A Phase I clinical trial that investigated the use of bacterial Clostridium novyi-NT spores as an injectable monotherapy showed toxicities that were manageable and early clinical efficacy in patients with treatment-refractory solid tumour malignancies.

"Even after a single injection of this bacterial therapy, we see biological and, in some patients, clinically meaningful activity," said Dr Filip Janku, Associate Professor at the Department of Investigational Cancer Therapeutics, The University of Texas MD Anderson Cancer Centre, Houston. 

"This strategy is feasible, has manageable adverse effects, and could be clinically meaningful in patients with few therapeutic options."

Previous therapies have tested the use of bacteria, but have often caused infection. In this study, the use of C. novyi-NT spores in the open-label, first-in-human study, the researchers explained how a hypoxic environemnt is necessary for the bacterium. It requires a feature of cancerous lesions to survive and proliferate, and thus does not affect healthy cells.

"By exploiting the inherent differences between healthy and cancerous tissue, C. novyi-NT represents a very precise anticancer therapeutic that can specifically attack a patient’s cancer," Prof Janku said.

Between 2013 and 2017, 24 patients were enrolled with treatment-refractory solid tumors, with 15 patients having sarcoma, seven patients having diverse carcinoma and two with melanoma.

Tumours were injected with a single dose of C. novyi-NT, from 10,000 to 3 million spores. Patients administered with 3 million spores experienced dose-limiting toxicities of grade 4 sepsis, and as such the highest tolerated dose was determined to be 1 million spores.

Tumour shrinkage of greater than 10 percent was identified in 23 percent of the patients, and 21 had stable disease, measured by RECIST. Prof Janku mentioned that RECIST may not accurately capture results of the trial.

"Despite the absence of clinical signs of germination in some patients, we saw improved tumor-specific immune responses through the increased secretion of T-cell cytokines and increased presence of tumor infiltrating lymphocytes in injected tumors," said Prof Janku.

"From these preliminary results, it appears that C. novyi-NT is able to activate the immune response besides causing tumor destruction."

C. novyi-NT elicits an immune response, and as such Prof Janku believes this therapy will be synergistic with checkpoint inhibition.

"We were extremely encouraged by the results of this trial, especially in patients with advanced sarcomas, where immunotherapy hasn’t proven very efficacious," Prof Janku concluded. "This bacteriolytic strategy has the potential to be clinically meaningful, especially in combination with checkpoint inhibitors, for patients with advanced solid tumors."

The data was presented at the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival.

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