Low Protein Dose Research Articles

Characterizing and Predicting Outcomes in Critically Ill Patients Receiving Low or High Protein Doses with Moderate Energy Support: A Retrospective Study.

Finding the best energy and protein dose and timing for critically ill patients remains challenging. Distinct populations may react differently to protein load. This study aimed to characterize and predict outcomes of critically ill patients who received moderate energy and high or low protein doses during their stay in the intensive care unit (ICU). The cohort included 646 adult patients (70% men and 30% women) hospitalized in Beilinson Hospital ICU (Petah Tikva, Israel) for over 5 days between 2011 and 2018. Patients received 10-20 kcal/kg/day and were classified into two groups: low (LP) and high (HP) protein support (≤1 g/kg/day vs. >1 g/kg/day), the LP group comprising 531 patients (82%) and the HP group 115 patients (18%). Multiple logistic regression was used to describe associations between patients' characteristics and 90-day survival in the LP and HP groups. Among LP, increased age, APACHE II, and receiving supplemental parenteral nutrition (SPN) were associated with decreased survival (OR = 0.986, 95% CI [0.973, 0.999]; OR = 0.915, 95% CI [0.886, 0.944], OR = 0.579, 95% CI [0.366, 0.917]). Trauma admission was associated with increased survival (OR = 1.826, 95% CI [1.001, 3.329]). Among HP, increased age was associated with decreased survival (OR = 0.956, 95% CI [0.924, 0.998]). Higher BMI was associated with improved survival (OR = 1.137, 95% CI [1.028, 1.258]). Likewise, in the HP group, the BMI of elderly survivors was higher compared to non-survivors (27.1 ± 6.2 vs. 24.7 ± 4.8, t (113) = 2.3, p < 0.05). Our results show that in patients with moderate energy support and low protein administration, survivors were younger, with a lower APACHE II score, mainly suffering from trauma and without renal failure. In the patients receiving high protein support, younger patients with a high BMI not suffering from sepsis were more likely to survive. We suggest confirming these findings with prospective RCTs.

Predictors of acute muscle loss in the intensive care unit: A secondary analysis of an in-bed cycling trial for critically ill patients

PurposeThe purpose of this study was to assist clinicians to identify critically ill patients at greatest risk of acute muscle loss and to analyse the associations between protein intake and exercise on acute muscle loss. Materials and methodsSecondary analysis of a single-centre randomised clinical trial of in-bed cycling using a mixed effects model was undertaken to examine the association between key variables and rectus femoris cross-sectional area (RFCSA). Groups were combined, and key variables for the cohort were modified Nutrition Risk in the Critically Ill (mNUTRIC) scores within the first days following intensive care unit admission, longitudinal RFCSA measurements, percent of daily recommended protein intake, and group allocation (usual care, in-bed cycling). RFCSA ultrasound measurements were taken at baseline and days 3, 7, and 10 to quantify acute muscle loss. All patients received usual care nutritional intake while in the intensive care unit. Patients allocated to the cycling group commenced in-bed cycling once safety criteria were met. ResultsAnalysis included all 72 participants, of which 69% were male, with a mean (standard deviation) age of 56 (17) years. Patients received a mean (standard deviation) of 59% (26%) of the minimum protein dose recommended for critically ill patients. Mixed-effects model results indicated that patients with higher mNUTRIC scores experienced greater RFCSA loss (estimate = −0.41; 95% confidence interval [CI] = −0.59 to −0.23). RFCSA did not share a statistically significant association with cycling group allocation (estimate = −0.59, 95% CI = −1.53 to 0.34), the percentage of protein requirements received (estimate = −0.48; 95% CI = −1.16 to 0.19), or a combination of cycling group allocation and higher protein intake (estimate = 0.33, 95% CI = −0.76 to 1.43). Conclusions and relevanceWe found that a higher mNUTRIC score was associated with greater muscle loss, but we did not observe a relationship between combined protein delivery and in-bed cycling and muscle loss. The low protein doses achieved may have impacted the potential for exercise or nutrition strategies to reduce acute muscle loss. Trial registrationAustralian and New Zealand Clinical Trials Registry (ACTRN 12616000948493)

Do We Have Clinical Equipoise (or Uncertainty) About How Much Protein to Provide to Critically Ill Patients?

The current recommendation for protein dose in critically ill patients is 1.2-2.0 g/kg/d. Despite this recommendation, there is significant variation in the amount of protein prescribed and delivered worldwide. We contend clinical equipoise, or a state of genuine uncertainty about 2 (dosing) strategies, exists because guideline-based recommendations for protein dose in critically ill patients are rooted in a weak evidentiary base, leaving the clinician with no good basis for choosing a lower or higher protein dose. We outline evidence for and against high protein dose and introduce a pragmatic, registry-based, multicenter, randomized controlled trial, known as EFFORT, which aims to resolve the high vs low protein dose controversy.

Citrulline does not enhance blood flow, microvascular circulation, or myofibrillar protein synthesis in elderly men at rest or following exercise.

Aging is associated with anabolic resistance, a reduced sensitivity of myofibrillar protein synthesis (MPS) to postprandial hyperaminoacidemia, particularly with low protein doses. Impairments in postprandial skeletal muscle blood flow and/or microvascular perfusion with hyperaminoacidemia and hyperinsulinemia may contribute to anabolic resistance. We examined whether providing citrulline, a precursor for arginine and nitric oxide synthesis, would increase arterial blood flow, skeletal muscle microvascular perfusion, MPS, and signaling through mTORC1. Twenty-one elderly males (65-80 yr) completed acute unilateral resistance exercise prior to being assigned to ingest a high dose (45 g) of whey protein (WHEY) or a low dose (15 g) of whey protein with 10 g of citrulline (WHEY + CIT) or with 10 g of nonessential amino acids (WHEY + NEAA). A primed, continuous infusion of L-[ring-(13)C6] phenylalanine with serial muscle biopsies was used to measure MPS and protein phosphorylation, whereas ultrasound was used to measure microvascular circulation under basal and postprandial conditions in both a rested (FED) and exercised (EX-FED) leg. Argininemia was greater in WHEY + CIT vs. WHEY and WHEY + NEAA from 30 to 300 min postexercise (P < 0.001), but there were no treatment differences in blood flow or microvascular perfusion (all P > 0.05). Phosphorylation of p70S6K-Thr(389) was greater in WHEY vs. WHEY + NEAA (P = 0.02). Postprandial MPS was greater in WHEY vs. WHEY + CIT and WHEY + NEAA under both FED (WHEY: ~128%; WHEY + CIT: ~56%; WHEY + NEAA: ~38%) and EX-FED (WHEY: ~251%; WHEY + CIT: ~124%; WHEY + NEAA: ~108%) conditions (P = 0.003). Citrulline coingestion with a low quantity of protein was ineffective in augmenting the anabolic properties of protein compared with nonessential amino acids.

Specific imaging of VEGF‐A expression with radiolabeled anti‐VEGF monoclonal antibody

Vascular endothelial growth factor-A (VEGF-A) is one of the most important angiogenic factors. Here, we studied in a nude mouse model whether the expression of VEGF-A in a tumor could be imaged with a radiolabeled anti-VEGF antibody. The humanized anti-VEGF-A antibody A.4.6.1. (bevacizumab), which is reactive with all VEGF-A isoforms, was radiolabeled with In-111 or with I-125. The accumulation of the radiolabeled antibodies in VEGF-A expressing tumors (LS174T) in nude mice was examined in biodistribution studies and by gamma camera imaging. The uptake of the In-111-bevacizumab in the tumor at 3 days p.i. was significantly higher than that of I-125-bevacizumab (19.4 +/- 7.0 %ID/g vs. 9.6 +/- 3.3 %ID/g, p = 0.04). Coinjection of an excess unlabeled antibody resulted in a significant decrease in radioactivity concentration in the tumor (<2.9 +/- 1.9 %ID/g, p < 0.005), indicating VEGF-mediated antibody uptake. Highest uptake in the tumor was observed at relatively low antibody protein doses (<3 microg) (20-25 %ID/g). VEGF-A-expressing tumors could be clearly visualized on planar scintigraphic images from 24-hr post injection onwards. In conclusion, VEGF-A expression in tumors can be visualized specifically with radiolabeled anti-VEGF-A-mAb.

G250: A carbonic anhydrase IX monoclonal antibody

G250 or carbonic anhydrase IX (CA IX) is a membrane-associated carbonic anhydrase (CA) thought to play a role in the regulation of cell proliferation in response to hypoxic conditions and may be involved in oncogenesis and tumor progression. G250 refers to a monoclonal antibody (mAb) that was raised by immunization of mice with human renal cell carcinoma (RCC) homogenates. The RCC-associated transmembrane protein designated G250 has since proven to be identical to tumor-associated protein MN or CA IX. Previous studies using a mAb against CA IX have shown that CA IX is induced constitutively in certain tumor types, but is absent in most normal tissues with the exception of epithelial cells of the gastric mucosa. Furthermore, previous immunobiochemical studies of malignant and benign renal tissues revealed that CA IX was also highly expressed in RCC. Studies on tumor-bearing kidneys demonstrate selective uptake of mAb CA IX in antigen-positive cells versus antigen-negative cells. Furthermore, extraordinarily high uptake and the requirement of a low protein dose to obtain tumor saturation with respect to tumor targeting occur with mAb CA IX. These studies formed the basis of numerous clinical trials aimed at mAb-guided therapy in patients with metastatic RCC.

Intravenous Administration of Radiolabeled Immunoglobulin G to Cancer Patients: High or Low Protein Dose?

AbstractFor Abstract see ChemInform Abstract in Full Text.

A review of the intravenous administration of radiolabeled immunoglobulin G to cancer patients. High or low protein dose?

This retrospective analysis of preclinical and clinical radiolabeled immunoglobulin studies focuses on three well-known observations: (1) IV tumor reactive IgG provides higher response rates in patients with hematological malignancies than in patients with solid tumors. (2) Patients with CD20 positive B cell lymphoma require a high IV IgG protein dose for effective tumor targeting. (3) Most patients experience high uptake of IV administered radiolabeled IgG in normal liver. This review supports the following new hypotheses: (1) The blood-tumor barrier in most solid tumors is higher than in most hematological malignancies. (2) The blood-tumor barrier in CD20 positive B cell lymphomas is lowered by the IV administration of high doses [> 100 mg] of anti-CD20 IgG, presumably due to IgG induced intra-tumoral production of vaso-active biological response modifiers. (3) The blood-tumor barrier is low in Hodgkin's disease, presumably due to the continuous and innate production of biological response modifiers in tissues containing Hodgkin's disease. (4) The uptake of tumor reactive IgG in the normal liver is controlled by the Fc portion of the IgG. The radioimmunoconjugate is not catabolized in the liver. This appears to indicate that the F(c) portion of the IgG binds to the MHC class I like, F(c)gammaRn receptors in liver endothelium and hepatocytes and not to F(c)gamma RI, RII or RIII receptors The new hypotheses require verification and can be instrumental in the design of new more effective clinical RIT studies.

Effects of coligand variation on the in vivo characteristics of Tc-99m-labeled interleukin-8 in detection of infection.

In our previous studies, interleukin-8 (IL-8) was labeled with (99m)Tc using hydrazinonicotinamide (HYNIC) as bifunctional coupling agent and tricine as coligand. This preparation showed excellent characteristics for imaging of infection in a rabbit model of soft-tissue infection. In the present study, the propylaldehyde hydrazone formulation of HYNIC was introduced to stabilize HYNIC-IL-8. (99m)Tc-HYNIC-IL-8 was prepared using 5 different coligand formulations. The effect of these coligand formulations on the in vitro characteristics and in vivo behavior of (99m)Tc-HYNIC-IL-8 was investigated. HYNIC-conjugated IL-8 was labeled with (99m)Tc in the presence of either (A) tricine, (B) ethylenediaminediacetic acid (EDDA), (C) tricine and trisodium triphenylphosphinetrisulfonate (TPPTS), (D) tricine and nicotinic acid (NIC), or (E) tricine and isonicotinic acid (ISONIC). These preparations were characterized in vitro by RP-HPLC, determination of the octanol/water partition coefficient, stability studies, and receptor binding assays. The in vivo biodistribution of the radiolabel in rabbits with E. coli-induced soft-tissue infection was determined both by gamma-camera imaging as well as by tissue counting at 6 h pi. Specific activity (MBq/microg) was highest for (ISO)NIC (up to 80) > TPPTS (40) > tricine (15) > EDDA (7). RP-HPLC and octanol/water partition coefficients showed a shift toward higher lipophilicity for the TPPTS preparation. The leukocyte receptor binding fractions were around 40-55% for all preparations except for TPPTS, which showed predominantly nonspecific binding. All preparations were stabilized in serum, but the stability in PBS was highest for NIC and TPPTS > EDDA > ISONIC > tricine. The in vivo biodistribution showed highest abscess/muscle for NIC and ISONIC (>200) > EDDA and tricine (approximately 100) > TPPTS (<40). Gamma camera imaging rapidly visualized the abscess from 2 h pi onward for all formulations. The abscess/background (A/B) at 6 h pi for ISONIC was significantly higher (P < 0.05) than that of tricine and the A/B of TPPTS was significantly lower (P < 0.05). IL-8 can be rapidly and easily labeled with (99m)Tc using HYNIC as a chelator in combination with various coligands. The most optimal infection imaging characteristics were found for formulations using nicotinic acid/tricine as coligand system combining a high specific activity and high in vitro stability with high abscess/muscle ratios (>200) and high abscess/background ratios (>20). Protein doses to be administered were as low as 70 ng/kg bodyweight. At these low protein doses, side effects are not to be expected in the human system. This paves the way for infection imaging studies in patients.

Clinical Results and the Necessity of Estimating Patient-Specific Radiation Absorbed Dose in Radioimmunotherapy

Cancer Biotherapy & RadiopharmaceuticalsVol. 15, No. 4 Clinical Results and the Necessity of Estimating Patient-Specific Radiation Absorbed Dose in RadioimmunotherapyLawrence E. WilliamsLawrence E. WilliamsSearch for more papers by this authorPublished Online:29 Jan 2009https://doi.org/10.1089/cbr.2000.15.301AboutSectionsPDF/EPUB ToolsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail FiguresReferencesRelatedDetailsCited byDose Estimates and Correlations with Laboratory and Clinical Results7 February 2011A Review of the Intravenous Administration of Radiolabeled Immunoglobulin G to Cancer Patients. High or Low Protein Dose? Huib M. Vriesendorp and Francine J. Vriesendorp5 July 2004 | Cancer Biotherapy & Radiopharmaceuticals, Vol. 18, No. 1 Volume 15Issue 4Aug 2000 To cite this article:Lawrence E. Williams.Clinical Results and the Necessity of Estimating Patient-Specific Radiation Absorbed Dose in Radioimmunotherapy.Cancer Biotherapy and Radiopharmaceuticals.Aug 2000.301-303.http://doi.org/10.1089/cbr.2000.15.301Published in Volume: 15 Issue 4: January 29, 2009PDF download

The effect of antibody protein dose of anti-renal cell carcinoma monoclonal antibodies in nude mice with renal cell carcinoma xenografts.

Antibodies preferentially can direct radionuclides to solid tumors. However, antibody uptake in tumors is often highly heterogeneous. This heterogeneity may be overcome by increasing antibody protein dose. The biodistribution of increasing protein doses of radioiodinated antirenal cell carcinoma (RCC) monoclonal antibodies (MoAbs) G250 and RC 38 was studied in mice with NU-12 or SK-RC-52 RCC xenografts. In addition, MoAb affinity constants and antigen densities (Scatchard analysis) and MoAb processing (internalization) were determined in vitro. The relative uptake of G250 in NU-12 tumors was very high at low protein doses (125% injected dose/g [%ID/g]), but decreased at higher doses, suggesting tumor saturation. Indeed, saturation of G250 antigen occurred at 3 microg protein. In this model, 9200 G250 determinants per NU-12 cell could be targeted, which is only 6.1% of the 150,000 G250 determinants per NU-12 cell as determined in vitro. The RC 38 uptake in NU-12 tumors remained constant up to the 10 microg dose level (40% ID/g) and decreased at higher doses. RC 38 antigens were saturated at 25 microg of RC 38. With RC 38, 15% of the available RC 38 antigens per NU-12 tumor cell were targeted. In contrast, G250 uptake in SK-RC-52 tumors was very low at low antibody dose (4% ID/g at 1 microg) and increased with increasing protein dose. These differences in G250 biodistribution might be related to differences in the processing of G250 by the tumor cells. Our studies show that some RCC tumors can be saturated with anti-RCC MoAbs at low (25 microg) to very low (3 microg) protein doses. At nonsaturated doses relatively high tumor uptake can be achieved. Surprisingly, in NU-12 tumors only 6.1% and 15% of the available antigenic sites were targeted at the saturating dose levels with G250 and RC 38, respectively.

The effect of antibody protein dose of anti-renal cell carcinoma monoclonal antibodies in nude mice with renal cell carcinoma xenografts

Antibodies preferentially can direct radionuclides to solid tumors. However, antibody uptake in tumors is often highly heterogeneous. This heterogeneity may be overcome by increasing antibody protein dose.The biodistribution of increasing protein doses of radioiodinated antirenal cell carcinoma (RCC) monoclonal antibodies (MoAbs) G250 and RC 38 was studied in mice with NU-12 or SK-RC-52 RCC xenografts. In addition, MoAb affinity constants and antigen densities (Scatchard analysis) and MoAb processing (internalization) were determined in vitro.The relative uptake of G250 in NU-12 tumors was very high at low protein doses (125% injected dose/g [%ID/g]), but decreased at higher doses, suggesting tumor saturation. Indeed, saturation of G250 antigen occurred at 3 microg protein. In this model, 9200 G250 determinants per NU-12 cell could be targeted, which is only 6.1% of the 150,000 G250 determinants per NU-12 cell as determined in vitro. The RC 38 uptake in NU-12 tumors remained constant up to the 10 microg dose level (40% ID/g) and decreased at higher doses. RC 38 antigens were saturated at 25 microg of RC 38. With RC 38, 15% of the available RC 38 antigens per NU-12 tumor cell were targeted. In contrast, G250 uptake in SK-RC-52 tumors was very low at low antibody dose (4% ID/g at 1 microg) and increased with increasing protein dose. These differences in G250 biodistribution might be related to differences in the processing of G250 by the tumor cells.Our studies show that some RCC tumors can be saturated with anti-RCC MoAbs at low (25 microg) to very low (3 microg) protein doses. At nonsaturated doses relatively high tumor uptake can be achieved. Surprisingly, in NU-12 tumors only 6.1% and 15% of the available antigenic sites were targeted at the saturating dose levels with G250 and RC 38, respectively.

Preclinical analysis of radiolabeled anti-GD2 immunoglobulin G

Unlabeled murine monoclonal anti-GD2 immunoglobulin (Ig)G (14G2a) reactive with nervous system diganglioside and neuroblastoma, melanoma, and small cell lung carcinoma produces tumor regression. However, serious acute abdominal pain, paresthesia, hypotension and hypertension, syndrome of inappropriate secretion of antidiuretic hormone (SIADH), and occasional motor weakness occur. Studies in preclinical animal models can elucidate the mechanism of the observed neurotoxicity and lead to anti-GD2 antibody treatment with a higher therapeutic ratio.One mg of 14G2a or control IgG was labeled with 1-2 mCi of indium-111 and administered intravenously to beagles (n = 8). In 2 dogs, additional high dose (200 mg) unlabeled 14G2a was given over 5 days. Whole body gamma camera images and SPECT scans were obtained repeatedly over 7 days. On Day 7, sciatic nerve conduction studies were performed, and after euthanasia radioactivity was determined in major organs.Unlabeled high dose 14G2a administered to mice, rats, or rabbits did not cause neurotoxicity within 3 weeks. GD2 antigens were shown by immunochemistry to be present in brain and peripheral nerve tissues of rodents and beagles. After in vivo administration of radiolabeled 14G2a, canine lymph nodes showed specific uptake, but only minimal radioactivity was found in the nervous system. Dogs that received additional high dose unlabeled 14G2a showed much higher lymph node uptake and follicular lymph node hyperplasia. Low motor response amplitudes on nerve conduction studies were noted.A radioisotope label on IgG and its visualization in a large series of animal models indicate that a low protein dose of anti-GD2 IgG will not cause neurologic side effects in patients. High protein dose anti-GD2 IgG may enhance antineoplastic effects and contribute to neurotoxicity through stimulation of normal lymphocytes with subsequent release of cytokines.

Preclinical analysis of radiolabeled anti-GD2 immunoglobulin G.

Unlabeled murine monoclonal anti-GD2 immunoglobulin (Ig)G (14G2a) reactive with nervous system diganglioside and neuroblastoma, melanoma, and small cell lung carcinoma produces tumor regression. However, serious acute abdominal pain, paresthesia, hypotension and hypertension, syndrome of inappropriate secretion of antidiuretic hormone (SIADH), and occasional motor weakness occur. Studies in preclinical animal models can elucidate the mechanism of the observed neurotoxicity and lead to anti-GD2 antibody treatment with a higher therapeutic ratio. One mg of 14G2a or control IgG was labeled with 1-2 mCi of indium-111 and administered intravenously to beagles (n = 8). In 2 dogs, additional high dose (200 mg) unlabeled 14G2a was given over 5 days. Whole body gamma camera images and SPECT scans were obtained repeatedly over 7 days. On Day 7, sciatic nerve conduction studies were performed, and after euthanasia radioactivity was determined in major organs. Unlabeled high dose 14G2a administered to mice, rats, or rabbits did not cause neurotoxicity within 3 weeks. GD2 antigens were shown by immunochemistry to be present in brain and peripheral nerve tissues of rodents and beagles. After in vivo administration of radiolabeled 14G2a, canine lymph nodes showed specific uptake, but only minimal radioactivity was found in the nervous system. Dogs that received additional high dose unlabeled 14G2a showed much higher lymph node uptake and follicular lymph node hyperplasia. Low motor response amplitudes on nerve conduction studies were noted. A radioisotope label on IgG and its visualization in a large series of animal models indicate that a low protein dose of anti-GD2 IgG will not cause neurologic side effects in patients. High protein dose anti-GD2 IgG may enhance antineoplastic effects and contribute to neurotoxicity through stimulation of normal lymphocytes with subsequent release of cytokines.

99Tcm-LL1

LL1, a monoclonal antibody (MAb) to HLA Class-II-like antigen (li determinant) on the surface of B-lymphocytes, monocytes and histiocytes, was evaluated as an agent for bone marrow imaging. Six patients with diverse diseases (non-Hodgkin's lymphoma, n = 2; multiple myeloma, n = 1; polycythaemia vera, n = 1; lung cancer, n = 1; breast cancer, n = 1) were given low protein doses (< 1 mg) of 99Tcm (30 mCi) labelled Fab' of LL1. 99Tcm-sulphur colloid (SC) imaging was performed in three patients for comparison. Both planar and single photon emission tomographic images were acquired using Sopha gamma cameras. As early as 2 h post-MAb injection, excellent bone marrow images were achieved in all patients, demonstrating both normal or hyperproliferative marrow, as well as 'cold' bone marrow abnormalities such as radiation defects or cancer metastases. Similar to SC, relatively high uptake of LL1 was found in the liver and spleen. However, the bone marrow-to-liver and -spleen uptake ratios were approximately 19-fold higher (0.75 vs 0.04) and 6-fold higher (1.23 vs 0.22), respectively, with LL1 than with SC. The higher bone marrow uptake allowed clearly superior visualization of the thoracic spine when compared to SC. The mean T1/2 of blood and whole-body clearance were 0.4 and 66 h, respectively. The highest radiation absorbed doses (in cGy mCi-1) were observed in the spleen (0.47 +/- 0.24), kidneys (0.25 +/- 0.09) and liver (0.14 +/- 0.04). The bone marrow dose was only 0.05 +/- 0.02 cGy mCi-1. These results indicate that bone marrow imaging with 99Tcm-LL1 is feasible, and that LL1 may be a suitable alternative to SC because of better visualization of the lower thoracic spine. Potential applications include the improved detection of bone marrow metastases of solid tumours and the assessment of haematological disorders.

Quantitative and qualitative effects of experimental radioimmunotherapy on tumor vascular permeability

Localization of radiolabeled antibodies in the perivascular space of tumors resulted in morphological changes in blood vessel structure and physiological changes in tumor vessel function. Vessel diameter decreased by day 14 and was associated with a significant decline in vascular volume (VV). Upon recovery of VV, the basement membrane surrounding the endothelium had thickened. Tumor vascular permeability (VP) decreased within 7 days of treatment and remained suppressed throughout the 42-day observation period of our study. The decline in VP, which could be visualized by fluorescent microscopy of FITC-dextran extravasation, was dose-related and could be quantified at doses as low as 800 cGy. The radioantibody-induced 50-80% decline in tumor VP was observed in 3 human colonic xenografts (GW-39, LSI74T and MOSER). Decreases in VP have been observed for proteins ranging in size from 20 to 150 kDa. Similar effects on VP were noted when low protein doses (10-30 micrograms), which resulted in heterogeneous antibody distribution, were used or with high protein doses (400-750 micrograms), which resulted in more uniform penetration of antibody. If 188Re or 90Y, radiometals with higher beta-energy and longer path lengths, were substituted for 131I, a similar decrease in VP was observed. The radioimmunotherapy (RAIT)-induced decrease in tumor VP resulted in a 90% decline in accretion of a second dose of radioantibody. The 10% of the second dose that was taken up by the tumor targeted many already non-viable tumor regions and some, but not all, viable tumor cell clusters.

Quantitative autoradiographic evaluation of the influence of protein dose on monoclonal antibody distribution in human ovarian adenocarcinoma xenografts.

We studied the effect of monoclonal antibody protein dose on the uniformity of radioiodinated antibody distribution within tumor masses using quantitative autoradiography. Groups (n = 11-13/group) of athymic nude mice with subcutaneous HTB77 human ovarian carcinoma xenografts were injected intraperitoneally with an 125I-labeled anticarcinoma-associated antigen murine monoclonal antibody, 5G6.4 using a high or a low protein dose (500 micrograms or 5 micrograms). At 6 days post-injection the macroscopic and microscopic intratumoral biodistribution of radiolabeled antibody was determined. The degree of heterogeneity of the labeled antibody distribution within each tumor was quantified and expressed as the coefficient of variation (CV) of the activity levels in serial histological sections. Tumors from mice given the 500-micrograms protein doses had substantially lower CV values, 0.327 +/- 0.027, than did tumors from animals given 5-micrograms protein doses, 0.458 +/- 0.041, (P = 0.0078), indicating that the higher protein dose resulted in more homogeneous distribution of radioactivity in tumors than did the lower dose. While the percentage of the injected dose reaching the tumor was comparable between groups, injecting the higher dose of protein resulted in significantly lower tumor to non-tumor uptake ratios than those obtained for the lower protein dose. These data indicate, in this system, that to achieve more uniform intratumoral antibody (and radiation for radioimmunotherapy) delivery, a relatively high protein dose must be administered. However, to obtain this increased uniformity, a substantial drop in tumor/background uptake ratios was seen. Quantitative autoradiographic evaluation of human tumor xenografts is a useful method to assess the intratumoral distribution of antibodies.

Influence of antibody protein dose on therapeutic efficacy of radioiodinated antibodies in nude mice bearing GW-39 human tumor.

The biodistributions of three 131I-labeled murine monoclonal antibodies, NP-4 and Immu-14 anti(carcinoembryonic antigen), and Mu-9 anti-(colon-specific antigen p), were determined at antibody protein doses varying from 1 microgram to 1000 micrograms in nude mice with small (0.1-0.4 g) GW-39 human colonic cancer xenografts. For each antibody, the percentage of the injected dose per gram of tumor and tumor/nontumor ratios were constant over a wide protein dose range. However, at high protein doses (above 100 micrograms for NP-4 and Immu-14) the percentage of the injected dose per gram of tumor and tumor/nontumor ratios decreased. Assuming that the uptake of a control anti-(alpha-fetoprotein) antibody represents the amount of antibody that accumulates in the tumor nonspecifically (i.e., antigen-independently), it could be shown that for each antibody the amount of antibody protein that accumulates in the tumor specifically, increases linearly with the protein dose, reaching a plateau level at the highest doses tested. The growth inhibition of GW-39 tumor transplants in nude mice treated with 131I-labeled antibody at either low or high antibody protein dose was compared. These experiments indicated that, in this experimental model, enhanced antibody protein dose may decrease the therapeutic efficacy of radioiodinated antibodies. It is suggested that heterogeneous distribution at low protein dose, with intense localization around the blood vessels, may enhance the tumoricidal effect of radioantibodies.

The effect of antibody protein dose on the uniformity of tumor distribution of radioantibodies: an autoradiographic study.

The inaccessibility of radiolabeled antibody to poorly vascularized regions of solid tumors may reduce the therapeutic efficacy of these macromolecules. Theoretical mathematical models have predicted that increasing the protein dose administered would reduce the heterogeneity of radioantibody distribution. This investigation was undertaken to evaluate this hypothesis in experimental animal models. We have utilized the technique of macroautoradiography to demonstrate an increase in tumor penetration of the lower-affinity 125I-labeled NP-4 or higher-affinity Immu-14 anti-carcinoembryonic antigen (anti-CEA) mAbs into small (60.25-0.4 g) and large (0.8-1.5 g) GW-39 and LS174T human colonic xenografts, grown subcutaneously in the nude mouse, when 400 micrograms unlabeled antibody is administered simultaneously with 10 micrograms (100 microCi) radioantibody. Further increases in protein to 800 micrograms result in a reduction in total tumor uptake of the antibody. These in a reduction in total tumor uptake of the antibody. These differences in mAb distribution could be visualized as early as 1 day after antibody injection. Improved mAb penetration was also achieved for the Mu-9 anti-CSAp (anti-mucin) antibody using 800 micrograms unlabeled antibody. An irrelevant antibody (AFP-7-31) was found to be homogeneously distributed 3 days after injection, even at a low protein dose. Attempts to improve mAb penetration by increasing the protein dose in the GS-2 colorectal tumor, a model that has low NP-4 accretion as a result physiological barriers separating antibody from antigen, were not successful. These results suggest that a more homogeneous distribution of radioantibody can be achieved by carefully selecting a dose of unlabeled antibody to coadminister. Work is currently in progress to determine the effect of improved tumor distribution of radioantibody on the therapeutic potential of a single dose of radioantibody.

Trimetrexate: predictors of severe or life-threatening toxic effects.

In four phase II trials of trimetrexate given iv daily for 5 days, we noted marked variability among patients in the development of severe or life-threatening toxic effects. In an effort to define which of 15 patient characteristics were associated with toxic effects of this degree, we have carried out single-factor and multifactor analyses on toxic effects during the first cycle of therapy in 68 patients. The final logistic regression model identified both low pretreatment serum protein levels and metastatic liver disease as significant correlates of severe toxic effects (P = .02 and P = .0005, respectively). While drug dose was an important element of the best logistic model, its statistical significance was only borderline. Trimetrexate is extensively protein bound and is cleared primarily by hepatic metabolism, so it is not unreasonable to believe that alteration in protein binding of the drug or in metabolic capacity of the liver could produce enhanced toxic effects. Although the validity of these predictors should be confirmed, it seems prudent to recommend lower starting doses of trimetrexate for patients with metastatic liver disease and/or low protein levels and dose escalation if toxic effects allow it.