Abstract B49: The therapeutic effects of bromodomain inhibitors on the tumor microenvironment in pancreatic cancer
Authors: Leal Ana Sofia , Liby Karen T. 
Published: December 2016

Pancreatic cancer has a dismal prognosis, and the number of deaths from this disease are expected to continue to increase through 2030. Pancreatic cancer is complex, but the tumor microenvironment (TME), representing more than 50% of the tumor mass, plays a crucial role in drug resistance. The TME serves essential functions in progression, invasion and metastasis. The vasculature, immune cells, fibroblasts and extracellular matrix are part of the intricate structure of the TME and can have a profound effect on therapy.

Tumor cells can use epigenetic modulation to evade immune recognition and to shape the TME toward an immunogenic phenotype, without altering their DNA expression. Since epigenetic modulation is a mechanism used by tumors to temper the TME, using small molecules as epigenetic modulators to activate immune recognition is a therapeutically desirable approach. Bromodomain inhibitors, including JQ1 and I-BET 762, represent a promising new class of epigenetic modulators. These compounds are known to have growth inhibitory properties in lung cancer, neuroblastoma and multiple myeloid cell lines, mainly through downregulation of c-Myc. Nevertheless, little is know about their effects on the TME, although JQ1 has been reported to have beneficial effects on inflammation.

In cell lines derived from the KrasG12D/+;Trp53R172H/+;Pdx-1-Cre (KPC) mouse model, JQ1 and I-BET 762 down regulate several cytokines such as IL-6, CCL2 and GM-CSF. These cytokines are involved in cell signaling in the TME and elevated expression in patients correlates with a poor prognosis. These bromodomain inhibitors also inhibit p-STAT3 and p-Erk, important targets in pancreatic cancer required to maintain the TME.

LSL-KrasG12D/+;Pdx-1-Cre (KC) mice stimulated with caerulein (acute protocol - 75 μg/kg injected i.p. every hour for 8 hours for 2 consecutive days) serves as a useful model to study the influence of the TME on tumor progression. Treatment with I-BET 762 (60 mg/Kg BID once a day, starting 72 hours before caerulein stimulation and continued until the end of the study) decreases the levels of IL-6, p-STAT3, BRD4 and alpha-smooth muscle actin (α-SMA) in pancreas extracts of KC mice stimulated with caerulein, as measured by western blot. The percentage of macrophages and myeloid derived suppressor cells (MDSCs), as measured by flow cytometry, is also significantly lower in the spleen of these mice when compared with mice in the vehicle control group. The levels of macrophages in the spleen for KC mice stimulated with caerulein were 3.86±0.65 % of CD45+ cells; mice treated with I-BET 762 had levels of 1.14±0.29 % (p&lt;0.001). MDSCs levels in caerulein stimulated KC mice were 3.92±0.96 % (% of CD45+ cells), compared with KC mice treated with I-BET 762 that had a 0.97±0.25 % of MDSCs cells (p&lt;0.05). I-BET 762 treatment also downregulates the levels of IL-6, CCL2 and CxCL12 in pancreas extracts, as determined by ELISA.

These data suggest that these compounds have a modulatory activity in the TME and may be useful for treatment of pancreatic cancer. Currently several bromodomain inhibitors are being evaluated in clinical trials, with special emphasis on hematological malignancies. This work suggests an additional mechanism underlying the beneficial effects of bromodomain inhibitors.

Citation Format: Ana Sofia Leal, Karen T. Liby.{Authors}. The therapeutic effects of bromodomain inhibitors on the tumor microenvironment in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B49.