Abstract A59: Biologic rationale for radiation-induced release of circulating tumor DNA
Bibliographic record
Abstract
Abstract Purpose: Rapid release of circulating tumor DNA (ctDNA) during cytotoxic therapy could provide an early indication of treatment efficacy. However, the biologic basis for treatment-induced ctDNA release is poorly understood. To study this phenomenon, we evaluated ctDNA release in head and neck squamous cell carcinoma (HNSCC) treated with radiotherapy (RT) or chemoradiotherapy (CRT). We sought to characterize the kinetics and biologic underpinnings of this process. Methods: 33 HPV+ HNSCC patients treated with RT (n=17) or CRT (n=16) had blood collected at baseline, after the 4th fraction of RT (early-RT), mid-RT, and 3 months post-RT. ctDNA was quantified using digital PCR for HPV-16. Nine HNSCC cell lines (3 HPV+, 6 HPV-) were used for in vitro ctDNA kinetic analysis. Apoptosis was measured by luminescent DEVD cleavage assay, triggered by staurosporine and blocked by z-vad-fmk. Senescence was measured by SA-β-galactosidase activity, triggered by HrasG12V-transduction of fibroblast cell lines and blocked by navitoclax. Three HNSCC cell lines (2 HPV+, 1 HPV-) were grown as xenografts in NRG mice for in vivo analysis. Endpoint xenograft tumors were assessed for necrotic area and for markers of apoptosis (cleaved-caspase 3) and senescence (p21) by immunohistochemistry. ctDNA was quantified from media or mouse plasma by quantitative PCR using human-specific LINE-1 primers. Results: Of 30 patients with detectable HPV-16 ctDNA (90.9%), we observed variable kinetic patterns of release. We grouped patients into three categories: pattern 1, peak at early RT (12, 40%); pattern 2, peak at mid RT (7, 23.3%); pattern 3, no peak (11, 36.7%). Based on these findings, we characterized the mechanisms dictating RT-induced ctDNA release in preclinical models of HNSCC. Following RT, HNSCC cell lines exhibited variable kinetics of ctDNA release in vitro and in vivo with peak release observed after 72-96 hours. RT-induced ctDNA release was not associated with intrinsic radiosensitivity, HPV status, or propensity to undergo apoptosis. Although caspase inhibition resulted in a near-complete reduction in RT-induced caspase activity (-84%±8%), a comparatively minor reduction in ctDNA release (-29%±9%) was observed. There was an inverse association between RT-induced senescence and ctDNA release. HrasG12V-triggered senescence reduced ctDNA release, while navitoclax treatment reversed this effect. HNSCC models with greater RT-induced ctDNA release displayed more necrosis and less senescence in endpoint xenograft tumors. Conclusion: Dynamic changes in HPV-16 ctDNA are observed during treatment, with variable patterns of release. Preclinical HNSCC models demonstrate RT-induced spikes within 3-4 days of treatment, revealing a complex interplay between distinct mechanisms of cell death and ctDNA release. Necrosis and senescence are the major determinants of RT-induced ctDNA release, while apoptosis has a comparatively minor impact. This study will inform future work on implementing ctDNA as a response biomarker. Citation Format: Ariana Rostami, John N. Waldron, Scott V. Bratman. Biologic rationale for radiation-induced release of circulating tumor DNA [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr A59.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".