Metronomic topotecan impedes tumor growth of<i>MYCN</i>-amplified neuroblastoma cells<i>in vitro</i>and<i>in vivo</i>by therapy induced senescence

Abstract

// Sabine Taschner-Mandl 1 , Magdalena Schwarz 1 , Johanna Blaha 1 , Maximilian Kauer 1 , Florian Kromp 1 , Nelli Frank 1 , Fikret Rifatbegovic 1 , Tamara Weiss 1 , Ruth Ladenstein 1, 2 , Martin Hohenegger 3 , Inge M. Ambros 1 , Peter F. Ambros 1, 2 1 CCRI, Chlidren's Cancer Research Institute, Vienna, Austria 2 Department of Pediatrics, Medical University of Vienna, Vienna, Austria 3 Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria Correspondence to: Sabine Taschner-Mandl, e-mail: sabine.taschner@ccri.at Keywords: senescence-associated-secretory-phenotype, metronomic, topotecan, MYCN-amplified neuroblastoma, NFKB1 Received: November 04, 2015&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Accepted: November 17, 2015&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Published: December 09, 2015 ABSTRACT Poor prognosis and frequent relapses are major challenges for patients with high-risk neuroblastoma (NB), especially when tumors show MYCN amplification. High-dose chemotherapy triggers apoptosis, necrosis and senescence, a cellular stress response leading to permanent proliferative arrest and a typical senescence-associated secretome (SASP). SASP components reinforce growth-arrest and act immune-stimulatory, while others are tumor-promoting. We evaluated whether metronomic, i.e. long-term, repetitive low-dose, drug treatment induces senescence in vitro and in vivo . And importantly, by using the secretome as a discriminator for beneficial versus adverse effects of senescence, drugs with a tumor-inhibiting SASP were identified. We demonstrate that metronomic application of chemotherapeutic drugs induces therapy-induced senescence, characterized by cell cycle arrest, p21 WAF/CIP1 up-regulation and DNA double-strand breaks selectively in MYCN -amplified NB. Low-dose topotecan (TPT) was identified as an inducer of a favorable SASP while lacking NFKB1/p50 activation. In contrast, Bromo-deoxy-uridine induced senescent NB-cells secret a tumor-promoting SASP in a NFKB1/p50-dependent manner. Importantly, TPT-treated senescent tumor cells act growth-inhibitory in a dose-dependent manner on non-senescent tumor cells and MYCN expression is significantly reduced in vitro and in vivo . Furthermore, in a mouse xenotransplant-model for MYCN -amplified NB metronomic TPT leads to senescence selectively in tumor cells, complete or partial remission, prolonged survival and a favorable SASP. This new mode-of-action of metronomic TPT treatment, i.e. promoting a tumor-inhibiting type of senescence in MYCN-amplified tumors, is clinically relevant as metronomic regimens are increasingly implemented in therapy protocols of various cancer entities and are considered as a feasible maintenance treatment option with moderate adverse event profiles.