Rashmi Bharti

Disruption of the Gut Microbiota Confers Cisplatin Resistance in Epithelial Ovarian Cancer

Abstract Epithelial ovarian cancer (EOC) is the leading cause of gynecologic cancer death. Despite initial responses to intervention, up to 80% of patient tumors recur and require additional treatment. Retrospective clinical analysis of patients with ovarian cancer indicates antibiotic use during chemotherapy treatment is associated with poor overall survival. Here, we assessed whether antibiotic (ABX) treatment would impact growth of EOC and sensitivity to cisplatin. Immunocompetent or immunocompromised mice were given untreated control or ABX-containing (metronidazole, ampicillin, vancomycin, and neomycin) water prior to intraperitoneal injection with EOC cells, and cisplatin therapy was administered biweekly until endpoint. Tumor-bearing ABX-treated mice exhibited accelerated tumor growth and resistance to cisplatin therapy compared with control treatment. ABX treatment led to reduced apoptosis, increased DNA damage repair, and enhanced angiogenesis in cisplatin-treated tumors, and tumors from ABX-treated mice contained a higher frequency of cisplatin-augmented cancer stem cells than control mice. Stool analysis indicated nonresistant gut microbial species were disrupted by ABX treatment. Cecal transplants of microbiota derived from control-treated mice was sufficient to ameliorate chemoresistance and prolong survival of ABX-treated mice, indicative of a gut-derived tumor suppressor. Metabolomics analyses identified circulating gut-derived metabolites that were altered by ABX treatment and restored by recolonization, providing candidate metabolites that mediate the cross-talk between the gut microbiome and ovarian cancer. Collectively, these findings indicate that an intact microbiome functions as a tumor suppressor in EOC, and perturbation of the gut microbiota with ABX treatment promotes tumor growth and suppresses cisplatin sensitivity. Significance: Restoration of the gut microbiome, which is disrupted following antibiotic treatment, may help overcome platinum resistance in patients with epithelial ovarian cancer. See related commentary by Hawkins and Nephew, p. 4511

Leveraging dysregulated tumor metabolism for targeting anticancer bacteria

Widespread application of bacterial-based cancer therapy is limited because of the need to increase therapeutic bacteria specificity to the tumor to improve treatment safety and efficacy. Here, we harness the altered tumor metabolism and specifically elevated kynurenine accumulation to target engineered bacteria to the cancer site. We cloned and leveraged kynurenine-responsive transcriptional regulator (KynR) with its cognate promoter in Escherichia coli . Optimizing KynR expression coupled with overexpressing kynurenine transporter and amplifying the response through plasmid copy number–based signal amplification enabled the response to kynurenine at the low micromolar levels. Knocking out genes essential for cell wall synthesis and supplying these genes via kynurenine-controlled circuits allowed tuning Salmonella enterica growth in response to kynurenine. Our kynurenine-controlled S. enterica (hereafter named AD95+) showed superior tumor specificity in breast and ovarian cancer murine models compared to S. enterica VNP20009, one of the best characterized tumor-specific strains. Last, AD95+ showed anticancer properties compared to vehicle controls, demonstrating the potential as an anticancer therapeutic.