Hi @Hira Zaheer,

A radiosensitizing agent is any drug/chemical that will increase the effectiveness of radiotherapy. These most typically include inhibitors of the DNA damage response, since the primary outcome of IR is damage to the cell's DNA. Generally speaking, these treatments are not specifically targeted to cancer cells (unless used as an antibody-drug conjugate, nanoparticle conjugate, or similar). This means, of course, that normal tissue may also be sensitized to radiation from such a treatment. However, this can be mitigated by precise delivery of IR to the tumor site (e.g., conformal radiation or the use of high LET heavy ion radiation). In addition, it's important to remember that IR is more effective on rapidly dividing cells with compromised cell cycle checkpoints, which usually is most of a bulk tumor.

There are also cases where the tumor type and surrounding environment are advantageous for radiosensitizers. For example, we have shown that ATM kinase inhibitors are effective radiosensitizers of glioblastoma. In this case, p53-mutant GBM (~30% of these tumors) are particularly sensitive to ATM inhibitors + IR. In addition, we and others have shown that ATM inhibition or ablation in normal brain tissue appears to be radioprotective.

https://pubmed.ncbi.nlm.nih.gov/23620409/

https://pubmed.ncbi.nlm.nih.gov/29938225/

I hope this helps answer your questions.

this link clarify the mechanisms of interaction radiopharmacuticals with cells

https://pubs.rsna.org/doi/10.1148/rg.2018180072#:~:text=To%20provide%20a%20mental%20framework,uptake%2C%20which%20includes%20indium%20oxine%2C