123 P-MUC1C-ALLO1: A fully allogeneic stem cell memory T cell (TSCM) CAR-T therapy with broad potential in solid tumor

Background

While CAR-T have demonstrated potent activity against hematologic tumors, less success has been seen with solid tumors. Here we report generation of TSCM-enriched allogeneic MUC1-C-specific CAR T cells, P-MUC1C-ALLO1, with potential for a broad range of solid tumors. The proliferative capacity and metabolic profile of TSCM CAR-T are well-suited to activity in the solid tumor setting. MUC1 is comprised of an N-terminal subunit (MUC1-N) tethered to a C-terminal subunit (MUC1-C), forming a stable complex on the cell surface. During tumorigenesis, MUC1 becomes both overexpressed and hypo-glycosylated on many carcinomas. Furthermore, MUC1 undergoes proteolytic cleavage in the tumor microenvironment, leaving behind a proteolytic ‘stump’ of MUC1-C that is over-represented in cancer, making it an attractive therapeutic target.

Methods

P-MUC1C-ALLO1 is manufactured using the piggyBac® DNA Delivery System for CAR insertion and the Cas-CLOVER™ Gene Editing System to knockout both the TCR and MHC class I proteins. The addition of a selectable marker within the transposon allows for selection of a fully CAR-positive population while any residual TCR-positive cells are removed at the end of production to prevent TCR-mediated GvHD. Lastly, inclusion of a proprietary ‘booster molecule’ in our allogeneic process further improves cell expansion, along with phenotype and function, and enables the production of up to hundreds of patient doses from a single manufacturing run.

Results

Significant doses of P-MUC1C-ALLO1 products made from multiple healthy donors were achieved and comprised of an exceptionally high-percentage of desirable TSCM cells. Preclinical evaluation of these products showed potent tumor killing and cytokine secretion against MUC1-C-positive breast and ovarian tumor cell lines. P-MUC1C-ALLO1 demonstrates potent cytotoxicity against tumor cells, and minimal killing of normal MUC1-C-positive human primary cells. In a triple negative breast cancer xenograft model, MUC1C CAR-T eliminated established MDA-MB-468 tumor cells, mounted robust T cell expansion in peripheral blood and maintained a favorable TSCM percentage over time. Likewise, in an orthotopic ovarian cancer xenograft model, intraperitoneally administered MUC1C CAR-T eliminated established OVCAR3 cells to levels below the limit of detection. All together, these data demonstrated the efficacy of the MUC1C CAR-T cells and the robustness of the allogeneic platform.

Conclusions

P-MUC1C-ALLO1 is an allogeneic TSCM CAR-T therapy that has a potential to treat multiple MUC1-expressing indications. P-MUC1C-ALLO1 displayed specificity for tumor vs. normal cells as well as in vivo efficacy against xenograft models of breast and ovarian cancer. This allogeneic cell therapy is advancing rapidly towards the clinic.

PCA062, a P-cadherin Targeting Antibody-Drug Conjugate, Displays Potent Antitumor Activity Against P-cadherin-expressing Malignancies

The cell surface glycoprotein P-cadherin is highly expressed in a number of malignancies, including those arising in the epithelium of the bladder, breast, esophagus, lung, and upper aerodigestive system. PCA062 is a P-cadherin specific antibody-drug conjugate that utilizes the clinically validated SMCC-DM1 linker payload to mediate potent cytotoxicity in cell lines expressing high levels of P-cadherin in vitro, while displaying no specific activity in P-cadherin-negative cell lines. High cell surface P-cadherin is necessary, but not sufficient, to mediate PCA062 cytotoxicity. In vivo, PCA062 demonstrated high serum stability and a potent ability to induce mitotic arrest. In addition, PCA062 was efficacious in clinically relevant models of P-cadherin-expressing cancers, including breast, esophageal, and head and neck. Preclinical non-human primate toxicology studies demonstrated a favorable safety profile that supports clinical development. Genome-wide CRISPR screens reveal that expression of the multidrug-resistant gene ABCC1 and the lysosomal transporter SLC46A3 differentially impact tumor cell sensitivity to PCA062. The preclinical data presented here suggest that PCA062 may have clinical value for treating patients with multiple cancer types including basal-like breast cancer.

GPRC5D is a target for the immunotherapy of multiple myeloma with rationally designed CAR T cells

Early clinical results of chimeric antigen receptor (CAR) T cell therapy targeting B cell maturation antigen (BCMA) for multiple myeloma (MM) appear promising, but relapses associated with residual low-to-negative BCMA-expressing MM cells have been reported, necessitating identification of additional targets. The orphan G protein-coupled receptor, class C group 5 member D (GPRC5D), normally expressed only in the hair follicle, was previously identified as expressed by mRNA in marrow aspirates from patients with MM, but confirmation of protein expression remained elusive. Using quantitative immunofluorescence, we determined that GPRC5D protein is expressed on CD138⁺ MM cells from primary marrow samples with a distribution that was similar to, but independent of, BCMA. Panning a human B cell-derived phage display library identified seven GPRC5D-specific single-chain variable fragments (scFvs). Incorporation of these into multiple CAR formats yielded 42 different constructs, which were screened for antigen-specific and antigen-independent (tonic) signaling using a Nur77-based reporter system. Nur77 reporter screen results were confirmed in vivo using a marrow-tropic MM xenograft in mice. CAR T cells incorporating GPRC5D-targeted scFv clone 109 eradicated MM and enabled long-term survival, including in a BCMA antigen escape model. GPRC5D(109) is specific for GPRC5D and resulted in MM cell line and primary MM cytotoxicity, cytokine release, and in vivo activity comparable to anti-BCMA CAR T cells. Murine and cynomolgus cross-reactive CAR T cells did not cause alopecia or other signs of GPRC5D-mediated toxicity in these species. Thus, GPRC5D(109) CAR T cell therapy shows potential for the treatment of advanced MM irrespective of previous BCMA-targeted therapy.

Preclinical Antitumor Activity of a Novel Anti-c-KIT Antibody-Drug Conjugate against Mutant and Wild-type c-KIT-Positive Solid Tumors

Purpose: c-KIT overexpression is well recognized in cancers such as gastrointestinal stromal tumors (GIST), small cell lung cancer (SCLC), melanoma, non-small cell lung cancer (NSCLC), and acute myelogenous leukemia (AML). Treatment with the small-molecule inhibitors imatinib, sunitinib, and regorafenib resulted in resistance (c-KIT mutant tumors) or limited activity (c-KIT wild-type tumors). We selected an anti-c-KIT ADC approach to evaluate the anticancer activity in multiple disease models.Experimental Design: A humanized anti-c-KIT antibody LMJ729 was conjugated to the microtubule destabilizing maytansinoid, DM1, via a noncleavable linker (SMCC). The activity of the resulting ADC, LOP628, was evaluated in vitro against GIST, SCLC, and AML models and in vivo against GIST and SCLC models.Results: LOP628 exhibited potent antiproliferative activity on c-KIT-positive cell lines, whereas LMJ729 displayed little to no effect. At exposures predicted to be clinically achievable, LOP628 demonstrated single administration regressions or stasis in GIST and SCLC xenograft models in mice. LOP628 also displayed superior efficacy in an imatinib-resistant GIST model. Further, LOP628 was well tolerated in monkeys with an adequate therapeutic index several fold above efficacious exposures. Safety findings were consistent with the pharmacodynamic effect of neutropenia due to c-KIT-directed targeting. Additional toxicities were considered off-target and were consistent with DM1, such as effects in the liver and hematopoietic/lymphatic system.Conclusions: The preclinical findings suggest that the c-KIT-directed ADC may be a promising therapeutic for the treatment of mutant and wild-type c-KIT-positive cancers and supported the clinical evaluation of LOP628 in GIST, AML, and SCLC patients. Clin Cancer Res; 24(17); 4297-308. ©2018 AACR.

Abstract 1695: Development of a novel antibody-drug conjugate for the treatment of c-Kit expressing solid tumors and AML

c-Kit is an attractive target for the treatment of a variety of solid tumors [gastrointestinal tumors (GIST), small cell lung cancer (SCLC), melanoma] and acute myelogenous leukemia (AML) due to its role as an oncogenic driver and high level of expression. Several targeted therapies, such as imatinib, sunitinib and regorafenib, bind to c-Kit and are approved for clinical use. However, due to their insufficient activity on cancers expressing wildtype c-Kit or insensitive forms of mutant c-Kit, the clinical response has been quite varied. Moreover, despite initial anti-cancer benefits in c-Kit mutant settings (such as in GIST), resistance to c-Kit inhibitor therapies emerges due primarily to the development of additional mutations in c-Kit.

In an attempt to broaden the treatment of patients whose cancers express c-Kit (wildtype and mutant) and to enhance potency with comparable or better tolerability than the current therapeutics, we developed a c-Kit-targeting antibody-drug conjugate (ADC) that disrupts tumor growth through anti-mitotic activity. Hybridomas from mice immunized with the c-Kit extracellular domain (ECD) were screened for selective c-Kit binding and degradation. A humanized lead antibody (Ab) was identified, which rapidly internalized upon binding cell-surface c-Kit, but did not block binding to the c-Kit ligand (SCF). The Ab exhibited minimal-to-no cytotoxicity against c-Kit+ cell lines in vitro. To generate cytotoxic activity and to potentially overcome resistance to current c-Kit-targeting therapies, the Ab was conjugated to the maytansinoid DM1, a powerful anti-tubulin agent, via a non-cleavable linker, SMCC (technology licensed from ImmunoGen, Inc.). The ADC demonstrated robust anti-proliferative activity against cell lines expressing mutant c-Kit (GIST) and wildtype c-Kit (SCLC, AML) in vitro. The ADC also demonstrated potent anti-cancer activity in GIST and SCLC tumor xenograft models in vivo.

In summary, the anti-c-Kit ADC is highly selective and active against cancers with elevated c-Kit expression regardless of their mutational status, thus representing a promising novel therapeutic approach for the treatment of c-Kit+ solid tumors, such as GIST and SCLC, as well as hematological malignancies such as AML and aggressive systemic mastocytosis (ASM).

Citation Format: Tinya J. Abrams, Xiaohong Niu, Millicent Embry, Janine Kline, Montesa Patawaran, Christie Fanton, Marjorie Ison-Dugenny, Tracy Schneider, Kathy Miller, Zhen Wang, Majid Ghoddusi, Steven Cohen, E. Erica Hong, Emma Lees, Siew Schleyer. Development of a novel antibody-drug conjugate for the treatment of c-Kit expressing solid tumors and AML. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1695. doi:10.1158/1538-7445.AM2015-1695

Abstract 1682: Development and activity of a novel antibody-drug conjugate for the treatment of P-cadherin expressing cancers

The cell surface glycoprotein P-cadherin is an attractive target for an antibody-drug conjugate (ADC) therapy as it is known to be highly expressed in a number of malignancies, including those arising in the epithelium of the breast, lung, bladder, esophagus, stomach, endometrium and colon, among others. In breast cancer, P-cadherin is frequently overexpressed in high grade invasive tumors and is a reliable marker of the basal-like breast cancer molecular subtype, a disease with no effective therapeutic treatment options. Based on the expression profile of P-cadherin in human cancer, a highly selective and potent ADC was developed to target cancer types overexpressing this glycoprotein. This ADC consists of a fully human anti-P-cadherin-specific antibody conjugated to the potent maytansine-derived microtubule-disruptor, DM1, via an SMCC non-cleavable thioether linkage (technology licensed from ImmunoGen, Inc.). In vitro, the ADC was demonstrated to selectively bind P-cadherin expressing cell lines, to rapidly internalize and traffic to lysosomes, and to release a sufficient amount of activated payload to potently induce a cytotoxic response in cell viability assays. Profiling of activity in a cell line panel indicated that this ADC can effectively target and kill P-cadherin-positive cancer cells representing breast, head and neck, and bladder carcinomas. In vivo, the ADC was highly efficacious in numerous relevant xenograft models of P-cadherin expressing cancers, including breast, head and neck, bladder and lung. From this promising cellular and in vivo activity, this ADC may be an effective treatment for patients with P-cadherin positive cancers of high unmet medical need.

Citation Format: Daniel Menezes, Tinya J. Abrams, Christopher Karim, Yan Tang, Chi Ying, Kathy Miller, Christie Fanton, Majid Ghoddusi, Zhen Wang, Montesa Patawaran, Nancy Pryer, Emma Lees, Jason Damiano. Development and activity of a novel antibody-drug conjugate for the treatment of P-cadherin expressing cancers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1682. doi:10.1158/1538-7445.AM2015-1682

Vemurafenib cooperates with HPV to promote initiation of cutaneous tumors

Treatment with RAF inhibitors such as vemurafenib causes the development of cutaneous squamous cell carcinomas (cSCC) or keratoacanthomas as a side effect in 18% to 30% of patients. It is known that RAF inhibitors activate the mitogen-activated protein kinase (MAPK) pathway and stimulate growth of RAS-mutated cells, possibly accounting for up to 60% of cSCC or keratoacanthoma lesions with RAS mutations, but other contributing events are obscure. To identify such events, we evaluated tumors from patients treated with vemurafenib for the presence of human papilloma virus (HPV) DNA and identified 13% to be positive. Using a transgenic murine model of HPV-driven cSCC (K14-HPV16 mice), we conducted a functional test to determine whether administration of RAF inhibitors could promote cSCC in HPV-infected tissues. Vemurafenib treatment elevated MAPK markers and increased cSCC incidence from 22% to 70% in this model. Furthermore, 55% of the cSCCs arising in vemurafenib-treated mice exhibited a wild-type Ras genotype, consistent with the frequency observed in human patients. Our results argue that HPV cooperates with vemurafenib to promote tumorigenesis, in either the presence or absence of RAS mutations.

Abstract LB-61: Vemurafenib promotes RAS wild-type tumor formation in a mouse model of HPV-driven cutaneous squamous cell carcinoma

A subset of melanoma patients (18-30%) treated with Vemurafenib (and other RAF inhibitors) develop spontaneous cutaneous squamous-cell carcinoma (cSCC) and/or keratoacanthoma (KA). Preclinical studies demonstrate that RAF inhibitors paradoxically activate the MAPK pathway and stimulate growth of RAS mutated cells. Based on these observations it has been proposed that drug induced MAPK activation in pre-cancerous tissues may account for the high incidence of cSCC and KA in treated patients. Because human cSCC is frequently positive for human papillomavirus (HPV) DNA, we hypothesized that RAF inhibitors promote tumorigenesis in HPV infected epidermis. To investigate this possibility, we used a transgenic murine model (K14-HPV16) of cSCC, driven by basal keratinocyte-specific expression (K14 promoter) of HPV type 16 early genes including E6 and E7, which inactivates p53 and pRB tumor suppressors. Exposure to Vemurafenib elevated MAPK markers in epidermis and increased cSCC incidence from 22% to 70%. Exome sequencing revealed that 100% of cSCCs from untreated mice harbored activating RAS mutations, yet 55% of cSCCs from Vemurafenib treated mice were RAS wild-type. Concomitant treatment with a MEK inhibitor reduced cSCC frequency, and MEK inhibitor alone was sufficient to completely regress established cSCCs. Together, these results suggest that cSCC is dependent upon MAPK activation induced either by a RAS oncogene or alternatively by exposure to RAF inhibitors in HPV infected keratinocytes.

Citation Format: Matthew Holderfield, Edward Lorenzana, Ben Weisburd, Lisa Lomovasky, Majid Ghoddusi, Dylan Daniel, Nancy Pryer, Frank McCormick, Darrin Stuart. Vemurafenib promotes RAS wild-type tumor formation in a mouse model of HPV-driven cutaneous squamous cell carcinoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-61. doi:10.1158/1538-7445.AM2013-LB-61

Abstract B129: RAF inhibition promotes tumorigenesis in a mouse model of HPV-driven squamous cell carcinoma

Recent approval to market the RAF kinase inhibitor vemurafenib for treatment of metastatic melanomas positive for the BRAFV600E mutation highlights the clinical importance of MEK/ERK signaling in human cancers. Vemurafenib treatment resulted in objective responses in 52% of BRAFV600E mutation melanoma patients, although a subset of patients (20–30%) were reported to develop cutaneous squamous-cell carcinomas (cSCCs) and/or keratoacanthomas, which are independent of the melanoma and thought to be related to exposure to the RAF inhibitor. While vemurafenib effectively inhibits proliferation of BRAFV600E mutant melanomas, vemurafenib and other selective RAF kinase inhibitors can paradoxically activate the MAPK pathway and stimulate growth of BRAF wild-type cells. One hypothesis to explain the appearance cSCCs is that paradoxical activation of the MAPK pathway by RAF inhibitor treatment, in the presence of pre-existing genetic lesions, such as the loss of a tumor suppressor(s), is sufficient to promote cSCC growth. To investigate this hypothesis, we used a genetic murine model (K14-HPV16) for cSCC, which is driven by basal keratinocyte-specific expression (Keratin 14 promoter) of human papiloma virus (HPV) type 16 genes E6 and E7, inactivating the p53 and pRB tumor suppressor proteins respectively. The frequency of cSCC in K14-HPV16 mice is ∼10–20% by 8 months of age. Consistent with our hypothesis, 60 day exposure to vemurafenib at a clinically relevant dose increased the cSCC incidence to ∼65%. In addition, the incidence and severity of skin lesions was proportional to the dose of vemurafenib. Mice treated with vemurafenib also exhibited RAF activation as measured by increased levels of MAPK pathway transcriptional targets in dermal tissues where lesions most often arise. Together, these results suggest that hyperactivation of the MAPK pathway caused by vemurafenib promotes tumorigenesis of HPV-driven cSCC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B129.

14-Day Repeat-Dose Oral Toxicity Evaluation of Oxazyme in Rats and Dogs

Oxazyme (OC4) is an orally administered formulation that has as an active component a recombinant mutant form of Bacillus subtilis oxalate decarboxylase (OxDC) enzyme C383S, designed to degrade dietary oxalate in the stomach. Fourteen-day repeat-dose studies were conducted in rats and dogs to evaluate toxicity and determine a no observed adverse effect level (NOAEL). Animals were administered OC4 by oral gavage twice daily for 14 consecutive days. Reversibility, progression, and delayed appearance of any observed changes were evaluated in a subset of animals that underwent a recovery of 7 days following 14 days of control or test-article. There were no test-article-related adverse effects or deaths in either species. Results indicate that the NOAEL under the conditions used in the studies was 720.8 mg/kg/d in rats and 187.2 mg/kg/d in dogs, the high dose tested in each species.

Cutaneous pythiosis in a nontravelled California horse

An 18-year-old Arabian mare was examined with a large mass on the left hind pastern and fetlock. The mare was located in the Central Valley of northern California, and had never been out of the state. Routine histopathological processing and examination of biopsy samples from the mass showed several hyphal organisms that were delineated with a silver stain. Using immunohistochemistry the organism was diagnosed as Pythium insidiosum. The owner declined debulking surgery, and despite treatment with an immunotherapeutic vaccine, the horse's condition deteriorated leading to euthanasia.

Mechanisms underlying intranuclear rod formation

Specific mutations within the alpha-skeletal actin gene (ACTA1) result in intranuclear rod myopathy (IRM), characterized by rod-like aggregates containing actin and alpha-actinin-2 inside the nucleus of muscle cells. The mechanism leading to formation of intranuclear aggregates containing sarcomeric proteins and their impact on cell function and contribution to disease pathogenesis is unknown. In this study, we transfected muscle and non-muscle cells with mutants of alpha-skeletal actin (Val163Leu, Val163Met) associated with intranuclear rod myopathy. By live-cell imaging we demonstrate that nuclear aggregates of actin form within the nuclear compartment, rather than entering the nucleus after formation in the cytoplasm, and are highly motile and dynamic structures. Thus, the nuclear environment supports the polymerization of actin and the movement and coalescence of the polymerized actin into larger structures. We show that the organization of actin within these aggregates is influenced by the binding of alpha-actinin, and that alpha-actinin is normally present in the nucleus of muscle and non-muscle cells. Furthermore, we demonstrate that, under conditions of cell stress (cytoskeletal disruption and ATP depletion), WT skeletal actin forms aggregates within the nucleus that are similar in morphology to those formed by the mutant actin, suggesting a common pathogenic mechanism for aggregate formation. Finally, we show that the presence of intranuclear actin aggregates significantly decreases the mitotic index and hence impacts on the function of the cell. Intranuclear aggregates thus likely contribute to the pathogenesis of muscle weakness in intranuclear rod myopathy.

Ultrastructural changes and sarcoplasmic reticulum Ca2+ regulation in red vastus muscle following eccentric exercise in the rat

This study examined the effects of a bout of low-intensity, prolonged downhill exercise on sarcoplasmic reticulum (SR) Ca(2+)-ATPase activity, Ca(2+) uptake and release in rat red vastus muscle. Ionophore stimulation was determined to assess vesicle integrity by measuring the ratio of Ca(2+)-ATPase activities in the presence and absence of A23187. Observations of the muscle ultrastructure were made to evaluate muscle damage at the level of the myofibrils and SR. Adult male Sprague-Dawley rats (weight, 395 +/- 5.9 g) were either assigned as non-exercise controls or subjected to 90 min of downhill treadmill exercise (-16 deg; 15 m min(-1)), and then killed immediately, 4, 24, 48, 72 or 144 h after exercise (n = 7). Calcium uptake was significantly lower (P < 0.05) compared with control values (19.25 +/- 1.38 nmol min(-1) (mg protein)(-1)), by 29 and 36% immediately and 4 h postexercise, respectively, and remained depressed (P < 0.05) 24 h postexercise. Calcium release was also significantly lower (P < 0.05) compared with control values (31.06 +/- 2.36 nmol min(-1) (mg protein)(-1)), by 37 and 39% immediately and 4 h postexercise, respectively, and remained depressed (P < 0.05) 24 h postexercise. Ca(2+)-ATPase activity measured with ionophore was 31% lower (P < 0.05) 4 h postexercise, and remained lower (P < 0.05) 24 h postexercise. The ratio of Ca(2+)-ATPase activities in the presence and absence of A23187 was not significantly changed after exercise, indicating that membrane integrity was not altered by the exercise. Focal dilatations of the SR were observed immediately and 4 h following exercise, implying that SR may be susceptible to damage in the localized regions of overstretched sarcomeres. The results demonstrate that a bout of low-intensity, prolonged downhill exercise results in a long-lasting depression of SR function that is not fully restored after 2 days of recovery, which may underlie some functional impairments induced by eccentric exercise.

Skeletal muscle repair in a mouse model of nemaline myopathy

Nemaline myopathy (NM), the most common non-dystrophic congenital myopathy, is a variably severe neuromuscular disorder for which no effective treatment is available. Although a number of genes have been identified in which mutations can cause NM, the pathogenetic mechanisms leading to the phenotypes are poorly understood. To address this question, we examined gene expression patterns in an NM mouse model carrying the human Met9Arg mutation of alpha-tropomyosin slow (Tpm3). We assessed five different skeletal muscles from affected mice, which are representative of muscles with differing fiber-type compositions, different physiological specializations and variable degrees of pathology. Although these same muscles in non-affected mice showed marked variation in patterns of gene expression, with diaphragm being the most dissimilar, the presence of the mutant protein in nemaline muscles resulted in a more similar pattern of gene expression among the muscles. This result suggests a common process or mechanism operating in nemaline muscles independent of the variable degrees of pathology. Transcriptional and protein expression data indicate the presence of a repair process and possibly delayed maturation in nemaline muscles. Markers indicative of satellite cell number, activated satellite cells and immature fibers including M-Cadherin, MyoD, desmin, Pax7 and Myf6 were elevated by western-blot analysis or immunohistochemistry. Evidence suggesting elevated focal repair was observed in nemaline muscle in electron micrographs. This analysis reveals that NM is characterized by a novel repair feature operating in multiple different muscles.

Sorting of a nonmuscle tropomyosin to a novel cytoskeletal compartment in skeletal muscle results in muscular dystrophy

Tropomyosin (Tm) is a key component of the actin cytoskeleton and >40 isoforms have been described in mammals. In addition to the isoforms in the sarcomere, we now report the existence of two nonsarcomeric (NS) isoforms in skeletal muscle. These isoforms are excluded from the thin filament of the sarcomere and are localized to a novel Z-line adjacent structure. Immunostained cross sections indicate that one Tm defines a Z-line adjacent structure common to all myofibers, whereas the second Tm defines a spatially distinct structure unique to muscles that undergo chronic or repetitive contractions. When a Tm (Tm3) that is normally absent from muscle was expressed in mice it became associated with the Z-line adjacent structure. These mice display a muscular dystrophy and ragged-red fiber phenotype, suggestive of disruption of the membrane-associated cytoskeletal network. Our findings raise the possibility that mutations in these tropomyosin and these structures may underpin these types of myopathies.

Characterisation of three novel canine osteosarcoma cell lines producing high levels of matrix metalloproteinases

Three canine osteosarcoma cell lines were established from spontaneous pelvic and radial osteosarcomas. The cell populations cultured exhibited characteristics of malignancy and consisted of adherent, pleomorphic, mostly large spindle-shaped or polyhedral cells, characterised by the presence of numerous cytoplasmic granules and vacuoles. The main ultrastructural features included the presence of abundant rough endoplasmic reticulum and numerous cytoplasmic vesicles, deposit vacuoles and small cytoplasmic protrusions. Zymography showed that the cell lines produce high levels of MMP-2 and MMP-9, enzymes directly involved in crucial aspects of the metastatic process. Consistent with their osteoblastic lineage and malignant phenotype, all cell lines were immunoreactive to vimentin, osteopontin, PCNA, p53, MMP-2 and MMP-9, while they were negative for cytokeratin, desmin, SMA, Factor VIII, NSE, GFAP, Rb and p21 protein. No retroviral particles or RNA were detected ultrastructurally or with RT-PCR, although the possibility of viral involvement in osteosarcoma cannot be excluded. The new cell lines provide excellent in vitro models that may allow further studies on the pathobiology of canine osteosarcoma to be undertaken.

Muscle weakness in a mouse model of nemaline myopathy can be reversed with exercise and reveals a novel myofiber repair mechanism

Patients with the inherited muscle disease nemaline myopathy experience prolonged muscle weakness following periods of immobility. We have examined endurance exercise as a means of improving recovery following muscle inactivity in our alpha-tropomyosin(slow)(Met9Arg)-transgenic mouse model of nemaline myopathy. Physical inactivity, mimicked using a hindlimb immobilization protocol, resulted in fiber atrophy and severe muscle weakness. Following immobilization, the nemaline mice (NM) were weaker than WT mice but regained whole-body strength with exercise training. The disuse-induced weakness and the regain of strength with exercise in NM were associated with the respective formation and resolution of nemaline rods, suggesting a role for rods in muscle weakness. Muscles from NM did not show the typical features of muscle repair during chronic stretch-immobilization of the soleus muscle (regeneration occurred with relative lack of centralized nuclei). This indicates that the normal process of regeneration may be altered in nemaline myopathy and may contribute to poor recovery. In conclusion, endurance exercise can alleviate disuse-induced weakness in NM. The altered myofiber repair process in the nemaline mice may be a response to primary myofibrillar damage that occurs in nemaline myopathy and is distinct from the classical repair in muscular dystrophy resulting from plasma membrane defects.

C2C12 Co-culture on a fibroblast substratum enables sustained survival of contractile, highly differentiated myotubes with peripheral nuclei and adult fast myosin expression

We describe a simple culture method for obtaining highly differentiated clonal C2C12 myotubes using a feeder layer of confluent fibroblasts, and document the expression of contractile protein expression and aspects of myofibre morphology using this system. Traditional culture methods using collagen- or laminin-coated tissue-culture plastic typically results in a cyclic pattern of detachment and reformation of myotubes, rarely producing myotubes of a mature adult phenotype. C2C12 co-culture on a fibroblast substratum facilitates the sustained culture of contractile myotubes, resulting in a mature sarcomeric register with evidence for peripherally migrating nuclei. Immunoblot analysis demonstrates that desmin, tropomyosin, sarcomeric actin, alpha-actinin-2 and slow myosin are detected throughout myogenic differentiation, whereas adult fast myosin heavy chain isoforms, members of the dystrophin-associated complex, and alpha-actinin-3 are not expressed at significant levels until >6 days of differentiation, coincident with the onset of contractile activity. Electrical stimulation of mature myotubes reveals typical and reproducible calcium transients, demonstrating functional maturation with respect to calcium handling proteins. Immunocytochemical staining demonstrates a well-defined sarcomeric register throughout the majority of myotubes (70-80%) and a striated staining pattern is observed for desmin, indicating alignment of the intermediate filament network with the sarcomeric register. We report that culture volume affects the fusion index and rate of sarcomeric development in developing myotubes and propose that a fibroblast feeder layer provides an elastic substratum to support contractile activity and likely secretes growth factors and extracellular matrix proteins that assist myotube development.

Ultrastructure of in situ perfusion-fixed avian liver, with special reference to structure of the sinusoids

Broiler chicken and laying hen livers were fixed using a simple technique of in situ puncture perfusion of cacodylate-buffered fixative, which allowed characterisation of the fine structure of hepatic parenchyma, hepatocytes, bile ductules, and, in particular, the sinusoidal cells including endothelial, Kupffer, and Ito cells. Sinusoidal endothelial cells with their bulging perinuclear cytoplasm, evident in both transmission and scanning electron micrographs, were easily distinguishable from Kupffer cells, which possessed numerous pseudopodia. Bile ductular epithelium and hepatocytes of the laying hens contained large amounts of lipid. The ultrastructural characteristics of intercalated cells (putative extra-sinusoidal macrophages of chicken liver) are described and their possible role as precursors of Kupffer cells is discussed.

Occlusable corneas in toadfishes: light transmission, movement and ultrastruture of pigment during light- and dark-adaptation

The toadfishes Tetractenos hamiltoni and Torquigener pleurogramma (Tetraodontidae) possess occlusable yellow corneas. We examine the light transmission and location of the yellow/orange pigment throughout the cornea, the temporal properties of pigment migration and the ultrastructure of the pigmented processes during light- and dark-adaptation. Each species was dark-adapted during the day and light-adapted during the night and then exposed to either sun illumination or darkness for different lengths of time (0-70 min). Movement of corneal pigment could be induced in both species regardless of time of day or night. The pigment was able to migrate in a dorsal or ventral direction and changed from minimal to maximal pigmentation within 60 min. Three types of transmission curves were found with varying degrees of transmission in the 400-500 nm waveband, indicating that the pigment distribution is not uniform across the cornea; some areas of the cornea transmit near UV light, while others absorb blue light. The gradual change of the transmission characteristics in different areas of the cornea indicates the presence of different concentrations of a single type of pigment. Ultrastructural examination of the corneas showed that the layer containing the pigment is situated within the scleral cornea either surrounding (T. pleurogramma) or abutting (T. hamiltoni) an iridescent layer. Long sheet-like processes or chromatophores extending centrally from dorsal and ventral reservoirs are filled with pigment during the light-adapted state but empty in the dark-adapted state.

Renal pathology of polycystic kidney disease and concurrent hereditary nephritis in Bull Terriers

OBJECTIVE

To describe the renal lesions in Bull Terrier polycystic kidney disease (BTPKD), to confirm that the renal cysts in BTPKD arise from the nephron or collecting tubule, and to identify lesions consistent with concurrent BTPKD and Bull Terrier hereditary nephritis (BTHN).

DESIGN

Renal tissue from five Bull Terriers with BTPKD and eight control dogs was examined by light and transmission electron microscopy. Clinical data were collected from all dogs, and family history of BTPKD and BTHN for all Bull Terriers.

RESULTS

In BTPKD the renal cysts were lined by epithelial cells of nephron or collecting duct origin that were usually squamous or cuboidal, with few organelles. They had normal junctional complexes, and basal laminae of varying thicknesses. Glomeruli with small, atrophic tufts and dilated Bowman's capsules, tubular loss and dilation, and interstitial inflammation and fibrosis were common. Whereas the lesions seen in BTHN by light microscope were nonspecific, the presence of characteristic ultrastructural glomerular basement membrane (GMB) lesions and a family history of this disease indicated concurrent BTHN was likely in three of five cases of BTPKD.

CONCLUSION

This paper provides evidence that renal cysts in BTPKD are of nephron or collecting duct origin. In addition, GBM lesions are described that strongly suggest that BTPKD and BTHN may occur simultaneously.

Role of capsule in the pathogenesis of fowl cholera caused by Pasteurella multocida serogroup A

We have constructed a defined acapsular mutant in Pasteurella multocida X-73 (serogroup A:1) by disrupting the hexA gene through the insertion of a tetracycline resistance cassette. The genotype of the hexA::tet(M) strain was confirmed by PCR and Southern hybridization, and the acapsular phenotype of this strain was confirmed by electron microscopy. The hexA::tet(M) strain was attenuated in both mice and chickens. Complementation of the mutant with an intact hexAB fragment restored lethality in mice but not in chickens. In contrast to the results described previously for P. multocida serogroup B (J. D. Boyce and B. Adler, Infect. Immun. 68:3463-3468, 2000), the hexA::tet(M) strain was sensitive to the bactericidal action of chicken serum, whereas the wild-type and complemented strains were both resistant. Following inoculation into chicken muscle, the bacterial count of the hexA::tet(M) strain decreased significantly, while the wild-type and complemented strains both grew rapidly over 4 h. The capsule is thus an essential virulence determinant in the pathogenesis of fowl cholera.

An apparent outbreak of cutaneous papillomatosis in merino sheep in patagonia, Argentina

A retrospective study was performed on skin samples from an outbreak of cutaneous papillomatosis in Merino sheep that occurred in 1995. The samples were processed for routine histology, electron microscopy and immunocytochemistry for papilloma viruses. Particles of approximately 55 nm diameter were found in some nuclei of the stratum granulosum cells, while immunocytochemistry gave positive staining of cell nuclei in this layer. This study confirms that papillomas associated with papillomaviruses occur in sheep in Patagonia.

Comparison of the effects of Clostridium perfringens type D culture supernates in ligated intestinal loops of goats and sheep

The effects of Clostridium perfringens type D culture supernates were compared in ligated loops of the small intestine (ileum) and colon of four goat kids and four lambs, the loops being examined histopathologically and electron microscopically 7 h after inoculation. No lesions were observed in the small intestine of any animal, or in control colonic loops. In the caprine and ovine colonic loops treated with culture supernates, most goblet cells were empty and the lumina contained a layer of mucus, polymorphonuclear leucocytes, bacteria and sloughed epithelial cells. The apical cytoplasm of the superficial epithelial cells was lost. Moderate oedema was observed in the submucosa and muscular layer. The colonic lesions were more severe in kids than in lambs. No changes were seen in vascular endothelial cells in any loop. 1999 W.B. Saunders and Company Ltd.