Abstract

Malignant pleural mesothelioma (MM) remains an almost universally fatal disease with limited treatment options. Preclinical models indicate the preferential oncolytic activity of the modified vaccine strain measles virus carrying the gene for the human sodium-iodine symporter (NIS) – MV-NIS. Intraperitoneal and intravenous administration of MV-NIS was recently found to be potentially effective in patients with refractory ovarian cancer and multiple myeloma. However, whether MV-NIS is directly oncolytic or triggers an anti-tumor immune response remains unclear. We conducted a phase I dose escalation study with 3+3 design and ongoing maximal tolerated dose (MTD) expansion cohort. MV-NIS was administered as first or second line therapy via a tunneled intrapleural catheter to patients with MM. MV-NIS dose ranged from 108 TICID50 to 9 x 109 TICID50. In the absence of dose limiting toxicity and disease progression, patients received up to 6 cycles of MV-NIS therapy (Phase I). Currently additional patients are being randomized between a single and multiple cycles. MV-NIS infection and replication are monitored by Iodine123 SPECT/CT (Phase I only) as well as by RT-PCR and/or plaque-assay. Anti-tumor immunity is monitored in the blood and pleural fluid and patients are followed clinically by chest CT using the modified RECIST criteria. Twelve patients (3/dose level) received MV-NIS therapy. There were no dose limiting adverse events and therapy was well tolerated. The best therapeutic response was stable disease, which was achieved at 1 month by 8/12 evaluable patients (67%). Median overall survival was 449 days (95%CI: 221, 484) (∼15 months) (4/12 patients remain alive), and median progression free survival was 63 days (95% CI: 33, 174) (∼2 months). MV infection and replication were detectable by RT-PCR and plaque assay in the pleural fluid between 24-72 hours after treatment. I123 SPECT-CT demonstrated only marginal viral gene expression in a single patient treated with the highest dose level. MV-NIS therapy effectively boosted pre-existing anti-MV neutralizing antibody responses in the plasma and pleural fluid of most patients. We observed a transient inflammatory response in the pleural space after MV-NIS administration. In addition, induction or boosting of anti-tumor antibody responses was observed. The intrapleural administration of MV-NIS is safe, resulted in stable disease for 67% of patients and may be associated with favorable overall survival in MM. While there was only transient infection and viral replication, we observed the induction of anti-tumor immune responses supportive of potential long-term therapeutic impact. The study continues with the MTD expansion cohort.

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