The development of a ‘smart’ drug capable of distinguishing tumor from host cells has been sought for centuries, but the microenvironment of solid tumors continues to confound therapeutics. Solid tumors present several challenges for current oncotherapeutics, including aberrant vascularization, hypoxia, necrosis, abnormally high pH and local immune suppression. While traditional chemotherapeutics are limited by such an environment, oncolytic microbes are drawn to it – having an innate ability to selectively infect, colonize and eradicate solid tumors. Development of an oncolytic species would represent a shift in the cancer therapeutic paradigm, with ramifications reaching from the medical into the socio-economic. Modern genetic engineering techniques could be implemented to customize ‘Frankenstein’ bacteria with advantageous characteristics from several species.

The tumor microenvironment is characterized by anomalous vascularization, hypoxia, and acidity at the core of solid tumors that culminates in concentrated necrosis and immune system dysregulation among other effects. While this environment presents several challenges for the development of oncotherapeutics that deliver their activity via the enhanced permeability and retention (EPR) effect of the leaky blood vessels around a tumor, oncolytic bacteria, or a class of bacteria with a noted capacity to lyse solid tumors, are attracted to the very environment found at the center of solid tumors that confounds other therapeutics. It is this capacity that allows for a potent, active penetration from the tumor margins into the core, and subsequent colonization to facilitate lysis and immune reactivation. Clostridium novyi in particular has recently shown great promise in preclinical and clinical trials when administered directly to the tumor. These studies indicate that C. novyi is uniquely poised to effectively accomplish the long sought after “holy grail” of oncotherapeutics: selective tumor localization via intravenous delivery. This study reports the development of efficient methods that facilitate experimental work and therapeutic translation of C. novyi including the ability to work with this obligate micro-anaerobe on the benchtop. Additionally, this study seeks to utilize this newfound experimental flexibility to address several gaps in the current knowledge regarding the efficacy of CRIPSR/Cas9-mediated gene insertion in this species to further develop this oncolytic bacteria and the genetic customization of bacteria in general.

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The efficacy of current oncotherapeutics is largely limited by an inability to access avascular tissues, which is in part responsible for forty years of stagnant pancreatic cancer statistics where the median survival remains a mere six months. Oncolytic bacteria such as Clostridium novyi-NT overcome this challenge with its ultrasensitive, innate affinity for hypoxic/necrotic areas found at the center of solid tumors and their metastases. While preclinical and clinical data from intratumoral injections of C. novyi-NT are promising, many tumors are inaccessible to such injections. Preclinical trials of analogous IV injections have uncovered other obstacles such as rapid clearance of C. novyi-NT by the immune system independent of septic complications. To mitigate rapid clearance, CRISPR/Cas9n was used to genetically modify a non-toxic form of C. novyi-NT to express a tumor targeting RGD peptide on the spore surface. Through this novel, first of its kind, methodology, spores with stronger affinity to a surface coated with the targeted binding partner of RGD, aVb3 integrin, have been generated. Importantly, there was no statistically significant difference in the genetically modified spore’s capacity for sporulation or germination when compared to unmodified C. novyi-NT spores, nor was a difference in lytic capacity observed, suggesting no relevant off-target effects from genomic modification. Biodistribution and efficacy of non-toxic RGD-modified spores was evaluated in an immunocompetent, syngeneic, pancreatic cancer murine model. Ongoing efforts to characterize the biodistribution and efficacy of the intravenously injected RGD-modified C. novyi-NT include the application of multiplex immunofluorescence, laser microdissection, and live, whole animal imaging. Supported as a pilot project by funds from NIH COBRE grant 1P20GM109024, Doctoral Dissertation Funds to KMD from NDSU, and by discretionary funds from investigators at UNMC. Citation Format: Kaitlin M. Dailey, Krysten Vance, Kyle McAndrews, Reed I. Jacobson, Jandro Delgado, Paige R. Johnson, Taylor M. Woolery, Megan Orr, Jiha Kim, Sanku Mallik, Kenneth W. Bayles, Michael A. Hollingsworth, Amanda E. Brooks. Development of an RGD CRISPR-modified Clostridium novyi NT spores as an intravenous oncotherapy [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-037.