I currently work with T47D cells, which are cells that are used in breast cancer research. I am excited to work in this lab and make progress toward effective photoactivated chemotherapy because it is a non-invasive form of cancer treatment with few side effects. Photoactivated chemotherapy derives from photoactivated metal agents or prodrugs which are known as being nontoxic in the dark. Once exposed to UV light, these prodrugs release cytotoxic species to kill cancer cells (Chen et al., 2021). More specifically, the cytotoxic species that are released are free ligands that may have anticancer activity. What is exceptional about photoactivated chemotherapy is that it is a non-invasive treatment, in comparison to the typical chemotherapy treatments that cancer patients endure, typically associating side effects such as hair loss and tiredness (Cancer Care Inc., 2022). As many of us know, breast cancer is a prevailing disease that many women encounter at some point in their lives. In 2019, an estimated 41,000 women died of metastatic breast cancer, and to this day, metastatic breast cancer remains fatal for 97-99% of women diagnosed (Metavivor Research and Support Inc, 2022).

Women with family members that have had breast cancer run a higher chance of having breast cancer as well. Taking myself into consideration, I also face the fear of having breast cancer since it runs in my family. Typically, an early warning sign of breast cancer is having a breast lump located anywhere along your chest wall to under your armpit. However, when the tumor is small in the early stages of breast cancer, it is barely noticeable to the touch or the naked eye. When women are diagnosed, most women do not have any visible signs of breast cancer ​​(COH HoldCo Inc., 2018). Fortunately, mammogram screenings (x-ray pictures of the breast) can detect tumors that are not yet visible and fight the tumor during its early stages when it is not as aggressive. In other circumstances, however, the only way to treat breast cancer tumors is through chemotherapy which can be hard on the body. This is why research on photoactivated chemotherapy is so important since it has the potential of making the process of killing breast cancer less painful and demanding.

Of the many experiments we conduct in the lab, the experiment I find the most interesting is the cell viability assay experiment. It accurately demonstrates the cytotoxicity (how toxic the compound is to the cell) of the compound being measured. This experiment is conducted to determine cancer cell death in the presence of a specific compound at a wide range of concentrations. To determine the amount of live vs. dead cells, we expose them to a blue dye called resazurin. Live cells can convert the dye to a different color (red) but dead cells cannot. When looking at the plate, the wells with the live cells will look purple and the wells with the dead cells will look blue.

We then use an instrument called SpectraMax to accurately calculate the total cancer cell death in each well by measuring their fluorescence. Fluorescence is the radiation emitted by the red dye as a result of radiation from ultraviolet light. When the plate is placed into the SpectraMax, the instrument measures emission of light at 590 nm after excitation at 570 nm. If there are more cells alive in the wells, there will be more emission at 590 nm, but if the cells are dead, there will be less.

The entire process of investigating cell death is quite lengthy because, before the cancer cells in the wells can be tested for fluorescence, they need to be incubated for 72 hours with the potential chemotherapy drugs. 48 hours before that, the cells have to be placed into the well. After we make it through our almost week-long process and obtain our data, we use a program called Prism to graph the data and determine the IC50 of the compounds. IC50, otherwise known as the half-maximal inhibitory concentration, is widely used to measure a drug’s efficacy (Aykul & Martinez-Hackert, 2016). A promising anti-cancer drug will have a low IC50 because it means that the compound is effective at inhibiting biological processes at low concentrations. So what does this mean in the context of photoactivated chemotherapy that I work on? Well, we want the IC50 of our prodrugs to be high (meaning that they are not good at killing cells) but that after exposure to UV light the IC50 decreases significantly as the compound turns into something that is cytotoxic and can effectively kill the cancer cells.

To put this into perspective, imagine yourself taking aspirin (also known as a prodrug) when you are feeling some kind of discomfort such as having a fever, menstrual periods, etc. is the first thing that comes to mind, how does aspirin relieve my pain? Or are you thinking, how can I quickly get rid of this pain or discomfort? I would assume you would be more worried about feeling better than thinking about what kinds of processes are occurring in your body in order to feel better. When taking aspirin, the prodrug is rapidly biotransformed into the active metabolite, salicylate in the stomach and the liver. Salicylate is responsible for most anti-inflammatory and analgesic effects (relieving pain) (UNIL, n.d.). Like our potential photoactivated chemotherapy compounds, aspirin needs to be activated to obtain its anticipated outcome of relieving pain. Our prodrug, in this case, is not cytotoxic, but once it is activated by being exposed to UV light, it can do its job of becoming cytotoxic and killing cancer cells. Keeping this in mind, I am excited to see how these potential photoactivated chemotherapy drugs can be optimized to treat breast cancer cells.

-Briseily Cejudo


Chen, Y.,Bai, L., Zhang, P., Zhao, H., & Zhou, Q. (2021). The Development of Ru(II)-Based Photoactivated Chemotherapy Agents. Molecules, 26(18), 5679. https://doi.org/10.3390/molecules26185679

Metavivor Research and Support Inc.(2022). Metastatic Breast Cancer Statistics | METAvivor. Www.metavivor.org. https://www.metavivor.org/mbc-prep/metastatic-breast-cancer-statistics/?gclid=Cj0KCQjw2MWVBhCQARIsAIjbwoO7eYaGYPjM4cJDTeQ7_M8cioN8cRk8gUn0rVuR8TxptL-Oj-y7Ut0aAv7GEALw_wcB

Cancer Care Inc.(2022).Chemotherapy Side Effects.CancerCare. https://www.cancercare.org/chemo-side-effects?gclid=Cj0KCQjw2MWVBhCQARIsAIjbwoMBlIxV8VPLoObLwr_Qw8y3LkF5JUSI5-dH9cUHipxSgQ9la924VK0aAsThEALw_wcB

Aykul,S.,&Martinez-Hackert,E.(2016).Determination of half-maximal inhibitory concentration using biosensor-based protein interaction analysis. Analytical Biochemistry, 508, 97–103. https://doi.org/10.1016/j.ab.2016.06.025

COH HoldCo Inc.(2018,October 5). What are the Symptoms and Signs of Breast Cancer? Cancer Treatment Centers of America. https://www.cancercenter.com/cancer-types/breast-cancer/symptoms#Q1

UNIL.(n.d.). Aspirin–Pharmacokinetics. PHARMACOKINETICS. https://sepia2.unil.ch/pharmacology/drugs/aspirin/