S-531011, a Novel Anti-Human CCR8 Antibody, Induces Potent Antitumor Responses through Depletion of Tumor-Infiltrating CCR8-Expressing Regulatory T Cells

Although regulatory T cells (Treg) are inhibitory immune cells that are essential for maintaining immune homeostasis, Tregs that infiltrate tumor tissue promote tumor growth by suppressing antitumor immunity. Selective reduction of tumor-infiltrating Tregs is, therefore, expected to activate antitumor immunity without affecting immune homeostasis. We previously reported that selective Treg depletion targeted by a C-C motif chemokine receptor 8 (CCR8) resulted in induction of strong antitumor immunity without any obvious autoimmunity in mouse models. Thus, herein, we developed a novel humanized anti-CCR8 monoclonal antibody, S-531011, aimed as a cancer immunotherapy strategy for patients with cancer. S-531011 exclusively recognized human CCR8 among all chemokine receptors and showed potent antibody-dependent cell-mediated cytotoxicity activity toward CCR8+ cells and neutralization activity against CCR8-mediated signaling. We observed that S-531011 reduced tumor-infiltrating CCR8+ Tregs and induced potent antitumor activity in a tumor-bearing human-CCR8 knock-in mouse model. Moreover, combination therapy with S-531011 and anti-mouse programmed cell death 1 (PD-1) antibody strongly suppressed tumor growth compared with anti-PD-1 antibody alone with no observable adverse effects. S-531011 also depleted human tumor-infiltrating Tregs, but not Tregs derived from human peripheral blood mononuclear cells. These results suggest that S-531011 is a promising drug for inducing antitumor immunity without severe side effects in the clinical setting.

Immunotherapy Targeting CCR8+ Regulatory T Cells Induces Antitumor Effects via Dramatic Changes to the Intratumor CD8+ T Cell Profile

Regulatory T cells (Tregs) contribute to the formation of a tumor-immunosuppressive microenvironment. CCR8 is reportedly selectively expressed in tumor Tregs, and an anti-CCR8 Ab can exert potent antitumor effects by eliminating intratumor Tregs in murine tumor models. In this study, we analyzed changes to intratumor immunity after anti-CCR8 Ab administration, especially in CD8+ T cells, which are involved in cancer cell killing, using the CT26 colorectal carcinoma mouse model. Immunophenotyping of tumor-infiltrating cells by mass cytometry after Ab administration on day 5 of tumor inoculation revealed that CD8+ T cell subsets were dramatically altered in the CCR8 Ab-treated group, with an increase in naive cells and nonexhausted effector cells and a decrease in exhausted cells with high expression levels of TOX. These results were corroborated with flow cytometry analysis. Delayed administration of the anti-CCR8 Ab on day 9 or 12, when the amount of CCR8+ Tregs and CD8+ T cell exhaustion were more progressed, also resulted in a decrease in exhausted CD8+ T cells, leading to tumor regression. Finally, we confirmed that high CCR8+ Treg infiltration was associated with high TOX expression in CD8+ T cells in human cancer patients. In conclusion, administration of an anti-CCR8 Ab can dramatically alter the activation and exhaustion state of intratumor CD8+ T cells, resulting in strong antitumor effects. In cancer patients with an advanced tumor-immunosuppressive environment, CD8+ T cell exhaustion has progressed along with CCR8+ Treg induction. Therefore, targeted depletion of CCR8+ Tregs is expected to be effective in these patients.

873 S-531011, a novel anti-human CCR8 antibody: anti-tumor responses through depletion of tumor-infiltrating CCR8-positive Tregs

Background

Regulatory T cells (Tregs) are suppressive immune cells required for the maintenance of immune homeostasis, but tumor-infiltrating Tregs are known to suppress the antitumor immune system and promote tumor progression. Therefore, selective reduction of tumor-infiltrating Tregs is anticipated to reinvigorate antitumor immunity without inducing autoimmunity. S-531011 is a novel anti-human IgG1 antibody targeting human CCR8 (C-C motif chemokine receptor 8) which is selectively expressed in tumor-infiltrating Tregs, with both in vitro antibody dependent cellular cytotoxicity (ADCC) against CCR8-expressing cells and neutralizing activity against CCL1-CCR8 signaling. Here, to evaluate antitumor activities and safety aspects of S-531011, we conducted non-clinical pharmacology studies of S-531011 using human CCR8 knock-in (KI) mice and human tissues.

Methods

S-531011 was administrated to CT26WT tumor-bearing hCCR8-KI mice, and the effect on the presence of tumor-infiltrating CCR8+ Treg and tumor growth were evaluated. We also investigated the antitumor efficacy of S-531011 in combination with anti-mouse PD-1 antibody. Next, human lung cancer tissues and human NK-cells were co-cultured, and the ex vivo ADCC against tumor-infiltrating Tregs by S-531011 was verified. We also incubated human peripheral blood-derived mononuclear cells (PBMC) from healthy individuals with S-531011 to investigate the effects on the proportion of Tregs in human PBMC.

Results

Intravenous administration of S-531011 to CT26WT tumor-bearing hCCR8-KI mice significantly reduced tumor-infiltrating CCR8+ Tregs and markedly suppressed tumor growth. Furthermore, the combined therapy of S-531011 with anti-mouse PD-1 antibody showed greater anti-tumor effect than monotherapy without any apparent side effects. Ex vivo ADCC studies using human lung cancer tissues and FCM analysis of CCR8 expression in tumor-infiltrating Tregs suggested that most of the tumor-infiltrating CCR8+ Tregs were depleted by S-531011. On the other hand, S-531011 didn’t reduce Tregs in human PBMC.

Conclusions

S-531011 is a promising drug which has a strong antitumor effect by depleting tumor-infiltrating CCR8+ Tregs, as a not only monotherapy but also combination therapy with other immune checkpoint inhibitors.

Ethics Approval

The present study was approved by the Institutional Ethics Committee of Osaka University Hospital (approved number: 13266-15) and Shionogi Co., Ltd. (approved number: 021-003). Animal studies were approved by the Institutional Animal Care and Use Committee (approved number: S20093D, S20197D and S20198D).

Characterization of CD44-positive Cancer Stem-like Cells in COLO 201 Cells

BACKGROUND/AIM

Cancer stem cells (CSCs) are considered to be one of the causes of tumor recurrence after chemotherapy. The purpose of our study was to isolate CSCs from human colorectal cancer cell (CRC) lines.

MATERIALS AND METHODS

Nine CRC lines were screened based on the expression level of potential CSC markers to identify putative CSCs. Tumor formation capacity in immunodeficient mice was compared with that of their counterparts. Stemness, differentiation potency and sensitivity to 5-fluorouracil (5-FU), in vitro, were also assessed. Microarray analysis was used to characterize the features of the putative CSCs.

RESULTS

COLO 201 cells were separated into two populations based on CD44 expression. CD44 positive (CD44⁺) cells showed significantly higher tumor formation capacity than CD44^- cells in immunodeficient mice. CD44⁺ cells also possessed stemness properties and lower sensitivity to 5-FU in vitro. Moreover, cancer stemness and chemoresistance-related genes were highly up-regulated in CD44⁺ cells.

CONCLUSION

CD44⁺ COLO 201 cells possessed the features of CSCs; therefore, the present CSC model could serve as a valuable tool to accelerate CSC research.

Abstract 372: VGF is functionally responsible for chemotherapy resistance in non-small cell lung cancer

Despite the success of immune checkpoint therapy, most non-small cell lung cancer (NSCLC) patients still receive conventional chemotherapy. Overcoming chemotherapy resistance by identifying specific targets should improve cancer treatment and patient survival. In this study, we examined a prospective chemotherapy-resistant subpopulation in NCI-H1975 NSCLC cells and identified a novel target, neurosecretory protein VGF (VGF). Using flow cytometry, we first analyzed the expression profile of cancer stem cell markers in 100 cancer cell lines and found that NCI-H1975 cells could be divided into three subpopulations, CD44-low (CD44-L), CD44-middle (CD44-M) and CD44-high cells based on the expression pattern of CD44. CD44-M cells account for less than 5% of the NCI-H1975 cells under normal conditions, but only this subpopulation can proliferate in vitro and in vivo after treatment with cytotoxic agents, such as paclitaxel, pemetrexed and 5-fluorouracil. Affymetrix microarray analysis revealed that VGF is specifically expressed in CD44-M cells and we hypothesized that VGF would play a critical role in chemotherapy resistance. We next employed patient-derived xenograft (PDX) models of NSCLC to confirm this hypothesis with human clinical samples. NOD/SCID mice were subcutaneously transplanted with PDX and treated with either vehicle or paclitaxel (12 mg/kg, Q3Dx3, i.v.). VGF immunohistochemistry on resected PDX revealed that the number of VGF-expressing cells increased 5.6-fold in the paclitaxel-treated group compared to the vehicle control. We also performed VGF immunohistochemistry on NSCLC surgical specimens which were obtained from 127 patients, consisting of 42 neoadjuvant chemotherapy treated cases and 85 non-treated cases. The frequency of VGF-expressing specimens was higher in neoadjuvant chemotherapy treated cases (50%) than non-treated cases (18%). These results suggest that VGF-expressing tumor subpopulation is paclitaxel-resistant even in clinical settings. We also analyzed the molecular functions of VGF. Knockdown of VGF expression by siRNAs could signifıcantly suppress paclitaxel resistance in CD44-M cells. On the other hand, overexpression of VGF could significantly induce paclitaxel resistance in CD44-L cells. These results suggest that VGF is functionally responsible for chemotherapy resistance in NSCLC patients and combined administration of an anti-VGF drug and chemotherapy could be effective for preventing cancer recurrence and prolonging cancer free survival.

Citation Format: Wataru Nogami, Yumi Tona, Soichi Tofukuji, Yoshino Ishioka, Mitsunobu Matsumoto, Hajime Yamada, Kenji Kuwabara, Hidekazu Tanaka, Shigeki Adachi, Yoko Yamamoto, Ryu Kanzaki, Soichiro Funaki, Yasushi Shintani, Meinoshin Okumura, Taisei Nomura. VGF is functionally responsible for chemotherapy resistance in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 372.

Development of a new knock-in mouse model and evaluation of pharmacological activities of lusutrombopag, a novel, nonpeptidyl small-molecule agonist of the human thrombopoietin receptor c-Mpl

Lusutrombopag (S-888711), an oral small-molecule thrombopoietin receptor (TPOR) agonist, has gained first approval as a drug to treat thrombocytopenia of chronic liver disease in patients undergoing elective invasive procedures in Japan. Preclinical studies were performed to evaluate its efficacy against megakaryopoiesis and thrombopoiesis. To investigate the proliferative activity and efficacy of megakaryocytic colony formation via human TPOR, lusutrombopag was applied to cultured human c-Mpl-expressing Ba/F3 (Ba/F3-hMpl) cells and human bone marrow-derived CD34-positive cells, respectively. Lusutrombopag caused a robust increase in Ba/F3-hMpl cells by activating pathways in a manner similar to that of thrombopoietin and induced colony-forming units-megakaryocyte and polyploid megakaryocytes in human CD34-positive cells. Because lusutrombopag has high species specificity for human TPOR, there was no suitable experimental animal model for drug evaluation, except for immunodeficient mouse-based xenograft models. Therefore, a novel genetically modified knock-in mouse, TPOR-Ki/Shi, was developed by replacing mouse Mpl with human-mouse chimera Mpl. In TPOR-Ki/Shi mice, lusutrombopag significantly increased circulating platelets in a dose-dependent manner during 21-day repeated oral administration. Histopathological study of the TPOR-Ki/Shi mice on day 22 also revealed a significant increase in megakaryocytes in the bone marrow. These results indicate that lusutrombopag acts on human TPOR to upregulate differentiation and proliferation of megakaryocytic cells, leading to platelet production.

Abstract 4085: Distribution analysis of S-222611 in brain metastases of HER2-positive breast cancer by quantitative imaging mass spectrometry: prospect for antitumor activity of EGFR/HER2/HER4 kinase inhibitor S-222611 against brain metastases

S-222611 is a potent and selective reversible tyrosine kinase inhibitor of epidermal growth factor receptor (EGFR), human EGFR2 (HER2), and human EGFR4 developed in Shionogi. Greater potency of anti-tumor activity than lapatinib was demonstrated in vitro and in animal models. In the intracranial implantation mice model implanted the HER2-positive cell line (MDA-MB-361-luc-2), S-222611 showed more potent anti-tumor activity than lapatinib. On the basis of higher penetration in brain of S-222611 than lapatinib indicated by the preclinical pharmacokinetic studies, we demonstrated the application of S-222611 to brain metastases with breast cancer. In order to enhance the clinical predictability of S-222611 to the treatment of brain metastases, we have developed the experimental brain metastases models in mice of HER2-positive breast cancer (MDA-MB-361-luc-2-BR2/BR3) or T790M-EGFR expressing lung cancer (NCI-H1975-luc). After a single oral administration of S-222611 or lapatinib, the concentrations of S-222611 and lapatinib in the brain metastatic regions of these mice models were analyzed by quantitative imaging mass spectrometry (IMS). In the NCI-H1975 lung cancer model (intraventricular injection model), the concentrations of S-222611 in brain metastases quantified by IMS were comparable to those of lapatinib. In contrast, in the MDA-MB-361 breast cancer model (intraventricular injection model), the concentrations of S-222611 in brain metastases were over 10 times higher than those of lapatinib, and the tumor-to-normal brain ratio of S-222611 was approximately 4 times higher than that of lapatinib. IMS revealed that the concentrations in brain metastases and tumor-to-normal brain ratio of S-222611 were significantly higher than those of lapatinib in the breast cancer mice model. In addition, the blood-tumor barrier (BTB) permeability in each brain metastatic region using these mice models was assessed simultaneously. In the lung cancer model, fluorescently labeled dextran was highly detected in the brain metastatic regions than brain parenchyma. However, in the breast cancer models, fluorescence intensities for dextran in the brain metastatic regions and brain parenchyma were comparable, indicating that the BTB was remained to be largely intact in brain metastases of the breast cancer model but disrupted in the lung cancer model. These results show that S-222611 is expected to be useful for the prevention and the prompt treatment of patients with HER2-positive breast cancer having brain metastases.

Citation Format: Yukari Tanaka, Michinari Hirata, Satomi Shinonome, Mitsunobu Matsumoto, Wataru Nogami, Mikinori Torii, Ken-ichi Nezasa, Hidekazu Tanaka. Distribution analysis of S-222611 in brain metastases of HER2-positive breast cancer by quantitative imaging mass spectrometry: prospect for antitumor activity of EGFR/HER2/HER4 kinase inhibitor S-222611 against brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4085. doi:10.1158/1538-7445.AM2017-4085

Subcellular localization and physiological significance of intracellular mannan-binding protein

Mannan-binding protein (MBP) is a C-type mammalian lectin specific for mannose and N-acetylglucosamine. MBP is mainly synthesized in the liver and occurs naturally in two forms, serum MBP (S-MBP) and intracellular MBP (I-MBP). S-MBP activates complement in association with MBP-associated serine proteases via the lectin pathway. Despite our previous study (Mori, K., Kawasaki, T., and Yamashina, I. (1984) Arch. Biochem. Biophys. 232, 223-233), the subcellular localization of I-MBP and its functional implication have not been clarified yet. Here, as an extension of our previous studies, we have demonstrated that the expression of human MBP cDNA reproduces native MBP differentiation of S-MBP and I-MBP in human hepatoma cells. I-MBP shows distinct accumulation in cytoplasmic granules, and is predominantly localized in the endoplasmic reticulum (ER) and involved in COPII vesicle-mediated ER-to-Golgi transport. However, the subcellular localization of either a mutant (C236S/C244S) I-MBP, which lacks carbohydrate-binding activity, or the wild-type I-MBP in tunicamycin-treated cells shows an equally diffuse cytoplasmic distribution, suggesting that the unique accumulation of I-MBP in the ER and COPII vesicles is mediated by an N-glycan-lectin interaction. Furthermore, the binding of I-MBP with glycoprotein intermediates occurs in the ER, which is carbohydrate- and pH-dependent, and is affected by glucose-trimmed high-mannose-type oligosaccharides. These results strongly indicate that I-MBP may function as a cargo transport lectin facilitating ER-to-Golgi traffic in glycoprotein quality control.

Long-duration low-flow sevoflurane and isoflurane effects on postoperative renal and hepatic function

Sevoflurane degradation by carbon dioxide absorbents during low-flow anesthesia forms the haloalkene Compound A, which causes nephrotoxicity in rats. Numerous studies have shown no effects of Compound A formation on postoperative renal function after moderate-duration (3-4 h) low-flow sevoflurane; however, effects of longer exposures remain unresolved. We compared renal function after long-duration low-flow (<1 L/min) sevoflurane and isoflurane anesthesia in consenting surgical patients with normal renal function. To maximize degradant exposure, Baralyme was used, and anesthetic concentrations were maximized (no nitrous oxide and minimal opioids). Inspired and expired Compound A concentrations were quantified. Blood and urine were obtained for laboratory evaluation. Sevoflurane (n = 28) and isoflurane (n = 27) groups were similar with respect to age, sex, weight, ASA status, and anesthetic duration (9.1 +/- 3.0 and 8.2 +/- 3.0 h, mean +/- SD) and exposure (9.2 +/- 3.6 and 9.1 +/- 3.7 minimum alveolar anesthetic concentration hours). Maximum inspired Compound A was 25 +/- 9 ppm (range, 6-49 ppm), and exposure (area under the concentration-time curve) was 165 +/- 95 (35-428) ppm. h. There was no significant difference between anesthetic groups in 24- or 72-h serum creatinine, blood urea nitrogen, creatinine clearance, or 0- to 24-h or 48- to 72-h urinary protein or glucose excretion. Proteinuria and glucosuria were common in both groups. There was no correlation between Compound A exposure and any renal function measure. There was no difference between anesthetic groups in 24- or 72-h aspartate aminotransferase or alanine aminotransferase. These results show that the renal and hepatic effects of long-duration low-flow sevoflurane and isoflurane were similar. No evidence for low-flow sevoflurane nephrotoxicity was observed, even at high Compound A exposures as long as 17 h. Proteinuria and glucosuria were common and nonspecific postoperative findings. Long-duration low-flow sevoflurane seems as safe as long-duration low-flow isoflurane anesthesia.

IMPLICATIONS

Postoperative renal function after long-duration low-flow sevoflurane (with Compound A exposures greater than those typically reported) and isoflurane anesthesia were not different, as assessed by serum creatinine, blood urea nitrogen, and urinary excretion of protein and glucose. This suggests that low-flow sevoflurane is as safe as low-flow isoflurane, even at long exposures.

Structure of Bordetella pertussis peptidoglycan

Bordetella pertussis Tohama phases I and III were grown to the late-exponential phase in liquid medium containing [3H]diaminopimelic acid and treated by a hot (96 degrees C) sodium dodecyl sulfate extraction procedure. Washed sodium dodecyl sulfate-insoluble residue from phases I and III consisted of complexes containing protein (ca. 40%) and peptidoglycan (60%). Subsequent treatment with proteinase K yielded purified peptidoglycan which contained N-acetylglucosamine, N-acetylmuramic acid, alanine, glutamic acid, and diaminopimelic acid in molar ratios of 1:1:2:1:1 and less than 2% protein. Radiochemical analyses indicated that 3H added in diaminopimelic acid was present in peptidoglycan-protein complexes and purified peptidoglycan as diaminopimelic acid exclusively and that pertussis peptidoglycan was not O acetylated, consistent with it being degraded completely by hen egg white lysozyme. Muramidase-derived disaccharide peptide monomers and peptide-cross-linked dimers and higher oligomers were isolated by molecular-sieve chromatography; from the distribution of these peptidoglycan fragments, the extent of peptide cross-linking of both phase I and III peptidoglycan was calculated to be ca. 48%. Unambiguous determination of the structure of muramidase-derived peptidoglycan fragments by fast atom bombardment-mass spectrometry and tandem mass spectrometry indicated that the pertussis peptidoglycan monomer fraction was surprisingly homogeneous, consisting of greater than 95% N-acetylglucosaminyl-N-acetylmuramyl-alanyl-glutamyl-diaminopimelyl++ +-alanine.

Major fragment of soluble peptidoglycan released from growing Bordetella pertussis is tracheal cytotoxin

Bordetella pertussis is known to release a factor which promotes the loss of ciliated respiratory epithelium and copurifies with a soluble peptidoglycan (PG) fragment termed tracheal cytotoxin (TCT). The objective of this study was to determine whether pertussis organisms turn over and release PG derivatives in addition to TCT. B. pertussis Tohama (phase III) was grown in liquid Stainer-Scholte medium containing [3H]diaminopimelic acid (DAP) to label PG specifically, washed to remove free label, and suspended in fresh medium without [3H]DAP. Molecular sieve chromatography of supernatants obtained from such cultures revealed a single included peak of 3H, the elution volume of which corresponded roughly to a disaccharide peptide monomer standard (ca. 10(3) daltons). This material (i) contained [3H]DAP in acid-hydrolyzable linkage, (ii) comigrated with 1,6-anhydro-N-acetylmuramic acid-containing disaccharide peptides on paper chromatography, (iii) was resistant to degradation by mild alkali, and (iv) was indistinguishable from authentic TCT by high-voltage paper electrophoresis and two reversed-phase high-performance liquid chromatography systems. Together, the data suggest that B. pertussis releases a markedly homogeneous set of PG fragments, consisting principally of TCT, and that TCT is possibly a nonreducing, anhydromuramic acid-containing fragment or a cyclic PG derivative.

Synergistic effect of coumadin and cytoxan in reducing lung metastases

Lung metastasis is a frequent cancer complication resulting in significant mortality. This study evaluates the effect of coumadin and cytoxan alone and in combination on lung metastases in rats challenged with Morris hepatoma 3924A. Seventy-seven male American Cancer Institute (ACI) rats weighing 200 g were studied. Thirty-seven rats received coumadin orally for six days, which resulted in a prothrombin time 2 times that of controls (30 sec). All rats received 1 X 10(5) clumped Morris hepatoma cells via tail vein injection. Animals were divided into four groups: Group I (controls, n = 20) received no antitumor treatment; group II rats (n = 20) received 25 mg/kg cytoxan intraperitoneally at the time of tumor challenge; group III animals (n = 19) received coumadin alone; while group IV (n = 18) received both coumadin and cytoxan. Rats were evaluated for number of lung metastases and lung weight at 3 weeks postinjection. Data was subjected to statistical analysis by the Student's test. The mean number of lung metastases were 580 +/- 45 in group I, 350 +/- 310 in group II, 330 +/- 263 in group III, and 200 +/- 161 in group IV (P less than .005 [IV] v [I], P less than .05 [IV] v [II], [III]), (P less than .05 [II] v [I]), (P less than .05 [III] v [I]). Mean lung weights were 2.597 g +/- 1.65 in group I, 2.049 g +/- 0.75 in group II, 1.898 g +/- 0.80 in group III, and 1,677 g +/- 0.31 in group IV. (P less than .025 [IV] v [I], P less than .05 [IV] v [II]).(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial/fungal growth in a combined parenteral nutrition solution

Appropriately mixed, compatible solutions of glucose, amino acids and lipid have recently become available for clinical use. While a single hyperalimentation solution has several advantages over the conventional two-bottle technique, its effect on infusion-related septicemia is unknown. An in vitro, mock infusion system identical to that used in our new-born intensive care unit was set up to assess the relative growth rates of three microorganisms in several parenteral nutrition mixtures. Growth of Staphylococcus epidermidis, Escherichia coli and Candida albicans was measured in seven different alimentation solutions, including two combined solutions. Generally, microbial growth was the same or decreased in combined solutions as compared to fat alone although considerably greater than that observed in nonlipid containing solutions. In addition, the ability of these organisms to pass in-line terminal filters of pore size 0.22 and 1.2 microns was assessed.

Reverse electrical pacing improves intestinal absorption and transit time

This study evaluates the effect of reverse electrical pacing on intestinal absorption and transit time in an enterostomy model. Twenty-five male Sprague-Dawley rats (148 to 208 gm) underwent division and anastomosis of the proximal jejunum to eliminate the proximal gastroduodenal pacemaker. A 30.0 cm loop ileostomy was formed, and leads were placed at 1.0 and 3.0 cm proximal to the stoma. Reverse pacing was done with a 0.25 Hz, 50 msec pulse at 0.1 mA. Transit time was evaluated with 1.0 ml barium gavage and was 12 +/- 4 minutes in group I controls (n = 13) versus 27 +/- 21 minutes in group II (n = 12) reverse-paced rats (p less than 0.025). D-Xylose absorption was determined in 18 rats. Levels were 14.0 +/- 3.6 mg/dl in control rats (n = 6) and 15.5 +/- 3.4 mg/dl in reverse-paced rats (n = 6). Increasing the pulse milliamperage to 2.0 mA (n = 6) increased D-xylose serum levels to 38.8 +/- 27.7 mg/dl (p less than 0.05). Transit rate and net water flux were determined in eight additional rats with 15 cm Theiry-Vella loops. Transit rate was measured with 0.2 ml of methylene blue and was 3.00 +/- 2.32 ml/min in unpaced rats compared with 9.95 +/- 0.71 ml/min with reverse pacing (p less than 0.025). Water flux studies showed that control rats had a net secretory loss of 0.20 +/- 0.48 ml/cm while paced rats absorbed 0.08 +/- 0.12 ml/cm. These data indicate that reverse electrical pacing increases transit time and nutrient and fluid absorption. These observations suggest that reverse electrical pacing may be a useful adjunct in instances of short gut associated with an enterostomy.