Andrew J. Wagner

Multicenter Phase II Trial of Sunitinib in the Treatment of Nongastrointestinal Stromal Tumor Sarcomas

PURPOSE To evaluate the potential benefit of continuous daily dosing sunitinib in patients with advanced nongastrointestinal stromal tumor (GIST) sarcomas. PATIENTS AND METHODS A total of 53 patients with advanced non-GIST soft tissue sarcomas received sunitinib 37.5 mg daily. Primary end point was Response Evaluation Criteria in Solid Tumors defined response. Secondary end points were stable disease at 16 and 24 weeks. [(18)F]-fluorodeoxyglucose positron emission tomography was performed on a subset of 24 patients at baseline and after 10 to 14 days of therapy. Results Forty-eight patients were eligible for response. One patient (desmoplastic round cell tumor [DSRCT]) achieved a confirmed partial response (PR) and remained on study for 56 weeks. Ten patients (20%) achieved stable disease for at least 16 weeks. Metabolic PR was seen in 10 (47%) of 21 of patients. Metabolic stable disease was seen in 11 (52%) of 21. There were no unexpected toxicities observed. CONCLUSION Sunitinib demonstrated notable evidence of metabolic response in several patients with non-GIST sarcoma. The relevance of disease control observed in subtypes with an indolent natural history is unknown, however, the durable disease control observed in DSRCT, solitary fibrous tumor, and giant cell tumor of bone suggests that future evaluation of sunitinib in these subtypes may be warranted.

Myc-mediated apoptosis is blocked by ectopic expression of Bcl-2.

The product of the c-myc proto-oncogene is an important positive regulator of cell growth and proliferation. Recently, c-Myc has also been demonstrated to be a potent inducer of apoptosis when expressed in the absence of serum or growth factors. To further examine Myc-induced apoptosis, we coexpressed the proto-oncogene bcl2, which has been shown to block apoptosis in other systems, with c-myc in serum-deprived Rat 1a fibroblasts. Here we report that ectopic expression of bcl2 specifically blocks apoptosis induced by constitutive c-myc expression. Constitutive c-myc expression in serum-deprived Rat 1a cells caused a > 15-fold increase in the number of dead cells, accompanied by DNA fragmentation. However, coexpression of bcl2 with c-myc in these cells led to a 10-fold increase in the number of live cells and a significant decrease in DNA fragmentation. Thus, Bcl-2 effectively inhibits Myc-induced apoptosis in serum-deprived Rat 1a fibroblasts without blocking entry into the cell cycle. These results imply that apoptosis serves as a protective mechanism to prevent tumorigenicity elicited by deregulated Myc expression. This protective mechanism is abrogated, however, by Bcl-2 and therefore may explain the synergism between Myc and Bcl-2 observed in certain tumor cells.

Clinical Activity of mTOR Inhibition With Sirolimus in Malignant Perivascular Epithelioid Cell Tumors: Targeting the Pathogenic Activation of mTORC1 in Tumors

PURPOSE Perivascular epithelioid cell tumors (PEComas) represent a family of mesenchymal neoplasms, mechanistically linked through activation of the mTOR signaling pathway. There is no known effective therapy for PEComa, and the molecular pathophysiology of aberrant mTOR signaling provided us with a scientific rationale to target this pathway therapeutically. On this mechanistic basis, we treated three consecutive patients with metastatic PEComa with an oral mTOR inhibitor, sirolimus. PATIENTS AND METHODS Patients with advanced PEComa were treated with sirolimus and consented to retrospective collection of data from their medical records and analysis of archival tumor specimens. Tumor response was determined by computed tomography scans obtained at the clinical discretion of the treating physicians. Tumors were assessed for immunohistochemical evidence of mTORC1 activation and genetic evidence of alterations in TSC1 and TSC2. Results Radiographic responses to sirolimus were observed in all patients. PEComas demonstrated loss of TSC2 protein expression and evidence of baseline mTORC1 activation. Homozygous loss of TSC1 was identified in one PEComa. CONCLUSION Inhibition of mTORC1, pathologically activated by loss of the TSC1/TSC2 tumor suppressor complex, is a rational mechanistic target for therapy in PEComas. The clinical activity of sirolimus in PEComa additionally strengthens the pathobiologic similarities linking PEComas to other neoplasms related to the tuberous sclerosis complex.

Efficacy and Safety of Regorafenib in Patients With Metastatic and/or Unresectable GI Stromal Tumor After Failure of Imatinib and Sunitinib: A Multicenter Phase II Trial

PURPOSE Metastatic GI stromal tumor (GIST) is a life-threatening disease with no therapy of proven efficacy after failure of imatinib and sunitinib. Regorafenib is a structurally unique inhibitor of multiple cancer-associated kinases, including KIT and platelet-derived growth factor receptor (PDGFR), with broad-spectrum anticancer activity in preclinical and early-phase trials. Because KIT and PDGFR-α remain drivers of GIST after resistance to imatinib and sunitinib, we performed a multicenter single-stage phase II trial of regorafenib in patients with advanced GIST after failure of at least imatinib and sunitinib. PATIENTS AND METHODS Patients received regorafenib orally, 160 mg daily, on days 1 to 21 of a 28-day cycle. Disease assessment was performed every two cycles per RECIST 1.1. Primary end point was clinical benefit rate (CBR), defined as objective responses (ie, complete or partial response [PR] as well as stable disease [SD] ≥ 16 weeks). Serial tumor biopsies were obtained from consenting patients whenever possible. RESULTS From February to December 2010, 34 patients were enrolled at four US centers. As of July 28, 2011, 33 patients had received at least two cycles of regorafenib (range, two to 17 cycles). CBR was 79% (95% CI, 61% to 91%). Four patients achieved PR, and 22 exhibited SD ≥ 16 weeks. Median progression-free survival was 10.0 months. The most common grade 3 toxicities were hypertension and hand-foot-skin reaction. CONCLUSION Regorafenib has significant activity in patients with advanced GIST after failure of both imatinib and sunitinib. A phase III trial of regorafenib versus placebo is ongoing to define more fully the safety and efficacy of regorafenib in this setting.

Combination mTOR and IGF-1R Inhibition: Phase I Trial of Everolimus and Figitumumab in Patients with Advanced Sarcomas and Other Solid Tumors

Purpose: Preclinical models demonstrate synergistic antitumor activity with combination blockade of mTOR and IGF-1R signaling. We aimed to determine the safety, tolerability, and recommended phase II dose (RP2D) of the combination of figitumumab, a fully human IgG2 anti-insulin-like growth factor-1 receptor (IGF-1R) monoclonal antibody (Pfizer) and the mTOR inhibitor, everolimus (Novartis). Pharmacokinetics and preliminary antitumor effects of the combination were evaluated. Experimental Design: Phase I trial in patients with advanced sarcomas and other solid tumors. Initial cohort combined full phase 2 dose figitumumab (20 mg/kg IV every 21 days) with full dose everolimus (10 mg orally once daily). Intercohort dose de-escalation was planned for unacceptable toxicities. Dose modifications were allowed beyond cycle 1. Results: No DLTs were observed in the initial cohort during cycle one, therefore full dose figitumumab and everolimus was declared the RP2D. In total, 21 patients were enrolled on study. Most toxicities were grade 1 or 2, and were similar to reported toxicities of the single agents. Mucositis was the most frequently observed grade 3 toxicity. Median time on study was 104 days (range 17–300). Of 18 patients evaluable for response, best response was partial response in 1 patient with malignant solitary fibrous tumor and, stable disease in 15 patients. There were no apparent pharmacokinetic interactions between everolimus and figitumumab. Conclusions: Combination figitumumab plus everolimus at full doses appears safe and well tolerated with no unexpected toxicities. Dose reductions in everolimus may be required after prolonged drug administration. This regimen exhibits interesting antitumor activity warranting further investigation. Clin Cancer Res; 17(4); 1–9. ©2010 AACR.

Induction of cell cycle progression and acceleration of apoptosis are two separable functions of c-Myc: transrepression correlates with acceleration of apoptosis.

ABSTRACT Analysis of amino-terminus mutants of c-Myc has allowed a systematic study of the interrelationship between Mycs ability to regulate transcription and its apoptotic, proliferative, and transforming functions. First, we have found that c-Myc-accelerated apoptosis does not directly correlate with its ability to transactivate transcription using the endogenous ornithine decarboxylase (ODC) gene as readout for transactivation. Furthermore, deletion of the conserved c-Myc box I domain implicated in transactivation does not inhibit apoptosis. Second, the ability of c-Myc to repress transcription, using the gadd45 gene as a readout, correlates with its ability to accelerate apoptosis. A conserved region of c-Myc implicated in mediating transrepression is absolutely required for c-Myc-accelerated apoptosis. Third, a lymphoma-derived Thr58Ala mutation diminishes c-Myc-accelerated apoptosis through a decreased ability to induce the release of cytochrome c from mitochondria. This mutation in a potential phosphorylation site does not affect cell cycle progression, providing genetic evidence that induction of cell cycle progression and acceleration of apoptosis are two separable functions of c-Myc. Finally, we show that the increased ability of Thr58Ala mutant to elicit cellular transformation correlates with its diminished ability to accelerate apoptosis. Bcl-2 overexpression blocked and the lymphoma-associated Thr58Ala mutation decreased c-Myc-accelerated apoptosis, and both led to a significant increase in the ability of Rat1a cells to form colonies in soft agar. This enhanced transformation was greater in soft agar containing a low concentration of serum, suggesting that protection from apoptosis is a mechanism contributing to the increased ability of these cells to proliferate in suspension. Thus, we show here for the first time that, in addition to mutations in complementary antiapoptotic genes, c-Myc itself can acquire mutations that potentiate neoplastic transformation by affecting apoptosis independently of cell cycle progression.

Structure-Guided Blockade of CSF1R Kinase in Tenosynovial Giant-Cell Tumor

BACKGROUND Expression of the colony-stimulating factor 1 (CSF1) gene is elevated in most tenosynovial giant-cell tumors. This observation has led to the discovery and clinical development of therapy targeting the CSF1 receptor (CSF1R). METHODS Using x-ray co-crystallography to guide our drug-discovery research, we generated a potent, selective CSF1R inhibitor, PLX3397, that traps the kinase in the autoinhibited conformation. We then conducted a multicenter, phase 1 trial in two parts to analyze this compound. In the first part, we evaluated escalations in the dose of PLX3397 that was administered orally in patients with solid tumors (dose-escalation study). In the second part, we evaluated PLX3397 at the chosen phase 2 dose in an extension cohort of patients with tenosynovial giant-cell tumors (extension study). Pharmacokinetic and tumor responses in the enrolled patients were assessed, and CSF1 in situ hybridization was performed to confirm the mechanism of action of PLX3397 and that the pattern of CSF1 expression was consistent with the pathological features of tenosynovial giant-cell tumor. RESULTS A total of 41 patients were enrolled in the dose-escalation study, and an additional 23 patients were enrolled in the extension study. The chosen phase 2 dose of PLX3397 was 1000 mg per day. In the extension study, 12 patients with tenosynovial giant-cell tumors had a partial response and 7 patients had stable disease. Responses usually occurred within the first 4 months of treatment, and the median duration of response exceeded 8 months. The most common adverse events included fatigue, change in hair color, nausea, dysgeusia, and periorbital edema; adverse events rarely led to discontinuation of treatment. CONCLUSIONS Treatment of tenosynovial giant-cell tumors with PLX3397 resulted in a prolonged regression in tumor volume in most patients. (Funded by Plexxikon; ClinicalTrials.gov number, NCT01004861.).

Efficacy of imatinib mesylate for the treatment of locally advanced and/or metastatic tenosynovial giant cell tumor/pigmented villonodular synovitis

Pigmented villonodular synovitis (PVNS) (also known as diffuse‐type giant cell tumor) and tenosynovial giant cell tumors (TGCT) are rare, usually benign neoplasms that affect the synovium and tendon sheaths in young adults. These tumors are driven by the overexpression of colony stimulating factor‐1 (CSF1). CSF1 is expressed by a minority of tumor cells, which, in turn attract non‐neoplastic inflammatory cells that express CSF1 receptor (CSF1R) through a paracrine effect.

Tivantinib (ARQ 197), a selective inhibitor of MET, in patients with microphthalmia transcription factor-associated tumors: results of a multicenter phase 2 trial.

Microphthalmia transcription factor (MITF)‐associated (MiT) tumors are a family of rare malignancies, including alveolar soft part sarcoma (ASPS), clear cell sarcoma (CCS), and translocation‐associated renal cell carcinoma (tRCC) that have dysregulated expression of oncogenic MITF family proteins. The MET receptor tyrosine kinase gene is transcriptionally activated by MITF family proteins, making MET a potential therapeutic target for MiT tumors. This study assessed the activity of tivantinib (ARQ 197), a selective MET inhibitor, in patients with MiT‐associated tumors.

Sequence-specific transcriptional activation by Myc and repression by Max

The c-Myc oncoprotein, which is required for cellular proliferation, resembles in its structure a growing number of transcription factors. However, the mechanism of its action in vivo is not yet clear. The discovery of the specific cognate DNA-binding site for Myc and its specific heterodimerization partner, Max, enabled the use of direct experiments to elucidate how Myc functions in vivo and how this function is modulated by Max. Here we demonstrate that exogenously expressed Myc is capable of activating transcription in vivo through its specific DNA-binding site. Moreover, transcriptional activation by Myc is dependent on the basic region, the integrity of the helix-loop-helix and leucine zipper dimerization motifs located in the carboxy-terminal portion of the protein, and the regions in the amino terminus conserved among Myc family proteins. In contrast to Myc, exogenously expressed Max elicited transcriptional repression and blocked transcriptional activation by Myc through the same DNA-binding site. Our results suggest a functional antagonism between Myc and Max which is mediated by their relative levels in the cells. A model for the activity of Myc and Max in vivo is presented.