Improved systemic delivery of oncolytic reovirus to established tumors using preconditioning with cyclophosphamide-mediated Treg modulation and interleukin-2.
OBJECTIVE
The goals of this study were (a) to investigate whether preconditioning of immunocompetent mice with PC-61-mediated regulatory T-cell (Treg) depletion and interleukin-2 (IL-2) would enhance systemic delivery of reovirus into subcutaneous tumors and (b) to test whether cyclophosphamide (CPA), which is clinically approved, could mimic PC-61 for modification of Treg activity for translation into the next generation of clinical trials for intravenous delivery of reovirus.


METHODS
C57Bl/6 mice bearing subcutaneous B16 tumors were treated with CPA or PC-61 followed by 10 injections of low-dose IL-2. Mice were then treated with intravenous reovirus. Virus localization to tumor and other organs was measured along with tumor growth and systemic toxicity.


RESULTS
Preconditioning with PC-61 and IL-2 enhanced localization of intravenous oncolytic reovirus to tumors with significantly increased antitumor therapy compared with controls (P < 0.01). However, with the maximal achievable dose of reovirus, Treg modification + IL-2 was also associated with systemic toxicity. CPA (100 mg/kg) did not deplete, but did functionally inhibit, Treg. CPA also mimicked PC-61, in combination with IL-2, by inducing "hyperactivated" NK cells. Consistent with this, preconditioning with CPA + IL-2 enhanced therapy of intravenously delivered, intermediate-dose reovirus to a level indistinguishable from that induced by PC-61 + IL-2, without any detectable toxicity.


CONCLUSIONS
With careful reference to ongoing clinical trials with dose escalation of reovirus alone and in combination with CPA, we propose that future clinical trials of CPA + IL-2 + reovirus will allow for both improved levels of virus delivery and increased antitumor efficacy.
Kottke
Timothy
T
Department of Molecular Medicine, Ophthalmology, and Immunology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
Thompson
Jill
J
Diaz
Rosa Maria
RM
Pulido
Jose
J
Willmon
Candice
C
Coffey
Matt
M
Selby
Peter
P
Melcher
Alan
A
Harrington
Kevin
K
Vile
Richard G
RG
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D045744:Cell Line, Tumor; D003520:Cyclophosphamide / Q000494:pharmacology*; D016503:Drug Delivery Systems; D005260:Female; D007376:Interleukin-2 / Q000378:metabolism*; D008297:Male; D008546:Melanoma, Experimental; D051379:Mice; D008810:Mice, Inbred C57BL; D009369:Neoplasms / Q000378:metabolism*; D050130:Oncolytic Virotherapy / Q000379:methods*; D013154:Spleen / Q000166:cytology; D050378:T-Lymphocytes, Regulatory / Q000378:metabolism*
D000970:Antineoplastic Agents; D007376:Interleukin-2; D003520:Cyclophosphamide