Here is the article demonstrating that: Papaverine and its derivatives radiosensitize solid tumors by inhibiting mitochondrial metabolism  https://www.ncbi.nlm.nih.gov/pubmed/30201710

A 150-year-old drug might improve radiation therapy for cancer  https://www.sciencedaily.com/releases/2018/10/181017172829.htm

Nearly 40 years ago, it has been also shown that Papaverine can work well with hyperthermia and chemotherapy  https://www.sciencedirect.com/science/article/pii/S0022346880803034

Papaverine indirectly inhibits telomerase  https://www.mdpi.com/1420-3049/19/8/11846/htm

Its also a RAGE inhibitor. RAGE has been implicated in multiple pathogenic processes, in cancer and numerous other diseases, including diabetes, atherosclerosis, inflammatory and neurodegenerative diseases  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5835888/

It's an approved FDA drug  https://en.wikipedia.org/wiki/Papaverine

A longer list of mito inhibitors is here  https://www.cancertreatmentsresearch.com/a-list-of-mitochondria-inhibitors/