The development of rickets as a complication of chemotherapy for the treatment of Wilms' tumor

Biological effects of short-term or prolonged administration of 9-[2-(phosphonomethoxy)propyl]adenine (tenofovir) to newborn and infant rhesus macaques

The reverse transcriptase inhibitor 9-[2-(phosphonomethoxy)propyl]adenine (PMPA; tenofovir) was previously found to offer strong prophylactic and therapeutic benefits in an infant macaque model of pediatric human immunodeficiency virus (HIV) infection. We now summarize the toxicity and safety of PMPA in these studies. When a range of PMPA doses (4 to 30 mg/kg of body weight administered subcutaneously once daily) was administered to 39 infant macaques for a short period of time (range, 1 day to 12 weeks), no adverse effects on their health or growth were observed; this included a subset of 12 animals which were monitored for more than 2 years. In contrast, daily administration of a high dose of PMPA (30 mg/kg subcutaneously) for prolonged periods of time (>8 to 21 months) to 13 animals resulted in a Fanconi-like syndrome (proximal renal tubular disorder) with glucosuria, aminoaciduria, hypophosphatemia, growth restriction, bone pathology (osteomalacia), and reduced clearance of PMPA. The adverse effects were reversible or were alleviated following either complete withdrawal of PMPA treatment or reduction of the daily regimen from 30 mg/kg to 2.5 to 10 mg/kg subcutaneously. Finally, to evaluate the safety of a prolonged low-dose treatment regimen, two newborn macaques were started on a 10-mg/kg/day subcutaneous regimen; these animals are healthy and have normal bone density and growth after 5 years of daily treatment. In conclusion, our findings suggest that chronic daily administration of a high dose of PMPA results in adverse effects on kidney and bone, while short-term administration of relatively high doses and prolonged low-dose administration are safe.

The effect of chemotherapy on the growing skeleton

With the increasing use of high dose (poly)chemotherapy schedules in the treatment of childhood cancer it is particularly important to know the adverse effects of these treatments. Growth is a complex mechanism affected not only by chemotherapy but also by the malignancy itself as well as nutritional status, the use of corticosteroids and (cranial) radiation. In vitro and animal studies are often the most useful in determining the effect of a single chemotherapeutic agent on the growing skeleton. In vitro studies have shown doxorubicin, actinomycin D and cisplatin to have a direct effect on growth plate chondrocytes that in animals results in decreased growth and final height. Clinical studies with multiagent chemotherapy have demonstrated that antimetabolites decrease bone growth and final height. Childhood cancer survivors are at risk of a reduced bone mineral density, mainly due to methotrexate, ifosfamide and corticosteroids. This reduced bone mineral density persists into adult life and may increase bone fracture risk at an older age.

Cytoprotection in the treatment of pediatric cancer: review of current strategies in adults and their application to children

BACKGROUND

The protection of patients from the acute and/or chronic toxicity of antineoplastic therapy has become a major concern of oncology centers around the world. However, most of the effort has been directed toward the adult population, and limited studies have been performed in the group that may gain the most from such strategies, namely, children.

PROCEDURES

The MedLine and CancerLit databases were surveyed, and the relevant biomedical literature on cytoprotection during antineoplastic treatment was analyzed.

RESULTS

Cytotoxicity from antineoplastic therapy customarily is addressed by altering dosing schedules, a technique that can seriously impact the efficacy of the therapy. Colony stimulating factors have been used posttherapy to stimulate recovery from neutropenia, and various agents have been proposed as pretherapy cytoprotectors. Trials in adults have produced mixed results, and, to date, only amifostine and dexrazoxane have been approved as cytoprotectors for very narrow indications. Few trials have been performed in children, although these patients often can look forward to long-term remission.

CONCLUSIONS

To prevent permanent toxicities from antineoplastic therapies that impact long-term pediatric survivors, the experience gained in adults should be extended more aggressively to children, and formal, randomized trials should be performed to determine the type of protection most suitable for the pediatric population.

Bone density in survivors of childhood malignancies

PURPOSE

The purpose of this study was to assess bone mineralization in survivors of childhood malignancies.

PATIENTS AND METHODS

Bone mineral density (BMD) of the lumbar spine was measured in 60 patients aged 5.5-20.1 years (mean, 12.4 years) who had no known disease 1.0-14.5 years (mean, 4.3 years) after completing treatment for a malignancy. The age-normalized BMD findings (Z scores) were correlated with multiple variables, including measures of growth and nutrition, type of malignancy, and various treatments, including use of steroids, methotrexate, or cranial irradiation.

RESULTS

BMD was normal in most patients with a mean Z score of -0.28 + 0.14 (+/- SE). Only 8% of the patients were more than 2 SDs below age-matched normal BMD. Weight Z score was the major determinant of BMD Z score. Calcium intake and height Z score were also important variables.

CONCLUSIONS

Most survivors of childhood malignancies will not be left with a clinically significant deficit in BMD. Risk factors for diminished BMD include low-weight and low-height Z scores and low calcium intake. Therapeutic interventions are available to address these risk factors in those patients with significantly diminished BMD.