In vivo mechanisms of resistance to cytarabine in acute myeloid leukaemia

Post-transplant complications revealed by mycophenolate mofetil related transporters and metabolic enzymes gene polymorphisms in pediatric patients with hematological disorders

BACKGROUND

Haploidentical hematopoietic stem cell transplantation (Haplo-HSCT) serves as an important option for patients without an HLA matched donor in treating hematological disorders, while patients may experience various complications after transplantation. Mycophenolate mofetil (MMF), a cornerstone drug for graft-versus-host disease (GvHD) prophylaxis, effectively reduces the incidence of acute GvHD, and the efficacy of MMF varies among individuals associated with MMF-related transporters and metabolic enzymes single nucleotide polymorphisms (SNPs). However, limited studies have systematically reported the correlations between the MMF-related SNPs and post-transplant complications.

METHODS

Here, we conducted a retrospective study involving 90 pediatric patients with hematological disorders who underwent haplo-HSCT at a single center. All patients were subjected to MMF-related SNP testing, combined with common clinical characteristics, to be correlated with post-transplant complications.

RESULTS

We observed that all 15 MMF-related SNPs were in Hardy-Weinberg equilibrium. Based on multivariate Cox regression analysis of post-transplant complications, we discovered that SLCO1B1 (521T > C) variant genotype was an independent protective factor for chronic GvHD (HR = 0.25, 95% confidence interval (CI) (0.08-0.84)). For viral infection, CYP2C8 (1291 + 106T > C) variant genotype was an independent risk factor for cytomegalovirus infection (HR = 2.98, 95% CI (1.18-7.53)). As to hemorrhagic cystitis, SLCO1B1 (1865 + 4846T > C) variant genotype was an independent protective factor, while older age was considered as an independent risk factor (HR = 0.41, 95% CI (0.19-0.85); HR = 2.52, 95% CI (1.14-5.54), respectively). No statistical significance was discovered between common clinical characteristics and MMF-related SNPs with other complications, including grade II-IV/III-IV acute GvHD, Epstein-Barr virus infection, peri-engraftment syndrome, and capillary leak syndrome. We also discovered SLCO1B1 (597 C > T) and SLC29A1 (-162 + 228 A > C) variant genotypes are both independent factors for cumulative incidence of relapse after haplo-HSCT (HR = 4.02, 95% CI (1.42-11.44); HR = 0.18, 95% CI (0.07-0.43), respectively).

CONCLUSIONS

Our findings highlight the significance of MMF-related transporters and metabolic enzymes SNPs in the development of post-transplant complications, contributing to facilitating personalized risk assessment and improving the clinical management in haplo-HSCT patients.

Bilosomes and Niosomes for Enhanced Intestinal Absorption and In Vivo Efficacy of Cytarabine in Treatment of Acute Myeloid Leukemia

Cytarabine (CTR) is a hydrophilic anticancer drug used to treat leukemia. It suffers from poor permeability and intestinal metabolism, diminishing its oral bioavailability.

BACKGROUND/OBJECTIVES

The objective was to develop and evaluate niosomes and bilosomes for enhanced intestinal absorption; hence, oral bioavailability.

RESULTS

CTR-loaded niosomes and bilosomes with vesicle sizes of 152 and 204.3 nm were successfully prepared with acceptable properties. The presence of bile salts increased the zeta potential of bilosomes. The recorded entrapment efficiency of cytarabine was acceptable for such a hydrophilic drug. CTR-bilosomes showed a pH-dependent drug release pattern with preferred release in pH 6.8. Intestinal absorption behavior indicated a site-dependent CTR absorption pattern with unfavorable absorption in the distal intestine. Niosomal and bilosomal formulations enhanced intestinal absorption parameters with evidence for a predominant paracellular absorption mechanism that bypasses intestinal barriers. The investigation of the anti-leukemic effect of niosomal and bilosomal formulations indicated that both formulations ameliorated the blood parameters, reflecting significant improvement in leukemia treatment compared with the drug solution. Pathological examination of blood films revealed decreased blast cells in peripheral blood in groups treated with tested formulations.

METHODS

Tested formulations were prepared according to the pro-concentrate method and characterized for particle size, zeta potential, entrapment efficiency, and in vitro release. CTR-loaded niosomes and bilosomes were evaluated for enhanced intestinal absorption utilizing the single-pass in situ intestinal perfusion method in rabbits, and the anti-leukemic effect was assessed using the benzene-induced leukemia model in rats.

CONCLUSIONS

This study introduced surfactant vesicles for enhanced oral bioavailability of CTR.

The Drug Transporter P-Glycoprotein and Its Impact on Ceramide Metabolism-An Unconventional Ally in Cancer Treatment

The tumor-suppressor sphingolipid ceramide is recognized as a key participant in the cytotoxic mechanism of action of many types of chemotherapy drugs, including anthracyclines, Vinca alkaloids, the podophyllotoxin etoposide, taxanes, and the platinum drug oxaliplatin. These drugs can activate de novo synthesis of ceramide or stimulate the production of ceramide via sphingomyelinases to limit cancer cell survival. On the contrary, dysfunctional sphingolipid metabolism, a prominent factor in cancer survival and therapy resistance, blunts the anticancer properties of ceramide-orchestrated cell death pathways, especially apoptosis. Although P-glycoprotein (P-gp) is famous for its role in chemotherapy resistance, herein, we propose alternate interpretations and discuss the capacity of this multidrug transporter as a "ceramide neutralizer", an unwelcome event, highlighting yet another facet of P-gp's versatility in drug resistance. We introduce sphingolipid metabolism and its dysfunctional regulation in cancer, present a summary of factors that contribute to chemotherapy resistance, explain how P-gp "neutralizes" ceramide by hastening its glycosylation, and consider therapeutic applications of the P-gp-ceramide connection in the treatment of cancer.

Metabolic Plasticity of Glioblastoma Cells in Response to DHODH Inhibitor BAY2402234 Treatment

Glioblastoma (IDH-wildtype) represents a formidable challenge in oncology, lacking effective chemotherapeutic or biological interventions. The metabolic reprogramming of cancer cells is a hallmark of tumor progression and drug resistance, yet the role of metabolic reprogramming in glioblastoma during drug treatment remains poorly understood. The dihydroorotate dehydrogenase (DHODH) inhibitor BAY2402234 is a blood-brain barrier penetrant drug showing efficiency in in vivo models of many brain cancers. In this study, we investigated the effect of BAY2402234 in regulating the metabolic phenotype of EGFRWT and EGFRvIII patient-derived glioblastoma cell lines. Our findings reveal the selective cytotoxicity of BAY2402234 toward EGFRWT glioblastoma subtypes with minimal effect on EGFRvIII patient cells. At sublethal doses, BAY2402234 induces triglyceride synthesis at the expense of membrane lipid synthesis and fatty acid oxidation in EGFRWT glioblastoma cells, while these effects are not observed in EGFRvIII glioblastoma cells. Furthermore, BAY2402234 reduced the abundance of signaling lipid species in EGFRWT glioblastoma. This study elucidates genetic mutation-specific metabolic plasticity and efficacy in glioblastoma cells in response to drug treatment, offering insights into therapeutic avenues for precision medicine approaches.

Can pharmacogenetics impact the therapeutic effect of cytarabine and anthracyclines in adult acute myeloid leukaemia patients?: A Serbian experience

Background

Cytarabine-anthracycline-based induction chemotherapy remains the standard of care for remission induction among patients with newly diagnosed acute myeloid leukaemia (AML). There are remarkable differences in therapy response among AML patients. This fact could be partly explained by the patients' genetic variability related to the metabolic paths of cytarabine and anthracyclines. This study aims to evaluate the effect of variants in pharmacogenes SLC29A1, DCK, ABCB1, GSTM1, and GSTT1, as well as laboratory and AML-related parameters on clinical outcomes in adult AML patients.

Methods

A total of 100 AML patients were included in the study. Pharmacogenetic variants SLC29A1 rs9394992, DCK rs12648166, ABCB1 rs2032582, and GSTM1 and GSTT1 gene deletions were detected by methodology based on PCR, fragment analysis and direct sequencing. The methods of descriptive and analytic statistics were used. Survival analysis was done using the Kaplan-Meier method using the Log-Rank test.

Results

This is the first study of adult AML pharmacogenetics in the Serbian population. Clinical outcomes in our cohort of AML patients were not impacted by analysed variants in SLC29A1, DCK, ABCB1 and GSTT1, and GSTM1 genes, independently or in combinations. Achievement of complete remission was identified as an independent prognostic indicator of clinical outcome.

Conclusions

The population-specific genomic profile has to be considered in pharmacogenetics. Since the data on AML pharmacogenetics in European populations is limited, our results contribute to knowledge in this field and strongly indicate that a high-throughput approach must be applied to find particular pharmacogenetic markers of AML in the European population.

8-Hydroxydaidzein Induces Apoptosis and Inhibits AML-Associated Gene Expression in U-937 Cells: Potential Phytochemical for AML Treatment

BACKGROUND

8-hydroxydaidzein (8-OHD) is a compound derived from daidzein, known for its anti-inflammatory and anti-proliferative properties in K562 human chronic myeloid leukemia (CML) cells. However, its effects on acute myeloid leukemia (AML) cells have not been fully understood.

METHOD

To investigate its potential anti-AML mechanism, we employed an integrated in vitro-in silico approach.

RESULTS

Our findings demonstrate that 8-OHD suppresses the expression of CDK6 and CCND2 proteins and induces cell apoptosis in U-937 cells by activating Caspase-7 and cleaving PARP-1. Microarray analysis revealed that 8-OHD downregulates differentially expressed genes (DEGs) associated with rRNA processing and ribosome biogenesis pathways. Moreover, AML-target genes, including CCND2, MYC, NPM1, FLT3, and TERT, were downregulated by 8-OHD. Additionally, molecular docking software predicted that 8-OHD has the potential to interact with CDK6, FLT3, and TERT proteins, thereby reducing their activity and inhibiting cell proliferation. Notably, we discovered a synergic pharmacological interaction between 8-OHD and cytarabine (Ara-C).

CONCLUSIONS

Overall, this study provides insights into the therapeutic applications of 8-OHD in treating AML and elucidates its underlying mechanisms of action.

Resistance Mechanism of Acute Myeloid Leukemia Cells Against Daunorubicin and Cytarabine: A Literature Review

Acute myeloid leukemia (AML) is a hematological malignancy commonly found in adult patients. Low overall survival and resistance to therapy are the main issues in AML. The first line of treatment for AML chemotherapy is the induction phase, namely, the phase to induce remission by administering a combination of daunorubicin (DNR) for three days followed by administration of cytarabine (Ara-C) with continuous infusion for seven days, which is referred to as "3 + 7." Such induction therapy has been the standard therapy for AML for the last four decades. This review article is made to discuss daunorubicin and cytarabine from their chemical structure, pharmacodynamics, pharmacokinetics, and mechanisms of resistance in AML.

Is Monitoring of the Intracellular Active Metabolite Levels of Nucleobase and Nucleoside Analogs Ready for Precision Medicine Applications?

Nucleobase and nucleoside analogs (NAs) play important roles in cancer therapy. Although there are obvious individual differences in NA treatments, most NAs lack direct relationships between their plasma concentration and efficacy or adverse effects. Accumulating evidence suggests that the intracellular active metabolite levels of NAs predict patient outcomes. This article reviewed the relationships between NA intracellular active metabolite levels and their efficacy or adverse effects. The factors affecting the formation of intracellular active metabolites and combination regimens that elevate intracellular active metabolite levels were also reviewed. Given the mechanism of NA cytotoxicity, NA intracellular active metabolite levels may be predictive of clinical outcomes. Many clinical studies support this hypothesis. Therefore, the monitoring of intracellular active metabolite levels is beneficial for individualized NA treatment. However, to perform clinical monitoring in practice, well-designed studies are needed to explore the optimal threshold or range and the appropriate regimen adjustment strategies based on these parameters.

Marine Natural Products in Clinical Use

Marine natural products are potent and promising sources of drugs among other natural products of plant, animal, and microbial origin. To date, 20 drugs from marine sources are in clinical use. Most approved marine compounds are antineoplastic, but some are also used for chronic neuropathic pain, for heparin overdosage, as haptens and vaccine carriers, and for omega-3 fatty-acid supplementation in the diet. Marine drugs have diverse structural characteristics and mechanisms of action. A considerable increase in the number of marine drugs approved for clinical use has occurred in the past few decades, which may be attributed to increasing research on marine compounds in laboratories across the world. In the present manuscript, we comprehensively studied all marine drugs that have been successfully used in the clinic. Researchers and clinicians are hopeful to discover many more drugs, as a large number of marine natural compounds are being investigated in preclinical and clinical studies.

The Nuclear Proteins TP73 and CUL4A Confer Resistance to Cytarabine by Induction of Translesion DNA Synthesis via Mono-ubiquitination of PCNA

Resistance to cytarabine is a key problem in the treatment of acute myeloid leukemia (AML). To understand the molecular biology of resistance to cytarabine, a viability-based chemosensitizer screen was utilized. We screened synthetic lethal targets using 437 different small interfering RNAs (siRNAs) directed against factors involved in DNA repair mechanisms and cytarabine as the chemical compound. Three hits were identified: CUL4A, TP73, and RFC2. We show here that the ubiquitin ligase CULLIN 4A (CUL4A) and the tumor-suppressive transcription factor p73 contribute to drug resistance by modulating DNA damage response. P73 confers resistance to cytarabine therapy by transactivation of REV3L, encoding the catalytic subunit of translesion DNA polymerase ζ, and CUL4A probably by influencing proliferating cell nuclear antigen (PCNA) and the polymerase switch towards error-prone translesion DNA polymerases. Abrogation of the polymerase ζ by siRNA causes identical effects as siRNAs against CUL4A or TP73 and resensitizes cells towards cytarabine therapy in vitro. As CUL4A needs to be activated by neddylation to facilitate the degradation of several proteins including PCNA, we propose a novel explanation for the synergism between cytarabine and the neddylation inhibitor pevonedistat by inhibition of translesion synthesis. In keeping with this, in AML patients treated with cytarabine, we found high expression of CUL4A and TP73 to be associated with poor prognosis.

Systematic Review of Pharmacogenetics of ABC and SLC Transporter Genes in Acute Myeloid Leukemia

Antineoplastic uptake by blast cells in acute myeloid leukemia (AML) could be influenced by influx and efflux transporters, especially solute carriers (SLCs) and ATP-binding cassette family (ABC) pumps. Genetic variability in SLC and ABC could produce interindividual differences in clinical outcomes. A systematic review was performed to evaluate the influence of SLC and ABC polymorphisms and their combinations on efficacy and safety in AML cohorts. Anthracycline intake was especially influenced by SLCO1B1 polymorphisms, associated with lower hepatic uptake, showing higher survival rates and toxicity in AML studies. The variant alleles of ABCB1 were related to anthracycline intracellular accumulation, increasing complete remission, survival and toxicity. Similar findings have been suggested with ABCC1 and ABCG2 polymorphisms. Polymorphisms of SLC29A1, responsible for cytarabine uptake, demonstrated significant associations with survival and response in Asian populations. Promising results were observed with SLC and ABC combinations regarding anthracycline toxicities. Knowledge of the role of transporter pharmacogenetics could explain the differences observed in drug disposition in the blast. Further studies including novel targeted therapies should be performed to determine the influence of genetic variability to individualize chemotherapy schemes.

Role of Pharmacogenetics in the Treatment of Acute Myeloid Leukemia: Systematic Review and Future Perspectives

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by remarkable toxicity and great variability in response to treatment. Plenteous pharmacogenetic studies have already been published for classical therapies, such as cytarabine or anthracyclines, but such studies remain scarce for newer drugs. There is evidence of the relevance of polymorphisms in response to treatment, although most studies have limitations in terms of cohort size or standardization of results. The different responses associated with genetic variability include both increased drug efficacy and toxicity and decreased response or resistance to treatment. A broad pharmacogenetic understanding may be useful in the design of dosing strategies and treatment guidelines. The aim of this study is to perform a review of the available publications and evidence related to the pharmacogenetics of AML, compiling those studies that may be useful in optimizing drug administration.

Differential Inhibition of Equilibrative Nucleoside Transporter 1 (ENT1) Activity by Tyrosine Kinase Inhibitors

Background and Objectives

Equilibrative nucleoside transporter (ENT) 1 is a widely-expressed drug transporter, handling nucleoside analogues as well as endogenous nucleosides. ENT1 has been postulated to be inhibited by some marketed tyrosine kinase inhibitors (TKIs). To obtain insights into this point, the interactions of 24 TKIs with ENT1 activity have been analyzed.

Methods

Inhibition of ENT1 activity was investigated in vitro through quantifying the decrease of [³H]-uridine uptake caused by TKIs in HAP1 ENT2-knockout cells, exhibiting selective ENT1 expression. TKI effects towards ENT1-mediated transport were additionally characterized in terms of their in vivo relevance and of their relationship to TKI molecular descriptors. Putative transport of the TKI lorlatinib by ENT1/ENT2 was analyzed by LC-MS/MS.

Results

Of 24 TKIs, 12 of them, each used at 10 µM, were found to behave as moderate or strong inhibitors of ENT1, i.e., they decreased ENT1 activity by at least 35%. This inhibition was concentration-dependent for at least the strongest ones (IC₅₀ less than 10 µM) and was correlated with some molecular descriptors, especially with atom-type E-state indices. Lorlatinib was notably a potent in vitro inhibitor of ENT1/ENT2 (IC₅₀ values around 1.0–2.5 µM) and was predicted to inhibit these nucleoside transporters at relevant clinical concentrations, without, however, being a substrate for them.

Conclusion

Our data unambiguously add ENT1 to the list of drug transporters inhibited by TKIs, especially by lorlatinib. This point likely merits attention in terms of possible drug–drug interactions, notably for nucleoside analogues, whose ENT1-mediated uptake into their target cells may be hampered by co-administrated TKIs such as lorlatinib.

Development of Marine-Derived Compounds for Cancer Therapy

Cancer has always been a threat to human health with its high morbidity and mortality rates. Traditional therapy, including surgery, chemotherapy and radiotherapy, plays a key role in cancer treatment. However, it is not able to prevent tumor recurrence, drug resistance and treatment side effects, which makes it a very attractive challenge to search for new effective and specific anticancer drugs. Nature is a valuable source of multiple pharmaceuticals, and most of the anticancer drugs are natural products or derived from them. Marine-derived compounds, such as nucleotides, proteins, peptides and amides, have also shed light on cancer therapy, and they are receiving a fast-growing interest due to their bioactive properties. Their mechanisms contain anti-angiogenic, anti-proliferative and anti-metastasis activities; cell cycle arrest; and induction of apoptosis. This review provides an overview on the development of marine-derived compounds with anticancer properties, both their applications and mechanisms, and discovered technologies.

Escape From Treatment; the Different Faces of Leukemic Stem Cells and Therapy Resistance in Acute Myeloid Leukemia

Standard induction chemotherapy, consisting of an anthracycline and cytarabine, has been the first-line therapy for many years to treat acute myeloid leukemia (AML). Although this treatment induces complete remissions in the majority of patients, many face a relapse (adaptive resistance) or have refractory disease (primary resistance). Moreover, older patients are often unfit for cytotoxic-based treatment. AML relapse is due to the survival of therapy-resistant leukemia cells (minimal residual disease, MRD). Leukemia cells with stem cell features, named leukemic stem cells (LSCs), residing within MRD are thought to be at the origin of relapse initiation. It is increasingly recognized that leukemia "persisters" are caused by intra-leukemic heterogeneity and non-genetic factors leading to plasticity in therapy response. The BCL2 inhibitor venetoclax, combined with hypomethylating agents or low dose cytarabine, represents an important new therapy especially for older AML patients. However, often there is also a small population of AML cells refractory to venetoclax treatment. As AML MRD reflects the sum of therapy resistance mechanisms, the different faces of treatment "persisters" and LSCs might be exploited to reach an optimal therapy response and prevent the initiation of relapse. Here, we describe the different epigenetic, transcriptional, and metabolic states of therapy sensitive and resistant AML (stem) cell populations and LSCs, how these cell states are influenced by the microenvironment and affect treatment outcome of AML. Moreover, we discuss potential strategies to target dynamic treatment resistance and LSCs.

Response and Toxicity to Cytarabine Therapy in Leukemia and Lymphoma: From Dose Puzzle to Pharmacogenomic Biomarkers

Simple Summary

In this review, the authors propose a crosswise examination of cytarabine-related issues ranging from the spectrum of clinical activity and severe toxicities, through updated cellular pharmacology and drug formulations, to the genetic variants associated with drug-induced phenotypes. Cytarabine (cytosine arabinoside; Ara-C) in multiagent chemotherapy regimens is often used for leukemia or lymphoma treatments, as well as neoplastic meningitis. Chemotherapy regimens can induce a suboptimal clinical outcome in a fraction of patients. The individual variability in clinical response to Leukemia & Lymphoma treatments among patients appears to be associated with intracellular accumulation of Ara-CTP due to genetic variants related to metabolic enzymes. The review provides exhaustive information on the effects of Ara-C-based therapies, the adverse drug reaction will also be provided including bone pain, ocular toxicity (corneal pain, keratoconjunctivitis, and blurred vision), maculopapular rash, and occasional chest pain. Evidence for predicting the response to cytarabine-based treatments will be highlighted, pointing at their significant impact on the routine management of blood cancers.

Abstract

Cytarabine is a pyrimidine nucleoside analog, commonly used in multiagent chemotherapy regimens for the treatment of leukemia and lymphoma, as well as for neoplastic meningitis. Ara-C-based chemotherapy regimens can induce a suboptimal clinical outcome in a fraction of patients. Several studies suggest that the individual variability in clinical response to Leukemia & Lymphoma treatments among patients, underlying either Ara-C mechanism resistance or toxicity, appears to be associated with the intracellular accumulation and retention of Ara-CTP due to genetic variants related to metabolic enzymes. Herein, we reported (a) the latest Pharmacogenomics biomarkers associated with the response to cytarabine and (b) the new drug formulations with optimized pharmacokinetics. The purpose of this review is to provide readers with detailed and comprehensive information on the effects of Ara-C-based therapies, from biological to clinical practice, maintaining high the interest of both researcher and clinical hematologist. This review could help clinicians in predicting the response to cytarabine-based treatments.

Deciphering molecular mechanisms underlying chemoresistance in relapsed AML patients: towards precision medicine overcoming drug resistance

Background

Acute myeloid leukemia (AML) remains a devastating disease with a 5-year survival rate of less than 30%. AML treatment has undergone significant changes in recent years, incorporating novel targeted therapies along with improvements in allogeneic bone marrow transplantation techniques. However, the standard of care remains cytarabine and anthracyclines, and the primary hindrance towards curative treatment is the frequent emergence of intrinsic and acquired anticancer drug resistance. In this respect, patients presenting with chemoresistant AML face dismal prognosis even with most advanced therapies. Herein, we aimed to explore the potential implementation of the characterization of chemoresistance mechanisms in individual AML patients towards efficacious personalized medicine.

Methods

Towards the identification of tailored treatments for individual patients, we herein present the cases of relapsed AML patients, and compare them to patients displaying durable remissions following the same chemotherapeutic induction treatment. We quantified the expression levels of specific genes mediating drug transport and metabolism, nucleotide biosynthesis, and apoptosis, in order to decipher the molecular mechanisms underlying intrinsic and/or acquired chemoresistance modalities in relapsed patients. This was achieved by real-time PCR using patient cDNA, and could be readily implemented in the clinical setting.

Results

This analysis revealed pre-existing differences in gene expression levels between the relapsed patients and patients with lasting remissions, as well as drug-induced alterations at different relapse stages compared to diagnosis. Each of the relapsed patients displayed unique chemoresistance mechanisms following similar treatment protocols, which could have been missed in a large study aimed at identifying common drug resistance determinants.

Conclusions

Our findings emphasize the need for standardized evaluation of key drug transport and metabolism genes as an integral component of routine AML management, thereby allowing for the selection of treatments of choice for individual patients. This approach could facilitate the design of efficacious personalized treatment regimens, thereby reducing relapse rates of therapy refractory disease.

The Novel Phospholipid Mimetic KPC34 Is Highly Active Against Acute Myeloid Leukemia with Activated Protein Kinase C

Acute myeloid leukemia (AML) is an aggressive malignancy with poor outcomes. Nucleoside analogs are subject to resistance mechanisms including downregulation of equilibrative nucleoside transporter (ENT1) and deoxycytidine kinase (dCK). KPC34 is a novel phospholipid mimetic that when cleaved by phospholipase C (PLC) liberates gemcitabine monophosphate and a diacylglycerol mimetic that inhibits the classical isoforms of protein kinase C (PKC). KPC34 acts independently of ENT1 and dCK. KPC34 was active against all AML cell lines tested with IC₅₀s in the nanomolar range. Enforced expression of PLC increased response to KPC34 in vivo. In an orthotopic, xenograft model, KPC34 treatment resulted in a significant increase in survival compared to control animals and those treated with high-dose cytarabine. In a PDX model with activated PKC, there was a significant survival benefit with KPC34, and at progression, there was attenuation of PKC activation in the resistant cells. In contrast, KPC34 was ineffective against a syngeneic, orthotopic AML model without activated PKC. However, when cells from that model were forced to express PKC, there were significantly increased sensitivity in vitro and survival benefit in vivo. These data suggest that KPC34 is active against AML and that the presence of activated PKC can be a predictive biomarker.

Magnetotactic Bacteria and Magnetosomes as Smart Drug Delivery Systems: A New Weapon on the Battlefield with Cancer?

An important direction of research in increasing the effectiveness of cancer therapies is the design of effective drug distribution systems in the body. The development of the new strategies is primarily aimed at improving the stability of the drug after administration and increasing the precision of drug delivery to the destination. Due to the characteristic features of cancer cells, distributing chemotherapeutics exactly to the microenvironment of the tumor while sparing the healthy tissues is an important issue here. One of the promising solutions that would meet the above requirements is the use of Magnetotactic bacteria (MTBs) and their organelles, called magnetosomes (BMs). MTBs are commonly found in water reservoirs, and BMs that contain ferromagnetic crystals condition the magnetotaxis of these microorganisms. The presented work is a review of the current state of knowledge on the potential use of MTBs and BMs as nanocarriers in the therapy of cancer. The growing amount of literature data indicates that MTBs and BMs may be used as natural nanocarriers for chemotherapeutics, such as classic anti-cancer drugs, antibodies, vaccine DNA, and siRNA. Their use as transporters increases the stability of chemotherapeutics and allows the transfer of individual ligands or their combinations precisely to cancerous tumors, which, in turn, enables the drugs to reach molecular targets more effectively.

Harnessing Gene Expression Profiles for the Identification of Ex Vivo Drug Response Genes in Pediatric Acute Myeloid Leukemia

Novel treatment strategies are of paramount importance to improve clinical outcomes in pediatric AML. Since chemotherapy is likely to remain the cornerstone of curative treatment of AML, insights in the molecular mechanisms that determine its cytotoxic effects could aid further treatment optimization. To assess which genes and pathways are implicated in tumor drug resistance, we correlated ex vivo drug response data to genome-wide gene expression profiles of 73 primary pediatric AML samples obtained at initial diagnosis. Ex vivo response of primary AML blasts towards cytarabine (Ara C), daunorubicin (DNR), etoposide (VP16), and cladribine (2-CdA) was associated with the expression of 101, 345, 206, and 599 genes, respectively (p < 0.001, FDR 0.004–0.416). Microarray based expression of multiple genes was technically validated using qRT-PCR for a selection of genes. Moreover, expression levels of BRE, HIF1A, and CLEC7A were confirmed to be significantly (p < 0.05) associated with ex vivo drug response in an independent set of 48 primary pediatric AML patients. We present unique data that addresses transcriptomic analyses of the mechanisms underlying ex vivo drug response of primary tumor samples. Our data suggest that distinct gene expression profiles are associated with ex vivo drug response, and may confer a priori drug resistance in leukemic cells. The described associations represent a fundament for the development of interventions to overcome drug resistance in AML, and maximize the benefits of current chemotherapy for sensitive patients.

Expression of the nucleoside transporters hENT1 (SLC29) and hCNT1 (SLC28) in pediatric acute myeloid leukemia

Cellular uptake of clinically important deoxynucleoside analogs is mediated by nucleoside transporters including the human equilibrative nucleoside transporter 1 (hENT1) and the concentrative nucleoside transporter-1 (hCNT1). These transporters are responsible for influx of cytarabine and reduced hENT1 expression is a major resistance mechanism in acute myeloid leukemia. We determined hENT1 and hCNT1 protein expression by immunocytochemistry in 50 diagnostic pediatric acute myeloid leukemia patient samples. All samples expressed hENT1 [9/43 (21%) low; 26/43 (60%) medium and 8/43 (19%) high] and hCNT1 [2/42 (5%) low; 35/42 (83%) medium and 5/42 (12%) high] at the cell membrane and cytoplasm. Statistical analysis showed a non-significant relationship between survival and transporter expression and in vitro drug sensitivity. In conclusion, the nucleoside transporters hENT1 and hCNT1 are broadly expressed in pediatric acute myeloid leukemia at diagnosis.

Genomic Variants of Cytarabine Sensitivity Associated with Treatment-Related Mortality in Pediatric AML: A Report from the Children's Oncology Group

PURPOSE

Cytarabine is an effective treatment for AML with associated toxicities including treatment related mortality (TRM). The purpose is to determine the clinical relevance of SNPs identified through the use of HapMap lymphoblastoid cell-based models, in predicting cytarabine response and toxicity in AML.

EXPERIMENTAL DESIGN

We tested clinical significance of SNPs associated with cytarabine sensitivity in children with AML treated on Children's Oncology Group regimens (CCG 2941/2961). Endpoints included overall survival (OS), event-free survival (EFS), and TRM. Patients who received bone marrow transplant were excluded. We tested 124 SNPs associated with cytarabine sensitivity in HapMap cell lines in 348 children to determine whether any associated with treatment outcomes. In addition, we tested five SNPs previously associated with TRM in children with AML in our independent dataset of 385 children.

RESULTS

Homozygous variant genotypes of rs2025501 and rs6661575 had increased in vitro cellular sensitivity to cytarabine and were associated with increased TRM. TRM was particularly increased in children with variant genotype randomized to high-dose cytarabine (rs2025501: P = 0.0024 and rs6661575 P = 0.0188). In analysis of previously reported SNPs, only the variant genotype rs17202778 C/C was significantly associated with TRM (P < 0.0001).

CONCLUSIONS

We report clinical importance of two SNPs not previously associated with cytarabine toxicity. Moreover, we confirm that SNP rs17202778 significantly impacts TRM in pediatric AML. Cytarabine sensitivity genotypes may predict TRM and could be used to stratify to standard versus high-dose cytarabine regimens, warranting further study in prospective AML trials.

Chemotherapy selection pressure alters sphingolipid composition and mitochondrial bioenergetics in resistant HL-60 cells

The combination of daunorubicin (dnr) and cytarabine (Ara-C) is a cornerstone of treatment for acute myelogenous leukemia (AML); resistance to these drugs is a major cause of treatment failure. Ceramide, a sphingolipid (SL), plays a critical role in cancer cell apoptosis in response to chemotherapy. Here, we investigated the effects of chemotherapy selection pressure with Ara-C and dnr on SL composition and enzyme activity in the AML cell line HL-60. Resistant cells, those selected for growth in Ara-C- and dnr-containing medium (HL-60/Ara-C and HL-60/dnr, respectively), demonstrated upregulated expression and activity of glucosylceramide synthase, acid ceramidase (AC), and sphingosine kinase 1 (SPHK1); were more resistant to ceramide than parental cells; and displayed sensitivity to inhibitors of SL metabolism. Lipidomic analysis revealed a general ceramide deficit and a profound upswing in levels of sphingosine 1-phosphate (S1P) and ceramide 1-phosphate (C1P) in HL-60/dnr cells versus parental and HL-60/Ara-C cells. Both chemotherapy-selected cells also exhibited comprehensive upregulations in mitochondrial biogenesis consistent with heightened reliance on oxidative phosphorylation, a property that was partially reversed by exposure to AC and SPHK1 inhibitors and that supports a role for the phosphorylation system in resistance. In summary, dnr and Ara-C selection pressure induces acute reductions in ceramide levels and large increases in S1P and C1P, concomitant with cell resilience bolstered by enhanced mitochondrial remodeling. Thus, strategic control of ceramide metabolism and further research to define mitochondrial perturbations that accompany the drug-resistant phenotype offer new opportunities for developing therapies that regulate cancer growth.

MicroRNAs Mediated Regulation of Expression of Nucleoside Analog Pathway Genes in Acute Myeloid Leukemia

Nucleoside analog, cytarabine (ara-C) is the mainstay of acute myeloid leukemia (AML) chemotherapy. Cytarabine and other nucleoside analogs require activation to the triphosphate form (ara-CTP). Intracellular ara-CTP levels demonstrate significant inter-patient variation and have been related to therapeutic response in AML patients. Inter-patient variation in expression levels of drug transporters or enzymes involved in their activation or inactivation of cytarabine and other analogs is a prime mechanism contributing to development of drug resistance. Since microRNAs (miRNAs) are known to regulate gene-expression, the aim of this study was to identify miRNAs involved in regulation of messenger RNA expression levels of cytarabine pathway genes. We evaluated miRNA and gene-expression levels of cytarabine metabolic pathway genes in 8 AML cell lines and The Cancer Genome Atlas (TCGA) data base. Using correlation analysis and functional validation experiments, our data demonstrates that miR-34a-5p and miR-24-3p regulate DCK, an enzyme involved in activation of cytarabine and DCDT, an enzyme involved in metabolic inactivation of cytarabine expression, respectively. Further our results from gel shift assays confirmed binding of these mRNA-miRNA pairs. Our results show miRNA mediated regulation of gene expression levels of nucleoside metabolic pathway genes can impact interindividual variation in expression levels which in turn may influence treatment outcomes.

MALAT1 knockdown inhibits proliferation and enhances cytarabine chemosensitivity by upregulating miR-96 in acute myeloid leukemia cells

Drug resistance remains a major cause of relapse and therapeutic failure in acute myeloid leukemia (AML). Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) has been documented to act as an oncogene and is frequently highly expressed in human cancers including AML. However, the function and molecular mechanism of MALAT1 in regulating cytarabine (Ara-C) resistance of AML are largely unknown. The expressions of MALAT1 and miR-96 in AML patients and healthy controls were examined by qRT-PCR. CCK-8 and flow cytometry assay were performed to assess the proliferation and apoptosis of AML cells. The interaction between MALAT1 and miR-96 was investigated by luciferase reporter assay. We found that MALAT1 was upregulated while miR-96 was downregulated in AML patients compared with healthy controls. A negative correlation between MALAT1 and miR-96 expressions was observed in AML patients. Knockdown of MALAT1 inhibited the proliferation, induced apoptosis, and enhanced Ara-C sensitivity of AML cells. Additionally, MALAT1 suppressed miR-96 expression by acting as a molecular sponge of miR-96 in AML cells. miR-96 downregulation abolished the effects of MALAT1 knockdown on the proliferation, apoptosis, Ara-C sensitivity in AML cells. In conclusion, MALAT1 knockdown inhibited proliferation, promoted apoptosis and enhanced Ara-C sensitivity in AML cells by upregulating miR-96, providing novel insights into the critical role of MALAT1 as a miRNA sponge in AML.

In-silico comparison of two induction regimens (7 + 3 vs 7 + 3 plus additional bone marrow evaluation) in acute myeloid leukemia treatment

BACKGROUND

Clinical integration of systems biology approaches is gaining in importance in the course of digital revolution in modern medicine. We present our results of the analysis of an extended mathematical model describing abnormal human hematopoiesis. The model is able to describe the course of an acute myeloid leukemia including its treatment. In first-line treatment of acute myeloid leukemia, the induction chemotherapy aims for a rapid leukemic cell reduction. We consider combinations of cytarabine and anthracycline-like chemotherapy. Both substances are widely used as standard treatment to achieve first remission. In particular, we compare two scenarios: a single-induction course with 7 days cytarabine and 3 day of anthracycline-like treatment (7 + 3) with a 7 + 3 course and a bone marrow evaluation that leads, in case of insufficient leukemic cell reduction, to the provision of a second chemotherapy course. Three scenarios, based on the leukemias growth kinetics (slow, intermediate, fast), were analyzed. We simulated different intensity combinations for both therapy schemata (7 + 3 and 7 + 3 + evaluation).

RESULTS

Our model shows that within the 7 + 3 regimen a wider range of intensity combinations result in a complete remission (CR), compared to 7 + 3 + evaluation (fast: 64.3% vs 46.4%; intermediate: 63.7% vs 46.7%; slow: 0% vs 0%). Additionally, the number of simulations resulting in a prolonged CR was higher within the standard regimen (fast: 59.8% vs 40.1%; intermediate: 48.6% vs 31.0%; slow: 0% vs 0%). On the contrary, the 7 + 3 + evaluation regimen allows CR and prolonged CR by lower chemotherapy intensities compared to 7 + 3. Leukemic pace has a strong impact on treatment response and especially on specific effective doses. As a result, faster leukemias are characterized by superior treatment outcomes and can be treated effectively with lower treatment intensities.

CONCLUSIONS

We could show that 7 + 3 treatment has considerable more chemotherapy combinations leading to a first CR. However, the 7 + 3 + evaluation regimen leads to CR for lower therapy intensity and presumably less side effects. An additional evaluation can be considered beneficial to control therapy success, especially in low dose settings. The treatment success is dependent on leukemia growth dynamics. The determination of leukemic pace should be a relevant part of a personalized medicine.

Nanopharmaceuticals and nanomedicines currently on the market: challenges and opportunities

There has been a revolution in nanotechnology and nanomedicine. Since 1980, there has been a remarkable increase in approved nano-based pharmaceutical products. These novel nano-based systems can either be therapeutic agents themselves, or else act as vehicles to carry different active pharmaceutical agents into specific parts of the body. Currently marketed nanostructures include nanocrystals, liposomes and lipid nanoparticles, PEGylated polymeric nanodrugs, other polymers, protein-based nanoparticles and metal-based nanoparticles. A range of issues must be addressed in the development of these nanostructures. Ethics, market size, possibility of market failure, costs and commercial development, are some topics which are on the table to be discussed. After passing all the ethical and biological assessments, and satisfying the investors as to future profitability, only a handful of these nanoformulations, successfully obtained marketing approval. We survey the range of nanomedicines that have received regulatory approval and are marketed. We discuss ethics, costs, commercial development and possible market failure. We estimate the global nanomedicine market size and future growth. Our goal is to summarize the different approved nanoformulations on the market, and briefly cover the challenges and future outlook.

Gene expression of hENT1, dCK, CDA, dCMPD and topoisomerase IIα as an indicator of chemotherapy response in AML treated with cytarabine and daunorubicin

Purpose

Acute myeloid leukemia patients are commonly treated with cytarabine (Ara-C) and anthracyclines but the sustained remission rate is not very promising. We explored the role of drug-metabolizing enzymes and transporters in the therapeutic response.

Patients and methods

Bone marrow and peripheral blood samples of 90 newly diagnosed acute myeloid leukemia patients treated with standard 3+7 regimen were analyzed through real-time PCR for expression of human equilibrative nucleoside transporter 1, deoxycytidine kinase, cytidine deaminase (CDA), deoxycytidine monophosphate deaminase (dCMPD) and topoisomerase IIα (Topo-IIa). The expression of these markers was studied in relationship with good (persistent remission) and poor therapeutic response (relapse/resistance).

Results

High Topo-IIa expression in peripheral blood was associated with good response (P=0.006). Relapse was higher among low expressors of Topo-IIa in peripheral blood (OR: 26.25). Bone marrow Topo-IIa expression followed a similar trend but did not reach statistical significance. In contrast, patients with high bone marrow dCMPD expression had poor response (OR: 3; P=0.043). One-year disease-free survival (DFS) was better among those with high bone marrow Topo-IIa (P=0.04) or CDA (P=0.03) expression. High bone marrow Topo-IIa expression also had better DFS at 6 months (P=0.04) and at 12 months (P=0.04).

Conclusion

High expression of Topo-IIa in peripheral blood is a favorable indicator of persistent remission, good therapeutic response and DFS. High dCMPD and low CDA expression in bone marrow is associated with poor therapeutic outcome.

Toward Predicting Acute Myeloid Leukemia Patient Response to 7 + 3 Induction Chemotherapy via Diagnostic Microdosing

Acute myeloid leukemia (AML) is a rare yet deadly cancer of the blood and bone marrow. Presently, induction chemotherapy with the DNA damaging drugs cytarabine (ARA-C) and idarubicin (IDA), known as 7 + 3, is the standard of care for most AML patients. However, 7 + 3 is a relatively ineffective therapy, particularly in older patients, and has serious therapy-related toxicities. Therefore, a diagnostic test to predict which patients will respond to 7 + 3 is a critical unmet medical need. We hypothesize that a threshold level of therapy-induced 7 + 3 drug-DNA adducts determines cytotoxicity and clinical response. We further hypothesize that in vitro exposure of AML cells to nontoxic diagnostic microdoses enables prediction of the ability of AML cells to achieve that threshold during treatment. Our test involves dosing cells with very low levels of ¹⁴C-labeled drug followed by DNA isolation and quantification of drug-DNA adducts via accelerator mass spectrometry. Here, we have shown proof of principle by correlating ARA-C- and DOX-DNA adduct levels with cellular IC₅₀ values of paired sensitive and resistant cancer cell lines and AML cell lines. Moreover, we have completed a pilot retrospective trial of diagnostic microdosing for 10 viably cryopreserved primary AML samples and observed higher ARA-C- and DOX-DNA adducts in the 7 + 3 responders than nonresponders. These initial results suggest that diagnostic microdosing may be a feasible and useful test for predicting patient response to 7 + 3 induction chemotherapy, leading to improved outcomes for AML patients and reduced treatment-related morbidity and mortality.

Nucleobase and Nucleoside Analogues: Resistance and Re-Sensitisation at the Level of Pharmacokinetics, Pharmacodynamics and Metabolism

Antimetabolites, in particular nucleobase and nucleoside analogues, are cytotoxic drugs that, starting from the small field of paediatric oncology, in combination with other chemotherapeutics, have revolutionised clinical oncology and transformed cancer into a curable disease. However, even though combination chemotherapy, together with radiation, surgery and immunotherapy, can nowadays cure almost all types of cancer, we still fail to achieve this for a substantial proportion of patients. The understanding of differences in metabolism, pharmacokinetics, pharmacodynamics, and tumour biology between patients that can be cured and patients that cannot, builds the scientific basis for rational therapy improvements. Here, we summarise current knowledge of how tumour-specific and patient-specific factors can dictate resistance to nucleobase/nucleoside analogues, and which strategies of re-sensitisation exist. We revisit well-established hurdles to treatment efficacy, like the blood-brain barrier and reduced deoxycytidine kinase activity, but will also discuss the role of novel resistance factors, such as SAMHD1. A comprehensive appreciation of the complex mechanisms that underpin the failure of chemotherapy will hopefully inform future strategies of personalised medicine.

The Onus of Sphingolipid Enzymes in Cancer Drug Resistance

Chemotherapy resistance, inherent or acquired, represents a serious barrier to the successful treatment of cancer. Although drug efflux, conducted by plasma membrane-resident proteins, detoxification enzymes, cell death inhibition, and DNA damage repair are ensemble players in this unwanted biology, a full understanding of the many in concert molecular mechanisms driving drug resistance is lacking. Recent discoveries in sphingolipid (SL) metabolism have provided significant insight into the role of these lipids in cancer growth; however, considerably less is known with respect to SLs and the drug-resistant phenotype. One exception here is enhanced ceramide glycosylation, a hallmark of multidrug resistance that is believed responsible, in part, for diminishing ceramides tumor-suppressor potential. This chapter will review various aspects of SL biology that relate to chemotherapy resistance and extend this topic to acknowledge the role of chemotherapy selection pressure in promoting dysregulated SL metabolism, a characteristic in cancer and an exploitable target for therapy.

miR-134 increases the antitumor effects of cytarabine by targeting Mnks in acute myeloid leukemia cells

The relapse and resistance to cytarabine (Ara-C) therapy is still a dominating obstacle to the successful clinical treatment of acute myeloid leukemia (AML). Recent studies have shown that dysregulation of miRNAs might modulate the resistance of cancer cells to anticancer drugs; yet, the mechanism is not fully understood. In this study, we showed a significant downregulation of miR-134 in human multidrug-resistant leukemia cells and relapsed/refractory AML patient samples. Overexpression of miR-134 sensitized K562/A02 and HL-60/ADM cells to Ara-C, inhibited cell colony formation, and enhanced the ability of Ara-C to induce apoptosis. Mechanistic analyses revealed that Mnks was a putative target of miR-134, which was inversely correlated with miR-134 expression in human multidrug-resistant leukemia cells and relapsed/refractory AML patient samples. Further investigation showed that miR-134 increased the anti-tumor effects of Ara-C through inhibiting phosphorylation of eukaryotic initiation factor 4E and downregulating Mcl-1 and bcl2, which was independent of p38 and Erk1/2 activation. Taken together, our results demonstrate that miR-134 plays a pivotal role in AML Ara-C resistance through increasing cell sensitivity to Ara-C and promoting apoptosis by targeting Mnks.

Superresolution imaging of individual replication forks reveals unexpected prodrug resistance mechanism

Many drugs require extensive metabolism en route to their targets. High-resolution visualization of prodrug metabolism should therefore utilize analogs containing a small modification that does not interfere with its metabolism or mode of action. In addition to serving as mechanistic probes, such analogs provide candidates for theranostics when applied in both therapeutic and diagnostic modalities. Here a traceable mimic of the widely used anticancer prodrug cytarabine (ara-C) was generated by converting a single hydroxyl group to azide, giving "AzC." This compound exhibited the same biological profile as ara-C in cell cultures and zebrafish larvae. Using azide-alkyne "click" reactions, we uncovered an apparent contradiction: drug-resistant cells incorporated relatively large quantities of AzC into their genomes and entered S-phase arrest, whereas drug-sensitive cells incorporated only small quantities of AzC. Fluorescence microscopy was used to elucidate structural features associated with drug resistance by characterizing the architectures of stalled DNA replication foci containing AzC, EdU, γH2AX, and proliferating cell nuclear antigen (PCNA). Three-color superresolution imaging revealed replication foci containing one, two, or three partially resolved replication forks. Upon removing AzC from the media, resumption of DNA synthesis and completion of the cell cycle occurred before complete removal of AzC from genomes in vitro and in vivo. These results revealed an important mechanism for the low toxicity of ara-C toward normal tissues and drug-resistant cancer cells, where its efficient incorporation into DNA gives rise to highly stable, stalled replication forks that limit further incorporation of the drug, yet allow for the resumption of DNA synthesis and cellular division following treatment.

Polymorphisms at microRNA binding sites of Ara-C and anthracyclines-metabolic pathway genes are associated with outcome of acute myeloid leukemia patients

Background

Gene polymorphisms at microRNA-binding sites (poly-miRTS) may affect gene transcription and expression through miRNA regulation, which is associated with cancer susceptibility, sensitivity to chemotherapy and prognosis. This study investigated the association between poly-miRTS of Ara-C/anthracycline metabolic pathways genes and the outcome of acute myeloid leukemia (AML) in Chinese patients after Ara-C-based chemotherapy.

Methods

A total of 17 poly-miRTS were selected from the SNPinfo Web Server and genotyped in 206 Chinese Han non-FAB-M3 AML patients using the SEQUENOM Mass-ARRAY system.

Results

Among these 17 poly-miRTS, five Ara-C metabolic gene single nucleotide polymorphisms (SNPs, NT5C2 rs10786736 and rs8139, SLC29A1 rs3734703, DCTD rs7278, and RRM1 rs1042919) were identified to significantly associate with complete AML remission and/or overall and relapse-free survival (OS and RFS, respectively), and four anthracycline-metabolic gene SNPs (ABCC1 rs3743527, rs212091, and rs212090 and CBR1 rs9024) were significantly associated with chemotherapy-related toxicities. Moreover, SLC29A1 rs3734703 was shown to associate with both chemotherapy response and survival (adjusted OR 2.561 in the overdominant model; adjusted HR 2.876 for OS and 2.357 for RFS in the dominant model).

Conclusions

The data from the current study demonstrated that the poly-miRTS of Ara-C/anthracyclines metabolic genes predicted the sensitivity and side effects of AML to Ara-C-based chemotherapy and patient survival. Further study will confirm them as biomarkers for AML patients after Ara-C-based chemotherapy.

Electronic supplementary material

The online version of this article (10.1186/s12967-017-1339-9) contains supplementary material, which is available to authorized users.

Resistance of leukemia cells to cytarabine chemotherapy is mediated by bone marrow stroma, involves cell-surface equilibrative nucleoside transporter-1 removal and correlates with patient outcome

The interaction between acute myeloid leukemia cells (AML) with the bone marrow stroma cells (BMSCs) determines a protective environment that favors tumor development and resistance to conventional chemotherapy. We showed that BMSCs secrete soluble factors that protect AML cells from Ara-C induced cytotoxicity. This leukemia chemoresistance is associated with a decrease in the equilibrative nucleoside transporter (ENT1) activity by inducing removal of ENT1 from the cell surface. Reduction of cell proliferation was also observed with activation of AKT and mTOR-dependent cell survival pathways, which may also contribute to the tumor chemoprotection. Analysis of primary BMSC cultures has demonstrated that AML patients with stroma capable to confer Ara-C resistance in vitro compared to AML patients without this stroma capacity were associated with a worse prognosis. The two year overall survival rate was 0% versus 80% respectively (p=0.0001). This is the first report of a chemoprotection mechanism based on the removal of a drug transporter from the cell surface and most importantly the first time that a stroma phenotype has correlated with prognostic outcome in cancer.

The novel phospholipid mimetic KPC34 is highly active against preclinical models of Philadelphia chromosome positive acute lymphoblastic leukemia

Philadelphia chromosome positive B cell acute lymphoblastic leukemia (Ph+ ALL) is an aggressive cancer of the bone marrow. The addition of tyrosine kinase inhibitors (TKIs) has improved outcomes but many patients still suffer relapse and novel therapeutic agents are needed. KPC34 is an orally available, novel phospholipid conjugate of gemcitabine, rationally designed to overcome multiple mechanisms of resistance, inhibit the classical and novel isoforms of protein kinase C, is able to cross the blood brain barrier and is orally bioavailable. KPC34 had an IC50 in the nanomolar range against multiple ALL cell lines tested but was lowest for Ph+ lines. In mice bearing either naïve or resistant Ph+ ALL, KPC34 treatment resulted in significantly improved survival compared to cytarabine and gemcitabine. Treatment with KPC34 and doxorubicin was more effective than doxorubicin and cytarabine. Mice with recurrence of their ALL after initial treatment with cytarabine and doxorubicin saw dramatic improvements in hind limb paralysis after treatment with KPC34 demonstrating activity against established CNS disease. Consistent with this KPC34 was better than gemcitabine at reducing CNS leukemic burden. These promising pre-clinical results justify the continued development of KPC34 for the treatment of Ph+ALL.

OCTN1 Is a High-Affinity Carrier of Nucleoside Analogues

Resistance to xenobiotic nucleosides used to treat acute myeloid leukemia (AML) and other cancers remains a major obstacle to clinical management. One process suggested to participate in resistance is reduced uptake into tumor cells via nucleoside transporters, although precise mechanisms are not understood. Through transcriptomic profiling, we determined that low expression of the ergothioneine transporter OCTN1 (SLC22A4; ETT) strongly predicts poor event-free survival and overall survival in multiple cohorts of AML patients receiving treatment with the cytidine nucleoside analogue cytarabine. Cell biological studies confirmed OCTN1-mediated transport of cytarabine and various structurally related cytidine analogues, such as 2'deoxycytidine and gemcitabine, occurs through a saturable process that is highly sensitive to inhibition by the classic nucleoside transporter inhibitors dipyridamole and nitrobenzylmercaptopurine ribonucleoside. Our findings have immediate clinical implications given the potential of the identified transport system to help refine strategies that could improve patient survival across multiple cancer types where nucleoside analogues are used in cancer treatment. Cancer Res; 77(8); 2102-11. ©2017 AACR.

Using genome-wide CRISPR library screening with library resistant DCK to find new sources of Ara-C drug resistance in AML

Acute myeloid leukemia (AML) can display de novo or acquired resistance to cytosine arabinoside (Ara-C), a primary component of induction chemotherapy. To identify genes capable of independently imposing Ara-C resistance, we applied a genome-wide CRISPR library to human U937 cells and exposed to them to Ara-C. Interestingly, all drug resistant clones contained guide RNAs for DCK. To avoid DCK gene modification, gRNA resistant DCK cDNA was created by the introduction of silent mutations. The CRISPR screening was repeated using the gRNA resistant DCK, and loss of SLC29A was identified as also being capable of conveying Ara-C drug resistance. To determine if loss of Dck results in increased sensitivity to other drugs, we conducted a screen of 446 FDA approved drugs using two Dck-defective BXH-2 derived murine AML cell lines and their Ara-C sensitive parental lines. Both cell lines showed an increase in sensitivity to prednisolone. Guide RNA resistant cDNA rescue was a legitimate strategy and multiple DCK or SLC29A deficient human cell clones were established with one clone becoming prednisolone sensitive. Dck-defective leukemic cells may become prednisolone sensitive indicating prednisolone may be an effective adjuvant therapy in some cases of DCK-negative AML.

Monitoring therapy responses at the leukemic subclone level by ultra-deep amplicon resequencing in acute myeloid leukemia

In our individualized systems medicine program, personalized treatment options are identified and administered to chemorefractory acute myeloid leukemia (AML) patients based on exome sequencing and ex vivo drug sensitivity and resistance testing data. Here, we analyzed how clonal heterogeneity affects the responses of 13 AML patients to chemotherapy or targeted treatments using ultra-deep (average 68 000 × coverage) amplicon resequencing. Using amplicon resequencing, we identified 16 variants from 4 patients (frequency 0.54-2%) that were not detected previously by exome sequencing. A correlation-based method was developed to detect mutation-specific responses in serial samples across multiple time points. Significant subclone-specific responses were observed for both chemotherapy and targeted therapy. We detected subclonal responses in patients where clinical European LeukemiaNet (ELN) criteria showed no response. Subclonal responses also helped to identify putative mechanisms underlying drug sensitivities, such as sensitivity to azacitidine in DNMT3A mutated cell clones and resistance to cytarabine in a subclone with loss of NF1 gene. In summary, ultra-deep amplicon resequencing method enables sensitive quantification of subclonal variants and their responses to therapies. This approach provides new opportunities for designing combinatorial therapies blocking multiple subclones as well as for real-time assessment of such treatments.

Pharmacogenomics and the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is a clinically and biologically heterogeneous malignancy that is primarily treated with combinations of cytarabine and anthracyclines. Although this scheme remains effective in most of the patients, variability of outcomes in patients has been partly related with their genetic variability. Several pharmacogenetic studies have analyzed the impact of polymorphisms in genes encoding transporters, metabolizers or molecular targets of chemotherapy agents. A systematic review on all eligible studies was carried out in order to estimate the effect of polymorphisms of anthracyclines and cytarabine pathways on efficacy and toxicity of AML treatment. Other emerging genes recently studied in AML, such as DNA repair genes, genes potentially related to chemotherapy response or AML prognosis, have also been included.

Oncogene- and drug resistance-associated alternative exon usage in acute myeloid leukemia (AML)

In addition to spliceosome gene mutations, oncogene expression and drug resistance in AML might influence exon expression. We performed exon-array analysis and exon-specific PCR (ESPCR) to identify specific landscapes of exon expression that are associated with DEK and WT1 oncogene expression and the resistance of AML cells to AraC, doxorubicin or azacitidine. Data were obtained for these five conditions through exon-array analysis of 17 cell lines and 24 patient samples and were extended through qESPCR of samples from 152 additional AML cases. More than 70% of AEUs identified by exon-array were technically validated through ESPCR. In vitro, 1,130 to 5,868 exon events distinguished the 5 conditions from their respective controls while in vivo 6,560 and 9,378 events distinguished chemosensitive and chemoresistant AML, respectively, from normal bone marrow. Whatever the cause of this effect, 30 to 80% of mis-spliced mRNAs involved genes unmodified at the whole transcriptional level. These AEUs unmasked new functional pathways that are distinct from those generated by transcriptional deregulation. These results also identified new putative pathways that could help increase the understanding of the effects mediated by DEK or WT1, which may allow the targeting of these pathways to prevent resistance of AML cells to chemotherapeutic agents.

Low expression of equilibrative nucleoside transporter 1 is associated with poor prognosis in chemotherapy-naïve pT2 gallbladder adenocarcinoma patients

AIMS

Equilibrative nucleoside transporter 1 (ENT1) is the major transporter of the chemotherapeutic drug gemcitabine, the current therapy for advanced gallbladder cancer (GBC). ENT1 expression has been proposed as a predictive marker for gemcitabine-treated pancreatic cancer patients. The aim of study was to explore the value of ENT1 measurement in chemotherapy-naïve patients with advanced GBC.

MATERIALS AND RESULTS

Immunohistochemistry for ENT1 was performed on 214 GBC samples from patients who had never undergone co-adjuvant or neo-adjuvant chemotherapy. Advanced GBC cases were divided into groups with low or high ENT1 expression. Kaplan-Meier tests were used for survival analyses. The Cox regression method was used to assess the association of ENT1 expression with overall survival (OS). Low ENT1 expression was associated with younger patient age (P = 0.03) and moderate-to-poor histological differentiation (P = 0.01). pT2 patients with low ENT1 expression had shorter median survival (17.3 versus 28.7 months) and lower OS (17.3% versus 33.3%, P < 0.05) than patients with high ENT1 expression. Low ENT1 expression was an independent prognostic factor for OS (P = 0.036).

CONCLUSIONS

ENT1 is a prognostic marker for pT2 GBC patients. Additional studies are needed to determine whether ENT1 has predictive value for gemcitabine response in GBC.

RNA expression of genes involved in cytarabine metabolism and transport predicts cytarabine response in acute myeloid leukemia

BACKGROUND

Variation in terms of outcome and toxic side effects of treatment exists among acute myeloid leukemia (AML) patients on chemotherapy with cytarabine (Ara-C) and daunorubicin (Dnr). Candidate Ara-C metabolizing gene expression in primary AML cells is proposed to account for this variation.

METHODS

Ex vivo Ara-C sensitivity was determined in primary AML samples using MTT assay. mRNA expression of candidate Ara-C metabolizing genes were evaluated by RQPCR analysis. Global gene expression profiling was carried out for identifying differentially expressed genes between exvivo Ara-C sensitive and resistant samples.

RESULTS

Wide interindividual variations in ex vivo Ara-C cytotoxicity were observed among samples from patients with AML and were stratified into sensitive, intermediately sensitive and resistant, based on IC50 values obtained by MTT assay. RNA expression of deoxycytidine kinase (DCK), human equilibrative nucleoside transporter-1 (ENT1) and ribonucleotide reductase M1 (RRM1) were significantly higher and cytidine deaminase (CDA) was significantly lower in ex vivo Ara-C sensitive samples. Higher DCK and RRM1 expression in AML patient's blast correlated with better DFS. Ara-C resistance index (RI), a mathematically derived quotient was proposed based on candidate gene expression pattern. Ara-C ex vivo sensitive samples were found to have significantly lower RI compared with resistant as well as samples from patients presenting with relapse. Patients with low RI supposedly highly sensitive to Ara-C were found to have higher incidence of induction death (p = 0.002; RR: 4.35 [95% CI: 1.69-11.22]). Global gene expression profiling undertaken to find out additional contributors of Ara-C resistance identified many apoptosis as well as metabolic pathway genes to be differentially expressed between Ara-C resistant and sensitive samples.

CONCLUSION

This study highlights the importance of evaluating expression of candidate Ara-C metabolizing genes in predicting ex vivo drug response as well as treatment outcome. RI could be a predictor of ex vivo Ara-C response irrespective of cytogenetic and molecular risk groups and a potential biomarker for AML treatment outcome and toxicity. Original submitted 22 December 2014; Revision submitted 9 April 2015.