This could actually be useful in fighting cancers, but you are right that it would be indiscriminate as a pill or injection. At that level in the system it would affect the body like chemo- or radiotherapy, stopping all actively reproducing cells. The benefit of this is that you could (in theory) identify exactly which cells are cancerous and find a way to target them with a tailored retrovirus. (The retrovirus would contain the enzyme reverse transciptase and viral RNA coding for the mitosis inhibition protein. The reverse transcriptase would make cDNA from the RNA, insert this into the cell nucleus, and trick the cell into making the protein itself.) This would be more accurate but way trickier to make, and probably more expensive.
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This could actually be useful in fighting cancers, but you are right that it would be indiscriminate as a pill or injection. At that level in the system it would affect the body like chemo- or radiotherapy, stopping all actively reproducing cells. The benefit of this is that you could (in theory) identify exactly which cells are cancerous and find a way to target them with a tailored retrovirus. (The retrovirus would contain the enzyme reverse transciptase and viral RNA coding for the mitosis inhibition protein. The reverse transcriptase would make cDNA from the RNA, insert this into the cell nucleus, and trick the cell into making the protein itself.) This would be more accurate but way trickier to make, and probably more expensive.