Insights on the conformation and appropriate drug-target sites on retinal IMPDH1 using the 604-aa isoform lacking the C-terminal extension

Background and purpose

Retinitis pigmentosa (RP) accounts for 2 percent of global cases of blindness. The RP10 form of the disease results from mutations in isoform 1 of inosine 5'-monophosphate dehydrogenase (IMPDH1), the rate-limiting enzyme in the de novo purine nucleotide synthesis pathway. Retinal photoreceptors contain specific isoforms of IMPDH1 characterized by terminal extensions. Considering previously reported significantly varied kinetics among retinal isoforms, the current research aimed to investigate possible structural explanations and suitable functional sites for the pharmaceutical targeting of IMPDH1 in RP.

Experimental approach

A recombinant 604-aa IMPDH1 isoform lacking the carboxyl-terminal peptide was produced and underwent proteolytic digestion with α-chymotrypsin. Dimer models of wild type and engineered 604-aa isoform were subjected to molecular dynamics simulation.

Findings/Results

The IMPDH1 retinal isoform lacking C-terminal peptide was shown to tend to have more rapid proteolysis (~16% digestion in the first two minutes). Our computational data predicted the potential of the amino-terminal peptide to induce spontaneous inhibition of IMPDH1 by forming a novel helix in a GTP binding site. On the other hand, the C-terminal peptide might block the probable inhibitory role of the N-terminal extension.

Conclusion and implications

According to the findings, augmenting IMPDH1 activity by suppressing its filamentation is suggested as a suitable strategy to compensate for its disrupted activity in RP. This needs specific small molecule inhibitors to target the filament assembly interface of the enzyme.

Apoptotic Janus-faced mycotoxins against thoracal and breast metastases

Abdominal organs (liver, kidney, spleen) are frequent targets of cancer cell invasion but their primary tumours are less known for their metastatic potential to other organs e.g. to the breast. Despite the known connection of the pathogenesis from breast cancer to liver metastasis, the study of the spread in the opposite direction has been neglected. The notion that breast cancer could be a metastasis besides being a primary tumour is based on rodents' tumour models upon implantation of tumour cells under the capsule of the kidney or under the Glisson's capsule of the liver of rats and mice. Tumour cells develop into a primary tumour at the site of subcutaneous implantation. The metastatic process starts with peripheral disruptions of blood vessels near the surface of primary tumours. Tumour cells released into the abdomen cross the apertures of the diaphragm, enter the thoracal lymph nodes and accumulate in parathymic lymph nodes. Abdominal colloidal carbon particles injected into the abdomen faithfully mimicked the migration of tumour cells and deposited in parathymic lymph nodes (PTNs). An explanation is provided why the connection between abdominal tumours and mammary tumours escaped attention, notably, parathymic lymph nodes in humans were referred to as internal mammary or parasternal lymph nodes. The apoptotic effect of Janus-faced cytotoxins is suggested to provide a new approach against the spread of abdominal primary tumours, and metastatic development.

Higher mycophenolate dosage is associated with an increased risk of squamous cell carcinoma in kidney transplant recipients

BACKGROUND

Kidney transplant recipients are at increased risk of keratinocyte cancers, namely squamous cell and basal cell carcinomas (SCCs and BCCs). This is primarily due to the high levels of immunosuppression that are required to prevent allograft rejection. Different immunosuppressive medications confer different risks, and the effect of mycophenolate mofetil on SCC and BCC risk is unclear. We explored the relationship between mycophenolate dose prescribed over the entire transplant period and the risk of SCC and BCC.

METHODS

Kidney transplant recipients from Queensland, Australia, were recruited between 2012 and 2014 and followed until mid-2016. During this time transplant recipients underwent regular skin examinations to diagnose incident SCCs and BCCs. Immunosuppressive medication regimens were obtained from hospital records, and the average mycophenolate dose/day over the entire transplantation period was calculated for each patient. Doses were divided into three ranked groups, and adjusted relative risks (RR_adj) of developing SCC and BCC tumours were calculated using negative binomial regression with the lowest dosage group as reference. Recipients who had used azathioprine previously were excluded; further sub-group analysis was performed for other immunosuppressant medications.

RESULTS

There were 134 kidney transplant recipients included in the study. The average age was 55, 31% were female and 69% were male. At the highest median mycophenolate dose of 1818 mg/day the SCC risk doubled (RR_adj 2.22, 95% CI 1.03-4.77) when compared to the reference group of 1038 mg/day. An increased risk persisted after accounting for ever-use of ciclosporin, ever-use of tacrolimus, and when excluding mammalian target of rapamycin users. This increased risk was mainly carried by kidney transplant recipients immunosuppressed for five or more years (RR_adj = 11.05 95% CI 2.50-48.81). In contrast, there was no significant association between BCC incidence and therapy with the highest compared with the lowest mycophenolate dosage (RR_adj = 1.27 95% CI 0.56-2.87).

CONCLUSION

Higher mycophenolate dosage is associated with increased SCCs in kidney transplant recipients, particularly those immunosuppressed for more than five years. The increased SCC risk persists after accounting for usage of other immunosuppressant medications.

Reducing non-melanoma skin cancer risk in renal transplant recipients

With an increasing number of renal transplant recipients (RTRs) and improving patient survival, a higher incidence of non-melanoma skin cancer (NMSC) has been observed. NMSC in RTRs are often more numerous and biologically more aggressive than the general population, thus contributing towards an increase in morbidity and to a lesser degree, mortality. The resultant cumulative health and financial burden is a recognized concern. Proposed strategies in mitigating risks of developing NMSC and early therapeutic options thereof include tailored modification of immunosuppressants in conjunction with sun protection in all transplant patients. This review highlights the clinical and financial burden of transplant-associated skin cancers, carcinogenic mechanisms in association with immunosuppression, importance of skin cancer awareness campaign and integrated transplant skin clinic, and the potential role of chemoprotective agents. A scheme is proposed for primary and secondary prevention of NMSC based on the available evidence.

Mycophenolic acid and cancer risk in solid organ transplant recipients: Systematic review and meta-analysis

AIM

Mycophenolic acid (MPA) is an immunosuppressive drug commonly used for prophylaxis of graft rejection in solid organ transplant recipients. The main concern with the prolonged use of immunosuppressive drugs is the risk of developing cancer. However, it remains unclear whether the immunosuppressive regimens containing MPA confer an increased degree of cancer risk. The present study aimed to determine the association between MPA exposure and the incidence of cancer in solid organ transplant recipients.

METHODS

A systematic search was performed on the PubMed, EMBASE and Cochrane Library databases. Relevant articles that had findings on the incidence (or event) of cancer in cohorts with and without MPA exposure were retrieved for data extraction. A meta-analysis was conducted by means of the random-effects model, and the relative risk (RR) and its 95% confidence interval (95% CI) were used as a summary effect measure.

RESULTS

A total of 39 studies were eligible for inclusion, with 32 studies that enabled meta-analysis. MPA exposure was significantly associated with a lower risk of cancer when compared to azathioprine exposure (RR = 0.66, 95% CI = 0.53-0.81, P < .001) or no exposure to any additional treatments (RR = 0.85, 95% CI = 0.73-0.99, P = .04). There was no significant difference in cancer risk for the comparison between MPA exposure and mammalian target of rapamycin (mTOR) inhibitor exposure (RR = 1.54, 95% CI = 0.96-2.46, P = .07).

CONCLUSIONS

MPA exposure was not associated with an increased risk of cancer and may even be associated with a lower risk of cancer when compared to azathioprine or no treatment.

Machine Learning Modeling for Ultrasonication-Mediated Fermentation of Penicillium brevicompactum to Enhance the Release of Mycophenolic Acid

Described here is the modeling used to improve the mycophenolic acid (MPA) titer from Penicillium brevicompactum using central composite design and a comparatively newer, data-centric approach method k-nearest-neighbor algorithm. The two models for enhancing MPA production using P. brevicompactum were compared with respect to ultrasonic stimulation. During the ultrasonic treatment, we studied different independent factors such as ultrasound power, irradiation duration, treatment frequency and duty cycle to determine their ability to enhance the MPA titer value. The optimized factors such as a treatment time of 10 min (50% duty cycles) with a 12-h interlude at fixed ultrasonic power and frequency (200 W, 40 kHz) were used for ultrasonic treatment of a mycelial culture from the 2nd to 10th day of fermentation. Thus the production of MPA was improved 1.64-fold under the optimized sonication conditions compared with the non-sonicated batch fermentation (non-optimized conditions).

Reuse of Molecules for Glioblastoma Therapy

Glioblastoma multiforme (GBM) is a highly malignant primary brain tumor. The current standard of care for GBM is the Stupp protocol which includes surgical resection, followed by radiotherapy concomitant with the DNA alkylator temozolomide; however, survival under this treatment regimen is an abysmal 12-18 months. New and emerging treatments include the application of a physical device, non-invasive 'tumor treating fields' (TTFs), including its concomitant use with standard of care; and varied vaccines and immunotherapeutics being trialed. Some of these approaches have extended life by a few months over standard of care, but in some cases are only available for a minority of GBM patients. Extensive activity is also underway to repurpose and reposition therapeutics for GBM, either alone or in combination with the standard of care. In this review, we present select molecules that target different pathways and are at various stages of clinical translation as case studies to illustrate the rationale for their repurposing-repositioning and potential clinical use.

Premature senescence of placental decidua cells as a possible cause of miscarriage produced by mycophenolic acid

BACKGROUND

Successful pregnancy is supported by a healthy maternal-fetal interface (i.e., the decidual tissues) which holds the conceptus and safeguards it against stressors from the beginning of pregnancy. Any disturbance of this interface can presumably lead to the loss of pregnancy. The use of the immunosuppressive drug mycophenolic acid (MPA) should be discontinued in pregnancy given its abortive and embryotoxic effects. Direct teratogenic effects have been observed in mammalian embryos cultured in MPA, but the underlying mechanisms of abortion by MPA are less understood.

METHODS

Decidual stromal cells isolated from human placentas are cultured in the presence of clinically relevant doses of MPA. Data regarding the effects of MPA on the proliferation and viability of decidua cultures are first analysed and then, molecular pathways contributing to these effects are unravelled.

RESULTS

MPA treatment of decidual stromal cells results in loss of proliferation capacity and a decrease in the viability of decidua cultures. The molecular pathways involved in the effects of MPA on decidual stromal cells are a reduction in pre-rRNA synthesis and subsequent disruption of the nucleolus. The nucleolar stress stabilizes p53, which in turn, leads to a p21-mediated cell cycle arrest in late S and G2 phases, preventing the progression of the decidua cells into the mitosis. Furthermore, MPA does not induce apoptosis but activate mechanisms of autophagy and senescence in decidual stromal cells.

CONCLUSION

The irreversible growth arrest of decidua cells, whose role in the maintenance of the pregnancy microenvironment is known, may be one cause of miscarriage in MPA treated pregnant women.

Rhabdomyosarcoma in a child with nephrotic syndrome treated with cyclosporine: a case report with literature review

Background

In patients with frequently relapsing nephrotic syndrome, immunosuppressive therapy such as cyclosporine are often required to maintain remission. Cyclosporine has been noted to have tumorgenesis effects. In this case report, we present a child with relapsing nephrotic syndrom developed a rhabdomyosarcoma on her tongue after adout 4 years of continual immunosuppressive therapy.

Case presentation

A 2-year-old female child had nephrotic syndrome (urine protein-creatinine ratio 749.1 mg/mg; blood urea nitrogen 11 mg/dL; serum creatinine 0.3 mg/dL; and serum albumin 1.8 g/dL.) Proteinuria resolved on treatment with daily prednisolone for 4 weeks at the dose of 45 mg (2.5 mg/kg/day) but recurred with taper from 25 mg/day to 10 mg/day. At least five more episodes of relapse occurred within about a 3-year period. After the third relapse, she was treated with prednisolone and cyclosporine (at initial dose of 50 mg/day [1.7 mg/kg/day]) for immunosuppression. About 4 years after the diagnosis of nephrotic syndrome had been made, an embryonal rhabdomyosarcoma developed on her tongue. The cancer was treated with TPOG-RMS-LR protocol, with vincristine, actinomycin, and cyclophosphamide. Magnetic resonance imaging scan, performed about 3 years after the start of TPOG-RMS-LR therapy, revealed complete remission of the cancer.

Conclusions

Although treatment with cyclosporine cannot be conclusively implicated as the cause the rhabdomyosarcoma in this patient, the association should prompt consideration of its use in the treatment of frequently relapsing nephrotic syndrome in children.

Metabolic Compartmentalization at the Leading Edge of Metastatic Cancer Cells

Despite advances in targeted therapeutics and understanding in molecular mechanisms, metastasis remains a substantial obstacle for cancer treatment. Acquired genetic mutations and transcriptional changes can promote the spread of primary tumor cells to distant tissues. Additionally, recent studies have uncovered that metabolic reprogramming of cancer cells is tightly associated with cancer metastasis. However, whether intracellular metabolism is spatially and temporally regulated for cancer cell migration and invasion is understudied. In this review, we highlight the emergence of a concept, termed “membraneless metabolic compartmentalization,” as one of the critical mechanisms that determines the metastatic capacity of cancer cells. In particular, we focus on the compartmentalization of purine nucleotide metabolism (e.g., ATP and GTP) at the leading edge of migrating cancer cells through the uniquely phase-separated microdomains where dynamic exchange of nucleotide metabolic enzymes takes place. We will discuss how future insights may usher in a novel class of therapeutics specifically targeting the metabolic compartmentalization that drives tumor metastasis.

Therapeutic potential and molecular mechanisms of mycophenolic acid as an anticancer agent

Mycophenolic acid (MPA) is the active metabolite of mycophenolate mofetil (MMF), an immunosuppressive drug approved for the prophylaxis of allograft rejection in transplant recipients. Recent advances in the role of the type II isoform of inosine-5'-monophosphate dehydrogenase (IMPDH2) in the tumorigenesis of various types of cancer have called for a second look of MPA, the first IMPDH2 inhibitor discovered a hundred years ago, to be repurposed as an anticancer agent. Over a half century, a number of in vitro and in vivo experiments have consistently shown anticancer activity of MPA against several cell lines obtained from different malignancies and murine models. However, a few clinical trials have been conducted to investigate its anticancer activity in humans, and most of which have shown unsatisfactory results. Understanding of available evidence and underlying mechanism of action is a key step to be done so as to facilitate further investigations of MPA to reach its full therapeutic potential as an anticancer agent. This article provides a comprehensive review of non-clinical and clinical evidence available to date, with the emphasis on the molecular mechanism of action in which MPA exerts its anticancer activities: induction of apoptosis, induction of cell cycle arrest, and alteration of tumor microenvironment. Future perspective for further development of MPA to be an anticancer agent is extensively discussed, with the aim of translating the anticancer property of MPA from bench to bedside.

Liposomal Delivery of Mycophenolic Acid With Quercetin for Improved Breast Cancer Therapy in SD Rats

The present study explores the influence of mycophenolic acid (MPA) in combination therapy with quercetin (QC) (impeding MPA metabolic rate) delivered using the liposomal nanoparticles (LNPs). Mycophenolic acid liposome nanoparticles (MPA-LNPs) and quercetin liposome nanoparticles (QC-LNPs) were individually prepared and comprehensively characterized. The size of prepared MPA-LNPs and QC-LNPs were found to be 183 ± 13 and 157 ± 09.8, respectively. The in vitro studies revealed the higher cellular uptake and cytotoxicity of combined therapy (MPA-LNPs + QC-LNPs) compared to individual ones. Moreover pharmacokinetics studies in female SD-rat shown higher T 1 / 2 value (1.94 fold) of combined therapy compared to MPA. Furthermore, in vivo anticancer activity in combination of MPA-LNPs and QC-LNPs was also significantly higher related to other treatments groups. The combination therapy of liposomes revealed the new therapeutic approach for the treatment of breast cancer.

IMP dehydrogenase-2 drives aberrant nucleolar activity and promotes tumorigenesis in glioblastoma

In many cancers, high proliferation rates correlate with elevation of rRNA and tRNA levels, and nucleolar hypertrophy. However, the underlying mechanisms linking increased nucleolar transcription and tumorigenesis are only minimally understood. Here we show that IMP dehydrogenase-2 (IMPDH2), the rate-limiting enzyme for de novo guanine nucleotide biosynthesis, is overexpressed in the highly lethal brain cancer glioblastoma. This leads to increased rRNA and tRNA synthesis, stabilization of the nucleolar GTP-binding protein nucleostemin, and enlarged, malformed nucleoli. Pharmacological or genetic inactivation of IMPDH2 in glioblastoma reverses these effects and inhibits cell proliferation, whereas untransformed glia cells are unaffected by similar IMPDH2 perturbations. Impairment of IMPDH2 activity triggers nucleolar stress and growth arrest of glioblastoma cells even in the absence of functional p53. Our results reveal that upregulation of IMPDH2 is a prerequisite for the occurance of aberrant nucleolar function and increased anabolic processes in glioblastoma, which constitutes a primary event in gliomagenesis.

A RNA sequencing-based six-gene signature for survival prediction in patients with glioblastoma

Glioblastoma (GBM) is an aggressive tumor of the central nervous system that has poor prognosis despite extensive therapy. Therefore, it is essential to identify a gene expression-based signature for predicting GBM prognosis. The RNA sequencing data of GBM patients from the Chinese Glioma Genome Atlas (CGGA) and The Cancer Genome Atlas (TCGA) databases were employed in our study. The univariate and multivariate regression models were utilized to assess the relative contribution of each gene to survival prediction in both cohorts, and the common genes in two cohorts were identified as a final prognostic model. A prognostic risk score was calculated based on the prognostic gene signature. This prognostic signature stratified the patients into the low- and high-risk groups. Multivariate regression and stratification analyses were implemented to determine whether the gene signature was an independent prognostic factor. We identified a 6-gene signature through univariate and multivariate regression models. This prognostic signature stratified the patients into the low- and high-risk groups, implying improved and poor outcomes respectively. Multivariate regression and stratification analyses demonstrated that the predictive value of the 6-gene signature was independent of other clinical factors. This study highlights the significant implications of having a gene signature as a prognostic predictor in GBM, and its potential application in personalized therapy.

Use of Inosine Monophosphate Dehydrogenase Activity Assay to Determine the Specificity of PARP-1 Inhibitors

Inosine monophosphate dehydrogenase (IMPDH) is a rate-limiting enzyme involved in purine nucleotide biosynthesis. It is responsible for catalyzing the oxidation of inosine monophosphate (IMP) into xanthosine monophosphate (XMP). Concurrently, the cofactor NAD⁺ is reduced to NADH. Poly(ADP-ribose) polymerase 1 (PARP-1) also utilizes NAD⁺ as a substrate to synthesize poly(ADP-ribose). It has been demonstrated that inhibition of PARP-1 activity can be an effective cancer therapeutic. However, most PARP-1 inhibitors, including olaparib, were developed as NAD⁺ analogs. Therefore, these inhibitors likely interfere with other NAD⁺-dependent pathways such as the one involved in de novo purine metabolism. In this chapter, we describe a method to quantitatively measure IMPDH activity by taking advantage of the autofluorescence of the product NADH. We use this method to analyze the effects of olaparib and non-NAD⁺-like PARP-1 inhibitor (5F02) on IMPDH activity. We found that olaparib, unlike 5F02, significantly inhibits IMPDH activity in a dose-dependent manner. Our results suggest that IMPDH inhibition is an off-target effect of olaparib treatment. The consequences of this effect should be addressed by future clinical studies.

Molecular targeting of inosine-5'-monophosphate dehydrogenase by FF-10501 promotes erythropoiesis via ROS/MAPK pathway

One of the major symptoms of myelodysplastic syndromes (MDS) is severe cytopenia. Despite cytokine therapies, such as erythropoiesis-stimulating agents, many patients still require blood transfusions, and the development of new therapeutic approaches is needed. In this work, we studied the effects of the inosine-5'-monophosphate (IMP) dehydrogenase (IMPDH) inhibitor FF-10501 on erythropoiesis of human hematopoietic cells. Differentiation of K562 chronic myeloid leukemia cells to an erythroid lineage was promoted by FF-10501 in a dose-dependent manner. Interestingly, we found that metabolic conversion of IMP to hypoxanthine leads to elevation of reactive oxygen species (ROS). The differentiative effects of FF-10501 were abolished by the ROS scavenger dimethylthiourea or the p38 MAPK inhibitor SB203580. Furthermore, FF-10501 promoted erythropoiesis from CD34⁺ hematopoietic stem/progenitor cells, accompanied with ROS accumulation, while high-dose FF-10501 mainly showed cytotoxic effects. These findings denote the potential of IMPDH inhibition therapy with FF-10501 in amelioration of anemia in MDS patients.