Faculty Bibliography

BACKGROUND:Rituximab combined with chemotherapy has improved the survival of previously untreated patients with follicular lymphoma (FL). Nevertheless, many patients neither want nor can tolerate chemotherapy, leading to interest in biological approaches. Epratuzumab is a humanized anti-CD22 monoclonal antibody with efficacy in relapsed FL. Because both rituximab and epratuzumab have single-agent activity in FL, the antibody combination was evaluated as initial treatment of patients with FL. METHODS:Fifty-nine untreated patients with FL received epratuzumab 360 mg/m2 with rituximab 375 mg/m2 weekly for 4 induction doses. This combination was continued as extended induction in weeks 12, 20, 28, and 36. Response assessed by computed tomography was correlated with clinical risk factors, [18F]fluorodeoxyglucose positron emission tomography findings at week 3, Fcγ polymorphisms, immunohistochemical markers, and statin use. RESULTS:Therapy was well-tolerated, with toxicities similar to expected with rituximab monotherapy. Fifty-two (88.2%) evaluable patients responded, including 25 complete responses (42.4%) and 27 partial responses (45.8%). At 3 years follow-up, 60% of patients remain in remission. Follicular Lymphoma International Prognostic Index (FLIPI) risk strongly predicted progression-free survival (P = .022). CONCLUSIONS:The high response rate and prolonged time to progression observed with this antibody combination are comparable to those observed after standard chemoimmunotherapies and further support the development of biologic, nonchemotherapeutic approaches for these patients.

UNLABELLED:Although aberrant DNA methylation patterning is a hallmark of cancer, the relevance of targeting DNA methyltransferases (DNMT) remains unclear for most tumors. In diffuse large B-cell lymphoma (DLBCL) we observed that chemoresistance is associated with aberrant DNA methylation programming. Prolonged exposure to low-dose DNMT inhibitors (DNMTI) reprogrammed chemoresistant cells to become doxorubicin sensitive without major toxicity in vivo. Nine genes were recurrently hypermethylated in chemoresistant DLBCL. Of these, SMAD1 was a critical contributor, and reactivation was required for chemosensitization. A phase I clinical study was conducted evaluating azacitidine priming followed by standard chemoimmunotherapy in high-risk patients newly diagnosed with DLBCL. The combination was well tolerated and yielded a high rate of complete remission. Pre- and post-azacitidine treatment biopsies confirmed SMAD1 demethylation and chemosensitization, delineating a personalized strategy for the clinical use of DNMTIs. SIGNIFICANCE/CONCLUSIONS:The problem of chemoresistant DLBCL remains the most urgent challenge in the clinical management of patients with this disease. We describe a mechanism-based approach toward the rational translation of DNMTIs for the treatment of high-risk DLBCL.

Pericytes and vascular smooth muscle cells (VSMCs), which are recruited to developing blood vessels by platelet-derived growth factor BB, support endothelial cell survival and vascular stability. Here, we report that imatinib, a tyrosine kinase inhibitor of platelet-derived growth factor receptor β (PDGFRβ), impaired growth of lymphoma in both human xenograft and murine allograft models. Lymphoma cells themselves neither expressed PDGFRβ nor were growth inhibited by imatinib. Tumor growth inhibition was associated with decreased microvascular density and increased vascular leakage. In vivo, imatinib induced apoptosis of tumor-associated PDGFRβ(+) pericytes and loss of perivascular integrity. In vitro, imatinib inhibited PDGFRβ(+) VSMC proliferation and PDGF-BB signaling, whereas small interfering RNA knockdown of PDGFRβ in pericytes protected them against imatinib-mediated growth inhibition. Fluorescence-activated cell sorter analysis of tumor tissue revealed depletion of pericytes, endothelial cells, and their progenitors following imatinib treatment. Compared with imatinib, treatment with an anti-PDGFRβ monoclonal antibody partially inhibited lymphoma growth. Last, microarray analysis (Gene Expression Omnibus database accession number GSE30752) of PDGFRβ(+) VSMCs following imatinib treatment showed down-regulation of genes implicated in vascular cell proliferation, survival, and assembly, including those representing multiple pathways downstream of PDGFRβ. Taken together, these data indicate that PDGFRβ(+) pericytes may represent a novel, nonendothelial, antiangiogenic target for lymphoma therapy.

Phosphatidylinositol-3-kinase (PI3K) signaling is constitutive in most human cancers. Selective inhibition of PI3Kδ (p110δ) by GS-1101 has emerged as a promising therapy in chronic lymphocytic leukemia and indolent lymphomas. In aggressive non-Hodgkin lymphomas such as mantle cell lymphoma (MCL), however, efficacy has been observed, but the extent and duration of tumor control is modest. To determine if tumor killing by GS-1101 is cell cycle-dependent, we show in primary MCL cells by whole-transcriptome sequencing that, despite aberrant expression and recurrent mutations in Cyclin D1, mutations are rare in coding regions of CDK4, RB1 and other genes that control G1-S cell cycle progression or PI3K/AKT signaling. PI3Kδ is the predominant PI3K catalytic subunit expressed, and inhibition by GS-1101 transiently inhibits AKT phosphorylation but not proliferation in MCL cells. Induction of prolonged early G1-arrest (pG1) by selective inhibition of CDK4/CDK6 with PD 0332991 amplifies and sustains PI3Kδ inhibition, which leads to robust apoptosis. Accordingly, inhibition of PI3Kδ induces apoptosis of primary MCL tumor cells once they have ceased to cycle ex vivo, and this killing is enhanced by PD 0332991 inhibition of CDK4/CDK6. PIK3IP1, a negative PI3K regulator, appears to mediate pG1 sensitization to PI3K inhibition; it is markedly reduced in MCL tumor cells compared with normal peripheral B cells, profoundly induced in pG1 and required for pG1 sensitization to GS-1101. Thus, the magnitude and duration of PI3K inhibition and tumor killing by GS-1101 is pG1-dependent, suggesting induction of pG1 by CDK4/CDK6 inhibition as a strategy to sensitize proliferating lymphoma cells to PI3K inhibition.

Diffuse large B-cell lymphoma, the most common lymphoma subtype, is curable in the majority of patients. However, one of the greatest unmet needs in lymphoma treatment remains novel approaches to prevent relapsed or refractory disease. Genomic profiling has provided important prognostic information that is being used in the development of novel therapeutic strategies currently in clinical trials. It is clear, however, that epigenetic alterations provide an additional series of targets that can be pharmacologically modified and offer great potential to improving patient outcomes. Greater understanding of this area is providing important new insights that are now being explored in the clinical setting. Demethylating agents and drugs that disrupt histone modifiers are in early clinical trials with promising results, and other approaches targeting epigenetic pathways are in active preclinical and early clinical development.

Patients with relapsed or refractory diffuse large B-cell lymphoma may experience extended survival with second-line chemotherapy and autologous stem cell transplant (ASCT). Since a major determinant of outcome after ASCT is responsiveness to second-line therapy, the development of more effective second-line treatments is desirable. We investigated the addition of bortezomib to rituximab, dexamethasone, ifosfamide, cisplatin and etoposide (VIPER). Fifteen patients were enrolled, of whom seven were refractory to first-line chemotherapy and only three had maintained first response for 1 year. Nine (60%) patients achieved objective responses, of which three (20%) were IWC-PET (International Workshop Criteria positron emission tomography) complete responses. Median progression-free survival was 3 months, and median overall survival was 10 months. At a median follow-up of 26 months, five patients (33%) remained alive. Treatment was well tolerated with no unexpected toxicity. Although response rates did not meet predefined criteria, activity was at least comparable to other second-line approaches despite a poor-prognosis patient population.

Mantle cell lymphoma (MCL) carries an unfavorable prognosis and requires new treatment strategies. The associated t(11:14) translocation results in enhanced cyclin D1 expression and cyclin D1-dependent kinase activity to promote cell-cycle progression. A pharmacodynamic study of the selective CDK4/6 inhibitor PD0332991 was conducted in 17 patients with relapsed disease, using 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) and 3-deoxy-3[(18)F]fluorothymidine (FLT) positron emission tomography (PET) to study tumor metabolism and proliferation, respectively, in concert with pre- and on-treatment lymph node biopsies to assess retinoblastoma protein (Rb) phosphorylation and markers of proliferation and apoptosis. Substantial reductions in the summed FLT-PET maximal standard uptake value (SUV(max)), as well as in Rb phosphorylation and Ki-67 expression, occurred after 3 weeks in most patients, with significant correlations among these end points. Five patients achieved progression-free survival time of > 1 year (range, 14.9-30.1+ months), with 1 complete and 2 partial responses (18% objective response rate; 90% confidence interval, 5%-40%). These patients demonstrated > 70%, > 90%, and ≥ 87.5% reductions in summed FLT SUV(max) and expression of phospho-Rb and Ki67, respectively, parameters necessary but not sufficient for long-term disease control. The results of the present study confirm CDK4/6 inhibition by PD0332991 at a well-tolerated dose and schedule and suggest clinical benefit in a subset of MCL patients. This study is registered at www.clinicaltrials.gov under identifier NCT00420056.

BACKGROUND:Metronomic therapy is the application of continuous, low dose chemotherapy. The doses of chemotherapy are usually not sufficient to destroy neoplastic cells, but impact the milieu, particularly angiogenesis. OBJECTIVE:To determine if the oral PEP-C regimen, consisting of prednisone 20 mgm, etoposide 50 mgm, procarbazine 50 mgm, and cyclophosphamide 50 mgm given in either a daily, alternate day, or fractionated basis, is effective in a variety of lymphomas. METHODS:One hundred twenty two patients were studied although the majority had low grade or mantle cell lymphoma. All had received at least two or more prior therapies. RESULTS:Overall, 75% achieved an objective response (OR) with 38% complete responses (CRs) or CRs unconfirmed, and 37% partial responses. ORs were achieved in mantle cell (85%), follicular (88%), marginal zone (71%), and small lymphocytic (67%) lymphomas. Chemosensitive disease was more responsive. Toxicity was minimal. CONCLUSION/CONCLUSIONS:The PEP-C regimen is an easily administered highly effective treatment for heavily pretreated mantle cell and low grade lymphomas.