title: A look inside the mechanistic black box: Are red blood cells the critical effectors of RRx-001 cytotoxicity?
abstract: The therapeutic potential of epi-immunotherapeutic anticancer agent RRx-001 in cancer has been validated with preclinical and clinical studies, since RRx-001 has successfully completed a phase 1 trial and multiple single-agent and combination phase 2 trials with preliminary evidence of promising activity are underway. Previous experimental work has implicated diverse anticancer mechanisms such as oxidative stress, ATP and NADPH depletion, anti-angiogenesis and epigenetic modulation in the overall antitumor effect of RRx-001. The hypothesis of this study was that the RRx-001 red blood cells are the essential and de facto intermediaries responsible for the reprograming of tumor behavior via transfer of their intracellular and membrane contents. To test this hypothesis, and thereby resolve the "black box" incompleteness in the continuity of the mechanism, the fate of red blood cells incubated with RRx-001 was explored in vitro and in vivo both in healthy animals and in tumor-bearing mice. The collective results establish that RRx-001-derivatized red blood cells are the critical "missing links" to explain the specificity and anticancer activity of RRx-001, including its immunomodulatory effects on tumor-associated macrophages. These experimental results delineate a novel erythrocyte-based mechanism without precedent in the annals of oncology and open the door to rational combination strategies with RRx-001 both in cancer therapy and beyond, particularly in disease states that affect red blood cell and vascular function such as malaria, leishmaniasis, sickle-cell disease and hemorrhagic shock.
authors.affiliation: Department of Bioengineering, University of California San Diego, La Jolla, CA, 92093, USA.
authors.forename: Pedro
authors.initials: P
authors.lastname: Cabrales
authors.affiliation: EpicentRx, Inc., 800 W El Camino Real, Suite 180, Mountain View, CA, 94040, USA.
authors.forename: Jan
authors.initials: J
authors.lastname: Scicinski
authors.affiliation: Moores Cancer Center, University of California San Diego, La Jolla, CA, 92093, USA.
authors.forename: Tony
authors.initials: T
authors.lastname: Reid
authors.affiliation: Children's Hospital Oakland Research Institute, Oakland, CA, 94609, USA.
authors.forename: Frans
authors.initials: F
authors.lastname: Kuypers
authors.affiliation: Children's Hospital Oakland Research Institute, Oakland, CA, 94609, USA.
authors.forename: Sandra
authors.initials: S
authors.lastname: Larkin
authors.affiliation: Children's Hospital Oakland Research Institute, Oakland, CA, 94609, USA.
authors.forename: Marcel
authors.initials: M
authors.lastname: Fens
authors.affiliation: InterWest Partners, Menlo Park, CA, 94025, USA.
authors.forename: Arnold
authors.initials: A
authors.lastname: Oronsky
authors.affiliation: EpicentRx, Inc., 800 W El Camino Real, Suite 180, Mountain View, CA, 94040, USA. boronsky@epicentrx.com.
authors.forename: Bryan
authors.initials: B
authors.lastname: Oronsky
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001384:Azetidines / Q000494:pharmacology*; D004195:Disease Models, Animal; D004912:Erythrocytes / Q000187:drug effects*; D008264:Macrophages / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D009374:Neoplasms, Experimental / Q000188:drug therapy* / Q000276:immunology / Q000473:pathology; D009574:Nitro Compounds / Q000494:pharmacology*; D011897:Random Allocation
chemical_list: D000970:Antineoplastic Agents; D001384:Azetidines; D009574:Nitro Compounds; C577469:RRx-001
keywords: Anti-angiogenesis; Anticancer mechanisms; Epigenetic modulation; Immunomodulation; RRx-001; Red blood cell