Assessing N w-hydroxy-L-arginine applicability as a novel ethnic specific estrogen-negative breast cancer marker

NOHA: A Promising Biomarker for Determining Estrogen Receptor Status Among Patients With Breast Cancer in Resource-Constrained Settings

PURPOSE

Challenges to breast cancer control in low-and middle-income countries exist because of constrained access to care, including pathology services. Immunohistochemistry (IHC)-based estrogen receptor (ER) analysis is limited-nonexistent because of few and inadequately staffed and equipped pathology laboratories. We have identified N^w-hydroxy-L-Arginine (NOHA) as a blood-based biomarker to distinguish ER status in US patients with breast cancer. Here, we examine NOHA's clinical utility as an ER IHC alternative in Tanzanian patients.

MATERIALS AND METHODS

Following informed consent, 70 newly diagnosed, known or suspected patients with breast cancer were enrolled at Kilimanjaro Christian Medical Center; basic, deidentified clinical and sociodemographic data were collected. For each, a needle prick amount of blood was collected on a Noviplex plasma card and stored at -80°C. Plasma cards and unstained tumor pathology slides were shipped regularly to US laboratories for NOHA, histologic and IHC analysis. NOHA and IHC assay operators were blinded to each other's result and patient clinical status. Paired NOHA and IHC results were compared.

RESULTS

Slides from 43 participants were available for pathological analysis in the United States. Of those with confirmed malignancy (n = 39), 44%, 51%, 5% were ER-positive, ER-negative, and ER inconclusive, respectively. NOHA levels were available among 33 of 43 of those with pathological data and showed distinct threshold levels correlating 100% to tumor ER IHC and disease categorization where a level below 4 nM, from 4 to 8 nM, and above 8 nM signified ER-negative, ER-positive, and no cancer, respectively.

CONCLUSION

The results are consistent with findings from US patients and suggest NOHA's clinical utility as an accessible IHC replacement in determining ER status among low-and middle-income country patients with breast cancer, promising to extend access to cost-efficient, available hormonal agents and improve outcomes.

Assessing the predictive response of a simple and sensitive blood-based biomarker between estrogen-negative solid tumors

PURPOSE

We investigated N^w-hydroxy l-Arginine (NOHA) predictive response in serous ovarian carcinoma based on estrogen-hormone receptor expression status; and assessed the distinctive NOHA response between estrogen-receptor-negative (ER-) tumor subtypes of ovarian and breast cancer.

MATERIALS/METHODS

Three-dimensional (3D) spheroids models of ER- and estrogen-receptor-positive (ER+) from breast and ovarian tumor, cultured for 9 weeks, were assayed for cellular levels of inducible nitric oxide synthase (NOS2), nitric oxide (as total nitrite) and l-Arginine, and compared to NOHA in culture medium. Statistical difference was set at p < 0.01.

RESULTS

Nine-week in vitro studies showed a progressive NOHA reduction in culture medium by at least 0.4-0.8 fold, and 0.65-0.92 fold only in the ER- breast tumor and ER- ovarian tumor 3D spheroids, respectively; with increases in cellular NOS2 and nitric-oxide levels, by at least 1.0-2.45 fold in both ER- tumor subtype 3D spheroids (p < 0.01; n = 6). Within ER- subtypes, medium NOHA decreased by ≥ 38.9% in ovarian cancer over breast cancer 3D-spheroids, with cellular increases in NOS2 (by ≥ 17.4%), and nitric oxide (by ≥ 18.8%). Cellular l-Arginine to medium NOHA ratio was higher, and by at least 6.5-22.5 fold in ER- breast tumor 3D-spheroids, and at least 10-70 fold in ER- ovarian tumor 3D spheroids, than in ER+ and control conditions; and was ≥48% higher in ER- ovarian cancer than in ER- breast cancer 3D-spheroids.

CONCLUSIONS

The present study shows NOHA as a sensitive and selective indicator differentiating and distinguishing ER- subtypes based on the tumor grade.

Elucidating the Electrochemical Mechanism of NG-Hydroxy-L-arginine

NG-Hydroxy-L-arginine (NOHA) is a stable intermediate product in the urea cycle that can be used to monitor the consumption of L-arginine by nitrous oxide synthase (NOS) to produce nitric oxide (NO) and L-citrulline. Research has implicated the urea cycle in many diseases and NO has cultivated interest as a potential biomarker for neural health. Electrochemical detection is an established, cost-effective method that can successfully detect low levels of analyte concentrations. As one of the few electrochemically active species in the urea cycle, NOHA shows promise as a biomarker for monitoring disruptions in this biochemical process. In this study, we show that NOHA has an oxidation peak at +355 mV vs Ag/AgCl at a glassy carbon electrode. In addition, cyclic voltammetry studies with structural analogs - alanine and N-hydroxyguanidine - allowed us to approximate the oxidation wave at +355 mV vs Ag/AgCl to be a one electron process. Diffusivity of NOHA was found using linear scan voltammetry with a rotating disk electrode and approximated at 5.50×10-5 cm2/s. Ample work is still needed to make a robust biosensor, but the results here characterize the electrochemical activity and represent principle steps in making a NOHA biosensor.

GC-MS measurement of biological NG-hydroxy-L-arginine, a stepmotherly investigated endogenous nitric oxide synthase substrate and arginase inhibitor

L-Arginine is converted by nitric oxide synthase (NOS) to L-citrulline and nitric oxide (NO). N^G-Hydroxy-L-arginine (NOHA) is the isolable intermediate of this reaction. NOHA has been identified in biological samples by gas chromatography-mass spectrometry (GC-MS) and quantified by high-performance liquid chromatography (HPLC). Reportedly, NOHA concentrations in human plasma and serum range over four orders of magnitude (e.g., 2 nM-34 µM). The natural occurrence of NOHA in urine has not been reported thus far. Here, we report a validated stable-isotope dilution GC-MS method for the quantitative determination of NOHA in 10-µL aliquots of human serum and urine samples. The method is based on a two-step derivatization of NOHA to the methyl ester pentafluoropropionyl (PFP) derivatives using newly synthesized trideuteromethyl ester NOHA (d₃Me-NOHA) as the internal standard and GC-MS quantification. NOHA was found to form a methyl ester-N^G,N^δ,N^α-pentafluoropropionyl derivative, i.e., Me-(PFP)₃ (M, 642) with the N^G-hydroxy group remaining non-derivatized. Selected-ion monitoring of mass-to-charge (m/z) ratio of 458 for endogenous NOHA and m/z 461 for d₃Me-NOHA in the negative-ion chemical ionization mode revealed NOHA concentrations of the order of 0.2 µM in human serum and 3 µM in urine samples. Accuracy (recovery, %) was 91.6 ± 1.6% in serum and 39.9 ± 4.5% in urine. Inorganic nitrate was found to decrease NOHA recovery from urine presumably through the reaction of the OH group of NOHA with nitric acid. Imprecision (RSD,  %) ranged between 1.4 and 14.8% in serum, and between 5.3 and 18.4% in urine in the investigated concentration range (0-15 µM NOHA). Ten healthy kidney donors excreted in the urine (mean ± SEM) 13.9 ± 1.81 µmol NOHA per day before and 10.9 ± 1.4 µmol NOHA per day after kidney donation (P = 0.24). Similar results were observed for dimethylamine (DMA), the major urinary metabolite of asymmetric dimethylarginine (ADMA). Changes in NOHA and DMA correlated positively (r = 0.718, P = 0.019). This is the first report on the occurrence and measurement of NOHA in human urine and on the effect of human unilateral nephrectomy on urinary NOHA and DMA. Healthy kidney donation may be useful as a model for kidney disease.

Metabolic relevance for N-hydroxy L-arginine reduction in estrogen-negative breast cancer cells

We had shown N^w-hydroxy-L-arginine (NOHA) as a promising blood-based biomarker for estrogen-receptor-negative (ER^-) breast cancer (BC) that differentiates ER^- BC based on grade and molecular phenotype. In this in vitro study, we assessed the metabolic relevance for ER^- BC-specific NOHA modulation and correlated them with NOHA regulatory responses. This study aids future NOHA clinical utility in ER^- BC diagnosis and therapy management and would prove useful for potential drug discovery and development process.