A 70-kDa protein is phosphorylated in cellfree preparations from rat or mouse fibroblasts by an endogenous protein kinase. This protein is immunologically related to a group of 68-kDa to 87-kDa proteins described in the literature as substrates for protein kinase C (PK-C). Although the phosphorylation of the 70-kDa protein by isolated plasma membranes takes place in the presence of EGTA, we conclude that the reaction is catalyzed by PK-C based on its inhibition by staurosporin. As shown previously, pure PK-C phosphorylates a synthetic random polymer of arginine and serine in the absence of Ca2+ and lipids, a reaction markedly stimulated by an endogenous unidentified activator of PK-C. When the '70-kDa protein from normal fibroblasts was exposed to the cytosol of chemically or ras-transformed fibroblasts, it disappeared as measured by phosphorylation by added PK-C. Cytosol ofnormal fibroblasts was much less effective (ca. 20%). Cathepsin L purified from rat kidney or from the medium of transformed cells had an effect similar to that of the cytosol of transformed cells. When the 70-kDa protein was phosphorylated by PK-C prior to exposure to cathepsin L or to the cytosol of transformed cells, there was a marked protection of the 70-kDa protein. We conclude that the 70-kDa protein is degraded by cathepsin L as ascertained by both immunological and biochemical assays and that it is protected by prior phosphorylation with PK-C. The possible role of this effect in signal transduction is discussed.
There is no FDA approved therapy for the treatment of celiac disease (CeD), aside from avoidance of dietary gluten. Larazotide acetate (LA) is a first in class oral peptide developed as a tight junction regulator, which is a lead candidate for management of CeD. A delayed release formulation was tested in vitro and predicted release in the mid duodenum and jejunum, the target site of CeD. The aim of this study was to follow the concentration versus time profile of orally administered LA in the small intestine using a porcine model. A sensitive liquid chromatography/tandem mass spectrometry method was developed to quantify LA concentrations in porcine intestinal fluid samples. Oral dosing of LA (1 mg total) in overnight fasted pigs resulted in time dependent appearance of LA in the distal duodenum and proximal jejunum. Peak LA concentrations (0.32–1.76 μM) occurred at 1 hour in the duodenum and in proximal jejunum following oral dosing, with the continued presence of LA (0.02–0.47 μM) in the distal duodenum and in proximal jejunum (0.00–0.43 μM) from 2 to 4 hours following oral dosing. The data shows that LA is available in detectable concentrations at the site of CeD.
Triple-negative breast cancer (TNBC) accounts for approximately 15-20 % of all breast cancers, is an aggressive disease with a poor prognosis, and lacks targeted therapy. Recent studies suggest that cancer stem cells (CSCs) play an important role in TNBC progression and tumorigenesis and that targeting CSCs may be a promising, novel strategy for the treatment of this disease. Both CD44+/CD24- and CD44+/CD24 low CSCs are enriched in TNBCs and may contribute to chemotherapy resistance, emphasizing the need to target this population. In this regard, recent studies have shown that salinomycin (SAL) preferentially targets CSCs; however, the preclinical toxicity associated with this agent has limited its clinical development.In the current studies, we have generated novel biodegradable QUATRAMER polymeric nanoparticles comprised of a polyethylene glycol (PEG)-polypropylene glycol (PPG)-PEG modified polylactic acid (PLA)-tetra-block copolymer (SAL-NPs; HSB-1216) for the intracellular delivery of SAL. Treatment of human TNBC MDA-MB-231 cells with HSB-1216 was associated with significant cell death with an IC50 of around 2 uM. Similar results were obtained when other TNBC cell line SUM149 was treated with HSB-1216 (IC50 ~ 0.5 uM). Based on the characteristic formation of TNBC mammospheres in in vitro 3D culture conditions, the mammosphere formation assay has become an essential tool for quantifying CSC activity. Cultured MDA-MB-231 mammospheres were therefore exposed to different concentrations and durations of HSB-1216. Our results demonstrate dose-dependent inhibition of mammosphere formation in response to HSB-1216. Additionally, CD44+/CD24- enriched CSCs were isolated from a TNBC patient tumor biopsy, grown as 3D culture/mammospheres and then treated with HSB-1216. Interestingly, in contrast to Paclitaxel, treatment with HSB-1216 was associated with nearly complete inhibition of mammosphere formation. Taken together, these results demonstrate an effective method for sustained delivery of a potent stem cell inhibitor, SAL, and its potential for the treatment of TNBC. Citation Format: Surender M. Kharbanda, Anees Mohammad, Bhawana Gupta, Sireesh Appajosyula, Sandeep Laumas, Jugnu Jain, Donald Kufe, Harpal Singh. A Novel QUATRAMER sustained injectable suspension for the intracellular delivery of Salinomycin, a stem cell inhibitor (HSB-1216), for the treatment of triple negative breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 492.
Intestinal ischemia results in mucosal injury, including paracellular barrier loss due to disruption of tight junctions. Larazotide acetate (LA), a small peptide studied in Phase III clinical trials for treatment of celiac disease, regulates tight junctions (TJs). We hypothesized that LA would dose-dependently hasten recovery of intestinal ischemic injury via modulation of TJs. Ischemia-injured tissue from 6-8-week-old pigs was recovered in Ussing chambers for 240-minutes in the presence of LA. LA (1 μM but not 0.1 μM or 10 μM) significantly enhanced transepithelial electrical resistance (TER) above ischemic injured controls and significantly reduced serosal-to-mucosal flux LPS (P<0.05). LA (1 μM) enhanced localization of the sealing tight junction protein claudin-4 in repairing epithelium. To assess for the possibility of fragmentation of LA, anin vitroenzyme degradation assay using the brush border enzyme aminopeptidase M, revealed generation of peptide fragments. Western blot analysis of total protein isolated from uninjured and ischemia-injured porcine intestine showed aminopeptidase M enzyme presence in both tissue types, and mass spectrometry analysis of samples collected duringex vivoanalysis confirmed formation of LA fragments. Treatment of tissues with LA fragments had no effect alone, but treatment with a fragment missing both amino-terminus glycines inhibited barrier recovery stimulated by 1 μM LA. To reduce potential LA inhibition by fragments, a D-amino acid analog of larazotide Analog #6, resulted in a significant recovery response at a 10-fold lower dose (0.1 μM) similar in magnitude to that of 1 μM LA. We conclude that LA stimulates repair of ischemic-injured epithelium at the level of the tight junctions, at an optimal dose of 1 μM LA. Higher doses were less effective because of inhibition by LA fragments, which could be subverted by chirally-modifying the molecule, or microdosing LA.
Small cell lung cancer (SCLC) represents approximately 15% of all cases of lung cancer. SCLC patients have a poor prognosis and limited treatment options. Conventional chemotherapy can reduce the bulk of SCLC lesions, but cancer stem cells (CSCs) survive, reconstitute the tumor and contribute to metastases. Thus, targeting CSCs, which are resistant to many current treatments, may significantly improve outcomes of SCLC patients. Salinomycin (SAL), a potassium ionophore, preferentially targets CSCs. However, SAL is extensively metabolized in animal models and is associated with substantial toxicity at higher doses, limiting its potential for anti-cancer activity in patients In this study, we report a novel QUATRAMER polymeric nanoparticle (NP)-based formulation, that potentially overcomes toxicity of SAL. SAL was encapsulated in polymeric NPs comprised of a polyethylene glycol (PEG)-polypropylene glycol (PPG)-PEG-modified PLA-tetra-block copolymer (SAL-NPs; HSB-1216). SAL release from the NPs was controlled by both PEG/PEG-PPG-PEG chain length and the PLA molecular weight, permitting time-dependent release over sustained periods. Treatment of the human SCLC cell line NCI-H69 with HSB-1216 demonstrated an IC50 of 0.5 uM. Once weekly treatment of BALB/c nu/nu mice harboring NCI-H69 xenografts with HSB-1216 at a dose of 5 mg/kg resulted in substantial tumor growth inhibition The tumor growth inhibition was without any effect on the body weights of the mice. These results demonstrate that a novel formulation for sustained delivery of SAL in a sustained injectable suspension represents an approach for targeting CSCs in SCLCs and potentially other cancer types. Citation Format: Surender M. Kharbanda, Anees Mohammad, Sireesh Appajosyula, Mark Rosenberg, James Hill, Sandeep Laumas, Donald W. Kufe, Harpal Singh. Encapsulation of the stem cell inhibitor Salinomycin in novel QUATRAMER sustained injectable suspension (HSB-1216) for the treatment of small cell lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 491.
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