Cancer cells and immunosuppressive myeloid cells (MDSC and Tumor Cells)

This target profile describes a complex cellular environment within the tumor microenvironment consisting of malignant cells and immunosuppressive myeloid-derived suppressor cells (MDSCs) that are specifically sensitive to 5-fluorouracil (5-FU). 5-FU is a classic chemotherapeutic antimetabolite that inhibits thymidylate synthase, disrupting DNA synthesis and repair, which leads to cytotoxicity in rapidly dividing cancer cells (Longley et al., 2003, Nature Reviews Cancer). Beyond direct tumor cell killing, research has identified that MDSCs are uniquely susceptible to 5-FU-mediated apoptosis compared to other immune cells like T cells or B cells (Vincent et al., 2010, Cancer Research). By depleting MDSCs, 5-FU reduces the production of immunosuppressive factors such as arginase-1 and reactive oxygen species, effectively 're-priming' the immune system to recognize and attack the tumor (Gabrilovich & Nagaraj, 2009, Nature Reviews Immunology). This dual mechanism—direct tumor debulking and immune-mediated clearance—is often leveraged in local delivery strategies, such as prodrug gene therapy using cytosine deaminase to convert 5-fluorocytosine into 5-FU directly within the tumor site to minimize systemic toxicity (Toca 511/Toca FC platform).

Other names

Myeloid-derived suppressor cellsMDSCsTumor microenvironment5-FU sensitive cell populationsTumor-associated myeloid cells

5-fluorouracil (5-FU) acts as an antimetabolite that inhibits thymidylate synthase (TS), leading to the depletion of thymidine triphosphate pools and causing 'thymineless death' through DNA damage and RNA interference (Longley et al., 2003, Nature Reviews Cancer). In the context of the tumor microenvironment, 5-FU selectively induces apoptosis in myeloid-derived suppressor cells (MDSCs) by triggering reactive oxygen species (ROS) production and activating the caspase-dependent apoptotic pathway, thereby relieving the suppression of CD8+ T cells and enhancing anti-tumor immunity (Vincent et al., 2010, Cancer Research).