Resistance to therapy is the major hurdle in the current cancer management. Cancer cells often rewire their cellular process to alternate mechanisms to resist the deleterious effect mounted by different therapeutic approaches. The major signaling pathways involved in the developmental process, such as Notch, Hedgehog, and Wnt, play a vital role in development, tumorigenesis, and also in the resistance to the various anticancer therapies. Understanding how cancer utilizes these developmental pathways in acquiring the resistance to the multi-therapeutic approach cancer can give rise to a new insight of the anti-therapy resistance mechanisms, which can be explored for the development of a novel therapeutic approach. We present a brief overview of Notch, Hedgehog, and Wnt signaling pathways in cancer and its role in providing resistance to various cancer treatment modalities such as chemotherapy, radiotherapy, molecular targeted therapy, and immunotherapy. Understanding the importance of these molecular networks will provide a rational basis for novel and safer combined anticancer therapeutic approaches for the improvement of cancer treatment by overcoming drug resistance.

Photon-based radiotherapy upregulates Notch signaling in cancer, leading to the acquisition of the stem cell phenotype and induction of invasion/migration, which contributes to the development of resistance to therapy. However, the effect of carbon ion radiotherapy (CIRT) on Notch signaling in glioma and its impact on stemness and migration is not explored yet. Human glioma cell lines (LN229 and U251), stable Notch1 intracellular domain (N1ICD) overexpressing phenotype of LN229 cells, and Notch inhibitor resistant LN229 cells (LN229R) were irradiated with either photon (X-rays) or (carbon ion irradiation) CII, and expressions of Notch signaling components were accessed by RT-PCR, Western blotting, and enzymatic assays and flow cytometry. Spheroid forming ability, cell migration, and clonogenic assay were used to evaluate the effect of modulated Notch signaling by irradiation. Our results show that X-ray irradiation induced the expression of Notch signaling components such as Notch receptors, target genes, and ADAM17 activity, while CII reduced it in glioma cell lines. The differential modulation of ADAM17 activity by CII and X-rays affected the cell surface levels of NOTCH1 and NOTCH2 receptors, as they were reduced by X-ray irradiation but increased in response to CII. Functionally, CII reduced the spheroid formation and migration of glioma cells, possibly by downregulating the N1ICD, as stable overexpression of N1ICD rescued these inhibitory effects of CII. Moreover, LN229R that are less reliant on Notch signaling for their survival showed less response to CII. Therefore, downregulation of Notch signaling resulting in the suppression of stemness and impaired cell migration by CII seen here may reduce tumor regrowth and disease dissemination, in addition to the well-established cytotoxic effects.

Notch receptors are single pass transmembrane glycoproteins with an extracellular domain (ECD) comprised of many epidermal growth factor‐like (EGF) repeats. Specific Ser and Thr residues in numerous EGF repeats have an attached O‐glycan initiated by fucose, glucose, or N‐acetylglucosamine (GlcNAc), and elongated with additional sugars. Notch receptors signal following binding of Notch ligands to the Notch receptor ECD, leading to release of the intracellular domain and activation of many Notch target genes. Notch signaling regulates cell fate decisions in many organs during development and differentiation. Dysregulation of Notch signaling leads to developmental disorders and to cancer. Lunatic (LFNG), Manic (MFNG) and Radical (RFNG) Fringe are GlcNAc transferases that extend Notch EGF repeats which already carry a fucose. EOGT is also a GlcNAc‐transferase that transfers O‐GlcNAc directly to EGF repeats. We are investigating roles for EOGT and each Fringe in T and B cell development using mice lacking various combinations of the Eogt, Lfng , Mfng and Rfng genes. We are also identifying individual roles for Fng genes using a co‐culture assay of bone marrow hemopoietic stem cells (HSC) from compound mutant mice stimulated by OP9 stromal cells expressing one of the four Notch ligands, DLL1, DLL4, JAG1 or JAG2. The combined results show that the O‐fucose glycans on NOTCH1 are key regulators of the strength of NOTCH1 signaling which, in turn, determines differentiation of HSC to T cell progenitors.