| Rank |
Pathway / Axis |
Cancer / Tumor Context |
Normal Tissue Context |
TSF |
Primary Effect |
Notes / Interpretation |
| 1 |
Thymidylate synthase (TS) inhibition → dTMP depletion |
dTMP ↓ → DNA synthesis ↓ → replication stress ↑ |
Also affects normal proliferating tissues (marrow, GI mucosa) |
P, R |
Core cytotoxic mechanism |
5-FU is converted to FdUMP, which forms a ternary complex with TS and folate, blocking thymidylate production (“thymineless death”). |
| 2 |
RNA misincorporation (FUTP incorporation) |
RNA processing/translation defects ↑ |
Contributes to mucositis and systemic toxicity |
P, R |
Transcription/translation disruption |
RNA effects are a major contributor to cytotoxicity, particularly with bolus dosing. |
| 3 |
DNA misincorporation (FdUTP incorporation) |
DNA damage signaling ↑; apoptosis ↑ (context) |
DDR activation in normal tissues contributes to toxicity |
R, G |
Genome instability |
Misincorporation triggers mismatch repair and DNA damage responses. |
| 4 |
S-phase specificity (cell-cycle dependence) |
Greater killing in actively cycling/S-phase cells |
Bone marrow & GI epithelium vulnerability ↑ |
R, G |
Cell-cycle–linked cytotoxicity |
Antimetabolite activity is strongest in proliferating cells. |
| 5 |
Folate modulation (leucovorin synergy) |
TS inhibition ↑ when combined with leucovorin |
— |
R |
Mechanism amplification |
Leucovorin stabilizes the FdUMP–TS–folate complex, enhancing cytotoxicity. |
| 6 |
Myelosuppression |
— |
Neutropenia/anemia risk ↑ |
R, G |
Dose-limiting toxicity |
Expected on-target effect in rapidly dividing marrow progenitors. |
| 7 |
Gastrointestinal toxicity (mucositis/diarrhea) |
— |
GI epithelial injury ↑ |
R, G |
Dose-limiting toxicity |
Reflects RNA/DNA effects in rapidly renewing GI mucosa. |
| 8 |
Cardiotoxicity (vasospasm; rare cardiomyopathy) |
— |
Chest pain/ischemia risk ↑ (rare but important) |
R |
Serious adverse effect |
Coronary vasospasm is the most recognized mechanism; monitoring required in symptomatic patients. |
| 9 |
DPD metabolism (DPYD enzyme) |
Severe toxicity risk ↑ if DPD deficient |
— |
— |
Pharmacogenetic constraint |
Dihydropyrimidine dehydrogenase (DPD) metabolizes 5-FU; deficiency can cause life-threatening toxicity. Pre-treatment DPYD testing is increasingly recommended. |
| 10 |
Infusion vs bolus pharmacodynamics |
Continuous infusion → more TS-driven DNA effect |
Bolus → more RNA-mediated toxicity |
P, R, G |
Dosing-dependent mechanism balance |
Administration schedule alters relative DNA vs RNA contribution and toxicity profile. |