leptin levels are significantly increased in obese individuals. Leptin-induced signaling crosstalk [Notch, Interleukin-1 (IL-1) and leptin outcome, NILCO] has been associated with breast cancer progression. This complex signaling crosstalk affects cancer cell proliferation, migration, invasion, angiogenesis, apoptosis and chemoresistance. NILCO expression was previously detected in human EmCa. However, it is unknown whether leptin regulates NILCO and alters EmCa's response to chemotherapeutics. It is hypothesized that leptin induces NILCO and increases aggressiveness and chemoresistance in EmCa cells.
Aim: To determine whether leptin induces NILCO molecules in EmCa affecting cell proliferation, aggressiveness and chemoresistance.
Methods: Leptin's effects on the expression of NILCO molecules [mRNAs and proteins for Notch receptors (Notch1-4), ligands (JAG1 and DLL4) and downstream effectors (survivin, Hey2), and leptin (OB-R) and IL-1 (IL-1R tI) receptors] was examined in EmCa cells (type I: Ishikawa, and HEC-1A, and type II: An3Ca and KLE) using Real-time PCR and Western blot analysis, respectively. In addition, the effects of leptin on cell cycle, proliferation and cell invasion were determined using cytometric analysis (Cellometer Vision CBA system), MTT cell proliferation and Matrigel-based invasion assays, respectively. Inhibitors of leptin (nanoparticle-bound leptin peptide receptor antagonist-2, IONP-LPrA2), IL-1 (anti-IL-1R tI antibody) and Notch (siRNA interference RNA) were used to investigate NILCO's effects on cell proliferation and invasion. Leptin's effects on Paclitaxel cytotoxicity in EmCa cells was determined by the CCK8 and Cellometer-based Annexin V assays.
Results: For the first time it was shown that leptin is an inducer of Notch in EmCa. Experimental data suggest that leptin induced the expression of NILCO molecules, promoted proliferation and S- phase progression, and reduced Paclitaxel cytotoxicity on EmCa cells. Leptin's effects were higher in type II EmCa cells. The progression of this more aggressive form of the disease is associated with obesity. Remarkably, the use of the leptin signaling antagonist, IONP-LPrA2, re-sensitized EmCa cells to Paclitaxel.
Conclusion: Present data suggest the notion that leptin-induced NILCO could be a link between obesity and EmCa progression and chemoresistance. Most aggressive type II EmCa cells were higher sensitive to leptin, which appears to increase proliferation, cell cycle progression, aggressiveness, and chemoresistance to Paclitaxel. Therefore, leptin and NILCO could be novel therapeutic targets for type II EmCa, which does not have targeted therapy. Overall, IONP-LPrA2 has a potential as a novel adjuvant drug to enhance the effectiveness of type II EmCa chemotherapy.
Keywords: Chemoresistance; Endometrial cancer; Interleukin-1; Leptin; Notch; Notch, IL-1 and Leptin crosstalk outcome.