Hematologic β-tubulin VI isoform exhibits genetic variability that influences paclitaxel toxicity

Randomized controlled trial on the effect of 1-hour infusion of vincristine versus push injection on neuropathy in children with cancer (final analysis)

INTRODUCTION

Vincristine is an integral component of treatment for children with cancer. Its main dose-limiting side effect is vincristine-induced peripheral neuropathy (VIPN). The VINCA trial was a randomized controlled trial that explored the effect of 1-hour infusion compared with push injection of vincristine on the development of VIPN in children with cancer. The short-term outcomes (median follow-up 9 months) showed that there was no difference in VIPN between the randomization groups. However, 1-hour infusion was less toxic in children who also received azoles. We now report the results of the final analyses (median follow-up 20 months), which includes treatment outcome as a secondary objective (follow-up 3 years).

METHODS

VIPN was measured 1-7 times per participant using the Common Terminology Criteria for Adverse Events (CTCAE) and the pediatric-modified total neuropathy score. Poisson mixed model and logistic generalized estimating equation analysis for repeated measures were performed.

RESULTS

Forty-five participants per randomization group were included. There was no significant effect of 1-hour infusion compared with push injection on VIPN. In participants receiving concurrent azoles, the total CTCAE score was significantly lower in the one-hour group (rate ratio 0.52, 95% confidence interval 0.33-0.80, p = 0.003). Four patients in the one-hour group and one patient in the push group relapsed. Two patients in the one-hour group died.

CONCLUSION

1-hour infusion of vincristine is not protective against VIPN. However, in patients receiving concurrent azoles, 1-hour infusion may be less toxic. The difference in treatment outcome is most likely the result of differences in risk profile.

A Population Pharmacokinetic Modelling Approach to Unravel the Complex Pharmacokinetics of Vincristine in Children

Background

Vincristine, a chemotherapeutic agent that extensively binds to β-tubulin, is commonly dosed at 1.4–2.0 mg/m2 capped at 2 mg. For infants, doses vary from 0.025–0.05 mg/kg or 50–80% of the mg/m2 dose. However, evidence for lower doses in infants compared to older children is lacking. This study was conducted to unravel the complex pharmacokinetics of vincristine, including the effects of age, to assist optimal dosing in this population.

Methods

206 patients (0.04–33.9 years; 25 patients < 1 years), receiving vincristine, with 1297 plasma concentrations were included. Semi-mechanistic population pharmacokinetic analyses were performed using non-linear mixed effects modelling.

Results

A three-compartment model, with one saturable compartment resembling saturable binding to β-tubulin and thus, saturable distribution, best described vincristine pharmacokinetics. Body weight and age were covariates significantly influencing the maximal binding capacity to β-tubulin, which increased with increasing body weight and decreased with increasing age. Vincristine clearance (CL) was estimated as 30.6 L/h (95% confidence interval (CI) 27.6–33.0), intercompartmental CL (Q) as 63.2 L/h (95%CI 57.2–70.1), volume of distribution of the central compartment as 5.39 L (95%CI 4.23–6.46) and of the peripheral compartment as 400 L (95%CI 357–463) (all parameters correspond to a patient of 70 kg). The maximal binding capacity was 0.525 mg (95%CI 0.479–0.602) (for an 18 year old patient of 70 kg), with a high association rate constant, fixed at 1300 /h and a dissociation constant of 11.5 /h.

Interpretation

A decrease of vincristine β-tubulin binding capacity with increasing age suggests that young children tolerate higher doses of vincristine.

Single-nucleotide polymorphism associations with efficacy and toxicity in metastatic castration-resistant prostate cancer treated with cabazitaxel

Background: The aim of this study was to evaluate the impact of certain single-nucleotide polymorphisms (SNPs) in cabazitaxel activity and toxicity in patients with metastatic castration-resistant prostate cancer (mCRPC). Patients & methods: 56 SNPs in five genes (CYP3A4, CYP3A5, ABCB1, TUBB1 and CYP2C8) were genotyped in 67 mCRPC patients and their correlation with outcomes analyzed. Results: TUBB1-rs151352 (hazard ratio: 0.52) and CYP2C8-rs1341164 (hazard ratio: 0.53) were associated with better overall survival, and CYP2C8-rs1058932 with biochemical progression (odds ratio: 6.60) in multivariate analysis. ABCB1-rs17327624 correlated with severe toxicity ≥ grade 3 (odds ratio: 8.56) and CYP2C8-rs11572093 with asthenia (odds ratio: 8.12). Conclusion: Genetic variants in mCRPC patients could explain different outcomes with cabazitaxel. Nonetheless, the small sample size and the high number of SNPs analyzed mean that the results are only hypothesis-generating and require further validation.

Interaction of Colchicine-Site Ligands With the Blood Cell-Specific Isotype of β-Tubulin—Notable Affinity for Benzimidazoles

Tubulin, the main component of microtubules, is an α-β heterodimer that contains one of multiple isotypes of each monomer. Although the isotypes of each monomer are very similar, the beta tubulin isotype found in blood cells is significantly divergent in amino acid sequence compared to other beta tubulins. This isotype, beta class VI, coded by human gene TUBB1, is found in hematologic cells and is recognized as playing a role in platelet biogenesis and function. Tubulin from the erythrocytes of the chicken Gallus gallus contains almost exclusively βVI tubulin. This form of tubulin has been reported to differ from brain tubulin in binding of colchicine-site ligands, previously thought to be a ubiquitous characteristic of tubulin from higher eukaryotes. In this study, we sought to gain a better understanding of the structure-activity relationship of the colchicine site of this divergent isotype, using chicken erythrocyte tubulin (CeTb) as the model. We developed a fluorescence-based assay to detect binding of drugs to the colchicine site and used it to study the interaction of 53 colchicine-site ligands with CeTb. Among the ligands known to bind at this site, most colchicine derivatives had lower affinity for CeTb compared to brain tubulin. Remarkably, many of the benzimidazole class of ligands shows increased affinity for CeTb compared to brain tubulin. Because the colchicine site of human βVI tubulin is very similar to that of chicken βVI tubulin, these results may have relevance to the effect of anti-cancer agents on hematologic tissues in humans.

The tubulin code in platelet biogenesis

Blood platelets are small non-nucleated cellular fragments that prevent and stop hemorrhages. They are produced in the bone marrow by megakaryocytes through megakaryopoiesis. This intricate process involves profound microtubule rearrangements culminating in the formation of a unique circular sub-membranous microtubule array, the marginal band, which supports the typical disc-shaped morphology of platelets. Mechanistically, these processes are thought to be controlled by a specific tubulin code. In this review, we summarize the current knowledge on the key isotypes, notably β1-, α4A- and α8-tubulin, and putative post-translational modifications, involved in platelet and marginal band formation. Additionally, we provide a provisional list of microtubule-associated proteins (MAPs) involved in these processes and a survey of tubulin variants identified in patients presenting defective platelet production. A comprehensive characterization of the platelet tubulin code and the identification of essential MAPs may be expected in the near future to shed new light on a very specialized microtubule assembly process with applications in platelet diseases and transfusion.

Expanding the genetic spectrum of TUBB1-related thrombocytopenia

β1-Tubulin plays a major role in proplatelet formation and platelet shape maintenance, and pathogenic variants in TUBB1 lead to thrombocytopenia and platelet anisocytosis (TUBB1-RT). To date, the reported number of pedigrees with TUBB1-RT and of rare TUBB1 variants with experimental demonstration of pathogenicity is limited. Here, we report 9 unrelated families presenting with thrombocytopenia carrying 6 β1-tubulin variants, p.Cys12LeufsTer12, p.Thr107Pro, p.Gln423*, p.Arg359Trp, p.Gly109Glu, and p.Gly269Asp, the last of which novel. Segregation studies showed incomplete penetrance of these variants for platelet traits. Indeed, most carriers showed macrothrombocytopenia, some only increased platelet size, and a minority had no abnormalities. Moreover, only homozygous carriers of the p.Gly109Glu variant displayed macrothrombocytopenia, highlighting the importance of allele burden in the phenotypic expression of TUBB1-RT. The p.Arg359Trp, p.Gly269Asp, and p.Gly109Glu variants deranged β1-tubulin incorporation into the microtubular marginal ring in platelets but had a negligible effect on platelet activation, secretion, or spreading, suggesting that β1-tubulin is dispensable for these processes. Transfection of TUBB1 missense variants in CHO cells altered β1-tubulin incorporation into the microtubular network. In addition, TUBB1 variants markedly impaired proplatelet formation from peripheral blood CD34+ cell-derived megakaryocytes. Our study, using in vitro modeling, molecular characterization, and clinical investigations provides a deeper insight into the pathogenicity of rare TUBB1 variants. These novel data expand the genetic spectrum of TUBB1-RT and highlight a remarkable heterogeneity in its clinical presentation, indicating that allelic burden or combination with other genetic or environmental factors modulate the phenotypic impact of rare TUBB1 variants.

Identification of novel TUBB1 variants in patients with macrothrombocytopenia

Background/aim

Macrothrombocytopenia is an autosomal-dominant disorder characterized by increased platelet size and a decreased number of circulating platelets. The membrane skeleton and the link between actin filaments of the skeleton and microtubules, which consist of alpha and beta tubulin [including the tubulin beta-1 chain (TUBB1)] heterodimers, are important for normal platelet morphology, and defects in these systems are associated with macrothrombocytopenia.

Materials and methods

In this study, we sequenced the exons of the TUBB1 gene using DNA isolated from the peripheral blood samples of healthy controls (n = 47) and patients with macrothrombocytopenia (n = 37) from Turkey. The TUBB1 expression levels in fractioned blood samples from patients and healthy controls were analyzed by RT-qPCR and Western blot. Microtubule organization of the platelets in the peripheral blood smears of patients, and in mutant TUBB1-transfected HeLa cells, were analyzed by immunofluorescence staining.

Results

A new TUBB1 c.803G>T (p.T178T) variant was detected in all of the control and patient samples. Importantly, we found 3 new heterozygous TUBB1 variants predicting amino acid substitutions: G146R (in 1 patient), E123Q (in 1 patient), and T274M (in 4 patients); the latter variant was associated with milder thrombocytopenia in cancer patients treated with paclitaxel. Ectopic expression of TUBB1 T274M/R307H variant in HeLa cells resulted in irregular microtubule organization.

Conclusion

Further clinical and functional studies of the newly identified TUBB1 variants may offer important insights into their pathogenicity in macrothrombocytopenia.

The development of a targeted and more potent, anti-Inflammatory derivative of colchicine: Implications for gout

BACKGROUND

Colchicine is routinely used for its anti-inflammatory properties to treat gout and Familial Mediterranean fever. More recently, it was also shown to be of therapeutic benefit for another group of diseases in which inflammation is a key component, namely, cardiovascular disease. Whilst there is considerable interest in repurposing this alkaloid, it has a narrow therapeutic index and is associated with undesirable side effects and drug interactions. We, therefore, developed a derivatives of colchicine that preferentially target leukocytes to increase their potency and diminish their side effects. The anti-inflammatory activity of the colchicine derivatives was tested in experimental models of neutrophil activation by the etiological agent of gout, monosodium urate crystals (MSU).

METHODS

Using a rational drug design approach, the structure of colchicine was modified to increase its affinity for βVI-tubulin, a colchicine ligand preferentially expressed by immune cells. The ability of the colchicine analogues with the predicted highest affinity for βVI-tubulin to dampen neutrophil responses to MSU was determined with in vitro assays that measure MSU-induced production of ROS, release of IL-1 and CXCL8/IL-8, and the increase in the concentration of cytoplasmic calcium. The anti-inflammatory property of the derivatives was assessed in the air pouch model of MSU-induced inflammation in mice.

RESULTS

The most effective compound generated, CCI, is more potent than colchicine in all the in vitro assays. It inhibits neutrophil responses to MSU in vitro at concentrations 10-100-fold lower than colchicine. Similarly, in vivo, CCI inhibits the MSU-induced recruitment of leukocytes at a 10-fold lower concentration than colchicine when administered prior to or after MSU.

CONCLUSIONS

We provide evidence that colchicine can be rendered more potent atinhibiting MSU-induced neutrophil activation and inflammation using a rational drug design approach. The development of compounds such as CCI will provide more efficacious drugs that will not only alleviate gout patients of their painful inflammatory episodes at significantly lower doses than colchicine, but also be of potential therapeutic benefit for patients with other diseases treated with colchicine.

The tubulin code at a glance

Microtubules are key cytoskeletal elements of all eukaryotic cells and are assembled of evolutionarily conserved α-tubulin-β-tubulin heterodimers. Despite their uniform structure, microtubules fulfill a large diversity of functions. A regulatory mechanism to control the specialization of the microtubule cytoskeleton is the 'tubulin code', which is generated by (i) expression of different α- and β-tubulin isotypes, and by (ii) post-translational modifications of tubulin. In this Cell Science at a Glance article and the accompanying poster, we provide a comprehensive overview of the molecular components of the tubulin code, and discuss the mechanisms by which these components contribute to the generation of functionally specialized microtubules.

Structure-based approaches for the design of benzimidazole-2-carbamate derivatives as tubulin polymerization inhibitors

Microtubules are highly dynamic assemblies of α/β-tubulin heterodimers whose polymerization inhibition is among one of the most successful approaches for anticancer drug development. Overexpression of the class I (βI) and class III (βIII) β-tubulin isotypes in breast and lung cancers and the highly expressed class VI (βVI) β-tubulin isotype in normal blood cells have increased the interest for designing specific tubulin-binding anticancer therapies. To this end, we employed our previously proposed model of the β-tubulin-nocodazole complex, supported by the recently determined X-ray structure, to identify the fundamental structural differences between β-tubulin isotypes. Moreover, we employed docking and molecular dynamics (MD) simulations to determine the binding mode of a series of benzimidazole-2-carbamete (BzC) derivatives in the βI-, βIII-, and βVI-tubulin isotypes. Our results demonstrate that Ala198 in the βVI isotype reduces the affinity of BzCs, explaining the low bone marrow toxicity for nocodazole. Additionally, no significant differences in the binding modes between βI- and βIII-BzC complexes were observed; however, Ser239 in the βIII isotype might be associated with the low affinity of BzCs to this isotype. Finally, our study provides insight into the β-tubulin-BzC interaction features essential for the development of more selective and less toxic anticancer therapeutics.

New treatment strategies for HIV-positive cancer patients undergoing antiblastic chemotherapy

INTRODUCTION

The introduction of Highly Active Antiretroviral Therapy (HAART) into clinical practice has dramatically changed the outcome of HIV-infected patients by prolonging their survival. The increase in life expectancy has led to an increased risk of non-AIDS-related mortality and morbidity, including cardiovascular diseases, neurocognitive diseases, neuroendocrine dysfunctions and cancer. Areas covered: The GICAT (Italian Cooperation Group on AIDS and Tumors) has demonstrated that patients who receive a multidisciplinary approach with the combination of anticancer agents (AC) and HAART can achieve better responses and survival rates than patients who receive AC alone. The first obstacle for the oncologist to plan treatment for cancer HIV-patients is the preliminary evaluation of drug-drug interactions between AC and HAART. Recent progress in pharmacogenomics could provide a new approach for personalized treatments. The rationale of this review is to summarize the existing data on the impact of HAART on the clinical management of cancer patients with HIV/AIDS and DDIs between antiretrovirals and AC. In addition, to maximize the efficacy of both concomitant therapy and to minimize the risk of DDIs, a currently useful list of pharmacogenomic markers of key metabolic enzymes is provided. Expert opinion: In this scenario, the importance of cooperation between oncologists and other health specialists (i.e., infectivologists, pharmacists, genetics and lab specialists) must not be underestimated in the management of these patients with the aim of planning an individual treatment strategy.

Pharmacogenetic analysis of advanced non-small-cell lung cancer patients treated with first-line paclitaxel and carboplatin chemotherapy

BACKGROUND

Genetic polymorphisms contribute toward interindividual variations in drug response. We investigated the effects of genetic polymorphisms on the clinical outcome of advanced non-small-cell lung cancer patients with first-line paclitaxel and carboplatin.

MATERIALS AND METHODS

A total of 194 non-small-cell lung cancer patients were prospectively enrolled from January 2010 to January 2013. We genotyped 11 polymorphisms in seven genes involved in the glycolysis pathway and the related pharmacokinetic/pharmacodynamic pathway. Genetic associations with PET-SUV, survival outcome, and toxicity were analyzed, and in-vitro drug transport activity was measured in the oocyte system.

RESULTS

Patients with the c.334 T>G and c.699 G>A homozygous variant in SLCO1B3 showed a higher incidence of grade 3/4 anemia (P=0.002). Transport activities of oocyte that overexpress the SLCO1B3 c.699 G>A variant showed a significantly decreased uptake of paclitaxel compared with the wild-type expressing oocytes. In addition, patients with GG/GA/AA genotypes of ABCB1, c.2677 T>G/A locus showed inferior progression-free survival (hazard ratio=1.49, P=0.017) compared with other genotypes. The GA genotype of HIF1A, c.1834 G>A locus was associated with inferior progression-free survival compared with the GG genotype (hazard ratio=2.47, P=0.008).

CONCLUSION

This study showed that the SLCO1B3 c.699 G>A polymorphism may predict anemia and ABCB1, HIF1A polymorphism are highly predictive for worse survival in advanced NSCLC with first-line paclitaxel and carboplatin.

The structured core of human β tubulin confers isotype-specific polymerization properties

The tubulin gene family encodes multiple tubulin isotypes that can have distinct polymerization properties. Pamula et al. show that residue changes within β tubulin’s structured core are largely responsible for isotype-specific differences in dynamic instability.

Diversity in cytoskeleton organization and function may be achieved through variations in primary sequence of tubulin isotypes. Recently, isotype functional diversity has been linked to a “tubulin code” in which the C-terminal tail, a region of substantial sequence divergence between isotypes, specifies interactions with microtubule-associated proteins. However, it is not known whether residue changes in this region alter microtubule dynamic instability. Here, we examine recombinant tubulin with human β isotype IIB and characterize polymerization dynamics. Microtubules with βIIB have catastrophe frequencies approximately threefold lower than those with isotype βIII, a suppression similar to that achieved by regulatory proteins. Further, we generate chimeric β tubulins with native tail sequences swapped between isotypes. These chimeras have catastrophe frequencies similar to that of the corresponding full-length construct with the same core sequence. Together, our data indicate that residue changes within the conserved β tubulin core are largely responsible for the observed isotype-specific changes in dynamic instability parameters and tune tubulin’s polymerization properties across a wide range.

Drug-Drug Interactions Based on Pharmacogenetic Profile between Highly Active Antiretroviral Therapy and Antiblastic Chemotherapy in Cancer Patients with HIV Infection

The introduction of Highly Active Antiretroviral Therapy (HAART) into clinical practice has dramatically changed the natural approach of HIV-related cancers. Several studies have shown that intensive antiblastic chemotherapy (AC) is feasible in HIV-infected patients with cancer, and that the outcome is similar to that of HIV-negative patients receiving the same AC regimens. However, the concomitant use of HAART and AC can result in drug accumulation or possible toxicity with consequent decreased efficacy of one or both classes of drugs. In fact, many AC agents are preferentially metabolized by CYP450 and drug-drug interactions (DDIs) with HAART are common. Therefore, it is important that HIV patients with cancer in HAART receiving AC treatment at the same time receive an individualized cancer management plan based on their liver and renal functions, their level of bone marrow suppression, their mitochondrial dysfunction, and their genotype profile. The rationale of this review is to summarize the existing data on the impact of HAART on the clinical management of cancer patients with HIV/AIDS and DDIs between antiretrovirals and AC. In addition, in order to maximize the efficacy of antiblastic therapy and minimize the risk of drug-drug interaction, a useful list of pharmacogenomic markers is provided.

SNPs associated with activity and toxicity of cabazitaxel in patients with advanced urothelial cell carcinoma

AIM

We aimed to identify SNPs associated with cabazitaxel toxicity and response within a Phase II clinical trial using this compound in advanced transitional cell carcinoma after progression to a platinum-based regimen.

PATIENTS & METHODS

Eleven SNPs in CYP3A4, CYP3A5, CYP2C8, ABCB1 and TUBB1 were genotyped in 45 patients.

RESULTS

CYP3A5 rs776746 A allele was associated with protection against gastrointestinal toxicity (odds ratio: 0.06, 95% CI: 0.007-0.63, p = 0.018) and with reduced progression-free survival (hazard ratio: 5.1, 95% CI: 1.7-15.1, p = 0.0038, multivariable analysis). ABCB1 SNPs were associated with total number of grade 3-4 toxicity events (p-values of 0.009, 0.041 and 0.043, respectively).

CONCLUSION

Polymorphisms in CYP3A5 and ABCB1 may define a subset of patients with different cabazitaxel toxicity and efficacy and therefore could be used as markers for treatment optimization.

Prolactin-induced protein is required for cell cycle progression in breast cancer

Prolactin-induced protein (PIP) is expressed in the majority of breast cancers and is used for the diagnostic evaluation of this disease as a characteristic biomarker; however, the molecular mechanisms of PIP function in breast cancer have remained largely unknown. In this study, we carried out a comprehensive investigation of PIP function using PIP silencing in a broad group of breast cancer cell lines, analysis of expression microarray data, proteomic analysis using mass spectrometry, and biomarker studies on breast tumors. We demonstrated that PIP is required for the progression through G1 phase, mitosis, and cytokinesis in luminal A, luminal B, and molecular apocrine breast cancer cells. In addition, PIP expression is associated with a transcriptional signature enriched with cell cycle genes and regulates key genes in this process including cyclin D1, cyclin B1, BUB1, and forkhead box M1 (FOXM1). It is notable that defects in mitotic transition and cytokinesis following PIP silencing are accompanied by an increase in aneuploidy of breast cancer cells. Importantly, we have identified novel PIP-binding partners in breast cancer and shown that PIP binds to β-tubulin and is necessary for microtubule polymerization. Furthermore, PIP interacts with actin-binding proteins including Arp2/3 and is needed for inside-out activation of integrin-β1 mediated through talin. This study suggests that PIP is required for cell cycle progression in breast cancer and provides a rationale for exploring PIP inhibition as a therapeutic approach in breast cancer that can potentially target microtubule polymerization.

Regulation of microtubule motors by tubulin isotypes and post-translational modifications

The ‘tubulin-code’ hypothesis proposes that different tubulin genes or posttranslational modifications (PTMs), which mainly confer variation in the carboxy-terminal tail (CTT), result in unique interactions with microtubule-associated proteins for specific cellular functions. However, the inability to isolate distinct and homogenous tubulin species has hindered biochemical testing of this hypothesis. Here, we have engineered 25 α/β tubulin heterodimers with distinct CTTs and PTMs and tested their interactions with four different molecular motors using single molecule assays. Our results show that tubulin isotypes and PTMs can govern motor velocity, processivity and microtubule depolymerization rates, with substantial changes conferred by even single amino acid variation. Revealing the importance and specificity of PTMs, we show that kinesin-1 motility on neuronal β-tubulin (TUBB3) is increased by polyglutamylation and that robust kinesin-2 motility requires detyrosination of α-tubulin. Our results also show that different molecular motors recognize distinctive tubulin “signatures”, which supports the premise of tubulin-code hypothesis.

Germline pharmacogenetics of paclitaxel for cancer treatment

Paclitaxel is a highly effective chemotherapeutic agent used in a variety of solid tumors. Some paclitaxel-treated patients experience the intended therapeutic response with manageable side effects, while others have minimal response and/or severe toxicity. This variability in treatment outcome is partially determined by variability in drug exposure (pharmacokinetics) and by patient and tumor sensitivity (pharmacodynamics). Both pharmacokinetics and pharmacodynamics are dictated in part by common variants in the germline genome, known as SNPs. This article reviews the published literature on paclitaxel pharmacogenetics in cancer, focusing primarily on polymorphisms in genes relevant to paclitaxel pharmacokinetics and discusses preliminary work on pharmacodynamic genes and genome-wide association studies.

Pharmacogenetics, enzyme probes and therapeutic drug monitoring as potential tools for individualizing taxane therapy

The taxanes are a class of chemotherapeutic agents that are widely used in the treatment of various solid tumors. Although taxanes are highly effective in cancer treatment, their use is associated with serious complications attributable to large interindividual variability in pharmacokinetics and a narrow therapeutic window. Unpredictable toxicity occurrence necessitates close patient monitoring while on therapy and adverse effects frequently require decreasing, delaying or even discontinuing taxane treatment. Currently, taxane dosing is based primarily on body surface area, ignoring other factors that are known to dictate variability in pharmacokinetics or outcome. This article discusses three potential strategies for individualizing taxane treatment based on patient information that can be collected before or during care. The clinical implementation of pharmacogenetics, enzyme probes or therapeutic drug monitoring could enable clinicians to personalize taxane treatment to enhance efficacy and/or limit toxicity.

The beta 1 tubulin R307H single nucleotide polymorphism is associated with treatment failures in immune thrombocytopenia (ITP)

Predictive biomarkers are needed in immune thrombocytopenia (ITP). Single nucleotide polymorphisms (SNPs) in beta 1 tubulin are potential candidates, as beta 1 tubulin is integral for platelet production and function, and SNPs in beta 1 tubulin have been associated with distinct phenotypes in platelets. We investigated the most prevalent beta 1 tubulin SNP (R307H) as a biomarker in patients with ITP via a retrospective chart review. Allelic frequencies between a group of 191 ITP patients and a healthy control group showed no difference, suggesting no direct aetiological role for the SNP in ITP. However, over similar periods of follow-up, both heterozygote and homozygote minor allele ITP patients were treated with significantly more treatment modalities and had significantly higher risk of failure to immune-modulatory therapies [relative risk (RR) = 1·5, 95% confidence interval (CI) = 1·1-2·1; P = 0·01]; with rituximab, in particular, ITP patients with the SNP experienced a 58% failure rate (RR = 1·6, 95%CI = 1·03-2·5; P = 0·04). Analysis of the absolute immature platelet fraction (A-IPF) as a marker of platelet production showed that SNP patients had significantly higher median A-IPFs compared to non-SNP patients when complete responses were achieved using immune modulatory therapies. The data suggest that the beta 1 tubulin R307H SNP has potential for use as a biomarker in ITP and may affect platelet turnover.