Synthesis of a β-turn mimetic suitable for incorporation in the peptide hormone LHRH

Utilizing Alkyne-Nitrone Cycloaddition for the Convenient Multi-Component Assembly of Protein Degraders and Biological Probes

Proteolysis-targeting chimeras (PROTACs) have become a popular therapeutic strategy, and the development of multi-functional PROTACs has added complexity to their synthetic process. Although click reactions have been widely applied to prepare highly functionalized biomolecules, most of them are limited to two-component reactions, restricting the creation of more complex structures. Here, we developed a convenient multi-component assembly strategy via strain-promoted alkyne-nitrone cycloaddition (SPANC), which can be extended to a 3-component reaction when combined with nitrone formation. Using the 2-component assembly, we demonstrated the targeted protein degradation with both preassembled and in-cell assembled PROTACs. This strategy was also applied to facilitate the screening of E3 ligases in PROTACs and the preparation of various biological probes. Moreover, the 3-component assembly, via sequential nitrone formation and SPANC, enabled the synthesis of trifunctional 3-component PROTACs. The N-substituent, serving as an additional functional moiety, was designed as a photocage for sterically controlling PROTAC activity. The 3-component assembly can be further modified to provide additional control or enhance the cell-targeting ability of PROTACs. In short, our multi-component SPANC assembly strategy offers a modular and versatile synthetic platform for creating multi-functional PROTACs and biological probes.

Static to inducibly dynamic stereocontrol: The convergent use of racemic β-substituted ketones

The synthesis of stereochemically complex molecules in the pharmaceutical and agrochemical industries requires precise control over each distinct stereocenter, a feat that can be challenging and time consuming using traditional asymmetric synthesis. Although stereoconvergent processes have the potential to streamline and simplify synthetic routes, they are currently limited by a narrow scope of inducibly dynamic stereocenters that can be readily epimerized. Here, we report the use of photoredox catalysis to enable the racemization of traditionally static, unreactive stereocenters through the intermediacy of prochiral radical species. This technology was applied in conjunction with biocatalysts such as ketoreductases and aminotransferases to realize stereoconvergent syntheses of stereodefined γ-substituted alcohols and amines from β-substituted ketones.

Differential regulation of CXC ligand 1 transcription in melanoma cell lines by poly(ADP-ribose) polymerase-1

The continuous production of the CXC ligand 1 (CXCL1) chemokine by melanoma cells is a major effector of tumor growth. We have previously shown that the constitutive expression of this chemokine is dependent upon transcription factors nuclear factor-kappa B (NF-kappaB), stimulating protein-1 (SP1), high-mobility group-I/Y (HMGI/Y), CAAT displacement protein (CDP) and poly(ADP-ribose) polymerase-1 (PARP-1). In this study, we demonstrate for the first time the mechanism of transcriptional regulation of CXCL1 through PARP-1 in melanoma cells. In its inactive state, PARP-1 binds to the CXCL1 promoter in a sequence-specific manner and prevents binding of NF-kappaB (p65/p50) to its element. However, activation of the PARP-1 enzymatic activity enhances CXCL1 expression, owing to the loss of PARP-1 binding to the CXCL1 promoter, accompanied by enhanced binding of p65 to the promoter. The delineation of the role of NF-kappaB-interacting factors in the putative CXCL1 enhanceosome will provide key information in developing strategies to block constitutive expression of this and other chemokines in cancer and to develop targeted therapy.

Loss of E-cadherin leads to upregulation of NFkappaB activity in malignant melanoma

Malignant transformation of melanocytes frequently coincides with loss of E-cadherin expression. Here, we show that loss of E-cadherin leads to induction of nuclear factor kappa B (NFkappaB) activity in melanoma cell lines. Melanoma cells show constitutively active NFkappaB, whereas no activity is found in primary melanocytes. After re-expression of E-cadherin in melanoma cells, strong downregulation of NFkappaB activity was found. Consistently, NFkappaB activity was induced in primary human melanocytes after inhibition of E-cadherin activity by functionally blocking anti-E-cadherin antibodies. Interestingly, re-expression of E-cadherin-blocked p38 MAPK activity and the p38 MAPK inhibitors SB203580 and SB202190 almost completely prevented NFkappaB activation in melanoma cells. Furthermore, cytoplasmatic beta-catenin induced p38 and NFkappaB activation in malignant melanoma. To our knowledge, this is the first report suggesting a correlation between E-cadherin and NFkappaB activity in melanocytes and melanoma cells. In summary, we conclude that loss of E-cadherin and cytoplasmatic beta-catenin induces p38-mediated NFkappaB activation, potentially revealing an important mechanism of tumorigenesis in malignant melanomas.

Retinoid targets for apoptosis induction

Certain synthetic retinoid-related molecules induce apoptosis in cancer cells through a novel mechanism of retinoid action that is independent of the nuclear retinoid receptors. These compounds target protein kinases and protein phosphatases to trigger signal transduction pathways that lead to apoptosis. Whereas retinoid agonists such as CD437 activate stress kinases via inhibition of the phosphatase MKP-1, the retinoid antagonist MX781 inhibits the survival kinase IKK. These retinoid-mediated signaling pathways converge at the mitochondria, where they cause the release of cytochrome c and subsequent Apaf-1-dependent activation of caspases. Identification of the retinoid targets that mediate their apoptotic activity will enhance our understanding of the mechanism of this novel retinoid action, to allow appropriate optimization of currently available compounds to advance into the clinic as novel anticancer agents.

Apoptosis and melanoma chemoresistance

Melanoma is the most aggressive form of skin cancer and is notoriously resistant to all current modalities of cancer therapy. A large set of genetic, functional and biochemical studies suggest that melanoma cells become 'bullet proof' against a variety of chemotherapeutic drugs by exploiting their intrinsic resistance to apoptosis and by reprogramming their proliferation and survival pathways during melanoma progression. In recent years, the identification of molecules involved in the regulation and execution of apoptosis, and their alteration in melanoma, have provided new insights into the molecular basis for melanoma chemoresistance. With this knowledge in hand, the challenge is now to devise strategies potent enough to compensate or bypass these cell death defects and improve the actual poor prognosis of patients at late stages of the disease.

NF-kappaB is constitutively activated in high-grade squamous intraepithelial lesions and squamous cell carcinomas of the human uterine cervix

We demonstrate, for the first time, that the transcription factor NF-kappaB is constitutively activated during human cervical cancer progression. Immunohistochemical analysis was done using 106 paraffin-embedded cervical tissue specimens of different histological grades. In normal cervical tissue and low-grade squamous intraepithelial lesions, p50, RelA and IkappaB-alpha were mainly localized in the cytosol, whereas in high-grade lesions and squamous cell carcinomas, p50-RelA heterodimers translocated into the nucleus with a concurrent decrease in IkappaB-alpha protein. By Western blot analysis, p50 and RelA were detectable mainly in the cytosolic and nuclear extracts in normal and cancer tissues, respectively, and cytosolic IkappaB-alpha expression was detectable in normal but not in cancer cervical tissues. NF-kappaB DNA-binding activity increased during cervical cancer progression and the binding complex was mainly composed of the p50-RelA heterodimers as revealed by electrophoretic mobility shift assays. Semiquantitative RT-PCR analysis, however, showed increased levels of IkappaB-alpha mRNA in cancer samples presumably because of feedback regulation as a result of enhanced NF-kappaB DNA-binding activity and a consequent functional activation of NF-kappaB. Further immunohistochemical analysis with an antibody to phospho IkappaB-alpha revealed that phosphorylation occurs mainly in squamous intraepithelial lesions, suggesting that the IkappaB-alpha gets phosphorylated initially and degraded as the tumor progressed.