ALBERT

Description: Background: The amyloidoses comprise a heterogeneous group of diseases characterized by misfolding of amyloidogenic proteins and subsequent deposition as amyloid fibrils. To date, over 30 proteins are known to be amyloidogenic (Sipe Amyloid 2014). Immunoglobulin light chain (AL) amyloidosis, a plasma cell dyscrasia, is the most common subtype. The standard diagnostic algorithm in AL amyloidosis is to obtain a biopsy of a clinically involve organ, and once Congo red positivity is confirmed, perform subtyping analyses with immunohistochemistry or mass spectrometry. Accurate subtyping of amyloidosis is essential to appropriate treatment, as misdiagnosis occurs in up to 10% of patients and may lead to inappropriate administration of chemotherapy (Comenzo Blood 2006; Lachmann NEJM 2002). We sought to determine the patterns of amyloid subtyping among patients with a diagnosis of AL amyloidosis referred to a tertiary referral center for HDM/SCT. Methods: Sequential patients with confirmed amyloidosis, age ≥ 18 years who underwent HDM/SCT between 2001 and 2014 at the Fred Hutchinson Cancer Research Center and University of Washington Medical Center were eligible. Presence of a Congo red-positive biopsy for each patient referred for transplant was confirmed and the pathology reports and medical records were reviewed to determine if subtyping was performed, and which modality was used. Results: Fifty-one patients with AL amyloidosis were referred for transplant; of these, 45 proceeded with HDM/SCT. The organ systems most commonly involved were renal in 34/51, and gastrointestinal in 5/51. Of the biopsies, subtyping was performed in 35 (68.6%), and no subtyping was performed in 16 patients (31.3%). Immunofluorescence was the most common modality used for subtyping in 33 biopsies (94.2%) and laser capture/mass spectrometry (LC/MS) was used in 2 patients (5.7%). All patients had evidence of a clonal plasma cell dyscrasia by bone marrow biopsy and peripheral blood testing. Of the patients without subtyping, 8 (50%) were diagnosed before 2008. Discussion: Misdiagnosis of amyloidosis due to a lack of appropriate subtyping is a well-described and ongoing problem for patients with amyloidosis. These data suggest that definitive subtyping is still not routinely performed in the evaluation of amyloidosis. At our center, efforts to standardize the evaluation of Congo-red positive biopsies using definitive typing are underway. Disclosures Gopal: Seattle Genetics: Research Funding.

Description: Background: Bortezomib was originally incorporated into DT-PACE (thalidomide, dexamethasone, cisplatin, doxorubicin, cyclophosphamide, and etoposide) as an intensive induction regimen (VTD-PACE) prior to high-dose melphalan and autologous transplant for multiple myeloma (MM). This regimen is effective in the induction setting, and also for patients with relapsed disease (Barlogie British Journal of Haematology 2007, Singh ASCO 2013). At our center, we examined the outcomes of MM patients undergoing chemomobilization with a regimen that substituted carfilzomib and lenalidomide for bortezomib and thalidomide (CarRD-PACE). Methods: Twenty MM patients with measureable disease received CarRD-PACE for chemomobilization. We excluded in this report patients with plasma cell leukemia, renal insufficiency, heart failure, or those patients who were refractory to carfilzomib. Results: The median age was 61.5 years (range, 35- 69). Nine of these patients were women (45%). The median left ventricular ejection fraction pre-treatment was 62% (range, 50 - 77%). Of patients with initial staging information, 8 were ISS stage I (47%), 5 patients ISS II (29%), and 4 were ISS III (24%). High risk cytogenetics, defined as presence of deletion 17p, t(4;14), t(14;16), were present in 5 patients at time of chemomobilization (25%). Fourteen patients (82%) had bulky disease (defined as having 〉 3 lesions, or having a single lesion 〉 3 cm on PET-CT or MRI) prior to treatment, assessed by MRI (n=12) or PET-CT (n= 2). The median time from diagnosis to mobilization was 9.5 months (range, 4- 44). Patients had previously received a median of 2 regimens of therapy (range, 1- 5). Fifteen patients received 1 cycle of CarRD-PACE, and 5 patients received 2 cycles. Eighteen patients response evaluable; in these patients, the overall CR/PR response rate after completion of treatment was 25% (4 PR, 1 CR), with fifteen patients (75%) having SD. A total of 18 patients (90%) collected stem cells after mobilization, requiring a median of 1 day of collection (range, 1-2), and collected a median of 18.3 x 10^6 CD34+ cells/kg (range, 4.8 - 69.88). Grade 3-4 toxicities occurred in 6 patients (30%), most common was neutropenic fever (n=4) (20%). No patients experienced a cardiac toxicity. Hospital readmission following treatment occurred in 4 patients (20%) for a median of 6.5 days (range, 3 - 15). Eighteen patients (90%) underwent a single autologous transplant, and 2 (10%) received tandem autologous-allogeneic transplant. Following autologous transplant, the median time to neutrophil engraftment was 18 days (range, 14 - 29 days), and the median time to platelet engraftment was 13 days (range, 7 - 19 days). The PFS at 6 months was 63% (95% CI, 0.382 - 1), and the OS at 6 months was 91% (95% CI, 0.754 - 1) (Figure). Discussion: CarRD-PACE is a well-tolerated and effective therapy in heavily treated multiple myeloma patients with substantial disease burden at the time of autologous transplant, and can successfully mobilize autologous PBSC. Despite the theoretical concern regarding the combination of 2 agents with cardiac toxicity (carfilzomib and doxorubicin), we did not observe any cardiac toxicities of any grade during treatment. This approach may be particularly useful in individuals with bortezomib associated neuropathy and or those with bortezomib refractory disease. Figure Kaplan-meier plots for progression free and overall survival. Figure. Kaplan-meier plots for progression free and overall survival. Disclosures Becker: GlycoMimetics: Research Funding. Shadman:Pharmacyclics: Honoraria, Research Funding; Acerta: Research Funding; Gilead: Honoraria, Research Funding; Emergent: Research Funding. Gopal:Seattle Genetics: Research Funding.

Description: Key Points Astatination of anti-CD45 antibody via a closo-decaborate compound yields a stable conjugate that targets radiation to hematologic organs. 211At-anti-CD45 radioimmunotherapy combined with bone marrow transplantation prolongs survival in a disseminated murine leukemia model.

Description: Introduction: The role of brentuximab vedotin (BV) in Hodgkin Lymphoma (HL) is expanding, but factors predicting progression-free survival (PFS) after BV therapy are poorly defined. Age, tumor bulk, presence of extranodal disease, neutrophil:lymphocyte ratio (ANC/ALC), and lymphocyte:monocyte ratio (ALC/AMC) predict outcome in HL patients (pts) treated with chemotherapy, but their impact on PFS after BV has not been well-studied. Also, among pts with relapsed/refractory HL (rel/ref HL) who progress after BV, efficacy of additional chemotherapy is undefined. To inform patient selection and future clinical trial design with BV, we undertook a retrospective study to identify factors predicting PFS with BV therapy in rel/ref HL, and explore chemotherapy efficacy as salvage after BV failure. Methods: Pts receiving BV since 2009 were identified through pharmacy and research records and studied with IRB approval. Those with rel/ref HL receiving BV before or after transplant without intervening therapy were excluded. Age ≥40 at time, sex, pre-BV PET findings (SUV max, extranodal [EN] involvement, bulk 〉 5cm), prior therapy (# lines of therapy〉 median; prior transplant, platinum-containing, radiotherapy), and lab findings (AMC/ALC³4.3, ALC/AMC ratio³1) at time of start of BV were examined for an impact on PFS and OS via log-rank testing of Kaplan-meier projections(JMP 11.0 software). PFS was defined as time from first BV dose to radiographic or clinical progression, initiation of post-BV salvage, or death from any cause. OS was measured from date of first BV dose to death from any cause. Efficacy of salvage therapy for those failing BV was recorded. Results: Of 90 patient receiving BV, 43 met above criteria. Median age was 34 yrs (range 17-80), median # of pre-BV therapies was 3 (range 1-7). 31 (73%) had failed autologous transplant, 10 (23%) had undergone allogeneic transplant, and 20 (46%) received radiotherapy prior to BV. Pre-BV PET staging data was available in 26 pts; post-BV PET was not analyzed in this dataset as response criteria were nonstandardized. BV was administered for a median 6 cycles (range 2-20). Median PFS after BV was 6 mo. (Figure 1) with 4 pts having PFS 〉4 yrs. At 31 mo. median follow-up, 71% of pts were alive with no plateau in the survival curve. On univariate analysis, age 40 or older at time of BV predicted inferior PFS (p=.03) and inferior OS though 95% confidence intervals were wide (OS by age: Figure 2, p=.02). HR for death for pts age 40 or older was 4 (98% CI .03-2.3, p=.05). No other factor predicted PFS or OS. Among 29 pts who failed BV, OS was 3.4 yrs. 40 chemotherapy regimens were given with 11 responses. Five of 11 pts responded to bendamustine, but median time to progression was 4 mo. Two of 4 responded to gemcitabine as did 3/8 receiving platinum chemotherapy. Conclusions: In this cohort of rel/ref HL pts treated with BV, PFS was 6 mo. overall and inferior among pts 40 yrs or older. OS was also worse in this group, although confidence intervals were wide in both univariate analyses. We confirm and expand upon prior data showing features predicting outcomes in HL after chemotherapy do not clearly apply after BV; and that most pts progress

Description: Radioimmunotherapy (RIT) options for T-cell non-Hodgkin lymphomas (T-NHLs) are limited. We evaluated anti-CD45-RIT in human (h) and murine (m) T-NHL. CD45 was highly expressed on hT-NHL patient samples (median, 2.3 × 105 antigen-binding capacity units/cell) and hT-NHL cell lines (3.4 × 105 CD45 antigen-binding capacity units/cell). Biodistribution studies in hTNHL xenografts showed that 131I-labeled BC8 (anti-hCD45) delivered 154% (P = .01) and 237% (P = .002) more radioiodine to tumor sites over control antibodies at 24 hours and 48 hours, respectively. Importantly, tumor sites targeted with 131I-BC8 exhibited 2.5-fold (P = .05), 3.0-fold (P = .007), and 3.6-fold (P = .07) higher 131I retention over the nontarget organs of lungs, liver, and kidneys, respectively (24 hours). Because the clinical use of anti-hCD45 would target both T-NHL and other hematolymphoid tissues, we evaluated the ability of anti-mCD45 to target mT-NHL. mT-NHL grafts targeted with anti-mCD45 correspondingly retained 5.3 (P 〈 .001), 5.4 (P 〈 .001), and 8.7 (P 〈 .001) times the radioactivity in tumor sites compared with nontarget organs of lung, liver, and kidney. 131I-labeled BC8 therapy yielded improved complete remission rates (75% vs 0%, P 〈 .001) and progression-free survivals (median, 23 days vs 4.5 days, P 〈 .001) compared with controls. These data indicate that the high CD45 expression of T-NHL allows reliable tumor targeting and disease control supporting anti-CD45 RIT for T-NHL patients.

Description: Introduction: Marginal zone lymphoma (MZL) and lymphoplasmacytic lymphoma (LPL)/Waldenstrom's macroglobulinemia (WM) comprise approximately 7% and 2%, respectively, of non-Hodgkin's lymphomas (NHL) (Teras 2016). MZL is further subclassified as splenic MZL (sMZL), nodal MZL (nMZL), or extranodal MZL (eMZL). Standard first-line therapies for LPL/WM include rituximab plus an alkylating agent and/or proteasome inhibitor or ibrutinib (Castillo 2017), while standard first-line treatment for MZL varies by subtype (Rosand 2017). There are limited treatment options for patients who have relapsed after first-line therapy. Idelalisib, a selective oral inhibitor of PI3Kδ, demonstrated efficacy in indolent NHL (iNHL), including MZL and LPL/WM, at a median follow-up of 9.7 months (mos) in a phase 2 study (NCT01282424; 101-09; Gopal 2014). Here, we present the final, long-term results for patients with double-refractory MZL and LPL/WM from the 101-09 study. Methods: Eligible iNHL patients had measurable disease and were refractory to both rituximab and an alkylating agent. Refractory status was defined as lack of response to or progression of lymphoma within 6 mos of completion of preceding therapy, documented by imaging. Oral idelalisib 150 mg twice daily was administered continuously until disease progression or intolerance. Responses were evaluated by an independent review committee using standard criteria (Cheson 2007; Owen 2013). Endpoints included overall response rate (ORR), time to response, duration of response (DOR), lymph node response, progression-free survival (PFS), overall survival, and safety. The final data cutoff date was 22 Oct 2018. Results: Of 125 patients enrolled, 15 (12%) had MZL (sMZL, n = 1; nMZL, n = 5; eMZL, n = 9) and 10 (8.0%) had LPL/WM. Median age was 65 years and most were non-Hispanic (n = 24; 96%) and White (n = 23; 92%). At diagnosis, 80% of MZL and 100% of LPL/WM patients had stage IV disease. The largest lesion at baseline was ≥5 cm for 5 (33%) MZL and 3 (30%) LPL/WM patients. Baseline median IgM level was elevated for 80% of LPL/WM patients (median 1.9, IQR 1.0-2.7 g/dL). Baseline beta2-microglobulin level was 〉3 µg/mL for 1 of 9 LPL/WM patients with values recorded (median 2.5 [range 1.7-3.1] µg/mL). For MZL and LPL/WM patients, 7 (47%) and 7 (70%) had ≥3 prior therapies, respectively. Common regimens for all 25 patients included rituximab-cyclophosphamide-doxorubicin-vincristine-prednisone (44%), rituximab-cyclophosphamide-vincristine-prednisone (40%), rituximab only (28%), bendamustine only (24%), and bendamustine-rituximab (20%). For MZL, the ORR (95% confidence interval [CI]) was 47% (21%, 73%), with median duration of therapy of 6.4 (range 1.8-37) mos. Of 7 responders, 1 had a complete response and 6 had partial responses (PR). Seven had stable disease (SD) and 1 had progressive disease (PD). Fourteen (93%) patients had reduction in lymph nodes, with 8 (53%) having ≥50% reduction in the sum of the products of the greatest perpendicular diameters (SPD). Median PFS was 6.6 (95% CI 3.5, 22) mos and median DOR was 18 (range 0-18) mos (Table). For LPL/WM, the ORR (95% CI) was 80% (44%, 98%), with a median duration of therapy of 29 (range 6.4-51) mos. Of 8 responders, 7 had PR and 1 had a minor response. There was 1 SD and 1 PD. Nine (90%) patients had lymph node reduction, with 5 (50%) having ≥50% reduction in SPD. Median PFS was 22 (95% CI 1.4, 56) mos and median DOR was 20 (range 1.7-50) mos (Table). All 25 patients had ≥1 treatment-emergent adverse event (TEAE), 16 (64%) had a serious AE, and 11 (44%) had dose reduced due to a TEAE. Grade ≥3 TEAEs occurred for 22 (88%) patients; neutropenia (n = 7, 28%), diarrhea (7, 28%), alanine aminotransferase increased (4, 16%), asthenia (3, 12%), and pneumonia (3, 12%) were the most frequent. All patients eventually discontinued treatment due to disease progression (14, 56%), AE (6, 24%), death (3, 12%), investigator request (1, 4%), or other (1, 4%). Ten patients have died, 3 during the study and 7 during the long-term follow-up. Conclusions: Monotherapy with idelalisib showed high rates of antitumor activity in this small subset of patients with MZL and LPL/WM refractory to prior therapy with rituximab and an alkylating agent; prolonged disease control was achieved for LPL/WM patients. No new safety signals were identified despite longer follow-up. Disclosures Wagner-Johnston: Bayer: Membership on an entity's Board of Directors or advisory committees; Jannsen: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; ADC Therapeutics: Membership on an entity's Board of Directors or advisory committees. Schuster:Genentech: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Novartis: Honoraria, Patents & Royalties: Combination Therapies of CAR and PD-1 Inhibitors with royalties paid to Novartis, Research Funding; AstraZeneca: Honoraria; Pharmacyclics: Honoraria, Research Funding; Merck: Honoraria, Research Funding; Acerta: Honoraria, Research Funding; Loxo Oncology: Honoraria; Nordic Nanovector: Honoraria; Pfizer: Honoraria; AbbVie: Honoraria, Research Funding; Gilead: Honoraria, Research Funding. de Vos:Verastem: Consultancy; Portola Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Bayer: Consultancy. Salles:Epizyme: Consultancy, Honoraria; Roche, Janssen, Gilead, Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Educational events; Amgen: Honoraria, Other: Educational events; BMS: Honoraria; Merck: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Educational events; Novartis, Servier, AbbVie, Karyopharm, Kite, MorphoSys: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Educational events; Autolus: Consultancy, Membership on an entity's Board of Directors or advisory committees. Jurczak:Bayer: Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Research Funding; Sandoz: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novo Nordisk: Research Funding; Celtrion: Research Funding; MorphoSys: Research Funding; Gilead: Research Funding; Roche: Research Funding; Servier: Research Funding; Takeda: Research Funding; TG Therapeutics: Research Funding; Loxo: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Rajakumaraswamy:Gilead Sciences, Inc.: Employment. Xing:Gilead Sciences, Inc.: Employment. Gopal:Seattle Genetics, Pfizer, Janssen, Gilead, Sanofi, Spectrum, Amgen, Aptevo, BRIM bio, Acerta, I-Mab-pharma, Takeda, Compliment, Asana Bio, and Incyte.: Consultancy; Teva, Bristol-Myers Squibb, Merck, Takeda, Seattle Genetics, Pfizer, Janssen, Takeda, and Effector: Research Funding; Seattle Genetics, Pfizer, Janssen, Gilead, Sanofi, Spectrum, Amgen, Aptevo, BRIM bio, Acerta, I-Mab-pharma, Takeda, Compliment, Asana Bio, and Incyte: Honoraria. OffLabel Disclosure: Idelalisib is a selective oral inhibitor of PI3K-delta that has shown antitumor activity in previously treated indolent non-Hodgkins lymphomas in phase 1 and 2 studies. It is approved for treatment of relapsed follicular lymphoma that has progressed on 2 prior systemic therapies, relapsed chronic lymphocytic leukemia in combination with rituximab when rituximab alone would be considered appropriate due to other comorbidities, and relapsed small lymphocytic lymphoma that has progressed on 2 prior systemic therapies. In this presentation, we provide results of 2 less common subgroups of indolent non-Hodgkins lymphoma, Âmarginal zone lymphoma and lymphoplasmacytic lymphoma/Waldenstrom's Macroglobulinemia, Âfrom the completed phase 2 trial with long-term follow-up.

Description: Background: Despite improved treatment options, indolent non-Hodgkin lymphoma (NHL) and Mantle Cell Lymphoma (MCL) remain incurable for most patients. Fenretinide (4-hydroxy(phenyl)retinamide; 4-HPR), an orally bioavailable synthetic retinoid, has been shown to induce apoptotic cell death in a variety of tumor types, presumably via intratumoral induction of oxygen free radicals. Our group has shown single-agent fenretinide anti-B-NHL activity as well as synergy with anti-CD20 antibody therapy when tested in vitro (Shan et al Clin Cancer Res. 2001) and in human xenograft models (Gopal et al, Blood 2004). These preclinical data support the first trial to evaluate this strategy of fenretinide and rituximab in patients with B-cell malignancies. Here we report results from a phase I-II study evaluating the safety and efficacy of fenretinide with rituximab for indolent NHL and MCL. Methods: This was an open-label, phase I/II study conducted at the Fred Hutchinson Cancer Research Center (FHCRC) and Seattle Cancer Care Alliance, Seattle, WA (ClinicalTrials.gov identifier: NCT00288067). The study was approved by the institutional review board at FHCRC and written informed consent was obtained from all patients. Major eligibility criteria included: CD20 positive lymphoid malignancy, radiographically measurable disease, ECOG PS ²2, and adequate organ function. The phase I portion evaluated the safety of dosing single agent fenretinide at 900 mg/m2 PO BID for days 1-5 of a 7 day cycle and allowed de-escalation for excess toxicity. The phase II portion added 375 mg/m2 IV rituximab weekly on weeks 5-9 then every 3 months. All patients could remain on therapy until disease progression or unacceptable toxicity. Response assessment occurred approximately every 3 months. Correlative studies included fenretinide pharmacokinetics, serum retinol concentrations, and evaluation of tumor expression of BCL-2 family proteins. Response was scored by standard criteria (Cheson 1999). Results: Thirty-two patients enrolled in the study: 7 patients in phase I, and 25 patients in phase II. The median age was 64 years (range, 40 - 78), 81% were male, and the median number of prior therapies was 1 (range, 0 - 10) with 22 (69%) having received prior rituximab and 8 (25%) with rituximab-refractory disease. Histologies included 13 CLL/SLL, 10 follicular (FL), 7 mantle cell (MCL), 1 lymphoplasmacytic, and 1 marginal zone. No dose limiting toxicities were observed in the phase I portion, and 900 mg/m2 was the dose level delivered in combination with rituximab for the phase II component. The most common treatment-related adverse events (AE) of any grade were reversible night blindness (n=18, 56%), other eye disorders (n=17, 53%), rash (n=12, 38%), and photosensitivity (n=8, 25%). The most common treatment related AEs of grade 3 or higher included: maculopapular rash, night blindness, and decreased lymphocyte count. Three patients (9%) discontinued treatment early due to toxicity (rash-2, GI toxicity-1). One patient with MCL in the phase I portion experienced stable disease (SD) lasting 35 months. In the phase II portion of the study, 5 (20%) patientÕs disease responded (Figure), with 2 (8%) achieving complete remission (both SLL/CLL), and 3 (12%) achieving partial remission (2 FL, 1 MCL). In addition 16 (64%) patients had SD. The median progression-free survival was 9 months (range, 6 - 31 months), and the median overall survival was not reached (range, 33 months to not reached). Median time to progression of responders was 14.5 months. The one-month median peak and trough concentrations of fenretinide were 11.45 µM and 2.5 µM, respectively. Correlative studies assessing Bcl-2, BAX, and apoptosis in the 13 patients with circulating tumor cells were not able to associate these data with response, or survival. Discussion: In this phase I/II study, the combination of fenretinide and rituximab was well tolerated with predictable, reversible toxicities with up to 4.5 years of continuous therapy. Though the ORR was modest (20%), the majority had of patients had disease control (ORR + SD=84%) which lasted for 〉 6 months. Further study of this novel combination should focus on identifying the subset of B-NHL that is most likely to respond or the rational addition of other agents to augment these anti-tumor effects. Figure 1. Figure 1. Disclosures Pagel: Actinium Pharmacetuicals, Inc.: Equity Ownership. Gopal:Merck: Research Funding; Emergent/Abbott: Research Funding; Cephalon/Teva: Research Funding; BioMarin: Research Funding; Sanofi-Aventis: Honoraria; Millenium: Honoraria, Research Funding; Seattle Genetics: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Spectrum: Consultancy, Research Funding; Gilead: Consultancy, Research Funding; Piramal: Research Funding; Biogen Idec, BMS: Research Funding.

Description: Introduction Multiple myeloma (MM) is considered incurable but patients achieving minimal-residual disease (MRD) negative status following treatment have significantly better overall and progression-free survival. MM is highly heterogeneous both between and within patients, limiting the curative potential of novel agents targeting specific pathways. However all MM is highly sensitive to radiation. The α-emitter astatine-211 (211At) deposits a very large amount of energy (~100 keV/μm) within a few cell diameters (50-90 μm) resulting in irreparable double strand DNA breaks, making 211At, targeted to MM cells, particularly suited to eliminating MRD. CD38 is expressed on malignant plasma cells regardless of mutational status, and CD38 monoclonal antibodies (mAbs) constitute a proven targeted therapy for MM but do not alone eradicate disease. We proposed that 211At conjugated to an anti-CD38 mAb could effectively eliminate MM MRD, and tested this hypothesis in cellular and murine models. Methods We conjugated the anti-CD38 mAb OKT10 and an isotype matched control mAb, BHV1, to the amine-reactive labeling agent B10-NCS and labeled the final constructs with 211At. To assess in vitro cell binding we incubated each labeled construct with CD38+ cell lines, washed, and then measured cell pellet radioactivity in a gamma counter. To assess cytotoxicity we incubated CD38+ and CD38- cell lines with unlabeled or 211At-labeled OKT10-B10 for 60 hrs, then assayed viability. NOD.Cg-Rag1tm1MomIl2rgtm1Wjl/SzJ (NRG) mice bearing H929luc or OPM-2luc MM xenografts were generated by subcutaneous (SQ) flank injection of 107 cells 7 days prior to treatment. MRD was modeled by intravenous (IV) injection of 2.5 - 5 x 105 cells 5 days prior to treatment. Radioimmunotherapy (RIT) was administered by IV injection of 7.5 - 45 µCi of 211At-OKT10-B10 or 211At-BHV1-B10. For biodistribution studies (n = 5/group) mouse tissues were harvested 24 hrs post RIT and measured in a gamma counter. For therapy studies (n = 8-10/group), all mice received syngeneic bone marrow transplant 3 days post RIT. Disease progression was assessed by tumor dimensions, luminescence imaging and survival. Results 211At-CD38 mAb selectively bound and killed CD38+ but not CD38- MM cells in vitro. In vivo, biodistribution experiments demonstrated that 211At-CD38 RIT delivered 2.4 times more radiation to MM xenografts than did control 211At-BHV1 RIT (p = 0.007), and delivered significantly higher dose to tumor than to healthy tissues including lung (p = 0.04) and kidney (p = 0.015). In murine therapy studies, 211At-CD38 RIT at 15 - 45 µCi at least doubled median survival relative to untreated controls in each of two MM SQ xenograft models (p 〈 0.003). However, no mice in these models achieved complete remission and all eventually died of disease. In contrast, therapy studies using MRD models showed that 30 µCi 211At-CD38 RIT eliminated detectable disease in 80% of mice at day 21, compared to 20% of mice receiving nontargeted 211At RIT and 0% of untreated mice. At day 130, 50% of the 30 µCi 211At-CD38-RIT mice remained alive and disease-free, while all nontargeted and untreated mice died before day 85 (Fig. 1, survival of 30 µCi 〉 15 µCi 211At-CD38-RIT [p = 0.016] and all other groups [p 〈 0.0007]). The impact of therapy on body weight as well as hematopoietic, liver and kidney function was mild and returned to normal within 32 days of treatment. Conclusions The efficacy of CD38 targeted 211At appears to be a function of disease distribution and malignant plasma cell access, as compellingly demonstrated by our models. Bulky tumor geometry reduces mAb penetration. In contrast, the isolated cells and small tumor clusters that define MRD are readily accessible to mAbs, creating optimal conditions for α-emitter cell kill. In an era of highly potent MM therapy, preventing relapse remains frustratingly rare. Our approach is both agnostic to high-risk cytogenetic features and offers the potential to eliminate all residual MM cell clones. These encouraging findings will be explored in a clinical trial of 211At-CD38 RIT. Disclosures Orozco: Actinium Pharmaceuticals: Research Funding. Jones:Juno Therapeutics, a Celgene Company: Employment, Equity Ownership. Till:Mustang Bio: Patents & Royalties, Research Funding. Gopal:Teva: Research Funding; Spectrum: Research Funding; Janssen: Consultancy, Research Funding; BMS: Research Funding; Incyte: Consultancy; Gilead: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Brim: Consultancy; Pfizer: Research Funding; Aptevo: Consultancy; Takeda: Research Funding; Merck: Research Funding; Asana: Consultancy. Green:Juno Therapeutics: Patents & Royalties, Research Funding.

Description: Relapsed mantle cell lymphoma is a radiation-sensitive malignancy that is unlikely to be cured by treatment with conventional high-dose therapy and autologous stem cell transplantation. We tested the safety and efficacy of using a CD20-specific monoclonal antibody conjugated with 131I to deliver high-dose radiation selectively to all lymphoma sites. Patients with relapsed or refractory mantle cell lymphoma received infusions of 131I-labeled CD20-specific monoclonal antibody (Tositumomab). The antibody dose was 1.7 mg/kg body weight, and the amount of 131I was calibrated to deliver 20 to 25 Gy to vital normal organs. This treatment was followed 10 days later by administration of high-dose etoposide (30-60 mg/kg), cyclophosphamide (60-100 mg/kg), and infusion of cryopreserved autologous stem cells. The 16 patients in this study had received a median of 3 prior treatments, and 7 had chemotherapy-resistant disease. The median dose of 131I was 510 mCi (18.87 GBq). There were no therapy-related deaths. Among the 11 patients with conventionally measurable disease at the time of treatment, the respective complete and overall response rates were 91% and 100%. Fifteen patients remain alive, and 12 have had no progression of lymphoma at 6 to 57 months from transplantation and 16 to 97 months from diagnosis. Overall survival at 3 years from transplantation is estimated at 93%, and progression-free survival is estimated at 61%. High-dose treatment with 131I-Tositumomab, etoposide, and cyclophosphamide results in a high remission rate and may provide long-term disease-free survival for patients with relapsed or refractory mantle cell lymphoma.