Jeffery S. Russell

The irradiated tumor microenvironment: role of tumor-associated macrophages in vascular recovery

Radiotherapy is an important modality used in the treatment of more than 50% of cancer patients in the US. However, despite sophisticated techniques for radiation delivery as well as the combination of radiation with chemotherapy, tumors can recur. Thus, any method of improving the local control of the primary tumor by radiotherapy would produce a major improvement in the curability of cancer patients. One of the challenges in the field is to understand how the tumor vasculature can regrow after radiation in order to support tumor recurrence, as it is unlikely that any of the endothelial cells within the tumor could survive the doses given in a typical radiotherapy regimen. There is now considerable evidence from both preclinical and clinical studies that the tumor vasculature can be restored following radiotherapy from an influx of circulating cells consisting primarily of bone marrow derived monocytes and macrophages. The radiation-induced influx of bone marrow derived cells (BMDCs) into tumors can be prevented through the blockade of various cytokine pathways and such strategies can inhibit tumor recurrence. However, the post-radiation interactions between surviving tumor cells, recruited immune cells, and the remaining stroma remain poorly defined. While prior studies have described the monocyte/macrophage inflammatory response within normal tissues and in the tumor microenvironment, less is known about this response with respect to a tumor after radiation therapy. The goal of this review is to summarize existing research studies to provide an understanding of how the myelomonocytic lineage may influence vascular recovery within the irradiated tumor microenvironment.

Circulating mouse Flk1+/c-Kit+/CD45- cells function as endothelial progenitors cells (EPCs) and stimulate the growth of human tumor xenografts.

BackgroundEndothelial progenitor cells (EPCs) have been demonstrated to have stem-cell like as well as mature endothelial functions. However, controversy remains as to their origins, immunophenotypic markings, and contribution to the tumor vascular network and tumor survival.MethodsFlow cytometric analysis and sorting was used to isolate Flk-1+/c-Kit+/CD45- cells. Matrigel and methycellulose assays, flow cytometry, and gene array analyses were performed to characterize several murine EPC cell populations. Human tumor xenografts were used to evaluate the impact of EPCs on tumor growth and vascular development.ResultsFlk-1+/c-Kit+/CD45- cells were present at low levels in most murine organs with the highest levels in adipose, aorta/vena cava, and lung tissues. Flk-1+/c-Kit+/CD45- cells demonstrated stem cell qualities through colony forming assays and mature endothelial function by expression of CD31, uptake of acLDL, and vascular structure formation in matrigel. High passage EPCs grown in vitro became more differentiated and lost stem-cell markers. EPCs were found to have hemangioblastic properties as demonstrated by the ability to rescue mice given whole body radiation. Systemic injection of EPCs increased the growth of human xenograft tumors and vessel density.ConclusionsFlk-1+/C-Kit+/CD45- cells function as endothelial progenitor cells. EPCs are resident in most murine tissue types and localize to human tumor xenografts. Furthermore, the EPC population demonstrates stem-cell and mature endothelial functions and promoted the growth of tumors through enhanced vascular network formation. Given the involvement of EPCs in tumor development, this unique host-derived population may be an additional target to consider for anti-neoplastic therapy.

The Use of Epidermal Growth Factor Receptor Monoclonal Antibodies in Squamous Cell Carcinoma of the Head and Neck

Targeting of the EGF receptor (EGFR) has become a standard of care in several tumor types. In squamous cell carcinoma of the head and neck, monoclonal antibodies directed against EGFR have become a regular component of therapy for curative as well as palliative treatment strategies. These agents have anti-tumor efficacy as a single modality and have demonstrated synergistic tumor killing when combined with radiation and/or chemotherapy. While cetuximab has been the primary anti-EGFR monoclonal antibody used in the US, variant anti-EGFR monoclonal antibodies have been used in several clinical studies and shown benefit with improved toxicity profiles. Next generation anti-EGFR monoclonal antibodies may demonstrate multi-target epitope recognition, enhanced immune cell stimulation, or conjugation with radioisotopes in order to improve clinical outcomes. Identification of the specific patient subset that would optimally benefit from anti-EGFR monoclonal antibodies remains an elusive goal.

Efficacy and Safety of First-line Avelumab Treatment in Patients With Stage IV Metastatic Merkel Cell Carcinoma: A Preplanned Interim Analysis of a Clinical Trial

Importance Merkel cell carcinoma (MCC) is an aggressive skin cancer that is associated with poor survival outcomes in patients with distant metastatic disease. Results of part A of the JAVELIN Merkel 200 trial (avelumab in patients with Merkel cell carcinoma) showed that avelumab, an anti–programmed cell death ligand 1 (PD-L1) antibody, demonstrated efficacy in second-line or later treatment of patients with metastatic MCC (mMCC). Objective To evaluate the efficacy and safety of avelumab as first-line treatment for patients with distant mMCC. Design, Setting, and Participants JAVELIN Merkel 200 part B is an international, multicenter, single-arm, open-label clinical trial of first-line avelumab monotherapy. Eligible patients were adults with mMCC who had not received prior systemic treatment for metastatic disease. Patients were not selected for PD-L1 expression or Merkel cell polyomavirus status. Data were collected from April 15, 2016, to March 24, 2017, and enrollment is ongoing. Interventions Patients received avelumab, 10 mg/kg, by 1-hour intravenous infusion every 2 weeks until confirmed disease progression, unacceptable toxic effects, or withdrawal occurred. Main Outcomes and Measures Tumor status was assessed every 6 weeks and evaluated by independent review committee per Response Evaluation Criteria in Solid Tumors version 1.1. The primary end point was durable response, defined as an objective response with a duration of at least 6 months. Secondary end points include best overall response, duration of response, progression-free survival, safety, and tolerability. Results As of March 24, 2017, 39 patients were enrolled (30 men and 9 women; median age, 75 years [range, 47-88 years]), with a median follow-up of 5.1 months (range, 0.3-11.3 months). In a preplanned analysis, efficacy was assessed in 29 patients with at least 3 months of follow-up; the confirmed objective response rate was 62.1% (95% CI, 42.3%-79.3%), with 14 of 18 responses (77.8%) ongoing at the time of analysis. In responding patients, the estimated proportion with duration of response of at least 3 months was 93% (95% CI, 61%-99%); duration of response of at least 6 months, 83% (95% CI, 46%-96%). First-line avelumab treatment was generally well tolerated, and no treatment-related deaths or grade 4 adverse events occurred. Conclusions and Relevance High rates of response to first-line avelumab therapy in patients with distant mMCC build on previously reported antitumor activity after second-line or later treatment, and maturing progression-free survival data suggest that responses are durable. These data further support avelumab’s approval in the United States and European Union and use as a standard-of-care treatment for mMCC. Trial Registration clinicaltrials.gov Identifier: NCT02155647

Abstract CT079: Durable responses to avelumab (anti-PD-L1) in patients with Merkel cell carcinoma progressed after chemotherapy: 1-year efficacy update

Background: Merkel cell carcinoma (MCC), a rare, aggressive skin cancer, is a chemosensitive disease, but responses are seldom durable. Avelumab is a fully human anti-PD-L1 monoclonal antibody. In a phase 2 trial of avelumab in patients with previously treated metastatic MCC (mMCC), the objective response rate (ORR) after ≥6 months of follow-up was 31.8%, including complete response (CR) in 9.1%, the estimated proportion with duration of response (DOR) ≥6 months was 92%, and the 6-month progression-free survival (PFS) rate was 40% (95% CI 29-50) (Kaufman et al., Lancet Oncol 2016). Here we present updated efficacy data with ≥1 year of follow-up in all patients. Methods: Patients with distant mMCC and prior progression on chemotherapy received avelumab 10 mg/kg IV Q2W until confirmed progression, unacceptable toxicity, or withdrawal. Tumors were assessed every 6 weeks (RECIST v1.1 by independent review). ORR, DOR, PFS, and overall survival (OS) were evaluated. Time-to-event endpoints were analyzed using Kaplan-Meier methodology. Safety data were not analyzed for this update. Results: Patients with mMCC (N=88) were treated with avelumab. Median age was 72.5 years (range 33-88), and 53% had visceral disease. As of Sep 3, 2016, median follow-up was 16.4 months (range 12.0-25.3), and treatment was ongoing in 22% (n=19); main reasons for discontinuations were disease progression (n=44; 50%), death (n=7; 8%), adverse event (n=7; 8%), or withdrawal (n=4; 5%). ORR was 33.0% (95% CI 23.3-43.8) with 10 (11.4%) CRs and 19 (21.6%) partial responses, including 1 new CR and 1 patient improving from PR to CR since the 6-month analysis. The 6-month durable response rate was 30.6% (95% CI 20.9-40.3). Median DOR has not been reached (range 2.8-23.3+ months; 95% CI 18.0-not estimable), and responses were ongoing in 21/29 patients (72.4%) at the time of analysis. The estimated proportion of responders with ≥1-year duration of response was 74% (95% CI 53-87). Estimated 1-year PFS rate was 30% (95% CI 21-41) and 1-year OS rate was 52% (95% CI 41-62). Median OS was 12.9 months (95% CI 7.5-not estimable). Conclusion: In longer-term follow-up from this study of avelumab in patients with distant metastatic MCC progressed after chemotherapy, the majority of responses were durable beyond 1 year and 2 new CRs were reported. Maturing PFS and OS data suggest long-term benefit in a proportion of patients. Clinical trial information: NCT02155647. Citation Format: Howard L. Kaufman, Jeffery S. Russell, Omid Hamid, Shailender Bhatia, Patrick Terheyden, Sandra P. D’Angelo, Kent C. Shih, Celeste Lebbe, Michele Milella, Isaac Brownell, Karl D. Lewis, Jochen H. Lorch, Anja von Heydebreck, Lisa Mahnke, Paul Nghiem. Durable responses to avelumab (anti-PD-L1) in patients with Merkel cell carcinoma progressed after chemotherapy: 1-year efficacy update [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT079. doi:10.1158/1538-7445.AM2017-CT079

Abstract 383: Investigation of endothelial progenitor cells as mediators of radiation resistance.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Background: Radiation therapy delivered to locally advanced cancers is likely to kill most, if not all, of the endothelial cells lining the walls of blood vessels within and immediately surrounding the tumor. For the tumor to recur following radiation therapy, new vasculature must form either through angiogenesis, the sprouting of vessels from existing vessels, or by vasculogenesis, the seeding of blood vessels from circulating endothelial progenitor cells (EPCs). Because radiation is sufficient to abrogate local angiogenesis, we hypothesize that EPCs and other proangiogenic cells are recruited to tumors after radiation therapy, resulting in the recovery of the vascular network, and eventually, in the regrowth of the tumor. Methods: Nude mouse tissues and human U251 glioma xenografts were harvested, homogenized, and evaluated by flow cytometry for the EPC markers: CD117+, Flk-1+, and CD45-. EPCs were sorted and grown as primary cultures and examined for mature endothelial function using immunofluorescence for CD31 and acLDL uptake. Additionally, cultured EPCs were tested for stem cell and endothelial characteristics using tube formation and colony-forming assays. Finally, tumors and normal tissues were collected at various time points after radiation therapy and evaluated for % EPC populations present. Results: The highest concentrations of EPCs were in adipose tissue (7%), lungs (0.5%), aorta (0.5%) and glioma xenografts (0.5%) with other tissues demonstrating minimal EPC populations. EPCs could be isolated and grown as primary cultures where they demonstrated expression of the endothelial marker CD31, had endothelial function by uptake of acLDL, were able to form capillary networks on matrigel, and formed cell clusters in a colony-forming assay. Time course evaluation of EPC populations in tumors and normal lung tissue did not show an increase in EPCs at any time point after 10 Gy; however, there was approximately a 2-fold increase in EPCs present in peripheral blood at 7 days after irradiation. Additionally, an increased population of CD11b+ cells was present within the tumor 2-3 weeks after radiation therapy. Conclusions: EPCs (CD117+/Flk-1+/CD45-) were present in a variety of normal murine tissues and U251 human Glioma xenografts. While EPC populations did not increase within tumors after radiation, there was a consistent elevation of EPCs in peripheral blood during the first week after treatment with radiation. Furthermore, we were able to demonstrate a late influx of potentially proangiogenic CD11b+ monocytes within irradiated tumors. We are currently examining whether the EPC populations in irradiated tumors were originally present prior to radiation or were replaced by the radiation-induced EPC populations found in the peripheral blood. Finally, we are examining whether EPCs directly promote tumor initiation, tumor growth, and post-irradiation tumor recovery. Citation Format: Jeffery S. Russell, J. Martin Brown. Investigation of endothelial progenitor cells as mediators of radiation resistance. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 383. doi:10.1158/1538-7445.AM2013-383