Researchers in the UK and the United States have found that a drug composed of an antibody carrying a highly toxic anti-cancer agent is well tolerated by patients at much higher doses than have been used before.
The drug, BB-10901 (huN901-DM1), is being tested in a phase I clinical trial in patients who have relapsed or failed to respond to previous treatment for a range of cancers, such as small cell lung cancer (SCLC), other tumours in the lungs of neuroendocrine origin and non-pulmonary small cell carcinomas. Although the trial is not designed to test the efficacy of the drug, researchers report promising clinical responses in patients, including one patient who has remained in remission for more than a year.
Dr Paul Lorigan reported to the EORTC-NCI-AACR  Symposium on Molecular Targets and Cancer Therapeutics in Prague today (Friday): "The results are important in that, in contrast to a prior regimen investigated in a phase I trial in the United States, significantly higher dose intensity is achieved with the current schedule. This has implications for the design of future trials with this agent, especially as the amount of the drug given is likely to be important in determining clinical response and outcome. In addition, the presence of a durable, complete response as well as other hints of clinical activity are very encouraging.
"The tolerability of this agent compares very favourably with that of standard chemotherapy. The lack of clinically significant bone marrow toxicity by BB-10901 raises the possibility that such an agent could be used either alone or in combination with standard chemotherapy in future clinical trials."
Dr Lorigan, a senior lecturer in medical oncology at the Christie Hospital, Manchester, UK, worked with colleagues in the UK and USA to investigate different dose levels, any adverse effects and how the drug was cleared from the body (pharmacokinetics). The drug, also known as huN901-DM1, is an immunoconjugate – a hybrid molecule specifically designed to deliver a potent cell-killing agent to cancer cells – and is created by attaching a cytotoxic drug DM1 to a monoclonal antibody, huN901. It binds to cells that have the molecule CD56 on their cell surfaces and the DM1 then can kill the cells. Several tumours are CD56 positive, including SCLC, neuroendocrine tumours, Wilms' tumours, and multiple myeloma.
The researchers gave the drug by intravenous infusions for three consecutive days every three weeks. The researchers initially enrolled four patients at each dose level (4, 8, 16, 24, 36, 48, 60, 75 milligrams per squared metre of body surface area (mg/m2)). When a patient experienced a dose-limiting toxicity the cohort was enlarged to six patients at that dose. So far, 40 patients have been treated.
Adverse effects were seen in six patients and included constipation, fatigue, leg pain, headache, inflamed pancreas, hypotension and myocardial infarction. Dr Lorigan said: "In general, the study drug was well tolerated, particularly when compared to standard chemotherapy. There was no clinically significant myelosuppression, most probably because the immunoconjugate is targeted at the tumour rather than the normal cells. Also, there was no clinical evidence of serious allergic or infusion reactions. The one side effect we have seen at higher doses is headache. This seems to be reduced if we increase the infusion time, and it may respond to other medication given with the study drug – we are investigating this further."
One patient with metastatic, recurrent Merkel cell carcinoma (a rare, aggressive cancer that develops on, or just beneath, the skin and in hair follicles) had a durable, complete response and remains in clinical remission more than a year after treatment. "This patient had numerous prior relapses and had failed standard chemotherapy," said Dr Lorigan. Eight patients had stable disease lasting between six and 21 weeks.
"It is difficult to draw any reliable conclusions from an early phase study such as this, but we are encouraged to see early signs of activity. While some tumours treated were indolent, others such as extensive SCLC were very aggressive. The presence of stable disease in a patient with SCLC over six cycles of therapy is very encouraging," he continued.
Pharmacokinetics showed that drug was able to tackle tumour cells expressing CD56 more effectively at the higher doses. The researchers have not reached the maximum tolerated dose yet and are continuing to enrol new patients.
"We are considering amending the protocol and adding three patients at 75 mg/m2/day, with pre-medication prior to infusions of BB-10901. While we have not seen dose-limiting toxicity at this level with the slower infusion (without pre-medication), we have seen headache in two patients, which is a moderate adverse effect. We anticipate that pre-medication will ameliorate or prevent this symptom. If well tolerated, we would then increase the dose to 94 mg/m2/day," said Dr Lorigan.
He concluded: "Treatment options for these patients are limited and we are encouraged by the early results with this novel agent. We are grateful to the patients, their families, the investigators, clinical staff, and our colleagues at ImmunoGen (the sponsor of the clinical study) for their participation and continued support of this trial."
Emma Mason | EurekAlert!
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