Prkd1 regulates the formation and repair of plasma membrane disruptions (PMD) in osteocytes.

We and others have seen that osteocytes sense high-impact osteogenic mechanical loading via transient plasma membrane disruptions (PMDs) which initiate downstream mechanotransduction. However, a PMD must be repaired for the cell to survive this wounding event. Previous work suggested that the protein Prkd1 (also known as PKCµ) may be a critical component of this PMD repair process, but the specific role of Prkd1 in osteocyte mechanobiology had not yet been tested. We treated MLO-Y4 osteocytes with Prkd1 inhibitors (Go6976, kbNB 142-70, staurosporine) and generated an osteocyte-targeted (Dmp1-Cre) Prkd1 conditional knockout (CKO) mouse. PMD repair rate was measured via laser wounding and FM1-43 dye uptake, PMD formation and post-wounding survival were assessed via fluid flow shear stress (50 dyn/cm2), and in vitro osteocyte mechanotransduction was assessed via measurement of calcium signaling. To test the role of osteocyte Prkd1 in vivo, Prkd1 CKO and their wildtype (WT) littermates were subjected to 2 weeks of unilateral axial tibial loading and loading-induced changes in cortical bone mineral density, geometry, and formation were measured. Prkd1 inhibition or genetic deletion slowed osteocyte PMD repair rate and impaired post-wounding cell survival. These effects could largely be rescued by treating osteocytes with the FDA-approved synthetic copolymer Poloxamer 188 (P188), which was previously shown to facilitate membrane resealing and improve efficiency in the repair rate of PMD in skeletal muscle myocytes. In vivo, while both WT and Prkd1 CKO mice demonstrated anabolic responses to tibial loading, the magnitude of loading-induced increases in tibial BMD, cortical thickness, and periosteal mineralizing surface were blunted in Prkd1 CKO as compared to WT mice. Prkd1 CKO mice also tended to show a smaller relative difference in the number of osteocyte PMD in loaded limbs and showed greater lacunar vacancy, suggestive of impaired post-wounding osteocyte survival. While P188 treatment rescued loading-induced increases in BMD in the Prkd1 CKO mice, it surprisingly further suppressed loading-induced increases in cortical bone thickness and cortical bone formation. Taken together, these data suggest that Prkd1 may play a pivotal role in the regulation and repair of the PMD response in osteocytes and support the idea that PMD repair processes can be pharmacologically targeted to modulate downstream responses, but suggest limited utility of PMD repair-promoting P188 in improving bone anabolic responses to loading.

Design, synthesis, biological evaluation, and in silico studies of novel pyridopyridine derivatives as anticancer candidates targeting FMS kinase.

Design and synthesis of novel 4-carboxamidopyrido[3,2-b]pyridine derivatives as novel rigid analogues of sorafenib are reported herein. The target compounds showed potent antiproliferative activities against a panel of NCI-60 cancer cell lines as well as hepatocellular carcinoma cell line. Compounds 8g and 9f were among the most promising derivatives in terms of effectiveness and safety. Therefore, they were further examined to demonstrate their ability to induce apoptosis and alter cell cycle progression in hepatocellular carcinoma cells. The most potent compounds were tested against a panel of kinases that indicated their selectivity against FMS kinase. Compounds 8g and 8h showed the most potent activities against FMS kinase with IC50 values of 21.5 and 73.9 nM, respectively. The two compounds were also tested in NanoBRET assay to investigate their ability to inhibit FMS kinase in cells (IC50 = 563 nM (8g) and 1347 nM (8h) vs. IC50 = 1654 nM for sorafenib). Furthermore, compounds 8g and 8h possess potent inhibitory activities against macrophages when investigated in bone marrow-derived macrophages (BMDM) assay (IC50 = 56 nM and 167 nM, respectively, 164 nM for sorafenib). The safety and selectivity of these compounds were confirmed when tested against normal cell lines. Their safety profile was further confirmed using hERG assay. In silico studies were carried out to investigate their binding modes in the active site of FMS kinase, and to develop a QSAR model for these new motifs.

Autophagy inhibition potentiates energy restriction-induced cell death in hepatocellular carcinoma cells.

Hepatocellular carcinoma (HCC) significantly contributes to cancer-related mortality due to the limited response of HCC to current anticancer therapies, thereby necessitating more effective treatment approaches. Energy restriction mimetic agents (ERMAs) have emerged as potential therapies in targeting the Warburg effect, a unique metabolic process in cancer cells. However, ERMAs exhibit limited efficacy when used as monotherapy. Additionally, ERMAs have been found to induce autophagy in cancer cells. The role of autophagy in cancer survival remains a subject of debate. Thus, it is crucial to ascertain whether ERMA-induced autophagy is a mechanism for cell survival or cell death in HCC. Our study aims to investigate the effect of autophagy inhibition on the survival of HCC cells treated with ERMAs while also examining the potential of combining an autophagy inhibitor such as spautin-1 with ERMAs to enhance HCC cell death. Our results suggest a cytoprotective role for ERMA-induced autophagy in HCC cells, as combining the autophagy inhibitor spautin-1 with ERMAs effectively suppressed ERMA-induced autophagy and synergistically enhanced their antitumor activity. The treatment combination promoted HCC death through apoptosis, cell cycle arrest, and inhibition of AKT and ERK activation, which are known to play a key role in cellular proliferation. Collectively, our findings highlight a potential strategy to combat HCC by combining energy restriction with autophagy inhibition.

Orchiectomy sensitizes cortical bone in male mice to the harmful effects of kynurenine.

Kynurenine (Kyn) is a tryptophan metabolite that increases with age and promotes musculoskeletal dysfunction. We previously found a sexually dimorphic pattern in how Kyn affects bone, with harmful effects more prevalent in females than males. This raises the possibility that male sex steroids might exert a protective effect that blunts the effects of Kyn in males. To test this, orchiectomy (ORX) or sham surgeries were performed on 6-month-old C57BL/6 mice, after which mice received Kyn (10 mg/kg) or vehicle via intraperitoneal injection, once daily, 5×/week, for four weeks. Bone histomorphometry, DXA, microCT, and serum marker analyses were performed after sacrifice. In vitro studies were performed to specifically test the effect of testosterone on activation of aryl hydrocarbon receptor (AhR)-mediated signaling by Kyn in mesenchymal-lineage cells. Kyn treatment reduced cortical bone mass in ORX- but not sham-operated mice. Trabecular bone was unaffected. Kyn's effects on cortical bone in ORX mice were attributed primarily to enhanced endosteal bone resorption activity. Bone marrow adipose tissue was increased in Kyn-treated ORX animals but was unchanged by Kyn in sham-operated mice. ORX surgery increased mRNA expression of the aryl hydrocarbon receptor (AhR) and its target gene Cyp1a1 in the bone, suggesting a priming and/or amplification of AhR signaling pathways. Mechanistic in vitro studies revealed that testosterone blunted Kyn-stimulated AhR transcriptional activity and Cyp1a1 expression in mesenchymal-linage cells. These data suggest a protective role for male sex steroids in blunting the harmful effects of Kyn in cortical bone. Therefore, testosterone may play an important role in regulating Kyn/AhR signaling in musculoskeletal tissues, suggesting crosstalk between male sex steroids and Kyn signaling may influence age-associated musculoskeletal frailty.

Update on the Role of Glucocorticoid Signaling in Osteoblasts and Bone Marrow Adipocytes During Aging.

PURPOSE OF REVIEW: Bone marrow adipose tissue (BMAT) in the skeleton likely plays a variety of physiological and pathophysiological roles that are not yet fully understood. In elucidating the complex relationship between bone and BMAT, glucocorticoids (GCs) are positioned to play a key role, as they have been implicated in the differentiation of bone marrow mesenchymal stem cells (BMSCs) between osteogenic and adipogenic lineages. The purpose of this review is to illuminate aspects of both endogenous and exogenous GC signaling, including the influence of GC receptors, in mechanisms of bone aging including relationships to BMAT. RECENT FINDINGS: Harmful effects of GCs on bone mass involve several cellular pathways and events that can include BMSC differentiation bias toward adipogenesis and the influence of mature BMAT on bone remodeling through crosstalk. Interestingly, BMAT involvement remains poorly explored in GC-induced osteoporosis and warrants further investigation. This review provides an update on the current understanding of the role of glucocorticoids in the biology of osteoblasts and bone marrow adipocytes (BMAds).

Aryl hydrocarbon receptor (AhR)-mediated signaling as a critical regulator of skeletal cell biology.

The aryl hydrocarbon receptor (AhR) has been implicated in regulating skeletal progenitor cells and the activity of bone-forming osteoblasts and bone-resorbing osteoclasts, thereby impacting bone mass and the risk of skeletal fractures. The AhR also plays an important role in the immune system within the skeletal niche and in the differentiation of mesenchymal stem cells into other cell lineages including chondrocytes and adipocytes. This transcription factor responds to environmental pollutants which can act as AhR ligands, initiating or interfering with various signaling cascades to mediate downstream effects, and also responds to endogenous ligands including tryptophan metabolites. This review comprehensively describes the reported roles of the AhR in skeletal cell biology, focusing on mesenchymal stem cells, osteoblasts, and osteoclasts, and discusses how AhR exhibits sexually dimorphic effects in bone. The molecular mechanisms mediating AhR's downstream effects are highlighted to emphasize the potential importance of targeting this signaling cascade in skeletal disorders.

The inhibition of autophagy by spautin boosts the anticancer activity of fingolimod in multidrug-resistant hepatocellular carcinoma.

The contribution of autophagy to drug resistance has been studied in several cancers. However, there is no clear evidence about the role of autophagy in the resistance to chemotherapy in cancers, such as hepatocellular carcinoma (HCC). HCC is characterized by a poor prognosis and limited therapeutic options. Moreover, the emergence of multidrug-resistance (MDR) hinders successful treatment. Therefore, understanding how autophagy is regulated in resistant HCC is essential for sensitizing this malignancy to chemotherapy. This work demonstrated that basal and induced autophagy differ between parental and resistant Hep3B cells. In optimum growth conditions, the basal level of autophagy was low in resistant Hep3B (Hep3B-R) cells compared to the wild-type Hep3B (Hep3B-P) cells. However, in metabolic or therapeutic stress conditions, the rate of autophagy flux was much faster in the resistant cells. The work also confirmed the pro-survival function of autophagy in HCC. Besides, it demonstrated that the autophagy inhibitor, spautin, acted synergistically with fingolimod (FTY720) to promote cell death. The combination treatment resulted in superior reactive oxygen species (ROS) production and significant induction of apoptosis. In addition, spautin potentiated the effect of FTY720 against cell survival pathways like the Akt and ERK. Interestingly, the results indicated that Hep3B-R cells were more sensitive to autophagy inhibition than their parental counterparts. Collectively, this work revealed that combining spautin with chemotherapeutic agents that induce cytoprotective autophagy such as FTY720 is a promising approach to overcome MDR in HCC.

Camptothecin's journey from discovery to WHO Essential Medicine: Fifty years of promise.

Nature represents a rich source of compounds used for the treatment of many diseases. Camptothecin (CPT), isolated from the bark of Camptotheca acuminata, is a cytotoxic alkaloid that attenuates cancer cell replication by inhibiting DNA topoisomerase 1. Despite its promising and wide spectrum antiproliferative activity, its use is limited due to low solubility, instability, acquired tumour cell resistance, and remarkable toxicity. This has led to the development of numerous CPT analogues with improved pharmacodynamic and pharmacokinetic profiles. Three natural product-inspired drugs, namely, topotecan, irinotecan, and belotecan, are clinically approved and prescribed drugs for the treatment of several types of cancer, whereas other derivatives are in clinical trials. In this review, which covers literature from 2015 to 2020, we aim to provide a comprehensive overview and describe efforts that led to the development of a variety of CPT analogues. These efforts have led to the discovery of potent, first-in-class chemotherapeutic agents inspired by CPT. In addition, the mechanism of action, SAR studies, and recent advances of novel CPT drug delivery systems and antibody drug conjugates are discussed.

Tangeretin as an adjuvant and chemotherapeutic sensitizer against various types of cancers: a comparative overview.

OBJECTIVES: Cancer is a leading cause of disabling morbidities and death worldwide. Although there are various strategies for the management of cancer, the severe adverse effects negatively impact the patient's quality of life. In addition, the development of resistance limits the efficacy of many chemotherapeutics. Many natural agents are capable of reducing the adverse effects associated with chemotherapy and improving the therapeutic outcome. Tangeretin, a polymethoxy flavone, is one of the promising natural anticancer agents. KEY FINDINGS: Tangeretin not only targets various malignancies but also synergizes chemotherapeutic agents and reverses cancer resistance. Hence, the application of tangeretin as an adjuvant in cancer chemotherapy would be a promising strategy. SUMMARY: This work critically highlighted the proposed anticancer activity of tangeretin and discussed its potential combination with various chemotherapeutic agents. Additionally, it shed light on tangeretin chemical derivatives with improved pharmacokinetic and pharmacodynamic activity. Finally, this review described flavonoid biosynthetic pathways and how bioengineering can be employed to enhance the production yield of tangeretin. Thus, this work paves the way for the rational clinical utilization of tangeretin as a safe and effective adjuvant in chemotherapeutic protocols.

The dynamic association between COVID-19 and chronic disorders: An updated insight into prevalence, mechanisms and therapeutic modalities.

The devastating pandemic of coronavirus disease 2019 (COVID-19) has caused thousands of deaths and left millions of restless patients suffering from its complications. Increasing data indicate that the disease presents in a severe form in patients with pre-existing chronic conditions like cardiovascular diseases, diabetes, respiratory system diseases, and renal diseases. This denotes that these patients are more susceptible to COVID-19 and have higher mortality rates compared to patients with no comorbid conditions. Several factors can explain the heightened susceptibility and fatal presentation of COVID-19 in these patients, for example, the enhanced expression of the angiotensin-converting enzyme-2 (ACE2) in specific organs, cytokine storm, and drug interactions contribute to the increased morbidity and mortality. Adding to the findings that individuals with pre-existing conditions may be more susceptible to COVID-19, it has also been shown that COVID-19 can induce chronic diseases in previously healthy patients. Therefore, understanding the interlinked relationship between COVID-19 and chronic diseases helps in optimizing the management of susceptible patients. This review comprehensively described the molecular mechanisms that contribute to worse COVID-19 prognosis in patients with pre-existing comorbidities such as diabetes, cardiovascular diseases, respiratory diseases, gastrointestinal and renal diseases, blood disorders, autoimmune diseases, and finally, obesity. It also focused on how COVID-19 could, in some cases, lead to chronic conditions as a result of long-term multi-organ damage. Lastly, this work carefully discussed the tailored management plans for each specific patient population, aiming to achieve the best therapeutic outcome with minimum complications.

Ferroptosis: An emerging approach for targeting cancer stem cells and drug resistance.

Resistance to chemotherapeutic agents remains a major challenge in the fierce battle against cancer. Cancer stem cells (CSCs) are a small population of cells in tumors that possesses the ability to self-renew, initiate tumors, and cause resistance to conventional anticancer agents. Targeting this population of cells was proven as a promising approach to eliminate cancer recurrence and improve the clinical outcome. CSCs are less susceptible to death by classical anticancer agents inducing apoptosis. CSCs can be eradicated by ferroptosis, which is a non-apoptotic-regulated mechanism of cell death. The induction of ferroptosis is an attractive strategy to eliminate tumors due to its ability to selectively target aggressive CSCs. The current review critically explored the crosstalk and regulatory pathways controlling ferroptosis, which can selectively induce CSCs death. In addition, successful chemotherapeutic agents that achieve better therapeutic outcomes through the induction of ferroptosis in CSCs were discussed to highlight their promising clinical impact.

Tackling the cytokine storm in COVID-19, challenges and hopes.

The outbreak of Coronavirus disease 2019 (COVID-19) is the current world health concern, presenting a public health dilemma with ascending morbidity and mortality rates exceeding any previous viral spread, without a standard effective treatment yet. SARS-CoV-2 infection is distinguished with multiple epidemiological and pathological features, one of them being the elevated levels of cytokine release, which in turn trigger an aberrant uncontrolled response known as "cytokine storm". This phenomenon contributes to severe acute respiratory distress syndrome (ARDS), leading to pneumonia and respiratory failure, which is considered a major contributor to COVID-19-associated fatality rates. Taking into account that the vast majority of the COVID-19 cases are aggravated by the respiratory and multiorgan failure triggered by the sustained release of cytokines, implementing therapeutics that alleviate or diminish the upregulated inflammatory response would provide a therapeutic advantage to COVID-19 patients. Indeed, dexamethasone, a widely available and inexpensive corticosteroid with anti-inflammatory effects, has shown a great promise in reducing mortality rates in COVID-19 patients. In this review, we have critically compared the clinical impact of several potential therapeutic agents that could block or interfere with the cytokine storm, such as IL-1 inhibitors, IL-6 inhibitors, mast cell targeting agents, and corticosteroids. This work focused on highlighting and contrasting the current success and limitations towards the involvement of these agents in future treatment protocols.