Long-Term In vivo Effects of Cisplatin on γ-H2AX Foci Signaling in Peripheral Lymphocytes of Tumor Patients After Irradiation

Abstract

Purpose: This study determined the effects of cis-diamminedichloroplatinum(II) on radiationinduced foci formation of g-H2AX and Rad51in lymphocytes. Experimental Design: Twenty-eight cancer patients were irradiated for intrathoracic, pelvic, or head and neck tumors and received simultaneous cisplatin containing chemotherapy. The effect of cisplatin on radiation-induced g-H2AX and Rad51 foci as a response to ionizing radiationî nduced DNA double-strand breaks was measured in lymphocytes after in vivo and in vitro radiochemotherapy.The role of DNA-dependent protein kinase and ataxia-telangiectasia mutated kinase in g-H2AX signaling, the consequences of altered g-H2AX foci formation on doublestrand break end joining, was studied. Results: Cisplatin decreased the number of induced g-H2AX foci in lymphocytes after in vivo or in vitro irradiation by 34% F 6% at days 0 to 3 after cisplatin (P < 0.0001) and remained significant until day 6. The variation in this cisplatin effect from patient to patient was larger than the retest error within the same patient (P = 0.01).The cisplatin effect was not accompanied by an inhibition of end joining of double-strand break as analyzed using gel electrophoresis of DNA under neutral conditions. Cisplatin also decreased radiation induced Rad51foci formation in lymphocytes after stimulation of proliferation with phytohemagglutinin by 47% F 6% (P < 0.0001).Conclusion: Cisplatin has long-term effects on the early double-strand break response of g-H2AX and Rad51 foci formation after ionizing radiation. Inhibition of sensing and processing of double-strand break by g-H2AX and Rad51foci formation are important mechanisms by which cisplatin can alter the radiation response.

DNA Damage Response Assessments in Human Tumor Samples Provide Functional Biomarkers of Radiosensitivity

“…Cisplatin treatment led to a decrease in IR-induced γ-H2AX formation of about 30%. The foci variability was greater from patient to patient than for repeated measures within a patient 107 . Another commonly used agent, 5-fluorouracil (5-FU), is converted to the active metabolites fluorodeoxyuridine triphosphate and fluorouridine triphosphate which are incorporated into DNA and RNA.…”

“…Interestingly, after ex-vivo irradiation of PBL, the γ-H2AX assay was very precise in terms of predicting radiosensitivity relative to in-vivo irradiated PBL 109 . However, concurrently administered chemotherapeutics, especially cisplatin, limit the precision of this method for predicting radiosensitivity 107,109 . In contrast, as suggested in Table 1, γ-H2AX assays will likely be useful to assess combinations with radiosensitizing targeted drugs that do not increase DSB levels unless they are combined with IR.…”

DNA damage response (DDR) pathway engagement in cisplatin radiosensitization of non-small cell lung cancer

“…This would seemingly contradict the findings of Sak et al, who described a decrease in γ-H2Ax foci formation in peripheral blood lymphocytes obtained from patients treated with CDDP and then exposed to IR in vitro . 46 Our model uses NSCLC cells treated with clinically relevant doses of CDDP-IR. It is not surprising that the DDR induced by CDDP-IR differs between peripheral blood lymphocytes and clonally proliferating H460 and A549 NSCLC cells, which display the unchecked proliferation and cell cycle regulation characteristic of malignant cells.…”

DNA damage foci: Meaning and significance

“…Obviously, the same concepts and possibilities apply to the use of foci assays as pharmacodynamic tools for characterising anti-cancer therapies [Redon et al, 2010a], combinations of therapeutics [Sak et al, 2009] or DNA damage response modifiers, whether used alone or in combination with DNA-damaging treatments [e.g. Lim et al, 2014;Srivastava et al, 2014;Burdak-Rothkamm et al, 2015b].…”