Pancreatic ductal adenocarcinoma (PDAC) is the most common, and the most devastating form of pancreatic cancer, with an annual death rate approximating its incidence rate. If detected late, it defies virtually all molecularly targeted chemotherapy. The disease is legendary for the extensive stromal deposition it elicits; in fact, the stroma often exceeds the tumor in volume and has been increasingly recognized to play a pivotal role of in the disease progression. Deciphering the complex interplay between tumor and the various components in the stromal microenvironment ideally calls for in vivo observation. To this end, this dissertation sought to apply several optical molecular imaging techniques and fractal analysis to characterize changes in two components of the tumor microenvironment: microvasculature and collagen, following manipulation of the tumor genotype, as well as after therapy targeting the TGFβ pathway. Specifically, the dissertation begins with the validation of a fiber-optic confocal laser microcatheter in characterizing tumor surface microvasculature morphology in normal pancreas as well as PDAC. Next, this technique was applied to investigate the effect of active TGFβ pathway signaling in Smad4 wildtype and deficient PDAC using an orthotopic tumor model.
Smad4 encodes a transcription factor that mediates most of the TGFβ pathway activities, and its inactivating mutations are found in half of the patients with PDAC. This series of work found evidence that TGFβ signaling had opposing effect on Smad4 wildtype and null PDAC, promoting growth of the former while suppressing that of the latter. Based on this finding and using the same set of techniques, the work proceeded to examine the effect of inhibiting TGFβ receptor on tumor size, microvascular morphology, and stromal changes. Next, second harmonic generation imaging was applied to quantify the content and orientational isotropy of collagen-1 fibrils in the stroma of both Smad4 positive and negative PDAC. The findings were corroborated and reproduced in humans using excess samples removed during surgery. Finally, a small study was launched to visualize polarity defects in pancreas lacking LKB1 , a condition associated with Peutz Jeghers syndrome in human and which led to higher risk of developing PDAC. Through technique development, in vivo imaging, molecular biology, and microsurgery, this dissertation sought to apply novel live animal imaging to gain insights into the disease mechanism, and based on this understanding, to improve therapy for this terrible disease.
