Imaging shows how a tumor-fighting drug causes cellular breakdown

Cancer drugs are designed to attack the molecular machinery that allows tumors to grow, divide, and spread. Yet once a drug enters a living cell, its effects may extend far beyond the molecular target identified during development. New research published in Biophotonics Discovery provides a detailed view of this broader cellular response, showing that the cancer drug sunitinib can simultaneously disrupt mitochondria, lysosomes, and the endoplasmic reticulum—three organelle systems that are essential for energy production, waste processing, protein manufacture, and intracellular communication. Using super-resolution microscopy, researchers followed the drug inside living cells and documented a progressive breakdown of the cell’s internal architecture that ultimately contributes to cellular collapse.

Sunitinib is used clinically against several cancers, including kidney cancer, gastrointestinal stromal tumors, and certain neuroendocrine tumors. Its established pharmacological action involves inhibition of receptor tyrosine kinases and other enzymes that transmit growth and survival signals. By blocking these pathways, the drug can restrict tumor-cell proliferation and blood-vessel formation. However, the new study suggests that the drug’s biological effects cannot be understood solely by examining enzyme inhibition. The location of a drug inside the cell, the organelles in which it accumulates, and the physical changes those organelles undergo may also influence therapeutic activity, toxicity, and treatment response.

The research was conducted by scientists in the Diao Laboratory at the University of Cincinnati, who combined cell-viability measurements with structured illumination microscopy, commonly known as SIM. This super-resolution technique uses patterned illumination and computational reconstruction to resolve cellular features that are too close together to be distinguished with conventional light microscopy. A particularly useful feature of sunitinib is that the molecule is naturally fluorescent. As a result, the researchers could track its distribution in living cells without attaching an additional fluorescent label that might alter its chemical behavior, transport, or interactions with intracellular structures.

The team began by exposing HeLa cells, a widely used human cervical cancer cell line, to increasing concentrations of sunitinib. Standard viability assays showed a concentration-dependent response: as the amount of drug increased, a progressively larger fraction of cells lost viability. The researchers then used fluorescence imaging to determine where the compound accumulated. Sunitinib was found mainly within lysosomes, membrane-bound organelles that digest damaged proteins, cellular debris, and other materials delivered through the endocytic pathway. Quantitative colocalization analysis showed a substantially stronger association between sunitinib and lysosomes than between the drug and mitochondria, indicating that lysosomal sequestration may be an important component of its intracellular behavior.

Lysosomal accumulation was accompanied by major changes in the organelles themselves. In untreated cells, lysosomes were distributed as numerous relatively small compartments. Following sunitinib exposure, their number declined, while the remaining lysosomes became larger and more irregular. This pattern is consistent with increasing stress in the lysosomal system and may reflect fusion between lysosomes, altered trafficking, impaired degradation, or changes in the mechanisms that generate and maintain these compartments. Because lysosomes regulate recycling, nutrient availability, membrane turnover, and several forms of programmed cell death, damage to their structure can affect multiple cellular processes at once. Their accumulation of sunitinib may therefore create a localized source of persistent intracellular stress.

The researchers also observed a pronounced effect on mitochondria, the organelles responsible for producing much of the cell’s usable energy through oxidative phosphorylation. In untreated cells, mitochondria formed extended and interconnected networks that spread throughout the cytoplasm. After treatment, these networks became increasingly fragmented. Long, branched structures broke into shorter and more isolated segments, a process that can alter mitochondrial transport, exchange of genetic and metabolic material, and the cell’s ability to match energy production with local demand. Excessive mitochondrial fragmentation is frequently associated with impaired respiration, increased oxidative stress, and the release of signals that can promote cell death, although the present study focused primarily on structural changes rather than establishing a single biochemical pathway responsible for them.

A comparable loss of organization occurred in the endoplasmic reticulum, or ER. This organelle normally forms a continuous membrane network extending through much of the cell. It is responsible for synthesizing and folding many proteins, regulating calcium storage, producing lipids, and coordinating signaling between intracellular compartments. In sunitinib-treated cells, the ER progressively broke apart into disconnected fragments. To quantify this effect, the researchers applied topological image analysis, measuring the number of separate network segments and calculating an organelle connectivity index. These measurements revealed a concentration-dependent decline in ER connectivity, turning a normally integrated network into a disorganized collection of isolated structures.

The simultaneous disruption of lysosomes, mitochondria, and the ER is significant because these organelles do not operate independently. Lysosomes exchange materials with mitochondria and the ER through vesicular trafficking, direct membrane contacts, and signaling pathways that regulate metabolism and stress responses. Mitochondria depend on the broader cellular environment for the delivery of proteins and lipids, while the ER helps control calcium signals that influence mitochondrial activity. Lysosomal dysfunction can interfere with the removal of damaged mitochondria through mitophagy, and mitochondrial failure can increase the burden of damaged components that lysosomes must process. The imaging results therefore point to a coordinated collapse of interconnected systems rather than isolated injury to a single organelle.

The study’s broader contribution lies in its combination of optical engineering, quantitative image analysis, and cell biology. Instead of treating drug response as a simple question of whether cells live or die, the researchers measured how the physical organization of intracellular structures changed as treatment progressed. Natural fluorescence allowed them to map drug localization, while SIM provided the resolution needed to examine organelle morphology and network connectivity. Such approaches could help explain why a drug is effective in one cellular context but toxic in another, or why certain side effects emerge even when a drug reaches its intended molecular target. The findings do not establish that organelle disruption is the only mechanism through which sunitinib kills cancer cells, but they demonstrate that its action includes a complex structural response involving several essential cellular systems. As super-resolution imaging becomes more accessible, similar analyses may support the design of therapies that target not only cancer-associated enzymes but also the spatial organization and physical resilience of tumor cells.

News Publication Date: 19-Aug-2026

Web References: https://www.spiedigitallibrary.org/journals/biophotonics-discovery/volume-3/issue-04/043102/Sunitinib-induces-coordinated-mitochondrial-lysosomal-and-endoplasmic-reticulum-disruption-leading/10.1117/1.BIOS.3.4.043102.full

References: A. Yadav et al., “Sunitinib induces coordinated mitochondrial, lysosomal, and endoplasmic reticulum disruption, leading to cellular collapse,” Biophotonics Discovery 3(4), 043102 (2026). DOI: 10.1117/1.BIOS.3.4.043102