Risk of hematologic toxicities in patients with solid tumors treated with everolimus: A systematic review and meta-analysis

Targeting PI3K/AKT/mTOR Signaling Pathway in Breast Cancer

Breast cancer is the most frequently diagnosed cancer and the primary cause of cancer death in women worldwide. Although early diagnosis and cancer growth inhibition has significantly improved breast cancer survival rate over the years, there is a current need to develop more effective systemic treatments to prevent metastasis. One of the most commonly altered pathways driving breast cancer cell growth, survival, and motility is the PI3K/AKT/mTOR signaling cascade. In the past 30 years, a great surge of inhibitors targeting these key players has been developed at a rapid pace, leading to effective preclinical studies for cancer therapeutics. However, the central role of PI3K/AKT/mTOR signaling varies among diverse biological processes, suggesting the need for more specific and sophisticated strategies for their use in cancer therapy. In this review, we provide a perspective on the role of the PI3K signaling pathway and the most recently developed PI3K-targeting breast cancer therapies.

Mechanisms of Resistance to PI3K Inhibitors in Cancer: Adaptive Responses, Drug Tolerance and Cellular Plasticity

The phosphatidylinositol-3-kinase (PI3K) pathway plays a central role in the regulation of several signalling cascades which regulate biological processes such as cellular growth, survival, proliferation, motility and angiogenesis. The hyperactivation of this pathway is linked to tumour progression and is one of the most common events in human cancers. Additionally, aberrant activation of the PI3K pathway has been demonstrated to limit the effectiveness of a number of anti-tumour agents paving the way for the development and implementation of PI3K inhibitors in the clinic. However, the overall effectiveness of these compounds has been greatly limited by inadequate target engagement due to reactivation of the pathway by compensatory mechanisms. Herein, we review the common adaptive responses that lead to reactivation of the PI3K pathway, therapy resistance and potential strategies to overcome these mechanisms of resistance. Furthermore, we highlight the potential role in changes in cellular plasticity and PI3K inhibitor resistance.

Clinical outcomes of lung transplant recipients with telomerase mutations

BACKGROUND

Successful lung transplantation for patients with pulmonary fibrosis from telomerase mutations may be limited by systemic complications of telomerase dysfunction, including myelosuppression, cirrhosis, and malignancy. We describe clinical outcomes in 14 lung transplant recipients with telomerase mutations.

METHODS

Subjects underwent lung transplantation between February 2005 and April 2014 at 5 transplant centers. Data were abstracted from medical records, focusing on outcomes reflecting post-transplant treatment effects likely to be complicated by telomerase mutations.

RESULTS

The median age of subjects was 60.5 years (interquartile range = 52.0-62.0), 64.3% were male, and the mean post-transplant observation time was 3.2 years (SD ± 2.9). A mutation in telomerase reverse transcriptase was present in 11 subjects, a telomerase RNA component mutation was present in 2 subjects, and an uncharacterized mutation was present in 1 subject. After lung transplantation, 10 subjects were leukopenic and 5 did not tolerate lymphocyte anti-proliferative agents. Six subjects developed recurrent lower respiratory tract infections, 7 developed acute cellular rejection (A1), and 4 developed chronic lung allograft dysfunction. Eight subjects developed at least 1 episode of acute renal failure and 10 developed chronic renal insufficiency. In addition, 3 subjects developed cancer. No subjects had cirrhosis. At data censorship, 13 subjects were alive.

CONCLUSIONS

The clinical course for lung transplant recipients with telomerase mutations is complicated by renal disease, leukopenia with intolerance of lymphocyte anti-proliferative agents, and recurrent lower respiratory tract infections. In contrast, cirrhosis was absent, acute cellular rejection was mild, and development of chronic lung allograft dysfunction was comparable to other lung transplant recipients. Although it poses challenges, lung transplantation may be feasible for patients with pulmonary fibrosis from telomerase mutations.

The generation of neutrophils in the bone marrow is controlled by autophagy

Autophagy has been demonstrated to have an essential function in several cellular hematopoietic differentiation processes, for example, the differentiation of reticulocytes. To investigate the role of autophagy in neutrophil granulopoiesis, we studied neutrophils lacking autophagy-related (Atg) 5, a gene encoding a protein essential for autophagosome formation. Using Cre-recombinase mediated gene deletion, Atg5-deficient neutrophils showed no evidence of abnormalities in morphology, granule protein content, apoptosis regulation, migration, or effector functions. In such mice, however, we observed an increased proliferation rate in the neutrophil precursor cells of the bone marrow as well as an accelerated process of neutrophil differentiation, resulting in an accumulation of mature neutrophils in the bone marrow, blood, spleen, and lymph nodes. To directly study the role of autophagy in neutrophils, we employed an in vitro model of differentiating neutrophils that allowed modulating the levels of ATG5 expression, or, alternatively, intervening pharmacologically with autophagy-regulating drugs. We could show that autophagic activity correlated inversely with the rate of neutrophil differentiation. Moreover, pharmacological inhibition of p38 MAPK or mTORC1 induced autophagy in neutrophilic precursor cells and blocked their differentiation, suggesting that autophagy is negatively controlled by the p38 MAPK-mTORC1 signaling pathway. On the other hand, we obtained no evidence for an involvement of the PI3K-AKT or ERK1/2 signaling pathways in the regulation of neutrophil differentiation. Taken together, these findings show that, in contrast to erythropoiesis, autophagy is not essential for neutrophil granulopoiesis, having instead a negative impact on the generation of neutrophils. Thus, autophagy and differentiation exhibit a reciprocal regulation by the p38-mTORC1 axis.