sulfamethoxazole inhibits the synthesis of folic acid. This leads to inhibition of DNA synthesis, and some amino acids. Which hinders different viruses from growing. It may also inhibit growing cancer cells.

From Wikipedia https://en.wikipedia.org/wiki/Sulfamethoxazole

Sulfamethoxazole, a sulfanilamide, is a structural analog of para-aminobenzoic acid (PABA). They compete with PABA to bind to dihydropteroate synthetase and inhibit conversion of PABA and dihydropteroate diphosphate to dihydrofolic acid, or dihydrofolate. Inhibiting the production of dihydrofolate intermediate interferes with the normal bacterial synthesis of folic acid (folate). Folate is an essential metabolite for bacterial growth and replication because it is used in DNA synthesis, primarily at thymidylate and purine biosynthesis, and amino acids synthesis, including serine, glycine and methionine. Hence, blockage of folate production inhibits the folate-dependent metabolic processes for bacterial growth. Since it inhibits bacterial growth, sulfamethoxazole is considered a bacteriostatic antibiotic.

Sulfonamides are selective against bacteria because they interfere with the synthesis of folate, a process which does not occur in humans. Humans do not synthesize folate, and must acquire it through diet.

Also,

Trimethoprim used for Pneumocystis pneumonia in people with HIV/AIDS.

and had a close, harmonious mode of action with sulfamethoxazole.

from wikapedia

https://en.wikipedia.org/wiki/Trimethoprim

Trimethoprim binds to dihydrofolate reductase and inhibits the reduction of dihydrofolic acid (DHF) to tetrahydrofolic acid (THF).THF is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis.Trimethoprim's affinity for bacterial dihydrofolate reductase is several thousand times greater than its affinity for human dihydrofolate reductase. Sulfamethoxazole inhibits dihydropteroate synthase, an enzyme involved further upstream in the same pathway.Trimethoprim and sulfamethoxazole are commonly used in combination due to possible synergistic effects, and reduced development of resistance.

I have noticed some positive results of the compound Sulfamethoxazole against influenza viruses and herpes I have recorded it in a previous question on the researchgate

https://www.researchgate.net/post/Is_there_any_effect_of_Sulfamethoxazole_on_viruses

But I got a positive response

My hypothesis: We may use the Trimethoprim and Sulfamethoxazole or some of it analogous to inhibit the growth of viruses and also the cancer cells.