Discovery of a novel pan-RAF inhibitor with potent anti-tumor activity in preclinical models of BRAF V600E mutant cancer

Development of apigenin-loaded invasomes with anti-melanoma potential

Apigenin (APG), a plant-derived flavonoid, has attracted attention as an anti-melanoma agent because of its action on multiple cell signaling pathways and high selectivity for tumor cells. Despite this, extensive metabolism and slow oral absorption are found, which has motivated the development of topical delivery systems. In this context, invasomes were considered, for the first time, for flavonoid incorporation. Given that these vesicles have a more deformable structure than conventional liposomes, greater interaction with the skin is expected. In fact, ATR-FTIR analyses revealed more substantial changes in skin lipid domains with invasomes, which also were more stable to centrifugation and showed lower PDI values. Their reduced particle size (<200 nm), in turn, would allow reaching deeper tumor regions. The APG seems to interact with both polar and apolar domains of invasome lipids, which explains the high encapsulation efficiency (>99 %) and improved vesicle rigidity. Limonene, the terpene selected based on its already described anti-melanoma activity, was crucial for enhancing the retention of APG in the skin (an increase of more than 3.5x when compared to conventional liposomes) as well as vesicle stability. Cholesterol (CHOL) also slightly improved the permeation and retention of this flavonoid in the skin; however, it had a negative effect on the stability of APG-free invasomes. Taking into account the improved distribution of APG in the basal layer of the epidermis (the tumor site) and the advantages in terms of stability and membrane flexibility, invasomes can be considered promising colloidal carriers for the topical delivery of anti-melanoma drugs.

Challenges and Opportunities in the Crusade of BRAF Inhibitors: From 2002 to 2022

Serine/threonine-protein kinase B-Raf (BRAF; RAF = rapidly accelerated fibrosarcoma) plays an important role in the mitogen-activated protein kinase (MAPK) signaling cascade. Somatic mutations in the BRAF gene were first discovered in 2002 by Davies et al., which was a major breakthrough in cancer research. Subsequently, three different classes of BRAF mutants have been discovered. This class includes class I monomeric mutants (BRAFV600), class II BRAF homodimer mutants (non-V600), and class III BRAF heterodimers (non-V600). Cancers caused by these include melanoma, thyroid cancer, ovarian cancer, colorectal cancer, nonsmall cell lung cancer, and others. In this study, we have highlighted the major binding pockets in BRAF protein, their active and inactive conformations with inhibitors, and BRAF dimerization and its importance in paradoxical activation and BRAF mutation. We have discussed the first-, second-, and third-generation drugs approved by the Food and Drug Administration and drugs under clinical trials with all four different binding approaches with DFG-IN/OUT and αC-IN/OUT for BRAF protein. We have investigated particular aspects and difficulties with all three generations of inhibitors. Finally, this study has also covered recent developments in synthetic BRAF inhibitors (from their discovery in 2002 to 2022), their unique properties, and importance in inhibiting BRAF mutants.

New C2- and N3-Modified Thieno[2,3-d]Pyrimidine Conjugates with Cytotoxicity in the Nanomolar Range

AIMS

The aim of the current study was to develop and explore a series of new cytotoxic agents based on the conjugation between the thieno[2,3-d]pyrimidine moiety and a second pharmacophore at the C2 or N3 position.

BACKGROUND

As the thieno[2,3-d]pyrimidine core is a bioisostere of the 4-anilinoquinazoline, various new thienopyrimidine derivatives were synthesized by modifying the structure of the clinically used anticancer quinazoline EGFR inhibitors of the first generation - gefitinib, and second generation - dacomitinib and canertinib. It was reported that some thieno[2,3-d]pyrimidine derivatives showed improved EGFR inhibitory activity. On the other hand, the benzimidazole heterocycle is present as a pharmacophore unit in the structure of many clinically used chemotherapeutic agents. Some 2-aminobenzimidazole derivatives, possessing anticancer activity, demonstrated EGFR inhibition and the benzimidazole derivative EGF816 is currently in the second phase of clinical trials.

OBJECTIVE

The objectives of the study were design of a novel series thieno[2,3-d]pyrimidines, synthesis of the compounds and investigation of their effects towards human cancer HT-29, MDA-MB-231, HeLa, HepG2 and to normal human Lep3 cell lines. (American Type Culture Collection, ATCC, Rockville, MD, USA) Methods: The synthetic protocol implemented cyclocondensation of 2-amino-thiophenes and nitriles in inert medium, aza-Michael addition to benzimidazole derivatives and nucleophylic substitution at the N3 place. MTS test was used in order to establish the cytotoxicity of the tested compounds. SAR analysis and in silico assessment of the inhibitory potential towards human oncogenic V^599EB-Raf were performed using Molinspiration tool and Molecular Operating environment software.

RESULTS

The MTS test data showed that almost all studied thieno[2,3-d]pyirimidines (9-13, 21-22 and 25) manifest high inhibiting effect on the cell proliferation at nanomolar concentrations, whereat compounds 9 (IC₅₀ = 130 nM) and 10 (IC₅₀ = 261 nM) containing amino acid moiety, and 21 (IC₅₀ = 108 nM) possesing two thienopyrimidine moieties attached to a 1,3-disubstituted benzimidazole linker, revealed many times lower toxicity against Lep3 cells compared to the cancer cells. Thienopyrimidines 11-13 possessed high selectivity against HeLa cells. Compound 13 showed high inhibitory activity against MDA-MB-231 and HepG2, with IC50 1.44 nM and 1.11 nM respectively. To outline the possible biological target of the studied coumpounds, their potential to interact with human oncogenic V^599EB-Raf was explored by a docking study. As a result, it was suggested that the benzimidazolyl and glycyl fragments could enhance the binding ability of the new compounds by increasing the number of hydrogen bond acceptors and by stabilizing the inactive form of the enzyme.

CONCLUSION

The thienopyrimidines tested in vitro towards human cancer HT-29, MDA-MB-231, HeLa, HepG2 and normal human Lep3 cell lines demonstrated cytotoxicity in nanomolar range. It was established that compounds 9, 10 and 21 showed many times lower toxicity against normal Lep3 cells that can provide a high selectivity towards all four cancer cell lines at small concentrations. Based on the analysis of the structure-activity relationship, the observed trends in the cytotoxicity could be related to the lipophilicity and the topological polar surface area of the tested compounds. The docking study on the potential of the new thieno[2,3-d]pyrimidine-4-ones to interact with mutant V^599EB-Raf showed that the compounds might be able to stabilize the enzyme in its inactive form.

RAF-MEK-ERK pathway in cancer evolution and treatment

The RAF-MEK-ERK signaling cascade is a well-characterized MAPK pathway involved in cell proliferation and survival. The three-layered MAPK signaling cascade is initiated upon RTK and RAS activation. Three RAF isoforms ARAF, BRAF and CRAF, and their downstream MEK1/2 and ERK1/2 kinases constitute a coherently orchestrated signaling module that directs a range of physiological functions. Genetic alterations in this pathway are among the most prevalent in human cancers, which consist of numerous hot-spot mutations such as BRAF^V600E. Oncogenic mutations in this pathway often override otherwise tightly regulated checkpoints to open the door for uncontrolled cell growth and neoplasia. The crosstalk between the RAF-MEK-ERK axis and other signaling pathways further extends the proliferative potential of this pathway in human cancers. In this review, we summarize the molecular architecture and physiological functions of the RAF-MEK-ERK pathway with emphasis on its dysregulations in human cancers, as well as the efforts made to target the RAF-MEK-ERK module using small molecule inhibitors.

Design, synthesis and in silico insights of new 7,8-disubstituted-1,3-dimethyl-1H-purine-2,6(3H,7H)-dione derivatives with potent anticancer and multi-kinase inhibitory activities

Aiming to obtain an efficient anti-proliferative activity, structure- and ligand-based drug design approaches were expanded and utilized to design and refine a small compound library. Subsequently, thirty-two 7,8-disubstituted-1,3-dimethyl-1H-purine-2,6(3H,7H)-dione derivatives were selected for synthesis based on the characteristic pharmacophoric features required for PI3K and B-Raf oncogenes inhibition. All the synthesized compounds were evaluated for their in vitro anticancer activity. Compounds 17 and 22c displayed an acceptable potent activity according to the DTP-NCI and were further evaluated in the NCI five doses assay. To validate our design, compounds with the highest mean growth inhibition percent were screened against the target PI3Kα and B-Raf_V600E to confirm their multi-kinase activity. The tested compounds showed promising multi-kinase activity. Compounds 17 and 22c anticancer effectiveness and multi-kinase activity against PI3Kα and B-Raf_V600E were consolidated by the inhibition of B-Raf_WT, EGFR and VEGFR-2 with IC₅₀ in the sub-micromolar range. Further investigations on the most potent compounds 17 and 22c were carried out by studying their safety on normal cell line, in silico profiling and predicted ADME characteristics.

Is single versus combination therapy problematic in the treatment of cutaneous melanoma?

Introduction: The development of immunotherapies and targeted therapies has changed the treatment approach in resectable, nonresectable, and metastatic melanoma. Because of their different pharmacological profiles, immunotherapies and/or targeted therapies have been studied in various combinations. Areas covered: We reviewed PubMed for most important clinical trials investigating efficacy and tolerability of combinatorial and single-agent approaches for the treatment of melanoma that were published up to June 2019. We discuss the most promising therapy approaches and highlight challenges of melanoma treatment. Expert opinion: Combinatorial approaches seem to be very promising in the treatment of resectable and advanced melanoma. Currently, dual immune checkpoint inhibition (ICI) with nivolumab and ipilimumab offers the best first-line treatment option for patients with BRAF-wt and -mutated, advanced melanoma. It is therapy of choice in younger patients with good ECOG performance status and poor prognostic features, whereas ICI monotherapy should be preferred in elderly patients with advanced melanoma. Benefit-risk ratio, patient's QoL and expectations, as well as treatment costs have to be considered in the choice of treatment. However, to elucidate mechanisms of resistance, biomarkers of response and to better define personalized strategies in the treatment of cutaneous melanoma, larger clinical trials comparing combined versus sequential therapies are necessary.

Development of small-molecule therapeutics and strategies for targeting RAF kinase in BRAF-mutant colorectal cancer

RAF kinase is crucially involved in cell proliferation and survival in colorectal cancer (CRC). Patients with metastatic CRC (mCRC) harboring BRAF mutations (BRAFms) not only experience a poor prognosis but also benefit less from therapeutics targeting ERK signaling. With advances in RAF inhibitors and second-generation inhibitors including encorafenib and vemurafenib, which have been approved for treating BRAF-V600E malignancies, the combinatorial therapeutic strategies of RAF inhibitors elicit remarkable responses in patients with BRAF-V600E mCRC. However, the therapeutic efficacy is restricted by resistance, which might be due to RAF dimerization and reactivation of the MAPK pathway. In addition, the next-generation RAF inhibitors, which are characterized by varying structural and biochemical properties, have achieved preclinical and clinical advances. Herein, we summarize the existing mechanism of RAF kinases in CRC, including MAPK feedback reactivation of resistance to RAF inhibitors. We additionally summarize the development of three generations of RAF inhibitors and different therapeutic strategies including the combination of EGFR, BRAF, and PI3K inhibitors for BRAFm CRC treatment.