Central nervous system pathology in preclinical MPS IIIB dogs reveals progressive changes in clinically relevant brain regions

Mucopolysaccharidosis type IIIB (MPS IIIB; Sanfilippo syndrome B) is an autosomal recessive lysosomal storage disorder caused by the deficiency of alpha-N-acetylglucosaminidase activity, leading to increased levels of nondegraded heparan sulfate (HS). A mouse model has been useful to evaluate novel treatments for MPS IIIB, but has limitations. In this study, we evaluated the naturally occurring canine model of MPS IIIB for the onset and progression of biochemical and neuropathological changes during the preclinical stages (onset approximately 24-30 months of age) of canine MPS IIIB disease. Even by 1 month of age, MPS IIIB dogs had elevated HS levels in brain and cerebrospinal fluid. Analysis of histopathology of several disease-relevant regions of the forebrain demonstrated progressive lysosomal storage and microglial activation despite a lack of cerebrocortical atrophy in the oldest animals studied. More pronounced histopathology changes were detected in the cerebellum, where progressive lysosomal storage, astrocytosis and microglial activation were observed. Microglial activation was particularly prominent in cerebellar white matter and within the deep cerebellar nuclei, where neuron loss also occurred. The findings in this study will form the basis of future assessments of therapeutic efficacy in this large animal disease model

ADC payload chemical structures.

<p>The chemical structures of the ADC payloads are shown. Payload A was used to conjugate to pAF via an oxime bond. Payload B was used to conjugate to the thiols on cysteines via maleimide.</p

<i>In vitro</i> antibody stability.

<p>The anti-Her2 ADC antibodies were incubated in human serum or HSA at 37°C up to 28 days. (A) The amount of total antibody (naked and ADC) in the preparation was measured. (B) The amount of ADC in the preparation was measured. (C) % Concentration of ADC over the amount of total antibody. (D) The amount of drug conjugated HSA is measured.</p

Rat serum chemistry summary.

<p>Comparison of selected serum chemistry parameters (Day 15) between cysteine and site specifically conjugated Her2 ADCs. A panel of serum markers was evaluated post single dose, i.v. administration of 30 or 60 mg/kg or 90 mg/kg of the anti-Her2 Cys or 30, 45 or 60 mg/kg anti-Her2 position 1-ADC.</p

<i>In vitro</i> evaluation of Her2 expression and ADC cytotoxicity.

<p>The expression of Her2 and the <i>in vitro</i> cytotoxicity of the ADCs are evaluated in the HCC-1954, NCI-N87, MDA-MB-453 and MDA-MB-468 cell lines. (A) The cell surface expression of Her2 is measured via FACS for a panel of tumor cell lines. HCC-1954, MDA-MB-453 and NCI-N87 were selected as the Her2 expressing cell lines while MDA-MB-468 was selected as the Her2 negative cell line. MDA-MB-453 cells are resistant to Herceptin. (B) NCI-N87 and HCC-1954 tumor xenografts were evaluated for Her2 expression via IHC. (C) The <i>in vitro</i> cytotoxicity of the anti-Her2 ADCs were evaluated in the HCC-1954, NCI-N87, MDA-MB-453 and MDA-MB-468 cell lines.</p