Purpose: To define the maximum tolerated dose (MTD), toxicities, and pharmacokinetics of 17-allylamino-17-demethoxygeldanamycin (17-AAG) when administered using continuous and intermittent dosing schedules. Experimental Design: Patients with progressive solid tumor malignancies were treated with 17-AAG using an accelerated titration dose escalation schema. The starting dose and schedule were 5 mg/m 2 daily for 5 days with cycles repeated every 21days. Dosing modifications based on safety, pharmacodynamic modeling, and clinical outcomes led to the evaluation of the following schedules: daily  3 repeated every 14 days; twice weekly (days 1, 4, 8, and 11) for 2 weeks every 3 weeks; and twice weekly (days 1and 4) without interruption. During cycle 1, blood was collected for pharmacokinetic and pharmacodynamic studies. Results: Fifty-four eligible patients were treated. The MTD was schedule dependent: 56 mg/m 2 on the daily  5 schedule; 112 mg/m 2 on the daily  3 schedule; and 220 mg/m 2 on the days 1, 4, 8, and 11 every-21-day schedule. Continuous twice-weekly dosing was deemed too toxic because of delayed hepatotoxicity. Hepatic toxicity was also dose limiting with the daily  5 schedule. Other common toxicities encountered were fatigue, myalgias, and nausea. This latter adverse effect may have been attributable, in part, to the DMSO-based formulation. Concentrations of 17-AAG above those required for activity in preclinical models could be safely achieved in plasma. Induction of a heat shock response and down-regulation of Akt and Raf-1were observed in biomarker studies. Conclusion: The MTD and toxicity profile of 17-AAG were schedule dependent. Intermittent dosing schedules were less toxic and are recommended for future phase II studies.Heat shock protein 90 (Hsp90) is a molecular chaperone required for the stress-survival response, protein refolding, and the conformational maturation of a subset of signaling proteins (1 -3). Several natural products that bind selectively to Hsp90 and inhibit its function have been used to determine its biological role (4 -7). These natural products, which include geldanamycin and radicicol, induce the selective degradation of proteins whose activity and/or expression are regulated by . Sensitive Hsp90 clients include protein kinases [human epidermal growth factor receptor 2 (HER2), Raf-1, and Akt], steroid hormone receptors (androgen receptor and estrogen receptor), and mutant oncoproteins (mutant p53,.Geldanamycin, the lead compound of the class, proved too toxic for clinical use (16). However, 17-allylamino-17-demethoxygeldanamycin (17-AAG) has activity in human xenograft and genetic murine tumor models as a single agent (12, 17 -20). Hsp90 inhibition also has additive and synergistic effects in combination with cytotoxics, biologics, radiation, and antiangiogenics (17, 20 -24). The objectives of the current trial were to determine the safety, pharmacokinetics, and pharmacodynamics of 17-AAG and to define a dose and schedule of administration that could be used in ...

Mitogen-activated protein kinase phosphatase (MKP)1 -1 is a dual specificity phosphatase that is overexpressed in many human tumors and protects cells from apoptosis by the anticancer agent cisplatin (1), UV irradiation (2), and proteasome inhibitors (3). Over the past five years, reports have become more numerous describing high levels of MKP-1 in human tumors. For example, high levels of MKP-1 have been found in prostate (4), gastric (5), breast (6), and pancreatic cancer (7). In ovarian cancer samples, MKP-1 expression was correlated with decreased progression-free survival (8). High levels of MKP-1 expression were also found in the early phases of prostate, colon, and bladder carcinogenesis (9). Evidence that MKP-1 may actually support the transformed phenotype comes from a recent study by Liao et al. (7) who showed that PANC-1 human pancreatic cancer cells stably transfected with a full-length MKP-1 antisense construct had longer doubling times, decreased ability to form colonies in soft agar, and were unable to form tumors in nude mice. The precise mechanism by which loss of MKP-1 expression affects tumorigenicity, however, remains elusive. Several reports have implicated JNK/SAPK and p38 as the primary mediators of MKP-1 mediated cytoprotection (1-2). On the other hand, the data presented by Liao et al. (7) argue that the primary mechanism by which MKP-1 supports the transformed phenotype is mediated by ERK, but not JNK, as suppression of MKP-1 expression by antisense did not affect basal levels of phospho-JNK or phospho-p38, but instead increased basal ERK phosphorylation and prolonged ERK phosphorylation after epidermal growth factor stimulation in PANC-1 cells.The availability of a cell-active selective MKP-1 inhibitor would be a valuable tool for dissecting the complex regulatory processes involved in the attenuation of ERK, JNK, and p38 activation and for defining the contributions of MKP-1 and its cellular targets to the maintenance of the transformed phenotype. In light of recent findings, inhibitors of MKP-1 might also find applications as novel target-based antineoplastic therapies, either alone or in combination with clinically used antineoplastic agents (1-3).The search for MKP-1 inhibitors has been challenging for several reasons. In contrast to MKP-3, whose crystal structure has been reported and found to possess high structural similarity to the related VHR in its catalytic domain (10), no structural information is available for MKP-1. This may in part be due to difficulties in producing large amounts of recombinant enzyme and the need of MKPs to interact with their physiolog-

Mitogen-activated protein kinase phosphatase (MKP)-1 is a dual-specificity phosphatase that negatively regulates the activity of mitogen-activated kinases and that is overexpressed in human tumors. Contemporary studies suggest that induction of MKP-1 during chemotherapy may limit the efficacy of clinically used antineoplastic agents. Thus, MKP-1 is a rational target to enhance anticancer drug activity, but suitable small-molecule inhibitors of MKP-1 are currently unavailable. Here, we have used a high-content, multiparameter fluorescence-based chemical complementation assay for MKP activity in intact mammalian cells to evaluate the cellular MKP-1 and MKP-3 inhibitory activities of four previously described, quinonebased, dual-specificity phosphatase inhibitors, that is, NSC 672121, NSC 95397, DA-3003-1 (NSC 663284), and JUN-1111. All compounds induced formation of reactive oxygen species in mammalian cells, but only one (NSC 95397) inhibited cellular MKP-1 and MKP-3 with an IC 50 of 13 Mmol/L. Chemical induction of MKP-1 by dexamethasone protected cells from paclitaxel-induced apoptosis but had no effect on NSC 95397. NSC 95397 phenocopied the effects of MKP-1 small inhibitory RNA by reversing the cytoprotective effects of dexamethasone in paclitaxeltreated cells. Isobologram analysis revealed synergism between paclitaxel and NSC 95397 only in the presence of dexamethasone. The data show the power of a welldefined cellular assay for identifying cell-active inhibitors of MKPs and support the hypothesis that small-molecule inhibitors of MKP-1 may be useful as antineoplastic agents under conditions of high MKP-1 expression. [Mol Cancer Ther 2008;7(2):330 -40]

SUMMARYA variety of immune cell therapies proposed for use in the treatment of cancer, including both autologus cells (Lymphokine Activated Killer, Cytokine Induced Killer) or cell lines (TALL-104, NK-92), rely on recognition of NKG2D ligands on malignant cells for targeting. These ligands, such as MICA and MICB in humans are stress response ligands and are commonly, but not ubiquitously expressed within tumors. Several tumor escape mechanisms have been reported, including ligand down regulation and internalization, or proteolytic cleavage and shedding of their exposed portions (releasing soluble MICA and MICB; sMICA, sMICB). Therefore, an ability to pre-screen patients for the level of tumor cell surface expression and shedding of these ligands would prevent needless treatment of patients that are unable to respond, while targeted pretreatment of patients to increase surface expression and/ or block shedding would enhance the subsequent effectiveness of these therapies. Here we report that serum tests of sMICA and sMICB in conjunction with tumor measurements might be used to determine rates of shedding from a tumor and that treatment with a selected combination of histone deacetylase inhibitors (to upregulate cell surface MICA/B in some tumors), and metalloproteinase inhibitors (to block MICA/B shedding in others) can be incorporated to regulate cell surface MICA/B levels prior to immune cell therapy, significantly enhancing their effectiveness (either used alone or as carrier vehicles for oncolytic viruses). Ultimately pre-screening patients undergoing such immune cell therapies might be used to personalize cancer treatment regimens based on the NKG2D-ligand status of the tumor.