Utility of biomarkers in prediction of response to ablative therapy in Barrett's esophagus

Abstract

Background & aims: Photodynamic therapy (PDT) has been shown to be effective in the treatment of high-grade dysplasia (HGD)/mucosal carcinoma in Barrett's esophagus (BE). Substantial proportions of patients do not respond to PDT or progress to carcinoma despite PDT. The role of biomarkers in predicting response to PDT is unknown. We aimed to determine if biomarkers known to be associated with neoplasia in BE can predict loss of dysplasia in patients treated with ablative therapy for HGD/intramucosal cancer.

Methods: Patients with BE and HGD/intramucosal cancer were studied prospectively from 2002 to 2006. Biomarkers were assessed using fluorescence in situ hybridization performed on cytology specimens, for region-specific and centromeric probes. Patients were treated with PDT using cylindric diffusing fibers (wavelength, 630 nm; energy, 200 J/cm fiber). Univariate and multiple variable logistic regression was performed to determine predictors of response to PDT.

Results: A total of 126 consecutive patients (71 who underwent PDT and 55 patients who did not undergo PDT and were under surveillance, to adjust for the natural history of HGD), were included in this study. Fifty (40%) patients were responders (no dysplasia or carcinoma) at 3 months after PDT. On multiple variable analysis, P16 allelic loss (odds ratio [OR], 0.32; 95% confidence interval [CI], 0.10-0.96) predicted decreased response to PDT. BE segment length (OR, 0.71; 95% CI, 0.59-0.85), and performance of PDT (OR, 7.17; 95% CI, 2.50-20.53) were other independent predictors of loss of dysplasia.

Conclusions: p16 loss detected by fluorescence in situ hybridization can help predict loss of dysplasia in patients with BE and HGD/mucosal cancer. Biomarkers may help in the selection of appropriate therapy for patients and improve treatment outcomes.

Figure 1

ROC curve for cross-validated model (see Materials and Methods section) with P16 loss (adjusted for clinical variables: age, sex, Barrett’s segment length, PDT, and EMR, N = 126). Area under the curve, 0.79 (SE, 0.03).

Figure 2

(A) ROC curves for models with clinical variables (age, sex, Barrett’s segment length, PDT, and EMR), P16 loss, P53 loss, both P16 and P53 loss each adjusted for clinical variables. —, Model with clinical variables: AUC, 0.83 (SE, 0.03); - - -, model with clinical variables and P16 loss: AUC, 0.83 (SE, 0.03); – – –, model with clinical variables and P53 loss: AUC, 0.82 (SE, 0.03); — — —, model with clinical variables and P16 and P53 loss: AUC, 0.83 (SE, 0.03). (B) ROC curve for model with P16 loss and P53 loss and multiple gains, adjusting for clinical variables. AUC, 0.83 (SE, 0.03). AUC, area under the curve.

Figure 3

Mechanism of action of PDT. Reactive oxygen species produced by PDT after the interaction of light, photosensitizer, and oxygen mediate cellular damage by multiple mechanisms. The exact proportion of damage caused by each mechanism is dependent on the energy dose delivered (high doses causing more necrosis, lower doses cause apoptosis and ischemia, in addition to necrosis) as well as the photosensitizer used (sensitizers accumulating in the mitochondria and lysosomes are more likely to initiate apoptosis, whereas those accumulating in the cell membranes cause more necrosis).

Figure 4

Putative model of the influence of cell-cycle check point genes on PDT-induced cellular apoptosis. The p16 locus on chromosome 9 can transcribe 2 proteins: (1) P16INK4 protein, which inhibits CDK4 and CDK 6, leading to the inhibition of phosphorylation of the retinoblastoma gene product (Rb), causing inhibition of cell-cycle progression and growth arrest, and (2) p14ARF, which inhibits the degradation of p53 protein by MDM2, thereby potentiating the P53-mediated inhibition of cell-cycle progression and causing cell-cycle arrest. PDT causes oxidative stress, which can activate cellular apoptosis mechanisms by P53-dependent and -independent mechanisms. In the presence of intact p16 (p14 ARF) and p53 function, PDT can induce cell injury by apoptosis. Loss of p16 and p53 function allows the progression of cells to the G2 phase of the cell cycle, leading to cell proliferation. This may provide cells with a survival advantage, leading to decreased response to PDT.