Using atomic absorption spectroscopy, Guarnieri et al. and Kahn et al. have mapped the distribution of platinum after i.c. infusion of carboplatin with ALZET pumps into F98 glioma-bearing rats, with delivery parameters similar to those that we used. Platinum concentrations were CHIR-99021 molecular weight maximal in brain sections corresponding OICR-9429 order to the infusion site, with diminished amounts (5 to 1 μg/g

tissue) in sections that were 3 mm from the point of infusion [27, 28]. The importance of the DNA damage is dependent on the number of Pt atoms intercalated with DNA molecules. At the molecular level, a larger number of DSBs were detected when cells were pretreated with cisplatin and subsequently irradiated with synchrotron X-rays above the

Pt K-edge, compared to those below the K-edge [23, 29]. Three times more DSBs were detected when human SQ20B squamous carcinoma cells pretreated with 30 μM cisplatin (3 ×× 108 atoms of Pt atoms per cell) for 6 h [29], and 1.3 times more DSBs with the same treatment of F98 cells [23]. However, no such an enhancement was observed (even at the molecular level) with the much lower Pt concentrations that would not have been tumoricidal, when the SQ20B cells were pretreated with 3 μM cisplatin (4 × 106 Pt atoms per cell) for 6 h [29]. In our studies, i.t. injection of cisplatin (3 μg in 5 μl), followed 24 h later by 15 Gy of X-irradiation, also produced similar long-term www.selleckchem.com/products/cobimetinib-gdc-0973-rg7420.html survival of F98 glioma bearing rats, irrespective of whether the synchrotron X-rays had energies below or above the Pt K-edge [23]. Comparable long term cure rates (17% and 18%) also were observed when the animals were irradiated with 78.8 keV synchrotron

X-rays or 6 MV photons after cisplatin (6 μg in 20 μl) was administered i.c. by CED [13]. Overall, the present data and those previously reported [11–13, 23, 29] are in good agreement with Bernhardt et al’s. predictions [24]. They strongly suggest that the therapeutic gain obtained by the direct i.c. administration of Pt Fossariinae compounds, followed by X-ray irradiation, was not due to the production of Auger electrons and photoelectrons emitted from the Pt atoms, but rather involved other mechanisms. Only molecular studies performed using extremely high Pt concentrations, which were not attainable in vivo, demonstrated energy dependence. However, this is not an adequate explanation for the in vivo therapeutic efficacy of the combination of Pt based chemotherapy with X-irradiation. In order for synchrotron radiation therapy to be successful, a sufficient, but not lethal, concentration of high Z number atoms must be incorporated into or localized nearby tumor cells, to produce enough photoelectrons or Auger electrons.