Career planning for pediatric residents.

After having made decisions about college, medical school, and specialty training, some residents may delay consideration of their future career in pediatrics. Others, having decided what path they will pursue, are not clear as to what steps need to be taken to ensure that they approach their choice armed with the most appropriate and accurate information. Residents seek career choice information from various sources. For many, the resources may not be able to provide as complete information in all facets of career decision-making. An Internet accessible site for career planning for pediatric residents has been developed (). The advantages, beyond ease of access by all residents, are many, particularly the power of links to other Internet resources. In addition, a website provides the ability to rapidly update and add information, which is not feasible in printed form. career planning, pediatric residents, jobs, private practice, pediatric specialties.

Interpretation of the complete blood count.

The authors' impression is that the CBC provides much more information than is routinely used. When anemia is present, the CBC contains considerable information regarding its cause, which can assist in formulating a differential diagnosis and directing further evaluation. White blood cell and platelet count levels may similarly direct practitioners to consider or dismiss underlying conditions. This article assists the pediatrician in optimizing use of this familiar diagnostic tool.

Resolution of breath-holding spells with treatment of concomitant anemia.

We describe two children who had breath-holding spells that were accelerating in frequency and severity and in one case had recrudesced. Both patients had signs, symptoms, and laboratory findings of severe anemia. With correction of anemia the breath-holding spells promptly and completely resolved in each case. We conclude that in some patients anemia may be a factor contributing to breath-holding spells and that correction of concomitant anemia may produce amelioration or remission of the spells.

Lack of dihydrofolate reductase in human tumor and leukemia cells in vivo.

Dihydrofolate reductase (DHFR), the main target for methotrexate and other antifolate compounds was found to be present in 100-200 times higher concentration in human cell lines grown in vitro than in human tumors or cells obtained in situ. The DHFR content of human cell lines in vitro however were equivalent to rodent tumor lines also measured in vitro. The enzyme was quantitated by [3H]methotrexate binding, [3H]dihydrofolate reduction to [3H]tetrahydrofolate, and immunoprecipitation with a monospecific anti-serum to DHFR. Additional studies revealed only a liver sample to contain significant amounts of an inhibitor of DHFR activity. It is postulated either that low levels of DHFR in fresh human tissue reflect low cell turnover or conversely that high levels in vitro and in animal tissues reflect high levels of enzyme due to selection because of high levels of folic acid in culture medium and prepared feeds.

Amplification of specific DNA sequences correlates with multi-drug resistance in Chinese hamster cells.

Mammalian cells selected for resistance to certain cytotoxic drugs frequently develop cross-resistance to a broad spectrum of other drugs unrelated in structure to the original selective agent. This phenomenon constitutes a major problem in cancer chemotherapy. Multi-drug resistance arises from decreased intracellular drug accumulation, apparently due to an alteration of the plasma membrane. The observation of double minute chromosomes or homogeneously staining regions in some of the multi-drug-resistant cell lines suggests that gene amplification underlies this phenomenon. We have used the technique of DNA renaturation in agarose gels to detect, compare and clone amplified DNA sequences in Adriamycin- and colchicine-resistant sublines of Chinese hamster cells. We show that both Adriamycin- and colchicine-resistant cells contain amplified DNA fragments, some of which are amplified in both of these independently derived cell lines. Furthermore, loss of the multi-drug resistance phenotype on growth in the absence of drugs correlates with the loss of amplified DNA. These results strongly suggest that the DNA sequences which are amplified in common in multi-drug-resistant cell lines include the gene(s) responsible for a common mechanism of multi-drug resistance in these cells. We have cloned one of the commonly amplified DNA fragments and show that the degree of amplification of this fragment in the cells correlates with the degree of their drug resistance.

Absence of hypoxanthine:guanine phosphoribosyltransferase activity in murine Dunn osteosarcoma.

The transplantable murine Dunn osteosarcoma has no detectable hypoxanthine:guanine phosphoribosyltransferase (EC 2.4.2.8) activity. This was established from the tumors directly and from tissue culture cell lines derived from the tumor using a variety of assays: e.g., no [3H]hypoxanthine uptake into tumor or tissue culture cells, no conversion of [3H]hypoxanthine to [3H]IMP by cell extracts from tumors or tissue culture cells, no growth of tissue culture cells in hypoxanthine:aminopterin:thymidine medium, and normal growth of these cells in 10 microM 6-mercaptopurine. Ten human osteosarcomas have been assayed, and two have no apparent hypoxanthine:guanine phosphoribosyltransferase enzyme activity. After high-dose methotrexate treatment in vivo, murine tumors could be selectively killed and normal tissues could be spared by using a rescue regimen of hypoxanthine-thymidine-allopurinol.

Osteogenic sarcoma: alterations in the pattern of pulmonary metastases with adjuvant chemotherapy.

The number and time to appearance of pulmonary metastases were evaluated in 15 patients with osteogenic sarcoma receiving adjuvant chemotherapy with high-dose methotrexate and doxorubicin (adjuvant group). The results were compared to 33 age- and sex-matched controls (control group). The adjuvant group demonstrated a reduction in the number and a delay in the appearance of the metastases. The median time to development of metastases was 17 mo in the adjuvant group and 7 mo in the control group, and the median number of metastases was 2 and 12, respectively.

Methotrexate-induced renal impairment: clinical studies and rescue from systemic toxicity with high-dose leucovorin and thymidine.

Four separate groups of patients have been studied: (1) The effect of high-dose methotrexate (MTX) administration on glomerular filtration rate was determined by pre- and posttreatment inulin and creatinine clearances in nine patients. Measurements were made prior to and 24-40 hr after drug administration. Inulin and creatinine clearances both decreased a mean of 43%. No signs of systemic toxicity occurred. (2) Three other patients given high-dose courses of MTX developed MTX toxicity. Their creatinine clearance decreased an average of 61%. (3) In a separate group of five patients undergoing weekly MTX treatment, comparison of serum MTX pharmacokinetics with and without alkalinization of the urine demonstrated no significant difference in peak serum MTX levels or serum MTX decay. (4) Eight additional patients with severe renal dysfunction secondary to MTX were treated with increased doses of leucovorin and a continuous infusion of thymidine (8 g/m2/day) once renal failure was recognized. When high-dose leucovorin and thymidine were begun 48-72 hr after the MTX infusion, severe toxicity in the form of leukopenia, thrombocytopenia, diffuse mucositis, stomatitis, or skin rash was averted. We concluded the following: (1) high-dose MTX causes a subclinical decrease in glomerular filtration rate with each administration, even in nontoxic courses; (2) alkalinization of the urine with sodium bicarbonate does not alter plasma MTX decay, while volume expansion (hydration) is maintained constant; and (3) rigorous monitoring of serum creatinine and serum MTX levels 24-48 hr after MTX administration allows for the institution of rescue measures, including leucovorin and thymidine, which will abort the systemic toxicity that accompanies MTX-induced renal failure.

Pharmacologic studies on the dibutyl and gamma-monobutyl esters of methotrexate in the rhesus monkey.

The pharmacokinetics and metabolism of dibutyl methotrexate (DBMTX) and gamma-monobutyl methotrexate (gamma-MBMTX) were studied in Rhesus monkeys. When a bolus IV dose of either [3H]DBMTX or [3H] gamma-MBMTX was given, the principal species in serum for up to 1 h was the monoester, with MTX accounting for less than 10% of the total radioactivity. Products other than gamma-MBMTX and MTX were formed in substantial amounts with DBMTX, but not with gamma-MBMTX. Total radioactivity recovered in the bile 5 h after [3H]DBMTX injection accounted for 32% of the administered dose, indicating high hepatic extraction for this lipophilic compound. Serum and CSF levels of unchanged gamma-MBMTX, as well as of MTX arising via esterase cleavage, were measured by HPLC after IV infusion of gamma-MBMTX (10 g/m2). Efflux of monoester from CSF was slower than disappearance from serum. However, gamma-MBMTX levels in CSF were no higher than could be attained by infusing MTX itself at the same dose rate. While CSF/serum ratios were ca. 10-fold higher for gamma-MBMTX than for MTX, this difference could be explained on the basis of the very different affinities of the two compounds for serum proteins. HPLC analysis of serum processed by methanol precipitation as opposed to ultrafiltration of the proteins showed gamma-MBMTX to be greater than 99% bound, whereas for MTX this value was 50% or less. When gamma-MBMTX and MTX levels measured after ultrafiltration were corrected for this difference in serum protein binding the total amount of the two drugs in serum became almost equivalent.

High-dose methotrexate in osteogenic sarcoma.

From 1972 to 1979, high-dose methotrexate (HDMTX) and 3 adjuvant regimens were used at the Sidney Farber Cancer Institute and Children's Hospital Medical Center. In the first regiment, HDMTX was used alone; the second, HDMTX and adriamycin, and the third, weekly courses of HDMTX and combination. Actuarial disease-free survival achieved with these regimens in patient with local control of the primary lesion varied from 42 to 75% at 3 years. This compared favorably with historical control patients, of whom 50% were free of disease at 6 months and only 20% at 12 months. Among 41 patients with established pulmonary metastases, 14 were alive and free of disease from more than 4 to over 60 months. The most efficacious method of administering HDMTX was a weekly schedule which produced an overall response rate of 48% in the treatment of pulmonary metastases and primary tumor in patients previously not exposed to HDMTX. Urinary alkalinization was not a standard procedure, and investigations failed to demonstrate any significant effect of alkalinization on HDMTX pharmacokinetics.

Treatment of central nervous system tumors with methotrexate.

Thirteen patients with primary and metastatic CNS tumors have been treated with methotrexate (MTX) using three different approaches: (a) high-dose MTX with leucovorin (LV) rescue; (b) high-dose MTX with carboxypeptidase (CPDG) rescue; and (c) intraventricular administration of low doses of MTX for extended periods (concentration X time [CXT]). Eleven patients had central nervous system (CNS) lymphoma (one primary, one patient had recurrent medulloblastoma, and another patient had metastatic breast carcinoma. All 13 patients received high-dose MTX-LV rescue, while 3 patients were subsequently given MTX-CPDG. One patient received MTX by all three modalities. In patients with CNS lymphomas, complete responses (45%) and partial responses (36%) produced CNS disease-free intervals ranging from 1 to 23+ months. Survival for the complete responders has thus far ranged from 2.5 to 35 months, while the partial responders survived from 3 to 5 months. Two patients failed to respond and survived 2.5 and 3 months. Responses were obtainable with high-dose MTX-CPDG in patients resistant to MTX-LV. One patient who became sensitized to CPDG subsequently responded to MTX by intraventricular CXT administration. Thus, MTX can be effectively administered to patients with CNS tumors by several different approaches.

High-dose methotrexate in osteogenic sarcoma adjuvant chemotherapy and limb salvage results.

This communication provides a description and update of the three adjuvant regimens utilized at the Sidney Farber Cancer Institute. The disease-free survivals are: Study I--42% at 4 years; Study II--58% at 3 years; and Study III--currently 78%. In the limb salvage experience, among the evaluable patients, 6 of 12 treated with preoperative chemotherapy are disease free (median 32 months) and 12 of 14 (86%) treated without preoperative chemotherapy are disease free (median 13 months).

Natural resistance to methotrexate in human melanomas.

Human melanomas are naturally resistant to methotrexate (MTX). The mechanism of intrinsic drug resistance has been explored in 3 melanoma cell lines not previously exposed to this agent. All 3 lines exhibited relative MTX resistance with ID50 values of greater than 1 microM. Drug uptake studies were performed over an extracellular concentration range of 0.1 to 10 microM MTX. The uptake was linear over the initial 10 min at all concentrations and subsequently reached plateau levels only at the 10 microM concentration. Lineweaver-Burke transformations yielded apparent Km (uptake) values of 1.4 to 5 microM, similar to data obtained from other human cell lines. The level of dihydrofolate reductase (DHFR) in the human melanoma cells ranged between 8.42 to 11.98 pmoles/mg protein. The melanoma DHFR levels are several fold higher than in MTX-sensitive human tumor lines and up to a hundred-fold higher than that measured in human brain tumor cells by our assay. The intrinsic resistance of these melanoma lines has therefore been attributed to elevated intracellular levels of DHFR.