Analysis of transcription factor and growth factor vulnerabilities in tumor development and treatment resistance

Cancer is one of the leading causes of morbidity and mortality in Western countries. Despite advancements in our understanding of cancer development and treatment, an average of 10 million individuals lose their lives to cancer each year. Colorectal cancers (CRC) and melanoma are among the most prevalent cancers worldwide, while rhabdomyosarcoma (RMS) is a relatively common cancer in children. Contrary to popular belief, cancers originating from different tissues display significant differences. Even within the same tissue, cancers can exhibit distinct features that often impact their responsiveness to cancer treatments. Gaining a deeper understanding of the diverse cancers and their subtypes is essential for enhancing treatment outcomes. This knowledge not only enhances treatment effectiveness but also helps minimize the use of ineffective treatments, thereby reducing associated adverse effects, strain on hospital resources, and treatment costs. Despite the differences between individual cancers, it is noteworthy that all cancers involve the dysregulation of signaling pathways. In this study, my objective was to investigate the potential vulnerability of the Wnt/-catenin pathway in CRC and RMS, the Tgf--signaling in CRC, and angiopoietin (Ang) signaling pathways in CRC and melanoma. In the first study, we showed that during the early stages of CRC development, tumor cells are sensitive to TGF- mediated apoptosis, which is subsequently inhibited by oncogenic KRAS mutation. Additionally, we showed that BH3-mimetics can overcome the effects of inactivating mutations in the TGF-/SMAD4 pathway, which are common in CRC patients, and induce apoptosis in both early adenomas and late-stage CRC samples carrying KRAS mutations. Furthermore, we observed that both Tgf- and ABT-263 selectively target and damage tumor stem cells, offering a targeted approach for cancer treatment. In the second study, our aim was to investigate whether modulating the Ang2-Tie signaling pathway could enhance the effects of radiation on tumor vasculature. Our results demonstrated that the combination treatment involving Ang2 blocking antibodies and irradiation led to increased vascular damage, tumor necrosis, and a reduction in CRC and melanoma tumor growth. Moreover, we observed an extended lifespan in tumor-bearing mice following this combination treatment. Previous studies have indicated that the Wnt/-catenin signaling pathway target PROX1 is critical for healthy muscle stem cells. Consequently, we sought to explore whether PROX1 is involved in the development of RMS. Our third study revealed that PROX1 is expressed in a significant portion of RMS tumors, and silencing it results in decreased RMS cell proliferation. Furthermore, we observed a reduction in tumor RMS xenograft growth in mice upon silencing PROX1. In the fourth study, we investigated PROX1 and CRC stem cells, and the role of the PROX1+ stem cells in radiation resistance of CRC cells. We showed that almost all tumor stem cells in mouse intestinal adenomas express Prox1. Furthermore, we found that irradiation selects for PROX1-positive CRC cell line cells and in patient-derived 3D organoids. Deletion or silencing of PROX1 decreased both tumor numbers and the growth of CRC cells, and when combined with radiation, led to drastically decreased numbers of tumors in vivo and tumor cell colonies upon tumor replating in cell culture reflecting decreased stem cell activity. Overall, these findings contribute to our understanding of the complexities surrounding cancer development and treatment, and they provide valuable insights that can potentially be harnessed for improved therapeutic strategies.