Fellows' research: Identification of novel therapeutic targets in a prostate cancer subtype
12 Feb 2019
Indian Institute of Technology (IIT), Kanpur
Our team investigated the molecular mechanisms of SPINK1-positive prostate cancer, a highly aggressive subtype, and proposed an alternative strategy to treat these patients, who generally respond poorly to cancer drugs and have shorter disease-free survival. In this type of cancer, elevated levels of the SPINK1 (serine peptidase inhibitor, Kazal type 1) protein is found in body fluids (blood and urine) besides prostatic cancer tissue of patients, and thus, it is used as a biomarker for detecting SPINK1-positive prostate cancer.
To establish the underlying molecular mechanism involved in increased SPINK1 levels and its role in manifesting aggressive prostate cancer, we discovered the binding of miRNAs (small non-coding RNAs that regulate the expression of genes) on the SPINK1 gene using computational tools and cell-based reporter assays. In addition, we checked the expression pattern of microRNAs in SPINK1-positive vs. SPINK1-negative prostate cancer patients.
Based on our investigations, we found that microRNA-338-5p and microRNA-421 play a critical role in the regulation of SPINK1. Both the microRNAs were present at low levels in SPINK-positive cancer cells, and increasing their levels resulted in inhibition of oncogenic properties (such as cell proliferation, invasion, stemness, and drug resistance), including the remarkable decline in tumour burden and metastasis (as observed in mice xenograft model).
Importantly, we found that patients with SPINK1-positive prostate cancer also have increased levels of EZH2 (enhancer of zeste homolog 2), an epigenetic regulator with an established role in cancer progression. We showed that EZH2 protein gets recruited on the regulatory regions of these two microRNAs, and silences their expression thus leading to increased SPINK1 levels. In an agreement, intense repressive epigenetic marks (DNA modifications that switch the genes off) were detected on the regulatory region of both microRNA-338-5p and microRNA-421 in patients with SPINK1-positive prostate cancer.
When the level of the microRNAs was restored using epigenetic drugs or synthetic mimics, a reduction in SPINK1 levels and SPINK1-mediated tumorigenicity was noticed. Therefore, alternative treatment avenues such as adjuvant therapy using inhibitors against DNMTs, HDACs, or EZH2, several of which are already in clinical trials, could be used for SPINK1-positive malignancies. Taken together, the major findings of this study will not only advance the prostate cancer field but will also be valuable for treatment and disease management of other SPINK1-positive malignancies.
Epigenetic silencing of miRNA-338-5p and miRNA-421 drives SPINK1-positive prostate cancer. Vipul Bhatia, Anjali Yadav, Ritika Tiwari, Shivansh Nigam, Sakshi Goel, Shannon Carskadon, Nilesh Gupta, Apul Goel, Nallasivam Palanisamy and Bushra Ateeq. Clinical Cancer Research. December 2018.
Banner Image Description and Credits: A micrograph of high grade prostate cancer tissue (Gleason Score 9) stained for EZH2, a member of Polycomb group proteins by RNA in-situ hybridization (RNA-ISH). Magenta dots indicate the expression of EZH2 and blue represent hematoxylin stained nucleus. (By Bushra Ateeq)