Progressive Degenerative Myopathy and Myosteatosis in ASNSD1-Deficient Mice.

Mice with an inactivating mutation in the gene encoding asparagine synthetase domain containing 1 (ASNSD1) develop a progressive degenerative myopathy that results in severe sarcopenia and myosteatosis. ASNSD1 is conserved across many species, and whole body gene expression surveys show maximal expression levels of ASNSD1 in skeletal muscle. However, potential functions of this protein have not been previously reported. Asnsd1-/- mice demonstrated severe muscle weakness, and their normalized body fat percentage on both normal chow and high fat diets was greater than 2 SD above the mean for 3651 chow-fed and 2463 high-fat-diet-fed knockout (KO) lines tested. Histologic lesions were essentially limited to the muscle and were characterized by a progressive degenerative myopathy with extensive transdifferentiation and replacement of muscle by well-differentiated adipose tissue. There was minimal inflammation, fibrosis, and muscle regeneration associated with this myopathy. In addition, the absence of any signs of lipotoxicity in Asnsd1-/- mice despite their extremely elevated body fat percentage and low muscle mass suggests a role for metabolic dysfunctions in the development of this phenotype. Asnsd1-/- mice provide the first insight into the function of this protein, and this mouse model could prove useful in elucidating fundamental metabolic interactions between skeletal muscle and adipose tissue.

Targeting the cyclin dependent kinase and retinoblastoma axis overcomes standard of care resistance in BRAF V600E -mutant melanoma.

Patient-derived tumor xenograft (PDTX) mouse models were used to discover new therapies for naïve and drug resistant BRAFV600E -mutant melanoma. Tumor histology, oncogenic protein expression, and antitumor activity were comparable between patient and PDTX-matched models thereby validating PDTXs as predictive preclinical models of therapeutic response in patients. PDTX models responsive and non-responsive to BRAF/MEK standard of care (SOC) therapy were used to identify efficacious combination therapies. One such combination includes a CDK4/6 inhibitor that blocks cell cycle progression. The rationale for this is that the retinoblastoma protein (pRb) is 95% wildtype in BRAF mutant melanoma. We discovered that 77/77 stage IV metastatic melanoma tissues were positive for inactive phosphorylated pRb (pRb-Ser780). Rb is hyperphosphorylated and inactivated by CDK4/6:cyclin D1 and when restored to its hypophosphorylated active form blocks cell cycle progression. The addition of a CDK4/6 inhibitor to SOC therapy was superior to SOC. Importantly, triple therapy in an upfront treatment and salvage therapy setting provided sustained durable response. We also showed that CDK4/6 blockade resensitized drug resistant melanoma to SOC therapy. Durable response was associated with sustained suppression of pRb-Ser780. Thus, reactivation of pRb may prove to be a clinical biomarker of response and the mechanism responsible for durable response. In light of recent clinical trial data using this triple therapy against BRAFV600E -mutant melanoma, our findings demonstrating superior and prolonged durable response in PDTX models portend use of this therapeutic strategy against naïve and SOC resistant BRAFV600E -mutant metastatic melanoma coupled with pRB-Ser780 as a biomarker of response.

Novel patient-derived xenograft mouse model for pancreatic acinar cell carcinoma demonstrates single agent activity of oxaliplatin.

BACKGROUND: Pancreatic acinar cell carcinoma (PACC) is a rare malignancy, accounting for <1 % of all pancreatic neoplasms. Very few retrospective studies are available to help guide management. We previously reported the case of a patient with metastatic PACC who achieved prolonged survival following doxorubicin treatment. Personalized treatment was based on molecular and in vitro data collected from primary cells developed from their liver metastasis. We now report the characterization of a patient derived tumor xenograft (PDTX) mouse model that originated from this patient's PACC liver metastasis. METHODS: Fragments of biopsy tissue (5 mm(3)) from PACC liver metastasis were implanted into athymic nude mice. Tumors were grown and passaged from the host mice into new mice to be tested for therapeutic response. Immuno-histochemical (IHC) biomarkers were used to confirm that the PDTX model represents human PACC. The antitumor activities of multiple drugs (5-FU, irinotecan, oxaliplatin, gemcitabine, bevacizumab, erlotinib, doxorubicin and imatinib) were tested. Tumor size was measured over 74 days or until they reached an endpoint volume of ~800 mm(3). Tests to measure serum lipase levels and histological analyses of tumor tissues were also conducted to assess PACC progression and re-differentiation. RESULTS: The model presented here expresses the same IHC markers found in human PACC. In the chemotherapy study, oxaliplatin produced a prolonged durable growth response associated with increased apoptosis, decreased serum lipase levels and increased healthy acinar cells. Bevacizumab also produced a significant growth response, but the effect was not prolonged as demonstrated by oxaliplatin treatment. The other chemotherapies had moderate to little effect, particularly after treatment ceased. Mutations in DNA repair genes are common in PACC and increase tumor susceptibility to oxaliplatin. To explore this we performed IHC and found no nuclear expression of BRCA2 in our model, indicating a mutation affecting nuclear localization. Gene sequencing confirms BRCA2 has a homozygous gene deletion on Exon 10, which frequently causes a protein truncation. CONCLUSIONS: In summary, we report the development and characterization of the first and only preclinical PACC PDTX model. Here we show sustained anti-tumor activity of single agent oxaliplatin, a compound that is more effective in tumors that harbor mutations in DNA repair genes. Our data shows that BRCA2 is mutated in our PACC model, which could contribute to the oxaliplatin sensitivity observed. Further studies on this rare PACC model can serve to elucidate other novel therapies, biomarkers, and molecular mechanisms of signaling and drug resistance.

Disparity between ionic mediators of volume regulation and apoptosis in N1E 115 mouse neuroblastoma cells.

Cellular volume loss or shrinkage is a ubiquitous feature of apoptosis and thus may contribute to this form of degeneration. Chloride (Cl(-)) and potassium (K(+)) efflux has been shown to participate in volume regulation and several recent reports have implicated K(+) efflux in apoptotic neuronal death. Here pharmacological inhibitors of various K(+) and Cl(-) channels and transporters were used to decipher the relationship between cellular volume regulation and apoptosis. Following exposure to a hypotonic media, cells swell but over time gradually recover, returning to their original cell volume in a process known as regulatory volume decrease (RVD). RVD in N1E 115 neuroblastoma cells was monitored using time-lapse videomicroscopy, cell size and DNA degradation were followed using flow cytometry and fragmented apoptotic nuclei were visualized using Hoechst staining. RVD was blocked by high K(+), TEA and 4-AP (K(+) channel blockers), DIDS and niflumic acid but not SITS (Cl(-) channel blockers), ethacrynic acid (Cl(-) pump blocker), bumetanide (Na(+)/K(+)/Cl(-) cotransporter blocker) and furosemide (K(+)/Cl(-) cotransport blocker). In contrast, only DIDS and SITS (blockers of the Cl(-)/HCO(3) exchanger) inhibited apoptosis, suggesting that a common mechanistic link between RVD and apoptosis is the Cl(-)/HCO(3) exchanger. Thus, this study does not support the notion that K(+) channels are universal anti-apoptotic targets. Instead, the Cl(-)/HCO(3) exchanger may prove to be a viable target of therapeutic intervention for treating pathological apoptosis and neurodegeneration.