A Study of APR-246 in Oesophageal Cancer

Cancer of the oesophagus (OC) is distinguished by having a poor outcome for most patients and an incidence that is rising faster than any other solid cancer. It is already the eighth most common cancer, and the sixth most common cause of death from cancer, worldwide. The majority of patients are diagnosed with late stage disease, which is incurable with the current standard multimodality therapy. Thus, there is a critical need to develop new treatments for this disease. Surprisingly, despite its high prevalence in developing countries, and its increasing incidence in Western populations, metastatic OC remains an 'orphan disease' with very few good quality or randomised trials available to guide practice. As a result, treatment for OC has changed little over the past few decades, and as a consequence there has been only modest improvement in overall survival for patients with this disease. TP53, a key tumour suppressor gene, is mutated in 70-80% of OC (both adenocarcinoma and squamous cell carcinoma) providing an attractive potential target for an OC therapy. Although paired tissue studies in primary and metastatic OC are lacking, p53 mutations occur very early in oesophageal carcinogenesis and are unlikely to be lost in advanced disease. OC with mutant (mut)-p53 are more resistant to conventional chemotherapy and mut-p53 is associated with poor patient prognosis. Over the last decade, several novel drugs have been developed that target mut-p53 and restore wild-type (wt)-p53 function in cancer cells. Of these, APR-246 (also known as PRIMA-1MET), a first-in-class agent targeting mutant p53 resulting in re-expression of wild-type p53 activity, has proven to be the most effective against a wide range of mutants. APR-246 is a pro-drug that gives rise to the active compound methylene quinuclidinone (MQ), which covalently binds to thiol groups on cysteine residues in the p53 core domain resulting in refolding of mut-p53 protein and restoration of its tumour suppressor activity. While the reactivation of mut-p53 is thought to be the primary mode of action of APR-246, preclinical studies have suggested potential alternative mechanisms (e.g. through the depletion of cellular glutathione levels) may also be contributing to the efficacy of APR-246, especially when used in combination with cisplatin/5-FU chemotherapy. Thus, the anti-tumour activity of APR-246 may not be limited to mut-p53 bearing tumours. Mutation of p53 is the most common genetic aberration in oesophageal cancer being detected in up to 80% of both oesophageal squamous cell cancers and adenocarcinomas. APR-246 is a first-in-class agent targeting mutant p53. In vitro and in vivo preclinical models have demonstrated that APR-246 has excellent efficacy in OC (both adenocarcinoma and squamous cell carcinoma) and potently synergises with chemotherapies used in the treatment of OC, restoring sensitivity to chemotherapy-resistant tumours. An initial phase I clinical trial has shown APR-246 to be safe in humans and early results from a currently running phase Ib/II trial of APR-246 with carboplatin and liposomal doxorubicin in ovarian cancer have been promising. Together, these data provide a strong rationale for investigating the efficacy of APR-246 in OC.