Effects of folinic acid on 5-fluorouracil induced cell lethality with or without cisplatin against head and neck laryngeal squamous carcinoma multicellular tumor spheroids

We evaluated the efficacy of folinic acid (Leucovorin, LV) on cell lethality induced by 5-fluorouracil (FU) alone or in combination with cisplatin (DDP) by using the HEp-2 laryngeal squamous carcinoma multicellular tumor spheroids (MTS) system. For LV, non-toxic concentration of 10^-5 M was used. For cells in the monolayer, 6 and 24 h exposure to LV increased FU-induced cell lethality approximately 7- and 2-fold, respectively, whereas LV did not influence the effect of FU for MTS. LV's lack of effect on cells in MTS may be interpreted to mean that LV cannot penetrate the MTS. For the monolayer, simultaneous exposure to 3 drugs, DDP, FU and LV. produced synergistic interaction. However, sequential exposures were marginally synergistic or antagonistic, irrespective of sequence of DDP first or last. In contrast, DDP followed by FU plus LV was most synergistic for MTS. Simultaneous exposure was also synergistic, however. FU plus LV followed by DDP was antagonistic. These results suggest that LV is unable to penetrate into the MTS core to potentrate FU activity. DDP appears to have enhanced LV penetration into the MTS core. The exploration of means to overcome limited penetration of LV appears important for successful treatment of head and neck carcinoma.