Benefit of cyclosporine modulation of drug resistance in patients with poor-risk acute myeloid leukemia: a Southwest Oncology Group study

A clinical trial of zosuquidar plus gemtuzumab ozogamicin (GO) in relapsed or refractory acute myeloid leukemia (RR AML): evidence of efficacy based on leukemic blast P-glycoprotein functional phenotype

PURPOSE

To evaluate safety, tolerability, potential efficacy, and pharmacodynamics (PD) of zosuquidar (Zos) in combination with gemtuzumab ozogamicin (GO) in elderly patients with relapsed or refractory (RR) acute myeloid leukemia (AML).

METHODS

Patients with RR AML (N = 41) were treated with Zos as a 48-h continuous intravenous infusion initiated 4 h prior to a 2-h infusion of GO on days 1 and 15. P-glycoprotein (P-gp) status of the patients' leukemic blasts and PD determinations were assessed with ex vivo bioassays. Patient outcomes were analyzed for the total cohort and as stratified into P-gp-positive (P-gp +) and P-gp-negative (P-gp‒) subgroups.

RESULTS

The eligible cohort exhibited a 34% overall remission rate (ORR), a composite of patients that exhibited complete remission (CR), CR with incomplete platelet recovery, or morphologic remission. Patients with 1st relapsed disease exhibited 40% ORR. P-gp phenotype did not significantly predict ORR. However, the P-gp + subgroup exhibited a greater median overall survival (OS) of 6.0 months vs. 1.8 months for patients in the P-gp‒ subgroup (p = 0.01). PD analyses revealed 90-95% inhibition of blast P-gp function during Zos infusion. Treatment related toxicities were observed and resolved with decrease or discontinued Zos or GO dosages.

CONCLUSIONS

Zos plus GO elicited appreciable ORR for an elderly patient population with RR AML. The greater OS of the P-gp + subgroup vs. the P-gp‒ subgroup suggests that patients with P-gp + leukemic blasts were being more effectively targeted by GO with Zos co-therapy. The poorer OS of the P-gp‒ subgroup suggests activity of Zos-insensitive multidrug resistant mechanisms.

CLINICAL TRIALS

GOV IDENTIFIER

NCT00233909; First posted October 06, 2005.

Perspectives on drug repurposing to overcome cancer multidrug resistance mediated by ABCB1 and ABCG2

The overexpression of the human ATP-binding cassette (ABC) transporters in cancer cells is a common mechanism involved in developing multidrug resistance (MDR). Unfortunately, there are currently no approved drugs specifically designed to treat multidrug-resistant cancers, making MDR a significant obstacle to successful chemotherapy. Despite over two decades of research, developing transporter-specific inhibitors for clinical use has proven to be a challenging endeavor. As an alternative approach, drug repurposing has gained traction as a more practical method to discover clinically effective modulators of drug transporters. This involves exploring new indications for already-approved drugs, bypassing the lengthy process of developing novel synthetic inhibitors. In this context, we will discuss the mechanisms of ABC drug transporters ABCB1 and ABCG2, their roles in cancer MDR, and the inhibitors that have been evaluated for their potential to reverse MDR mediated by these drug transporters. Our focus will be on providing an up-to-date report on approved drugs tested for their inhibitory activities against these drug efflux pumps. Lastly, we will explore the challenges and prospects of repurposing already approved medications for clinical use to overcome chemoresistance in patients with high tumor expression of ABCB1 and/or ABCG2.

Comprehensive molecular and clinical characterization of NUP98 fusions in pediatric acute myeloid leukemia

NUP98 fusions comprise a family of rare recurrent alterations in AML, associated with adverse outcomes. In order to define the underlying biology and clinical implications of this family of fusions, we performed comprehensive transcriptome, epigenome, and immunophenotypic profiling of 2,235 children and young adults with AML and identified 160 NUP98 rearrangements (7.2%), including 108 NUP98-NSD1 (4.8%), 32 NUP98-KDM5A (1.4%) and 20 NUP98-X cases (0.9%) with 13 different fusion partners. Fusion partners defined disease characteristics and biology; patients with NUP98-NSD1 or NUP98-KDM5A had distinct immunophenotypic, transcriptomic, and epigenomic profiles. Unlike the two most prevalent NUP98 fusions, NUP98-X variants are typically not cryptic. Furthermore, NUP98-X cases are associated with WT1 mutations, and have epigenomic profiles that resemble either NUP98-NSD1 or NUP98-KDM5A. Cooperating FLT3-ITD and WT1 mutations define NUP98-NSD1, and chromosome 13 aberrations are highly enriched in NUP98-KDM5A. Importantly, we demonstrate that NUP98 fusions portend dismal overall survival, with the noteworthy exception of patients bearing abnormal chromosome 13 (clinicaltrials gov. Identifiers: NCT00002798, NCT00070174, NCT00372593, NCT01371981).

Verification of prognostic expression biomarkers is improved by examining enriched leukemic blasts rather than mononuclear cells from acute myeloid leukemia patients

BACKGROUND

Studies have not systematically compared the ability to verify performance of prognostic transcripts in paired bulk mononuclear cells versus viable CD34-expressing leukemic blasts from patients with acute myeloid leukemia. We hypothesized that examining the homogenous leukemic blasts will yield different biological information and may improve prognostic performance of expression biomarkers.

METHODS

To assess the impact of cellular heterogeneity on expression biomarkers in acute myeloid leukemia, we systematically examined paired mononuclear cells and viable CD34-expressing leukemic blasts from SWOG diagnostic specimens. After enrichment, patients were assigned into discovery and validation cohorts based on availability of extracted RNA. Analyses of RNA sequencing data examined how enrichment impacted differentially expressed genes associated with pre-analytic variables, patient characteristics, and clinical outcomes.

RESULTS

Blast enrichment yielded significantly different expression profiles and biological pathways associated with clinical characteristics (e.g., cytogenetics). Although numerous differentially expressed genes were associated with clinical outcomes, most lost their prognostic significance in the mononuclear cells and blasts after adjusting for age and ELN risk, with only 11 genes remaining significant for overall survival in both cell populations (CEP70, COMMD7, DNMT3B, ECE1, LNX2, NEGR1, PIK3C2B, SEMA4D, SMAD2, TAF8, ZNF444). To examine the impact of enrichment on biomarker verification, these 11 candidate biomarkers were examined by quantitative RT/PCR in the validation cohort. After adjusting for ELN risk and age, expression of 4 genes (CEP70, DNMT3B, ECE1, and PIK3CB) remained significantly associated with overall survival in the blasts, while none met statistical significance in mononuclear cells.

CONCLUSIONS

This study provides insights into biological information gained/lost by examining viable CD34-expressing leukemic blasts versus mononuclear cells from the same patient and shows an improved verification rate for expression biomarkers in blasts.

Modular Biomimetic Strategy Enabled Discovery of Simplified Pseudo-Natural Macrocyclic P-Glycoprotein Inhibitors Capable of Overcoming Multidrug Resistance

Natural macrocycles have shown impressive activity to overcome P-glycoprotein (P-gp)-mediated multidrug resistance (MDR). However, the total synthesis and structural modification of natural macrocycles are challenging, which would hamper the deeper investigations of their structure-activity relationship (SAR) and drug likeness. Herein, we describe a modular biomimetic strategy to expeditiously achieve a new class of macrocycles featuring polysubstituted 1,3-diene, which efficiently inhibited P-gp and reversed MDR in cancer cells. The SAR analysis revealed that the size and linker of the macrocycles are important structural characteristics to restore activity. Particularly, 32 containing a naphthyl group and (d)-Phe moiety has higher potency with an excellent reversal fold than verapamil at a concentration of 5 μM, which induces conformational change of P-gp and inhibits its function instead of altering P-gp expression. Furthermore, 23 and 32 were identified to be attractive leads, which possess a good pharmacokinetic profile and antitumor activity in a KBV200 xenograft mouse model.

Synergistic effect of p53 gene/DOX intracellular delivery and P-gp inhibition by pullulan thiomers on cancer cells: in vitro and in vivo evaluations

Numerous reports emphasize the inverse relationship between the mutant p53 protein and P-glycoprotein overexpression, which adversely affects the chemosensitivity of cancer cells. In this study, the cationised pullulan polysaccharide was conjugated with dithiobutyric acid (PPDBA) for the intracellular delivery of doxorubicin and the p53 gene. The transfection efficiency of PPDBA using the apoptotic gene p53 and its ability to modulate efflux pumps in the presence and absence of glutathione and the subsequent drug retention were studied in different cell lines. The percentage cell death mediated by the PPDBA/p53 nanoplex (4 : 1 ratio) was 59%, and by DOX alone a 50% cell death was attained at 3.13 μM in C6 cells, but the percentage cell death mediated by PPDBA/p53 (4 : 1) in combination with 1 μM DOX was as high as 98%. The effect of PPDBA II/p53/DOX nanoplexes on the mouse tumor model was evaluated in BALB/c mice which demonstrated good efficacy when compared with the drug or gene alone.

Thiosemicarbazones Can Act Synergistically with Anthracyclines to Downregulate CHEK1 Expression and Induce DNA Damage in Cell Lines Derived from Pediatric Solid Tumors

Anticancer therapy by anthracyclines often leads to the development of multidrug resistance (MDR), with subsequent treatment failure. Thiosemicarbazones have been previously suggested as suitable anthracycline partners due to their ability to overcome drug resistance through dual Pgp-dependent cytotoxicity-inducing effects. Here, we focused on combining anthracyclines (doxorubicin, daunorubicin, and mitoxantrone) and two thiosemicarbazones (DpC and Dp44mT) for treating cell types derived from the most frequent pediatric solid tumors. Our results showed synergistic effects for all combinations of treatments in all tested cell types. Nevertheless, further experiments revealed that this synergism was independent of Pgp expression but rather resulted from impaired DNA repair control leading to cell death via mitotic catastrophe. The downregulation of checkpoint kinase 1 (CHEK1) expression by thiosemicarbazones and the ability of both types of agents to induce double-strand breaks in DNA may explain the Pgp-independent synergism between anthracyclines and thiosemicarbazones. Moreover, the concomitant application of these agents was found to be the most efficient approach, achieving the strongest synergistic effect with lower concentrations of these drugs. Overall, our study identified a new mechanism that offers an avenue for combining thiosemicarbazones with anthracyclines to treat tumors regardless the Pgp status.

Aconiti Lateralis Radix Praeparata as Potential Anticancer Herb: Bioactive Compounds and Molecular Mechanisms

Aconiti Lateralis Radix Praeparata (Fuzi in Chinese) is a traditional herbal medicine widely used in China and other Asian countries. In clinical practice, it is often used to treat heart failure, rheumatoid arthritis, and different kinds of pains. Fuzi extract and its active ingredients exert considerable anticancer, anti-inflammatory, and analgesic effects. The main chemical substances of Fuzi include alkaloids, polysaccharides, flavonoids, fatty acids, and sterols. Among of them, alkaloids and polysaccharides are responsible for the anticancer efficacy. Most bioactive alkaloids in Fuzi possess C19 diterpenoid mother nucleus and these natural products show great potential for cancer therapy. Moreover, polysaccharides exert extraordinary tumor-suppressive functions. This review comprehensively summarized the active ingredients, antineoplastic effects, and molecular mechanisms of Fuzi by searching PubMed, Web of Science, ScienceDirect, and CNKI. The anticancer effects are largely attributed to inducing apoptosis and autophagy, inhibiting proliferation, migration and invasion, regulating body immunity, affecting energy metabolism, as well as reversing multidrug resistance. Meanwhile, several signaling pathways and biological processes are mainly involved, such as NF-κB, EMT, HIF-1, p38 MAPK, PI3K/AKT/mTOR, and TCA cycle. Collectively, alkaloids and polysaccharides in Fuzi might serve as attractive therapeutic candidates for the development of anticancer drugs. This review would lay a foundation and provide a basis for further basic research and clinical application of Fuzi.

Infigratinib (BGJ 398), a Pan-FGFR Inhibitor, Targets P-Glycoprotein and Increases Chemotherapeutic-Induced Mortality of Multidrug-Resistant Tumor Cells

The microtubule-targeting agents (MTAs) are well-known chemotherapeutic agents commonly used for therapy of a broad spectrum of human malignancies, exhibiting epithelial origin, including breast, lung, and prostate cancer. Despite the impressive response rates shortly after initiation of MTA-based therapy, the vast majority of human malignancies develop resistance to MTAs due to the different mechanisms. Here, we report that infigratinib (BGJ 398), a potent FGFR1-4 inhibitor, restores sensitivity of a broad spectrum of ABCB1-overexpressing cancer cells to certain chemotherapeutic agents, including paclitaxel (PTX) and doxorubicin (Dox). This was evidenced for the triple-negative breast cancer (TNBC), and gastrointestinal stromal tumor (GIST) cell lines, as well. Indeed, when MDR-overexpressing cancer cells were treated with a combination of BGJ 398 and PTX (or Dox), we observed a significant increase of apoptosis which was evidenced by an increased expression of cleaved forms of PARP, caspase-3, and increased numbers of Annexin V-positive cells, as well. Moreover, BGJ 398 used in combination with PTX significantly decreased the viability and proliferation of the resistant cancer cells. As expected, no apoptosis was found in ABCB1-overexpressing cancer cells treated with PTX, Dox, or BGJ 398 alone. Inhibition of FGFR-signaling by BGJ 398 was evidenced by the decreased expression of phosphorylated (i.e., activated) forms of FGFR and FRS-2, a well-known adaptor protein of FGFR signaling, and downstream signaling molecules (e.g., STAT-1, -3, and S6). In contrast, expression of MDR-related ABC-transporters did not change after BGJ 398 treatment, thereby suggesting an impaired function of MDR-related ABC-transporters. By using the fluorescent-labeled chemotherapeutic agent PTX-Alexa488 (Flutax-2) and doxorubicin, exhibiting an intrinsic fluorescence, we found that BGJ 398 substantially impairs their efflux from MDR-overexpressing TNBC cells. Moreover, the efflux of Calcein AM, a well-known substrate for ABCB1, was also significantly impaired in BGJ 398-treated cancer cells, thereby suggesting the ABCB1 as a novel molecular target for BGJ 398. Of note, PD 173074, a potent FGFR1 and VEGFR2 inhibitor failed to retain chemotherapeutic agents inside ABCB1-overexpressing cells. This was consistent with the inability of PD 173074 to sensitize Tx-R cancer cells to PTX and Dox. Collectively, we show here for the first time that BGJ 398 reverses the sensitivity of MDR-overexpressing cancer cells to certain chemotherapeutic agents due to inhibition of their efflux from cancer cells via ABCB1-mediated mechanism.

PEGylated Liposomes Remotely Loaded with the Combination of Doxorubicin, Quinine, and Indocyanine Green Enable Successful Treatment of Multidrug-Resistant Tumors

Multidrug resistance (MDR) of cancer cells remains a major obstacle to favorable outcomes of treatment with many drugs, including doxorubicin. Most of the clinical trials failed to demonstrate the benefit of the drug efflux transporter P-glycoprotein (P-gp) inhibitors to circumvent P-gp-mediated drug resistance in vivo. The present study explored the therapeutic potential of combined treatment with liposomal doxorubicin, P-gp inhibitor quinine, and the photodynamic therapy (PDT) using indocyanine green (ICG) in the adenocarcinoma drug-resistant tumor model. Liposomes were actively co-remotely loaded with doxorubicin and quinine, and ICG was passively adsorbed. The liposomes were characterized by differential scanning calorimetry (DSC) and cryogenic transmission microscopy (Cryo-TEM). We found that quinine impaired the crystalline structure of doxorubicin. In vitro, treatment with single agents themselves was insufficient to inhibit the growth of HT-29 MDR1 cells. However, pegylated liposomal doxorubicin and quinine (PLDQ) significantly diminished HT-29 MDR1 cell survival. Furthermore, survival inhibition intensified by the addition of ICG to the PLDQ (ICG + PLDQ). In vivo, ICG + PLDQ significantly decreased tumor growth when combined with tumor irradiation with NIR light (** p < 0.01). ICG + PLDQ + irradiation was superior to single treatments or combinational treatments without irradiation. These findings suggest that ICG + PLDQ can overcome P-gp-mediated MDR in cancer cells.

Predictive Value of MRP-1 in Localized High-Risk Soft Tissue Sarcomas: A Translational Research Associated to ISG-STS 1001 Randomized Phase III Trial

MRP-1 is implicated in multidrug resistance and was described as prognostic in high-risk patients with soft-tissue sarcoma (STS) in a previous study. The current research aimed to validate MRP-1 prognostic/predictive value in localized sarcomas treated with anthracyclines plus ifosfamide within the ISG-1001 phase III study. In addition, the inhibitory activity on MRP-1 was investigated in preclinical studies to identify new combinations able to increase the efficacy of standard chemotherapy in STS. MRP-1 expression was assessed by IHC in tissue microarrays from patients with STS and tested for correlation with disease-free survival (DFS) and overall survival (OS). In vitro studies tested the efficacy of MRP-1 inhibitors (nilotinib, ripretinib, selumetinib, and avapritinib) in sarcoma cell lines. The effect of combinations of the most active MRP-1 inhibitors and chemotherapy was measured on the basis of apoptosis. MRP-1 was evaluable in 231 of 264 cases who entered the study. MRP-1 expression (strong intensity) was independently associated with worse DFS [HR, 1.78; 95% confidence interval (CI), 1.11-2.83; P = 0.016], in the multivariate analysis, with a trend for a worse OS (HR, 1.78; 95% CI, 0.97-3.25; P = 0.062). In vitro studies showed that the addition of MRP-1 inhibitors (nilotinib or avapritinib) to doxorubicin plus palifosfamide, significantly increased cell death in SK-UT-1 and CP0024 cell lines. MRP-1 is an adverse predictive factor in localized high-risk patients with STS treated with neoadjuvant anthracyclines plus ifosfamide followed by surgery. In vitro findings support the clinical assessment of the combination of chemotherapy and MRP-1 inhibitors as a promising strategy to overcome the drug ceiling effect for chemotherapy.

Redox-sensitive cyclophilin A elicits chemoresistance through realigning cellular oxidative status in colorectal cancer

Cancer cells utilize rapidly elevated cellular antioxidant programs to accommodate chemotherapy-induced oxidative stress; however, the underlying mechanism remains largely unexplored. Here we screen redox-sensitive effectors as potential therapeutic targets for colorectal cancer (CRC) treatment and find that cyclophilin A (CypA) is a compelling candidate. Our results show that CypA forms an intramolecular disulfide bond between Cys115 and Cys161 upon oxidative stress and the oxidized cysteines in CypA are recycled to a reduced state by peroxiredoxin-2 (PRDX2). Furthermore, CypA reduces cellular reactive oxygen species levels and increases CRC cell survival under insults of H₂O₂ and chemotherapeutics through a CypA-PRDX2-mediated antioxidant apparatus. Notably, CypA is upregulated in chemoresistant CRC samples, which predicts poor prognosis. Moreover, targeting CypA by cyclosporine A exhibits promising efficacy against chemoresistant CRC when combined with chemotherapeutics. Collectively, our findings highlight CypA as a component of cellular noncanonical antioxidant defense and as a potential druggable therapeutic target to ameliorate CRC chemoresistance.

Treatment Failure in Acute Myeloid Leukemia: Focus on the Role of Extracellular Vesicles

Acute myeloblastic leukemia (AML) is one of the most common types of blood malignancies that results in an AML-associated high mortality rate each year. Several causes have been reported as prognostic factors for AML in children and adults, the most important of which are cytogenetic abnormalities and environmental risk factors. Following the discovery of numerous drugs for AML treatment, leukemic cells sought a way to escape from the cytotoxic effects of chemotherapy drugs, leading to treatment failure. Nowadays, comprehensive studies have looked at the role of extracellular vesicles (EVs) secreted by AML blasts and how the microenvironment of the tumor changes in favor of cancer progression and survival to discover the mechanisms of treatment failure to choose the well-advised treatment. Reports show that malignant cells secrete EVs that transmit messages to adjacent cells and the tumor's microenvironment. By secreting EVs, containing immune-inhibiting cytokines, AML cells inactivate the immune system against malignant cells, thus ensuring their survival. Also, increased secretion of EVs in various malignancies indicates an unfavorable prognostic factor and the possibility of drug resistance. In this study, we briefly reviewed the challenges of treating AML with a glance at the EVs' role in this process. It is hoped that with a deeper understanding of EVs, new therapies will be developed to eliminate the relapse of leukemic cells.

Advances in understanding the role of P-gp in doxorubicin resistance: Molecular pathways, therapeutic strategies, and prospects

P-glycoprotein (P-gp) is a drug efflux transporter that triggers doxorubicin (DOX) resistance. In this review, we highlight the molecular avenues regulating P-gp, such as Nrf2, HIF-1α, miRNAs, and long noncoding (lnc)RNAs, to reveal their participation in DOX resistance. These antitumor compounds and genetic tools synergistically reduce P-gp expression. Furthermore, ATP depletion impairs P-gp activity to enhance the antitumor activity of DOX. Nanoarchitectures, including liposomes, micelles, polymeric nanoparticles (NPs), and solid lipid nanocarriers, have been developed for the co-delivery of DOX with anticancer compounds and genes enhancing DOX cytotoxicity. Surface modification of nanocarriers, for instance with hyaluronic acid (HA), can promote selectivity toward cancer cells. We discuss these aspects with a focus on P-gp expression and activity.

Transcriptional Regulation by the NFAT Family in Acute Myeloid Leukaemia

Acute myeloid leukaemia (AML) is a haematological cancer with poor outcomes due to a lack of efficacious targeted therapies. The Nuclear Factor of Activated T Cells (NFAT) family of transcription factors is well characterised as a regulator of the cell cycle and differentiation in the myeloid lineage. Recent evidence has demonstrated that NFAT family members may have roles in regulating AML leukemogenesis and resistance to targeted therapy in myeloid leukaemia. Furthermore, gene expression data from patient samples show that some NFATs are more highly expressed in poorly differentiated AML and after disease relapse, implying that the NFAT family may have roles in specific types of AML. This review outlines the evidence for the role of NFAT in healthy myeloid tissue and explores how NFAT might regulate AML pathogenesis, highlighting the potential to target specific NFAT proteins therapeutically in AML.

The Evolving AML Genomic Landscape: Therapeutic Implications

Improved understanding of the genomic and molecular landscape of acute myeloid leukemia (AML) has resulted in a significant evolution of our understanding of AML biology and allows refined prognostication for those receiving standard combination chemotherapy induction. This dramatic increase in knowledge preceded, and was somewhat responsible for, at least some of eight new FDA drug approvals for AML. This review discusses the impact of genomics on clinical care of AML patients and highlights newly approved FDA drugs. Despite these recent clinical advances, however, the outcome for most patients diagnosed with AML remains dire. Thus, we describe here some of the challenges identified with treating AML including off-target toxicity, drug transporters, clonal heterogeneity, and adaptive resistance, and some of the most promising opportunities for improved therapy.

Drug and Solute Transporters in Mediating Resistance to Novel Therapeutics in Multiple Myeloma

Multiple myeloma remains an incurable malignancy of plasma cells. Novel therapies, notably proteasome inhibitors and immunomodulatory drugs, have improved the survival of multiple myeloma patients; however, patients either present with, or develop resistance to, these therapies. Resistance to traditional chemotherapeutic agents can be caused by cellular drug efflux via adenosine triphosphate (ATP)-binding cassette (ABC) transporters, but it is still not clear whether these transporters mediate resistance to proteasome inhibitors and immunomodulatory drugs in multiple myeloma. Solute carrier (SLC) transporters also play a role in cancer drug resistance due to changes in cell homeostasis caused by their abnormal expression and changes in the solutes they transport. In this review, we evaluate resistance to novel therapies used to treat multiple myeloma, as mediated by drug and solute transporters.

Discovery of Encequidar, First-in-Class Intestine Specific P-glycoprotein Inhibitor

Many chemotherapeutics, such as paclitaxel, are administered intravenously as they suffer from poor oral bioavailability, partly because of efflux mechanism of P-glycoprotein in the intestinal epithelium. To date, no drug has been approved by the U.S. Food and Drug Administration (FDA) that selectively blocks this efflux pump. We sought to identify a compound that selectively inhibits P-glycoprotein in the gastrointestinal mucosa with poor oral bioavailability, thus eliminating the issues such as bone marrow toxicity associated with systemic inhibition of P-glycoprotein. Here, we describe the discovery of highly potent, selective, and poorly orally bioavailable P-glycoprotein inhibitor 14 (encequidar). Clinically, encequidar was found to be well tolerated and minimally absorbed; and importantly, it enabled the oral delivery of paclitaxel.

Update on drug transporter proteins in acute myeloid leukemia: Pathological implication and clinical setting

Acute myeloid leukemia (AML) is one of the most common hematological neoplasia causing death worldwide. The long-term overall survival is unsatisfactory due to many factors including older age, genetic heterogeneity and molecular characteristics comprising additional mutations, and resistance to chemotherapeutic drugs. The expression of ABCB1/P-glycoprotein, ABCC1/MRP1, ABCG2/BCRP and LRP transporter proteins is considered the major reason for multidrug resistance (MDR) in AML, however conflicting data have been reported. Here, we review the main issues about drug transporter proteins in AML clinical scenario, and highlight the clinicopathological significance of MDR phenotype associated with ABCB1 polymorphisms and FLT3 mutation.

Genomic stability at the coding regions of the multidrug transporter gene ABCB1: insights into the development of alternative drug resistance mechanisms in human leukemia cells

AIM

Despite considerable efforts to reverse clinical multidrug resistance (MDR), targeting the predominant multidrug transporter ABCB1/P-glycoprotein (P-gp) using small molecule inhibitors has been unsuccessful, possibly due to the emergence of alternative drug resistance mechanisms. However, the non-specific P-gp inhibitor cyclosporine (CsA) showed significant clinical benefits in patients with acute myeloid leukemia (AML), which likely represents the only proof-of-principle clinical trial using several generations of MDR inhibitors. Nevertheless, the mutational mechanisms that may underlie unsuccessful MDR modulation by CsA are not elucidated because of the absence of CsA-relevant cellular models. In this study, our aims were to establish CsA-resistant leukemia models and to examine the presence or absence of ABCB1 exonic mutations in these models as well as in diverse types of human cancer samples including AMLs.

METHODS

Drug-resistant lines were established by stepwise drug co-selection and characterized by drug sensitivity assay, rhodamine-123 accumulation, [3H]-labeled drug export, ABCB1 cDNA sequencing, and RNase protection assay. The genomic stability of the ABCB1 coding regions was evaluated by exome sequencing analysis of variant allele frequencies in human populations. Moreover, the mutational spectrum of ABCB1 was further assessed in diverse types of cancer samples including AMLs in the Cancer Genome Atlas (TCGA) at the National Cancer Institute.

RESULTS

We report the development of two erythroleukemia variants, RVC and RDC, which were derived by stepwise co-selection of K562/R7 drug-resistant leukemia cells with the etoposide-CsA and doxorubicin-CsA drug combinations, respectively. Interestingly, both RVC and RDC cell lines, which retained P-gp expression, showed altered multidrug-resistant phenotypes that were resistant to CsA modulation. Strikingly, no mutations were found in the ABCB1 coding regions in these variant cells even under long-term stringent drug selection. Genomically, ABCB1 displayed relatively low variant allele frequencies in human populations when compared with several ABC superfamily members. Moreover, ABCB1 also exhibited a very low mutational frequency in AMLs compared with all types of human cancer. In addition, we found that CsA played a role in undermining the selection of highly drug-resistant cells via induction of low-level and unstable drug resistance.

CONCLUSION

Our data indicate that ABCB1 coding regions are genomically stable and relatively resistant to drug-induced mutations. Non-ABCB1 mutational mechanisms are responsible for the drug-resistant phenotypes in both RVC and RDC cell lines, which are also prevalent in clinical AML patients. Accordingly, we propose several relevant models that account for the development of alternative drug resistance mechanisms in the absence of ABCB1 mutations.

Association of Patient Demographic Characteristics and Insurance Status With Survival in Cancer Randomized Clinical Trials With Positive Findings

IMPORTANCE

Few new treatments tested in phase 3 cancer randomized clinical trials show an overall survival benefit. Although understanding whether the benefits are consistent among all patient groups is critical for informing guideline care, individual trials are designed to assess the benefits of experimental treatments among all patients and are too small to reliably determine whether treatment benefits apply to demographic or insurance subgroups.

OBJECTIVE

To systematically examine whether positive treatment effects in cancer randomized clinical trials apply to specific demographic or insurance subgroups.

DESIGN, SETTING, AND PARTICIPANTS

Cohort study of pooled patient-level data from 10 804 patients in SWOG Cancer Research Network clinical treatment trials reported from 1985 onward with superior overall survival for those receiving experimental treatment. Patients were enrolled from 1984 to 2012. Maximum follow-up was 5 years.

MAIN OUTCOMES AND MEASURES

Interaction tests were used to assess whether hazard ratios (HRs) for death comparing standard group vs experimental group treatments were associated with age (≥65 vs <65 years), race/ethnicity (minority vs nonminority populations), sex, or insurance status among patients younger than 65 years (Medicaid or no insurance vs private insurance) in multivariable Cox regression frailty models. Progression- or relapse-free survival was also examined. Data analyses were conducted from August 2019 to February 2020.

RESULTS

In total, 19 trials including 10 804 patients were identified that reported superior overall survival for patients randomized to experimental treatment. Patients were predominantly younger than 65 years (67.3%) and female (66.3%); 11.4% were black patients, and 5.7% were Hispanic patients. There was evidence of added survival benefits associated with receipt of experimental therapy for all groups except for patients with Medicaid or no insurance (HR, 1.23; 95% CI, 0.97-1.56; P = .09) compared with those with private insurance (HR, 1.66; 95% CI, 1.44-1.92; P < .001; P = .03 for interaction). Receipt of experimental treatment was associated with reduced added overall survival benefits in patients 65 years or older (HR, 1.21; 95% CI, 1.11-1.32; P < .001) compared with patients younger than 65 years (HR, 1.41; 95% CI, 1.30-1.53; P < .001; P = .01 for interaction), although both older and younger patients appeared to strongly benefit from receipt of experimental treatment. The progression- or relapse-free survival HRs did not differ by age, sex, or race/ethnicity but differed between patients with Medicaid or no insurance (HR, 1.32; 95% CI, 1.06-1.64; P = .01) vs private insurance (HR, 1.74; 95% CI, 1.54-1.97; P < .001; P = .03 for interaction).

CONCLUSIONS AND RELEVANCE

Patients with Medicaid or no insurance may have smaller added benefits from experimental therapies compared with standard treatments in clinical trials. A better understanding of the quality of survivorship care that patients with suboptimal insurance receive, including supportive care and posttreatment care, could help establish how external factors may affect outcomes for these patients.

Perplexing Role of P-Glycoprotein in Tumor Microenvironment

Development of multidrug resistance (MDR) still remains a major obstacle to the long-term success of cancer therapy. P-glycoprotein (P-gp) is a well-identified membrane transporter with capability to efflux drug molecules out of the cancer cell leading to reduced efficiency of chemotherapy. Cancer cells upregulate P-gp expression as an adaptive response to evade chemotherapy mediated cell death. While several P-gp inhibitors have been discovered by in silico and pre-clinical studies, very few have successfully passed all phases of the clinical trials. Studies show that application of P-gp inhibitors in cancer therapy regimen following development of MDR achieved limited beneficial outcomes. While, the non-specific substrate binding to P-gp has made the drug-design a challenge, a bigger perplexing challenge comes from its role in tumor immunology. Expression of P-gp was noted immune cell phenotypes with apparently antagonistic functionality. Both pro-tumor MΦ2-macrophages and, anti-tumor NK-cell and Th17/CD4⁺T cell subsets have shown enhanced expression of P-gp. While drug based inhibition of P-gp in pro-tumor immune cell phenotypes could promote tumor elimination, however, it would not be a rational choice to exert inhibition of P-gp on anti-tumor immune cell phenotypes. This mutually exclusive paradigm of P-gp functionality requires a more comprehensive and detailed understanding of its role in tumor microenvironment with active interplay of cancer and immune cells in the tumor mileu. In this review, we focus on the current understanding of the role of P-gp in cancer cells and immune cells and finally attempt to highlight some caveats in the current understanding of its role in comprehensive tumor microenvironment along with challenges in the development of P-gp inhibitors toward anti-cancer therapy.

Optimizing Targeted Inhibitors of P-Glycoprotein Using Computational and Structure-Guided Approaches

Overexpression of ABC transporters like P-glycoprotein (P-gp) has been correlated with resistances in cancer chemotherapy. Intensive efforts to identify P-gp inhibitors for use in combination therapy have not led to clinically approved inhibitors to date. Here, we describe computational approaches combined with structure-based design to improve the characteristics of a P-gp inhibitor previously identified by us. This hit compound represents a novel class of P-gp inhibitors that specifically targets and inhibits P-gp ATP hydrolysis while not being transported by the pump. We describe here a new program for virtual chemical synthesis and computational assessment, ChemGen, to produce hit compound variants with improved binding characteristics. The chemical syntheses of several variants, efficacy in reversing multidrug resistance in cell culture, and biochemical assessment of the inhibition mechanism are described. The usefulness of the computational predictions of binding characteristics of the inhibitor variants is discussed and compared to more traditional structure-based approaches.

Achillin Increases Chemosensitivity to Paclitaxel, Overcoming Resistance and Enhancing Apoptosis in Human Hepatocellular Carcinoma Cell Line Resistant to Paclitaxel (Hep3B/PTX)

Multidrug resistance (MDR) has become a major obstacle in the treatment of cancer, and is associated with mechanisms such as increased drug outflow, reduction of apoptosis, and/or altered drug metabolism. These problems can be mitigated by the coadministration of agents known as chemosensitizers, as they can reverse resistance to anticancer drugs and eventually resensitize cancer cells. We explore the chemosensitizing effect of Achillin, a guaianolide-type sesquiterpene lactone isolated from the Mexican medicinal plant Artemisia ludovisiana, to reverse MDR in Hep3B/PTX cells of hepatocellular carcinoma, which present resistance to paclitaxel (PTX). Achillin showed an important effect as chemosensitizer; indeed, the cytotoxic effect of PTX (25 nM) was enhanced, and the induction of G2/M phase cell cycle arrest and apoptosis were potentiated when combining with Achillin (100 μM). In addition, we observed that Achillin decreases P-gp levels and increases the intracellular retention of doxorubicin in Hep3B/PTX cells; in addition, homology structural modeling and molecular docking calculations predicted that Achillin interacts in two regions (M-site and R-site) of transporter drug efflux P-glycoprotein (P-gp). Our results suggest that the chemosensitizer effect demonstrated for Achillin could be associated with P-gp modulation. This work also provides useful information for the development of new therapeutic agents from guaianolide-type sesquiterpene lactones like Achillin.

Clinical Significance of ABCB1 in Acute Myeloid Leukemia: A Comprehensive Study

ABCB1 is a member of the ATP binding cassette transporter family and high ABCB1 activity is considered as a poor prognostic factor in acute myeloid leukemia (AML) treated with intensive chemotherapy, its direct relation with drug resistance remains unclear. We evaluated ABCB1 activity in relation with clinical parameters and treatment response to standard chemotherapy in 321 patients with de novo AML. We assessed multiple clinical relationships of ABCB1 activity—ex vivo drug resistance, gene expression, and the ABCB1 inhibitor quinine were evaluated. ABCB1 activity was observed in 58% of AML and was linked to low white blood cell count, high expression of CD34, absence of FLT3-ITD, and absence of mutant NPM1. Moreover, ABCB1 activity was associated with worse overall- and event-free survival. However, ABCB1 activity did not directly lead to ex vivo drug resistance to anthracyclines. We found that ABCB1 was highly correlated with gene expressions of BAALC, CD34, CD200, and CD7, indicating that ABCB1 expression maybe a passenger characteristic of high-risk AML. Furthermore, ABCB1 was inversely correlated to HOX cluster genes and CD33. Thus, low ABCB1 AML patients benefited specifically from anti-CD33 treatment by gemtuzumab ozogamicin in addition to standard chemotherapy. We showed prognostic importance of ABCB1 gene expression, protein expression, and activity. Furthermore, ABCB1 was not directly linked to drug resistance, ABCB1 inhibition did not improve outcome of high ABCB1 AML patients and thus high ABCB1 may represent a passenger characteristic of high-risk AML.

Valspodar-modulated chemotherapy in human ovarian cancer cells SK-OV-3 and MDAH-2774

Overcoming drug resistance in ovarian cancer is the overarching goal in gynecologic oncology. One way to increase drug cytotoxicity without increasing the drug dose is to simultaneously apply multidrug resistance modulator. Valspodar is the second generation P-glycoprotein 1 modulator capable of reversing multidrug resistance in different cancers. In this study, we evaluated the effect of valspodar and cisplatin co-treatment on cell viability, cell death and oxidative status in ovarian cancer cells. Two human ovarian cancer cell lines SK-OV-3 and MDAH-2774 were treated with cisplatin, valspodar, or cisplatin + valspodar for 24 or 48 hours. Untreated cells were used as control group. Cell viability was evaluated by MTT assay. Cell death was assessed by TUNEL and comet assay. Lipid peroxidation (malondialdehyde) and protein thiol groups were analyzed as oxidative stress markers. The expression of mitochondrial superoxide dismutase (MnSOD) was assessed by immunocytochemistry. Valspodar effectively reduced the resistance of SK-OV-3 cells to cisplatin, as demonstrated by increased oxidative stress, decreased cell viability and increased apoptosis in SK-OV-3 cells co-treated with valspodar and cisplatin compared to other groups. However, valspodar did not significantly affect the resistance of MDAH-2774 cells to cisplatin. Stronger staining for MnSOD in MDAH-2774 vs. SK-OV-3 cells after co-treatment with cisplatin and valspodar may determine the resistance of MDAH-2774 cell line to cisplatin.

Copenhagen Head Injury Ciclosporin Study: A Phase IIa Safety, Pharmacokinetics, and Biomarker Study of Ciclosporin in Severe Traumatic Brain Injury Patients

Traumatic brain injury (TBI) contributes to almost one third of all trauma-related deaths, and those that survive often suffer from long-term physical and cognitive deficits. Ciclosporin (cyclosporine, cyclosporin A) has shown promising neuroprotective properties in pre-clinical TBI models. The Copenhagen Head Injury Ciclosporin (CHIC) study was initiated to establish the safety profile and pharmacokinetics of ciclosporin in patients with severe TBI, using a novel parenteral lipid emulsion formulation. Exploratory pharmacodynamic study measures included microdialysis in brain parenchyma and protein biomarkers of brain injury in the cerebrospinal fluid (CSF). Sixteen adult patients with severe TBI (Glasgow Coma Scale 4–8) were included, and all patients received an initial loading dose of 2.5 mg/kg followed by a continuous infusion for 5 days. The first 10 patients received an infusion dosage of 5 mg/kg/day whereas the subsequent 6 patients received 10 mg/kg/day. No mortality was registered within the study duration, and the distribution of adverse events was similar between the two treatment groups. Pharmacokinetic analysis of CSF confirmed dose-dependent brain exposure. Between- and within-patient variability in blood concentrations was limited, whereas CSF concentrations were more variable. The four biomarkers, glial fibrillary acidic protein, neurofilament light, tau, and ubiquitin carboxy-terminal hydrolase L1, showed consistent trends to decrease during the 5-day treatment period, whereas the samples taken on the days after the treatment period showed higher values in the majority of patients. In conclusion, ciclosporin, as administered in this study, is safe and well tolerated. The study confirmed that ciclosporin is able to pass the blood–brain barrier in a TBI population and provided an initial biomarker-based signal of efficacy.

Resistance of t(17;19)-acute lymphoblastic leukemia cell lines to multiagents in induction therapy

t(17;19)(q21‐q22;p13), responsible for TCF3‐HLF fusion, is a rare translocation in childhood B‐cell precursor acute lymphoblastic leukemia(BCP‐ALL). t(1;19)(q23;p13), producing TCF3‐PBX1 fusion, is a common translocation in childhood BCP‐ALL. Prognosis of t(17;19)‐ALL is extremely poor, while that of t(1;19)‐ALL has recently improved dramatically in intensified chemotherapy. In this study, TCF3‐HLF mRNA was detectable at a high level during induction therapy in a newly diagnosed t(17;19)‐ALL case, while TCF3‐PBX1 mRNA was undetectable at the end of induction therapy in most newly diagnosed t(1;19)‐ALL cases. Using 4 t(17;19)‐ALL and 16 t(1;19)‐ALL cell lines, drug response profiling was analyzed. t(17;19)‐ALL cell lines were found to be significantly more resistant to vincristine (VCR), daunorubicin (DNR), and prednisolone (Pred) than t(1;19)‐ALL cell lines. Sensitivities to three (Pred, VCR, and l‐asparaginase [l‐Asp]), four (Pred, VCR, l‐Asp, and DNR) and five (Pred, VCR, l‐Asp, DNR, and cyclophosphamide) agents, widely used in induction therapy, were significantly poorer for t(17;19)‐ALL cell lines than for t(1;19)‐ALL cell lines. Consistent with poor responses to VCR and DNR, gene and protein expression levels of P‐glycoprotein (P‐gp) were higher in t(17;19)‐ALL cell lines than in t(1;19)‐ALL cell lines. Inhibitors for P‐gp sensitized P‐gp‐positive t(17;19)‐ALL cell lines to VCR and DNR. Knockout of P‐gp by CRISPRCas9 overcame resistance to VCR and DNR in the P‐gp‐positive t(17;19)‐ALL cell line. A combination of cyclosporine A with DNR prolonged survival of NSG mice inoculated with P‐gp‐positive t(17;19)‐ALL cell line. These findings indicate involvement of P‐gp in resistance to VCR and DNR in Pgp positive t(17;19)‐ALL cell lines. In all four t(17;19)‐ALL cell lines, RAS pathway mutation was detected. Furthermore, among 16 t(1;19)‐ALL cell lines, multiagent resistance was usually observed in the cell lines with RAS pathway mutation in comparison to those without it, suggesting at least a partial involvement of RAS pathway mutation in multiagent resistance of t(17;19)‐ALL.

Metabolic and non-metabolic pathways that control cancer resistance to anthracyclines

Anthracyclines Doxorubicin, Epirubicin, Daunorubicin and Idarubicin are used to treat a variety of tumor types in the clinics, either alone or, most often, in combination therapies. While their cardiotoxicity is well known, the emergence of chemoresistance is also a major issue accounting for treatment discontinuation. Resistance to anthracyclines is associated to the acquisition of multidrug resistance conferred by overexpression of permeability glycoprotein-1 or other efflux pumps, by altered DNA repair, changes in topoisomerase II activity, cancer stemness and metabolic adaptations. This review further details the metabolic aspects of resistance to anthracyclines, emphasizing the contributions of glycolysis, the pentose phosphate pathway and nucleotide biosynthesis, glutathione, lipid metabolism and autophagy to the chemoresistant phenotype.

Daunorubicin and cytarabine for certain types of poor-prognosis acute myeloid leukemia: a systematic literature review

INTRODUCTION

Induction chemotherapy based on anthracyclines and cytarabine (Ara-C) combination remains the standard of care for acute myeloid leukemia (AML) patients who are considered candidate for intensive and curative approaches. However, the toxicity of this regimen is high, with disappointing clinical outcomes among the so-called poor-prognosis AML subsets, which generally refer to patients with adverse cytogenetic risk, secondary AML including therapy-related AML, poor-prognosis mutations, especially FLT3-ITD, and relapse/refractory AML. Areas covered: To the best of our knowledge, the role and efficacy of 7 + 3 schedules containing daunorubicin (DNR) and Ara-C for certain types of poor-prognosis AML has not been systematically assessed. A critical approach to the role of DNR and Ara-C induction could be relevant to establish which patients should be enrolled in clinical trials using novel therapies. Expert commentary: In this regard, a recent randomized clinical trial (RCT) showed improved results in older patients with sAML or high-risk cytogenetics who received CPX-351 compared with standard 7 + 3 combination. We perform a systematic literature review to analyze the clinical outcomes reported with DNR plus Ara-C regimens in adult patients with poor-prognosis AML, the use of liposomal formulations of DNR and Ara-C and the RCTs which compared standard 7 + 3 with the addition of a third drug.

Analogues of the Lignan Pinoresinol as Novel Lead Compounds for P-glycoprotein (P-gp) Inhibitors

To find novel P-gp-inhibitors, a library of pregnane X receptor (PXR) ligands and the ZINC DrugsNow library were superimposed on the P-gp inhibitor (+)-pinoresinol (1) used as a query for a three-dimensional similarity search. After determining the TanimotoCombo index of similarity with 1, eight compounds from the PXR library and two ZINC compounds were selected for biological evaluation. The P-gp inhibition study showed that compounds 7, 8, and 9 successfully increased intracellular doxorubicin (DOX) accumulation in the P-gp overexpressed Lucena 1 cells from 25, 12.5, and 6.25 μM, respectively. Among a series of analogues of 9, compounds 26-30 were shown to be active, with 26 and 27 causing a significant increase in DOX accumulation from 1.56 μM and rendering Lucena 1 sensitive to DOX from 1.56 and 0.78 μM, respectively. Molecular modeling studies showed that both compounds bind to the P-gp at transmembrane helices (TMH) 4, 5, and 6, with 27 also showing contacts with TMH 3.

Evidence of a role for functional heterogeneity in multidrug resistance transporters in clinical trials of P-glycoprotein modulation in acute myeloid leukemia

BACKGROUND

Multidrug resistance (MDR) transporter proteins such as P-glycoprotein (P-gp) efflux a variety of chemotherapeutic drugs from acute myeloid leukemia (AML) blasts leading to clinical drug resistance.

METHODS

This study examined heterogeneity of MDR functional efflux by AML blasts using two flow cytometry bioassays. Bone marrow specimens (N = 50) from elderly patients with newly diagnosed AML were analyzed for CD34+ blasts with MDR efflux function. Efflux was measured with a fluorescent dye (DiOC₂ ) as a surrogate for oncology drugs that are substrates for MDR efflux. P-gp-mediated efflux was differentiated from non-P-gp MDR activities using zosuquidar, a highly selective P-gp modulator. The bioassays included a zosuquidar-dependent DiOC₂ accumulation bioassay that measured only P-gp. The second method, termed the efflux bioassay, could detect P-gp and other non-P-gp efflux depending on bioassay culture conditions.

RESULTS

Sixty-two percent of the specimens were considered positive for blasts with P-gp function, and 26% of such P-gp-positive specimens also exhibited zosuquidar-resistant (i.e., non-P-gp) MDR efflux activity; 37% of P-gp-negative AML blast specimens displayed zosuquidar-resistant MDR function in the efflux bioassay.

CONCLUSIONS

These results confirm the heterogeneous nature of MDR efflux pumps in AML blasts, and provide support for the hypothesis that non-P-gp MDR contributed to negative results with zosuquidar in AML trials like ECOG-ACRIN E3999. © 2018 International Clinical Cytometry Society.

MDR1 in immunity: friend or foe?

MDR1 is an ATP-dependent transmembrane transporter primarily studied for its role in the detoxification of tissues and for its implication in resistance of tumor cells to chemotherapy treatment. Several studies also report on its expression on immune cells where it plays a protective role from xenobiotics and toxins. This review provides an overview of what is known on MDR1 expression in immune cells in human, and its implications in different pathologies and their treatment options.

Revisiting the role of ABC transporters in multidrug-resistant cancer

Most patients who die of cancer have disseminated disease that has become resistant to multiple therapeutic modalities. Ample evidence suggests that the expression of ATP-binding cassette (ABC) transporters, especially the multidrug resistance protein 1 (MDR1, also known as P-glycoprotein or P-gp), which is encoded by ABC subfamily B member 1 (ABCB1), can confer resistance to cytotoxic and targeted chemotherapy. However, the development of MDR1 as a therapeutic target has been unsuccessful. At the time of its discovery, appropriate tools for the characterization and clinical development of MDR1 as a therapeutic target were lacking. Thirty years after the initial cloning and characterization of MDR1 and the implication of two additional ABC transporters, the multidrug resistance-associated protein 1 (MRP1; encoded by ABCC1)), and ABCG2, in multidrug resistance, interest in investigating these transporters as therapeutic targets has waned. However, with the emergence of new data and advanced techniques, we propose to re-evaluate whether these transporters play a clinical role in multidrug resistance. With this Opinion article, we present recent evidence indicating that it is time to revisit the investigation into the role of ABC transporters in efficient drug delivery in various cancer types and at the blood-brain barrier.

Acute Myeloid Leukemia: The Good, the Bad, and the Ugly

Acute myeloid leukemia (AML) was initially subdivided according to morphology (the French-American-British system), which proved helpful in pathologic categorization. Subsequently, clinical and genomic factors were found to correlate with response to chemotherapy and with overall survival. These included a history of antecedent hematologic disease, a history of chemotherapy or radiation therapy, the presence of various recurrent cytogenetic abnormalities, and, more recently, the presence of specific point mutations. This article reviews the biology and responses of one AML subgroup with consistent response and good outcomes following chemotherapy (core-binding factor leukemia), and two subgroups with persistently bad, and even ugly, outcomes (secondary AML and TP53-mutated AML).

Knockdown of the Wnt receptor Frizzled-1 (FZD1) reduces MDR1/P-glycoprotein expression in multidrug resistant leukemic cells and inhibits leukemic cell proliferation

Multidrug resistance (MDR) is a major obstacle to leukemia treatment. The Frizzled-1 (FZD1) Wnt receptor is involved in MDR in some solid cancers, but has rarely been reported to act in acute myeloid leukemia (AML). We investigated whether the knockdown of FZD1 affects MDR1 expression and P-glycoprotein (P-gp) function in multidrug resistant leukemic cell lines, as well as FZD1 and MDR1/P-gp expression in leukemic cells taken from patients with AML (n = 112). FZD1 knockdown significantly reduced MDR1 expression through the Wnt/β-catenin pathway, disrupted the P-gp efflux function, induced the recovery of sensitivity to chemotherapeutic agents, and hindered cell proliferation in cell lines. FZD1 expression in leukemic cells was significantly higher in patients experiencing relapse (n = 34) than in those with no relapse (n = 44, P = .003). Leukemic cells unable to achieve complete response (CR) showed an increased expression of MDR1 and P-gp, compared to patients who achieved CR. Obtaining CR in patients with higher FZD1 expression at diagnosis is difficult. Moreover, they tend to present instances of relapse, suggesting that AML cells with increased FZD1 expression are resistant to chemotherapy. We conclude that the activated FZD1 observed in leukemic cells likely confers acquired drug resistance, whereas FZD1 silencing may be more effective in reversing MDR.

Targeted inhibitors of P-glycoprotein increase chemotherapeutic-induced mortality of multidrug resistant tumor cells

Overexpression of ATP-binding cassette (ABC) transporters is often linked to multidrug resistance (MDR) in cancer chemotherapies. P-glycoprotein (P-gp) is one of the best studied drug transporters associated with MDR. There are currently no approved drugs available for clinical use in cancer chemotherapies to reverse MDR by inhibiting P-glycoprotein. Using computational studies, we previously identified several compounds that inhibit P-gp by targeting its nucleotide binding domain and avoiding its drug binding domains. Several of these compounds showed successful MDR reversal when tested on a drug resistant prostate cancer cell line. Using conventional two-dimensional cell culture of MDR ovarian and prostate cancer cells and three dimensional prostate cancer microtumor spheroids, we demonstrated here that co-administration with chemotherapeutics significantly decreased cell viability and survival as well as cell motility. The P-gp inhibitors were not observed to be toxic on their own. The inhibitors increased cellular retention of chemotherapeutics and reporter compounds known to be transport substrates of P-gp. We also showed that these compounds are not transport substrates of P-gp and that two of the three inhibit P-gp, but not the closely related ABC transporter, ABCG2/BCRP. The results presented suggest that these P-gp inhibitors may be promising leads for future drug development.

Inhibit or Evade Multidrug Resistance P-Glycoprotein in Cancer Treatment

Multidrug resistance (MDR) is a major cause of failure in cancer chemotherapy. P-glycoprotein (P-gp), a promiscuous drug efflux pump, has been extensively studied for its association with MDR due to overexpression in cancer cells. Several P-gp inhibitors or modulators have been investigated in clinical trials in hope of circumventing MDR, with only limited success. Alternative strategies are actively pursued, such as the modification of existing drugs, development of new drugs, or combination of novel drug delivery agents to evade P-gp-dependent efflux. Despite the importance and numerous studies, these efforts have mostly been undertaken without a priori knowledge of how drugs interact with P-gp at the molecular level. This review highlights and discusses progress toward and challenges impeding drug development for inhibiting or evading P-gp in the context of our improved understanding of the structural basis and mechanism of P-gp-mediated MDR.

Intestinal P-glycoprotein inhibitors, benzoxanthone analogues

OBJECTIVES

The inhibitors of P-glycoprotein (P-gp) which limits an access of exogenous compounds in the luminal membrane of the intestine have been studied to enhance the intestinal P-gp-mediated absorption of anticancer drugs.

METHODS

Inhibition of the efflux pump by synthesized benzoxanthone derivatives was investigated in vitro and in vivo. MCF-7/ADR cell line was used for cytotoxicity assay and [³ H]-daunomycin (DNM) accumulation/efflux study. Eight benzoxanthone analogues were tested for their effects on DNM cytotoxicity. Among them, three analogues were selected for the accumulation/efflux and P-gp ATPase studies. Paclitaxel (PTX), a P-gp substrate anticancer drug, was orally administered to rats with/without compound 1 (8,10-bis(thiiran-2-ylmethoxy)-7H-benzo[c]xanthen-7-one). The pharmacokinetic parameters of PTX in the presence/absence of compound 1 were evaluated from the plasma concentration-time profiles.

KEY-FINDINGS

Compound 1 increased the DNA accumulation to 6.5-fold and decreased the DNM efflux to approximately 1/2 in the overexpressing P-gp cell line. Relative bioavailability (RB) of PTX in rats was significantly increased up to 3.2-fold by compound 1 (0.5 or 2 mg/kg).

CONCLUSIONS

Benzoxanthone analogue, compound 1 is strongly suggested to be a promising inhibitor of P-gp to improve an oral absorption of compounds for cancer therapy.

Impact of Specimen Heterogeneity on Biomarkers in Repository Samples from Patients with Acute Myeloid Leukemia: A SWOG Report

INTRODUCTION

Current prognostic models for acute myeloid leukemia (AML) are inconsistent at predicting clinical outcomes for individual patients. Variability in the quality of specimens utilized for biomarker discovery and validation may contribute to this prognostic inconsistency.

METHODS

We evaluated the impact of sample heterogeneity on prognostic biomarkers and methods to mitigate any adverse effects of this heterogeneity in 240 cryopreserved bone marrow and peripheral blood specimens from AML patients enrolled on SWOG (Southwest Oncology Group) trials.

RESULTS

Cryopreserved samples displayed a broad range in viability (37% with viabilities ≤60%) and nonleukemic cell contamination (13% with lymphocyte percentages >20%). Specimen viability was impacted by transport time, AML immunophenotype, and, potentially, patients' age. The viability and cellular heterogeneity in unsorted samples significantly altered biomarker results. Enriching for viable AML blasts improved the RNA quality from specimens with poor viability and refined results for both DNA and RNA biomarkers. For example, FLT3-ITD allelic ratio, which is currently utilized to risk-stratify AML patients, was on average 1.49-fold higher in the viable AML blasts than in the unsorted specimens.

CONCLUSION

To our knowledge, this is the first study to provide evidence that using cryopreserved specimens can introduce uncontrollable variables that may impact biomarker results and enrichment for viable AML blasts may mitigate this impact.

Graphene Quantum Dots Downregulate Multiple Multidrug-Resistant Genes via Interacting with Their C-Rich Promoters

Multidrug resistance (MDR) is the major factor in the failure of many forms of chemotherapy, mostly due to the increased efflux of anticancer drugs that mediated by ATP-binding cassette (ABC) transporters. Therefore, inhibiting ABC transporters is one of effective methods of overcoming MDR. However, high enrichment of ABC transporters in cells and their broad substrate spectra made to circumvent MDR are almost insurmountable by a single specific ABC transporter inhibitor. Here, this study demonstrates that graphene quantum dots (GQDs) could downregulate the expressions of P-glycoprotein, multidrug resistance protein MRP1, and breast cancer resistance protein genes via interacting with C-rich regions of their promoters. This is the first example that a single reagent could suppress multiple MDR genes, suggesting that it will be possible to target multiple ABC transporters simultaneously with a single reagent. The inhibitory ability of the GQDs to these drug-resistant genes is validated further by reversing the doxorubicin resistance of MCF-7/ADR cells. Notably, GQDs have superb chemical and physical properties, unique structure, low toxicity, and high biocompatibility; hence, their capability of inhibiting multiple drug-resistant genes holds great potential in cancer therapy.

What are the most promising new agents in acute myeloid leukemia?

PURPOSE OF REVIEW

Although the treatment paradigm for acute myeloid leukemia (AML) had been largely unchanged for many years, in-depth molecular characterization has revolutionized our understanding of mutations that drive the disease, subsequently serving to guide current clinical investigation. Furthermore, recent advances in the field have highlighted the importance of optimizing known efficacious agents by improving drug delivery or bypassing resistance mechanisms. The current status of novel agents which are shaping the clinical management of AML patients are summarized in this review.

RECENT FINDINGS

Practice changing findings over the past year include improved overall survival (OS) in a molecularly defined AML subgroup as well as in elderly patients with secondary AML (sAML). Specifically, synergistic combination of daunorubicin and cytarabine (i.e., CPX-351) was found to improve OS in sAML patients. Furthermore, although multiple mutation specific inhibitors have been developed, optimal combination with additional agents appears critical, as monotherapies have not resulted in durable remissions or improved outcomes. Improved OS via the addition of midostaurin to intensive chemotherapy in FLT3 mutant AML supports this concept.

SUMMARY

For the first time in AML, personalized therapy has become possible through improved understanding of the molecular architecture and survival pathways of an individual's disease. The landscape of AML treatment is encouraging, with multiple novel agents likely to gain approval over the next 5 years.

The Effect of Positive SWOG Treatment Trials on Survival of Patients With Cancer in the US Population

Importance

Recently, tremendous prominence has been given to the investigation of the effect of different research processes as part of the Cancer Moonshot. More than half a century ago, the National Cancer Institute (NCI) established a network of publicly funded cancer cooperative research groups to systematically evaluate new treatments for efficacy and safety.

Objective

To examine the extent to which positive NCI-sponsored cancer treatment trials have benefited patients with cancer in the US population.

Design, Setting, and Participants

This investigation used study data from SWOG, an NCI-sponsored network cooperative research group. All treatment trials during SWOG's 60-year history (1956-2016) were identified for which the new, experimental therapy provided a statistically significant improvement in overall survival. It was assumed that the new, proven treatments from these trials established new standards for cancer care in the treatment community. Twenty-three positive SWOG treatment trials were identified from a variety of different disease settings.

Main Outcomes and Measures

This study estimated population life-years gained from the 23 treatment trials through 2015 by mapping the effect of the new treatments onto the US cancer population using an area under the Kaplan-Meier survival curve approach that combined trial-specific hazard function and hazard ratio results, along with Surveillance, Epidemiology, and End Results program and life table data. Calculations were age adjusted. The US dollar return on investment was estimated as the ratio of the total investment by the NCI in the treatment trial program divided by the estimate of life-years gained.

Results

In total, 12 361 patients were enrolled to the 23 positive trials from 1965 to 2012. The study estimated that 3.34 million (95% confidence limit, 2.39-4.15 million) life-years were gained from these 23 trials through 2015. Estimates were greater than 2 million life-years gained under most model simulations. The US dollar return on investment was $125 per life-year gained.

Conclusions and Relevance

SWOG treatment trials have had a substantial impact on population survival for patients with cancer over 60 years. The NCI's investment in its cancer cooperative group research program has provided exceptional value and benefit to the American public through its research programs generating positive cancer treatment trials.

Trial Registration

clinicaltrials.gov Identifiers: NCT00004001, NCT00075764, and NCT00644228.

Management of Acute Myelogenous Leukemia in the Elderly

BACKGROUND

Acute myelogenous leukemia (AML) is a hematopoietic neoplasm that primarily affects older adults. Despite scientific advances into the epidemiologic, genetic, and biological features of AML, this disease remains fatal to the majority of patients, particularly older individuals.

METHODS

We review the biologic and clinical characteristics of AML in the elderly and the treatment options that have emerged for them during the past several years.

RESULTS

Several biologic features of AML differ between older and younger individuals. Older patients often have disease that expresses multidrug resistance phenotype and cytogenetic abnormalities, which may be responsible in large part for the poor outcomes observed in older-aged subgroups. Traditional cytotoxic chemotherapy is associated with a low complete response rate and a high treatment-related mortality in older patients, which explains in part the poorer outcomes in cohorts over 60 years of age. Research into the pathophysiology of AML has revealed an abundance of intracellular signaling events that govern proliferation and survival of the malignant cell. Such discoveries have promoted recognition of new molecular and antigenic targets (eg, Flt-3 kinase, Ras, CD33 antigen) to which therapeutic development may be aimed.

CONCLUSIONS

New therapies directed against these unique targets may add to the current arsenal of antileukemic regimens and improve response rates and survival in older patients.

Reversal of ABCB1 mediated efflux by imatinib and nilotinib in cells expressing various transporter levels

Recently, it has been suggested that imatinib (IM) and nilotinib (NIL) could be studied beyond their original application, as inhibitors of the drug efflux pump ABCB1 (P-glycoprotein, MDR1). Since the reversal of ABCB1-mediated resistance has never been successfully demonstrated in the clinic, we addressed the question of whether IM and NIL may actually serve as efficient inhibitors of ABCB1. Here we define an efficient inhibitor as a compound that achieves full (90-100%) reversal of drug efflux at a concentration that does not exhibit significant off-target toxicity in vitro. In this study, human leukemia K562 cells expressing various levels of ABCB1 were used. We observed that cells expressing higher ABCB1 levels required higher concentrations of IM and NIL to achieve full reversal of drug efflux. Among the well-known ABCB1 inhibitors, a similar effect was found for cyclosporin A (CsA) but not for zosuquidar. IM was efficient only in cells with the low and moderate ABCB1 expression at high concentrations that were cytotoxic in the absence of Bcr-Abl. In contrast, NIL was as efficient an inhibitor of ABCB1 as CsA. Low and moderate expression levels of ABCB1 could be efficiently inhibited by NIL concentrations without cytotoxic effects in the absence of Bcr-Abl. However, high expression levels of ABCB1 required higher NIL concentrations with off-target cytotoxic effects. In conclusion, application of NIL, but not of IM, in clinics is promising, however, only in cells with low ABCB1 expression levels. We hypothesize that some patients may benefit from an inhibitor exhibiting an ABCB1 expression-dependent effect.

Mechanism Underlying the Reversal of Drug Resistance in P-Glycoprotein-Expressing Leukemia Cells by Pinoresinol and the Study of a Derivative

P-glycoprotein (P-gp) is a membrane protein associated with multidrug resistance (MDR) due to its key role in mediating the traffic of chemotherapeutic drugs outside cancer cells, leading to a cellular response that hinders efforts toward successful therapy. With the aim of finding agents that circumvent the MDR phenotype mediated by P-gp, 15 compounds isolated from native and naturalized plants of Argentina were screened. Among these, the non-cytotoxic lignan (±) pinoresinol successfully restored sensitivity to doxorubicin from 7 μM in the P-gp overexpressed human myelogenous leukemia cells, Lucena 1. This resistance-reversing effect was confirmed by competitively increasing the intracellular doxorubicin accumulation and by significantly inhibiting the efflux of doxorubicin and, to a lesser extent, that of rhodamine 123. The activity obtained was similar to that observed with verapamil. No such results were observed in the sensitive parental K562 cell line. To gain deeper insight into the mode of action of pinoresinol, its effect on P-gp function and expression was examined. The docking simulations indicated that the lignan bound to P-gp at the apex of the V-shaped transmembrane cavity, involving transmembrane helices 4, 5, and 6, and partially overlapped the binding region of tariquidar, which was used as a positive control. These results would shed some light on the nature of its interaction with P-gp at molecular level and merit further mechanistic and kinetic studies. In addition, it showed a maximum 29% activation of ATP hydrolysis and antagonized verapamil-stimulated ATPase activity with an IC₅₀ of 20.9 μM. On the other hand, pinoresinol decreased the presence of P-gp in the cell surface. Derivatives of pinoresinol with improved activity were identified by docking studies. The most promising one, the non-cytotoxic 1-acetoxypinoresinol, caused a reversion of doxorubicin resistance from 0.11 μM and thus higher activity than the lead compound. It also caused a significant increase in doxorubicin accumulation. Results were similar to those observed with verapamil. The results obtained positioned these compounds as potential candidates for effective agents to overcome P-gp-mediated MDR, leading to better outcomes for leukemia chemotherapy.