Exendin-4, originally isolated from saliva of the lizard Heloderma suspectum, shares 53% sequence homology and several potentially antidiabetic actions with the mammalian hormone glucagonlike peptide-1(7-36)amide (GLP-1). It shows a higher potency and longer duration of effect in vivo, which may be partly attributed to pharmacokinetic properties. The present study compares the pharmacokinetics of GLP-1 and exendin-4 in rats after intravenous (iv), subcutaneous (sc), or intraperitoneal (ip) administration. Samples were assayed for active GLP-1 (7-36) amide using an enzyme-linked immunosorbent assay that does not detect GLP-1 (1-36-amide), (1-37), (9-36-amide) or (9-37). In parallel experiments, samples were assayed for exendin-4 using a two-site immunoradiometric assay that reacts specifically with fulllength exendin-4. The estimated half-life for GLP-1 and exendin-4 were 0.8-4.7 min and 18-41 min for iv bolus, and 4.6-7.1 min and 90-216 min for SC administration, respectively. Half-lives after ip injection were 0.6-13.5 min for GLP-1 and 125-174 min for exendin-4. Bioavailability for GLP-1 and exendin-4 was 44-71% and 65-75%, respectively, for sc injection. For ip injection, bioavailability for GLP-1 and exendin-4 was 36-67% and 74-76%, respectively. Plasma clearance, as determined from iv infusion data, was 35-38 ml/min for GLP-1 and 4-8 ml/min for exendin-4. Both Co/C max and AUC values were proportional to dose with each route of administration. Plasma clearance of exendin-4 was reduced by 4.4-fold in nephrectomized animals. In conclusion, exendin-4 exhibited a much longer plasma half-life than GLP-1 in rats after iv, sc, or ip injection, which may contribute in some part to reported differences in duration of biological action of the two peptides. Drug Dev. Res. 53:260-267, 2001.

Recent preclinical and clinical data suggests enhanced metastatic fitness of hybrid epithelial/mesenchymal (E/M) phenotypes, but mechanistic details regarding their survival strategies during metastasis remain unclear. Here, we investigate immune-evasive strategies of hybrid E/M states. We construct and simulate the dynamics of a minimalistic regulatory network encompassing the known associations among regulators of EMT (epithelial-mesenchymal transition) and PD-L1, an established immune-suppressor. Our simulations for the network consisting of SLUG, ZEB1, miR-200, CDH1 and PD-L1, integrated with single-cell and bulk RNA-seq data analysis, elucidate that hybrid E/M cells can have high levels of PD-L1, similar to those seen in cells with a full EMT phenotype, thus obviating the need for cancer cells to undergo a full EMT to be immune-evasive. Specifically, in breast cancer, we show the co-existence of hybrid E/M phenotypes, enhanced resistance to anti-estrogen therapy and increased PD-L1 levels. Our results underscore how the emergent dynamics of interconnected regulatory networks can coordinate different axes of cellular fitness during metastasis.

By applying a newly developed ELISA technique for determining biologically active intact glucagon-like peptide [GLP-1, GLP-1-(7-36)amide] in mouse, plasma baseline GLP-1 in normal NMRI mice was found to be normally distributed (4.5 +/- 0.3 pmol/l; n = 72). In anesthetized mice, gastric glucose (50 or 150 mg) increased plasma GLP-1 levels two- to threefold (P < 0.01). The simultaneous increase in plasma insulin correlated to the 10-min GLP-1 levels (r = 0.36, P < 0.001; n = 12). C57BL/6J mice deleted of the gastrin-releasing peptide (GRP) receptor by genetic targeting had impaired glucose tolerance (P = 0.030) and reduced early (10 min) insulin response (P = 0.044) to gastric glucose compared with wild-type controls. Also, the GLP-1 response to gastric glucose was significantly lower in the GRP receptor-deleted mice than in the controls (P = 0.045). In conclusion, this study has shown that 1) plasma levels of intact GLP-1 increase dose dependently on gastric glucose challenge in correlation with increased insulin levels in mice, and 2) intact GRP receptors are required for normal GLP-1 and insulin responses and glucose tolerance after gastric glucose in mice.

Cancer metastasis remains a primary cause of cancer related mortality. Recent in vitro and in vivo data has indicated the high metastatic fitness of hybrid epithelial/mesenchymal (E/M) states, i.e. their enhanced abilities to initiate tumours at secondary tumour site. Mechanistic details about how such hybrid E/M cells survive the metastatic cascade remain unclear. Here, we investigate immune-evasive strategies of hybrid E/M states, an issue that to date has been largely unexplored. We construct a minimalistic regulatory network that captures known associations between regulators of EMT (the epithelial mesenchymal transition) and levels of PD-L1, an established suppressor of immune response, and simulated the network's emergent dynamics. Our model recapitulates observations that cells undergoing EMT have increased PD-L1 levels, while reverting EMT can decrease these levels, indicative of a causal link between EMT drivers and PD-L1. Further, we show that hybrid E/M cells can have high levels of PD-L1, similar to those seen in cells with a full EMT phenotype, thus obviating the need for cancer cells to undergo a full EMT to evade the immune system. Finally, we identify various signalling pathways and cellular processes that can independently or in concert affect PD-L1 levels and EMT status. For instance, hybrid E/M cells can gain both immune-evasion and stemness through largely independent paths. Our results underscore another underlying reason for the high metastatic ability of hybrid E/M cells.

The steroid hormone, Glucocorticoid (GC) is a well-known immunosuppressant that controls T cellmediated adaptive immune response. In this work, we have developed a minimal kinetic network model of T-cell regulation connecting relevant experimental and clinical studies to quantitatively understand the long-term effects of GC on pro-inflammatory T-cell (Tpro) and anti-inflammatory Tcell (Tanti) dynamics. Due to the antagonistic relation between these two types of T-cells, their longterm steady-state population ratio helps us to characterize three classified immune-regulations:), and (iii) moderate ([Tpro] ~ [Tanti]); holding the characteristic bistability). In addition to the differences in their long-term steady-state outcome, each immune-regulation shows distinct dynamical phases. In the pre-steady, a characteristic intermediate stationary phase is observed to develop only in the moderate regulation regime. In the medicinal field, the resting time in this stationary phase is distinguished as a clinical latent period. GC dose-dependent steady-state analysis shows an optimal level of GC to drive a phase-transition from the weak/autoimmune prone to the moderate regulation regime. Subsequently, the pre-steady state clinical latent period tends to diverge near that optimal GC level where [Tpro]: [Tanti] is highly balanced. The GCoptimized elongated stationary phase explains the rationale behind the requirement of long-term immune diagnostics, especially when long-term GC-based chemotherapeutics and other immunosuppressive drugs are administrated. Moreover, our study reveals GC sensitivity of clinical latent period which might serve as an early warning signal in the diagnosis of different immune phases and determining immune phase-wise steroid treatment.