O’Brien, Timothy D.

Abstract Introduction: Lymphomas are among the most common malignancies in dogs, and their morphologic and biological similarities to human counterparts have established them as widely accepted models of human disease. However, emerging molecular data suggest that conservation varies by subtype, and that many common lymphoma subtypes are principally convergent rather than homologous conditions, requiring a critical reassessment of when and how canine lymphomas provide relevant models of human disease. Methods: We employed conventional pathology, immunohistochemistry, and next generation sequencing platforms, including single-cell sequencing and spatial genomics, to characterize the transcriptional landscape and cellular organization of canine lymphomas, complemented by population metadata. Results: Our analysis revealed that canine DLBCL lacks the traditional GCB/ABC bifurcation seen in humans. While activation of NFκB pathways is seen commonly in these tumors, a germinal center-like DLBCL subtype is not apparent in dogs, and the transcriptional signatures are distinct from those of activated B-cell like DLBCL. Instead, we identified a novel canine-specific DLBCL subset driven by an AP-1-associated transcriptional signature, mirroring advanced human follicular lymphoma rather than human DLBCL. In contrast, emerging data suggest that downregulation of quiescence programs might be a shared feature of both human and canine MZLs, making this subtype a candidate for conserved disease mechanisms. While canine T-cell lymphomas exhibited extensive transcriptional heterogeneity, the samples in our dataset did not align with established human T-cell subgroups, suggesting that high incidence in dogs might not equate to molecular similarity. Conclusions: Our results suggest canine and human lymphomas are principally convergent rather than homologous diseases whose evolution and topological organization are constrained by developmental programs. The distinct transcriptional programs of canine and human DLBCLs reveal informative biological divergence, while potential shared features of MZL suggest contexts where comparative oncology may illuminate conserved disease mechanisms. Canine T-cell lymphomas exhibit extensive transcriptional heterogeneity that, at present, defies simple classification, mirroring challenges in their human counterparts and underscoring the need for larger studies to establish molecular patterns that inform causation, prognosis, and treatment. These findings highlight contexts where distinct and conserved molecular features between canine and human lymphoma can reveal shared and divergent disease mechanisms, ultimately underscoring the need for subtype-specific validation as canine lymphomas are adopted as models of human disease. Use of AI: Generative AI was used to improve clarity and readability of the abstract. AI was not used to conduct the study or to produce new text or material. Citation Format: Jaime F. Modiano, Amy E . Treeful, Grace E. Walker, Davis M. Seelig, Caitlyn M. Callaghan, Timothy D. O'Brien, Shruthi Naik, Aaron L. Sarver. Different paths to the same destination: Molecular divergence and functional convergence in human and canine lymphomas [abstract]. In: Proceedings of the Fifth AACR International Meeting on Advances in Malignant Lymphoma: From Discovery to Clinical Impact; 2026 Jun 24-27; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2026;7(3_Suppl):Abstract nr A023.

Islet amyloid derived from islet amyloid polypeptide (IAPP) is a well-recognized feature of type II diabetes. However, the mechanism of islet amyloidogenesis is unknown. In vitro studies suggest that amino acid residues 20–29 in human, but not mouse, IAPP confer amyloidogenicity consistent with the absence of spontaneous islet amyloidosis in mice. Several clinical and in vitro studies suggest that increased synthetic rates of IAPP predispose to IAPP-amyloidosis. In the present study, we sought to test the hypothesis that pharmacological induction of insulin resistance in a mouse transgenic (TG) for human IAPP would induce islet amyloid and β-cell dysfunction. TG and non-transgenic (N-TG) control mice were treated with both rat growth hormone (12 μg/day) and dexamethasone (0.24 mg/day) (dex/GH) or received no treatment for 4 weeks, after which animals were killed to examine islet morphology. Treatment with dex/GH caused hyperglycemia (7.3 ± 0.4 vs. 5.2 ± 0.1 mmol/l, TG vs. N-TG, P < 0.001) associated with a decreased plasma insulin concentration (595 ± 51 vs. 996 ± 100 pmol/1, TG vs. N-TG, P < 0.05) in TG versus control mice. Islet amyloid was induced in treated TG mice but not in control mice. Islet amyloid was identified in both intra- and extracellular deposits, the former being associated with evidence of β-cell degeneration. We conclude that dex/GH treatment in mice TG for human IAPP induces IAPP-derived islet amyloid, hyperglycemia, and islet dysfunction. The present model recapitulates the islet morphology and phenotype of type II diabetes.

Amyloid deposits that characteristically form in the pancreatic islets of patients with non-insulin-dependent diabetes mellitus (NIDDM) and in insulinomas are both derived from islet amyloid polypeptide (IAPP). Evidence from previous studies has suggested that deposition of IAPP-derived amyloid is related to inherent amyloidogenic sequences present within normal human IAPP, together with an increased production and local concentration of IAPP. However, whether the aggregation of IAPP to form amyloid fibrils is primarily an intra- or extracellular event is not clear. To address this question, we studied 20 human insulinomas by light and electron microscopy. By light microscopy, amyloid deposits were demonstrated in 13 of 20 (65%) human insulinomas. Furthermore, evaluation of Congo red-stained tumor sections showed small, globular or irregular, congophilic amyloid deposits within the cytoplasm of many tumor cells in 10 of 13 (77%) amyloid-containing insulinomas. Dense, punctate areas of IAPP immunoreactivity within tumor cells corresponded with the congophilic intracellular deposits. Ubiquitin immunoreactivity also was observed as punctate intracellular labeling and within large extracellular amyloid deposits. Among the 10 insulinomas available for electron microscopic evaluation, pathological IAPP-immunoreactive (immunogold) deposits were found in 3 of 5 insulinomas in which amyloid was demonstrated by light microscopy and in none of 5 tumors found negative for amyloid by light microscopy. Morphology of IAPP-immunoreactive deposits varied from those with the classical distinct 7- to 10-nm diameter nonbranching fibrils to those with distinct but faint fibrillarity to those without discernable fibrils. In each of the 3 tumors with ultrastructurally demonstrable amyloid deposits, intracellular aggregates of IAPP-immunoreactive amyloid fibrils were observed either free in the cytoplasmic matrix or in membrane-bound structures. Intracellular IAPP-immunoreactive deposits were up to 10 urn in the greatest dimension. Free intracellular aggregates of amyloid fibrils sometimes contained degenerating secretory vesicles and fragments of membranous organelles. These observations suggest that IAPP-derived amyloid deposits are initially formed intracellularly and are subsequently released to the extracellular space by exocytosis of the membrane-bound structures and/or after necrosis of the tumor cells. Our observations raise the possibility that IAPP-derived islet amyloid deposits (characteristically present in NIODM patients) also may be initially formed within the cytoplasm of β-cells, thus leading to β-cell necrosis and a reduction of β-cell mass as seen in NIDDM.

Islet amyloidosis (IA) is the principal lesion in the endocrine pancreas of human beings with non-insulin-dependent diabetes mellitus (NIDDM) and in the similar forms of diabetes mellitus in domestic cats and macaques. As such, the delineation of the pathogenesis of this form of amyloidosis may be crucial to the understanding of the development and progression of NIDDM. Islet amyloid polypeptide (IAPP) is a recently discovered polypeptide that is the principal constituent of IA in human beings, cats, and macaques. IAPP is produced by the pancreatic β-cells and is co-packaged with insulin in the β-cell secretory vesicles. Immunohistochemical and physiologic evidence supports the notion that the β-cells are heterogenous with respect to their relative contents of insulin and IAPP. Therefore, although IAPP is co-secreted with insulin in response to a variety of well-known insulin secretogogues, the molar ratio of these two proteins that is released from the islets may vary, depending upon the glucose concentration and prevailing metabolic milieu. IAPP is highly conserved among mammalian species and has about 45% homology to another neuropeptide, calcitonin gene-related peptide. IAPP is encoded by a single-copy gene located, in the human being, on chromosome 12. IAPP is expressed as a 93 (murine)–89 (human)-amino acid prepropolypeptide that is processed enzymatically, resulting in the removal of amino- and carboxy-terminal propeptide segments. The 20–29 region of the IAPP molecule is most important in the ability of IAPP to form amyloid fibrils. The role of IAPP and IA in the pathogenesis of human NIDDM and similar forms of diabetes mellitus in cats and macaques may involve several possible mechanisms, including 1) direct physical/chemical damage to β-cells, resulting in necrosis and loss of functional islet tissue, 2) biologic activities of IAPP that oppose those of insulin or abnormally suppress insulin secretion, and 3) interference by IA deposits of passage of insulin out of β-cells and/or entrance of glucose and other secretogogues into the islet. The roles of each of these possible mechanisms have yet to be demonstrated. In addition, the physiological significance of the apparent IAPP deficiency in both insulin-dependent diabetes mellitus and NIDDM is currently unknown.

To further characterize spontaneous diabetes mellitus in cynomolgus macaques ( Macaca fascicularis) as a model for human non-insulin-dependent diabetes mellitus (NIDDM), we evaluated the morphologic characteristics of the endocrine pancreas of 4 diabetic and 12 age-matched nondiabetic cynomolgus macaques. In addition, the cDNA-predicted amino acid sequence for islet amyloid polypeptide (IAPP) of this species was determined. Islet amyloid deposits exhibiting typical congophilia and green birefringence were found in 4/4 diabetic animals and in 8/12 nondiabetics. Islet amyloid deposits were significantly more extensive in the diabetic macaques ( P = 0.001), in which they occupied a mean of 60% of the islet area. In contrast, in the nondiabetic group the maximum islet area occupied by amyloid was 24% (group mean = 6.8%), with four animals having no detectable islet amyloid. Amyloid deposits consistently showed immunoreactivity for IAPP but not for insulin. Comparisons between group means for diabetic versus nondiabetic macaques showed significantly greater islet area ( P = 0.01, 85,390 versus 36,540 μm 2 ) and significantly greater islet area fraction ( P = 0.02, 0.065 versus 0.032) for the diabetic group. The cDNA-predicted amino acid sequence for cynomolgus IAPP was identical to that previously reported for pig-tail macaques ( M. nemestrina) and had 92%, 86%, and 84% amino acid sequence identity with human, domestic cat, and murine IAPPs, respectively. These findings support the use of cynomolgus macaques as an animal model of human NIDDM.