The development of resistance against chemotherapy remains one of the major challenges in the clinical management of leukemia. There is still limited insight into the molecular mechanisms that maintain the chemotherapy-resistant phenotype, despite the obvious clinical relevance that such knowledge would have. In this study, we show that the chemotherapy-resistant phenotype of myeloid leukemia cells correlates with activation of the Hedgehog (Hh) pathway, whereas in chemosensitive cells, such activation is less pronounced. Importantly, the overexpression of Hh pathway components induces chemoprotection and inhibition of the pathway reverts chemoresistance of Lucena-1 cells, apparently by interfering with P-glycoprotein-dependent drug resistance. Our data thus identify the Hh pathway as an essential component of multidrug resistance (MDR) myeloid leukemia and suggest that targeting the Hh pathway might be an interesting therapeutic avenue for overcoming MDR resistance in myeloid leukemia.

Natural-food-based compounds show substantial promise for prevention and biotherapy of cancers including leukemia. In general, their mechanism of action remains unclear, hampering rational use of these compounds. Herein we show that the common dietary flavonoid apigenin has anticancer activity, but also may decrease chemotherapy sensitivity, depending on the cell type. We analyzed the molecular consequences of apigenin treatment in two types of leukemia, the myeloid and erythroid subtypes. Apigenin blocked proliferation in both lineages through cell-cycle arrest in G2/M phase for myeloid HL60 and G0/G1 phase for erythroid TF1 cells. In both cell lines the JAK/STAT pathway was one of major targets of apigenin. Apigenin inhibited PI3K/PKB pathway in HL60 and induced caspase-dependent apoptosis. In contrast, no apoptosis was detected in TF1 cells, but initiation of autophagy was observed. The block in cell cycle and induction of autophagy observed in this erythroleukemia cell line resulted in a reduced susceptibility toward the commonly used therapeutic agent vincristine. Thus, this study shows that although apigenin is a potential chemopreventive agent due to the induction of leukemia cell-cycle arrest, caution in dietary intake of apigenin should be taken during disease as it potentially interferes with cancer treatment.

Summaryβ-Catenin-dependent WNT signal transduction governs development, tissue homeostasis, and a vast array of human diseases. Signal propagation through a WNT-Frizzled/LRP receptor complex requires proteins necessary for clathrin-mediated endocytosis (CME). Paradoxically, CME also negatively regulates WNT signaling through internalization and degradation of the receptor complex. Here, using a gain-of-function screen of the human kinome, we report that the AP2 associated kinase 1 (AAK1), a known CME enhancer, inhibits WNT signaling. Reciprocally, AAK1 genetic silencing or its pharmacological inhibition using a potent and selective inhibitor activates WNT signaling. Mechanistically, we show that AAK1 promotes clearance of LRP6 from the plasma membrane to suppress the WNT pathway. Time-course experiments support a transcription-uncoupled, WNT-driven negative feedback loop; prolonged WNT treatment drives AAK1-dependent phosphorylation of AP2M1, clathrin-coated pit maturation, and endocytosis of LRP6. We propose that, following WNT receptor activation, increased AAK1 function and CME limits WNT signaling longevity.

Inhibitors based on a 3-acylaminoindazole scaffold were synthesized to yield potent dual AAK1/BMP2K inhibitors. Optimization of this 3-acylaminoindazole scaffold furnished a small molecule chemical probe (SGC-AAK1-1, 25) that is potent and selective for AAK1/BMP2K over other NAK family members, demonstrates narrow activity in a kinome-wide screen, and is functionally active in cells. This inhibitor represents one of the best available small molecule tools to study the functions of AAK1 and BMP2K.The human protein Ser/Thr kinases Adaptor protein 2-Associated Kinase 1 (AAK1) and BMP-2-Inducible Kinase (BMP2K/BIKE) play critical roles in mediating endocytosis and other key signaling pathways. Both are broadly expressed and are members of the NAK family of human kinases, which also includes Cyclin G-Associated Kinase (GAK) and Myristoylated and Palmitoylated Serine/Threonine Kinase 1 (MPSK1/STK16). The family shares little homology outside of their kinase domains. 1 AAK1 and BMP2K are the most closely related, with overall sequence identity of 50% and kinase domain sequence identity of 74%. 2 A key function of AAK1 is regulation of receptor-mediated endocytosis via binding directly to clathrin and phosphorylating the medium subunit of AP2 (adaptor protein 2), which stimulates binding to cargo proteins. [3][4][5] AAK1 also modulates the Notch pathway, partially through its phosphorylation of Numb. 6, 7 BMP2K plays a role in osteoblast differentiation, is a clathrin-coated vesicle-associated protein, and, like AAK1, also associates with Numb. 8, 9 Due to their many functions, AAK1 and BMP2K have been implicated as potential drug targets for diverse conditions. AAK1 has been linked to diseases affecting the brain such as schizophrenia, Parkinson's disease and amyotrophic lateral sclerosis as well as implicated as a potential anti-viral target for the treatment of Hepatitis C. 5, 10, 11 BMP2K has been associated with myopia and evaluated as a potential treatment for HIV. 12, 13 A dual AAK1/BMP2K small molecule inhibitor was recently reported as a novel therapeutic to treat neuropathic pain. 14 X-ray crystal structures for the kinase domains of all NAK family members have been solved and reported. 2, 15, 16 Published and novel high-resolution crystal structures of AAK1 and BMP2K reveal target-specific structural features that have enabled our design of specific chemical probes and allowed further

Phosphatases have long been regarded as tumor suppressors, however there is emerging evidence for a tumor initiating role for some phosphatases in several forms of cancer. Low Molecular Weight Protein Tyrosine Phosphatase (LMWPTP; acid phosphatase 1 [ACP1]) is an 18 kDa enzyme that influences the phosphorylation of signaling pathway mediators involved in cancer and is thus postulated to be a tumor-promoting enzyme, but neither unequivocal clinical evidence nor convincing mechanistic actions for a role of LMWPTP have been identified. In the present study, we show that LMWPTP expression is not only significantly increased in colorectal cancer (CRC), but also follows a step-wise increase in different levels of dysplasia. Chemical inhibition of LMWPTP significantly reduces CRC growth. Furthermore, downregulation of LMWPTP in CRC leads to a reduced migration ability in both 2D- and 3D-migration assays, and sensitizes tumor cells to the chemotherapeutic agent 5-FU. In conclusion, this study shows that LMWPTP is not only overexpressed in colorectal cancer, but it is correlated with the malignant potential of this cancer, suggesting that this phosphatase may act as a predictive biomaker of CRC stage and represents a rational novel target in the treatment of this disease.

It is now generally recognised that different modes of programmed cell death (PCD) are intimately linked to the cancerous process. However, the mechanism of PCD involved in cancer chemoprevention is much less clear and may be different between types of chemopreventive agents and tumour cell types involved. Therefore, from a pharmacological view, it is crucial during the earlier steps of drug development to define the cellular specificity of the candidate as well as its capacity to bypass dysfunctional tumoral signalling pathways providing insensitivity to death stimuli. Studying the cytotoxic effects of violacein, an antibiotic dihydro-indolone synthesised by an Amazon river Chromobacterium, we observed that death induced in CD34+/c-Kit+/P-glycoprotein+/MRP1+ TF1 leukaemia progenitor cells is not mediated by apoptosis and/or autophagy, since biomarkers of both types of cell death were not significantly affected by this compound. To clarify the working mechanism of violacein, we performed kinome profiling using peptide arrays to yield comprehensive descriptions of cellular kinase activities. Pro-death activity of violacein is actually carried out by inhibition of calpain and DAPK1 and activation of PKA, AKT and PDK, followed by structural changes caused by endoplasmic reticulum stress and Golgi apparatus collapse, leading to cellular demise. Our results demonstrate that violacein induces kinome reprogramming, overcoming death signaling dysfunctions of intrinsically resistant human leukaemia cells.

The development of multidrug resistance (MDR) limits the efficacy of continuous chemotherapeutic treatment in chronic myelogenous leukemia (CML). Low molecular weight protein tyrosine phosphatase (LMW-PTP) is up-regulated in several cancers and has been associated to poor prognosis. This prompted us to investigate the involvement of LMW-PTP in MDR. In this study, we investigated the role of LMW-PTP in a chemoresistant CML cell line, Lucena-1. Our results showed that LMW-PTP is highly expressed and 7-fold more active in Lucena-1 cells compared to K562 cells, the non-resistant cell line. Knocking down LMW-PTP in Lucena-1 cells reverted chemoresistance to vincristine and imatinib mesylate, followed by a decrease of Src and Bcr-Abl phosphorylation at the activating sites, inactivating both kinases. On the other hand, overexpression of LMW-PTP in K562 cells led to chemoresistance to vincristine. Our findings describe, for the first time, that LMW-PTP cooperates with MDR phenotype, at least in part, through maintaining Src and Bcr-Abl kinases in more active statuses. These findings suggest that inhibition of LMW-PTP may be a useful strategy for the development of therapies for multidrug resistant CML.

Phoneutria nigriventer spider venom (PNV) contains Ca(2+), K(+) and Na(+) channel-acting peptides that affect neurotransmitter release and causes excitotoxicity in PNS and CNS. It has been demonstrated that PNV causes blood-brain barrier (BBB) breakdown of hippocampal microvessels time-dependently through enhanced microtubule-mediated vesicular transport. Herein, it is hypothesized that PNV can cause BBB breakdown in the hippocampus and cerebellum time-dependently through other molecular mechanisms. The BBB integrity was assessed through the analysis of expression of Poly-glycoprotein (P-gp) efflux transporter protein, laminin from basement membrane and endothelial tight junctional and adhesion junctional (TJ/AJ) proteins. Phosphatase and tensin homolog (PTEN) and protein phosphatase 2A (PP2A) expression, which are known to have a role in the phosphorylation of junctional proteins and BBB opening, were also investigated. Astrocytes P-gp activity was determined by flow cytometry. The study demonstrated temporary decreased expression of laminin, TJ and AJ proteins (ZO1//occludin//claudin-5//beta-catenin) and P-gp (more prominently in hippocampus), which was completely or partially resolved between 2 and 5 h (and more quickly for cerebellum). PNV inhibited P-gp activity in astrocytes. PP2A phosphorylation, which inhibits the enzyme activity, was increased in both regions (15-45 min); however the phosphorylation level returned to baseline after 2 h. In conclusion, PNV disrupts paracellular transport in the BBB and possesses substrates for the active P-gp efflux transporter located in the BBB complex. Further studies into cellular mechanisms of astrocyte/endothelial interactions, using PNV as tool, may identify how astrocytes regulate the BBB, a characteristic that may be useful for the temporary opening of the BBB.