BET-directed PROTACs in triple negative breast cancer cell lines MDA-MB-231 and MDA-MB-436.

PURPOSE: This study aims to find whether the proliferation and migration of triple negative breast cancer (TNBC) cell lines can be reduced by treatment with bromodomain and extra-terminal domain (BET) inhibitor JQ1 and BET protein targeting chimeras (PROTACs) ARV-771 and MZ1. METHODS: Cytotoxicity tests, scratch migration assays and western blot proteome profiler arrays for protein expression of cancer-related proteins were used to evaluate the impact of a BET-inhibitor and two BET-directed PROTACs on cell viability, migration and on protein expression. RESULTS: JQ1 and the PROTACs MZ1 and ARV-771 significantly inhibited the growth and migration of the KRAS G13D-mutated MDA-MB-231 cells. In this cell line, the PROTACs suppressed the residual expression of ERBB2/HER2, 3 and 4 that are essential for the proliferation of breast cancer cells and this cell line proved sensitive to HER2 inhibitors. In contrast, the effects of the PROTACs on the protein expression of MDA-MB-436 cells mostly affected cytokines and their cognate receptors. CONCLUSION: The degradation of BET-protein by PROTACs demonstrated significant anti-proliferative effects. The KRAS-mutated MDA-MB-231 cells belong to the low-HER2 expressing tumors that have a poorer prognosis compared to HER2-null patients. Since first oral PROTACs against tumor hormone receptors are in clinical trials, this mode of tumor therapy is expected to become an important therapeutic strategy in the future treatment of TNBC.

Targeting KRAS in pancreatic cancer.

Pancreatic cancer has a dismal prognosis due to late detection and lack of efficient therapies. The Kirsten rat sarcoma virus (KRAS) oncogene is mutated in up to 90% of all pancreatic ductal adenocarcinomas (PDACs) and constitutes an attractive target for therapy. However, the most common KRAS mutations in PDAC are G12D (44%), G12V (34%) and G12R (20%) that are not amenable to treatment by KRAS G12C-directed cysteine-reactive KRAS inhibitors such as Sotorasib and Adagrasib that exhibit clinical efficacy in lung cancer. KRAS G12C mutant pancreatic cancer has been treated with Sotorasib but this mutation is detected only in 2%-3% of PDAC. Recently, the KRAS G12D-directed MRTX1133 inhibitor has entered clinical trials and more of such inhibitors are in development. The other KRAS mutations may be targeted indirectly via inhibition of the cognate guanosine exchange factor (GEF) Son of Sevenless 1 that drives KRAS. These agents seem to provide the means to target the most frequent KRAS mutations in PDAC and to improve patient outcomes.

Bromodomain Protein-directed Agents and MYC in Small Cell Lung Cancer.

Small cell lung cancer (SCLC) has a dismal prognosis. In addition to the inactivation of the tumor suppressors TP53 and RB1, tumor-promoting MYC and paralogs are frequently overexpressed in this neuroendocrine carcinoma. SCLC exhibits high resistance to second-line chemotherapy and all attempts of novel drugs and targeted therapy have failed so far to achieve superior survival. MYC and paralogs have key roles in the oncogenic process, orchestrating proliferation, apoptosis, differentiation, and metabolism. In SCLC, MYC-L and MYC regulate the neuroendocrine dedifferentiation of SCLC cells from Type A (ASCL1 expression) to the other SCLC subtypes. Targeting MYC to suppress tumor growth is difficult due to the lack of suitable binding pockets and the most advanced miniprotein inhibitor Omomyc exhibits limited efficacy. MYC may be targeted indirectly via the bromodomain (BET) protein BRD4, which activates MYC transcription, by specific BET inhibitors that reduce the expression of this oncogenic driver. Here, novel BET-directed Proteolysis Targeting Chimeras (PROTACs) are discussed that show high antiproliferative activity in SCLC. Particularly, ARV-825, targeting specifically BRD4, exhibits superior cytotoxic effects on SCLC cell lines and may become a valuable adjunct to SCLC combination chemotherapy.

Expression of cytokines in pleural effusions and corresponding cell lines of small cell lung cancer.

Background: Small cell lung cancer (SCLC) is a neuroendocrine aggressive tumor with a dismal prognosis due to the lack of curative therapeutic modalities. Approximately 11% of these patients show a malignant pleural effusion (MPE) that increase in frequency with progression of the disease. In MPE, fluid accumulates due to leaky vessels and mesothelial surfaces as well as impaired removal of fluid due to impaired drainage. Methods: For this investigation, three SCLC MPE samples and supernatants of the corresponding isolated cell lines were analyzed for the content of 105 cytokines, chemokines, and growth factors. Overexpressed pathways including these cytokines were identified using Reactome analysis tools. Results: A large range of cytokines, including vascular endothelial growth factor A (VEGFA), were found to be expressed in the MPEs and conditioned media of the corresponding cell line. These mediators are involved in pathways such as interleukin (IL) signaling, growth factor stimulation, modulation of cell adhesion molecules and proliferative cell signaling. Cytokine expression by the corresponding SCLC cell lines revealed the specific contributions of the tumor cells and included high expression of VEGFA, tumor-promoting factors and mediators exerting immunosuppressive and protumor effects. MPEs used here showed marked stimulation of the proliferation of four permanent SCLC cell lines. Conclusions: MPEs comprise a large number of cytokines with mixed activities on tumor cells and the invading SCLC cells release a number of protumor mediators and induce an immunosuppressive pleural environment.

Overcoming resistance in small-cell lung cancer.

INTRODUCTION: Small-cell lung cancer (SCLC) accounts for 15% of lung cancers and has a dismal prognosis due to early dissemination and acquired chemoresistance. The initial good response to chemotherapy is followed by refractory relapses within 1-2 years. Mechanisms leading to chemoresistance are not clear and progress is poor. AREAS COVERED: This article reviews the current evidence of the resistance of SCLCs at the cellular level including alteration of key proteins and the possible presence of cancer stem cells (CSCs). Without compelling evidence for cellular mechanisms and clinical failures of novel approaches, the study of SCLC has advanced to the role of 3D tumor cell aggregates in chemoresistance. EXPERT OPINION: The scarcity of viable tumor specimen from relapsed SCLC patients has hampered the investigations of acquired chemoresistance but a panel of nine SCLC circulating tumor cell (CTC) cell lines have revealed characteristics of SCLC in the advanced refractory states. The chemoresistance of relapsed SCLC seems to be linked to the spontaneous formation of large spheroids, termed tumorospheres, which contain resistant quiescent and hypoxic cells shielded by a physical barrier. So far, drugs to tackle large tumor spheroids are in preclinical and early clinical development.

Development of PROTACS degrading KRAS and SOS1.

The Kirsten rat sarcoma virus-son of sevenless 1 (KRAS-SOS1) axis drives tumor growth preferentially in pancreatic, colon, and lung cancer. Now, KRAS G12C mutated tumors can be successfully treated with inhibitors that covalently block the cysteine of the switch II binding pocket of KRAS. However, the range of other KRAS mutations is not amenable to treatment and the G12C-directed agents Sotorasib and Adragrasib show a response rate of only approximately 40%, lasting for a mean period of 8 months. One approach to increase the efficacy of inhibitors is their inclusion into proteolysis-targeting chimeras (PROTACs), which degrade the proteins of interest and exhibit much higher antitumor activity through multiple cycles of activity. Accordingly, PROTACs have been developed based on KRAS- or SOS1-directed inhibitors coupled to either von Hippel-Lindau (VHL) or Cereblon (CRBN) ligands that invoke the proteasomal degradation. Several of these PROTACs show increased activity in vitro and in vivo compared to their cognate inhibitors but their toxicity in normal tissues is not clear. The CRBN PROTACs containing thalidomide derivatives cannot be tested in experimental animals. Resistance to such PROTACS arises through downregulation or inactivation of CRBN or factors of the functional VHL E3 ubiquitin ligase. Although highly active KRAS and SOS1 PROTACs have been formulated their clinical application remains difficult.

BRD4-targeting PROTACs Synergize With Chemotherapeutics Against Osteosarcoma Cell Lines.

BACKGROUND/AIM: Osteosarcoma at an advanced stage has a poor outcome, and novel targeted therapies are needed, especially for metastatic disease. Bromodomain inhibitors (BETi) are epigenetic modulators that broadly impair the expression of oncogenic proteins and exert antitumor effects. BETi can be combined with chemotherapeutics to increase therapeutic responses with superior effects in the form of proteolysis targeting chimeras (PROTACs) that degrade proteins of interest (POI) in multiple cycles. This work aimed to investigate the efficacy of BETi, such as JQ1, dBET57, and MZ1 PROTACs in combination with cytotoxic drugs against osteosarcoma cell lines. MATERIALS AND METHODS: Chemosensitivity of the osteosarcoma cell lines HOS, Saos-2, MG-63, and G292 were tested with BET-directed agents alone or in combination with cytotoxic drugs comprising cisplatin, doxorubicin, topotecan, and gemcitabine using cell viability assays. RESULTS: The BET degraders exhibited highest toxicity to HOS cells and showed synergistic activity in combination with the chemotherapeutics, except for the degrader - topotecan/gemcitabine combinations. Highest synergy between BET agents and chemotherapeutics were found for the more chemoresistant Saos-2 cells and potentiation of toxicity in MG-63 cells for the BET agents - doxorubicin combinations and the MZ1-topotecan pair. HOS and Saos-2 cell lines had reduced protein expression of AXL, BCL-X, e-cadherin, CAIX, EpCAM, ErbB2, and vimentin in response to JQ1, MZ1, and BET57. CONCLUSION: The study suggests that the application of novel BET PROTACs in combination with chemotherapeutics could represent a new therapeutic option to improve the therapy of osteosarcomas. First orally available PROTACs have reached clinical trials.