NPI-0052 Enhances Tumoricidal Response to Conventional Cancer Therapy in a Colon Cancer Model JamesC.Cusack,Jr., 1,2 RongLiu, 1 LijunXia, 1 Ta-HsiangChao, 3 ChristinePien, 3 Wei Niu, 3 VitoJ.Palombella, 3 Saskia T.C.Neuteboom, 3 andMichaelA.Palladino 3 Abstract Purpose: Inthecurrentstudy,weexaminetheeffectsofanovelproteasomeinhibitor,NPI-0052 (salinosporamideA), on proteasome function and nuclear factor-nB activation and evaluate its abilitytoenhancetreatmentresponseincoloncancerxenograftswhenadministeredorally. Experimental Design: Theeffectsof treatmentonnuclear factor-nBactivation,cellcycleregu- lation, and apoptosis were determined.The pharmacodynamic effect of NPI-0052 on 20S pro- teasome function was assayed in vivo following oral and i.v. drug administration and compared withtreatmentwithbortezomib.Theeffectofcombinedtreatmentwithchemotherapywasdeter- minedinacoloncancerxenograftmodel. Results: WefoundthatNPI-0052isapotent,well-toleratedproteasomeinhibitor thathasphar- macodynamicpropertiesdistinctfrombortezomibinthatitachievessignificantlyhigherandmore sustained levels of proteasome inhibition.When combined with chemotherapy, NPI-0052 increases apoptosis and shifts cells toward G 2 cell cycle arrest.When added to chemotherapy in vivo [usingcombinationsof5-fluorouracil(5-FU),CPT-11,Avastin(bevacizumab),leucovorin, andoxaliplatin],NPI-0052significantlyimprovedthetumoricidalresponseandresultedina1.8- foldincreased response to CPT-11, 5-FU, andleucovorin triple-drug combination (P = 0.0002, t test),a1.5-foldincreasedresponsetotheoxaliplatin,5-FU,andleucovorintriple-drugcombina- tion(P =0.013, t test),anda2.3-foldgreaterresponsetotheCPT-11,5-FU,leucovorin,andAvas- tinregimen( P =0.00057). Conclusions: ThehighlevelofproteasomeinhibitionachievedbyNPI-0052iswelltoleratedand significantlyimprovesthetumoricidalresponsetomultidrugtreatmentinacoloncancerxenograft model.Furtherevaluationof thisnovelproteasomeinhibitorinclinicaltrialsisindicated. The proteasome has been identified as an attractive target for cancer therapy because of the central role it plays in the regulation of proteins that control cell cycle progression and cancer cell survival (1). The direct effects of proteasome inhibition on cancer cells include cell cycle arrest with accumulation of cells typically in the G 2 phase as well as the direct induction of apoptosis (2). In addition, proteasome inhibition has been shown to augment the cancer cell response to chemotherapy and radiation by decreasing proteasome-dependent regulatory proteins involved in treat- ment resistance such as Bcl2, the caspases, and the transcription factor nuclear factor-nB (NF-nB; refs. 1, 3, 4). Currently, bortezomib/PS-341 (Velcade), a selective, revers- ible proteasome inhibitor that targets the 20S proteasome, is the only drug that targets proteasome function and is Food and Drug Administration approved for clinical use (2). We have previously shown that bortezomib overcomes treatment resistance induced by the chemotherapeutic agent CPT-11 (3) or g-irradiation (4) by suppressing stress-induced activation of the transcription factor NF-nB and expression of genes involved in cancer cell survival. The suppression of NF-nB activation by proteasome inhibition occurs pri- marily through the stabilization of the NF-nB inhibitor InBa, which is phosphorylated in response to genotoxic stress and then targeted for ubiquitination-dependent degradation by the proteasome (1, 2). In the current study, we examine a novel proteasome inhibitor, NPI-0052 (salinosporamide A), which is a natural product isolated from a marine micro- organism that irreversibly inhibits all three active sites within the 20S core proteasome (5–7). Unlike bortezomib, which reversibly inhibits the chymotryptic site within the 20S core particle, NPI-0052 inhibits the chymotryptic, tryptic, and caspase sites of the proteasome (7). Our results show that NPI-0052 is a potent, orally active proteasome inhibitor with unique pharmacodynamic properties that achieves high levels of proteasome inhibition in vivo and is well tolerated. Furthermore, NPI-0052 is an effective adjuvant to anticancer therapies that enhances the apoptotic response to Cancer Therapy: Preclinical Authors’ Affiliations: 1 Divisionof Surgical Oncology, Massachusetts General Hospital; 2 Harvard Medical School, Boston, Massachusetts; and 3 Nereus Pharmaceuticals,SanDiego,California Received5/12/06;revised7/27/06;accepted8/18/06. Grant support: National Cancer Institute grants CA77278 and CA98871 (J.C. Cusack,Jr.). Thecostsofpublicationofthisarticleweredefrayedinpartbythepaymentofpage charges.This articlemust thereforebeherebymarked advertisement inaccordance with18U.S.C.Section1734solelytoindicatethisfact. Requests for reprints: James C. Cusack, Jr., Divisionof Surgical Oncology, Massachusetts General Hospital,Yawkey 7th Floor, 55 Fruit Street, Boston, MA 02114.Phone:617-724-4093;Fax:617-724-3895;E-mail:jcusack@partners.org. F 2006AmericanAssociationforCancerResearch. doi:10.1158/1078-0432.CCR-06-1151 www.aacrjournals.org Clin Cancer Res 2006;12(22) November 15, 2006 6758 Research. on May 25, 2016. © 2006 American Association for Cancer clincancerres.aacrjournals.org Downloaded from