Final answer:
The best treatment to make a cancer cell line with inappropriate expression of telomerase mortal would be a drug that methylates the promoter of the telomerase gene. This approach would shut down the production of telomerase, leading to the senescence and death of cancer cells, as the extension of telomeres would be prevented.
Step-by-step explanation:
Given a cancer cell line with inappropriate expression of telomerase, the BEST treatment option to make this cell line mortal would be a drug that inhibits the action of telomerase. Telomerase is an enzyme that maintains the telomeres, which are regions of repetitive DNA at the end of a chromosome, and is active in germ cells, adult stem cells, and cancer cells. In cancer cells, telomerase becomes active after telomeres are already shortened and contributes to the uncontrolled division of these cells.
To curb the immortality of cancer cells, a treatment that targets and inhibits telomerase would prevent further extension of telomeres, thus leading to senescence and death of cancer cells. Out of the options provided, a drug that methylates the promoter of the telomerase gene would be the best choice as it would shut down the production of telomerase by blocking its gene expression. DNA methylation is a common epigenetic signaling tool that cells use to lock genes in the "off" position.
It is important to note that using a drug that inhibits a tumor-suppressor gene or one that increases the levels of telomerase expression would be counterproductive, as they could potentially promote cancer progression. Repairing the mutation or allowing lower expression levels of telomerase does not directly aim at making the cancer cells mortal, which is the goal of the treatment.