Company: NCNA
Filing Date: 2025-03-20
Form Type: 20-F
Source: 0000950170-25-042709
Chunk: 133

Company: NuCana plc
Filing Date: 2025-03-20
Form: 20-F
Item: Item 4
Chunk 133
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 to cause cell death. This confirms that NUC‑3373 causes cancer cell death by inhibiting TS and reducing thymidine levels. In addition, when cancer cells were treated with NUC-3373, more of them had TS in the cytoplasm of the cell compared to untreated cells, which mostly had TS in the nucleus of the cell. We believe that by keeping TS in the cell cytoplasm and preventing it from moving to the nucleus, NUC-3373 causes a further imbalance in the levels of dUMP and dTMP.

 In another set of experiments, the activity and metabolism of NUC-3373 was directly compared to that of 5-FU in colorectal cancer cell lines. The active anti-cancer metabolite, FUDR-MP, inhibits thymidine synthesis through binding to and forming a ternary complex with TS. This causes an imbalance in the cellular nucleotide pools by preventing the conversion of dUMP to dTMP and leads to disruption of DNA synthesis and repair. In these experiments, NUC-3373 was shown to cause greater TS complex formation than 5-FU, even at lower drug concentrations. This suggests that NUC-3373 may be a more potent inhibitor of TS than 5‑FU. Furthermore, when anti-cancer metabolite generation was assessed in these cell lines it was found that NUC-3373 generated significantly higher levels of FUDR-MP compared to 5-FU and had a more pronounced effect on the dUMP levels, suggesting a greater impact on nucleotide pools. NUC-3373’s ability to generate high intracellular levels of FUDR-MP resulted in the generation of the triphosphate form of the anti-cancer metabolite, or FUDR-TP (also referred to as FdUTP), which was shown to be incorporated into the DNA of cancer cells. This effect was not observed with 5-FU. These results suggest that NUC-3373 may be not only a more potent TS inhibitor, but also a more efficient DNA- damaging agent compared to 5-FU. Finally, while 5-FU treatment led to the production of the toxic metabolite FUTP in these cells, FUTP was not detectable following treatment of these cells with NUC-3373.
 
 A further set of experiments showed that NUC-3373 also causes a prolonged type of cell stress, called endoplasmic reticulum, or ER, stress in cancer cells