Factors Associated with Clinical Research Recruitment in a Pediatric Academic Medical Center—A Web-Based Survey

Background

One of the most difficult aspects of conducting clinical research is the ability to successfully recruit participants. Pediatric clinical research presents unique recruitment challenges that relate to the need for parental consent on behalf of a minor, child assent, and school attendance. Yet, this has been less well studied. We conducted a survey of investigators performing human subjects research in a single large academic pediatric hospital to better understand characteristics of studies with successful recruitment.

Methods

We conducted a web-based survey from September 2011 to December 2011 of all principal investigators with an Institutional Review Board approved human subjects protocol at Boston Children’s Hospital, a pediatric Academic Medical Center. The survey captured various characteristics of the protocols including study design, staffing, resources, and investigator experience and training as well as respondents’ perceived barriers and facilitators to recruitment. We used chi square tests and Mantel-Haenszel test for linear trend to examine the relationship between selected predictor variables and the binary outcome of successful vs. unsuccessful recruitment and multivariable logistic regression analyses to examine the simultaneous influence of potential predictors on each outcome.

Results

Among the 349 eligible investigators, 52% responded to the survey, and 181 with valid data were included in the analyses. Two-thirds of the 87 protocols closed to enrollment reached 80% or more of their target enrollment, whereas, only one-third of the 94 protocols actively recruiting were meeting 80% of their target. Recruitment method appeared to be the only significant and independent factor associated with achieving 80% or more of target enrollment in closed to enrollment protocols. Closed to enrollment protocols that used recruitment in person were 4.55 times (95% CI 1.30 to 15.93; p = 0.02) more likely to achieve 80% or more of their target enrollment when compared to those that used other recruitment methods. Other potentially modifiable factors such as number of study visits, study duration and investigator experience were suggestive of being meaningfully related to recruitment.

Conclusion

Recruiting in person may promote reaching an acceptable target enrollment in pediatric as well as adult clinical research. Future research is needed on larger and more diverse samples to gain a better understanding of how the characteristics and qualifications of the individuals who conduct recruitment influence participant enrollment as well as how best to approach patient and families for their participation.     

Enhanced loading efficiency and retention of 225Ac in rigid liposomes for potential targeted therapy of micrometastases

Targeted alpha-particle emitters are promising therapeutics for micrometastatic disease. Actinium-225 has a 10-day half-life and generates a total of four alpha-particles per parent decay rendering (225)Ac an attractive candidate for alpha-therapy. For cancer cells with low surface expression levels of molecular targets, targeting strategies of (225)Ac using radiolabeled carriers of low specific radioactivities (such as antibodies) may not deliver enough alpha-particle emitters at the targeted cancer cells to result in killing. We previously proposed and showed using passive (225)Ac entrapment that liposomes can stably retain encapsulated (225)Ac for long time periods, and that antibody-conjugated liposomes (immunoliposomes) with encapsulated (225)Ac can specifically target and become internalized by cancer cells. However, to enable therapeutic use of (225)Ac-containing liposomes, high activities of (225)Ac need to be stably encapsulated into liposomes. In this study, various conditions for active loading of (225)Ac in preformed liposomes (ionophore-type, encapsulated buffer solution, and loading time) were evaluated, and liposomes with up to 73 +/- 9% of the initial activity of (225)Ac (0.2-200 microCi) were developed. Retention of radioactive contents by liposomes was evaluated at 37 degrees C in phosphate buffer and in serum-supplemented media. The main fraction of released (225)Ac from liposomes occurs within the first two hours of incubation. Beyond this two hour point, the encapsulated radioactivity is released from liposomes slowly with an approximate half-life of the order of several days. In some cases, after 30 days, (225)Ac retention as high as 81 +/- 7% of the initially encapsulated radioactivity was achieved. The (225)Ac loading protocol was also applied to immunoliposome loading without significant loss of targeting efficacy. Liposomes with surface-conjugated antibodies that are loaded with (225)Ac overcome the limitations of low specific activity for molecular carriers and are expected to be therapeutically useful against tumor cells having a low antigen density.     

Palladium(II) and platinum(II) complexes of 2-hydroxy acetophenone N(4)-ethylthiosemicarbazone - crystal structure and description of bonding properties

Reaction of H₂PtCl₄ and K₂PdCl₄ with 2-hydroxyacetophenone N(4)-ethylthiosemicarbazone, H₂Ap4Et, afforded [Pt(Ap4Et)(H₂Ap4Et)] and [Pd(Ap4Et)(H₂Ap4Et)]. Their crystal and molecular structures are reported and represent the first 1:2 thiosemicarbazone complexes with ligands having both different formal charge and denticity. The dianion, Ap4Et²⁻, coordinates in a planar conformation to palladium(II) or platinum(II) via the phenolato O, imine N and thiolato S atoms, while the neutral molecule exhibits monodentate coordination by the thione S atom. Intra-, intermolecular hydrogen bonds and C-H?π contacts lead to aggregation and a supramolecular assembly. Electronic, IR, and NMR spectral data, as well as electrochemical measurements, are included. The pK_a values of the poorly water soluble H₂Ap4Et were obtained spectrophotometrically in aqueous solutions of constant ionic strength.     

Generation of human anti-MUC3 IgG antibodies after in vitro immunization of naive peripheral blood B-lymphocytes

It has been demonstrated that IgG antibodies can be generated to self-antigen peptides as well as against viral antigens by an antigen-specific in vitro immunization system of resting human peripheral B-lymphocytes. Using a synthetic peptide from the consensus variable tandem-repeat region of the MUC3 mucin (TSSITTTGTTSHSTPSP) as the B cell epitope, we immunized blood donor B-lymphocytes in vitro and tested for MUC3-specific antibodies by ELISA. After the primary activation step all antibodies were IgM. At the end of the secondary immunization step we obtained 1.8% (21/1138) of the cultures with IgG-switched antibodies. In a competitive inhibition ELISA using the MUC1, MUC2, MUC3, MUC4 and PIP2 peptides, only one culture (F8.1) gave satisfactory specific inhibition. Using this antibody in fluorometric studies, it stained cells from two colon carcinoma cell lines predominantly in the cytoplasm, whereas those from a breast cancer cell line stained predominantly the cell surface. In a preliminary immunohistological evaluation with formalin-fixed sections, the antibody appeared to moderately stain colon sections, but not breast sections or lymph node. This method of in vitro immunization may be a useful tool in generating IgG antibodies specific to self-antigens and could find applications in tumour targeting and immunotherapy. Received: 12 October 2000 / Accepted: 11 January 2001     

Hematocrit,viscosity and velocity distributions of aggregating and non-aggregating blood in a bifurcating microchannel

Microscale blood flow is characterised by heterogeneous distributions of hematocrit, viscosity and velocity. In microvascular bifurcations, cells are unevenly distributed between the branches, and this effect can be amplified in subsequent branches depending on a number of parameters. We propose an approach to infer hematocrit profiles of human blood flowing through a bifurcating microchannel. The influence of aggregation, induced by the addition of Dextran 2000 to the samples, is also considered. Averaged values indicate plasma skimming, particularly in the presence of red blood cell (RBC) aggregation. Using an empirical model, the hematocrit profiles are used to estimate local relative viscosity distributions. Simulations are used to predict how the non-uniform viscosity influences the velocity profiles. Comparing these data to velocity profiles of RBCs measured using particle image velocimetry provides validation of the model. It is observed that aggregation blunts velocity profiles after a long straight section of channel. Downstream of the bifurcation, skewing of the velocity profiles is detected, which is enhanced by aggregation. The proposed methodology is capable of providing hitherto unreported information on important aspects of microscale blood rheology.     

Enhanced retention of the alpha-particle-emitting daughters of Actinium-225 by liposome carriers

Targeted alpha-particle emitters hold great promise as therapeutics for micrometastatic disease. Because of their high energy deposition and short range, tumor targeted alpha-particles can result in high cancer-cell killing with minimal normal-tissue irradiation. Actinium-225 is a potential generator for alpha-particle therapy: it decays with a 10-day half-life and generates three alpha-particle-emitting daughters. Retention of (225)Ac daughters at the target increases efficacy; escape and distribution throughout the body increases toxicity. During circulation, molecular carriers conjugated to (225)Ac cannot retain any of the daughters. We previously proposed liposomal encapsulation of (225)Ac to retain the daughters, whose retention was shown to be liposome-size dependent. However, daughter retention was lower than expected: 22% of theoretical maximum decreasing to 14%, partially due to the binding of (225)Ac to the phospholipid membrane. In this study, Multivesicular liposomes (MUVELs) composed of different phospholipids were developed to increase daughter retention. MUVELs are large liposomes with entrapped smaller lipid-vesicles containing (225)Ac. PEGylated MUVELs stably retained over time 98% of encapsulated (225)Ac. Retention of (213)Bi, the last daughter, was 31% of the theoretical maximum retention of (213)Bi for the liposome sizes studied. MUVELs were conjugated to an anti-HER2/neu antibody (immunolabeled MUVELs) and were evaluated in vitro with SKOV3-NMP2 ovarian cancer cells, exhibiting significant cellular internalization (83%). This work demonstrates that immunolabeled MUVELs might be able to deliver higher fractions of generated alpha-particles per targeted (225)Ac compared to the relative fractions of alpha-particles delivered by (225)Ac-labeled molecular carriers.     

<Emphasis Type="Italic">CER1</Emphasis>gene variations associated with bone mineral density,bone markers,and early menopause in postmenopausal women

Background

Osteoporosis has a multifactorial pathogenesis characterized by a combination of low bone mass and increased fragility. In our study, we focused on the effects of polymorphisms in CER1 and DKK1 genes, recently reported as important susceptibility genes for osteoporosis, on bone mineral density (BMD) and bone markers in osteoporotic women. Our objective was to evaluate the effect of CER1 and DKK1 variations in 607 postmenopausal women. The entire DKK1 gene sequence and five selected CER1 SNPs were amplified and resequenced to assess whether there is a correlation between these genes and BMD, early menopause, and bone turnover markers in osteoporotic patients.

Results

Osteoporotic women seem to suffer menopause 2 years earlier than the control group. The entire DKK1 gene sequence analysis revealed six variations. There was no correlation between the six DKK1 variations and osteoporosis, in contrast to the five common CER1 variations that were significantly associated with BMD. Additionally, osteoporotic patients with rs3747532 and rs7022304 CER1 variations had significantly higher serum levels of parathyroid hormone and calcitonin and lower serum levels of osteocalcin and IGF-1.

Conclusions

No significant association between the studied DKK1 variations and osteoporosis was found, while CER1 variations seem to play a significant role in the determination of osteoporosis and a potential predictive role, combined with bone markers, in postmenopausal osteoporotic women.