Prospects and challenges for the development of new therapies for Ewing sarcoma

Abstract

The Ewing sarcoma family of tumors or Ewing sarcoma (ES) is the second most common malignant bone tumor of childhood. The prognosis for localized Ewing sarcoma has improved through the development of intense multimodal therapy over the past several decades. Unfortunately, patients with recurrent or metastatic disease continue to have a poor prognosis. Therefore, a number of complementary approaches are being developed in both the preclinical and clinical arenas to improve these outcomes. In this review, we will discuss efforts to directly target the biologic drivers of this disease and relate these efforts to the experience with several different agents both in the clinic and under development. We will review the data for compounds that have shown excellent activity in the clinic, such as the camptothecins, and summarize the biological data that supports this activity. In addition, we will review the clinical experience with IGF1 targeted agents, ET-743 and epigenetically targeted therapies, the substantial amount of literature that supports their activity in Ewing sarcoma and the challenges remaining translating these therapies to the clinic. Finally, we will highlight recent work aimed at directly targeting the EWS-FLI1 transcription factor with small molecules in Ewing tumors.

Fig. 1.

Chemical structures of the common camptothecins. Topotecan is substituted at the 9 and 10 positions while irinotecan is substituted at the 7 and 10 positions. Both have been extensively evaluated in Ewing sarcoma.

Fig. 2.

Response of 26 year old Ewing sarcoma patient treated with IGF1R antibody R1507. CT scan showing response to treatment of lung metastasis at baseline (on left) and following 6 weeks of treatment with 9 mg/kg/week of R1507. The yellow arrows highlight specific metastatic lesions.