METTL3-Mediated m6A Modification Controls Splicing Factor Abundance and Contributes to Aggressive CLL

RNA splicing dysregulation underlies the onset and progression of cancers. In chronic lymphocytic leukemia (CLL), spliceosome mutations leading to aberrant splicing occur in ∼20% of patients. However, the mechanism for splicing defects in spliceosome-unmutated CLL cases remains elusive. Through an integrative transcriptomic and proteomic analysis, we discover that proteins involved in RNA splicing are posttranscriptionally upregulated in CLL cells, resulting in splicing dysregulation. The abundance of splicing complexes is an independent risk factor for poor prognosis. Moreover, increased splicing factor expression is highly correlated with the abundance of METTL3, an RNA methyltransferase that deposits N6-methyladenosine (m6A) on mRNA. METTL3 is essential for cell growth in vitro and in vivo and controls splicing factor protein expression in a methyltransferase-dependent manner through m6A modification-mediated ribosome recycling and decoding. Our results uncover METTL3-mediated m6A modification as a novel regulatory axis in driving splicing dysregulation and contributing to aggressive CLL.

SIGNIFICANCE

METTL3 controls widespread splicing factor abundance via translational control of m6A-modified mRNA, contributes to RNA splicing dysregulation and disease progression in CLL, and serves as a potential therapeutic target in aggressive CLL. See related commentary by Janin and Esteller, p. 176. This article is highlighted in the In This Issue feature, p. 171.

Abstract 3482: METTL3-mediated m6A modification controls splicing factor abundance and contributes to CLL progression

RNA splicing dysregulation is a hallmark of cancers and underlies the onset and progression of diseases. Chronic lymphocytic leukemia (CLL) is one of the most common adult leukemia in western countries. Spliceosome mutations occur in ~20% of patients. However, the mechanism for splicing defects in spliceosome unmutated CLL cases remains elusive. Through an integrative transcriptomic and proteomic analysis of primary CLL samples, we discovered proteins involved in RNA splicing are post-transcriptionally upregulated. Coupled with clinical annotation, we found spliceosome protein abundance is an independent risk factor and associated with poor prognosis. Splice variants found in CLL are highly overlapped with those driven by high spliceosome abundance but not splicing factor mutations, indicating high spliceosome abundance contributes to genetic lesion-independent splicing defects. To identify potential regulators for spliceosome, we proteome-widely analyzed the proteins that highly correlated with splicing factors expression. Analysis of 113 CLL samples has consistently identified METTL3 upregulation with positive correlation with 77.6% of detected splicing factors. METTL3 is an RNA methyltransferase that modifies N6-methyladenosine (m6A) on mRNA and regulates the translation of m6A-installed transcripts. m6A level on mRNA is increased in CLL cells with differential m6A highly enriched on splicing related transcripts. Moreover, high METTL3 expression in CLL is also associated with poor clinical outcomes. These results suggested that METTL3 translationally controls splicing factors through m6A and plays a role in CLL progression. Toward this end, we demonstrated that METTL3 is essential for CLL growth in both in vitro and in vivo studies. Knock out (KO) and pharmaceutical inhibition of METTL3 decreased cell growth and splicing factor expression. Overexpression of wildtype but not catalytic mutant METTL3 restored both defects in METTL3 KO cells, indicating that the regulation of splicing factor is m6A-dependent. To dissect the underlying mechanism, we performed an integrated Ribo-seq, RNA-seq, and MeRIP-seq on CLL cells with or without METTL3. KO of METTL3 decreased overall translation efficiency (TE) with RNA splicing as the most significantly affected pathway. Splicing factors with reduced TE displayed either hypo-m6A at stop codon region or hyper-m6A at CDS regions upon METTL3 KO, as direct or indirect targets of METTL3. Moreover, we found that m6A at stop codon and CDS regions regulates splicing factor translation via ribosome recycling and ribosome pausing, respectively. Taken together, our results uncovered a novel regulatory axis for METTL3 that controls splicing factor translation and contributes to CLL progression. Our study highlights a post-transcriptional layer of m6A modification as a major contributor to genetic lesion-independent splicing defects in CLL.

Citation Format: Yiming Wu, Meiling Jin, Mike Fernandez, Kevyn Hart, Aijun Liao, Stacey M. Fernandes, Tinisha McDonald, Zhenhua Chen, Daniel Röth, Lucy Ghoda, Guido Marcucci, Markus Kalkum, Raju K. Pillai, Alexey V. Danilov, Jianjun Chen, Jennifer R. Brown, Steven T. Rosen, Tanya Siddiqi, Lili Wang. METTL3-mediated m6A modification controls splicing factor abundance and contributes to CLL progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3482.

Advances in Diagnosis and Risk Stratification of Acute Myeloid Leukemia and Myelodysplastic Syndromes

Advances in high-throughput DNA sequencing technology in the past decade have made a tremendous impact on basic science and clinical practice. Methods using the latest next generation sequencing technology can sequence an entire human genome within a few hours. Diagnosis and prognostication of hematologic neoplasms have moved from traditional histology and immunophenotyping to integration of cytogenetic and genomic alterations. Using illustrative cases, this chapter provides an overview of the utility of using genomic data for prognostication as well as treatment decision-making for patients with bone marrow neoplasms.

Genetics and Diagnostic Approach to Lymphoblastic Leukemia/Lymphoma

Our understanding of the genetics and biology of lymphoblastic leukemia/lymphoma (acute lymphoblastic leukemia, ALL) has advanced rapidly in the past decade with advances in sequencing and other molecular techniques. Besides recurrent chromosomal abnormalities detected by karyotyping or fluorescence in situ hybridization, these leukemias/lymphomas are characterized by a variety of mutations, gene rearrangements as well as copy number alterations. This is particularly true in the case of Philadelphia-like (Ph-like) ALL, a major subset which has the same gene expression signature as Philadelphia chromosome-positive ALL but lacks BCR-ABL1 translocation. Ph-like ALL is associated with a worse prognosis and hence its detection is critical. However, techniques to detect this entity are complex and are not widely available. This chapter discusses various subsets of ALL and describes our approach to the accurate classification and prognostication of these cases.

Harnessing the Power of Induced Pluripotent Stem Cells and Gene Editing Technology: Therapeutic Implications in Hematological Malignancies

In vitro modeling of hematological malignancies not only provides insights into the influence of genetic aberrations on cellular and molecular mechanisms involved in disease progression but also aids development and evaluation of therapeutic agents. Owing to their self-renewal and differentiation capacity, induced pluripotent stem cells (iPSCs) have emerged as a potential source of short in supply disease-specific human cells of the hematopoietic lineage. Patient-derived iPSCs can recapitulate the disease severity and spectrum of prognosis dictated by the genetic variation among patients and can be used for drug screening and studying clonal evolution. However, this approach lacks the ability to model the early phases of the disease leading to cancer. The advent of genetic editing technology has promoted the generation of precise isogenic iPSC disease models to address questions regarding the underlying genetic mechanism of disease initiation and progression. In this review, we discuss the use of iPSC disease modeling in hematological diseases, where there is lack of patient sample availability and/or difficulty of engraftment to generate animal models. Furthermore, we describe the power of combining iPSC and precise gene editing to elucidate the underlying mechanism of initiation and progression of various hematological malignancies. Finally, we discuss the power of iPSC disease modeling in developing and testing novel therapies in a high throughput setting.

Chronic myelomonocytic leukemia genomic signature correlates with the degree of bone marrow fibrosis: A single-institutional retrospective study

7559

Background: Chronic myelomonocytic leukemia (CMML) has features of both a myeloproliferative neoplasm and a myelodysplastic syndrome. The median overall survival (OS) in most series is 20-40 months. CMML is a relatively rare entity, and there is limited understanding of prognostic molecular markers. CMML associated with bone marrow fibrosis grade 1, appear to have shorter progression free survival. In this study we investigated the correlation of mutations with bone marrow reticulin fibrosis in patients with CMML. Methods: We investigated a cohort of 41 consecutive patients diagnosed with CMML 0, 1, 2, and CMML-AML from 2014 to 2019 at our institute. The median age of 41 patients was 68 years (range, 34-82). 27% were females and 73% were males. This cohort consists of 8 (20%) patients with CMML0, 19 (46%) with CMML1, 8 (20%) with CMML2 and 6 (15%) with CMML-AML. Genomic DNA was extracted from the bone marrow aspirates and targeted mutation NGS libraries were prepared from 200 ng of genomic DNA using the SureSelect target enrichment system (Agilent Technologies Inc.). The gene panel consists of 73 genes focused on myeloid neoplasms. The data were curated on the basis of our molecular pathology and national databases. Additionally, clinical data and bone marrow (BM) reticulin fibrosis grades (n = 27 available) were retrieved from the patient’s medical record. Results: The mutational profile frequency in our cohort showed that the most common mutations were TET2 (31%), ASXL1 (31%), and SRSF2 (23%), with frequencies very similar to those reported in the literature. Of the 27 cases with an available reticulin stain, only low grade fibrosis (MF-0, n = 18. MF-1, n = 9) were identified in our cohort. The frequencies of mutations in ASXL1, U2AF1, TP53, JAK2 and RUNX1, positively correlated with low grade fibrosis (MF-1). Additionally, patients with higher frequencies of SRSF2, TET2, and SETBP1 mutations showed no fibrosis (MF-0). Conclusions: This study is the first to correlate the degree of fibrosis with the frequency of mutations in CMML. We found similar mutations spectrum reported in the literature in patients with CMML. The mutational profile associated with CMML cases appears to affect the degree of the bone marrow fibrosis at the time of diagnosis.

Gene expression profiling of unresectable pancreatic cancer patients treated with gemcitabine, nab-paclitaxel, metformin, and dietary supplements (DS)

736

Background: Pancreatic cancer commonly causes weight loss and many patients take supplements to improve nutrition but also for any potential anticancer properties. We conducted a pilot trial evaluating a standardized combination of dietary supplements, metformin and gemcitabine plus nab-paclitaxel chemotherapy. Methods: The supplements were custom designed by a nutritionally trained oncologist. 17 supplements were given as 12 pills and 2 smoothie packets divided twice per day. Patients began metformin on day (D)-6 to evaluate GI tolerance before starting the DS on D-3. On D1, gemcitabine and nab-paclitaxel chemotherapy was administered at standard doses. Serum samples were collected D-6, C1D1, C3D1 and at the end of treatment. RNA was extracted from PBMC samples and a total of 48 samples were analyzed from 19 patients. NanoString Human Immune Profiling and PanCancer Pathways were performed to evaluate changes in gene expression with treatment. Results: The differential expression of genes was small with dietary supplements alone and in combination with chemotherapy. After 2 months of treatment, 17 genes were upregulated while 4 genes were down regulated. At the time of tumor resistance, 33 genes were upregulated while 17 genes were downregulated. We observed downregulation of tumor suppressor gene expression with upregulation in growth factor pathways. Interestingly, SPRY2 mRNA expression was also up regulated which functions as a negative feedback regulator of multiple receptor tyrosine kinases. Conclusions: Increasing number of genes were upregulated with continued treatment. The most common pathway affected was cell cycle and apoptosis. During the initial supplement run-in period from D-6 to C1D1, IL-8 mRNA expression was upregulated the most. IL-8 is a neutrophil chemotactic factor secreted by cells involved in the innate immune response as well as pancreatic cancer cells associated with a pro-inflammatory state. Treatment with gemcitabine and nab-paclitaxel decreased the IL-8 mRNA expression. Additional studies with longer course treatment with supplements alone would be required to explore its impact on differential gene expression.

B Cell Lymphoma Immunotherapy Using TLR9-Targeted Oligonucleotide STAT3 Inhibitors

Growing evidence links the aggressiveness of non-Hodgkin’s lymphoma, especially the activated B cell-like type diffuse large B cell lymphomas (ABC-DLBCLs) to Toll-like receptor 9 (TLR9)/MyD88 and STAT3 transcription factor signaling. Here, we describe a dual-function molecule consisting of a clinically relevant TLR9 agonist (CpG7909) and a STAT3 inhibitor in the form of a high-affinity decoy oligodeoxynucleotide (dODN). The CpG-STAT3dODN blocked STAT3 DNA binding and activity, thus reducing expression of downstream target genes, such as MYC and BCL2L1, in human and mouse lymphoma cells. We further demonstrated that injections (i.v.) of CpG-STAT3dODN inhibited growth of human OCI-Ly3 lymphoma in immunodeficient mice. Moreover, systemic CpG-STAT3dODN administration induced complete regression of the syngeneic A20 lymphoma, resulting in long-term survival of immunocompetent mice. Both TLR9 stimulation and concurrent STAT3 inhibition were critical for immune-mediated therapeutic effects, since neither CpG7909 alone nor CpG7909 co-injected with unconjugated STAT3dODN extended mouse survival. The CpG-STAT3dODN induced expression of genes critical to antigen-processing/presentation and Th1 cell activation while suppressing survival signaling. These effects resulted in the generation of lymphoma cell-specific CD8/CD4-dependent T cell immunity protecting mice from tumor rechallenge. Our results suggest that CpG-STAT3dODN as a systemic/local monotherapy or in combination with PD1 blockade can provide an opportunity for treating patients with B cell NHL.

Complete regression of cutaneous metastases with systemic immune response in a patient with triple negative breast cancer receiving p53MVA vaccine with pembrolizumab

A heavily pretreated patient with triple negative breast cancer distinguished by cutaneous metastases received p53MVA vaccine in combination with pembrolizumab. Her cutaneous metastases regressed and after 2 cycles of therapy, a skin biopsy showed a complete pathological response. Systemic response was confirmed with restaging CT and bone scans. Activation of p53-specific T cell responses and elevation of multiple immune response genes in peripheral blood correlated with the rapid clinical response which lasted for 6 months after the initiation of combined therapy.

A phase I study to assess the safety, pharmacokinetics (PK), pharmacodynamics (PD), and anti-tumor activity of oral COH29, a novel ribonucleotide reductase (RNR) inhibitor in adult patients (pts) with advanced solid tumors

TPS2600

Background: Human RNR catalyzes the rate-limiting step in the formation of deoxyribonucleotide triphosphates (dNTPs) necessary for DNA repair and replication. Rapidly dividing tumor cells are especially sensitive to RNR inhibition due to elevated dNTP requirements. Overexpression of the RNR RRM2 subunit is also associated with neoplasia, metastasis, and poor prognosis. COH29 is an aromatically substituted thiazole compound that is a novel small molecule inhibitor of RNR activity, and exhibits unique mechanisms and target specificity that overcomes the weaknesses of other small molecule RNR inhibitors. Preclinically, it is more potent than hydroxyurea and gemcitabine, and is not associated with iron chelating-related toxicities such as hypoxia. Cell lines deficient in BRCA1 also exhibit greater sensitivity to COH29 than BRCA1 wildtype cell lines, implicating inhibition of DNA repair mechanisms in line with PARP inhibitors. Methods: In this Phase I, single site, dose escalation, safety study pts will receive oral COH29 twice a day for 21 days of a 28-day cycle. Eligible pts are age ≥ 18 years, ECOG ≤ 2, able to take oral medication, have adequate organ and marrow function, and diagnosed with any solid tumor refractory to standard therapies. Dose escalation will be pursued utilizing a Simon’s accelerated titration design, which allows skipping of dose levels (dose doubling) during the accelerated dose-finding phase. Primary objectives are to determine the maximum tolerated dose of COH29, toxicities per CTCAEv4, and PKs. Secondary objectives include assessment of objective response per RECIST 1.1 every 2 cycles. PD assessment includes measurement of plasma CK18 levels to determine degree of cellular apoptosis, evaluation of dNTP pool levels in peripheral blood mononuclear cells (PBMCs) to evaluate RNR inhibition, as well as measurement of PAR expression in PBMCs to assess PARP inhibition. Quantitation of tumor RRM2 expression using dual-color immunohistochemistry will be explored as a predictive biomarker of anti-tumor response to COH29. Clinical trial information: NCT02112565.

Effects of TTI-621 (SIRPαFc) on CD47 and serum cytokines associated with phagocytosis in subjects with relapsed, refractory hematologic malignancies: Pharmacodynamic findings from a first-in-human clinical trial

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Background: CD47 delivers an anti-phagocytic (“do not eat”) signal by binding SIRPα on macrophages and is overexpressed on many cancers enabling immune surveillance evasion. TTI-621 is a decoy receptor that promotes phagocytosis of tumors by blocking CD47 and engaging activating FcR on macrophages. A first-in-human, phase 1a, open label, multicenter study (NCT02663518) evaluating safety and tolerability of weekly, intravenous infusions of TTI-621 was conducted. As of October 12, 2016, 18 subjects were treated with TTI-621 with doses of 0.05-0.3 mg/kg. Multiple pharmacodynamic and hematologic assessments were performed to characterize the effects of TTI-621 and better understand the mechanism of action. Methods: Serial blood draws were analyzed for CD47 receptor occupancy (RO), complete blood counts, cytokines, T cell repertoire changes and CD47, SIRPα and FcR sequences. CD47 expression, macrophage and T cell infiltration was assessed on biopsies by IHC. Results: Peripheral CD47 levels varied considerably between subjects and were inversely correlated with RO. A maximum of 80% RO was achieved on peripheral leukocytes. Circulating monocytes, neutrophils, and lymphocytes were transiently decreased at the end of the TTI-621 infusion and generally returned to baseline levels by 24 to 72 hours. Platelet counts decreased immediately after TTI-621 infusions, typically recovering to baseline levels prior to the subsequent treatment cycle. Hemoglobin levels did not meaningfully change during treatment. Cytokines associated with macrophage activation or phagocytosis, notably MIP-1α, MIP-1β, TNF-α and IP-10 were elevated in a dose dependent manner. Conclusions: Systemic administration of TTI-621 leads to CD47 blockade and dose dependent increases in cytokines associated with phagocytosis, temporally associated with reversible thrombocytopenia, suggesting enhanced macrophage mediated clearance of circulating platelets followed by a robust marrow regenerative response. Enrollment into multiple expansion cohorts addressing a wide range of hematopoietic cancers is ongoing. Clinical trial information: NCT02663518.

The State of the Art in Colorectal Cancer Molecular Biomarker Testing

The number of molecular biomarkers to inform treatment decisions in patients with metastatic colorectal cancer (mCRC) continues to expand and with it the methodologies that can be employed to evaluate these biomarkers. Beyond standard diagnostic and prognostic biomarkers, such as those used for Lynch syndrome, mutations in KRAS exon 2 are well established as predictive for lack of response to the antiepidermal growth factor receptor therapies panitumumab and cetuximab. Recent studies have extended these findings by demonstrating that mutations in KRAS exons 3 and 4 and in NRAS exons 2, 3, and 4 (with all KRAS and NRAS mutations collectively referred to as RAS) are also predictive for treatment outcomes among patients with mCRC receiving panitumumab and cetuximab in combination with chemotherapy or as monotherapy. Consequently, evaluation of these additional loci has been incorporated into current clinical guidelines, and pathologists will need to develop testing procedures and algorithms to reliably and rapidly evaluate RAS status. With the increased number of mutations that must be examined to evaluate the status of RAS and other emerging biomarkers, next-generation sequencing technologies are likely to become increasingly important in mCRC testing. This review describes new considerations for pathologists that have arisen as a consequence of the incorporation of additional biomarker testing into clinical practice for mCRC.

Follicular lymphoma-like B cells of uncertain significance (in situ follicular lymphoma) may infrequently progress, but precedes follicular lymphoma, is associated with other overt lymphomas and mimics follicular lymphoma in flow cytometric studies

In situ follicular lymphoma, more recently known as follicular lymphoma-like B cells of uncertain/undetermined significance is well accepted. However, the morphological criteria have evolved since it was first described and data are limited and conflicting regarding its clinical implications and whether the extent of involvement predicts an association with overt lymphoma. It is also unknown how often it will be identified by flow cytometric studies and how often it precedes overt follicular lymphomas. A multiparameter study of 31 biopsies with follicular lymphoma-like B cells of uncertain significance and 4 'benign' lymph node biopsies that preceded an overt follicular lymphoma was, therefore, performed. Fifty-two percent of biopsies with follicular lymphoma-like B cells were associated with a prior or concurrent lymphoma but only 6% subsequently developed lymphoma (median follow up 26 months). Neither the number, proportion or density of BCL2(+) germinal centers were associated with overt follicular lymphoma/diffuse large B-cell lymphoma. Flow cytometric studies identified follicular lymphoma-like B cells in 8 of 15 evaluable cases. The proportion but not the absolute number of BCL2(+) germinal centers was associated with the likelihood of positive flow cytometric studies (P<0.01). All 4 'benign' biopsies that preceded an overt follicular lymphoma demonstrated follicular lymphoma-like B cells. Thus, although few patients with follicular lymphoma-like B cells of uncertain significance progress within the follow-up period, it at least precedes many follicular lymphomas. The extent of involvement does not predict the occurrence of prior or concurrent lymphomas. Flow cytometric studies demonstrating follicular lymphoma-like B cells must not be over-interpreted as they may only reflect follicular lymphoma-like B cells.

Clonal T-cell receptor β-chain gene rearrangements in differential diagnosis of lymphomatoid papulosis from skin metastasis of nodal anaplastic large-cell lymphoma

BACKGROUND

In patients with a history of nodal anaplastic large-cell lymphoma (ALCL), differentiation of type C lymphomatoid papulosis from cutaneous involvement of systemic ALCL may be challenging because the 2 entities may exhibit identical histologic features. Although metastatic ALCL generally carries the same clone as the primary lymphoma, expression of a distinct clone likely represents a distinct process.

OBSERVATIONS

A 54-year-old white man had a history of anaplastic lymphoma kinase 1-negative ALCL in the right inguinal lymph node 6 years ago. A complete response was achieved after 6 cycles of CHOP (cyclophosphamide, doxorubicin, vincristine [Oncovin], and prednisone administered in 21-day cycles) and radiation therapy. After 3½ years, the patient observed waxing and waning papules and nodules. Examination of the biopsy specimen revealed a dense CD30(+) lymphocytic infiltrate; no evidence of systemic malignancy was evident on positron emission tomography. Although clinically the presentation was consistent with lymphomatoid papulosis, metastatic ALCL had to be excluded. Polymerase chain reaction analysis with T-cell receptor γ-chain gene rearrangement (TCR-γR) was performed on the original lymph node and new skin lesions. Results of the TCR-γR analysis were positive for clonality in both lesions. However, separate clonal processes were identified. The identification of distinct clones supported the clinical impression of lymphomatoid papulosis.

CONCLUSION

Polymerase chain reaction analysis of TCR-γR is a useful method for distinguishing different clonal processes and is recommended when differentiation of primary and secondary lymphoproliferative disorders is required.

Reno-protective effect of N-acetyl cysteine in patients with impaired renal function undergoing coronary angiography and interventions

BACKGROUND

The increasingly frequent use of contrast enhanced imaging for diagnosis or interventions in patients with CAD has generated concern about avoidance of contrast induced nephropathy (CIN). Reactive oxygen species have been shown to cause CIN.

OBJECTIVES

Angiographic contrasts worsen the renal function in patients with renal failure. We studied the reno-protective action of the antioxidant N-Acetyl cysteine (NAC) in patients undergoing coronary procedures.

METHODS

Retrospective analysis of 51 patients with elevated serum creatinine levels (> or = 15mg%) was done, 24 of whom received NAC prior to the procedure(NAC group) and 27 who did not (Non NAC group). NAC was administered in a dose of 400 mg twice daily for four doses starting on the day prior to the procedure. Both groups of patients were hydrated with 0.45% saline at 1 ml/kg/hr for 12 hours prior to and 12 hours following the procedure. Both groups were comparable with regard to age, sex, coronary risk profile, myocardial infarction history, left ventricular function and the drugs received. Serum urea and creatinine were measured on the day prior to and the day following the angiographic procedure.

RESULTS

Nine out of 51 patients developed more than 0.5mg% rise in serum creatinine level; 1 in the NAC group and 8 in the non NAC group (p<0.05), 24 hours after injection of the contrast medium. In the NAC group mean serum creatinine level decreased from 1.94 +/- 0.56 to 1.67 +/- 0.56 and blood urea from 47.58 +/- 20 to 41.58 +/- 15.1. In the non NAC group serum creatinine increased from 1.75 +/- 0.31 to 1.98 +/- 0.56 and blood urea from 44.96 +/- 15.5 to 52.85 +/- 20.1 (p<0.05). This corresponds to an increase in creatinine clearance from 30ml/min to 35.92ml/min in the NAC group and a decrease from 34.42ml/min to 29.87ml/min in the non NAC group. There was no significant difference in the levels of sodium and potassium before and after the procedure in both the groups.

CONCLUSION

We conclude that prophylactit administration of N-Acetyl Cysteine along with hydration diminishes the incidence of deterioration of renal function induced by contrast agents in patients with renal insufficiency during coronary angiographic procedures.

Design of conformationally rigid dimeric MRI agents

The conformational flexibility of the linkage mechanism or tether between paramagnetic metal centers is explored to assess optimal structural characteristics of multimeric MRI contrast agents. Two dimeric paramagnetic chelates differing in linkage flexibility but similar in symmetry are compared Relaxivity, water hydration number, and reorientational times of the chelate groups are obtained, and the results demonstrate that greater linkage flexibility reduces overall relaxivity.