A Phase 2 Biomarker - Enriched Study of TH-302 in Subjects With Advanced Melanoma

Hypoxia is an independent marker of a poor prognosis for subjects with metastatic melanoma (Simonetti 2012, Lartigau 1997). Hypoxic melanoma cells are more likely to exhibit a stem-cell like phenotype with an associated increased propensity for invasion, angiogenesis, and metastasis formation compared to normoxic cells. Moreover, this phenotype is also associated with treatment resistance. TH-302, a hypoxia activated prodrug (HAP), was designed to target the hypoxic nature of tumours while having a minimal effect on normoxic tissue. TH-302 belongs to a class of alkylating agents that have significant experimental and clinical activity (Brock 1989). Preclinical data support the hypothesis that TH-302 targets hypoxic regions of tumours and is also able to kill tumour cells in normoxic regions as a result of cytotoxin diffusion, leading to significant effects on tumour growth (Meng 2011). TH-302 has been investigated in over 700 subjects with solid tumours or hematologic malignancies, including subjects with metastatic melanoma. In this subset a disease control rate of 63% (3 subjects with partial responses and 9 subjects with stable disease out of a total of 19) was observed in an early phase clinical trial of TH-302 (Weber 2010). Predictive biomarkers for response and toxicity have yet to be identified for subjects with advanced melanoma treated with TH-302. Optimal patient selection may be critical to maximize the clinical benefit. A predictive biomarker approach will be investigated to try to identify subjects most likely to benefit from TH-302. Given the hypoxia-targeting mechanism of TH- 302, it is believed that hypoxia biomarkers will be the most informative for identifying subjects likely to benefit from TH- 302; however, additional biomarkers including DNA repair biomarkers will also be investigated. In addition, this approach will also have potential to synergise with future immunotherapeutic approaches as suppressive T regulatory cells are thought to reside within hypoxic niches within the tumour microenvironment that would be amenable to targeting by TH-302.