RNA-seq analysis of immunogenic actions of metronomic cyclophosphamide treatment: dependence of gene responses on tumor model, mouse host, and drug schedule

RNA-seq analysis was performed using RNA isolated from three tumor models (GL261 glioma, LLC Lewis lung carcinoma, B16F10 melanoma) implanted subcutaneousy in C57BL/6 mice, or in ICR scid mice. Mice were untreated or were treated with cyclophosphamide (CPA) given on a 6-day repeating metronomic schedule (CPA/6d), except as noted. Results from these global transcriptome analysis indicated substantial elevation of basal GL261 immune infiltration and strong activation by CPA/6d treatment of GL261 immune stimulatory pathways and their upstream regulators, but without preferential depletion of negative immune regulators compared to LLC and B16F10 tumors. In LLC tumors, where CPA/6d treatment was found to be anti-angiogenic, CPA/6d suppressed VEGFA target genes and down regulated cell adhesion and leukocyte transendothelial migration genes. In GL261 tumors implanted in adaptive immune-deficient scid mice, where CPA/6d-induced GL261 regression is incomplete and late tumor growth rebound can occur, T cell receptor signaling and certain cytokine-cytokine receptor responses seen in B6 mice were deficient. Extending the CPA treatment interval from 6 to 9 days (CPA/9d) - which results in a strong but transient natural killer cell response followed by early tumor growth rebound - induced fewer cytokines and increased expression of drug metabolism genes. Taken together, these findings elucidate molecular response pathways activated by intermittent metronomic CPA treatment and identify deficiencies that characterize immune-unresponsive tumor models and drug schedules. Overall design: RNA isolated from various tumor cell lines implanted s.c in C57BL/6 mice or scid mice, untreated or treated with cyclophosphamide (CPA) given on a metronomic schedule, were prepared and used for stranded or unstranded RNA-seq.

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Wu J, Jordan M, Waxman DJ