Cellular Foundations of Radiotherapy Protocols Frequently Used in Pulmonary Pathology

FERRARIS, GUSTAVO; ELIANA E. OCOLOTOBICHE; BANEGAS YULIANA; MARTINEZ MARCELO; ALBA GÜERCI

Montevideo

Conferencia; IASLC 2023 Latin America Conference on Lung Cancer; 2023

IASLC. International Association for the study of lung cancer

Introduction: Although the role of radiotherapy in the management of lung cancer has alwaysbeen a leading role, it has now been further enhanced, given advances in the administration ofradiation, with doses much more adjusted to the objective, which make it possible to shortenconventional treatments (CRT) through protocols with fewer sessions but with higher doses(hypofractionation: HRT and ablative radiotherapy: SBRT). The efficacy of these protocols hasbeen proven both for early stages without surgical resolution and for advanced stages throughphase II clinical trials, which demonstrated better progression-free survival and overall patientsurvival. However, its cellular foundations are not yet known, whose determination has beenthe objective of this work.Methods: cell cultures of human lung cancer cell line A549 were irradiated with doses used inCRT (2 Gy), HRT (4 and 8 Gy) or SBRT (12, 16 and 20 Gy). The direct effect of these doses wasanalyzed, as well as the Bystander Effect, from the treatment with conditioned medium fromthe irradiated cultures. The tumoricidal effect was evaluated through the Clonogenic Assay,MTT, Trypan Blue and direct cell count and the initial and residual lesions on the DNA throughthe Comet Assay. Each experimental point was evaluated in duplicate. Statistical analysis:ANOVA; Tukey, Kaplan-Meier and Mantel-Cox test was implemented. In addition, weevaluated survival and toxicity in a retrospective study of 49 lung cancer patients undergoingradiotherapy treatment.Results: Our findings showed that the greater efficacy of ablative regimens should not only beattributed to events of direct cell death induced by genotoxic damage, but also to a lower cellrepopulation and the indirect action of clastogenic factors secreted. The comparative analysisof the protocols showed that the number of genotoxic lesions varies with the dose, but alsosignificantly their complexity. While the doses per session used in conventional protocols givea certain advantage in terms of DNA repair and cell repopulation, in ablative or hypo-fractionated treatments, these cellular processes are unlikely. From 8 Gy potentially lethalgenotoxic damage is observed, accompanied by a significant decrease in mitochondrial activityand functional loss of plasma cell membrane. Simultaneously, a synchronous result wasobtained in viability tests, between doses of 12, 16 and 20 Gy.Conclusion: The greater efficacy of the proposed ablative regimens could be attributed to amultifactorial mechanism of action, which exceeds the processes of cell repair andrepopulation, in which conventional radiotherapy underlies.