Cancer drugs are often designed to block specific molecular targets, but what happens after they enter a cell is not always well understood. A new study published in Biophotonics Discovery demonstrates how advanced imaging technology can help answer that question. Using super-resolution microscopy, researchers tracked the cancer drug sunitinib inside living cells and observed how it altered several of the cell's most important structures. The work provides a detailed view of drug behavior at the microscopic level and highlights the growing role of optical imaging in drug development and cellular engineering.
Sunitinib is used to treat several cancers, including kidney cancer. Its therapeutic activity has traditionally been linked to its ability to inhibit enzymes that drive tumor growth. However, researchers have increasingly recognized that where a drug travels inside a cell can also influence its effectiveness and side effects.
To investigate, researchers in the Diao Laboratory at University of Cincinnati combined cell viability testing with structured illumination microscopy (SIM), a super-resolution imaging technique that can reveal structures too small to be clearly seen with conventional light microscopes. An unusual advantage of sunitinib is that the drug is naturally fluorescent, allowing the team to follow its movement inside living cells without chemically modifying it.
Rather than focusing only on whether cells survived treatment, the researchers examined how the drug affected three interconnected cellular systems: lysosomes, which recycle cellular materials; mitochondria, which generate energy; and the endoplasmic reticulum (ER), which helps produce proteins and regulate cellular signaling. These structures constantly exchange information and materials, making them critical components of the cell's internal infrastructure.
The team first confirmed that sunitinib reduced cell viability in a dose-dependent manner. Higher concentrations caused progressively greater cell death. They then used SIM imaging to determine where the drug accumulated. The images showed that sunitinib concentrated primarily inside lysosomes. Quantitative analysis confirmed a much stronger association with lysosomes than with mitochondria.
As imaging resolution increased, the researchers could also measure how organelle structures changed in response to the drug. Healthy mitochondria normally form extended, interconnected networks. After sunitinib treatment, those networks became increasingly fragmented, with elongated structures breaking into shorter, isolated segments. The findings suggest that the drug interferes with the systems that maintain mitochondrial organization and energy production.
The lysosomes themselves also changed dramatically. Although the drug continued to accumulate inside them, the number of lysosomes decreased while the remaining structures became larger and more irregular in shape. These measurements point to increasing stress within the lysosomal system as drug concentrations rose.
The research team observed a similar pattern in the endoplasmic reticulum. In untreated cells, the ER formed a continuous network extending throughout the cell. After exposure to sunitinib, that network progressively broke apart into disconnected fragments. To quantify the damage, the team developed topological analyses of ER connectivity, measuring how many separate network segments remained and calculating an organelle connectivity index. The results showed a clear, concentration-dependent loss of ER organization.
One of the most significant aspects of the work is the imaging methodology itself. Instead of relying solely on biochemical measurements, the researchers directly visualized how a therapeutic molecule moved through a living cell and how cellular structures responded over time. The approach combines optical engineering, image analysis, and cell biology to produce quantitative measurements of organelle architecture and connectivity.
The findings suggest that sunitinib's effects extend beyond enzyme inhibition. The drug appears to trigger coordinated disruption of multiple cellular systems, ultimately contributing to the loss of cell function and survival. More broadly, the study demonstrates how modern super-resolution imaging can transform the study of drug behavior by revealing interactions that are invisible to conventional microscopy. Such techniques could help researchers better understand why drugs succeed, fail, or produce side effects, while supporting the development of more effective therapies in the future.
For details, see the original Gold Open Access article by A. Yadav et al., " Sunitinib induces coordinated mitochondrial, lysosomal, and endoplasmic reticulum disruption, leading to cellular collapse ," Biophoton. Discovery 3(4), 043102 (2026), doi: 10.1117/1.BIOS.3.4.043102
