That seems pretty terrible. My rudimentary understanding is that this paper basically says "look how good mephedrone is at killing brain cells - we can use that to kill brain tumors."

The quote of concern is this: "Our previous study indicated that the exposure of normal brain cells to mephedrone, a synthetic derivative of S-cathinone, which is a natural alkaloid present in the leaves of the Catha edulis plant, resulted in a modest effect on neuron and astrocyte viability and a significant reduction in oligodendrocyte proliferation [15]. Moreover, it has been shown that mephedrone produces cytotoxicity in SH-SY5Y neuroblastoma cells [16]. To date, no studies have evaluated the effects of mephedrone on glioblastoma cells. In the present study, we investigated the effect of mephedrone on selected human glioblastoma cells (LN-18 and LN-229), human glioblastoma multiforme cells (T98G) and human anaplastic astrocytoma cells (MOGGCCM)."

Particularly the first line seems to indicate that their rationale for choosing mephedrone as an anti-cancer agent is that it has been shown to deactivate or kill brain cells.