Effect of stereotactic radiation (SBRT) on survival in a preclinical model of spontaneous pancreatic cancer with induction gemcitabine/nab-paclitaxel.

Abstract

273 Background: There are no useful preclinical models that resemble relevant fractionated radiation, such as SBRT, with relevant chemotherapy. Most preclinical studies use a single fraction of radiation to large fields, causing significant toxicity and/or insufficient dose which leads to accelerated repopulation and worsened outcomes. Here, we employ mice with spontaneous pancreatic tumors, and treat them in a preclinical trial utilizing gemcitabine/nab-paclitaxel +/-SBRT. Methods: Mice with an activated KRas (G12D) allele and heterozygous for p53 expression only in the pancreas (KPC) were created and spontaneous tumors were diagnosed via weekly palpation and ultrasound. Mice with single tumors that were between 3-7mm at diagnosis were sequentially randomized to received either no treatment, gemcitabine/nab-paclitaxel x 2 weeks, or gemcitabine/nab-paclitaxel x 2 weeks followed by 8Gy x 5 daily fractions of SBRT to the pancreatic tumor. SBRT was delivered using X-RAD 225Cx (Precision X-Ray, Inc) small animal irradiator under image guidance by cone beam micro CT using AP/PA technique with a 10mm collimator. Every mouse was subjected to necropsy and a cause of death assigned. Tumor growth was monitored by small animal ultrasound. Kaplan-Meier survival analysis was performed to assess efficacy of treatments. Results: A total of 40 mice were enrolled with 12 receiving chemotherapy alone, 13 receiving chemotherapy +SBRT and 15 mice had no further treatment. The addition of induction chemotherapy improves lifespan compared to untreated mice. The addition of SBRT further improved survival. Causes of death in untreated animals of the gemcitabine/nab-paclitaxel group were largely from local progression, whereas the addition of SBRT provided local control causing most of the mice in this cohort to die from metastatic progression. Conclusions: SBRT improves survival when added to gem/nab-paclitaxel in a preclinical model, which may reflect favorable biology for this approach. Our novel system employs similar SBRT fields and doses, and may thus be useful for the evaluation of other chemotherapeutic regimens with SBRT.