Performance of a targeted methylation-based multi-cancer early detection test by race and ethnicity

Disparities in cancer screening and outcomes based on factors such as sex, socioeconomic status, and race and ethnicity in the United States are well documented. A blood-based multi-cancer early detection (MCED) test that detects a shared cancer signal across multiple cancer types and also predicts the cancer signal origin was developed and validated in the Circulating Cell-free Genome Atlas study (CCGA; NCT02889978). CCGA is a prospective, multicenter, case-control, observational study with longitudinal follow-up (overall N = 15,254). In this pre-specified, exploratory, descriptive analysis, test performance was evaluated among racial and ethnic groups. Overall, 4077 participants comprised the independent validation set with confirmed cancer status (cancer: n = 2823; non-cancer: n = 1254). Participants were stratified into the following racial/ethnic groups: Black (non-Hispanic), Hispanic (all races), Other (non-Hispanic), Other/unknown and White (non-Hispanic). Cancer and non-cancer participants were predominantly White (n = 2316, 82.0% and n = 996, 79.4%, respectively). Across groups, specificity for cancer signal detection ranged from 98.1% [n = 103; 95% CI: 93.2-99.5%] to 100% [n = 85; 95% CI: 95.7-100.0%]. The sensitivity for cancer signal detection across groups ranged from 43.9% [n = 57; 95% CI: 31.8-56.7%] to 63.0% [n = 192; 95% CI: 56.0-69.5%] and generally increased with clinical stage. The MCED test had consistently high specificity and similar sensitivity across racial and ethnic groups, though results are limited by sample size for some groups. Results support the broad applicability of this MCED test and clinical implementation on a population scale as a complement to standard screening.

Real-world Impact of Age at Diagnosis on Treatment Patterns and Survival Outcomes of Patients with Metastatic Pancreatic Ductal Adenocarcinoma

BACKGROUND

Sixty-eight percent of patients with pancreatic ductal adenocarcinoma (PDAC) are 65 years and older. Older adults are under-represented in clinical trials and their care is complicated with multiple age-related conditions. Research suggests that older patients can experience meaningful responses to treatment for PDAC. The objective of this study was to evaluate the characteristics, rate of treatment, and survival outcomes of patients with metastatic PDAC (mPDAC) based on age at diagnosis.

MATERIALS AND METHODS

Data were extracted for patients diagnosed with mPDAC between January 1, 2015, and March 31, 2020, from the Flatiron Health database. Patients were stratified into 3 age groups: <70 years old, 70-79 years, and ≥80 years. The proportion of patients who received first-line therapy, the types of regimens received in the metastatic setting, overall survival (OS) from the start of treatment were evaluated.

RESULTS

Of the 8382 patients included, 71.3% (n = 5973) received treatment. Among patients who received treatment 55.5% (n = 3313) were aged <70 years at diagnosis, 33.0% (n = 1972) were 70-79 years, and 11.5% (n = 688) were ≥80 years. Patients ≥80 years of age were more likely to receive gemcitabine monotherapy and less likely to receive FOLFIRINOX. Among first-line treated patients, median OS significantly decreased with age. However, when comparing patients treated with the same first-line regimen, no significant differences in median OS were observed by age.

CONCLUSIONS

This study highlights that older adults with mPDAC can benefit substantially by receiving appropriate levels of treatment.

Real-world prognostic factors for survival among treated patients with metastatic pancreatic ductal adenocarcinoma

Background

Many real‐world studies of patients with metastatic pancreatic ductal adenocarcinoma (mPDAC) are restricted to single centers, limiting the generalizability of their insights. This study aimed to identify important population‐based predictors for survival in patients diagnosed with mPDAC in a broader setting.

Methods

Data between 1 January 2017 and 31 December 2019 were extracted from the Flatiron Health EHR database. Treatment‐specific predictive models were generated for patients treated with first‐line gemcitabine+nab­paclitaxel (GNP), FOLFIRINOX, gemcitabine monotherapy (gem‐mono), and second‐line liposomal irinotecan‐based regimens. The holdout method was used for cross‐validation. Age at diagnosis, sex, BMI, smoking status, and ECOG performance score were included in all models with additional demographic, clinical characteristics, and hematological function assessed for inclusion.

Results

Of the 3625 patients, 43% received GNP, 26% received FOLFIRINOX, 7% received gem‐mono, and 23% received other regimens; 40% (n = 1448) advanced to the second line. Among all first‐line patients, the following were included in the final model: prior surgery, white blood cell (WBC) counts, serum albumin (SA), liver function tests (LFTs), serum bilirubin, serum carbohydrate antigen 19–9, and ascites. Models for patients receiving specific therapies differed from the overall model, GNP (ascites removed), FOLFIRINOX (stage at initial diagnosis added), and gem‐mono (LFTs omitted). Alkaline phosphatase (ALP), SA, and WBC counts were important predictors of survival among patients treated with second‐line liposomal irinotecan. Across all regimens, the strongest predictors of survival were ECOG score, SA, and ALP.

Conclusions

In this real‐world study of patients with mPDAC, important population prognostic factors of survival were identified in a large cohort of patients receiving systemic treatment.

Comparison of first-line (1L) treatment (tx) patterns and overall survival by age at diagnosis among patients with metastatic pancreatic ductal adenocarcinoma (mPDAC)

388

Background: Pancreatic cancer is mostly diagnosed in patients (pts) aged ≥ 65 years and the mortality rate is the highest among older adults. As the population ages, it is expected that there will be a significant rise in the number of older pts with mPDAC but guidance regarding their management is limited as these pts are under-represented in clinical trials. The oncological care of older adults in daily practice is challenged by various age-related conditions. Therefore, a better understanding of the real-world population will help in the development of more effective tx strategies. This study describes the proportion of pts with mPDAC who were treated, the types of regimens received, and the associated survival outcomes by age at diagnosis. Methods: Data were extracted for pts diagnosed with mPDAC between Jan 2015 and Mar 2020 from the Flatiron Health database. Pts were stratified into three age groups at diagnosis: <70y, 70-79y, and ≥ 80y. The proportion of pts was evaluated who received 1L tx and the types of regimens received in the metastatic setting. ECOG performance scores (PS) at tx initiation were described. Overall survival (OS) from the start of 1L was estimated using Kaplan-Meier methods. Results: Overall, of the 8,382 pts identified, 71.3% (n=5,973) received tx. Among pts who received tx, 55.5% (n=3,313) were aged <70y at diagnosis, 33.0% (n=1,972) were 70-79y, and 11.5% (n=688) were 80y+. Among those with data available, ECOG PS ≥2 was observed in 15.9% (n=381) of pts <70y, 21.0% (n=309) of pts 70-79y, and 29.9% (n=147) of pts 80y+(p < 0.001). The proportion of pts who received tx decreased with increasing age at diagnosis: 74.9%, 70.9%, and 58.5% for pts aged <70y, 70-79y, and 80y+, respectively. Gemcitabine monotherapy (gem-mono) and gemcitabine + nab-paclitaxel (GNP) accounted for > 70% of regimens prescribed to pts aged 80y+. The median OS (mOS) for patients treated with GNP, gem-mono, FOLFIRINOX, and liposomal irinotecan-based regimens are presented in the table. Conclusions: This study of treatment patterns among pts with mPDAC found that older pts were more likely to have a decreased performance status and are less likely to receive treatment. However, older adults who received systemic therapy had comparable survival outcomes to younger pts treated with a similar regimen. The results of this large descriptive analysis suggest that the treatment strategy of mPDAC should not be based on age but rather on an overall assessment of the performance/functional status and geriatric profile of older pts. [Table: see text]

Population-based, real-world prognostic factors related to survival among patients with metastatic pancreatic ductal adenocarcinoma (mPDAC)

389

Background: Pancreatic cancer is expected to be the third deadliest cancer in the US in 2020. Many real-world studies of pts with mPDAC are restricted to single centers, limiting the generalizability of the insights they generate. There is a need to understand prognostic factors of survival in a broader setting to aid in tailoring treatment strategies for pts. This study aimed to identify important population-based predictors related to survival among pts diagnosed with mPDAC. Methods: Data were extracted for pts diagnosed with mPDAC between Jan 2017 and Dec 2019 from the Flatiron Health database. Predictive models for overall survival from the start of each treatment were developed using multivariable Cox proportional hazards regression. Treatment specific predictive models were generated for pts treated with first line (1L) gemcitabine + nab-paclitaxel (GNP), 1L FOLFIRINOX, 1L gemcitabine monotherapy (gem-mono), and 2L liposomal irinotecan-based regimens. The holdout method was used for cross-validation, splitting the data into 70% training / 30% validation. Age at diagnosis, sex, body mass index, smoking status, and ECOG performance score (PS) were included in all models due to clinical importance. Demographic, clinical characteristics, hematological labs, liver function tests (LFTs), and serum bilirubin levels were assessed for inclusion into the models. Uno’s concordance statistic (c-statistic) was used to assess the predictive accuracy of the models. Results: Of the 3,572 pts included in the study, 44% (n = 1,557) received 1L GNP, 27% (n = 954) received 1L FOLFIRINOX, 7% (n = 265) received gem-mono, and 22% (n = 796) received other regimens. 38% (n = 1,345) pts received 2L and of those, 17% (n = 222) received liposomal irinotecan-based regimens. Among all 1L pts, the following were included in the final model: prior surgery, white blood cell (WBC) counts, serum albumin, LFTs (ALP and ALT), serum bilirubin, and ascites (c-statistic: 0.65). The model for pts treated with GNP differed from the overall model via the addition of neutrophil counts and removal of serum bilirubin and ascites (c-statistic: 0.67). Stage at initial diagnosis was included in the model only for pts treated with 1L FOLFIRINOX (c-statistic: 0.68). Among pts treated with gem-mono the LFTs were not included in the model (c-statistic: 0.78). ALP, serum albumin, and WBC counts were important predictors of survival among pts treated with 2L liposomal irinotecan-based regimens (c-statistic: 0.70). Across all regimens the strongest predictors of survival were ECOG PS, serum albumin, and ALP. Conclusions: In one of the largest contemporary real-world studies of patients with mPDAC to date, important population predictors of survival in pts receiving systemic treatment were identified. Further validation studies are needed to understand the generalizability of these results.

Effectiveness of durvalumab versus chemotherapy in metastatic urothelial cancer: an observational, indirect comparison

Aim: To compare the overall survival of patients with metastatic urothelial carcinoma (mUC) who failed platinum-based chemotherapy and received durvalumab or chemotherapy. Patients & methods: In an indirect comparison of patients with mUC who failed platinum-based chemotherapy, those who received durvalumab in a single-arm study were matched to patients from the Flatiron oncology electronic medical record database who received chemotherapy (n = 158 for each cohort). Matching was based on propensity scores. Kaplan-Meier methods and Cox regression models were utilized. Results: Median overall survival was 11.2 months (95% CI: 7.2-16.9) for durvalumab versus 8.2 months (95% CI: 6.7-9.8) for chemotherapy (hazard ratio: 0.63; 95% CI: 0.48-0.84). Conclusion: As a second-line therapy for mUC, durvalumab was associated with longer overall survival than chemotherapy.

Societal burden of cluster headache in the United States: a descriptive economic analysis

AIM

To estimate direct and indirect costs in patients with a diagnosis of cluster headache in the US.

METHODS

Adult patients (18-64 years of age) enrolled in the Marketscan Commercial and Medicare Databases with ≥2 non-diagnostic outpatient (≥30 days apart between the two outpatient claims) or ≥1 inpatient diagnoses of cluster headache (ICD-9-CM code 339.00, 339.01, or 339.02) between January 1, 2009 and June 30, 2014, were included in the analyses. Patients had ≥6 months of continuous enrollment with medical and pharmacy coverage before and after the index date (first cluster headache diagnosis). Three outcomes were evaluated: (1) healthcare resource utilization, (2) direct healthcare costs, and (3) indirect costs associated with work days lost due to absenteeism and short-term disability. Direct costs included costs of all-cause and cluster headache-related outpatient, inpatient hospitalization, surgery, and pharmacy claims. Indirect costs were based on an average daily wage, which was estimated from the 2014 US Bureau of Labor Statistics and inflated to 2015 dollars.

RESULTS

There were 9,328 patients with cluster headache claims included in the analysis. Cluster headache-related total direct costs (mean [standard deviation]) were $3,132 [$13,396] per patient per year (PPPY), accounting for 17.8% of the all-cause total direct cost. Cluster headache-related inpatient hospitalizations ($1,604) and pharmacy ($809) together ($2,413) contributed over 75% of the cluster headache-related direct healthcare cost. There were three sub-groups of patients with claims associated with indirect costs that included absenteeism, short-term disability, and absenteeism + short-term disability. Indirect costs PPPY were $4,928 [$4,860] for absenteeism, $803 [$2,621] for short-term disability, and $3,374 [$3,198] for absenteeism + disability.

CONCLUSION

Patients with cluster headache have high healthcare costs that are associated with inpatient admissions and pharmacy fulfillments, and high indirect costs associated with absenteeism and short-term disability.

No Evidence of an Association Between Efavirenz Exposure and Suicidality Among HIV Patients Initiating Antiretroviral Therapy in a Retrospective Cohort Study of Real World Data

Recently, published studies have reported conflicting results regarding the association between efavirenz exposure and the risk of suicidality among patients with human immunodeficiency virus. The objective of this analysis was to compare the rate of suicidality among patients initiating efavirenz-containing versus efavirenz-free antiretroviral (ARV) regimens.This retrospective cohort study used US administrative claims data for commercially and Medicaid-insured individuals for the years 2006 to 2013. ARV-naive patients aged ≥12 years initiating an efavirenz-containing or efavirenz-free ARV regimen with ≥6 months of continuous insurance enrollment prior to ARV initiation were selected. The primary outcome was suicidality, defined as the occurrence of any medical claim with a diagnosis code for suicidal ideation or an inpatient or emergency department medical claim for suicide attempt. Unadjusted incidence rates were calculated and propensity score-adjusted hazard ratios were estimated to account for differences in patient characteristics.There were 19,983 patients (efavirenz-containing, n = 11,187; efavirenz-free, n = 8796) in the commercial database and 5154 patients (efavirenz-containing, n = 2224; efavirenz-free, n = 2930) in the Medicaid database. Unadjusted incidence rates (95% confidence interval [CI]) of suicidality per 1000 person-years were: commercial, efavirenz-containing (3.3 [2.4-4.4]), efavirenz-free (4.0 [2.7-5.8]); Medicaid, efavirenz-containing (25.7 [18.8-34.4]), efavirenz-free (40.6 [31.9-50.9]). In propensity score-adjusted analyses, efavirenz use was not associated with suicidality: adjusted hazard ratio (95% CI) of suicidality compared with efavirenz-free regimen, commercial, 1.029 (0.636-1.665); Medicaid, 0.902 (0.617-1.319).This analysis found no conclusive evidence of an increased risk of suicidality among patients initiating an efavirenz-containing ARV regimen. However, channeling bias may exist even after adjusting for measured patient characteristics.

The value of linking hospital discharge and mortality data for comparative effectiveness research

Background: Linkage of US state hospital discharge records to state death certificate records offers the possibility of tracking long-term mortality outcomes across large, diverse patient populations, which may be useful for comparative effective analyses. Aim: To demonstrate the value of linking state community hospital discharge data to vital statistics death files for research by conducting a comparative effectiveness analysis. Methods: Linked Patient Discharge Data and Vital Statistics Death Files from the California Office of Statewide Health Planning and Development were used to compare survival rates for patients with an elective repair for abdominal aortic aneurysm who received open aneurysm repair (OAR) versus endovascular aneurysm repair (EVAR). The sample consisted of 13,652 hospitalized patients who underwent an OAR or EVAR for abdominal aortic aneurysm between 1 July 2000 and 31 January 2006. Patients were matched using propensity scores (8966 patients in the matched sample). In-hospital, 30-day, 1-year and 5-year mortality rates were compared between the OAR and EVAR populations, before and after propensity score matching. Results: We found a few data anomalies (92 out of 13,652), primarily in patients’ sex and date of death. The analysis revealed that in the matched cohort, in-hospital and 30-day postdischarge mortality rates were significantly lower following EVAR than OAR; however, consistent with previous clinical trials, differences in the 1- and 5-year rates were not statistically significant. Conclusion: The study demonstrates that linked US state discharge and mortality data can be a valuable resource for comparative effectiveness analyses. In particular, this approach may be useful when generally available data sets such as Medicare claims data limit the generalizability of findings. Policy-makers and others should consider greater investments in these data.

Abstract P5-20-12: Aromatase inhibitor failure: predictors and time to first failure among women with metastatic ER+/HER2− breast cancer in the US

Little information is available on the real-world use of aromatase inhibitors (AIs) among post-menopausal women with metastatic ER+/HER2− breast cancer (BC). This retrospective administrative claims study evaluated potential predictors of post-index AI failure (AIF) and time to first AIF by agent among these patients.

Women ≥ 55 years of age newly diagnosed with metastatic stage IV BC (index) were identified in the 2006–2010 Thomson Reuters MarketScan databases and followed until the earliest of chemotherapy, combination therapy, end of enrollment, inpatient death or end of study (03/31/2011). ER+/HER2− disease was defined as any endocrine therapy (ET: tamoxifen, fulvestrant) or AI (anastrozole - ANA, letrozole - LET, or exemestane - EXE) use in the variable length post-index period and no trastuzumab, lapatinib or toremifene use anytime in the 6-month pre-or post-index periods. Those with post-index AI use except when following chemotherapy or combination therapy, were retained for analysis. AIF post-index was defined as a switch to an alternative AI, ET, chemotherapy, or combination therapy. Logistic regression was used to assess the probability of having AIF as a function of demographic and clinical characteristics. A Cox proportional hazards model was used to assess the probability of AIF by first-line AI as a function of selected patient characteristics. Kaplan-Meier (KM) plots and log-rank tests evaluated differences in time to failure by first-line AI treatment.

Among 4,249 eligible patients, 36% had ≥1 AIF. Patients with pre-index ET use were more likely to fail AI treatment post-index (OR 1.43, CI: 1.08–1.89). Conversely, those receiving AI treatment pre-index were less likely to experience post-index AI failure (OR 0.73, CI: 0.63–0.85). Patients were also less likely to fail post-index AI treatment when having undergone lumpectomy or mastectomy pre-index (OR 0.62, CI: 0.47–0.83). When found at index, metastases to the lung, liver, or bone significantly increased the likelihood of experiencing AI failure while those to the brain had no association. First-line AI treatment was present in 96% of patients (n = 4,073) and those taking ANA remained on treatment the longest prior to AIF, followed by LET and EXE. Results of the Cox model suggest that compared to first-line ANA treatment, EXE use was significantly associated with increased probability of AIF (HR 1.57, CI: 1.35–1.83), controlling for other confounders. However, the association of first-line LET and probability of AIF was not significantly different than that of ANA (HR 1.09, CI: 0.97–1.22). Compared to EXE, LET was significantly associated with a lower probability of AIF (HR 0.69, CI: 0.59–0.81). The log-rank test based on the KM estimates suggests the overall difference between the three time-to-AIF curves is significantly different (p &lt; 0.01).

In patients with metastatic ER+/HER2− BC, AI failure was significantly associated with pre-index BC treatments and sites of metastases at diagnosis. In addition, the probability of first-line AIF and time to AIF differed by agent. Further examination of the interactions between BC disease characteristics, treatment history, and AIF is needed.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-20-12.

Costs of asthma among US working adults

OBJECTIVES

To evaluate the effect of asthma on direct and indirect costs among US working adults.

STUDY DESIGN

A case-control retrospective analysis was conducted. Data between January 1, 2003, and December 31, 2006, among patients aged 18 to 64 years with vs without asthma were extracted from MarketScan Research Databases. Patients with chronic obstructive pulmonary disease or emphysema were excluded, and all patients were required to have 12-month continuous enrollment before and after the index date. Outcomes included direct medical costs, the number of absence days, the number of short-term disability days, and associated indirect costs.

METHODS

Patients with asthma were propensity score-matched to patients without asthma using nearest neighbor 1:1 with caliper. Subsequent multivariate analysis was conducted on matched samples to examine the marginal effect of asthma on direct and indirect costs.

RESULTS

A total of 13,379 patients with asthma were propensity score-matched to 13,379 patients without asthma; in each cohort, 3453 patients had absence eligibility, and 8497 patients had short-term disability eligibility. Direct costs for patients with asthma were $3762, and indirect costs were $4572. Compared with the matched cohort without asthma, patients with asthma had $1785 higher direct medical expenditures (P <.001). Incremental indirect costs were $191 for absenteeism (P = .007) and $172 for short-term disability (P<.001).

CONCLUSIONS

Compared with patients without asthma, patients with asthma experience significantly higher direct medical costs and, although modest, significantly higher work loss. Treatments or interventions that prevent or reduce asthma symptoms may have a beneficial effect on medical costs and work absenteeism.

The effects of antidepressant step therapy protocols on pharmaceutical and medical utilization and expenditures

OBJECTIVE

This study examined the effects of step therapy for antidepressants on prescription drug and other medical utilization and spending. Step therapy is a type of pharmaceutical benefit design that requires that patients try certain specified medications (typically generic medications) prior to using alternative, more expensive medications within the same medication class. Step therapy is not the same as generic substitution.

METHOD

Using the 2003-2006 Thomson Reuters MarketScan claims databases, antidepressant users enrolled in employer plans that implemented antidepressant step therapy were compared with antidepressant users enrolled in employer plans that had not implemented step therapy. Multivariate generalized estimating equation models were used to analyze the relationship between step therapy for antidepressants and 1) pharmacy and medical utilization and 2) spending.

RESULTS

Antidepressant days supplied and medication costs decreased after step therapy was implemented, relative to the comparison group. However, overall and mental health-specific inpatient and emergency room utilization and costs increased.

CONCLUSIONS

Step therapy may have the unintended effect of reducing overall antidepressant use and increasing medical use and costs.

Correlates of persistent smoking in bars subject to smokefree workplace policy

This study's goal was to characterize physical and social environments of stand-alone bars associated with indoor smoking despite California's smokefree workplace law. In a random sample of 121 stand-alone bars in San Francisco, trained observers collected data on patrons, staff, neighborhood, indoor settings and smoking behaviors. Using bivariate (chi-square) and hierarchical linear modeling analyses, we identified four correlates of patrons' indoor smoking: 1) bars serving predominantly Asian or Irish patrons, 2) ashtrays, 3) bartender smoking, and 4) female bartenders. Public health officials charged with enforcement of smokefree bar policies may need to attend to social practices within bars, and heighten perceptions of consistent enforcement of smokefree workplace laws.

Drinking patterns and myocardial infarction: a linear dose-response model

BACKGROUND

The relation of alcohol intake to cardiovascular health is complex, involving both protective and harmful effects, depending on the amount and pattern of consumption. Interpretation of data available on the nature of these relations is limited by lack of well-specified, mathematical models relating drinking patterns to alcohol-related consequences. Here we present such a model and apply it to data on myocardial infarction (MI).

METHODS

The dose-response model derived assumes: (1) each instance of alcohol use has an effect that either increases or decreases the likelihood of an alcohol-related consequence, and (2) greater quantities of alcohol consumed on any drinking day add linearly to these increases or decreases in risk. Risk was reduced algebraically to a function of drinking frequency and dosage (volume minus frequency, a measure of the extent to which drinkers have more than 1 drink on days when they drink). In addition to estimating the joint impact of frequency and dosage, the model provides a method for calculating the point at which risk related to alcohol consumption is equal to background risk from other causes. A bootstrapped logistic regression based on the dose-response model was conducted using data from a case-control study to obtain the predicted probability of MI associated with current drinking patterns, controlling for covariates.

RESULTS

MI risk decreased with increasing frequency of drinking, but increased as drinking dosage increased. Rates of increasing MI risk associated with drinking dosage were twice as high among women as they were among men. Relative to controls, lower MI risk was associated with consuming < 4.55 drinks per drinking day for men (95% CI: 2.77 to 7.18) and < 3.08 drinks per drinking day for women (95% CI: 1.35 to 5.16), increasing after these cross-over points were exceeded.

CONCLUSIONS

Use of a well-specified mathematical dose-response model provided precise estimates for the first time of how drinking frequency and dosage each contribute linearly to the overall impact of a given drinking pattern on MI risk in men and women.

Diffusion-weighted MR findings in a reversible case of acute Wernicke encephalopathy

We report a case of acute Wernicke encephalopathy (WE) in which apparent diffusion coefficient maps showed areas of increased diffusion in the bilateral medial thalami that corresponded to the hyperintense lesions on T2-weighted imaging. The hyperintense lesions on T2-weighted imaging disappeared with full recovery from symptoms. These findings suggest that the hyperintense lesions of the acute changes of WE include reversible vasogenic edema and are not caused by acute ischemia.

MRI in seven cases of tacrolimus (FK-506) encephalopathy: utility of FLAIR and diffusion-weighted imaging

We assessed the utility of fluid-attenuated inversion-recovery (FLAIR) and diffusion-weighted (DWI) images in investigation of tacrolimus (FK-506) encephalopathy, and to see whether we could predict its cause from clinical and imaging data. In seven patients with presumed FK-506 toxicity the areas involved on MRI were similar to those in cyclosporin A (CsA) toxicity. The abnormal signal was most evident on FLAIR in all cases. In three of four patients who underwent DWI, no diffusion abnormalities were detected; in the remaining patient, increased diffusion was seen in the deep white matter bilaterally on the apparent diffusion coefficient map, consistent with the findings on T2-weighted spin-echo and FLAIR images. Five of the six patients for whom we had clinical data showed sudden changes in electrolyte or fluid equilibrium due to diarrhoea, a polyuria or oliguria one day before or on the day of onset of the central nervous system disturbances. We speculate that FK-506 encephalopathy is triggered by the disturbance of the electrolyte and/or fluid equilibrium, given a certain serum level of FK-506.

Intramedullary schwannoma of the spinal cord: report of two cases

We report magnetic resonance findings in the intramedullary schwannoma of the cervical spinal cord in two patients. In both cases, the solid portions of the tumours enhanced intensely after administration of Gd-DTPA and the enhanced border was sharply delineated from the adjacent spinal cord. Schwannomas should be considered in the differential diagnosis of intramedullary tumours when magnetic resonance images show a strongly enhancing mass with sharply delineated borders.

Inhibition of oligo(glutamine) precipitation by glutamine-containing peptides

When a solution of glutamine is added to solid 1,1'-carbonyldiimidazole, a mixture of oligo(glutamine)s up to about the 11-mer is formed rapidly. On standing overnight, the solution deposits a precipitate that does not easily redissolve. We have studied the inhibition of this precipitation by glutamine-containing peptides. We find that the alternating peptides (arg.gln)(4) and (arg.gln)(8) are efficient inhibitors of precipitation while arg(5), (glu.gln)(4), and a nonalternating octapeptide of the same composition as (arg.gln)(4) do not inhibit precipitation even though all the arg-containing peptides readily adsorb to oligo(glutamine) precipitates. A possible structural basis for this difference is discussed.

MR findings in spinal hemangioblastoma: correlation with symptoms and with angiographic and surgical findings

BACKGROUND AND PURPOSE

To our knowledge, a detailed analysis of MR findings in spinal hemangioblastoma has not been conducted to date. Our purpose was to elucidate the MR features of this disease with special attention to tumor size, correlation with MR findings and clinical symptoms, and any differences between patients with and without von Hippel-Lindau disease (VHLD).

METHODS

MR images in five patients with VHLD and seven patients without VHLD were reviewed retrospectively for spinal hemangioblastoma by two neuroradiologists. The MR findings were correlated with clinical symptoms and with angiographic and surgical findings.

RESULTS

The MR features depended on the size of the spinal hemangioblastoma. Small (10 mm or less) hemangioblastomas were mostly isointense on T1-weighted images, hyperintense on T2-weighted images, and showed homogeneous enhancement. Larger hemangioblastomas tended to be hypointense or mixed hypo- and isointense on T1-weighted images, heterogeneous on T2-weighted images, and tended to show heterogeneous enhancement. Small hemangioblastomas were located at the surface of the spinal cord, most frequently along its posterior aspect. These were subpial in location at surgery and showed well-demarcated, intense enhancement. Symptomatic small hemangioblastomas had relatively large associated syringes, whereas asymptomatic ones did not. A hemangioblastoma larger than 24 mm was invariably accompanied by vascular flow voids. There was no difference in the MR findings between the two patient groups except for the multiplicity and higher percentage of small tumors in patients with VHLD.

CONCLUSION

Knowledge of these MR features helps to differentiate spinal hemangioblastoma from other diseases that show enhancing nodules.

Flow volume in the common carotid artery detected by color duplex sonography: an approach to the normal value and predictability of cerebral blood flow

PURPOSE

To determine normal common carotid artery (CCA) flow volume, its relationship with age, and the predictability of cerebral blood flow (CBF) by color duplex sonography.

SUBJECTS AND METHODS

Forty-five healthy subjects (18 men, 27 women, 23-86 years old) and 13 patients (3 men, 10 women, 51-88 years old) without neurological disease underwent color duplex sonography. All 13 patients also underwent xenon CT. CCA flow volume in the healthy subjects was measured to determine normal values. This volume was divided by mean brain weight to estimate CBF, which was correlated with CBF measured by xenon CT in regions of ipsilateral internal carotid arteries (ICA).

RESULTS

In healthy subjects, CCA flow volume ranged from 155.0-458.8 ml/min (mean+/-SD: 267.77+/-59.91), corresponding to an estimated CBF of 12.43-32.84 ml/min/100 g brain weight (mean+/-SD: 20.63+/-4.22). No relationship was found between flow volume and age. A good correlation was found between estimated CBF and CBF measured by xenon CT in regions of both ICAs (gamma=0.713, p=0.0062 on the left; gamma=0.686, p=0.0096 on the right).

CONCLUSION

By using color duplex sonography, we established a set of normal CCA flow volumes, which do not decline with age. Estimated CBF derived from flow volume can predict actual CBF.

Retrospective self-reports of therapist flexibility in a manual-based treatment for youths with anxiety disorders

Evaluated retrospective therapist ratings of the flexibility used when applying the procedures and strategies prescribed in the treatment manual. Flexibility ratings were collected from 18 therapists who had treated 148 children with anxiety disorders (ages 9 through 13). Analyses revealed strong reliabilities for a flexibility questionnaire and that flexibility was used by therapists; however, significant relations between therapist-rated flexibility and treatment outcome were not found. Discussion focuses on the role of flexibility in manual-based psychological treatments and future directions for study.

Peptide-formation on cysteine-containing peptide scaffolds

Monomeric cysteine residues attached to cysteine-containing peptides by disulfide bonds can be activated by carbonyldiimidazole. If two monomeric cysteine residues, attached to a 'scaffold' peptide Gly-Cys-Glyn-Cys-Glu10, (n = 0, 1, 2, 3) are activated, they react to form the dipeptide Cys-Cys. in 25-65% yield. Similarly, the activation of a cysteine residue attached to the 'scaffold' peptide Gly-Cys-Gly-Glu10 in the presence of Arg5 leads to the formation of Cys-Arg5 in 50% yield. The significance of these results for prebiotic chemistry is discussed.

MRI of the brain in the Kearns-Sayre syndrome: report of four cases and a review

We report brain MRI findings in four patients with typical Kearns-Sayre syndrome (KSS) and correlate them with clinical manifestations. MRI was interpreted as normal in two patients; cerebral and cerebellar atrophy was seen in the other two. On T2-weighted spin-echo images, two patients had high-signal lesions bilaterally in subcortical white matter, thalamus and brain stem. In one patient, the white matter lesion extended into the deep cerebral white matter and the cerebellum was also affected. The other also had bilateral high-signal lesions in the globus pallidus. There was little correlation between neurological deficits and MRI findings. A review of the literature revealed that 10 of the 13 patients with typical KSS previously studied had bilateral subcortical white-matter lesions on T2-weighted images; at least 7 also had high-signal lesions in the brain stem, globus pallidus, thalamus or cerebellum. Although MRI may be normal or show atrophy, the characteristic finding in KSS is a combination of the high-signal foci in subcortical cerebral white matter and in the brain stem, globus pallidus or thalamus.

[The clinical application of diffusion weighted magnetic resonance imaging to acute cerebrovascular disorders]

Diffusion is a measure of motion freedom and is a sensitive parameter to characterize the tissue at the microscopic level. The methods of measuring in vivo diffusion by magnetic resonance imaging (MRI) have been based mainly on the addition of two motion-probing gradients (MPG) to the spin echo sequence to produce signal attenuation for the spins moving at random. The resultant MR images reflect the intravoxel incoherent motions (IVIM), which contain both water molecule diffusion and perfusion in the capillary network, and can be quantified by an apparent diffusion coefficient (ADC). Diffusion weighted MRI, acquired from IVIM MR imaging by the addition of the very strong MPG predicate water diffusion and anisotropy. High signal or reduced ADC can be observed in case of the slower diffusion. The anisotropy depends upon the orientation of the subjects and the gradients. Greater signal attenuation (faster diffusion) can be observed when the relative orientation of white matter tracts to the MPG is parallel as compared to that obtained with a perpendicular alignment. This anisotropy may preclude the detection or delineation of an ischemic lesion. Diffusion tensor trace has been designated to eliminate this anisotropy effect. In ischemic animal models, low signal (fast diffusion) and high signal (slow diffusion) have been noted in the vasogenic edema and cytotoxic edema, respectively. High signal appears only in case of cerebral blood flow below 15-20 ml/100 g per minute, a value identical to the threshold of tissue at high energetic metabolism and ion homeostasis. ADC value decreases following the cerebral vessel occlusion, or remains unchanged when collateral circulation develops. It has been speculated that reduction in ADC reflects the water shift from extracellular space to intracellular space due to the membrane permeability and/or intracellular osmolality increase. These results suggest that diffusion weighted MRI correlates well with the cell metabolism, and cytotoxic edema plays an important role in the acute cerebral stroke. In clinical setting of acute cerebral ischemia, diffusion weighted MRI may detect superacute infarction by showing high signal (slower ADC) over the 6 hours following the insult, whereas conventional MRI generally fails to do so. In chronic liquefied cerebral infarction, increased ADC, or attenuated signal are the most frequent findings, suggestive of an elevated diffusion. Therefore, diffusion weighted MRI improves early diagnosis of stroke and help differentiate acute from chronic stroke. One disadvantage of diffusion weighted MRI is motion artifact, which may be reduced by the introduction of a navigator echo to correct for the phase shift caused by the first imaging echo, or by the utility of ultrafast imaging technique, such as echo planar. Another shortcomings is the susceptibility artifact incorporating the diffusion weighted MRI. The eddy current may also result from the strong gradients, producing shiftlike artifact. Such artifacts can be compensated for by appropriate shaping of the current pulses sent into the gradient coils, or by use of shielded gradients. As with rapid progresses in perfusion imaging of ischemia penumbra, misery perfusion and luxury perfusion, new insight into the diffusion weighted MRI will be significant.

Demonstration of the distal end of the oesophagus by transabdominal ultrasound

This study aimed to demonstrate the distal end of the oesophagus using a transabdominal ultrasound technique (TUS) and to measure the normal oesophageal wall thickness in adults. 65 patients without oesophageal disease and 38 normal volunteers were examined by TUS. A left subcostal approach was used to demonstrate the oesophagus. The wall thickness and length were measured in both the supine and 45 degrees right side up oblique (RUO) positions. The abdominal oesophagus was visualized in 80% of patients in the supine position and 92% in the RUO position. Satisfactory demonstration was obtained in 67% of patients in the supine and 85% in the RUO position. The oesophageal wall thickness averaged 2.8 mm (range 2.0-4.0 mm, SD 0.7 mm). The visualized length in these subjects averaged 2.3 cm in the supine position and 3.0 cm in the RUO position, which included approximately 1.5 cm of the lowest portion of the thoracic oesophagus in addition to the abdominal oesophagus. TUS can demonstrate the abdominal oesophagus in the majority of patients and has the potential to provide information on disorders of structure and motility.

Presentation of ligands on hydroxylapatite

Conjugates of biotin with the decamer of glutamic acid (glu10) and the trimer of D,L-2-amino-5-phosphonovaleric acid (I) have been synthesized, and it has been shown that they mediate the binding of avidin to hydroxylapatite. In a similar way a conjugate of methotrexate with glu10 mediates the binding of dihydrofolate reducatase to the mineral. The presentation of ligands on the hydroxylapatite component of bone may find applications in clinical medicine.

Multiplexing of Michelson interferometer sensors in a matrix array topology

We report on the operation and performance of a matrix array topology for multiplexing reflective interferometric sensors that uses (a) frequency-division multiplexing (FDM) and (b) a combination of frequency-division and time-division multiplexing. The use of reflective sensors in this FDM topology illuminated by a cw source imposes a power limitation not encountered with the use of transmissive sensors. Combining FDM with time-division multiplexing improves the multiplexing gain of the network and improves the level of isolation of the lasers from the signal of the reflective sensors.

The stability of different forms of double-stranded decoy DNA in serum and nuclear extracts

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Faraday current sensor that uses a triangular-shaped bulk-optic sensing element

A new triangular topology for a bulk-optic Faraday current sensor is presented with a demonstrated resolution of 20 mA/ radicalHz over a measurement range of 1 to 3000 A. The sensitivity of the system is 2.35 x 10(-5)rad/A. This sensor is relatively easy to fabricate and overcomes problems encountered with the use of current sensors based on bulk-optic square configurations and all-fiber systems.

Crosslinking transcription factors to their recognition sequences with PtII complexes

We have prepared phosphorothioate-containing cyclic oligodeoxynucleotides that fold into 'dumbbells' containing CRE and TRE sequences, the binding sequences for the CREB and JUN proteins, respectively. Six phosphorothioate residues were introduced into each of the recognition sequences. K2PtCl4 crosslinks CRE to CREB and TRE to JUN. The extent of crosslinking is about eight times greater than that observed with standard oligodeoxynucleotides and amounts to 30-50% of the efficiency of non-covalent association as estimated by gel-shift assays. Crosslinking is reversed by incubation with NaCN. The crosslinking reaction is specific--a dumbbell oligonucleotide with six phosphorothioate groups introduced into the Sp1 recognition sequence could not be crosslinked efficiently to CREB or JUN proteins with K2PtCl4. The binding of TRE to CREB is not strong enough for effective detection by gel-shift assays, but the TRE-CREB complex is crosslinked efficiently by K2PtCl4 and can then readily be detected.

Binding of hairpin and dumbbell DNA to transcription factors

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Miniature Faraday current sensor based on multiple critical angle reflections in a bulk-optic ring

A novel optical element for a bulk glass current sensor that utilizes the Faraday effect is presented with a demonstrated sensitivity of 1 amp-turn and a flat frequency response in the range of 10-10(4) Hz. The new sensing element overcomes the problems associated with birefringence in optical fiber current sensors and the requirement to make bulk-optic current sensors in complex three-dimensional topologies.

Optimization of the efficiency of cross-linking PtII oligonucleotide phosphorothioate complexes to complementary oligonucleotides

We have investigated the efficiency with which PtII complexes cross-link phosphorothioates of oligonucleotides to complementary DNA targets. The A and G residues 2-5 bases downstream from the 5'-phosphorothioate group are preferred sites for cross-linking. Replacement of residues in this part of the target by T residues results in greatly decreased cross-linking when cis platinum diammine dichloride (cisPtII) or potassium platinous chloride (K2PtCl4) are used. Trans platinum diammine dichloride (transPtII) forms cross-links with T residues if A and G residues are absent from the susceptible region of the target. Oligomers containing an internal phosphorothioate group can also be linked to their templates with transPtII, but not with cisPtII or K2PtCl4. Cross-linking via an internal phosphorothioate group tends to be less efficient than cross-linking via a 5'-terminal phosphorothioate. The Sp isomers of internal phosphorothioates are cross-linked more efficiently than the Rp isomers. Preliminary experiments suggest that the efficiency of cross-linking to RNA targets will prove similar to that found for DNA targets.

A simple procedure for cross-linking complementary oligonucleotides

A simple, efficient procedure for cross-linking two complementary oligonucleotides, which does not require chemical modification of either oligonucleotide, is described. One of the oligonucleotides is first converted to the 5'-phosphorothioate derivative with polynucleotide kinase. It is then incubated with its complement in the presence of 1 microM trans-platinum(II)diammine dichloride. After overnight incubation, 40-50% cross-linking is observed. DNA synthesis by the Klenow fragment of Escherichia coli DNA polymerase I is blocked at the cross-linked site, resulting in the formation of truncated products. Potassium platinous chloride (K2PtCl4) and cis-platinum(II)diammine dichloride form cross-links less efficiently than the trans isomer.

Inhibition of DNA synthesis by cross-linking the template to platinum-thiol derivatives of complementary oligodeoxynucleotides

Unsubstituted oligodeoxynucleotides, or oligodeoxynucleotides linked to poly-(L)-lysine, when hybridized to a 322 base long template, did not inhibit the production of full length DNA copies by the Klenow fragment of E. coli DNA polymerase I. However, synthesis was inhibited if the cysteamine derivative of the same oligomer was cross-linked to the template via PtII. Truncated products were formed by termination of DNA synthesis a small number of bases upstream from the 5'-end of the cross-linked oligomer. AMV reverse transcriptase behaved similarly but was also slightly inhibited by the hybridized oligomer or its poly-lysine derivative.

The lack of effect of pentoxifylline on random skin flap survival

The effects of pentoxifylline on skin flap survival were studied in rabbits. A total of 40 rabbits had caudally based single-pedicle flaps measuring 4 x 14 cm raised on the mid dorsum of each animal. Twenty of these rabbits were given intraperitoneal injections of pentoxifylline in doses of 24 mg/kg per day beginning 48 hours prior to flap construction and continued daily for 7 days postoperatively. The remaining 20 control rabbits received intraperitoneal injections of saline in equal volumes as the experimental groups. At the end of 7 days, viable flap length was visually inspected and measured in all 40 rabbits. There was no significant difference in skin flap viability in rabbits treated with pentoxifylline compared to the control group.

Ligation of oligonucleotides to nucleic acids or proteins via disulfide bonds

We have developed general methods for joining together, via cleavable disulfide bonds, either two unprotected polynucleotides or a polynucleotide and a peptide or protein. To join two oligonucleotides, each is first converted to an adduct in which cystamine is joined to the 5'-terminal phosphate of the oligonucleotide by a phosphoramidate bond. The adducts are mixed and reduced with dithiothreitol. The dithiothreitol is then removed by dialysis. Oxidation by atmospheric oxygen occurs to yield the required dimer. To join an oligonucleotide to a cysteine-containing peptide or protein, the 5'-cystamine oligomer is first converted to a 2'-pyridyldisulfide adduct and then reacted with an excess of the peptide or protein. If the peptide does not contain a free cysteine residue, it is first treated with iminothiolane to introduce one or more sulfhydryl groups. We have used these procedures to join a 16 mer deoxynucleotide probe and MDV-1 RNA, a substrate of Q beta RNA polymerase. This adduct hybridizes with a complementary target DNA. We have also joined a 16mer probe to peroxidase and MDV-1 RNA to human IgG. The probe-peroxidase adduct maintains enzymatic activity and the MDV-1 RNA-IgG adduct binds to a complementary anti-IgG.

Synthesis of an amplifiable reporter RNA for bioassays

The replacement of reporter groups, such as fluorescent molecules or enzymes, by an amplifiable reporter should lead to bioassays of greatly increased sensitivity, since a very large number of copies of the reporter can be accumulated in a short time. Midivariant RNA is an appropriate reporter, since it is autocatalytically replicated by Q beta RNA polymerase in vitro. This RNA can be amplified exponentially, with a population doubling time of 36 seconds, resulting in the synthesis of 10(6) copies of each molecule in 12 minutes. We have used chemical methods to attach biotin to the 5' terminus of midivariant RNA via a disulfide linker. This biotinylated RNA combines with avidin to give a product that is readily purified by gel electrophoresis. The RNA-biotin-avidin adduct, and the RNA released from it by reductive cleavage of the linker arm, replicate normally. The RNA-biotin-avidin adduct should be a suitable reporter for a variety of replication-assisted bioassays involving biotinylated antibodies or biotinylated nucleic acid probes.

Detection of specific DNA sequences with short biotin-labeled probes

We have developed a simple, general synthesis of nonradioactive DNA probes in which biotin is attached to the 5'-terminal phosphate of an oligodeoxyribonucleotide 16 bases long via an ethylenediamine or hexamethylenediamine linker. The products are stable under normal hybridization conditions. They hybridize to target DNA as efficiently as the underivatized oligodeoxyribonucleotide. Color development, using a commercially available kit, is complete within 3 hr using the biotin-detection method. The sensitivity of detection of homologous DNA with a probe to which biotin was attached via a hexamethylenediamine linker is about one-tenth of that achieved overnight by autoradiography with the corresponding 32P-labeled probe.

Nonenzymatic sequence-specific cleavage of single-stranded DNA

Ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid have been attached covalently to the 5' terminus of the deoxynucleotide sequence C-A-C-A-A-T-T-C-C-A-C-A-C-A-A-C (16-mer) via an ethylenediamine linker. In the presence of Fe2+ and dithiothreitol, these reagents bring about the hybridization-dependent cleavage of the sequence T-C-G-T-A-T-G-T-T-G-T-G-T-G-G-A-A-T-T-G-T-G-A-G-C-G-G-A-T-A-A-C-A-A-T-T- T (37-mer), a sequence that contains an internal subsequence complementary to the 16-mer. The principal cleavage sites on the 37-mer are about four residues on each side of the terminal phosphate group of the 16-mer.

Preparation of ligation intermediates and related polynucleotide pyrophosphates

Unprotected oligonucleotides and oligodeoxynucleotides terminated with an unhindered 5'-phosphate group react with nucleoside 5'- phosphorimidazolides in aqueous solution to give 'capped' pyrophosphates in at least 70% yield. If adenosine 5'- phosphorimidazolide is used as a substrate in the reaction, ligase intermediates are obtained as products.

Derivatization of unprotected polynucleotides

A simple and efficient method for attaching amines to the terminal 5'-phosphate of unprotected oligonucleotides or nucleic acids in aqueous solution is described. The method is applicable to low molecular-weight amines, polypeptides, or proteins. The terminal 5'-phosphate of an oligonucleotide or nucleic acid reacts with a water-soluble carbodiimide in imidazole buffer at pH 6 to give good yields of the 5'-phosphorimidazolide. Exposure of the phosphorimidazolide to amine-containing molecules in aqueous solution results in the production of a wide range of stable phosphoramidates in high yield. The exposure of polynucleotides to carbodiimide does not result in significant breakage of phosphodiester bonds or damage to nucleoside bases. The biological activity of a drug resistant plasmid is not affected. The direct condensation of polynucleotides with amines in 1-methylimidazole buffer is also possible. However, it is not a satisfactory preparative method if the ligand is sensitive to carbodiimide.

Pharmacological and therapeutic properties of carrier bound methotrexate against tumor confined to a third space body compartment

The pharmacokinetics and therapeutic effectiveness of methotrexate (MTX) and MTX covalently bound to bovine serum albumin (MTX-BSA) and poly-l-lysine, MW 3,000 (MTX-PLL 3K) or MW 40,000 to 60,000 (MTX-PLL 40-60K) were compared when these drugs were injected directly into the pleural cavities of BDF1 mice containing the L1210 tumor. Simultaneous measurements od drug levels in both pleural fluid and blood after a single dose demonstrated that free MTX and MTX-PLL 3K were cleared from the pleural cavity and blood within 4 hr, MTX-PLL 40K-60K was cleared within 2 hr, and MTX-BSA was still present in the tumor compartment at 48 hr. The coupling of MTX to these carriers increased its toxicity by extending the half-life of MTX-BSA within the animal and by incorporating a toxic PLL derivative as a carrier. At equitoxic doses, a single dose of MTX-BSA gave a peak increase in lifespan (ILS) of 50% (at 35 mg/kg) compared with a peak ILS of 30 to 35% for both free drug (at 95 mg/kg) and the MTX-PLL derivatives (at 1.4-6 mg/kg). Systemic administration of sufficient leucovorin to provide partial marrow protection compromised the antitumor activity of both MTX and MTX-BSA in the pleural cavity, and although leucovorin permitted higher doses to be used, this resulted in only a small increase in peak ILS for MTX-BSA on a single dose schedule.

Activity of free and carrier-bound methotrexate against transport-deficient and high dihydrofolate dehydrogenase-containing methotrexate-resistant L1210 cells

A difference in the mechanism of transmembrane transport was demonstrated for methotrexate (MTX) and MTX bound to the high molecular weight carrier bovine serum albumin (MTX-BSA) when the drug dose needed to reduce growth of cells to 50% of that of untreated cells (ID50) was compared in the sensitive L1210 leukemia and 3 L1210 sublines resistant to MTX by virtue of either deficient MTX transport or high levels of dihydrofolate dehydrogenase (DHFD). The loss of transport increased the ID50 for inhibition of growth rate by free MTX tenfold to twentyfold, whereas the elevation of DHFD levels increased the ID50 by tenfold. In contrast, deficiency of transport resulted in only a twofold increase in the ID50 for MTX-BSA, and elevation of DHFD caused a tenfold increase similar to that for free MTX. This difference was confirmed in studies of inhibition of DHFD activity by free and BSA-bound MTX. MTX-BSA but not MTX had antitumor activity against the transport-deficient L1210 line in (C57BL/6 x DBA/2)F1. These studies confirm a separate mode of cell entry for MTX-BSA and suggest a role for these complexes in overcoming resistance.