Targeting metabolic reprogramming and plasticity of cancer stem cells to impact on tumor progression and treatment resistance

Tumor development, progression and treatment failures are likely supported by a subpopulation of cancer cells with stem-like properties or cancer stem cells (CSCs). There is increasing interest in the biological pathways that determine the ability of CSCs to adapt and survive to metabolic and micro-environmental stress and sustain tumor-initiating and metastatic properties. A better understanding of these pathways may lead to the identification of key nodes and targetable elements for development of novel strategies for cancer treatment by targeting the CSC component in human tumors.

This is a collaborative project between two groups with complementary expertise in cancer biology and experimental therapeutics (Catapano group in Switzerland) and biochemistry and medicinal chemistry (Wünsch group in Germany). Preliminary data, generated in the context of this collaboration between the applicant and co-applicant group, indicate that the s1 receptor has an important role in tumorigenesis likely due to its involvement in mitochondrial dynamics and metabolic reprogramming. The s1 receptor is a ligand-activated molecular chaperone localized preferentially at the endoplasmic reticulum (ER) and the mitochondria-associated ER membrane (MAM) domains. Our data suggest that the s1 receptor may be specifically implicated in ensuring long-term survival and self-renewal of tumorigenic and stem-like cancer cells. Knockdown of the s1 receptor using siRNAs resulted in reduced survival and proliferative potential of the CSC-enriched subpopulation in multiple tumor models. Recently generated stable s1 receptor knockdown cell lines using small hairpin RNAs (shRNAs) exhibit similar phenotypic changes. Moreover, testing a series of novel s1 receptor ligands synthesized by the Wünsch group identified selective antagonists that reproduced the effects of the receptor knockdown in cancer cells. Notably, both s1 receptor knockdown and pharmacological antagonists led to impaired mitochondrial function in cancer cells. The functional s1 receptor apparently sustains tumorigenic and stem-like properties by enhancing the metabolic flexibility of CSCs through the control of ER-mitochondria functions. We propose that highly selective s1 receptor antagonists are promising leads for discovering innovative therapeutic strategies and represent effective candidates for pharmacological targeting of stem-like and tumor-initiating cells in human cancers.

In this project, we intend to study the consequences of the genetic knockdown of s1 receptor in human cancer cells and determine the efficacy of small-molecule antagonists in vitro and in vivo. Targeting the s1 receptor by both strategies (genetic knockdown and pharmacological inhibitors) is expected to impact on tumor development and metastasis by affecting the metabolic adaptability and survival of CSCs. The specific aims of the project are:

• Aim 1. To evaluate the function of the s1 receptor in cancer stem cells using genetic knockdown in cell cultures and tumor xenografts.
• Aim 2. To generate novel potent and selective s1 receptor antagonists through a medicinal chemistry approach.
• Aim 3. To evaluate the efficacy of s1 receptor antagonists in cell cultures and tumor xenograft models.

These studies will provide important insights on the fundamental biological pathways involved in the maintenance and expansion of CSCs and for the development of CSC-targeted therapeutics. Novel and effective CSC-directed therapeutics might determine a fundamental shift in cancer treatment.