THE DIFFERENTIAL INDUCTION OF COLLATERAL RESISTANCE TO 62.5-MEV (P-]BE+) NEUTRONS AND 4-MEV PHOTONS BY EXPOSURE TO CISPLATINUM

Purpose: 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. Methods and Materials: The degree of cross-resistance of five human in-vitro cell lines to photons or fast neutrons was analysed for both cisplatinum-sensitive and resistant variants. Results: 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. Conclusion: 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 (alpha), 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.