Microdosing in early lead discovery.

Microdosing provides a tool to enhance drug development by initiating human studies prior to Phase I studies. The purpose is to assist in the go versus no-go decision-making process and to eliminate early ineffective compounds from the drug pipeline. Selection of multiple potential leads can be performed at the clinical stage instead of in preclinical studies. The microdosing approach can be easily used for a molecularly targeted potential drug compound with a known mechanism of action. It provides useful data regarding accessibility and biodistribution that can be used in many estimations benefiting the development of the molecule. In addition, steady state and genetic investigations are becoming possible. Microdosing has a sparing effect on timelines and costs, however, the real importance is not yet known because, although it is known to be widely performed, only a few original reports have been published.

Nuclear medicine methods for evaluation of skeletal infection among other diagnostic modalities.

Skeletal infection continues to be a common and difficult condition in clinical practice and early accurate diagnosis is very challenging. Clinical and laboratory features of skeletal infections are not always present, may be confusing, and are nonspecific for bone infection in its early stages, therefore, several imaging modalities are used for early detection of osteomyelitis. Plain films should always be the first step in the imaging assessment of osteomyelitis, however, the sensitivity for X-ray radiography has been reported to range from 43% to 75%, and the specificity from 75% to 83%. Over years, scintigraphic procedures have become an essential part of the diagnostic procedure for osteomyelitis. The standard approach for bone scintigraphy with tech 99mTc labeled methylene diphosphonate to assess for osteomyelitis is to perform a three-phase procedure. The positive uptake on all three phases is highly sensitive for osteomyelitis (sensitivity 73% to 100%). 67Ga citrate gained more attention for the more specific diagnosis of osteomyelitis due to its known capacity to localize in cases of active infection and pus. The reported specificity for 67Ga scintigraphy in osteomyelitis is around 67-70% and the specificity is much higher (92%) when 67Ga single photon emission tomography was obtained. Labeled white blood cell (WBC) imaging has become the procedure of choice to diagnose most cases of skeletal infections except for those of the spine. Labeling of leucocytes can be done either by 111In or 99mTc labeled hexamethylpropylene amineoxime. The sensitivity and specificity for labeled WBCs are in the high range of 80% to 90%. [18F]fluorodeoxyglucose positron emission tomography (PET) has been found to accumulate non-specifically at sites of infection and inflammation. Investigational studies showed that PET is particularly valuable in the evaluation of chronic osteomyelitis and infected prostheses. Other imaging modalities include sonography, computed tomography (CT) and magnetic resonance imaging (MRI). The sensitivity and specificity of CT for the diagnosis of osteomyelitis has not been established clearly and are in the range of 65% to 75%. The sensitivity of MRI for osteomyelitis has been generally reported as being between 82% and 100%, and specificity between 75% and 96%. Cases of osteomyelitis commonly referred to diagnostic imaging departments include chronic osteomyelitis, diabetic foot infections, vertebral osteomyelitis, joint prostheses and patients with suspected reinfection. These specific entities need special attention and careful selection of the correct tracer or combination of imaging modalities that is best suited for the proper therapeutic management protocols.

Detection of fungal infections using radiolabeled antifungal agents.

The outcome of antifungal therapy depends on the progression of the infection at the start of therapy. Unfortunately, most patients are diagnosed once the fungal infection has progressed considerably as a result of the non-specific clinical signs of fungal infections in immunocompromised patients and the poor sensitivity of current mycological diagnostic tests. This review will highlight current fungal diagnostic techniques and will focus on scintigraphic methods for the specific detection of fungal infections in mice. For this purpose, antifungal components (e.g. fluconazole and antifungal peptides) are radiolabeled e.g. with technetium-99m ((99m)Tc) and their in vivo distribution is monitored in infected mice. It has been demonstrated that (99m)Tc-fluconazole is an excellent tracer to detect Candida albicans infections in mice as it distinguishes these infections from bacterial infections and sterile inflammations. However, this radiopharmaceutical only poorly detects infections with Aspergillus fumigatus in mice. (99m)Tc-peptides derived from antifungal peptides/proteins, such as human ubiquicidin and lactoferrin, can distinguish C. albicans and A. fumigatus infections from sterile inflammations, but not from bacterial infections, in mice. Furthermore, the efficacy of fluconazole in C. albicans-infected mice could be successfully monitored using (99m)Tc-ubiquicidin. In conclusion, neither (99m)Tc-fluconazole nor the (99m)Tc-peptides tested are optimal tracers for fungal infections. Nonetheless, since early initiation of antifungal therapy for candidemia reduces its high mortality rate, a positive result with (99m)Tc-fluconazole scintigraphy is of clinical relevance. Finally, the possibility that other (radiolabeled) antifungal agents, e.g. voriconazole, caspofungin, antifungal plant or insect defensins, can be useful for detection of fungal infections should be considered.

Long-term renal function after hemopoietic stem cell transplantation in children.

Glomerular function of all long-term survivors who underwent hemopoietic stem cell transplantation (HSCT) from 1991 to 1998 (study I, n=121) was studied retrospectively. In addition, we prospectively analyzed glomerular and tubular function of all long-term surviving children who received an HSCT between 1998 and 2000 (study II, n=41). We found a lower prevalence of children with chronic renal failure (CRF) post-HSCT in our more recent cohort (study II: 10%) as compared to the older cohort (study I: 24%) 5.0 (0.7 s.d.) and 7.6 (2.4 s.d.) year's post-HSCT, respectively. Furthermore, it seems that renal function may stabilize after 1-year post-HSCT. None of the patients required dialysis or antihypertensive medication at long-term follow-up. The sole predictor of CRF in our study was high serum creatinine pre-HSCT (P=0.007), while acute renal failure within 3 months after HSCT (P=0.08) only showed a trend towards predicting CRF. We could not confirm a relation of conditioning with irradiation with CRF post-HSCT, as was shown in several other pediatric and adult studies. Proximal and distal tubular dysfunction only occurred in a minority of long-time survivors of HSCT (3-12 and 9-13%, respectively) and had no clinical consequences.

99mTc-antimicrobial peptides: promising candidates for infection imaging.

This review presents the state of the art of imaging of bacterial and fungal infections in laboratory animals using antimicrobial peptides labelled with technetium-99m ((99m)Tc). The mechanistic basis of this approach is that these peptides accumulate at sites of infection, but not in sterile inflammatory lesions, because of their preferential binding to bacteria and fungi over mammalian cells. For practical reasons, such as production of large amounts of peptides under good laboratory practice conditions and favourable pharmacokinetics, synthetic peptides representing such binding domains of natural antimicrobial peptides are preferred. On the basis of their preferential in vitro and in vivo binding to microorganisms over human cells, fast and easy penetration into the target area, and rapid clearance from the circulation via the urinary tract, various (99m)Tc-antimicrobial peptides were identified. Next, it was determined whether these radiopharmaceuticals distinguish infectious foci from sites of sterile inflammation. Further experiments with (99m)Tc-ubiquicidin-derived peptides in infected laboratory animals have revealed that the radioactivity at the infectious site correlated well with the number of viable bacteria present, indicating that these (99m)Tc-labelled peptides may enable the monitoring of the efficacy of antimicrobial therapy. Together, (99m)Tc-labelled synthetic peptides derived from human ubiquicidin are promising candidates for imaging of bacterial and fungal infections in nuclear medicine.

A reassessment of bone scintigraphy and commonly tested pretreatment biochemical parameters in newly diagnosed osteosarcoma.

PURPOSE: In patients with an osteosarcoma, the prognosis is still poor. The aim of the present study was to investigate whether routinely tested biochemical parameters or additional parameters on bone scintigraphy could be identified which can select prognostic subgroups at the time of diagnosis. METHODS: A retrospective study was performed in 115 consecutive patients (70 male, 45 female) (mean age: 25.6 years; range: 3.50-78.0 years) who were referred for bone scintigraphy prior to treatment from March 1986 to September 2000 because of a newly diagnosed osteosarcoma. All bone scans were reassessed for the intensity and pattern of uptake and a bone-scan index. All pre-treatment general, histological, biochemical, and scintigraphic data were correlated with clinical outcome during follow-up. RESULTS: During follow-up 54 patients died. Tumour volume and GGT showed significance as independent variables for metastases. Patients with metastases demonstrated a significantly lower survival rate (23% 5-year survival) than patients without metastases (98% 5-year survival). Tumours of the humerus and femur had a significantly lower survival rate. With respect to significant biochemical parameters (ALP, GGT, ASAT), it was not possible to determine a cut-off value that could be used to differentiate between high- and low-risk patients. Additional parameters assessed on bone scintigraphy were not important for prognostic stratification. CONCLUSION: The strongest predictor of survival in osteosarcoma is the presence or absence of metastasis. Some biochemical parameters have prognostic value, but they cannot be used for the unequivocal identification of subgroups. Additional scintigraphic parameters are irrelevant for prognostic stratification.

Circulating tumor markers and nuclear medicine imaging modalities: breast, prostate and ovarian cancer.

Clinical oncologists have always shown great interest in circulating tumor markers. There are several markers that in the clinical routine are a signal of particular tumor types; some of them are strictly tissue-specific such as prostatic specific antigen (PSA) for prostatic cancer, AFP and HCG for germ cell tumors of the testis and ovary, others such as CA 15.3, CA125, CEA or cytokeratins are less specific since their elevations can be found in different varieties of cancers even if they are preferentially associated to a certain tumor type, thus are considered markers for breast, ovarian cancer and colon adenocarcinoma. The most useful clinical applications of these parameters is their determination during the follow-up of the treated patients, in order to detect the tumor recurrence early, and also to evaluate the evolution of the disease by monitoring the treatment responses. During follow-up, increasing levels of tumor markers can be observed even several months before the clinical demonstration of cancer recurrence. The association of tumor marker tests with imaging modalities can lead to several advantages: the first is to confirm the diagnosis of relapses, possibly before the appearence of the related clinical symptoms due to tumor growth; the second is to localize the sites of lesions, while tumor markers provide only a general indication of the existence of metastases; the third is to make possible a correct whole body restaging. In the assessment of cancer response tumor markers are often very reliable and their changes are faster than the morphological ones. Among all the imaging modalities, nuclear medicine plays an important role in detecting recurrences and metastatic localizations as it is able to investigate functional rather than morphological aspects of tumors, and provide different information in comparison to morphologic imaging. In addition, the scintigraphic techniques offer the possibility to evaluate treatment responses, confirming or not the information from biochemical changes. This review aims to show some examples (breast, prostate and ovarian cancer) in which the combination of nuclear medicine imaging modalities and tumor marker tests is proposed for clinical practice. The advantages and some critical aspects are discussed on the basis of the clinical findings and the most important clinical indications are described.