Isabelle Hubeek

In vivo Induction of Resistance to Gemcitabine Results in Increased Expression of Ribonucleotide Reductase Subunit M1 as the Major Determinant

Gemcitabine is a deoxycytidine (dCyd) analogue with activity against several solid cancers. Gemcitabine is activated by dCyd kinase (dCK) and interferes, as its triphosphate dFdCTP, with tumor growth through incorporation into DNA. Alternatively, the metabolite gemcitabine diphosphate (dFdCDP) can interfere with DNA synthesis and thus tumor growth through inhibition of ribonucleotide reductase. Gemcitabine can be inactivated by the enzyme dCyd deaminase (dCDA). In most in vitro models, resistance to gemcitabine was associated with a decreased dCK activity. In all these models, resistance was established using continuous exposure to gemcitabine with increasing concentrations; however, these in vitro models have limited clinical relevance. To develop in vivo resistance to gemcitabine, we treated mice bearing a moderately sensitive tumor Colon 26-A (T/C = 0.25) with a clinically relevant schedule (120 mg/kg every 3 days). By repeated transplant of the most resistant tumor and continuation of gemcitabine treatment for >1 year, the completely resistant tumor Colon 26-G (T/C = 0.96) was created. Initial studies focused on resistance mechanisms known from in vitro studies. In Colon 26-G, dCK activity was 1.7-fold decreased; dCDA and DNA polymerase were not changed; and Colon 26-G accumulated 1.5-fold less dFdCTP, 6 hours after a gemcitabine injection, than the parental tumor. Based on in vitro studies, these relative minor changes were considered insufficient to explain the completely resistant phenotype. Therefore, an expression microarray was done with Colon 26-A versus Colon 26-G. Using independently grown nonresistant and resistant tumors, a striking increase in expression of the RRM1 subunit gene was found in Colon 26-G. The expression of RRM1 mRNA was 25-fold increased in the resistant tumor, as measured by real-time PCR, which was confirmed by Western blotting. In contrast, RRM2 mRNA was 2-fold decreased. However, ribonucleotide reductase enzyme activity was only moderately increased in Colon 26-G. In conclusion, this is the first model with in vivo induced resistance to gemcitabine. In contrast to most in vitro studies, dCK activity was not the most important determinant of gemcitabine resistance. Expression microarray identified RRM1 as the gene with the highest increase in expression in the Colon 26-G, which might clarify its complete gemcitabine-resistant phenotype. This study is the first in vivo evidence for a key role for RRM1 in acquired gemcitabine resistance.

Technical performance of a novel, fully automated electrochemiluminescence immunoassay for the quantitation of β-amyloid (1-42) in human cerebrospinal fluid.

Available assays for quantitation of the Alzheimers disease (AD) biomarker amyloid‐beta 1–42 (Aβ [1–42]) in cerebrospinal fluid demonstrate significant variability and lack of standardization to reference measurement procedures (RMPs). We report analytical performance data for the novel Elecsys β‐amyloid (1–42) assay (Roche Diagnostics).

Immunocytochemical detection of deoxycytidine kinase in haematological malignancies and solid tumours

Background: Deoxycytidine kinase (dCK) is responsible for the activation of several clinically important deoxynucleoside analogues used for the treatment of haematological and solid malignancies. Aim: To measure dCK expression in tumour cells from different origins. Method: A rabbit antihuman dCK antibody was used for the immunocytochemical detection of dCK expression in three leukaemic cell lines (HL60, U937, and CCRF-CEM) and 97 patient samples (paediatric acute myeloid leukaemia (AML) and lymphoid leukaemia (ALL), retinoblastoma, paediatric brain tumours, and adult non-small cell lung cancer (NSCLC)). Results: CCRF-CEM, U937, and HL60 cells stained positively for dCK and the degree of expression correlated with dCK activity. dCK expression varied between tumour types and between individual patients within one tumour type. dCK was located predominantly in the cytoplasm. The staining intensity was scored as negative (0), low (1+), intermediate (2+), or high (3+). Expression of dCK was high in AML blasts. In contrast, brain tumour samples expressed low amounts of dCK. dCK staining ranged from low (1+) to high (3+) in ALL blasts, retinoblastoma, and NSCLC tissue samples. Staining was consistent (interobserver variability, 88%; κ  =  0.83) and specific. Western blotting detected the dCK protein appropriately at 30 kDa, without additional bands. Conclusions: Immunocytochemistry is an effective and reliable method for determining the expression of dCK in patient samples and requires little tumour material. This method enables large scale screening of dCK expression in tumour samples.

Presence of human papillomavirus in semen in relation to semen quality

STUDY QUESTION Is the presence of human papillomavirus (HPV) in semen associated with impairment of semen quality? SUMMARY ANSWER In a large cohort of males seeking fertility evaluation, no associations were observed between seminal HPV presence and semen parameters. WHAT IS KNOWN ALREADY HPV is commonly detected in semen samples. Whether the presence of HPV is related to impairment of semen quality, remains unclear. STUDY DESIGN, SIZE, DURATION This cross-sectional study included a cohort of 430 males. PARTICIPANTS/MATERIALS, SETTING, METHODS Male partners in couples seeking fertility evaluation provided one semen sample per person. Semen samples were tested for HPV-DNA using GP5+/6+-PCR. Sperm concentration was counted and motility was assessed in a Makler counting chamber at a magnification of ×200. The presence of antisperm antibodies was assessed by a mixed agglutination reaction (MAR)-test. MAIN RESULTS AND THE ROLE OF CHANCE Overall HPV was detected in 14.9% (64/430) of semen samples, including 2.1% (9/430) that contained both high-risk (hr) HPV and low-risk (lr) HPV types, 8.8% (38/430) with exclusively hrHPV types and 4.0% (17/430) with exclusively lrHPV types. The presence of HPV in semen was not associated with the age of the participants, seminal pH, semen volume, total sperm count, sperm concentration, progressive motility or the presence of antisperm antibodies. LIMITATIONS, REASONS FOR CAUTION This study did not observe an association between HPV presence in semen and impairment of semen quality. However, we cannot exclude an effect of seminal HPV on early embryo development and clinical reproductive outcomes. WIDER IMPLICATIONS OF THE FINDINGS As HPV is frequently present in semen, screening of donor semen for HPV should be considered to prevent iatrogenic cervical HPV infections in the recipient. However our findings do not support standardized HPV testing of semen in the diagnostic work-up of subfertile couples. STUDY FUNDING/COMPETING INTERESTS This study was sponsored by an unrestricted grant of Stichting Researchfonds Pathology Amsterdam, the Netherlands. P.J.F.S. has been on the speakers bureau of Roche, Gen-Probe, Abbott, Qiagen and Seegene and has been a consultant for Crucell B.V. J.B. has been on the speakers bureau of Qiagen and has been a consultant for Roche, DDL Diagnostic Laboratory, GlaxoSmithKline and Merck. D.A.M.H. has been member of the scientific advisory boards of Amgen and Pfizer, and has been on the speakers bureau of Hologic/Gen-Probe. C.J.L.M.M. has been on the speakers bureau of GlaxoSmithKline, Qiagen, Merck, Roche, Menarini and Seegene, has served occasionally on the scientific advisory board of GlaxoSmithKline, Qiagen, Merck, Roche and Genticel, and has occasionally been a consultant for Qiagen. Formerly, C.J.L.M.M. was a minority shareholder of Delphi Biosciences, which bankrupted in 2014. C.J.L.M.M. is a minority shareholder of Diassay B.V. P.J.F.S., D.A.M.H. and C.J.L.M.M. have minority stake in Self-Screen B.V., a spin-off company of VU University Medical Center. R.L., M.G.D., P.G.A.H., D.T.M.P., and I.H. do not have any conflicts of interest to disclose. TRIAL REGISTRATION NUMBER Not applicable.

Methylation Specific PCR to Characterize Methylation of the Promoter of Deoxycytidine Kinase

Deoxycytidine kinase (dCK) is essential for phosphorylation of natural deoxynucleosides and analogs, such as gemcitabine and cytarabine, two widely used anticancer compounds. We hypothesized that DNA methylation of SP1 binding sites in the dCK promoter region might affect dCK expression. Using methylation specific PCR (MSP), methylation was detected in one of the SP1 binding sites of the dCK promoter, in most tested cancer cell lines and in patient samples from brain tumors and leukemia. This SP1 site is a 3′GC box, which upon hypomethylation negatively regulates dCK mRNA expression. In conclusion, we developed a new MSP method showing methylation of the 3′ GC-box in the dCK promoter region in tumor cells and patient samples. Methylation might therefore regulate transcription of dCK, and should be studied further to understand its role in influencing gemcitabine and cytarabine activity.

MLL gene rearrangements have no direct impact on Ara-C sensitivity in infant acute lymphoblastic leukemia and childhood M4/M5 acute myeloid leukemia.

The antimetabolite cytosine arabinoside (Ara-C) is a deoxycytidine analog that is used as a therapeutic agent in many leukemia treatment regimens. In combination with anthracyclines, Ara-C is the most effective agent in the treatment of acute myeloid leukemia (AML). In the treatment of acute lymphoblastic leukemia (ALL), the use of Ara-C is limited. However, leukemic cells from infants (<1 year of age) with ALL, which are resistant to several chemotherapeutic drugs, are in vitro more sensitive to Ara-C as compared to older children with ALL.1, 2 This observation suggested that infant ALL might resemble a subclass of childhood ALL, which may benefit from intensified treatment with Ara-C to improve the dismal prognosis for these patients who to date experience an event-free survival (EFS) of 35%. Therefore, in 1999, a novel collaborative treatment protocol (INTERFANT-99) was designed with intensified use of Ara-C, in order to provide a more specific treatment to infant ALL patients.

Modulation of Cytarabine Induced Cytotoxicity Using Novel Deoxynucleoside Analogs in the HL60 Cell Line

In order to enhance the cytotoxicity of ara‐C in the HL60 cell line the following deoxynucleoside analogs were used: cladribine, fludarabine and gemcitabine. HL60 cells were co‐incubated with ara‐C and each of the modulators at the ratios of their respective IC50s. Cytotoxicity was determined with the MTT‐assay and drug interactions were evaluated with the combination index (CI) method (Calcusyn; Chou & Talalay). CI < 1, CI ± 1 and > 1 indicate synergism, additive effect and antagonism, respectively. We observed moderate synergism between ara‐C/cladribine and ara‐C/gemcitabine, with CIs of 0.76 ± 0.14 and 0.82 ± 0.04, respectively. The interaction between ara‐C/fludarabine resulted in moderate antagonism (CI = 1.29 ± 0.11). In conclusion, in this in vitro study we showed that the cytotoxicity of ara‐C can be succesfully modulated in the HL60 cell line by cladribine and gemcitabine.

Immunocytochemical detection of hENT1 and hCNT1 in normal tissues, lung cancer cell lines, and NSCLC patient samples

Nucleoside transporters are essential for the cellular entry, efficacy, and cytotoxicity of several clinically important deoxynucleoside analogs (e.g., cytarabine and gemcitabine). We used immunohistochemistry to determine protein expression levels of the nucleoside transporters hENT1 and hCNT1 in NSCLC cell lines, NSCLC patient samples, and a variety of normal tissues. All 4 NSCLC cell lines expressed high to very high levels of both hENT1 and hCNT1. In NSCLC and normal tissues expression of hENT1 and hCNT1 ranged from completely negative to high. Immunohistochemistry might be a useful tool to predict response to deoxynucleoside analogs in malignancies treated with these drugs.

Immunocytochemical detection of deoxycytidine kinase in pediatric malignancies in relation to in vitro cytarabine sensitivity

Deoxycytidine kinase (dCK) is essential for the phosphorylation of cytarabine (ara‐C), a deoxycytidine analog active against acute leukemias. Resistance to ara‐C has been linked to dCK deficiency. In this study we determined the expression of the dCK protein in pediatric malignancies, using immunocytochemistry and related the expression levels to in vitro ara‐C sensitivity (measured with the MTT‐assay). dCK expression was high in the AML and retinoblastoma samples, in the ALL samples dCK expression ranged from low to very high. The brain tumor samples expressed low levels of dCK. AML was significantly more sensitive in vitro to ara‐C compared to ALL (p = 0.03). Retinoblastoma and brain tumor cells were extremely resistant in vitro, we were unable to detect more than 50% ara‐C induced cell kill in the majority of samples. Samples were combined in groups according to dCK expression. Samples with low dCK expression were significantly more resistant to ara‐C compared to samples with high dCK expression. In conclusion, dCK expression varies between individual samples and between different types of malignancies and may play a role in resistance to ara‐C in particular tumor types.

Discrepant Results of Serum Creatinine and Cystatin C in a Urological Patient

A 3-month-old boy was seen for routine follow-up at the pediatric nephrology outpatient clinic. He had been diagnosed as having Sotos syndrome manifesting with craniofacial dysmorphism, feeding difficulties, pulmonary artery stenosis, and atrial septal defect, as well as complex urological abnormalities. He had bilateral hydronephrosis with megaureter and grade V vesicoureteral reflux to the left and grade I to the right kidney. At the age of 6 weeks, static renal scintigraphy using DMSA (99mTc-dimercaptosuccinic acid) to assess renal morphology, structure, and function had demonstrated almost symmetrical kidney function (split kidney function left 44% vs right 56%) without cortical scarring. While his baseline serum creatinine had been 40 μmol/L (0.45 mg/dL), a sudden rise to 69 μmol/L (0.79 mg/dL) was noted. Urinary tract infection was ruled out, as was dehydration. On renal ultrasound, dilation of the right collecting system and ureter had increased significantly and a novel fluid collection at the upper pole was noted, which prompted an MRI study (Fig. 1). In addition to serum creatinine, cystatin C measurement was ordered and was within the reference interval for age (1.13 mg/L). Fig. 1. Abdominal MRI. Bilateral hydronephrosis and fluid collection at right upper pole (asterisk). Creatinine, the most commonly used endogenous marker of glomerular filtration rate (GFR),4 has in recent years been supplemented by cystatin C. In fact, todays most reliable equations for estimating GFR both in adults (1) and in children (2) make use of a combination of the 2. Still, in certain conditions the 2 markers can give very discordant findings, which may be diagnostic, as in the case presented here. Discordant findings may occur …