IGIB researchers’ first step to rein in cancer cells

We established that the DNA structure (G-quadrauplex) could be a possible drug target, says Shantanu Chowdhury (right).

Controlling the level of telomerase can probably prevent cancer metastasis.

Researchers at Delhi’s CSIR-Institute of Genomics and Integrative Biology (CSIR-IGIB) have found the mechanism by which controlling the levels of telomerase can help in reining in the growth of cancer cells and probably prevent cancer metastasis. The results were published in the Journal of Biological Chemistry.

Unlike normal cells, most cancer cells have high levels of telomerase and this leads to more than normal length of the telomere. Telomeres protect chromosome ends somewhat like the plastic clips at the end of shoelaces that prevent fraying of the ends. While cells die when the telomere becomes shorter beyond a certain limit, in the case of cancer cells the length of the telomere is maintained thereby ensuring extended life span of the cells.

In normal cells the telomerase is kept under tight control. But in about 85% of all cancers the telomerase levels are more than normal leading to malignant transformation and aggressive metastasis in many cases. “It is not clearly understood how telomerase is kept under tight control in normal cells and how the telomerase levels gets increased in cancerous cells,” says Dr. Shantanu Chowdhury from the Genomics and Molecular Medicine Unit at IGIB and the corresponding author of the paper. Dr. Chowdhury is a Senior Fellow of the Wellcome Trust DBT India Alliance and this paper was part of the fellowship work.

It is already known that when the amount of a particular protein that suppresses the spread of cancer (metastasis) called nonmetastatic 2 (NME2) is high the tendency of the cancer to spread is low. But what came as a surprise is the role of this protein in controlling the telomerase levels as well. “How NME2 controls metastasis is not clearly understood. But surprisingly we found that NME2 controls the levels of telomerase,” Dr. Chowdhury says.

Dhurjhoti Saha-Optimized
If you don’t have NME2 then the REST suppressor cannot bind to the telomerase promoter and control the production of telomerase, says Dhurjhoti Saha.

The mechanism

The researchers found that NME2 binds to a DNA structure (G-quadrauplex) found in the telomerase promoter. Once bound, the NME2 facilitates a well known suppressor of gene expression (REST complex) to bind to the telomerase promoter and control the production of telomerase.

“Experiments show that if you don’t have NME2 then the REST suppressor cannot bind to the telomerase promoter and control the production of telomerase,” says Dhurjhoti Saha from IGIB and one of the first authors of the paper.

“We used proteomics approach to study the protein-protein interactions. We could identify protein members of the REST complex that interact with NME2.  The IGIB team then confirmed the role of the REST complex and its function,” says Dr. Ramesh Ummanni, from the Centre for Chemical Biology at the CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad and a co-author of the paper.

Drug target

“We established that the DNA structure (G-quadrauplex) could be a possible drug target once we understood the mechanism of NME2 binding to the promoter followed by the REST suppressor complex,” Dr. Chowdhury says. The involvement of a DNA structural architecture allowed the team to use small molecules that recognised the specific structure.

Since the amount of NME2 is low in many metastatic cancerous cells, the researchers used small molecules that were able to function like NME2 by recognising and binding to the DNA structure. “We screened 20 molecules and 11 were able to bring down the telomerase level in fibrosarcoma cancer cells,” Dr. Chowdhury says.

Based on the initial lead from the small molecules, the researchers are planning to synthesise new molecules to optimise for drug-like characteristics for therapeutic use. The molecules will then be tested on animals.

Published in The Hindu on July 29, 2017

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