Update on Management of Cancer-Related Cachexia.

Cachexia is a metabolic syndrome driven by inflammation and characterized by loss of muscle with or without loss of fat mass. In cancer cachexia, the tumor burden and host response induce increased inflammation, decreased anabolic tone, and suppressed appetite leading to the clinical presentation of reduced body weight and quality of life (QOL). There is no approved treatment for cancer cachexia, and commonly used nutritional and anti-inflammatory strategies alone have proven ineffective for management of symptoms. Several other pharmacological agents are currently in development and have shown promise as a clinical strategy in early-phase trials. Recently, it has been proposed that multimodal strategies, with an anabolic focus, initiated early in the disease/treatment progression may provide the most therapeutic potential for symptom management. Here we review the data from recent clinical trials in cancer cachexia including pharmacological, exercise, and nutritional interventions.

Sex Differences in Muscle Wasting.

With aging and other muscle wasting diseases, men and women undergo similar pathological changes in skeletal muscle: increased inflammation, enhanced oxidative stress, mitochondrial dysfunction, satellite cell senescence, elevated apoptosis and proteasome activity, and suppressed protein synthesis and myocyte regeneration. Decreased food intake and physical activity also indirectly contribute to muscle wasting. Sex hormones also play important roles in maintaining skeletal muscle homeostasis. Testosterone is a potent anabolic factor promoting muscle protein synthesis and muscular regeneration. Estrogens have a protective effect on skeletal muscle by attenuating inflammation; however, the mechanisms of estrogen action in skeletal muscle are less well characterized than those of testosterone. Age- and/or disease-induced alterations in sex hormones are major contributors to muscle wasting. Hence, men and women may respond differently to catabolic conditions because of their hormonal profiles. Here we review the similarities and differences between men and women with common wasting conditions including sarcopenia and cachexia due to cancer, end-stage renal disease/chronic kidney disease, liver disease, chronic heart failure, and chronic obstructive pulmonary disease based on the literature in clinical studies. In addition, the responses in men and women to the commonly used therapeutic agents and their efficacy to improve muscle mass and function are also reviewed.

Changes in Bone Biomarkers, BMC, and Insulin Resistance Following a 10-Week Whole Body Vibration Exercise Program in Overweight Latino Boys.

PURPOSE: With the childhood obesity epidemic, efficient methods of exercise are sought to improve health. We tested whether whole body vibration (WBV) exercise can positively affect bone metabolism and improve insulin/glucose dynamics in sedentary overweight Latino boys. METHODS: Twenty Latino boys 8-10 years of age were randomly assigned to either a control (CON) or 3 days/wk WBV exercise (VIB) for 10-wk. RESULTS: Significant increases in BMC (4.5 ± 3.2%; p=0.01) and BMD (1.3 ± 1.3%; p<0.01) were observed for the VIB group when compared to baseline values. For the CON group BMC significantly increased (2.0 ± 2.2%; p=0.02), with no change in BMD (0.8 ± 1.3%; p=0.11). There were no significant between group changes in BMC or BMD. No significant change was observed for osteocalcin and (collagen type I C-telopeptide) CTx for the VIB group. However, osteocalcin showed a decreasing trend (p=0.09) and CTx significantly increased (p<0.03) for the CON group. This increase in CTx was significantly different between groups (p<0.02) and the effect size of between-group difference in change was large (-1.09). There were no significant correlations between osteocalcin and measures of fat mass or insulin resistance for collapsed data. CONCLUSION: Although bone metabolism was altered by WBV training, no associations were apparent between osteocalcin and insulin resistance. These findings suggest WBV exercise may positively increase BMC and BMD by decreasing bone resorption in overweight Latino boys.

Gold nanobelts as high confinement plasmonic waveguides.

Plasmon propagation in thin plasmonic waveguides is strongly damped, making it difficult to study with diffraction-limited optics. Here we directly characterize plasmon propagation in gold nanobelts with incoherent light. The data indicate a short average propagation length of 0.94 µm but also reveal a weakly excited antisymmetric mode that has a propagation length greater than 10 µm with strong confinement of 2400 nm(2). These results demonstrate that high confinement and long propagation length can be achieved with thin plasmonic structures.

Clinical Relevance of Physical Function Outcomes in Cancer Cachexia.

Managing clinical manifestations of cancer/treatment burden on functional status and quality of life remains paramount across the cancer trajectory, particularly for patients with cachexia who display reduced functional capacity. However, clinically relevant criteria for classifying functional impairment at a single point in time or for classifying meaningful functional changes subsequent to disease and/or treatment progression are lacking. This unmet clinical need remains a major obstacle to the development of therapies for cancer cachexia. This review aims to describe current literature-based evidence for clinically meaningful criteria for (1) functional impairment at a single timepoint between cancer patients with or without cachexia and (2) changes in physical function over time across interventional studies conducted in patients with cancer cachexia. The most common functional assessment in cross-sectional and interventional studies was hand grip strength (HGS). We observed suggestive evidence that an HGS deficit between 3 and 6 kg in cancer cachexia may display clinical relevance. In interventional studies, we observed that long-duration multimodal therapies with a focus on skeletal muscle may benefit HGS in patients with considerable weight loss. Future studies should derive cohort-specific clinically relevant criteria to confirm these observations in addition to other functional outcomes and investigate appropriate patient-reported anchors.

Neuromuscular electrical stimulation for physical function maintenance during hematopoietic stem cell transplantation: Study protocol.

Hematopoietic stem cell transplantation is a common life-saving treatment for hematologic malignancies, though can lead to long-term functional impairment, fatigue, muscle atrophy, with decreased quality of life. Although traditional exercise has helped reduce these effects, it is inconsistently recommended and infrequently maintained, and most patients remain sedentary during and after treatment. There is need for alternative rehabilitation strategies, like neuromuscular electrical stimulation, that may be more amenable to the capabilities of hematopoietic stem cell transplant recipients. Patients receiving autologous HCT are being enroled in a randomized controlled trial with 1:1 (neuromuscular electrical stimulation:sham) design stratified by diagnosis and sex. Physical function, body composition, quality of life, and fatigue are assessed prior to hematopoietic stem cell transplant (prior to initiating preparatory treatment) and 24±5 days post hematopoietic stem cell transplant (Follow-up 1); physical function and quality of life are also assessed 6-months post hematopoietic stem cell transplant (Follow-up 2). The primary outcome is between-group difference in the 6-minute walk test change scores (Follow-up 1-Pre-transplant; final enrolment goal N = 23/group). We hypothesize that 1) neuromuscular electrical stimulation will attenuate hematopoietic stem cell transplant-induced adverse effects on physical function, muscle mass, quality of life, and fatigue compared to sham at Follow-up 1, and 2) Pre-transplant physical function will significantly predict fatigue and quality of life at Follow-up 2. We will also describe feasibility and acceptability of neuromuscular electrical stimulation during hematopoietic stem cell transplant. This proposal will improve rehabilitative patient care and quality of life by determining efficacy and feasibility of a currently underutilized therapeutic strategy aimed at maintaining daily function and reducing the impact of a potent and widely used cancer treatment. This trial is registered with clinicaltrials.gov (NCT04364256).

A Review of Nutraceuticals in Cancer Cachexia.

Cancer cachexia is largely characterized by muscle wasting and inflammation, leading to weight loss, functional impairment, poor quality of life (QOL), and reduced survival. The main barrier to therapeutic development is a lack of efficacy for improving clinically relevant outcomes, such as physical function or QOL, yet most nutraceutical studies focus on body weight. This review describes clinical and pre-clinical nutraceutical studies outside the context of complex nutritional and/or multimodal interventions, in the setting of cancer cachexia, in view of considerations for future clinical trial design. Clinical studies mostly utilized polyunsaturated fatty acids or amino acids/derivatives, and they primarily focused on body weight and, secondarily, on muscle mass and/or QOL. The few studies that measured physical function almost exclusively utilized handgrip strength with, predominantly, no time and/or group effect. Preclinical studies focused mainly on amino acids/derivatives and polyphenols, assessing body weight, muscle mass, and occasionally physical function. While this review does not provide sufficient evidence of the efficacy of nutraceuticals for cancer cachexia, more preclinical and adequately powered clinical studies are needed, and they should focus on clinically meaningful outcomes, including physical function and QOL.

Metabolic and quality of life effects of growth hormone replacement in patients with TBI and AGHD: A pilot study.

OBJECTIVE: Traumatic brain injury (TBI), a common cause of adult growth hormone deficiency (AGHD), affects 20% of Veterans returning from Iraq and Afghanistan (OEF/OIF/OND). Growth hormone replacement therapy (GHRT) improves quality of life (QoL) in AGHD but remains unexplored in this population. This pilot, observational study investigates the feasibility and efficacy of GHRT in AGHD following TBI. DESIGN: In this 6-month study of combat Veterans with AGHD and TBI starting GHRT (N = 7), feasibility (completion rate and rhGH adherence) and efficacy (improvements in self-reported QoL) of GHRT were measured (primary outcomes). Secondary outcomes included body composition, physical and cognitive function, psychological and somatic symptoms, physical activity, IGF-1 levels and safety parameters. It was hypothesized that participants would adhere to GHRT and that QoL would significantly improve after six months. RESULTS: Five subjects (71%) completed all study visits. All patients administered daily rhGH injections, 6 (86%) of whom consistently administered the clinically-prescribed dose. While QoL demonstrated numeric improvement, this change did not reach statistical significance (p = 0.17). Significant improvements were observed in total lean mass (p = 0.02), latissimus dorsi strength (p = 0.05), verbal learning (Trial 1, p = 0.02; Trial 5, p = 0.03), attention (p = 0.02), short-term memory (p = 0.04), and post-traumatic stress disorder (PTSD) symptoms (p = 0.03). Body weight (p = 0.02) and total fat mass (p = 0.03) increased significantly. CONCLUSION: GHRT is a feasible and well-tolerated intervention for U.S. Veterans with TBI-related AGHD. It improved key areas impacted by AGHD and symptoms of PTSD. Larger, placebo-controlled studies testing the efficacy and safety of this intervention in this population are warranted.

Pilot clinical trial of macimorelin to assess safety and efficacy in patients with cancer cachexia.

BACKGROUND: Cancer cachexia is associated with reduced body weight, appetite and quality of life (QOL) with no approved treatments. Growth hormone secretagogues like macimorelin have potential to mitigate these effects. METHODS: This pilot study assessed the safety and efficacy of macimorelin for 1 week. Efficacy was defined a priori as 1-week change in body weight (≥0.8 kg), plasma insulin-like growth factor (IGF)-1 (≥50 ng/mL) or QOL (≥15%). Secondary outcomes included food intake, appetite, functional performance, energy expenditure and safety laboratory parameters. Patients with cancer cachexia were randomized to 0.5 or 1.0 mg/kg macimorelin or placebo; outcomes were assessed non-parametrically. RESULTS: Participants receiving at least one of either macimorelin dose were combined (N = 10; 100% male; median age = 65.50 ± 2.12) and compared with placebo (N = 5; 80% male; median age = 68.00 ± 6.19). Efficacy criteria achieved: body weight (macimorelin N = 2; placebo N = 0; P = 0.92); IGF-1 (macimorelin N = 0; placebo N = 0); QOL by Anderson Symptom Assessment Scale (macimorelin N = 4; placebo N = 1; P = 1.00) or Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F; macimorelin N = 3; placebo N = 0; P = 0.50). No related serious or non-serious adverse events were reported. In macimorelin recipients, change in FACIT-F was directly associated with change in body weight (r = 0.92, P = 0.001), IGF-1 (r = 0.80, P = 0.01), and caloric intake (r = 0.83, P = 0.005), and inversely associated with change in energy expenditure (r = -0.67, P = 0.05). CONCLUSIONS: Daily oral macimorelin for 1 week was safe and numerically improved body weight and QOL in patients with cancer cachexia compared with placebo. Longer term administration should be evaluated for mitigation of cancer-induced reductions in body weight, appetite and QOL in larger studies.

A tunable plasmon resonance in gold nanobelts.

Plasmonic nanowires with sub-100-nm rectangular cross sections were found to exhibit a strong transverse plasmon peak at visible wavelengths. By correlating atomic force microscopy measurements of individual nanobelts with their dark-field scattering spectra, it is seen that the transverse peak tunes with cross-sectional aspect ratio. Simulations revealed that the scattering plasmonic modes are transverse antisymmetric excitations across the nanobelt width. Unlike larger diameter silver nanowires, these nanobelts exhibit sharp, tunable plasmon resonances similar to those of nanoparticles.

Androgens and estrogens predict sexual function after autologous hematopoietic stem cell transplant in men.

BACKGROUND: Autologous hematopoietic stem cell transplantation (AHSCT) is associated with sexual dysfunction and hypogonadism. Androgens are associated with sexual function in healthy men, but the role of estrogens is less well-known, and the association of these sex steroids with sexual function during AHSCT has not been characterized. OBJECTIVES: The purpose of this study was to determine the predictive value of sex hormones before and acutely after AHSCT on sexual function recovery. MATERIALS AND METHODS: We examined sex hormones and self-reported sexual function before (PRE) and 1-month post-AHSCT (MONTH1; n = 19), and sexual function again 1-year post-AHSCT in men (YEAR1; n = 15). RESULTS: Sexual function decreased from PRE to MONTH1 (p ≤ 0.05) with no differences between PRE and YEAR1. Erectile dysfunction was prevalent at PRE (68.4%) and increased at MONTH1 (100%; p ≤ 0.05) but was not different between PRE and YEAR1 (60.0%). From PRE to MONTH1, total testosterone (TT), dihydrotestosterone (DHT), follicle-stimulating hormone, and sex-hormone-binding globulin (SHBG) increased (p ≤ 0.02) while estradiol (p ≤ 0.026) and estrone decreased (p ≤ 0.001). MONTH1 TT and DHT were associated with sexual function at MONTH1, while PRE SHBG, MONTH1 estradiol, and change in estrone predicted sexual function at YEAR1. DISCUSSION: Sexual dysfunction is very prevalent prior to AHSCT and is transiently and severely worsened acutely after. AHSCT induces acute decreases in total and free estrogens, with SHBG increases leading to increases in total androgens, without changes in free androgens. CONCLUSION: Androgens and estrogens are both adversely affected by AHSCT but may predict sexual dysfunction in this population. This supports the premise that estrogen impacts sexual function independent from androgens and that steroid hormones are associated with acute changes in sexual function in this setting. Larger, controlled trials with long-term sex hormone assessment will need to confirm the association between early changes in estrogens and long-term sexual function recovery.

Whole-body and adipose tissue metabolic phenotype in cancer patients.

BACKGROUND: Altered adipose tissue (AT) metabolism in cancer-associated weight loss via inflammation, lipolysis, and white adipose tissue (WAT) browning is primarily implicated from rodent models; their contribution to AT wasting in cancer patients is unclear. METHODS: Energy expenditure (EE), plasma, and abdominal subcutaneous WAT were obtained from men (aged 65 ± 8 years) with cancer, with (CWL, n = 27) or without (CWS, n = 47) weight loss, and weight-stable non-cancer patients (CON, n = 26). Clinical images were assessed for adipose and muscle area while plasma and WAT were assessed for inflammatory, lipolytic, and browning markers. RESULTS: CWL displayed smaller subcutaneous AT (SAT; P = 0.05) and visceral AT (VAT; P = 0.034) than CWS, and displayed higher circulating interleukin (IL)-6 (P = 0.01) and WAT transcript levels of IL-6 (P = 0.029), IL-1ß (P = 0.042), adipose triglyceride lipase (P = 0.026), and browning markers (Dio2, P = 0.03; PGC-1a, P = 0.016) than CWS and CON. There was no difference across groups in absolute REE (P = 0.061), %predicted REE (P = 0.18), circulating free fatty acids (FFA, P = 0.13) or parathyroid hormone-related peptide (PTHrP; P = 0.88), or WAT protein expression of inflammation (IL-6, P = 0.51; IL-1ß, P = 0.29; monocyte chemoattractant protein-1, P = 0.23) or WAT protein or gene expression of browning (uncoupling protein-1, UCP-1; P = 0.13, UCP-1, P = 0.14). In patients with cancer, FFA was moderately correlated with WAT hormone-sensitive lipase transcript (r = 0.38, P = 0.018, n = 39); circulating cytokines were not correlated with expression of WAT inflammatory markers and circulating PTHrP was not correlated with expression of WAT browning markers. In multivariate regression using cancer patients only, body mass index (BMI) directly predicted SAT (N = 25, R2  = 0.72, P < 0.001), VAT (N = 28, R2  = 0.64, P < 0.001), and absolute REE (N = 22, R2  = 0.43, P = 0.001), while BMI and WAT UCP-1 protein were indirectly associated with %predicted REE (N = 22, R2  = 0.45, P = 0.02), and FFA was indirectly associated with RQ (N = 22, R2  = 0.52, P < 0.001). CONCLUSIONS: Cancer-related weight loss was associated with elevated circulating IL-6 and elevations in some WAT inflammatory, lipolytic and browning marker transcripts. BMI, not weight loss, was associated with increased energy expenditure. The contribution of inflammation and lipolysis, and lack thereof for WAT browning, will need to be clarified in other tumour types to increase generalizability. Future studies should consider variability in fat mass when exploring the relationship between cancer and adipose metabolism and should observe the trajectory of lipolysis and energy expenditure over time to establish the clinical significance of these associations and to inform more mechanistic interpretation of causation.

Structural transition in the surfactant layer that surrounds gold nanorods as observed by analytical surface-enhanced Raman spectroscopy.

Surface-enhanced Raman spectroscopy (SERS) of gold nanorods in cetyltrimethylammonium bromide solution has been used to analyze the interfacial surfactant structure based on the distance-dependent electromagnetic enhancement. The spectra were consistent with a surfactant bilayer oriented normal to the surface. As the surfactant concentration was reduced, a structural transition in the surfactant layer was observed through a sudden increase in the signal from the alkane chains. The structural transition was shown to influence the displacement of the surfactant layer by thiolated poly(ethylene glycol). The monodisperse and thoroughly characterized gold nanorod samples yield consistent enhancement factors that were compared to electromagnetic simulations.

Experience of a Pituitary Clinic for US Military Veterans With Traumatic Brain Injury.

CONTEXT: Traumatic brain injury (TBI) is considered the "signature" injury of veterans returning from wartime conflicts in Iraq and Afghanistan. While moderate/severe TBI is associated with pituitary dysfunction, this association has not been well established in the military setting and in mild TBI (mTBI). Screening for pituitary dysfunction resulting from TBI in veteran populations is inconsistent across Veterans Affairs (VA) institutions, and such dysfunction often goes unrecognized and untreated. OBJECTIVE: This work aims to report the experience of a pituitary clinic in screening for and diagnosis of pituitary dysfunction. METHODS: A retrospective analysis was conducted in a US tertiary care center of veterans referred to the VA Puget Sound Healthcare System pituitary clinic with a history of TBI at least 12 months prior. Main outcome measures included demographics, medical history, symptom burden, baseline hormonal evaluation, brain imaging, and provocative testing for adrenal insufficiency (AI) and adult-onset growth hormone deficiency (AGHD). RESULTS: Fatigue, cognitive/memory problems, insomnia, and posttraumatic stress disorder were reported in at least two-thirds of the 58 patients evaluated. Twenty-two (37.9%) were diagnosed with at least one pituitary hormone deficiency, including 13 (22.4%) AI, 12 (20.7%) AGHD, 2 (3.4%) secondary hypogonadism, and 5 (8.6%) hyperprolactinemia diagnoses; there were no cases of thyrotropin deficiency. CONCLUSION: A high prevalence of chronic AI and AGHD was observed among veterans with TBI. Prospective, larger studies are needed to confirm these results and determine the effects of hormone replacement on long-term outcomes in this setting.

Evaluation of physical function and its association with body composition, quality of life and biomarkers in cancer cachexia patients.

BACKGROUND & AIMS: There are currently no approved treatments for cancer cachexia. One of the main barriers to developing a treatment for this indication is the lack of consensus on clinically important tools for assessing functional impairment in this setting. This issue is of critical importance because functional improvement is likely to be required for approval by regulatory agencies. This cross-sectional study aimed to evaluate various functional performance measures and establish their association with body composition, energy expenditure, biomarkers, and patient-reported quality of life (QOL). METHODS: Physical function, body composition, energy expenditure, cytokines, testosterone, and patient-reported QOL were compared between men with solid tumors with cachexia (CAC; N = 48), without cachexia (CNC; N = 48), and weight-stable patients without cancer (CON; N = 37). Receiver Operator Characteristic curves and multivariate regression were performed to identify functional impairment cut-points and predictors of physical function, respectively. RESULTS: Patients with CAC displayed lower total lean and appendicular lean mass, stair climb power (SCP), upper body strength, and bioavailable testosterone, and displayed higher energy expenditure than CNC or CON (p ≤ 0.03); CAC showed lower handgrip, respiratory quotient, and appetite, and higher cytokines and fatigue than CON (p ≤ 0.032). A cut-point of 336 Watts for SCP provided 78% sensitivity and 77% specificity for classification of CAC (p = 0.001); SCP also performed better than other measures tested when compared to CON-derived normatives. Upper body strength exhibited moderate sensitivity and specificity for classification of CAC (p ≤ 0.02). Elevated relative energy expenditure and cytokines negatively predicted, and muscle mass positively predicted, various muscle strength outcomes. CONCLUSION: Stair climb power and upper body strength may have potential as discriminatory tests for functional impairment in patients with cancer cachexia.

Weight Loss in Cancer Patients Correlates With p38ß MAPK Activation in Skeletal Muscle.

Unintentional weight loss, a first clinical sign of muscle wasting, is a major threat to cancer survival without a defined etiology. We previously identified in mice that p38ß MAPK mediates cancer-induced muscle wasting by stimulating protein catabolism. However, whether this mechanism is relevant to humans is unknown. In this study, we recruited men with cancer and weight loss (CWL) or weight stable (CWS), and non-cancer controls (NCC), who were consented to rectus abdominis (RA) biopsy and blood sampling (n = 20/group). In the RA of both CWS and CWL, levels of activated p38ß MAPK and its effectors in the catabolic pathways were higher than in NCC, with progressively higher active p38ß MAPK detected in CWL. Remarkably, levels of active p38ß MAPK correlated with weight loss. Plasma analysis for factors that activate p38ß MAPK revealed higher levels in some cytokines as well as Hsp70 and Hsp90 in CWS and/or CWL. Thus, p38ß MAPK appears a biomarker of weight loss in cancer patients.

Hot plasmonic interactions: a new look at the photothermal efficacy of gold nanoparticles.

The photothermal (PT) outputs of individual gold nanoparticles (NP) were compared at room (cold) and high transient (hot) temperatures. High temperatures were induced in NPs by a single 0.5 ns laser pulse. All NPs with near-infrared plasmon resonances (rods, shells and bi-pyramids) exhibited a significant decrease in their photothermal output at the resonant wavelengths under high temperature, while non-resonant excitation of the same NPs provided several times higher PT efficacy of the hot NPs. This "inversion" of the PT efficacy of hot plasmonic NPs near their plasmon resonances might have been caused by damping of their resonances due to heating and surface melting. Therefore, photothermal output of plasmonic nanoparticles significantly depends upon their thermal state including the shift in excitation wavelength in hot nanoparticles. In particular, NPs with near-infrared resonances perform several times more efficiently at non-resonant excitation wavelengths rather than at the resonant ones.

Muscle mass, not radiodensity, predicts physical function in cancer patients with or without cachexia.

BACKGROUND: There is a need to better understand the relationship between functional impairment and muscle mass in cancer cachexia. This study aimed to establish the relationship between computed tomography (CT)-derived muscle cross-sectional area (CSA), radiodensity, and skeletal muscle index (SMI) and dual energy X-ray absorptiometry (DXA) parameters with functional performance in cancer patients. MATERIALS AND METHODS: Handgrip strength, stair climb power (SCP), one-repetition maximum (1RM) strength, and body composition (CT and DXA) were compared across cancer patients with cachexia (CAC; N = 28), without cachexia (CNC; N = 28), and non-cancer patients (CON; N = 19). Multivariate regression was performed to find predictors of function. RESULTS: CAC had lower CT muscle CSA and SMI and lower DXA appendicular lean mass (ALM) than CNC or CON (p ≤ 0.011). Muscle radiodensity was not different across groups despite larger proportion of low CT SMI in CAC, and CAC performed worse in SCP than CON (p = 0.018). In cancer patients, DXA ALM and CT muscle CSA each predicted physical function (p ≤ 0.05); muscle radiodensity did not, and DXA ALM explained more variability in SCP and 1RM than CT muscle CSA. CONCLUSIONS: Stair climb power was reduced in cancer cachexia; muscle radiodensity was not. Muscle mass by CT or DXA, but not radiodensity, predicted functional performance in cancer patients.

The stabilization and targeting of surfactant-synthesized gold nanorods.

The strong cetyltrimethylammonium bromide (CTAB) surfactant responsible for the synthesis and stability of gold nanorod solutions complicates their biomedical applications. The critical parameter to maintain nanorod stability is the ratio of CTAB to nanorod concentration. The ratio is approximately 740,000 as determined by chloroform extraction of the CTAB from a nanorod solution. A comparison of nanorod stabilization by thiol-terminal PEG and by anionic polymers reveals that PEGylation results in higher yields and less aggregation upon removal of CTAB. A heterobifunctional PEG yields nanorods with exposed carboxyl groups for covalent conjugation to antibodies with the zero-length carbodiimide linker EDC. This conjugation strategy leads to approximately two functional antibodies per nanorod according to fluorimetry and ELISA assays. The nanorods specifically targeted cells in vitro and were visible with both two-photon and confocal reflectance microscopies. This covalent strategy should be generally applicable to other biomedical applications of gold nanorods as well as other gold nanoparticles synthesized with CTAB.