Could it replace chemotherapy? Indian scientists develop ‘smart’ cancer drug that targets only tumour cells

Cancer treatment could be moving a step closer to a more precise approach, with Indian scientists developing a drug candidate designed to remain largely inactive in healthy tissue and switch on when it encounters conditions found inside cancer cells.

The experimental drug, called RK-251, has been developed through a collaboration involving Dr Asis Bala of the Institute of Advanced Study in Science and Technology (IASST) and Dr KP Bhabak of the Indian Institute of Technology Guwahati. The research was published in the Journal of Medicinal Chemistry in July 2026.

But there is an important caveat: RK-251 is still a preclinical drug candidate and has not been tested in human clinical trials. So, while the findings are promising, it is too early to call it a replacement for chemotherapy.

Why chemotherapy can be difficult

Traditional chemotherapy works by attacking rapidly dividing cells. Since cancer cells often divide rapidly, they can be particularly vulnerable to these drugs. However, some healthy cells also divide quickly.

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As a result, chemotherapy can affect normal tissues and produce side effects. This has driven scientists to develop treatments capable of distinguishing cancer cells from healthy cells more precisely.

One strategy is the development of activatable prodrugs — medicines designed to remain inactive until they encounter a particular biological signal associated with a tumour. RK-251 follows this approach.

How does RK-251 work?

The key to the drug is a molecule called reactive oxygen species (ROS). Cancer cells can contain elevated levels of ROS compared with normal cells.

The researchers designed RK-251 to exploit this difference. When the drug encounters ROS, it undergoes a chemical reaction that releases the active anticancer compound NBDHEX.

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In simple terms, the drug is designed to behave like a molecular switch:

RK-251 enters the cell → encounters elevated ROS → switches on → releases NBDHEX → NBDHEX attacks cancer-related targets.

The researchers also incorporated a near-infrared fluorescent component into the prodrug. This allows scientists to track the drug's activation through a fluorescence signal.

What does NBDHEX do?

NBDHEX targets glutathione-S-transferase pi (GSTP1), a protein that is overexpressed in many cancer cells and can contribute to cellular survival and resistance to certain treatments.

The researchers designed RK-251 to release NBDHEX inside the cellular environment where the drug is activated. Once released, NBDHEX can inhibit GSTP1 and interfere with mechanisms that help cancer cells survive.

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This is significant because the researchers are not simply developing another cytotoxic compound. They are attempting to control where and when the active compound is released.

What the early tests show?

The researchers tested RK-251 against MDA-MB-231 cells, a laboratory model of aggressive triple-negative breast cancer.

The study found that RK-251 displayed anticancer activity against these cancer cells while showing comparatively lower activity against non-malignant cells. The researchers also examined the compound in developing zebrafish embryos, where they reported no noticeable abnormalities or acute toxicity under the conditions tested.

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The drug also produced the expected fluorescence response in the presence of ROS, providing evidence that its activation mechanism was functioning as designed.

Why this could matter

The larger idea behind RK-251 is selective drug activation. Instead of sending an already active anticancer molecule throughout the body and hoping it preferentially affects tumours, an activatable prodrug attempts to deliver an inactive form and use a characteristic of the tumour — such as elevated ROS — to activate it.

If this approach can eventually be demonstrated to work safely in humans, it could potentially reduce unwanted exposure of healthy tissues to active anticancer compounds. However, that remains a future possibility rather than an established clinical benefit.