Polymorphisms in the multiple drug resistance protein 1 and in P-glycoprotein 1 are associated with time to event outcomes in patients with advanced multiple myeloma treated with bortezomib and pegylated liposomal doxorubicin

Genetic Polymorphisms Affecting Cardiac Biomarker Concentrations in Children with Cancer: an Analysis from the "European Paediatric Oncology Off-patents Medicines Consortium" (EPOC) Trial

BACKGROUND AND OBJECTIVES

Doxorubicin plays an essential role in the treatment of paediatric cancers. Defining genotypes with a higher risk for developing anthracycline-induced cardiotoxicity could help to reduce cardiotoxicity.

METHODS

Data originated from a phase II study assessing the pharmacokinetics of doxorubicin in 100 children. Studied patients (0-17 years) were treated for solid tumours or leukaemia. Two cycles of doxorubicin were studied. Concentrations of natriuretic peptides proANP, BNP and NT-proBNP and cardiac troponins T and I were measured at five time points before, during and after two cycles of doxorubicin treatment. Genotypes of 17 genetic polymorphisms in genes encoding for anthracycline metabolizing enzymes and drug transporters were determined for each patient. We analysed the influence of genotypes on cardiac biomarker concentrations at different time points by a Kruskal-Wallis test. To perform a pairwise comparison significant genetic polymorphisms with more than two genotypes were analysed by a post hoc test.

RESULTS

The Kruskal-Wallis tests and the post hoc-tests showed a significant association for seven genetic polymorphisms (ABCB1-rs1128503, ABCB1-rs1045642, ABCC1-rs4148350, CBR3-rs8133052, NQO2-in/del, SLC22A16-rs714368 and SLC22A16-rs6907567) with the concentration of at least one biomarker at one or more time points. We could not identify any polymorphism with a consistent effect on any biomarker over the whole treatment period.

CONCLUSIONS

In this study of patients treated with doxorubicin for different tumour entities, seven genetic polymorphisms possibly influencing the pharmacokinetics and pharmacodynamics of doxorubicin could lead occasionally to differences in the concentration of cardiac biomarkers. Since, the role of cardiac biomarkers for monitoring anthracycline-induced cardiotoxicity has not yet been clarified, further trials with a long follow-up time are required to assess the impact of these genetic polymorphisms on chemotherapy-related cardiotoxicity.

TRIAL REGISTRATION

EudraCT number: 2009-011454-17.

Role for Drug Transporters in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a common and dose-limiting toxicity to widely used chemotherapeutics. Although the exact molecular mechanism of chemotherapy-induced peripheral neuropathy remains elusive, there is consensus that it is caused by damage to the peripheral nervous system leading to sensory symptoms. Recently developed methodologies have provided evidence of expression of drug transporters in the peripheral nervous system. In this literature review, we explore the role for drug transporters in CIPN. First, we assessed the transport of chemotherapeutics that cause CIPN (taxanes, platins, vincristine, bortezomib, epothilones, and thalidomide). Second, we cross-referenced the transporters implicated in genetic or functional studies with CIPN with their expression in the peripheral nervous system. Several drug transporters are involved in the transport of chemotherapeutics that cause peripheral neuropathy and particularly efflux transporters, such as ABCB1 and ABCC1, are expressed in the peripheral nervous system. Previous literature has linked genetic variants in efflux transporters to higher risk of peripheral neuropathy with the taxanes paclitaxel and docetaxel and the vinca alkaloid vincristine. We propose that this might be due to accumulation of the chemotherapeutics in the peripheral nervous system due to reduced neuronal efflux capacity. Thus, concomitant administration of efflux transporter inhibitors may lead to higher risk of adverse events of drugs that cause CIPN. This might prove valuable in drug development where screening new drugs for neurotoxicity might also require drug transporter consideration. There are ongoing efforts targeting drug transporters in the peripheral nervous system to reduce intraneuronal concentrations of chemotherapeutics that cause CIPN, which might ultimately protect against this dose-limiting adverse event.

Multiple myeloma exploits Jagged1 and Jagged2 to promote intrinsic and bone marrow-dependent drug resistance

Multiple myeloma is still incurable due to an intrinsic aggressiveness or, more frequently, to the interactions of malignant plasma cells with the bone marrow (BM) microenvironment. Myeloma cells educate BM cells to support neoplastic cell growth, survival, acquisition of drug resistance resulting in disease relapse. Myeloma microenvironment is characterized by Notch signaling hyperactivation due to the increased expression of Notch1 and 2 and the ligands Jagged1 and 2 in tumor cells. Notch activation influences myeloma cell biology and promotes the reprogramming of BM stromal cells. In this work we demonstrate, in vitro, ex vivo and by using a zebrafish multiple myeloma model, that Jagged inhibition causes a decrease in both myeloma-intrinsic and stromal cell-induced resistance to currently used drugs, i.e. bortezomib, lenalidomide and melphalan. The molecular mechanism of drug resistance involves the chemokine system CXCR4/SDF1α. Myeloma cell-derived Jagged ligands trigger Notch activity in BM stromal cells. These, in turn, secrete higher levels of SDF1α in the BM microenvironment increasing CXCR4 activation in myeloma cells, which is further potentiated by the concomitant increased expression of this receptor induced by Notch activation. Consistently with the augmented pharmacological resistance, SDF1α boosts the expression of BCL2, Survivin and ABCC1. These results indicate that a Jagged-tailored approach may contribute to disrupting the pharmacological resistance due to intrinsic myeloma cell features or to the pathological interplay with BM stromal cells and, conceivably, improve patients' response to standard-of-care therapies.

Multiple Myeloma: Personalised Medicine Based on Pathogenesis

Multiple myeloma is increasingly being recognised as more than one disease, characterised by marked cytogenetic, molecular, and proliferative heterogeneity. The prognosis is widely varied, ranging from low to very high-risk, based on cytogenetic and molecular studies. Although novel agents, such as proteasome inhibitors and immunomodulators, have been developed, which have improved treatment responses and disease prognosis, multiple myeloma remains an incurable disease. Based on highly sensitive detection tools, such as gene expression profiling and next generation sequence analysis, and the understanding of the pathogenesis of multiple myeloma, many potential agents, including monoclonal antibodies, drug-conjugated antibodies, drugs targeted to molecular abnormalities, microRNA inhibitors or mimics, and immune therapies, such as chimeric antigen receptors T cells and anti-PD1 agents, can be considered personalised therapies. In this paper, multiple myeloma pathogenesis and potential molecular and immunotherapies are reviewed.

Protein targeting chimeric molecules specific for bromodomain and extra-terminal motif family proteins are active against pre-clinical models of multiple myeloma

Bromodomain and extraterminal (BET) domain containing protein (BRD)-4 modulates the expression of oncogenes such as c-myc, and is a promising therapeutic target in diverse cancer types. We performed pre-clinical studies in myeloma models with bi-functional protein-targeting chimeric molecules (PROTACs) which target BRD4 and other BET family members for ubiquitination and proteasomal degradation. PROTACs potently reduced the viability of myeloma cell lines in a time- and concentration-dependent manner associated with G₀/G₁ arrest, reduced levels of CDKs 4 and 6, increased p21 levels, and induction of apoptosis. These agents specifically decreased cellular levels of downstream BRD4 targets, including c-MYC and N-MYC, and a Cereblon-targeting PROTAC showed downstream effects similar to those of an immunomodulatory agent. Notably, PROTACs overcame bortezomib, dexamethasone, lenalidomide, and pomalidomide resistance, and their activity was maintained in otherwise isogenic myeloma cells with wild-type or deleted TP53. Combination studies showed synergistic interactions with dexamethasone, BH3 mimetics, and Akt pathway inhibitors. BET-specific PROTACs induced a rapid loss of viability of primary cells from myeloma patients, and delayed growth of MM1.S-based xenografts. Our data demonstrate that BET degraders have promising activity against pre-clinical models of multiple myeloma, and support their translation to the clinic for patients with relapsed and/or refractory disease.

Pharmacogenetic study of the impact of ABCB1 single-nucleotide polymorphisms on lenalidomide treatment outcomes in patients with multiple myeloma: results from a phase IV observational study and subsequent phase II clinical trial

PURPOSE

Despite therapeutic advances, patients with multiple myeloma (MM) continue to experience disease relapse and treatment resistance. The gene ABCB1 encodes the drug transporter P-glycoprotein, which confers resistance through drug extrusion across the cell membrane. Lenalidomide (Len) is excreted mainly via the kidneys, and, given the expression of P-gp in the renal tubuli, single-nucleotide polymorphisms (SNPs) in the ABCB1 gene may influence Len plasma concentrations and, subsequently, the outcome of treatment. We, therefore, investigated the influence of ABCB1 genetic variants on Len treatment outcomes and adverse events (AEs).

METHODS

Ninety patients with relapsed or refractory MM, who received the second-line Len plus dexamethasone in the Rev II trial, were genotyped for the ABCB1 SNPs 1199G>A (Ser400Asn, rs2229109), 1236C>T (silent, rs1128503), 2677G>T/A (Ala893Ser, rs2032582), and 3435C>T (silent, rs1045642) using pyrosequencing, and correlations to response parameters, outcomes, and AEs were investigated.

RESULTS

No significant associations were found between genotype and either best response rates or hematological AEs, and 1236C>T, 2677G>T or 3435C>T genotypes had no impact on survival. There was a trend towards increased time to progression (TTP) in patients carrying the 1199A variant, and a significant difference in TTP between genotypes in patients with standard-risk cytogenetics.

CONCLUSIONS

Our findings show a limited influence of ABCB1 genotype on lenalidomide treatment efficacy and safety. The results suggest that 1199G>A may be a marker of TTP following Len treatment in standard-risk patients; however, larger studies are needed to validate and clarify the relationship.

MDR1 polymorphisms affect the outcome of Chinese multiple myeloma patients

OBJECTIVE

To illustrate the association of MDR1 (Multidrug Resistance 1) polymorphisms at loci 1236, 2677, 3435 and the prognosis of multiple myeloma (MM) in Jiangsu population.

METHODS

A total of 129 MM patients were recruited from Jiangsu Province, China. The DNA was extracted from white blood cells (WBC) of peripheral blood and was amplified by polymerase chain reaction-allele specific primers (PCR-ASP). MDR1 polymorphisms at 3 loci were analyzed by electrophoresis followed by photograph or DNA direct sequencing. The association between the MDR1 and clinical outcomes were calculated by Graphpad and SPSS.

RESULTS

MDR1 alleles at locus C1236T with T had significant lower calcium level in MM patients compared with C. The genotype CT had a significantly prolonged progress free survival (PFS) compared genotype CC at locus C1236T (median time: 48 months vs. 28 months, respectively; p=0.0062; HR=0.21; 95%CI0.061-0.715) while patients carrying T allele (CT and TT) at locus C3435T had a longer PFS than patients without T allele (CC) (median time: 60 months vs. 29 months, respectively; p=0.038; HR=0.508; 95%CI 0.264-0.978). And a borderline significance was found in haplotype at loci 2677-3435 and PFS. No significant findings were revealed between OS and MDR1 polymorphisms.

CONCLUSION

MDR1 polymorphisms could affect the prognosis of multiple myeloma whereas more samples and a longer follow-up are also needed.

Effects of TNFα, NOS3, MDR1 Gene Polymorphisms on Clinical Parameters, Prognosis and Survival of Multiple Myeloma Cases

It is not clear how gene polymorphisms affecting drugs can contributes totheir efficacy in multiple myeloma (MM). We here aimed to explore associations among gene polymorphisms of tumor necrosis factor alpha (TNFα), nitric oxide synthesis 3 (NOS3) and multi-drug resistance 1 (MDR1), clinical parameters, prognosis and survival in MM patients treated with VAD (vincristine-adriamycine-dexamethasone), MP (mephalane-prednisolone), autolougus stem cell transplantation (ASCT), BODEC (bortezomib-dexamethasone-cyclophosphamide) and TD (thalidomide-dexamethasone). We analyzed TNFα, NOS 3 and MDR1 in 77 patients with MM and 77 healthy controls. The genotyping was performed with PCR and/or PCR-RFLP. There was no clinically significant difference between MM and control groups when TNF α(-238) and (-857) and MDR1 gene polymorphisms were studied. However, the TNFαgene polymorphism (-308) GG genotype (p=0.012) and NOS3 (+894) TT genotype (p=0.008) were more common in the MM group compared to healthy controls. NOS3 (VNTR) AA (p=0.007) and NOS3 (+894) GG genotypes (p=0.004) were decreased in the MM group in contrast. In conclusion, the NOS3 (+894) TT and TNF α(-308) GG genotypes may have roles in myeloma pathogenesis.

Efflux transporter variants as predictors of drug toxicity in lung cancer patients: systematic review and meta-analysis

Chemotherapeutic drugs are underutilized in lung cancer management due in part to serious adverse drug reactions (ADRs).

AIM

With studies revealing an association between interindividual patient ADR variation and efflux transporter variants, we carried out a meta-analysis and systemic review, in order to highlight current knowledge regarding the strength of association between efflux transporter SNPs variants and chemotherapeutic-drug induced ADRs.

MATERIALS & METHODS

Papers were sourced from MEDLINE, Cochrane Library, CINHL, EMBASE, Web of Knowledge, Scopus. The Cochrane Collaboration Risk of Bias Tool v13 was used to evaluate six types of bias domains for each of the publications reviewed.

RESULTS

Twenty-five publications comprising three randomised control trials, two retrospective case-controls and 20 clinical observation studies, totalling 3578 patients, were deemed eligible for review. Of the known efflux drug transporters, we report findings on the ABC members ABCB1, ABCC1, ABCC2, ABCG2, ABCA1, ABCC4 and ABCC5. Meta-analysis showed an decreased risk of irinotecan-induced neutropenia in patients expressing ABCB1 2677G>T/G (odds ratio [OR]: 0.24; 95% CI: 0.1-0.59; p = 0.002) but increased risk for ABCC2 3972T>T (OR: 1.67; 95% CI: 1.01-2.74; p = 0.04). ABCG2 34G>A was associated with a threefold increased risk of irinotecan-induced diarrhea (95% CI: 1.00-6.24; p = 0.05).

CONCLUSION

The majority of studies have identified a role for variants in effluxdrug transporters in contributing to lung cancer treatment-associated ADRs. However, for implementation of use of these transporter genetic variants as prognostic markers for ADR risk, future studies must incorporate larger patient numbers.

Multiple myeloma and persistence of drug resistance in the age of novel drugs (Review)

Multiple myeloma (MM) is a mature B cell neoplasm that results in multi-organ failure. The median age of onset, diverse clinical manifestations, heterogeneous survival rate, clonal evolution, intrinsic and acquired drug resistance have impact on the therapeutic management of the disease. Specifically, the emergence of multidrug resistance (MDR) during the course of treatment contributes significantly to treatment failure. The introduction of the immunomodulatory agents and proteasome inhibitors has seen an increase in overall patient survival, however, for the majority of patients, relapse remains inevitable with evidence that these agents, like the conventional chemotherapeutics are also subject to the development of MDR. Clinical management of patients with MM is currently compromised by lack of a suitable procedure to monitor the development of clinical drug resistance in individual patients. The current MM prognostic measures fail to pick the clonotypic tumor cells overexpressing drug efflux pumps, and invasive biopsy is insufficient in detecting sporadic tumors in the skeletal system. This review summarizes the challenges associated with treating the complex disease spectrum of myeloma, with an emphasis on the role of deleterious multidrug resistant clones orchestrating relapse.

CNS uptake of bortezomib is enhanced by P-glycoprotein inhibition: implications for spinal muscular atrophy

The development of therapeutics for neurological disorders is constrained by limited access to the central nervous system (CNS). ATP-binding cassette (ABC) transporters, particularly P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), are expressed on the luminal surface of capillaries in the CNS and transport drugs out of the endothelium back into the blood against the concentration gradient. Survival motor neuron (SMN) protein, which is deficient in spinal muscular atrophy (SMA), is a target of the ubiquitin proteasome system. Inhibiting the proteasome in a rodent model of SMA with bortezomib increases SMN protein levels in peripheral tissues but not the CNS, because bortezomib has poor CNS penetrance. We sought to determine if we could inhibit SMN degradation in the CNS of SMA mice with a combination of bortezomib and the ABC transporter inhibitor tariquidar. In cultured cells we show that bortezomib is a substrate of P-gp. Mass spectrometry analysis demonstrated that intraperitoneal co-administration of tariquidar increased the CNS penetrance of bortezomib, and reduced proteasome activity in the brain and spinal cord. This correlated with increased SMN protein levels and improved survival and motor function of SMA mice. These findings show that CNS penetrance of treatment for this neurological disorder can be improved by inhibiting drug efflux at the blood-brain barrier.

Mechanisms of Drug Resistance in Relapse and Refractory Multiple Myeloma

Multiple myeloma (MM) is a hematological malignancy that remains incurable because most patients eventually relapse or become refractory to current treatments. Although the treatments have improved, the major problem in MM is resistance to therapy. Clonal evolution of MM cells and bone marrow microenvironment changes contribute to drug resistance. Some mechanisms affect both MM cells and microenvironment, including the up- and downregulation of microRNAs and programmed death factor 1 (PD-1)/PD-L1 interaction. Here, we review the pathogenesis of MM cells and bone marrow microenvironment and highlight possible drug resistance mechanisms. We also review a potential molecular targeting treatment and immunotherapy for patients with refractory or relapse MM.

Carfilzomib: a second-generation proteasome inhibitor for the treatment of multiple myeloma

PURPOSE

The pharmacology, clinical efficacy, safety, cost, dosage and administration, and place in therapy of carfilzomib for the treatment of multiple myeloma (MM) are reviewed.

SUMMARY

Proteasome inhibition in MM has become a cornerstone in treatment regimens. Carfilzomib, a second-generation proteasome inhibitor, has demonstrated efficacy in patients with relapsed or refractory disease who have received at least two prior therapies including bortezomib and an immunomodulatory agent. Carfilzomib is an irreversible inhibitor and binds to a different site than bortezomib on the proteasome. A Phase II study evaluated 266 heavily pretreated patients with relapsed or refractory MM who had received at least two prior therapies, including bortezomib and either thalidomide or lenalidomide. The overall response rate was 23.7%, with a median duration of response of 7.8 months. The median overall survival time was 15.6 months. Carfilzomib has a similar adverse-effect profile to bortezomib, including anemia, thrombocytopenia, fatigue, dyspnea, and nausea; however, it does not result in the development or worsening of peripheral neuropathy. Carfilzomib is infused intravenously over 2-10 minutes for 2 consecutive days every week for three out of four weeks, with a 12-day rest period. Dosing is based on the patient's actual body surface area. Carfilzomib is available in 60-mg vials for single infusion. The total cost for a year of therapy is approximately $155,852.

CONCLUSION

Carfilzomib, a second-generation proteasome inhibitor that irreversibly inhibits the 26S proteasome, has shown efficacy in clinical studies of patients with relapsed or refractory MM, though the drug's role in the management of MM is not yet clear.

MRP1 and its role in anticancer drug resistance

The phenomenon of multidrug resistance (MDR) in cancer is associated with the overexpression of the ATP-binding cassette (ABC) transporter proteins, including multidrug resistance-associated protein 1 (MRP1) and P-glycoprotein. MRP1 plays an active role in protecting cells by its ability to efflux a vast array of drugs to sub-lethal levels. There has been much effort in elucidating the mechanisms of action, structure and substrates and substrate binding sites of MRP1 in the last decade. In this review, we detail our current understanding of MRP1, its clinical relevance and highlight the current environment in the search for MRP1 inhibitors. We also look at the capacity for the rapid intercellular transfer of MRP1 phenotype from spontaneously shed membrane vesicles known as microparticles and discuss the clinical and therapeutic significance of this in the context of cancer MDR.

Impact of ABCB1 single-nucleotide polymorphisms on treatment outcomes with salmeterol/fluticasone combination therapy for stable chronic obstructive pulmonary disease

OBJECTIVES

To investigate the relationship between ABCB1 single-nucleotide polymorphisms and the efficacy of salmeterol/fluticasone combination (SFC) inhalation therapy for stable chronic obstructive pulmonary disease (COPD) in a Chinese Han population.

METHODS

A total of 362 patients with stable COPD were recruited between July 2012 and March 2014. Based on the therapeutic effects of lung function improvement and COPD Assessment Test (CAT) scores, all patients were either placed into the effective group (n = 138) or the ineffective group (n = 224). Three common polymorphisms (rs1045642C > T, rs1128503C > T, and rs1202184A > G) in the ABCB1 gene were analyzed by polymerase chain reaction-restriction fragment length polymorphism in these patients. All data were analyzed by SPSS version 18.0 software.

RESULTS

The genotype and allele frequencies of the ABCB1 rs1045642C > T polymorphic locus were significantly different between the effective group and the ineffective group under the codominant, recessive, and allele models (all p < 0.05). Haplotype analysis of ABCB1 indicated that CTA (rs1045642C-rs1128503T-rs1202184A) haplotype frequencies in the effective group were significantly lower than the ineffective group (p = 0.022), but TCG (rs1045642T-rs1128503C-rs1202184G) haplotype frequencies in the effective group were significantly higher than the ineffective group (p = 0.048). Logistic regression analysis showed that smoking history and rs1045642 CT + CC/TT may be correlated with the efficacy of SFC inhalation therapy in stable COPD patients.

CONCLUSION

ABCB1 rs1045642C > T polymorphism and CTA/TCG haplotypes, as well as smoking history may influence the efficacy of SFC inhalation therapy in stable COPD patients in the Chinese Han population.

Molecular Classification and Pharmacogenetics of Primary Plasma Cell Leukemia: An Initial Approach toward Precision Medicine

Primary plasma cell leukemia (pPCL) is a rare and aggressive variant of multiple myeloma (MM) which may represent a valid model for high-risk MM. This disease is associated with a very poor prognosis, and unfortunately, it has not significantly improved during the last three decades. New high-throughput technologies have allowed a better understanding of the molecular basis of this disease and moved toward risk stratification, providing insights for targeted therapy studies. This knowledge, added to the pharmacogenetic profile of new and old agents in the analysis of efficacy and safety, could contribute to help clinical decisions move toward a precision medicine and a better clinical outcome for these patients. In this review, we describe the available literature concerning the genomic characterization and pharmacogenetics of plasma cell leukemia (PCL).

Characterisation of the clinical pharmacokinetics of actinomycin D and the influence of ABCB1 pharmacogenetic variation on actinomycin D disposition in children with cancer

Background and Objective

Despite its important role in cancer treatment, there is currently very limited available information concerning the clinical pharmacology of actinomycin D (Act D). The study was designed to characterise Act D pharmacokinetics and investigate the impact of pharmacogenetic variation on Act D disposition in children with cancer.

Methods

A total of 650 plasma samples collected over an 8 year period from 117 patients ≤21 years receiving Act D (0.4–1.6 mg/m²) were used to characterise a population pharmacokinetic model. Polymorphisms in ABCB1 were analysed in 140 patients.

Results

A 3-compartment model provided a good fit to the data. Median values for Act D clearance and volume of distribution in the central compartment (V₁) obtained from the model were 5.3 L/h and 1.9 L (13.9 L/h/70 kg and 7.5 L/70 kg), respectively. There was substantial inter-subject variation in all pharmacokinetic parameters (coefficients of variation 53–81 % for non-normalised values). Body weight was a major determinant of Act D clearance, such that dose capping at 2 mg in larger children at a protocol dose of 1.5 mg/m² resulted in significantly lower area under the plasma concentration-time curves (mean AUC values: 9.3 versus 12.8 mg·min/L; P < 0.0001). No significant relationships were found between ABCB1 genetic variants and Act D pharmacokinetic parameters, nor between CL, V₁ or dose and incidence of grade 3 or 4 toxicity.

Conclusion

We have defined the pharmacokinetics of Act D in a paediatric patient population, providing robust estimates of key pharmacokinetic parameters. Pharmacokinetic data bring into question the current clinical practice of dose capping at 2 mg in larger patients. Pharmacogenetic variation in candidate drug transporter genes identified from preclinical studies does not significantly impact on Act D exposure in a clinical setting.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-014-0153-2) contains supplementary material, which is available to authorized users.

Drug resistance in multiple myeloma: latest findings and new concepts on molecular mechanisms

In the era of new and mostly effective therapeutic protocols, multiple myeloma still tends to be a hard-to-treat hematologic cancer. This hallmark of the disease is in fact a sequel to drug resistant phenotypes persisting initially or emerging in the course of treatment. Furthermore, the heterogeneous nature of multiple myeloma makes treating patients with the same drug challenging because finding a drugable oncogenic process common to all patients is not yet feasible, while our current knowledge of genetic/epigenetic basis of multiple myeloma pathogenesis is outstanding. Nonetheless, bone marrow microenvironment components are well known as playing critical roles in myeloma tumor cell survival and environment-mediated drug resistance happening most possibly in all myeloma patients. Generally speaking, however; real mechanisms underlying drug resistance in multiple myeloma are not completely understood. The present review will discuss the latest findings and concepts in this regard. It reviews the association of important chromosomal translocations, oncogenes (e.g. TP53) mutations and deranged signaling pathways (e.g. NFκB) with drug response in clinical and experimental investigations. It will also highlight how bone marrow microenvironment signals (Wnt, Notch) and myeloma cancer stem cells could contribute to drug resistance in multiple myeloma.

Bortezomib in multiple myeloma: systematic review and clinical considerations

We conducted a systematic review to determine the appropriate use of bortezomib alone or in combination with other agents in patients with multiple myeloma (mm). We searched medline, embase, the Cochrane Library, conference proceedings, and the reference lists of included studies. We analyzed randomized controlled trials and systematic reviews if they involved adult mm patients treated with bortezomib and if they reported on survival, disease control, response, quality of life, or adverse effects. Twenty-six unique studies met the inclusion criteria. For patients with previously untreated mm and for candidates for transplantation, we found a statistically significant benefit in time to progression [hazard ratio (hr): 0.48, p < 0.001; and hr: 0.63, p = 0.006, respectively] and a better response with a bortezomib than with a non-bortezomib regimen (p < 0.001). Progression-free survival was longer with bortezomib and thalidomide than with thalidomide alone (p = 0.01). In non-candidates for transplantation, a significant benefit in overall survival was observed with a bortezomib regimen (hr compared with a non-bortezomib regimen: 0.61; p = 0.008), and in transplantation candidates receiving bortezomib, the response rate was improved after induction (p = 0.004) and after a first transplant (p = 0.016). In relapsed or refractory mm, overall survival (p = 0.03), time to progression (hr: 1.82; p = 0.000004), and progression-free survival (hr: 1.69; p = 0.000026) were significantly improved with bortezomib and pegylated liposomal doxorubicin (compared with bortezomib alone), and bortezomib monotherapy was better than dexamethasone alone (hr: 0.77; p = 0.027). Bortezomib combined with thalidomide and dexamethasone was better than either bortezomib monotherapy or thalidomide with dexamethasone (p < 0.001). In previously untreated or in relapsed or refractory mm patients, bortezomib-based therapy has improved disease control and, in some patients, overall survival.

The role of P-glycoprotein in drug resistance in multiple myeloma

Multiple myeloma (MM) is a malignant neoplastic cancer of the plasma cells that involves the bone marrow. The majority of patients with MM initially respond to chemotherapy, but they eventually become resistant to later drug therapy. One of the reasons for drug resistance in patients with MM is efflux transporters. P-glycoprotein (P-gp) is the most studied of the multidrug resistance proteins, and is up-regulated in response to many chemotherapeutic drugs. This up-regulation of P-gp causes a decrease in the intracellular accumulation of these drugs, limiting their therapeutic efficacy. In this review, we focus on the role of P-gp in drugs used for patients with MM. P-gp has been found to be an important factor with regard to drug resistance in many of the drug classes used in the treatment of MM (proteasome inhibitors, anthracyclines, alkylating agents and immunomodulators are examples). Thus, our further understanding of its mechanism and inhibitory effects will help us decrease drug resistance in patients with MM.

The role of reduced intracellular concentrations of active drugs in the lack of response to anticancer chemotherapy

A major difficulty in the treatment of cancers is the poor response of many tumors to pharmacological regimens. This situation can be accounted for by the existence of a variety of complex mechanisms of chemoresistance (MOCs), leading to reduced intracellular concentrations of active agents, changes in the molecular targets of the drugs, enhanced repair of drug-induced modifications in macromolecules, stimulation of anti-apoptotic mechanisms, and inhibition of pro-apoptotic mechanisms. The present review focuses on alterations in the expression and appearance of the genetic variants that affect the genes involved in reducing the amount of active agents inside tumor cells. These alterations can occur through two mechanisms: either by lowering uptake or enhancing efflux (so-called MOC-1a and MOC-1b, respectively), or by decreasing the activation of prodrugs or enhancing inactivation of active agents through their biotransformation (MOC-2). The development of chemosensitizers that are useful in implementing the pharmacological manipulation of these processes constitutes a challenge to modern pharmacology. Nevertheless, the important physiological roles of the most relevant genes involved in MOC-1a, MOC-1b, and MOC-2 make it difficult to prevent the side effects of chemosensitizers. A more attainable goal in this area of pharmacological enquiry is the identification of proteomic profiles that will permit oncologists to accurately predict a lack of response to a given regimen, which would be useful for adapting treatment to the personal situation of each patient.

Perspectives in the treatment of multiple myeloma

INTRODUCTION

The development of proteasome inhibitor (PI) and immunomodulatory drugs (IMiDs) and advances in supportive care have considerably changed the treatment paradigm of multiple myeloma (MM) and significantly improved survival. Nevertheless, almost all patients show disease relapse and develop drug resistance.

AREAS COVERED

We review the prognostic stratification and therapeutic strategy for newly diagnosed MM patients. Furthermore, mechanisms of drug resistance are discussed. Data regarding newer drugs, currently undergoing examination, such as PI (carfilzomib, ONX0912, MLN9708, and marizomib), IMiDs (pomalidomide), histone deacetylase inhibitors (vorinostat and panobinostat), kinase inhibitors (temsirolimus, everolimus, and tanespimycin), and immune-based therapies (elotuzumab, siltuximab, MOR03087, and MMBT062) are reported.

EXPERT OPINION

The use of three to four drug combination therapies including PI and IMiDs has significantly impacted on MM patient outcome. Moreover, new insights into MM biology from high-throughput technologies and availability of newer and more efficacious drugs will continue to influence our approach to MM treatment. In the immediate future molecular subgroup-specific trials using targeted agents may represent a very important step toward evaluating impact of interfering with relevant signaling pathways in MM. With the continued rapid evolution of progress in this field, MM will become a chronic illness having sustained complete response in a significant number of patients.

Emerging biological insights and novel treatment strategies in multiple myeloma

INTRODUCTION

Survival in multiple myeloma (MM) has improved significantly in the past 10 years due to new treatments, such as thalidomide and lenalidomide (immunomodulatory drugs or IMiDs) bortezomib and advances in supportive care. Nevertheless, almost all MM patients show disease relapse and develop drug resistance.

AREAS COVERED

The authors review the therapeutic approach for untreated MM patients. Furthermore, the prognostic stratification of patients and the proposed risk-adapted strategy are discussed. Finally, preclinical and clinical data regarding newer antimyeloma agents, currently undergoing examination such as proteasome inhibitors (PIs, carfilzomib), IMiDs (pomalidomide), epigenetic agents (histone deacetylase inhibitors vorinostat and panobinostat), humanized monoclonal antibodies (elotuzumab and MOR03087) and targeted therapies (inhibitors of NF-κB, MAPK, HSP90 and AKT) are reported.

EXPERT OPINION

MM patient outcome has remarkably improved due to the use of three to four drug combination therapies including PIs and IMiDs, which target the tumor in its bone marrow microenvironment, however MM treatment remains challenging. The use of high-throughput techniques has allowed to discover new insights into MM biology. The identification of candidate therapeutic targets and availability of respective investigative agents will allow for a substantial progress in the development and implementation of personalized medicine in MM.

Interaction of innovative small molecule drugs used for cancer therapy with drug transporters

Multiple new small molecules such as tyrosine kinase, mammalian target of rapamycin (mTOR) and proteasome inhibitors have been approved in the last decade and are a considerable progress for cancer therapy. Drug transporters are important determinants of drug concentrations in the systemic circulation. Moreover, expression of drug transporters in blood-tissue barriers (e.g. blood-brain barrier) can limit access of small molecules to the tumour (e.g. brain tumour). Finally, transporter expression and (up)regulation in the tumour itself is known to affect local drug concentrations in the tumour tissue contributing to multidrug resistance observed for multiple anticancer agents. This review summarizes the current knowledge on: (i) small molecules as substrates of uptake and efflux transporters; (ii) the impact of transporter deficiency in knockout mouse models on plasma and tissue concentrations; (iii) small molecules as inhibitors of uptake and efflux transporters with possible consequences for drug-drug interactions and the reversal of multidrug resistance; and (iv) on clinical studies investigating the association of polymorphisms in genes encoding drug transporters with pharmacokinetics, outcome and toxicity during treatment with the small molecules.

The single nucleotide polymorphism and haplotype analysis of MDR1 in Jiangsu Han population of China

The aim of this study was to perform the frequency distribution of MDR1 gene SNPs and haplotypes of Jiangsu Han population in China. A total of 225 Jiangsu Han unrelated volunteers were enrolled and genotyped by PCR-ASP method at three loci: C1236T (rs1128503), G2677T/A (rs2032582) and C3435T (rs1045642). In total, C and T were found at locus 1236, with the frequency of 35% and 65%, respectively. The most frequent allele at locus 2677 was G with the frequency of 44%, followed by T (41%) and A (15%). At locus 3435, C was more common (60%) than T (40%). The most common haplotype at loci 1236-2677-3435 was T-T-T (31.84%), at loci 1236-2677 was T-T (37.68%), at loci 2677-3435 was G-C (39.06%), and at loci 1236-3435 was T-T (34.28%). The haplotype linkage disequilibrium study found that all three loci were in linkage disequilibrium, such as T-T at loci 1236-2677, T-T at loci 2677-3435 and C-C at loci 1236-3435 (P<0.01). The dendrogram study indicated that the distribution of MDR1 SNPs in Jiangsu Han population were close to Japan and Malay populations and far away from European countries. These findings could shade new lights in population genetics and anthropology studies of Han-Chinese. It also provides basic data for research on MDR1 gene polymorphism, disease association and drug resistance study.

Pegylated liposomal doxorubicin: a review of its use in metastatic breast cancer, ovarian cancer, multiple myeloma and AIDS-related Kaposi's sarcoma

Pegylated liposomal doxorubicin (Caelyx™, Doxil®) represents an improved formulation of conventional doxorubicin, with reduced cardiotoxicity and an improved pharmacokinetic profile. This article reviews the efficacy and tolerability of pegylated liposomal doxorubicin in metastatic breast cancer, progressive ovarian cancer, relapsed or refractory multiple myeloma and AIDS-related Kaposi's sarcoma, as well as summarizing its pharmacological properties. In three randomized, open-label, multicentre trials, monotherapy with pegylated liposomal doxorubicin was as effective as doxorubicin or capecitabine in the first-line treatment of metastatic breast cancer, and as effective as vinorelbine or combination mitomycin plus vinblastine in taxane-refractory metastatic breast cancer. Pegylated liposomal doxorubicin alone was as effective as topotecan or gemcitabine alone in patients with progressive ovarian cancer resistant or refractory to platinum- or paclitaxel-based therapy, according to the results of three randomized multicentre trials. In addition, in patients with progressive ovarian cancer who had received prior platinum-based therapy, progression-free survival was significantly longer with pegylated liposomal doxorubicin plus carboplatin than with paclitaxel plus carboplatin, according to the results of a randomized, open-label multicentre trial. Combination therapy with pegylated liposomal doxorubicin plus bortezomib was more effective than bortezomib alone in patients with relapsed or refractory multiple myeloma, according to the results of a randomized, open-label, multinational trial. Randomized multinational trials also demonstrated the efficacy of pegylated liposomal doxorubicin in patients with advanced AIDS-related Kaposi's sarcoma. Pegylated liposomal doxorubicin exhibited a relatively favourable safety profile compared with conventional doxorubicin and other available chemotherapy agents. The most common treatment-related adverse events included myelosuppression, palmar-plantar erythrodysesthesia and stomatitis, although these are manageable with appropriate supportive measures. To conclude, pegylated liposomal doxorubicin is a useful option in the treatment of various malignancies, including metastatic breast cancer, ovarian cancer, multiple myeloma and AIDS-related Kaposi's sarcoma.

A comprehensive investigation on common polymorphisms in the MDR1/ABCB1 transporter gene and susceptibility to colorectal cancer

ATP Binding Cassette B1 (ABCB1) is a transporter with a broad substrate specificity involved in the elimination of several carcinogens from the gut. Several polymorphic variants within the ABCB1 gene have been reported as modulators of ABCB1-mediated transport. We investigated the impact of ABCB1 genetic variants on colorectal cancer (CRC) risk. A hybrid tagging/functional approach was performed to select 28 single nucleotide polymorphisms (SNPs) that were genotyped in 1,321 Czech subjects, 699 CRC cases and 622 controls. In addition, six potentially functional SNPs were genotyped in 3,662 German subjects, 1,809 cases and 1,853 controls from the DACHS study. We found that three functional SNPs (rs1202168, rs1045642 and rs868755) were associated with CRC risk in the German population. Carriers of the rs1202168_T and rs868755_T alleles had an increased risk for CRC (P(trend) = 0.016 and 0.029, respectively), while individuals bearing the rs1045642_C allele showed a decreased risk of CRC (P(trend) = 0.022). We sought to replicate the most significant results in an independent case-control study of 3,803 subjects, 2,169 cases and 1,634 controls carried out in the North of Germany. None of the SNPs tested were significantly associated with CRC risk in the replication study. In conclusion, in this study of about 8,800 individuals we show that ABCB1 gene polymorphisms play at best a minor role in the susceptibility to CRC.

Latest advances and current challenges in the treatment of multiple myeloma

Effectively treating patients with multiple myeloma is challenging. The development of therapeutic regimens over the past decade that incorporate the proteasome inhibitor bortezomib and the immunomodulatory drugs thalidomide and lenalidomide has been the cornerstone of improving the outcome of patients with myeloma. Although these treatment regimens have improved patient survival, nearly all patients eventually relapse. Our improved understanding of the biology of the disease and the importance of the microenvironment has translated into ongoing work to help overcome the challenge of relapse. Several classes of agents including next-generation proteasome inhibitors, immunomodulatory agents, selective histone-deacetylase inhibitors, antibody and antitumor immunotherapy approaches are currently undergoing preclinical and clinical evaluation. This Review provides an update on the latest advances in the treatment of multiple myeloma. In particular, we focus on novel therapies including modulating protein homeostasis, kinases inhibitors, targeting accessory cells and cytokines, and immunomodulatory agents. A discussion of the challenges associated with these therapeutic approaches is also presented.

Functional significance of genetic polymorphisms in P-glycoprotein (MDR1, ABCB1) and breast cancer resistance protein (BCRP, ABCG2)

Recent pharmacogenomic/pharmacogenetic (PGx) studies have disclosed important roles for drug transporters in the human body. Changes in the functions of drug transporters due to drug/food interactions or genetic polymorphisms, for example, are associated with large changes in pharmacokinetic (PK) profiles of substrate drugs, leading to changes in drug response and side effects. This information is extremely useful not only for drug development but also for individualized treatment. Among drug transporters, the ATP-binding cassette (ABC) transporters are expressed in most tissues in humans, and play protective roles; reducing drug absorption from the gastrointestinal tract, enhancing drug elimination into bile and urine, and impeding the entry of drugs into the central nervous system and placenta. In addition to PK/pharmacodynamic (PD) issues, ABC transporters are reported as etiologic and prognostic factors (or biomarkers) for genetic disorders. Although a consensus has not yet been reached, clinical studies have demonstrated that the PGx of ABC transporters influences the overall outcome of pharmacotherapy and contributes to the pathogenesis and progression of certain disorders. This review explains the impact of PGx in ABC transporters in terms of PK/PD, focusing on P-glycoprotein and breast cancer resistance protein (BCRP).

Liposome-encapsulated doxorubicin reverses drug resistance by inhibiting P-glycoprotein in human cancer cells

The most frequent drawback of doxorubicin is the onset of drug resistance, due to the active efflux through P-glycoprotein (Pgp). Recently formulations of liposome-encapsulated doxorubicin have been approved for the treatment of tumors resistant to conventional anticancer drugs, but the molecular basis of their efficacy is not known. To clarify by which mechanisms the liposome-encapsulated doxorubicin is effective in drug-resistant cancer cells, we analyzed the effects of doxorubicin and doxorubicin-containing anionic liposomal nanoparticles ("Lipodox") on the drug-sensitive human colon cancer HT29 cells and on the drug-resistant HT29-dx cells. Interestingly, we did not detect any difference in drug accumulation and toxicity between free doxorubicin and Lipodox in HT29 cells, but Lipodox was significantly more effective than doxorubicin in HT29-dx cells, which are rich in Pgp. This effect was lost in HT29-dx cells silenced for Pgp and acquired by HT29 cells overexpressing Pgp. Lipodox was less extruded by Pgp than doxorubicin and inhibited the pump activity. This inhibition was due to a double effect: the liposome shell per se altered the composition of rafts in resistant cells and decreased the lipid raft-associated amount of Pgp, and the doxorubicin-loaded liposomes directly impaired transport and ATPase activity of Pgp. The efficacy of Lipodox was not increased by verapamil and cyclosporin A and was underwent interference by colchicine. Binding assays revealed that Lipodox competed with verapamil for binding Pgp and hampered the interaction of colchicine with this transporter. Site-directed mutagenesis experiments demonstrated that glycine 185 is a critical residue for the direct inhibitory effect of Lipodox on Pgp. Our work describes novel properties of liposomal doxorubicin, investigating the molecular bases that make this formulation an inhibitor of Pgp activity and a vehicle particularly indicated against drug-resistant tumors.