Proceedings of the 52nd Annual ASTRO Meeting S129

not predict initial response, progression-free survival, or survival. However, the presence of EGFR exon 19 mutations was asso-ciated with higher local recurrence rates (100% [2/2] vs. 22% [13/57], p = 0.014).

Conclusions: While KRAS mutations have been linked with poor survival and limited benefit from chemotherapy in NSCLC,our findings suggest that patients with NSCLC and KRAS mutations may preferentially benefit from radiation therapy. To ourknowledge, this is the first study to show an association between KRAS mutation status and outcome after definitive radiationtherapy. Longer follow-up times are needed to determine if KRAS status is associated with a survival advantage. The high localfailure rates associated with EGFR exon 19 mutations suggest that such patients may benefit from intensification of localtherapies.

Author Disclosure: A. Likhacheva, None; J. Thomas, None; E. Kim, None; P.K. Allen, None; R. Komaki, None; J. Cox, None; R.Herbst, None; J. Welsh, None.

275 A b1 Integrin - Dependent Mechanism of Resistance to Ionizing Radiation

T. J. FitzGerald, H. L. Goel, L. L. Languino

University of Massachusetts Medical Center, Worcester, MA

Purpose/Objective(s): b1 integrins regulate cancer cell proliferation, migration and tumor growth as well as resistance to radi-ation therapy. The present study evaluates the role of b1 integrins in resistance to ionizing radiation in mouse models of prostatecancer.

Materials/Methods: TRAMP (Transgenic Adenocarcinoma of the Mouse Prostate) mice, which spontaneously develop prostatecancer and closely mimic the pathogenesis of the human disease were used in this study. We conditionally ablated b1 integrins inTRAMP prostates (b1pc-/- /TRAMP) and analyzed their survival in response to ionizing radiation. As control, b1wt /TRAMP lit-termate mice, which express b1 integrins, were used. Prostate regions of b1wt /TRAMP and b1pc-/- /TRAMP mice were irradiatedusing 6 MeV Varian 2300CD linear accelerator 6 with custom cut-out lead blocks. Total doses ranging from 20-50 Gy were used.We also analyzed the effect of an inhibitory antibody to b1 integrins, AIIB2, in combination with irradiation on prostate cancer PC3xenograft growth in nude mice.

Results: Our results show that irradiation significantly increases the survival of either b1pc-/-/TRAMP or b1wt/TRAMP mice; how-ever, irradiation increases the survival of b1pc-/-/TRAMP at a higher extent than b1wt/TRAMP mice. The combined treatment of aninhibitory antibody to b1 integrins, AIIB2, and irradiation also completely blocked PC3 xenograft growth in nude mice at a higherextent than either therapy alone.

Conclusions: b1 integrins promote resistance to ionizing radiation in prostate cancer in vivo. This study suggests that inhibition ofb1 in combination with radiotherapy will provide a better clinical outcome compared to individual treatments for patients withaggressive prostate cancer.The work was supported by NIH grants NIH R01 CA89720 and CA109874 to L.R.L. and American Cancer Society InstitutionalResearch Grant IRG-93-033 to H.L.G.

Author Disclosure: T.J. FitzGerald, None; H.L. Goel, None; L.L. Languino, None.

276 Reprimo-like is a P53 Responsive Gene Whose Promoter Methylation May Predict for Radiation

Responsiveness in Pancreatic Cancer

S. H. Lin1, H. Zhou2, R. Kumar2, J. M. Herman1, T. L. DeWeese2, C. Iacobuzio-Donahue2, S. B. Baylin2

1M.D. Anderson Cancer Center, Houston, TX, 2The Johns Hopkins University School of Medicine, Baltimore, MD

Purpose/Objective(s): REPRIMO is a radiation-inducible, p53 dependent gene that is commonly hypermethylated and silenced invarious GI malignancies and confers a poorer prognosis. We have identified a second gene called Reprimo-like (RPRML) that ishighly homologous to REPRIMO and conserved from Xenopus to mammals. We determined the methylation status of this gene inpatients with resected pancreas cancer and whether it has a functional and/or prognostic role.

Materials/Methods: DNA methylation was assessed by Methylation-Specific PCR (MSP). Gene expression knock down was per-formed using siRNA transfection in cells with or without RPRML methylation. Under these experimental conditions, cell cycleanalysis, apoptosis using Annexin V staining and radiation responsiveness using clonogenic assays were evaluated. DNA meth-ylation status in patient samples was performed using MSP from DNA extracted from paraffin-embedded tumor samples. Survivalanalysis was performed using Kaplan-Meier statistics.

Results: We found RPRML to be methylated in various tumors and cell lines of GI origin, albeit at lower frequency (25%-50%)in comparison to REPRIMO (60-80%). Treatment using 5-azacytidine reverses promoter methylation and causes gene re-expres-sion. This gene is inducible with gamma-irradiation, and like REPRIMO, is also p53 dependent. Unlike Reprimo, RPRML doesnot have effects on the cell cycle dynamics. However, siRNA knockdown of RPRML induced apoptosis and radiation sensiti-zation. We therefore hypothesized that RPRML methylation in tumors may predict for treatment responsiveness. Indeed, wefound RPRML methylation status predicts for improved survival compared to patients without RPRML methylation in 52non-metastatic pancreatic cancer patients treated with surgery and adjuvant chemoradiation (median survival of 28 months versus15 months, p = 0.05, log-rank test). Methylation status of 4 other genes (Chfr, DYPD, CXCL14, and Reprimo) was not predictiveof outcome.

Conclusions: These results suggest that RPRML gene silencing by promoter hypermethylation may confer tumor sensitivity toradiation treatment. RPRML methylation may be a useful marker to determine radiation sensitivity in pancreatic cancerpatients.

Author Disclosure: S.H. Lin, None; H. Zhou, None; R. Kumar, None; J.M. Herman, None; T.L. DeWeese, None; C. Iacobuzio-Donahue, None; S.B. Baylin, None.