An open-label, multicenter, randomized phase II study of atezolizumab and bevacizumab with Y90 TARE in patients with unresectable hepatocellular carcinoma (HCC)

TPS4177

Background: The anti–PD-L1 antibody atezolizumab (ATEZO) prevents PD-L1 from interacting with PD-1 and B7.1, thus reinvigorating antitumor T cell activity. Anti-VEGF bevacizumab (BEV) increases dendritic cell maturation, enhances T cell infiltration, and reduces myeloid-derived suppressor cells and regulatory T cells in tumors. ATEZO + BEV is FDA approved for first-line treatment of advanced HCC based on the IMbrave 150 study. Locoregional radiotherapy (e.g., Y90 TARE) enhances the diversity of the intratumoral T cell receptor repertoire and increases tumor antigen release. We hypothesize that the Y90 TARE + BEV + ATEZO combination induces synergistic tumor killing and prolongs progression-free survival in patients (pts) receiving Y90 TARE (HR = 0.6 when compared to Y-90 TARE alone). Methods: Eligible pts have HCC that cannot be surgically resected (confirmed by pathology review), is at least BCLC stage B, and is outside Milan criteria. Other requirements include ECOG PS of 0-1 at screening, measurable disease by RECIST 1.1, no prior systemic therapy, and FLR estimated at ≥ 40% post local therapy. Pts must have a pretreatment liver biopsy taken and then be randomized 1:1 to TARE (Arm A) or TARE + ATEZO + BEV (Arm B). Pts will have TARE mapping followed by TARE treatment. In Arm B, pts will begin TARE treatment followed by BEV + ATEZO (4 wks [± 1 wk] later). Pts will have abdominal MRI or CT scans every 12 weeks and CT scans of the chest every 24 wks. The primary study objective is to assess and compare pts' progression-free survival (per mRECIST 1.1) in each study arm. The main secondary objective is to determine the safety and tolerability (CTCAE v5) of pts in Arm B. Exploratory objectives are to define the use of cellular and circulating biomarkers in the prediction of improved clinical outcomes of pts in Arm B. Symptoms experienced by pts in both arms using patient-reported outcomes will be assessed. Disease progression will be captured by both RECIST 1.1 and mRECIST. We plan to assess the safety of Y90 TARE + BEV + ATEZO in the first 10 pts randomized to Arm B for two cycles, and if there are no grade ≥ 3 unexpected toxicities possibly, probably, or definitely related to combined TARE + BEV + ATEZO, continue to accrue 128 pts in total (current enrollment n- = 5). Pts will continue study treatment (Arm B) for a total of 24 months from initiation of TARE or until intolerable toxicity or disease progression occur, whichever is earlier. Enrollment began in September 2020. Clinical trial information: NCT04541173.

Comparison of iRECIST and choi criteria for evaluation of response to ipilimumab plus nivolumab in advanced non-translocated sarcomas

e23524

Background: Patients (pts) with locally advanced or metastatic sarcoma have limited treatment options and a poor prognosis, with PFS of < 6mos and OS of < 15mos. A phase 2 trial showed encouraging response with combination ipilimumab and nivolumab immunotherapy (IO). RECIST and iRECIST both determine response rate. Recent data within GIST shows the Choi criteria better predicts clinical responses (assessing size and density of target lesions) than RECIST. We compared response to IO using iRECIST and Choi. Methods: In this single-institution retrospective analysis, pts with sarcoma were treated with at least one cycle of ipilimumab and nivolumab until disease progression (PD) or unacceptable toxicity between 2018-2021. Routine imaging was performed with CT or MRI to monitor for response. Responses were assessed using iRECIST, and Choi criteria for stable disease (SD), partial response (PR) and PD were correlated with clinical outcomes such as best response and progression free survival (PFS). The Kaplan-Meier method was used for survival analysis. Results: For 74 pts demographics were as follows: median age 55, 47% male; 11% African American, 88% Caucasian, 1% Asian; 78% metastatic disease, and 22% locally advanced disease. 85% of pts had high grade, 3% had intermediate grade, and 12% had low grade sarcoma. At the start of treatment, median tumor mutation burden was low (< 10mut/Mb) in 39%, high (> 10mut/Mb) in 3% and unknown in 58%. The PDL1 was negative in 4%, < 20 in 5% and > 20 in 1% with unknown PDL1 status in majority of patients, 89%. Overall response rate (ORR) was 45.3% (N = 59). The best response was SD in 34%, PR in 11% and PD in 55% based on iRESIST and Choi criteria. Median overall survival (OS) was 10.9m (95% CI 5.0-17.7) from the start of treatment. The mPFS was 4.1m (95% CI 2.8-5.7) based on iRESIST compared to mPFS was 2.9m (95% CI 2.1-5.7) based on Choi criteria. 55% of patients experienced any grade immune mediated toxicity with 54% requiring systemic steroids, and 19% resulting in treatment delay. The mOS for patients with toxicity was 14.7mo (95% CI 10.9-NR) versus 3.4m (95% CI 2.1-10.3) for those without IO toxicity. Conclusions: This real-world IO experience in advanced sarcomas shows remarkable ORR even with majority of patients having low TMB and unknown PD-L1 status. mPFS differed greatly between iRECIST and Choi criteria. iRECIST requires two scans to confirm PD, whereas Choi identifies PD with one scan, thus not delaying declaring PD. Another observation is that the Choi criteria was created for CT scans in GIST but has limitations within MRI. The development of immune mediated toxicity appears to be an independent predictor for prolonged OS in advanced sarcoma pts receiving IO therapy. A larger study is needed for confirmation of these trends.

Feasibility of acupressure intervention to improve chemotherapy-related symptoms and functioning among gastrointestinal cancer patients

657

Background: Chemotherapy-related symptoms, including fatigue, pain, insomnia, nausea, and vomiting, affect cancer patients’ (pt) physical and mental functioning. Acupressure (AP), which uses fingers to stimulate acupoints in the body per traditional Chinese medicine, has shown beneficial effects in improving chemotherapy-related symptoms. Yet, AP has been understudied in gastrointestinal cancer (GI) pts’ symptom management. Methods: This single-arm pilot trial enrolled 24 patients with stage I-IV GI cancers undergoing chemotherapy. They were trained to self-administer AP to 4 acupoints (Li4, PC6, ST36, SP6) on each side of the body, then practice one minute per acupoint for 8 minutes every day and fill daily logs through an 8-week intervention period. The primary endpoint examined the feasibility (interest, retention, and adherence rates) of delivering self-administered AP. Chemotherapy-related symptoms and functional status at baseline and 8-week post-intervention follow-up were assessed using NIH patient-reported outcome assessments (PRO-CTCAE and PROMIS short forms). Paired t-tests were run to examine change scores in symptom outcomes before and after intervention. Results: Pt demographics were 50% male, 21% African American, 67% Caucasian and 12% other (mean age = 56). They included 38% colorectal cancer, 25% pancreatic cancer, 17% cholangiocarcinoma, and 20% upper GI cancers. Feasibility outcomes showed that 83% of approached pts were interested in participation; 24 of 31 eligible pts (77%) were enrolled; retention rate was 71% (N = 17). Seven pts did not complete the trial due to two with infections, three concerning time to fill daily logs, and two with unspecified reasons. Approximately 65% of pts adhered to performing AP for over 80% of the time and filling daily logs every week. No adverse events were attributed to AP. Data from PRO-CTCAE showed that over 93% of pts reported no or mild nausea and vomiting through the intervention period except one reporting a moderate level of vomiting. Data from PROMIS surveys showed that after the 8-week intervention, patient-reported pain interference with daily activities and physical functioning remained similar to the baseline level. Yet, pts had reduced fatigue (-4.4 points), sleep disturbance (-3.1), depression (-3.3), anxiety (-2.7), and increased cognitive function (2.6) after AP intervention. These improvements were not statistically significant due to the small sample size, but a 3-point change in the PROMIS symptom scores is clinically meaningful. Conclusions: This trial shows that self-administered AP proves to be a feasible, safe, and low-cost approach and may be beneficial for GI cancer pts to relieve treatment-related symptoms. Future randomized trials are needed to determine efficacy.

Phase II study of combination pembrolizumab and olaparib in patients with advanced cholangiocarcinoma: Interim results

452

Background: Unresectable cholangiocarcinoma (CCA) remains a cancer of dismal prognosis as these tumors tend to be highly chemotherapy-refractory, providing patients (pts) a median survival of only around nine months. We herein provide an interim update to this phase II, single-arm, open-label study, where we investigate the safety and efficacy of olaparib plus pembrolizumab in pts with CCA after first-line gemcitabine-based therapy. We hypothesize that olaparib will increase tumoral response to pembrolizumab by inducing DNA damage and increasing tumor antigen number to produce a durable immune response against CCA - thereby increasing the overall response rate (ORR) of pts from 17.5% (historic chemotherapy control) to 35%. Methods: In total, 36 histologically confirmed advanced cholangiocarcinoma pts will be enrolled onto this trial. Pts receive pembrolizumab, 200 mg, on day 1 of each 21-day cycle, and oral olaparib, 300 mg, twice daily. The primary objective is to assess ORR, while a secondary aim is to evaluate safety. Tumor biopsies are collected at baseline, the third week after treatment initiation, and disease progression; the tissue is tested for ERCC1, PD-1/PD-L1 expression, IDH1/2 mutation status, and immune cell (CD3 and CD8) response. CT or MRI is carried out every 6 weeks for the first 6 months and every 9 weeks for the next 6 months to assess clinical response. Results: At the cutoff date of September 26, 2021, 12 pts had been enrolled and received at least one dose of olaparib plus pembrolizumab. The median age is 62 years (range 47-74); most are female (N = 10) and Caucasian (N = 8). Ten pts were diagnosed with cholangiocarcinoma and 2 with gallbladder carcinoma. According to RECIST v1.1, partial response (PR) was seen in one pt (-50%), stable disease (SD) in 4 pts (one with promising ongoing response at 23% tumor shrinkage), and disease progression in 7 pts. Three pts are actively on trial (1 PR and 2 SD). Complete molecular analysis by FoundationOne CDx revealed mutations in ATM (N = 2), SKT11 (N = 1) , ARID1A (N = 2) , and IDH1 (N = 2); the full tumor profile will be presented at the ASCO-GI meeting. Primary grade 3 treatment-related adverse events (AEs) included anemia (N = 2) and diarrhea (N = 1. Grade 1/2 AEs included thrombocytopenia (N = 2), anemia (N = 1), rash (N = 1), and diarrhea (N = 1). Conclusions: Interim trial results indicate that combination olaparib and pembrolizumab has acceptable safety and manageable toxicity in pts with advanced cholangiocarcinoma. Clinical trial information: NCT04306367.

Outcome of early and intermediate-stage hepatocellular carcinoma (HCC): A single institution experience at MGUH

328

Background: Liver transplant (LT) remains the best curative standard for HCC within Milan criteria (Milan). Nonsurgical locoregional treatments, including TACE and ablation, offer a bridge to surgical management and attempt to downstage or maintain patients (pts) within Milan pending liver transplant and donor organ availability. We investigated clinical factors that predict successful downstaging of HCC and liver transplant. Methods: In this single-institutional retrospective analysis, pts with early-intermediate stage HCC within Milan (control) vs beyond Milan were evaluated for clinical outcome. Clinical factors including treatment and response, demographics, TACE distribution (number of treatments, timing, and response), and status of liver transplantation (timing and if received) were correlated to overall survival (OS). OS was calculated using the Kaplan-Meier method. Results: HCC pts (n = 343) considered for LT or downstage to LT were included in the study: 75% male, 13% African American, 55% Caucasian, and 14% Asian. 12% of pts had HBV, 53% had HCV, 2% had both HBV and HCV. 221 pts were diagnosed within Milan vs 122 beyond Milan, in which 36% (n = 44) were still within UCSF criteria (UCSF). 43% of those diagnosed within Milan ultimately received LT vs 16% of those diagnosed beyond Milan. 49% of pts (n = 60) initially beyond Milan were downstaged to within Milan, via TACE, wherein 27% received LT; this group accounted for 13% all LT. However, in the subset of pts beyond Milan but within UCSF, 68% were downstaged to within Milan, wherein 40% received LT. In pts initially within Milan, 21% (n = 47) progressed beyond Milan, but 40% of this subset was downstaged back to within Milan. Pts both within and beyond Milan had a median of 2 TACE procedures. Differences in the rates of LT relative to the number of TACE were significant (p = 0.022) for pts initially within Milan; for < / = 2 TACE, 54% had LT; for > 2 TACE, 26% had LT. Similar comparison was nonsignificant for pts initially beyond Milan (p = 0.95); rates of LT for < / = 2 TACE and > 2 TACE were 17% and 16% respectively. Median OS for non-LT recipients was 5 years vs not reached for LT recipients ( > 70% alive at 8 years, p < 0.001). Pts initially beyond Milan but within UCSF criteria had similar OS vs those initially within Milan (both 75% at 4 years), but OS was worse (50% at 4 years) for those beyond UCSF (p = 0.024). Conclusions: Liver transplantation significantly increased OS in early-intermediate stage HCC. Increased number of TACE procedures was associated with decreased likelihood of ultimate LT in pts initially diagnosed within Milan, particularly when they had > 2 TACE. Pts initially beyond Milan but within UCSF criteria had similar OS vs those initially within Milan; this former subset had a good chance of being downstaged to Milan and ultimately receive LT. Additional clinical factors that predict successful downstaging of HCC and LT are being investigated.

Predictors of immunotherapy (IO) response and subsequent tyrosine kinase inhibitor (TKI) response in hepatocellular carcinoma (HCC)

e16642

Background: Despite advances in understanding the molecular pathways of HCC, therapeutic options are limited and patient survival is dismal. IO is a promising HCC treatment and predicted to become first line therapy. Little is known about indicators predicting a prolonged response to IO or the effects of IO on subsequent TKI treatment. Methods: In this single-institutional retrospective analysis, pts received one of five IO containing regimens with nivolumab, pembrolizumab, atezolizumab plus bevacizumab, durvalumab or cemiplimab until disease progression (PD) or unacceptable toxicity. Relevant clinical factors including, but not limited to: stage, viral etiology, vascular invasion, tumor thrombus, multifocal disease, toxicity grade and additional therapies, were correlated to clinical outcome: progression free survival (PFS), overall survival (OS), response rate (RR), using Pearson’s chi-square test or student's t-test. Responses were assessed using RECIST v 1.1 criteria for stable disease (SD), partial response (PR) and PD were correlated with best response and PFS. OS was calculated by the Kaplan-Meier method. Results: Cohort demographics (n = 76) were: 72% male; 38% African American, 30% Caucasian and 16% Asian; 29% of pts had HBV, 41% had HCV, 1% had both HBV/HCV and 13% had no viral etiology (n = 64). The majority of pts were stage III (43%) or IV (38%). Best response to IO was SD in 65.7% of pts, PR in 25.7% and PD in 8.6%. Median OS was 13m (95% CI 7.9-18.1) from the start of IO and median PFS (n = 65) was 14m (95% CI 6.8-21.2). Median OS and PFS were significantly improved in pts with PR compared to PD (45 vs 8m, p < 0.0005, PFS 15 vs 3m p = 0.007). Both OS and PFS showed benefits for SD of ≥2 months compared to those with PD (11 vs 8m, p < .0005, PFS 5 vs 3m p = .007). Abnormal TSH anytime during IO treatment tended toward prolonged mOS (20 vs 9m p = 0.126). Thirty-five pts received additional lines of therapy after IO, 57% (N = 20) received a TKI and 14.2% (N = 5) received additional IO agents. Those who received TKI upon completion of IO had a significantly improved OS (p = 0.014) versus those who did not; median OS 22 m (95%CI 12.7-31.3) versus 10m (95%CI 5.4-14.6). Conclusions: PR and SD are independent predictors for prolonged PFS and OS in HCC pts receiving IO therapy. Abnormal TSH during IO treatment tended toward improved mOS. In addition data strongly indicates subsequent TKI therapy improves patient outcomes after IO.

Predictors of immunotherapy (IO) response in hepatocellular carcinoma (HCC)

555

Background: Despite advances in understanding the molecular pathways of HCC, therapeutic options are limited and patient survival is dismal. IO is a promising HCC treatment. There are currently no indicators to identify which patients (pts) will have a prolonged response. Methods: In this single-institutional retrospective analysis, pts received one of five IO containing regimens with nivolumab, pembrolizumab, atezolizumab plus bevacizumab, durvalumab or cemiplimab until disease progression (PD) or unacceptable toxicity. Relevant factors including: stage, viral etiology, vascular invasion (VI), tumor thrombus (TT), multifocal disease, toxicity grade, steroid use for IO mediated toxicities and derived Neutrophil-to Lymphocyte ratio (dNLR), were correlated to clinical outcome: progression free survival (PFS), overall survival (OS), response rate (RR), using Pearson’s chi-square test or student's t-test . Responses were assessed using RECIST v 1.1 criteria for stable disease (SD), partial response (PR) and PD were correlated with best response and PFS. OS was calculated by the Kaplan-Meier method. Results: Cohort demographics (n = 76) were: 72% male; 38% African American, 30% Caucasian and 16% Asian; 29% of pts had HBV, 41% had HCV, 1% had both HBV/HCV and 13% had no viral etiology (n = 64). The majority of pts were stage III (43%) or IV (38%). At the start of IO, 32% had VI, 32% had TT and 80% had multifocal or metastatic disease. 65% of pts experienced IO toxicity, with 24.3% at grade 3 or higher, and 34% requiring steroids. Best response to IO was SD in 65.7% of pts, PR in 25.7% and PD in 8.6%. Median OS was 13m (95% CI 7.9-18.1) from the start of IO and median PFS (n = 65) was 14m (95% CI 6.8-21.2). Median OS and PFS were significantly improved in pts with PR compared to PD (45 vs 8m, p < 0.0005, PFS 15 vs 3m p = 0.007). Both OS and PFS showed benefits for SD of ≥2 months compared to those with PD (11 vs 8m, p < .0005, PFS 5 vs 3m p = .007). VI, TT, stage, viral etiology, toxicity grade or dNLR did not correlate with OS, PFS and RR, however need of steroid treatment trended toward worse outcome. Conclusions: PR and SD are independent predictors for prolonged PFS and OS in HCC pts receiving IO therapy. Absence of steroid use for toxicity trended toward improved IO response.

Predictors of poor outcome for transarterial chemoembolization (TACE) in hepatocellular carcinoma (HCC)

4100

Background: The use of TACE in select patients with BCLC stage B HCC has been shown to improve survival. Despite this, it remains unclear which patients will benefit from repeated TACE versus switching to systemic therapy upon disease progression. The purpose of this study is to identify prognostic factors that predict poor outcomes in patients who receive TACE. Methods: In this single-institutional retrospective analysis, patients with unresectable HCC were treated with TACE between 2007-2016. Relevant factors such as staging by BCLC stage B, Child-Pugh score, vascular invasion (VI), tumor thrombus (TT), AFP levels, and number of TACE treatments within six months from the initiation of TACE were analyzed using either Pearson’s chi-square test or the student's t-test. The Kaplan-Meier method was used for survival analysis. Results: Patients (n = 176) underwent TACE; 45% had stage I-II disease, 42% were BCLC stage B prior to TACE, 71% were Child-Pugh A, 21% had extrahepatic spread, 34.7% had VI, and 26% had TT. The median number of TACE treatments was 2 (range, 1- 6). The median overall survival (mOS) was 43 months (m) (95% CI 31.3-54.7) and mOS from start of TACE was 34m (95% CI 26.2-41.8). Elevated AFP (>400) correlated with decreased mOS (25m vs. 35m, p=0.041). Similarly, the presence of TT correlated with poor outcomes (25m vs. 37m, p=0.015). The mOS was also negatively impacted by having 3 or more TACE treatments within a 6 m period (25m vs. 38m, p = 0.09). AFP >400, TT, and interval between TACE were all independent factors in this multivariate analysis, resulting in a shorter mOS of approx. 2 years compared to 3 years in patients without these negative prognostic factors. There was a strong association with both elevated AFP and TT (Chi square p=0.009). Conclusions: Elevated AFP (>400), the presence of TT, and a need for 3 or more TACE treatments within 6 months appear to be independent predictors for shorter mOS in patients receiving TACE. Patients with these poor prognostic factors tend to have more aggressive HCC, and earlier initiation of systemic therapy might provide benefit to these patients. A larger study is needed for confirmation of these findings.

Time of rumen fluid collection relative to feeding alters in vitro fermentation volatile fatty acid production

The objective of this study was to determine the effect of time of rumen fluid collection relative to feeding on volatile fatty acid (VFA) production for in vitro rumen fermentation. Three ruminally cannulated Holstein heifers were used as rumen fluid donors. Feed was removed from heifers 12 h prior to feeding, rumen fluid was collected from each heifer before feeding (0 h), and at 2, 4, and 6 h after feeding, repeated on three separate incubation days. Buffered rumen fluid (100 mL) was incubated in 250-mL bottles containing 1.4 g of dried TMR, in duplicate for each heifer at each collection time. All bottles were incubated for 24 h at 39°C and constant agitation (60 rpm), and capped with monitors to capture temperature and pressure every 15 min (RF1, Ankom Technology, Macedon, NY). At the end of incubation, final pH and a sample of rumen fluid were collected for VFA and ammonia nitrogen. Data were analyzed using PROC GLIMMIX of SAS, with donor as the experimental unit and day as the random blocking factor; significance is defined as P ≤ 0.05. Time of rumen fluid collection significantly affected acetate (mmol/liter; P = 0.0004), propionate (mmol/liter; P = 0.02), isobutyrate (mmol/liter; P &lt; 0.0001), valerate (mmol/liter; P = 0.004), isovalerate (mmol/liter; P &lt; 0.00001), and total VFA concentrations (mmol/liter; P = 0.004). All VFA relative proportions were altered due to time of rumen fluid collection (P &lt; 0.02). VFA production was highest when rumen fluid was collected 4-h post-feeding. There was little to no effect on pH. Our findings suggest that VFA production is maximized when rumen fluid is collected between 2 and 4 h after feeding.

Time of rumen fluid collection relative to feeding alters in vitro fermentation gas parameters

The objective of this study was to determine the effect of time of rumen fluid collection relative to feeding on gas production kinetics for in vitro rumen fermentation. Three ruminally cannulated Holstein heifers were rumen fluid donors. Feed was removed from heifers 12 h prior to feeding, rumen fluid was collected from each heifer before feeding (0 h), and at 2, 4, and 6 h after feeding, repeated on three separate incubation days. Buffered rumen fluid (100 mL) was incubated in 250-mL bottles containing 1.4 g of dried TMR, in duplicate for each heifer at each collection time. All bottles were incubated for 24 h at 39°C and constant agitation (60 rpm), and capped with monitors to capture temperature and pressure every 15 min (RF1, Ankom Technology, Macedon, NY). At the end of incubation, final pH was recorded. Gas data were fit with nonlinear regression comparison of fit in GraphPad Prism 7 to find best fit regression. The formula with best fit was as follows: y = Vm(1 - (e(-Kd(x - lag)))), where y is gas produced at time X (mmol), Vm is the asymptotic gas production (mmol), Kd indicates the fractional rate of gas production (mmol/h), X is time (h), and lag refers to the lag time before the start of fermentation (h) as indicated by positive gas production (R 2 = 0.98). Data were analyzed using PROC GLIMMIX of SAS, with donor as the experimental unit and day as the random blocking factor; significance is defined as P ≤ 0.05. Time of rumen fluid collection significantly affected gas production kinetics (lag P = 0.01, Vm P = 0.03, Kd P <0.0001). Gas production was highest in fermenter units fed with rumen fluid collected 2-h post-feeding. Fractional rate of fermentation (Kd) was fastest in rumen fluid collected at 0 h. Lag time was longest in rumen fluid collected at 4-h post-feeding and slowest in rumen fluid collected at 0 h. Time of rumen fluid collection did not alter final pH. Our findings suggest that gas production is maximized when rumen fluid is collected between 2 and 4 h after feeding.

Demographic, clinical, and outcomes characteristics associated with screening colonoscopy in colorectal cancer patients

554

Background: Screening colonoscopy has well established role in CRC prevention. Factors associated with underutilization of screening colonoscopy, and how underutilization affects the CRC outcomes is unclear. We conducted a retrospective study with an aim to identify demographic, clinical and outcome characteristics associated with screening colonoscopy in patients with CRC. Methods: The Indiana Network for Patient Care (INPC) was used to identify patients diagnosed with CRC between 2001-2015. The INPC is the largest and longest tenured clinical data warehouse of the Indiana Health Information Exchange in the USA. Patient demographic (age, race, gender, median household income, insurance type, geographical location), clinical (BMI, year of diagnosis, stage, tumor location, CEA, surgery, chemotherapy, comorbidity) and outcome characteristics were obtained. Only patients who had colonoscopy prior to diagnosis were included, and divided those who received screening colonoscopy versus diagnostic colonoscopy. Chi-square was used for univariate analysis. Multivariate logistic regression was used to model the association of colonoscopy with overall mortality, and CRC-specific mortality. Results: A total of 1546 patients were identified, of which 361 (23.3%) and 1185 (76.6%) had screening and diagnostic colonoscopy, respectively. On univariate analyses, older age, female gender, Caucasian race, lower BMI and lack of insurance, were significantly associated with screening colonoscopy (P < 0.05). Additionally, patients receiving screening colonoscopy had higher likelihood to undergo surgery and receive chemotherapy (P < 0.05). Multivariate analyses adjusted for age, gender, race, surgery, chemotherapy and insurance status showed that screening colonoscopy (as compared with diagnostic colonoscopy) is associated with a 38% lower odds of overall mortality (adjusted OR = 0.62, 95% CI, 0.46-0.83, p < 0.001), and 68% lower odds of CRC-specific mortality (adjusted OR = 0.32, 95% CI, 0.19-0.51, p < 0.001). Conclusions: Screening colonoscopy is associated with decreased odds of overall and CRC-specific mortality and individuals with older age are more likely to receive it.

Patient-derived xenotransplants can recapitulate the genetic driver landscape of acute leukemias

Genomic studies have identified recurrent somatic mutations in acute leukemias. However, current murine models do not sufficiently encompass the genomic complexity of human leukemias. To develop pre-clinical models, we transplanted 160 samples from patients with acute leukemia (AML, MLL, B-ALL and T-ALL) into immunodeficient mice. Of these, 119 engrafted with expected immunophenotype. Targeted sequencing of 374 genes and 265 frequently rearranged RNAs detected recurrent and novel genetic lesions in 48 paired primary tumor (PT) and patient-derived xenotransplant (PDX) samples. Overall, the frequencies of 274 somatic variant alleles correlated between PT and PDX samples, although the data were highly variable for variant alleles present at 0-10%. 17% of variant alleles were detected in either PT or PDX samples only. Based on variant allele frequency changes, 24 PT-PDX pairs were classified as concordant while the other 24 pairs showed various degree of clonal discordance. There was no correlation of clonal concordance with clinical parameters of diseases. Significantly more bone marrow samples than peripheral blood samples engrafted discordantly. These data demonstrate the utility of developing PDX banks for modeling human leukemia, and emphasize the importance of genomic profiling of PDX and patient samples to ensure concordance before performing mechanistic or therapeutic studies.

Effect of molecular weight and concentration of legume condensed tannins on in vitro larval migration inhibition of Haemonchus contortus

The effect of molecular weight of condensed tannins (CT) from a variety of warm-season perennial legumes commonly consumed by sheep and goats on anthelmintic activity has not been previously explored. The objectives of this study were to determine if molecular weight of CT from warm-season perennial legumes could predict the biological activity of CT relative to anthelmintic activity against ivermectin resistant L3 stage Haemonchus contortus (HC) using a larval migration inhibition (LMI) assay. A second objective was to determine if CT from warm-season perennial legumes possess anthelmintic properties against L3 stage (HC). Lespedeza stuevei had the greatest concentration of total condensed tannin (TCT; 11.7%), whereas, with the exception of Arachis glabrata, a CT-free negative control, Leucaena retusa had the least TCT (3.3%). Weight-average molecular weight of CT ranged from 552 Da for L. stuevei to 1483 Da for Lespedeza cuneata. The treatments demonstrating the greatest percent LMI were L. retusa, L. stuevei and Acacia angustissima var. hirta (65.4%, 63.1% and 42.2%, respectively). The ivermectin treatment had the smallest percent LMI (12.5%) against ivermectin resistant L3 HC. There was a weak correlation (R(2)=0.34; P=0.05) between CT MW and percent LMI, suggesting that molecular weight of CT is a weak contributing factor to CT biological activity as it relates to LMI of L3 stage HC. L. stuevei, L. retusa and A. angustissima var. hirta STP5 warrant further evaluation of anthelmintic properties in vivo.

Cell of origin determines clinically relevant subtypes of MLL-rearranged AML

Mixed lineage leukemia (MLL)-fusion proteins can induce acute myeloid leukemias (AMLs) from either hematopoietic stem cells (HSCs) or granulocyte-macrophage progenitors (GMPs), but it remains unclear whether the cell of origin influences the biology of the resultant leukemia. MLL-AF9-transduced single HSCs or GMPs could be continuously replated, but HSC-derived clones were more likely than GMP-derived clones to initiate AML in mice. Leukemia stem cells derived from either HSCs or GMPs had a similar immunophenotype consistent with a maturing myeloid cell (LGMP). Gene expression analyses demonstrated that LGMP inherited gene expression programs from the cell of origin including high-level Evi-1 expression in HSC-derived LGMP. The gene expression signature of LGMP derived from HSCs was enriched in poor prognosis human MLL-rearranged AML in three independent data sets. Moreover, global 5'-mC levels were elevated in HSC-derived leukemias as compared with GMP-derived leukemias. This mirrored a difference seen in 5'-mC between MLL-rearranged human leukemias that are either EVI1 positive or EVI1 negative. Finally, HSC-derived leukemias were more resistant to chemotherapy than GMP-derived leukemias. These data demonstrate that the cell of origin influences the gene expression profile, the epigenetic state and the drug response in AML, and that these differences can account for clinical heterogeneity within a molecularly defined group of leukemias.

The clathrin-binding domain of CALM and the OM-LZ domain of AF10 are sufficient to induce acute myeloid leukemia in mice

The t(10;11)(p13-14;q14-21) translocation, giving rise to the CALM-AF10 fusion gene, is a recurrent chromosomal rearrangement observed in patients with poor prognosis acute myeloid leukemia (AML). Although splicing of the CALM-AF10 fusion transcripts has been described in AML patients, the contribution of different CALM and AF10 domains to in vivo leukemogenesis remains to be defined. We therefore performed detailed structure-function studies of the CALM-AF10 fusion protein. We demonstrate that fusion of the C-terminal 248 amino acids of CALM, which include the clathrin-binding domain, to the octapeptide motif-leucine-zipper (OM-LZ) domain of AF10 generated a fusion protein (termed CALM-AF10 minimal fusion (MF)), with strikingly enhanced transformation capabilities in colony assays, providing an efficient system for the expeditious assessment of CALM-AF10-mediated transformation. Leukemias induced by the CALM-AF10 (MF) mutant recapitulated multiple aspects of full-length CALM-AF10-induced leukemia, including aberrant Hoxa cluster upregulation, a characteristic molecular lesion of CALM-AF10 leukemias. In summary, this study indicates that collaboration of the clathrin-binding and the OM-LZ domains of CALM-AF10 is sufficient to induce AML. These findings further suggest that future approaches to antagonize CALM-AF10-induced transformation should incorporate strategies, which aim at blocking these key domains.

Defining leukemia stem cells in MLL-translocated leukemias: implications for novel therapeutic strategies

Hematological malignancies and probably many other tumors are dependent on highly proliferating and self-renewing cancer stem cells. An important question in the development of novel, less toxic antileukemic strategies specifically targeting leukemia stem cells is how closely leukemia stem cells are related to normal hematopoietic stem cells. It has been recently demonstrated that leukemia stem cells can be derived from different stages in normal hematopoiesis and have unique phenotypic and genetic features. Introduction of Mixed-lineage leukemia ( MLL)-fusion oncoproteins, frequently found in infant leukemias and therapy-related leukemias, into differentiated hematopoietic progenitor cells results in the generation of leukemias with a high frequency of leukemia stem cells. The progenitor-derived leukemia stem cells ectopically express a limited stem cell program while maintaining the global identity of differentiated myeloid cells. Development of therapeutic strategies that specifically target the leukemia stem cell program while sparing normal hematopoietic stem cells may represent a novel therapeutic approach in human leukemias with high efficacy yet less side effects.

MLL-AF9 and FLT3 cooperation in acute myelogenous leukemia: development of a model for rapid therapeutic assessment

Human leukemias harboring chromosomal translocations involving the mixed lineage leukemia (MLL, HRX, ALL-1) gene possess high-level expression, and frequent activating mutations of the receptor tyrosine kinase FLT3. We used a murine bone marrow transplant model to assess cooperation between MLL translocation and FLT3 activation. We demonstrate that MLL-AF9 expression induces acute myelogenous leukemia (AML) in approximately 70 days, whereas the combination of MLL-AF9 and FLT3-ITD does so in less than 30 days. Secondary transplantation of splenic cells from diseased mice established that leukemia stem cells are present at a very high frequency of approximately 1:100 in both diseases. Importantly, prospectively isolated granulocyte macrophage progenitors (GMPs) coinfected with MLL-AF9 and FLT3-ITD give rise to a similar AML, with shorter latency than from GMP transduced with MLL-AF9 alone. Cooperation between MLL-AF9 and FLT3-ITD was further verified by real-time assessment of leukemogenesis using noninvasive bioluminescence imaging. We used this model to demonstrate that MLL-AF9/FLT3-ITD-induced leukemias are sensitive to FLT3 inhibition in a 2-3 week in vivo assay. These data show that activated FLT3 cooperates with MLL-AF9 to accelerate onset of an AML from whole bone marrow as well as a committed hematopoietic progenitor, and provide a new genetically defined model system that should prove useful for rapid assessment of potential therapeutics in vivo.

Silencing of the tumor suppressor gene FHIT is highly characteristic for MLL gene rearranged infant acute lymphoblastic leukemia

MLL rearranged acute lymphoblastic leukemia (MLL) is an aggressive type of acute lymphoblastic leukemia (ALL), diagnosed predominantly in infants (<1 years of age). Since current chemotherapy fails in >50% of patients with MLL, new therapeutic strategies are desperately needed. For this, understanding the biological features characterizing MLL is necessary. Analysis of gene expression profiles revealed that the expression of the tumor suppressor gene FHIT is reduced in children with MLL rearranged ALL as compared to ALL patients carrying germ line MLL. This finding was confirmed by quantitative real-time PCR. In 100% of the infant MLL cases tested, methylation of the FHIT 5'CpG region was observed, resulting in strongly reduced mRNA and protein expression. In contrast, FHIT methylation in infant and non-infant ALL patients carrying germ line MLL was found in only approximately 60% (P< or =0.004). FHIT expression was restored upon exposing leukemic cells to the demethylating agent decitabine, which induced apoptosis. Likewise and more specifically, leukemic cell death was induced by transfecting MLL rearranged leukemic cells with expression vectors encoding wild-type FHIT, confirming tumor suppressor activity of this gene. These observations imply that suppression of FHIT may be required for the development of MLL, and provide new insights into leukemogenesis and therapeutic possibilities for MLL.

Genomic organization of the Papaver rhoeas self-incompatibility S(1) locus

The self-incompatibility (SI) response in Papaver rhoeas depends upon the cognate interaction between a pollen-expressed receptor and a stigmatically expressed ligand. The genes encoding these components are situated within the S-locus. In order for SI to be maintained, the genes encoded by the S-locus must be co-inherited with no recombination between them. Several hypotheses, including sequence heterogeneity and chromosomal position, have been put forward to explain the maintenance of the S-locus in the SI systems of the Brassicaceae and the Solanaceae. A region of the Papaver rhoeas genome encompassing part of the self-incompatibility S(1) locus has been cloned and sequenced. The clone contains the gene encoding the stigmatic component of the response, but does not contain a putative pollen S-gene. The sequence surrounding the S(1) gene contains several diverse repetitive DNA elements. As such, the P. rhoeas S-locus bears similarities to the S-loci of other SI systems. An attempt to localize the P. rhoeas S-locus using fluorescence in situ hybridization (FISH) has also been made. The potential relevance of the findings to mechanisms of recombination suppression is discussed.

Amplification of AML1 in childhood acute lymphoblastic leukemias

Amplification of AML1 has been confirmed by fluorescence in situ hybridization analysis in two cases of childhood acute lymphoblastic leukemia. It remains to be elucidated whether this amplification results in up-regulation of the normal AML1 gene product or a potentially mutant AML1 transcript.

The prevalence of positive hepatitis B, hepatitis C, and HIV serology in cornea donors prescreened by medical and social history in Ontario, Canada

PURPOSE

To determine the prevalence of hepatitis B (HBV), hepatitis C (HCV), and human immunodeficiency virus (HIV) in the serum of cornea donors who had been previously screened by social and medical history by the Eye Bank of Canada, Ontario Division.

METHOD

A retrospective examination of the donor records of the Eye Bank of Canada, Ontario Division, was conducted. A total of 3,228 records were examined covering the period from May 17, 1993 to May 31, 1996.

RESULTS

The prevalence of HBV was determined to be 0.25%, HCV, 0.93%; and HIV, 0.031%.

CONCLUSION

The data revealed that despite the use of medical and social history to prescreen, a small percentage of prescreened donors test serologically positive. A comparison of the prevalence of HBV, HCV, and HIV in the prescreened cornea donors to a similarly screened cohort of blood donors over a similar time period reveals a higher prevalence in all three diseases in the cohort of cornea donors. An examination of the demographic characteristics of the population as a whole versus the three groups with confirmed serology failed to show a significant difference between the seropositive and seronegative groups. This study confirms the value and necessity of serologic prescreening of cornea donors as is currently the standard of practice.

Casein kinase II-mediated phosphorylation of the C terminus of Sp1 decreases its DNA binding activity

We have previously observed that Sp1, a ubiquitous zinc finger transcription factor, is phosphorylated during terminal differentiation in the whole animal, and this results in decreased DNA binding activity (Leggett, R. W., Armstrong, S. A., Barry, D., and Mueller, C. R. (1995) J. Biol. Chem. 270, 25879-25884). In this study, we demonstrate that casein kinase II (CKII) is able to phosphorylate the C terminus of Sp1 and results in a decrease in DNA binding activity. This suggests that CKII may be responsible for the observed regulation of Sp1. Mutation of a consensus CKII site at amino acid 579, within the second zinc finger, eliminates phosphorylation of this site and the CKII-mediated inhibition of Sp1 binding. Phosphopeptide analysis confirms the presence of a CKII site at Thr-579 as well as additional sites within the C terminus. No gross changes in CKII subunit levels were seen during de-differentiation associated with liver regeneration. The serine/threonine phosphatase PP1 was identified as the endogenous liver nuclear protein able to dephosphorylate Sp1 but again no gross changes in activity were observed in the regenerating liver. Okadaic acid treatment of K562 cells increases Sp1 phosphorylation and inhibits its DNA binding activity suggesting that steady state levels of Sp1 phosphorylation are established by a balance between kinase and phosphatase activities.

Defective forebrain development in mice lacking gp330/megalin

gp330/megalin, a member of the low density lipoprotein (LDL) receptor gene family, is expressed on the apical surfaces of epithelial tissues, including the neuroepithelium, where it mediates the endocytic uptake of diverse macromolecules, such as cholesterol-carrying lipoproteins, proteases, and antiproteinases. Megalin knockout mice manifest abnormalities in epithelial tissues including lung and kidney that normally express the protein and they die perinatally from respiratory insufficiency. In brain, impaired proliferation of neuroepithelium produces a holoprosencephalic syndrome, characterized by lack of olfactory bulbs, forebrain fusion, and a common ventricular system. Similar syndromes in humans and animals are caused by insufficient supply of cholesterol during development. Because megalin can bind lipoproteins, we propose that the receptor is part of the maternal-fetal lipoprotein transport system and mediates the endocytic uptake of essential nutrients in the postgastrulation stage.

Sp1 is phosphorylated and its DNA binding activity down-regulated upon terminal differentiation of the liver

Using nuclear extracts prepared from rat liver it was demonstrated that binding of a transcription factor to site II of the D-site binding protein promoter could be induced by dephosphorylation of these extracts. Competition band shifts and supershift assays reveal this protein to be the general transcription factor Sp1. Phosphorylation of Sp1 appears to occur as a result of terminal differentiation of the liver. Proteins from both 1-day-old rat liver and adult liver undergoing regeneration have less of the phosphorylated form of Sp1 present with consequent increased DNA binding activity. Sp1 is similarly phosphorylated in brain, kidney, and spleen with phosphatase treatment of the extracts significantly increasing the level of DNA binding activity. Dephosphorylation of Sp1 results in a 10-fold increase in the affinity of Sp1 for its cognate site. Two-dimensional gel electrophoresis reveals that approximately 20% of the detectable protein appears to be in the phosphorylated form in adult liver extracts. Another protein with similar characteristics also appears to be present in the liver. Decreasing Sp1 DNA binding activity by phosphorylation may be an important mechanism for regulating gene expression, and possibly bringing about growth arrest during terminal differentiation.

Functional expression of low density lipoprotein receptor-related protein is controlled by receptor-associated protein in vivo

The 39-kDa receptor-associated protein (RAP) associates with the multifunctional low density lipoprotein (LDL) receptor-related protein (LRP) and thereby prevents the binding of all known ligands, including alpha 2-macroglobulin and chylomicron remnants. RAP is predominantly localized in the endoplasmic reticulum, raising the possibility that it functions as a chaperone or escort protein in the biosynthesis or intracellular transport of LRP. Here we have used gene targeting to show that RAP promotes the expression of functional LRP in vivo. The amount of mature, processed LRP is reduced in liver and brain of RAP-deficient mice. As a result, hepatic clearance of alpha 2-macroglobulin is impaired and remnant lipoproteins accumulate in the plasma of RAP-deficient mice that also lack functional LDL receptors. These results are consistent with the hypothesis that RAP stabilizes LRP within the secretory pathway. They also suggest a further mechanism by which the activity of an endocytic receptor may be modulated in vivo.

CAAX geranylgeranyl transferase transfers farnesyl as efficiently as geranylgeranyl to RhoB

RhoB, a small GTP-binding protein, was shown previously to contain farnesyl (C-15) as well as geranylgeranyl (C-20) groups (Adamson, P., Marshall, C. J., Hall, A., and Tilbrook, P. A. (1992) J. Biol. Chem. 267, 20033-20038). The COOH-terminal sequence of the protein is CCKVL. According to current rules of prenylation, the COOH-terminal leucine should render the protein a substrate for CAAX geranylgeranyl transferase (GGTase-1), but not for CAAX farnesyltransferase (FTase). To determine the mechanism of farnesylation, we prepared recombinant RhoB and incubated it with recombinant preparations of either FTase or GGTase-1. RhoB was neither farnesylated nor geranylgeranylated efficiently by FTase, but it was farnesylated as well as geranylgeranylated by GGTase-1. The enzyme attached farnesyl more efficiently than geranylgeranyl to RhoB. Neither farnesylation nor geranylgeranylation required the cysteine at the fifth position from the COOH terminus. However, replacement of the cysteine at the fourth position abolished attachment of both prenyl groups. We conclude that the previously observed farnesylation of RhoB is attributable to the FTase activity of GGTase-1. These data, and other accumulating data, indicate that GGTase-1 is a highly unusual enzyme that efficiently transfers both farnesyl and geranylgeranyl groups and that the choice of prenyl group is dictated by the nature of the protein acceptor.

REP-2, a Rab escort protein encoded by the choroideremia-like gene

Rab escort proteins (REPs) bind to newly synthesized Rab proteins and remain bound during and after the attachment of a geranylgeranyl (GG) group by the catalytic component of the Rab GG transferase. Transfer of the GG group is absolutely dependent on the participation of a REP. REP-1, the first characterized REP, is produced by a gene on the X chromosome that is defective in patients with choroideremia, a form of retinal degeneration. Cremers et al. (Cremers, F.P.M., Molloy, C. M., van de Pol, D. J. R., van den Hurk, J. A. J. M., Bach, I., Geurts van Kessel, A. H. M., and Ropers, H.-H. (1992) Hum. Mol. Genet. 1, 71-75) isolated a related gene, designated choroideremia-like, which encodes a protein that closely resembles REP-1. In the current studies, we produced REP-1 and REP-2 by recombinant DNA methods and showed that both proteins were approximately equal in facilitating the attachment of GG groups to several Rab proteins, including Rab1A, Rab5A, and Rab6. However, REP-2 was only 25% as active as REP-1 in supporting GG attachment to Rab3A and Rab3D. The low activity toward Rab3A was increased to that of Rab1A when the COOH-terminal 12 amino acids of Rab3A were replaced with the corresponding residues of Rab1A. We suggest that REP-2 substitutes for the absent function of REP-1 in nonretinal cells of patients with choroideremia, thus preventing cellular dysfunction throughout the body. In the retina, REP-2 may be only partially effective, leading eventually to retinal degeneration and blindness.

cDNA cloning of component A of Rab geranylgeranyl transferase and demonstration of its role as a Rab escort protein

cDNA cloning of component A of rat Rab geranylgeranyl transferase confirms identity of the protein with the human choroideremia gene product and its resemblance to Rab3A guanine nucleotide dissociation inhibitor (GDI), which binds prenylated Rabs. In biochemical assays we demonstrate that component A binds unprenylated Rab1A, presents it to the catalytic component B, and remains bound to it after the geranylgeranyl transfer reaction. In the absence of detergents, the reaction terminates when all of component A is occupied with prenylated Rab. Detergents allow multiple rounds of catalysis, apparently by dissociating the component A-Rab complex and thus allowing recycling of component A. Within the cell, component A may be regenerated by transferring its prenylated Rab to a protein acceptor, such as Rab3A GDI. In view of its function in escorting Rab proteins during and presumably after the prenyl transfer reaction, we propose to rename component A as Rab escort protein (REP). A genetic defect in REP underlies human choroideremia, a disease of retinal degeneration.

cDNA cloning and expression of the alpha and beta subunits of rat Rab geranylgeranyl transferase

Rab geranylgeranyl transferase (Rab GG transferase) attaches 20-carbon geranylgeranyl groups to cysteine residues in Rab proteins that contain the COOH-terminal sequence Cys-X-Cys or Cys-Cys. Rab GG transferase consists of two components that are separable in high salt solutions. Component A is a 95-kDa protein, and Component B is a heterodimer consisting of a 60-kDa alpha subunit and a 38-kDa beta subunit. In the current paper, we have cloned cDNAs for the alpha and beta subunits of Component B. The cDNAs for the rat alpha and beta subunits predict proteins of 567 and 331 amino acids, respectively. The mRNAs for both subunits are expressed in many tissues. When transfected together in embryonic kidney 293 cells, the alpha and beta subunit cDNAs produced Rab GG transferase activity that was stimulated in vitro by the addition of purified Component A. Comparisons of the amino acid sequences suggest that the proteins encoded by the Saccharomyces cerevisiae genes MAD2 and BET2 are the yeast counterparts of the mammalian Rab GG transferase alpha and beta subunits, respectively.

Nonidentical subunits of p21H-ras farnesyltransferase. Peptide binding and farnesyl pyrophosphate carrier functions

The protein farnesyltransferase purified from rat brain contains two nonidentical subunits, alpha and beta. The holoenzyme forms a stable complex with [3H]farnesyl pyrophosphate (FPP) that can be isolated by gel filtration. The [3H]FPP is not covalently bound to the enzyme; it is released unaltered when the enzyme is denatured. When incubated with an acceptor such as p21H-ras, the complex transfers [3H]farnesyl from the bound [3H]FPP to the ras protein. This transfer is not sensitive to dilution by unbound FPP, suggesting that the [3H]FPP is bound at a site that leads to direct transfer to the p21H-ras acceptor. Cross-linking studies show that the p21H-ras binds to the lower molecular weight subunit (beta-subunit), raising the possibility that the [3H]FPP binds to the alpha-subunit. If this suggestion can be confirmed, it would invoke a reaction mechanism in which the alpha-subunit acts as a prenyl pyrophosphate carrier that delivers FPP to p21H-ras which is bound to the beta-subunit.

The active site of membrane-bound meizothrombin. A fluorescence determination of its distance from the phospholipid surface and its conformational sensitivity to calcium and factor Va

The distance between the phospholipid surface and the active site of membrane-bound meizothrombin, a derivative of prothrombin, was determined directly using fluorescence energy transfer. The active site of prothrombin was exposed after a single cleavage by Echis carinatus protease in the presence of [5-(dimethylamino)-1-naphthalenesulfonyl]glutamylglycylarginyl+ ++ (DEGR) chloromethyl ketone to yield DEGR-meizothrombin and thereby minimize secondary proteolysis. When DEGR-meizothrombin was titrated with 80% phosphatidylcholine, 20% phosphatidylserine vesicles containing octadecylrhodamine, singlet-singlet energy transfer was observed between the donor dyes in the active sites of the membrane-bound proteins and the acceptor dyes at the outer surface of the phospholipid bilayer. This energy transfer required both Ca2+ and phosphatidylserine. Assuming k2 = 2/3, the dependence of the efficiency of energy transfer upon the acceptor density showed that the distance of closest approach between the active site probe and the bilayer surface was 71 +/- 2 A. In the presence of factor Va, the distance was 67 +/- 3 A. These direct measurements show that the active site of meizothrombin is located far above the membrane surface. Also, association of factor Va with meizothrombin on the phospholipid surface appears to cause a slight movement of the meizothrombin protease domain toward the membrane surface. The environment of the dansyl dye covalently attached to the active site of meizothrombin was particularly sensitive to the presence of calcium: addition of Ca2+ ions to metal-free DEGR-meizothrombin reduced the dansyl fluorescence lifetime from 11.7 to 9.0 ns and the dansyl emission intensity by 24%. Hence, the conformation of the active site changed when Ca2+ ions bound to meizothrombin. Since the intensity change was half-maximal at 0.2 mM and was also elicited by the binding of Mg2+ ions, this spectral change correlates with the calcium-dependent conformational change previously observed in fragment 1. We conclude, therefore, that the binding of Ca2+ ions to meizothrombin and, by extension, perhaps to prothrombin, elicits a conformational change that extends beyond the fragment 1 domains into the distant (cf. above) active site or protease domain. The association of factor Va with membrane-bound DEGR-meizothrombin increased both the dansyl emission intensity (by 7%) and polarization. This intensity change and the factor-Va dependent change in energy transfer indicate that the cofactor of the prothrombinase complex functions to modulate the conformation and orientation of both the substrate and the enzyme of the complex.

Measurement of pectin methylation in plant cell walls

A procedure was developed to measure the degree of pectin methylation in small samples of isolated cell walls from nonlignified plant tissues or pectin solutions. Galacturonic acid was determined colorimetrically with the 3,5-dimethylphenol reagent. Methylation was measured by base hydrolysis of galacturonic acid methyl esters, followed by gas chromatographic determination of released methanol. Estimates of the precision of analysis of pectin and cell wall samples were made. The coefficient of variation for estimates of the pectin esterification in cell walls isolated from 10-g samples of cucumber tissue ranged from 7.7 to 13.2%.