The differential induction of collateral resistance to 62.5 MeV (p→Be+) neutrons and 4 MeV photons by exposure to CIS-platinum

The purpose of this study was to determine the relative sensitivity to cis-platinum, 4 MeV photons and 62.5 MeV (p→Be+) neutrons in five human tumor cell lines, and their cis-platinum resistant variants. The degree of cross-resistance of five human in-vitro cell lines to photons or fast neutrons was analyzed for both cisplatinum-sensitive and resistant variants. The development of acquired cis-platinum resistance conferred collateral resistance to 62.5 MeV (p-Be+) neutrons in all five cell lines, but did not consistently decrease the photon sensitivity of these same cells. The reduction in photon and neutron sensitivity following the development of acquired cis-platinum resistance may possibly be regulated by different mechanisms. The reduction in neutron sensitivity was primarily due to a 1.3-1.7 fold reduction in the magnitude of the initial slope (α), which was independent of the degree of platinum resistance induced, suggesting a non-stochiometric relationship between the mechanisms responsible for acquired cis-platinum, and 62.5 MeV (p→Be+) neutron resistance. 18 refs., 5 figs., 3 tabs