p53 Modulation as a Therapeutic Strategy in Gastrointestinal Stromal Tumors

The KIT-inhibitor imatinib mesylate (IM) has greatly improved the treatment of metastatic gastrointestinal stromal tumors (GIST). IM exhibits strong antiproliferative effects but fails to induce sufficient levels of apoptosis resulting in low pathologic complete remission rates and a high rate of secondary progression in the metastatic setting. Upregulation of p53 by MDM2 inhibitors has been shown to induce apoptosis in p53 wildtype tumors. Analyzing a series of 62 mostly untreated, localized and metastatic GIST we detected a low rate (3%) of inactivating p53 mutations, thus providing a rationale for further exploration of p53-directed therapeutic strategies. To this end, we studied nutlin-3, an inhibitor of the p53 antagonist MDM2, and RITA, a putative p53 activator, in GIST cell lines. Nutlin-3 effectively induced p53 at therapeutically relevant levels, which resulted in moderate antiproliferative effects and cell cycle arrest in p53 wildtype GIST cell lines GIST430, GIST48 and GIST48B. P53 reactivation substantially improved the apoptotic response after effective KIT inhibition with sunitinib and 17-AAG in IM-resistant cell lines. The commonly used imatinib-sensitive cell lines GIST882 and GIST-T1 were shown to harbor defective p53 and therefore failed to respond to nutlin-3 treatment. RITA induced p53 in GIST48B, followed by antiproliferative effects and a strong induction of apoptosis. Surprisingly, GIST-T1 was also highly sensitive to RITA despite lacking functional p53. This suggested a more complex, p53-independent mechanism of action for the latter compound. No antagonistic effects from p53-activating drugs were seen with any drug combination. Our data provide first evidence that modulation of the MDM2/p53 pathway may be therapeutically useful to improve the apoptotic response of KIT-inhibitory drugs in the treatment of naïve GIST, with p53 mutation status being a predictive factor of response

Calcitonin substitution in calcitonin deficiency reduces particle-induced osteolysis

<p>Abstract</p> <p>Background</p> <p>Periprosthetic osteolysis is a major cause of aseptic loosening in joint arthroplasty. This study investigates the impact of CT (calcitonin) deficiency and CT substitution under in-vivo circumstances on particle-induced osteolysis in <it>Calca </it>-/- mice.</p> <p>Methods</p> <p>We used the murine calvarial osteolysis model based on ultra-high molecular weight polyethylene (UHMWPE) particles in 10 C57BL/6J wild-type (WT) mice and twenty <it>Calca </it>-/- mice. The mice were divided into six groups: WT without UHMWPE particles (Group 1), WT with UHMWPE particles (Group 2), <it>Calca </it>-/- mice without UHMWPE particles (Group 3), <it>Calca </it>-/- mice with UHMWPE particles (Group 4), <it>Calca </it>-/- mice without UHMWPE particles and calcitonin substitution (Group 5), and <it>Calca </it>-/- mice with UHMWPE particle implantation and calcitonin substitution (Group 6). Analytes were extracted from serum and urine. Bone resorption was measured by bone histomorphometry. The number of osteoclasts was determined by counting the tartrate-resistant acid phosphatase (TRACP) + cells.</p> <p>Results</p> <p>Bone resorption was significantly increased in <it>Calca </it>-/- mice compared with their corresponding WT. The eroded surface in <it>Calca </it>-/- mice with particle implantation was reduced by 20.6% after CT substitution. Osteoclast numbers were significantly increased in <it>Calca </it>-/- mice after particle implantation. Serum OPG (osteoprotegerin) increased significantly after CT substitution.</p> <p>Conclusions</p> <p>As anticipated, <it>Calca </it>-/- mice show extensive osteolysis compared with wild-type mice, and CT substitution reduces particle-induced osteolysis.</p

Overexpression of the drug resistance-associated protein metallothionein does not correlate with response of sarcomas to isolated limb perfusion treatment

Hyperthermic isolated limb perfusion with TNF-α and melphalan (HILP-TM) achieves high response rates in sarcomas. Melphalan resistance was previously reported to be associated with overexpression of metallothioneins (MTs). Objective of this study was to investigate the influence of MT expression on tumor responses in HILP-TM-treated soft tissue (STSs) and bone sarcomas (BS). In primary biopsies of 41 HILP-TM-treated sarcomas (37 STSs and 4 BS), MT expression was assessed by an immunoreactive score. The pathologic response to HILP-TM was quantified in the corresponding tumor resection specimens. We studied the association of MT-IRS between histological regression (responder >90%, or non-responder ≤90% regression), tumor proliferation, and other clinico-pathological parameters. MT expression was found in 70.7% (N = 29) of tumors (high 12.2%, moderate 19.5%, and low 39.0%). After HILP-TM, 20 cases (48.8%) were categorized as “responders” and 21 (51.2%) as “non-responders.” Six “responders” (14.6%) presented with complete regression. MT expression positively correlated with tumor proliferation but not with HILP-TM. HILP-TM showed a favorable response in a high rate of sarcomas. Although MT overexpression was observed in this cohort of sarcomas, the immunohistochemical MT status was not predictive of the tumor response after HILP-TM treatment