A NOVEL AZETIDINE-BASED STAT3 INHIBITOR INDUCES ANTI-TUMOR RESPONSES IN EXPERIMENTAL MODELS OF PANCREATIC CANCER

Background: Pancreatic cancer (PC) features highly proliferative cancer cells and a dense stroma modulating tumor growth. Due to the invasive behavior of PC and the lack of effective treatments, there is a pressing need to develop therapies targeted at tumorigenic events to slow down PC progression. Signal transducer and activator of transcription 3 (STAT3) is a transcription factor operating in neoplastic and stromal cells that inhibits immune activation factors and promotes tumor growth. We reported that STAT3 is overactivated in obese KC mice expressing mutant KRasG12D, a key PC driver, in the pancreas. Compared to mice fed control diet (CD; 13% fat), obese KC mice fed high fat diet (HFD; 45% fat) display rapid stromal expansion and accelerated pre-cancerous lesion (PanIN) progression and cancer incidence. This study investigates the therapeutic potential of a novel STAT3 inhibitor, H182 to reduce PC progression. Methods: KC (Kras^G12D/+;Ptf1^Cre/+) mice were fed HFD for two months to allow PanIN development, and then administered 10 mg/kg H182 or vehicle control (intraperitoneally; twice per week) for 6 weeks. Tissues were collected 4 days after the last injection and histologically analyzed. We also tested the effects of H182 on STAT3 activation and downstream responses in human AsPC-1 cancer cells, mouse KC and KPC cells, and pancreatic stellate cells (PaSC) derived from PC tumors. Results: In vehicle-treated mice, the HFD imposed marked body-weight-gain, and extensive loss of normal acinar cells, abundant acinar-to-ductal metaplasia, high numbers of advanced PanINs and expansion of stromal cells in pancreas. These features were especially prominent in the pancreas head compared to the tail portion and were associated with high levels of total STAT3 and phosphorylated STAT3^Tyr705, supporting STAT3 activity. Using QuPath software, we analyzed H&E-stained pancreas tissues to assess tumor growth in vehicle- and H182-treated mice. H182 treatment had no effect on body weight gain but significantly reduced the number of PanINs (from 69% of all cells in vehicle-treated to 43% in H182-treated mice in the pancreas head; and from 57% to 34% in the pancreas tail) and markedly increased the number of acinar cells (from 1.9% to 14% in the pancreas head; and from 12% to 50% in the pancreas tail). The findings indicate that H182 prevents neoplastic transformation of acinar cells and slows down PanIN progression. In cell culture systems, H182 reduced cancer cell growth and effectively inhibited IL6-induced STAT3^Tyr705 phosphorylation and nuclear translocation in cancer cells and PaSC. These effects were linked to decreased secretion by these cell types of cytokines and chemokines with key pro-tumor activities. Conclusions: our findings indicate that STAT3 inhibition in neoplastic and stromal cells is a promising strategy to halt obesity-induced PC progression.