Flow cytometry analysis of single-strand DNA damage in neuroblastoma cell lines using the F7-26 monoclonal antibody

Secretory pathway Ca2+-ATPase SPCA2 regulates mitochondrial respiration and DNA damage response through store-independent calcium entry

A complex interplay between the extracellular space, cytoplasm and individual organelles modulates Ca2+ signaling to impact all aspects of cell fate and function. In recent years, the molecular machinery linking endoplasmic reticulum stores to plasma membrane Ca2+ entry has been defined. However, the mechanism and pathophysiological relevance of store-independent modes of Ca2+ entry remain poorly understood. Here, we describe how the secretory pathway Ca2+-ATPase SPCA2 promotes cell cycle progression and survival by activating store-independent Ca2+ entry through plasma membrane Orai1 channels in mammary epithelial cells. Silencing SPCA2 expression or briefly removing extracellular Ca2+ increased mitochondrial ROS production, DNA damage and activation of the ATM/ATR-p53 axis leading to G0/G1 phase cell cycle arrest and apoptosis. Consistent with these findings, SPCA2 knockdown confers redox stress and chemosensitivity to DNA damaging agents. Unexpectedly, SPCA2-mediated Ca2+ entry into mitochondria is required for optimal cellular respiration and the generation of mitochondrial membrane potential. In hormone receptor positive (ER+/PR+) breast cancer subtypes, SPCA2 levels are high and correlate with poor survival prognosis. We suggest that elevated SPCA2 expression could drive pro-survival and chemotherapy resistance in cancer cells, and drugs that target store-independent Ca2+ entry pathways may have therapeutic potential in treating cancer.

An antibody-drug conjugate directed to the ALK receptor demonstrates efficacy in preclinical models of neuroblastoma

Enthusiasm for the use of antibody-drug conjugates (ADCs) in cancer therapy has risen over the past few years. The success of this therapeutic approach relies on the identification of cell surface antigens that are widely and selectively expressed on tumor cells. Studies have shown that native ALK protein is expressed on the surface of most neuroblastoma cells, providing an opportunity for development of immune-targeting strategies. Clinically relevant antibodies for this target have not yet been developed. Here, we describe the development of an ALK-ADC, CDX-0125-TEI, which selectively targets both wild-type and mutated ALK-expressing neuroblastomas. CDX-0125-TEI exhibited efficient antigen binding and internalization, and cytotoxicity at picomolar concentrations in cells with different expression of ALK on the cell surface. In vivo studies showed that CDX-0125-TEI is effective against ALK wild-type and mutant patient-derived xenograft models. These data demonstrate that ALK is a bona fide immunotherapeutic target and provide a rationale for clinical development of an ALK-ADC approach for neuroblastomas and other ALK-expressing childhood cancers such as rhabdomyosarcomas.

Annexin A2 could enhance multidrug resistance by regulating NF-κB signaling pathway in pediatric neuroblastoma

Background

Chemotherapy is one of major therapeutic regimens for neuroblastoma (NB) in children. However, recurrence and metastasis associated with poor prognosis caused by acquired multidrug resistance remains a challenge. There is a great need to achieve new insight into the molecular mechanism of drug resistance in NB. The aim of this study is to identify novel drug sensitivity-related biomarkers as well as new therapeutic targets to overcome chemoresistance.

Methods

We proteome-wide quantitatively compared protein expression of two NB cell lines with different drug sensitivities, isolated from the same patient prior to and following chemotherapy. Annexin A2 (ANXA2) emerged as a key factor contributing to drug resistance in NB. Then, we assessed the correlation of ANXA2 expression and clinical characteristics using a tissue microarray. Further, the roles of ANXA2 in chemoresistance for NB and the underlying mechanisms were studied by using short hairpin RNA (shRNA) in vitro and vivo.

Results

First in total, over 6000 proteins were identified, and there were about 460 significantly regulated proteins which were up- or down-regulated by greater than two folds. We screened out ANXA2 which was upregulated by more than 12-fold in the chemoresistant NB cell line, and it might be involved in the drug resistance of NB. Then, using a tissue chip containing 42 clinical NB samples, we found that strong expression of ANXA2 was closely associated with advanced stage, greater number of chemotherapy cycles, tumor metastasis and poor prognosis. Following knockdown of ANXA2 in NB cell line SK-N-BE(2) using shRNA, we demonstrate enhanced drug sensitivity for doxorubicin (2.77-fold) and etoposide (7.87-fold) compared with control. Pro-apoptotic genes such as AIF and cleaved-PARP were upregulated. Inhibiting ANXA2 expression attenuated transcriptional activity of NF-κB via down-regulated nuclear translocation of subunit p50. Finally, simulated chemotherapy in a xenograft NB nude mouse model suggests that ANXA2 knockdown could improve clinical results in vivo.

Conclusion

Our profiling data provided a rich source for further study of the molecular mechanisms of acquired drug resistance in NB. Further study may determine the role of ANXA2 as a prognostic biomarker and a potential therapeutic target for patients with multidrug-resistant NB.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0581-6) contains supplementary material, which is available to authorized users.

ATR inhibition facilitates targeting of leukemia dependence on convergent nucleotide biosynthetic pathways

Leukemia cells rely on two nucleotide biosynthetic pathways, de novo and salvage, to produce dNTPs for DNA replication. Here, using metabolomic, proteomic, and phosphoproteomic approaches, we show that inhibition of the replication stress sensing kinase ataxia telangiectasia and Rad3-related protein (ATR) reduces the output of both de novo and salvage pathways by regulating the activity of their respective rate-limiting enzymes, ribonucleotide reductase (RNR) and deoxycytidine kinase (dCK), via distinct molecular mechanisms. Quantification of nucleotide biosynthesis in ATR-inhibited acute lymphoblastic leukemia (ALL) cells reveals substantial remaining de novo and salvage activities, and could not eliminate the disease in vivo. However, targeting these remaining activities with RNR and dCK inhibitors triggers lethal replication stress in vitro and long-term disease-free survival in mice with B-ALL, without detectable toxicity. Thus the functional interplay between alternative nucleotide biosynthetic routes and ATR provides therapeutic opportunities in leukemia and potentially other cancers.

Leukemic cells depend on the nucleotide synthesis pathway to proliferate. Here the authors use metabolomics and proteomics to show that inhibition of ATR reduced the activity of these pathways thus providing a valuable therapeutic target in leukemia.

The glutathione synthesis inhibitor buthionine sulfoximine synergistically enhanced melphalan activity against preclinical models of multiple myeloma

Melphalan (L-PAM) has been an integral part of multiple myeloma (MM) treatment as a conditioning regimen before stem cell transplant (SCT). After initial response, most treated patients experience relapse with an aggressive phenotype. Increased glutathione (GSH) in MM may mediate resistance to L-PAM. We demonstrated that the GSH synthesis inhibitor buthionine sulfoximine (BSO) synergistically enhanced L-PAM activity (inducing 2–4 logs of cell kill) against nine MM cell lines (also in the presence of marrow stroma or cytokines) and in seven primary MM samples (combination indices <1.0). In MM cell lines, BSO significantly (P<0.05) depleted GSH, increased L-PAM-induced single-strand DNA breaks, mitochondrial depolarization, caspase cleavage and apoptosis. L-PAM depleted GSH, but GSH rapidly recovered in a L-PAM-resistant MM cell line unless also treated with BSO. Treatment with N-acetylcysteine antagonized BSO+L-PAM cytotoxicity without increasing GSH. In human MM xenografted into beige-nude-xid mice, BSO significantly depleted MM intracellular GSH and significantly increased apoptosis compared with L-PAM alone. BSO+L-PAM achieved complete responses (CRs) in three MM xenograft models including maintained CRs >100 days, and significantly increased the median event-free survival relative to L-PAM alone. Combining BSO with L-PAM warrants clinical testing in advanced MM.

Activity of irinotecan and temozolomide in the presence of O6-methylguanine-DNA methyltransferase inhibition in neuroblastoma pre-clinical models

Background:

The combination of temozolomide (TMZ) and irinotecan is a regimen used in neuroblastoma patients with recurrent disease. O⁶-methylguanine-DNA methyltransferase (MGMT) may have a function in resistance to TMZ. Using neuroblastoma pre-clinical models, we determined whether the inhibition of MGMT by O⁶-benzylguanine (O6-BG) could enhance the anti-tumour activity of TMZ and irinotecan.

Methods:

The cytotoxicity of TMZ and irinotecan, either alone or in combination, was measured in five neuroblastoma cell lines in the presence or absence of O6-BG with a fluorescence-based cell viability assay (DIMSCAN). Anti-tumour activity was measured in three neuroblastoma xenograft models.

Results:

MGMT mRNA and protein were expressed in 9 out of 10 examined cell lines. Pretreatment of cells with 25 μM O6-BG decreased MGMT protein expression and enhanced The TMZ cytotoxicity by up to 0.3–1.4 logs in four out of five tested cell lines. TMZ (25 mg kg⁻¹ per day for 5 days every 3 weeks for four cycles) did not significantly improve mice survival, whereas the same schedule of irinotecan (7.5 mg kg⁻¹ per day) significantly improved survival (P<0.0001) in all three xenograft models. Combining O6-BG and/or TMZ with irinotecan further enhanced survival.

Conclusion:

Our in vitro and in vivo findings suggest that irinotecan drives the activity of irinotecan and TMZ in recurrent neuroblastoma. Inhibitors of MGMT warrant further investigation for enhancing the activity of regimens that include TMZ.