(Lb) Pine Needles
The compound they isolated, Suramin, doesn't have solubility info I can find, though there is. Lot of info about the sodium salt.
So maybe the natural form isn't soluble in the GI environment or had other absorption limitations.
Maybe the effective dose is so high that they have to do injections.
I mean a tea is not gonna hurt you and is probably full of other good stuff, but a tea will only draw out the water soluble compounds.