Mesenchymal stromal cells (MSCs) are explored as a novel treatment for a variety of medical conditions. Their fate after infusion is unclear, and long-term safety regarding malignant transformation and ectopic tissue formation has not been addressed in patients. We examined autopsy material from 18 patients who had received human leukocyte antigen (HLA)-mismatched MSCs, and 108 tissue samples from 15 patients were examined by PCR. No signs of ectopic tissue formation or malignant tumors of MSC-donor origin were found on macroscopic or histological examination. MSC donor DNA was detected in one or several tissues including lungs, lymph nodes, and intestine in eight patients at levels from 1/100 to <1/1,000. Detection of MSC donor DNA was negatively correlated with time from infusion to sample collection, as DNA was detected from nine of 13 MSC infusions given within 50 days before sampling but from only two of eight infusions given earlier. There was no correlation between MSC engraftment and treatment response. We conclude that MSCs appear to mediate their function through a “hit and run” mechanism. The lack of sustained engraftment limits the long-term risks of MSC therapy.

Cisplatin is a broad-spectrum anticancer drug that is also widely used in experimental studies on DNA damage-induced apoptosis. Induction of apoptosis within 24-48 hr requires cisplatin concentrations that are at least one order of magnitude higher than the IC 50 . Here, we show that such high, apoptosis-inducing cisplatin concentrations induce cellular superoxide formation and that apoptosis is inhibited by superoxide scavengers. The same concentration limit and the requirement for superoxide are also true for induction of caspase activation in enucleated cells (cytoplasts), showing that cisplatin-induced apoptosis occurs independently of nuclear DNA damage. In contrast, lower cisplatin concentrations, which do not induce acute apoptosis, are sufficient for induction of DNA damage signaling. We propose that the antiproliferative effects of cisplatin at IC 50 doses involve premature senescence and secondary, nonstress-induced apoptosis. The higher doses currently used in in vitro studies lead to acute, stress-induced apoptosis that involves induction of superoxide but is largely DNA damage-independent. ' 2006 Wiley-Liss, Inc.Key words: cisplatin; DNA damage; apoptosis; senescence Cis-diamminedichloroplatinum (II) (cisplatin) is a commonly used anticancer agent, especially effective in the treatment of testicular carcinoma and also used to treat other malignancies such as ovarian, cervix, head-and-neck and small-cell lung cancer. 1 Cisplatin forms covalent bonds to the N7 positions of DNA purines to form intra-or interstrand crosslinks, and DNA is generally acknowledged as the primary target of cisplatin. 2,3 Cisplatin is a commonly used model agent for induction of DNA damage-dependent apoptosis in vitro. Acute apoptosis is induced within 24-36 hr, and major efforts have been performed to elucidate apoptotic signaling pathways induced by cisplatin within this time frame. These various studies have highlighted the roles of c-ABL, stressactivated protein kinases and p53 as downstream mediators of cisplatin-induced DNA damage and as mediators of apoptotic signaling (recently reviewed in 3 ). In addition to induction of apoptosis, cisplatin also induces premature senescence. 4 Premature senescence is currently thought to be related to replicative senescence, which has been demonstrated to be a DNA damage response. 5 During replicative senescence, signaling pathways involving ATM (Ataxia telangiectasia mutated) and p53 are activated by telomere uncapping. 5,6 The same signaling mechanisms are believed to be involved in premature senescence induced by DNA damaging drugs. 6,7 Apoptosis and senescence are obviously mutually exclusive cellular outcomes. The factors that decide whether cisplatin will trigger apoptosis or senescence are not clearly understood. In one scenario, senescence and apoptosis represent graded responses to increasing DNA damage. In more complex scenarios, cisplatin induces senescence and apoptosis by different (or partially different) mechanisms.As inducer of apoptosis, cisplatin is used at very d...

Background: Human melanoma cells are able to sustain low pH conditions characterizing many solid tumors. Results: Acidic stress in melanoma cells induces reduced nutrients uptake, inhibition of mammalian target of rapamycin, and activation of autophagy. Conclusion: Melanoma cells activate autophagy as a protective and adaptive response to acidic stress. Significance: Adaptation to acidosis via autophagy confirms the feasibility of anticancer therapy targeting autophagy.

Caspase-cleaved proteins are released from disintegrated apoptotic cells and can be detected in the circulation. We here addressed whether caspase-cleaved cytokeratin 18 (CK18-Asp396) can be used as a serum biomarker for assessment of the clinical efficiency of chemotherapy in hormone-refractory prostate cancer (HRPC). A total of 82 patients with HRPC were evaluated during 751 treatment cycles, either with estramustine (EMP)/vinorelbine or with EMP/docetaxel. The levels of CK18-Asp396 and of total CK18 were measured in patient serum before and during therapy by ELISA. Docetaxel induced significant increases in serum CK18-Asp396 (Po0.0001) and total CK18 (Po0.0002), suggesting induction of apoptosis. Similarly, vinorelbine induced increases in both CK18-Asp396 and CK18 (Po0.001 and 0.011). In contrast, EMP induced increases in total serum CK18 (Po0.0001), but not in CK18-Asp396 (P ¼ 0.13). The amplitudes of docetaxel-induced increases were associated with baseline prostate-specific antigen (PSA) and CK18 serum levels in these patients, consistent with tumoral origin of caspase-cleaved fragments. Docetaxel induced significant increases in CK18-Asp396 during second-, third-and fourth-line therapy and induced increased levels of CK18-Asp396 during treatment cycles 1 -8. In contrast, vinorelbine induced significant increases only during cycles 1 -3. In a subgroup of 32 patients that received EMP/vinorelbine in second line followed by EMP/docetaxel in third line, docetaxel induced stronger increases than vinorelbine (P ¼ 0.008). These results show that the CK18-Asp396 serum marker can be used to assess tumour apoptosis in vivo and suggest that the clinical efficiency of docetaxel in HRPC is due to induction of apoptosis during multiple treatment cycles.