TDP1 and PARP1 deficiency are cytotoxic to rhabdomyosarcoma cells.

UNLABELLED: Rhabdomyosarcoma is the most common soft tissue sarcoma in children. Metastatic rhabdomyosarcoma in children has a 5-year event-free survival rate of <30%, and a recent clinical trial with irinotecan, a topoisomerase I inhibitor, failed to improve outcome. Therefore, it was surmised that failure of irinotecan may be the result of overexpression of the DNA repair enzyme tyrosyl-DNA phosphodiesterase (TDP1), which processes topoisomerase I-DNA complexes resulting from topoisomerase I inhibitor treatment. Using human tissue microarrays and gene expression arrays, a marked overexpression of TDP1 protein and mRNA in RMS tumors was observed. Critically, knockdown of TDP1 or inhibition of poly(ADP-ribose) polymerase-1 (PARP-1), an enzyme in the same complex as TDP1, sensitized rhabdomyosarcoma cell lines to analogues of irinotecan. Interestingly, BRCA1/2 mutations or altered expression was not detectable in rhabdomyosarcoma cells; however, TDP1 knockdown and PARP-1 inhibition alone were cytotoxic to a subset of rhabdomyosarcoma cells, suggesting that they harbor genetic lesions in DNA repair components that have synthetic lethal interactions with loss of TDP1 or PARP1 function. Furthermore, culturing embryonal rhabdomyosarcoma cells in serum/nutrient-restricted medium increased cellular cytotoxicity upon PARP-1 inhibition and was intrinsically cytotoxic to alveolar, though not embryonal rhabdomyosarcoma cells. The results of these studies suggest a compensatory role for TDP1 in rhabdomyosarcoma after topoisomerase-I based therapy and further demonstrate that TDP1 knockdown, PARP-1 inhibition, and dietary restriction have therapeutic validity. IMPLICATIONS: Selective targeting of TDP1 and/or PARP-1 in rhabdomyosarcoma induces cytotoxicity and sensitizes to DNA damaging agents.

IgG4-related disease with hypergammaglobulinemic hyperviscosity and retinopathy.

Immunoglobulin G4-related disease (IgG4-RD) is a recently described entity with protean manifestations. We describe a novel case of IgG4-RD with hypergammaglobulinemic hyperviscosity responsive to fludarabine and rituximab. A 33-year-old Asian man developed bilateral lacrimal gland and submandibular salivary gland swelling with cervical lymphadenopathy. Biopsies of the affected tissues revealed reactive follicular hyperplasia. Seven years later, he presented with bilateral retinal hemorrhages due to hyperviscosity syndrome from profound polyclonal increase in IgG, including marked IgG4 elevation. Despite plasmapheresis, overproduction of IgG continued and he was refractory to systemic steroids, azathioprine, interferon alpha, and cyclophosphamide. IgG4-RD was suspected following a myocardial infarction and detection of aneurysmal coronary arteries indicating large vessel vasculitis. Review of the cervical lymph node and lacrimal gland biopsies with immunohistochemical staining for IgG4-positive plasma cells confirmed IgG4-RD. B-cell depletion with rituximab produced a partial response, but clinical symptoms and elevated protein levels persisted. Fludarabine was added to rituximab to suppress T-cell activity, and this resulted in an excellent clinical and biochemical response. Combination therapy with fludarabine and rituximab in IgG4-RD has not previously been reported and can be considered in patients with severe refractory disease.

PRL-3: a metastasis-associated phosphatase in search of a function.

The molecular and cellular events involved in cancer progression and metastasis remain much less well-defined than those involved in oncogenesis, despite the fact that cell metastasis is the major factor in cancer mortality. Thus, the discovery that the expression of a protein tyrosine phosphatase, protein of regenerating liver-3 (PRL-3), is upregulated in colon cancer metastases provided an exciting indication that the altered regulation of specific protein tyrosine phosphorylation events and signaling pathways might characterize these metastatic cells and/or be key in promoting the tumor-to-metastasis transition in this, and perhaps other, cancers of epithelial origin. However, the cellular substrate(s) of PRL-3 has not been identified, and little is known of PRL-3-mediated cellular signaling pathways. This review illustrates the significance of PRL-3 in promoting metastasis and the importance of determining the endogenous role of PRL-3.