Increase In Tumor Doubling Time Research Articles

Abstract 2816: BUB1 inhibition radiosensitizes triple-negative breast cancer by targeting the DNA-damage repair pathways

Abstract Triple-negative breast cancer (TNBC) is the most lethal type of breast cancer (BC). TNBC has a substantial risk of locoregional recurrence and is difficult to cure due to absence of molecular targets or intrinsic heterogeneity. As radiotherapy (RT) is crucial in the treatment of BC, there is a need to identify novel molecular targets for increasing the efficacy of radiation therapy. BUB1 (Budding uninhibited by benzimidazoles 1) is a serine/threonine kinase implicated in chromosomal segregation during mitosis. However, it is still uncertain how BUB1 contributes to radioresistance in TNBC. By performing expression analysis (Oncomine), we observed that BUB1 is overexpressed in BC and even more in TNBC, indicating that this overexpression could be a prognostic factor for TNBC. MTT assay in several TNBC cell lines demonstrated that pharmacological (BAY1816032) or genomic (CRISPR) ablation of BUB1 was cytotoxic. By performing clonogenic survival assays, we observed that BUB1 ablation led to clinically meaningful radiosensitization in TNBC cell lines (SUM159, MDA-MB-231, MDA-MB-468) with radiation enhancement ratios ranging from 1.1 - 1.38. In addition, we showed that inhibition of BUB1 kinase function is essential for the radiosensitization phenotype using siRNAs and CRISPR knockouts by depleting endogenous BUB1 and reintroducing wild-type (WT) or kinase-dead (KD) BUB1. We observed significant increase in tumor doubling time in SUM159 xenografts (mammary fat pads in CB17/SCID mice) when BUB1i was combined with RT (DT=29.6 vs 7.9 days). A reduction in Ki67 was observed in these tumors further confirming the effectiveness of combination treatment. The effect of BUB1 depletion on DNA double strand break repair was assessed using γ-H2AX foci formation assay, which revealed sustained increase in γ-H2AX foci following radiation in BUB1i-treated cells. Further, BLRR assays confirmed that BUB1i reduces non-homologous end joining (NHEJ) efficiency. Biochemical analyses showed that BUB1i increases and stabilizes radiation-induced DNAPKcs phosphorylation (S2056). To evaluate the recruitment of DDR proteins to the chromatin following irradiation (IR), soluble nuclear and the chromatin-enriched fractionation was performed which demonstrated that cells pretreated with BUB1i had increased recruitment of DDR proteins to chromatin suggesting that BUB1 may play a role in the initial recruitment of NHEJ proteins to DSBs. Our findings demonstrate that both genetic and pharmacological inhibition of BUB1 sensitizes TNBC cells to RT and that BUB1 mediated radiosensitization may occur through NHEJ pathway. Our results suggest that BUB1 may represent a novel molecular target for radiosensitization in women with TNBC. Citation Format: Sushmitha Sriramulu, Shivani Thoidingjam, Pin Li, Stephen L. Brown, Farzan Siddiqui, Benjamin Movsas, Michael Green, Corey Speers, Shyam Nyati. BUB1 inhibition radiosensitizes triple-negative breast cancer by targeting the DNA-damage repair pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2816.

Phase II Trial of Cabozantinib Plus Erlotinib in Patients With Advanced Epidermal Growth Factor Receptor (EGFR)-Mutant Non-small Cell Lung Cancer With Progressive Disease on Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor Therapy: A California Cancer Consortium Phase II Trial (NCI 9303).

Introduction: Mesenchymal epidermal transition and vascular endothelial growth factor pathways are important in mediating non-small cell lung cancer (NSCLC) tumorigenesis and epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) resistance. We hypothesized that treatment with cabozantinib plus erlotinib in EGFR mutation-positive NSCLC following progression on EGFR TKI therapy may allow tumors to overcome this resistance or restore sensitivity to therapy regardless of T790M status.Methods: Patients with advanced NSCLC, known EGFR mutation and progressive disease on an EGFR TKI immediately prior to enrollment without intervening therapy were enrolled. Patients received erlotinib 150 mg and cabozantinib 40 mg daily. The primary endpoint was evaluation of efficacy by objective response rate. Secondary endpoints included assessment of progression free survival (PFS), overall survival, change in tumor growth rate, safety and toxicity, and the evaluation of specific EGFR mutations and MET amplification in pre-treatment tissue and plasma.Results: Thirty-seven patients were enrolled at 4 centers. Four patients had partial response (10.8%) and 21 had stable disease (59.5%). A greater than 30% increase in tumor doubling time was observed in 79% of assessable patients (27/34). Median PFS was 3.6 months for all patients. Diarrhea (32%) was the most common grade 3 adverse event; 3 patients had asymptomatic grade 4 elevation of amylase and lipase.Conclusions: Combination erlotinib and cabozantinib demonstrates activity in a highly pretreated population of patients with EGFR mutation and progression on EGFR TKI. Further elucidation of beneficial patient subsets is warranted.Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT01866410

Abstract A089: The effect of lactate dehydrogenase-A (LDH-A) knockdown and human prostate-specific membrane antigen (hPSMA) directed CAR T-cell treatment on hPSMA(+) Myc-CaP tumors

Abstract Objective: Determine whether LDH-A knockdown enhances CAR T-cell tumor-targeting and treatment response.Background: It has been shown that T-cells are restricted from entering many human and murine solid tumors, including both murine and human prostate tumors. CD3(+) T-cells are restricted from Myc-CaP murine prostate tumors and localize around the periphery of the tumor nodules (1). Human prostate specific membrane antigen (hPSMA) targeted CAR T-cells are also restricted from hPSMA(+) Myc-CaP tumors and this is only partially reversed by anti-PD1 treatment (1). This report describes the benefit of LDH-A depletion and a greater response of CAR T-cells targeting Myc-CaP tumors with low expression of LDH-A. Methods: LDH-A depletion in hPSMA(+) Myc-CaP cells bearing a bioluminescence reporter (Renilla Luciferase), was achieved by shRNA knockdown (KD) (1). A scrambled IgG shRNA was used as a control (NC). LDH-A expression was quantified by digital droplet PCR (ddPCR), Western blotting and LDH enzyme activity. The glycolytic activity of KD and NC cells was measured using Seahorse XF96 and XFp analyzers. Intratumoral lactate levels were monitored by magnetic resonance spectroscopy (MRS). The preparation and characterization of “second generation” hPSMA-directed CAR T-cells and the hPSMA(+) Myc-CaP tumor models in SCID mice have been described (1). To monitor CAR T-cell trafficking, T-cells were transduced with a Click Beetle Red luciferase reporter to enable efficient visualization by bioluminescence imaging (BLI) of CAR T-cell trafficking, persistence and viability within the hPSMA(+)Myc-CaP tumor mass. Tumor volume was calculated from caliper measurements. CD31 and PD-L1 expression was quantified with immunofluorescent staining and Metamorph Offline image analysis. Results and Discussion: These studies demonstrated that LDH-A KD was the dominant factor in reducing tumor growth. The difference in tumor doubling time (DT) between KD and NC tumors in the presence of CAR T-cell therapy was significant (p<0.0001): DT= 5.0±0.3 vs 2.9±0.5 days, respectively. A significant difference was also found in the absence of CAR T-cell therapy. Although LDH-A KD produced the larger single-treatment effect, the addition of CAR T-cells was additive. To explain these observations and study the effect of LDH-A KD on tumor metabolism and microenvironment, Seahorse and MRS experiments were performed. LDH-A depletion (KD) resulted in: lower rates of basal (NC: 24.0±1.9 vs KD: 6.9±1.9 pmol H+/min/µg protein; p<0.0001) and compensatory glycolysis (NC: 43.0±2.3 vs KD: 18.3±3.9 pmol H+/min/µg protein, p<0.0001), and lactate production. In contrast, basal and maximal respiration increased following LDH-A KD (NC: 4.0±0.8 vs KD: 8.3±0.6, p=0.0011, and NC: 6.7±1.4 vs KD: 13.8±0.6 pmol O2/min/µg protein, p=0.0003, respectively). However, total tumor lactate, measured in vivo by MRS, showed only marginal differences between KD and NC tumors. Nevertheless, there were significant differences in CAR T-cell trafficking-to and persistence-in KD compared to NC tumors, and the increase in tumor doubling time was directly related to the CAR T-cell expansion ratio. Interestingly, tumor vascularity (CD31), but not PD-L1, was significantly lower in KD compared to NC tumors. Necrosis was minimal in both KD and NC tumors, with or without CAR T-cell treatment. Conclusions: LDHA knockdown (KD) in the Myc-CaP murine prostate tumor model has a significant effect on tumor cell metabolism resulting in reduced glycolysis, reduced lactate production and increased oxidative phosphorylation that impacts the tumor microenvironment. The LDH-A KD induced changes in tumor metabolism and the microenvironment diminish Myc-CaP tumor growth rate and impact CAR T-cell trafficking and persistence in the tumor. Future studies will compare the effects of anti-PD1 and anti-CTLA4 therapy in combination with LDH-A knockdown. Reference: 1. Serganova I, et al. Molecular Therapy: Oncolytics 2017;4:41. Citation Format: Mayuresh M. Mane, Khalid Shalaby, Ivan Cohen, Avi Albeg, Jenny Ijoma, Myat Ko, Masatomo Maeda, Kiranmayi Vemuri, Jaya Satagopan, Anna Moroz, Juan Zurita, Larissa Shenker, Ellen Ackerstaff, Masahiro Shindo, Ekaterina Moroz, Maxim A. Moroz, Inna Serganova, Jason Koutcher, Vladimir Ponomarev, Ronald G. Blasberg. The effect of lactate dehydrogenase-A (LDH-A) knockdown and human prostate-specific membrane antigen (hPSMA) directed CAR T-cell treatment on hPSMA(+) Myc-CaP tumors [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A089.

Abstract 3091: Targeting low molecular weight (LMW) cyclin E-Cdk2 pathway for the prevention of breast cancer

Abstract Our laboratory was first to discover that full length cyclin E is proteolytically cleaved into low-molecular weight isoforms (LMW-E) specifically in tumor cells. The LMW-E isoforms are hyperactive and over-expressed in 70% of all triple negative breast cancer (TNBC) compared to only 30% of non-TNBC patients. Overexpression of LMW-E in transgenic mice induces mammary tumors similar to the basal subtype of breast cancer, which accounts for 70% of all human TNBCs. We have reported that Cdk2 deficient mice were completely resistant to LMW-cyclin E mediated mammary tumors. In this study, we have interrogated the ability of roscovitine in preventing the development of triple negative mammary tumors in the MMTV-LMW-E; p53+/- mouse model. Initially, a group of mice were treated from age 3 months with vehicle (DMSO/PBS, 40:60v/v, N = 8) or roscovitine (100 mg/kg, N = 8) once every 4 and 5 days alternatively by intraperitoneal injection and were followed up for mammary tumor development. Mice did not show any signs of toxicity. In this schedule of treatment, we did not find any difference in time to tumor formation or survival between the 2 groups (8.3 vs 7.9 months, P = 0.70, and 8.9 vs 8.4 months, P = 0.98, respectively). However, we found a 2.8-fold increase in tumor doubling time in the roscovitine-treated group indicating that roscovitine treatment decreased tumor growth (12.1+/-4.4 vs 4.4+/-0.9 days, P<0.05). This was due to a decreased proliferation as measured by BrdU immunohistochemistry (IHC) (13.6+/-0.9% vs 30.0 +/- 7.7%, P<0.05) and an increased apoptotic index as measured by cleaved caspase 3 IHC (49.6+/-9.4 CC3+ cells/x40 field vs 25.9 +/- 9.9, P<0.05). A second group of mice were treated at age 3 months with the same schedule but were killed after 2 months of treatment and the mammary glands were collected to investigate the effects of drug treatment on normal and premalignant mammary cells. The BrdU staining showed that 2 months of roscovitine treatment caused a 3-fold decrease in the number of BrdU positive cells (5.4+/-1.5% vs 14.6+/-3.8%, P<0.05) but did not completely block cyclin E-induced proliferation. This result may explain why the roscovitine-treated mice developed tumor with similar kinetics as the control group. Our ongoing work is to use gene expression profiling to determine the RNA changes induced by roscovitine for the discovery of potential biomarkers. The results from the first trial is suggestive that the mice need to be treated on a continued schedule to ensure that proliferation of the cyclin E overexpressing mammary tissue is completely inhibited. To this end, we are now treating the mice twice a day, 7 days on, 21 days off. We predict that the new treatment schedule will be more efficacious in inhibiting tumor formation. These preliminary data could support the development of a clinical trial testing cyclin-dependent kinase inhibitors for the prevention of human triple negative breast cancer especially those with LMW-E overexpression. Citation Format: Said Akli, Dong Yang, Tuyen N. Bui, Khandan Keyomarsi. Targeting low molecular weight (LMW) cyclin E-Cdk2 pathway for the prevention of breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3091. doi:10.1158/1538-7445.AM2015-3091

Encapsulation of mitoxantrone into pegylated SUVs enhances its antineoplastic efficacy

Mitoxantrone (MIT) was encapsulated into 60, 80 and 100 nm pegylated hydrogenated soy phosphatidylcholine/cholesterol (HSPC/chol) vesicles using a transmembrane (NH 4) 2SO 4 gradient. In-vitro release studies revealed that small-sized formulation had fast drug-release rate. Acute toxicity studies performed in c57 mice proved that all pegylated liposomal MIT (plm) formulations could be well-tolerated at a dose of 9 mg/kg, significantly compared to severe toxicity induced by free mitoxantrone (f-M). In KM mice, plm60 was at least 2- to 3-fold less toxic than f-M. After intravenous injection, plm60 was slowly eliminated from plasma relative to f-M, resulting in about 6459-fold increase in AUC and its plasma kinetics exhibited dose dependence. In S-180 bearing KM mice, plm60 preferentially accumulated into tumor zone, with a ∼12-fold increase in AUC and ∼10-fold increase in C max Furthermore, the accumulation of plm60 in almost all normal tissues markedly decreased. The antitumor efficacy of plm60 was also considerably enhanced. In L1210 ascitic tumor model, plm60 was the most efficacious which led to a ∼70% long-term survival, significantly compared to 16–33% survival rate in plm80, plm100 and f-M groups at the same dose level (4 mg/kg). The antitumor efficacy of plm60 was more encouraging in L1210 liver metastasis model. At a dose of 6 mg/kg, ∼90% animals receiving plm60 treatment could survive 60 days; however, in f-M group at the same dose, all the mice died at ∼14 days post inoculation. Similarly, plm60 could effectively inhibit the growth of RM-1 tumor in BDF1 mice, resulting in marked increase in tumor doubling time at different dose levels relative to f-M. The improved antineoplastic effects could be ascribed to its small vesicle size, which allowed more drug release after the accumulation into tumor zone. Theoretical considerations revealed that the reduction of vesicle size could increase the specific area of MIT/sulfate precipitate inside the vesicle and the release constant K, which is inversely proportional to vesicle volume ( K = pA m k 2 k 2 ′ / ( [ H + ] i 2 V i ) ) .

Peptide-Induced Inflammatory Increase in Vascular Permeability Improves Photosensitizer Delivery and Intersubject Photodynamic Treatment Efficacy

Photodynamic therapy (PDT) treatment can exhibit high intersubject variability due to the inherent differences in drug delivery within the tissue to be treated. In this study, the increased perfusion of the lipid-associated photosensitizer verteporfin was studied using substance P, a peptide known to increase vascular permeability. The transvascular permeability coefficient was quantified before and after administration of substance P, and the mean value increased from 0.026 to 0.043 microm/s with the induced inflammation. Correspondingly, there was a 40-50% increase in uptake of verteporfin in the tumor parenchyma in tumors injected with substance P compared to those without. This increased drug uptake resulted in a modest increase in tumor doubling time from 4 days with regular PDT to 6.2 days with substance P and PDT. There was also a significant reduction in the interindividual variability in with substance P plus PDT from 64% to 13%. The resulting treatment was therefore more effective and there was less variability in dose between subjects.

Alpha6 Integrin Cleavage: Sensitizing human prostate cancer to ionizing radiation

Purpose: The goal was to determine if prostate tumor cells containing a mutant α6 integrin would be defective in tumor re-population following clinically relevant fractionated ionizing radiation (IR) treatments.Material and methods: Human prostate cancer cells derived from PC3N cells were used which conditionally expressed a cleavable, wild type form of α6 integrin (PC3N-α6-WT) or a mutated non-cleavable form of α6 integrin (PC3N-α6-RR). The resulting tumor growth before, during and after fractionated doses of IR (3 Gy×10 days) was analyzed using the endpoints of tumor growth inhibition (T/C), tumor growth delay (T-C), tumor doubling time (Td) and tumor cell kill (Log10 cell kill).Results: The T/C values were 36.1% and 39.5%, the T-C values were 20.5 days and 28.5 days and the Td values were 5.5 and 10.5 days for the irradiated PC3N-α6-WT and PC3N-α6-RR cells, respectively. The Log10 was 1.1 for the PC3N-α6-WT cells and 0.8 for the PC3N-α6-RR cells. The tumor response to IR was altered in tumors expressing the mutant α6 integrin as indicated by a significant increase in tumor growth inhibition, an increase in tumor growth delay, an increase in tumor doubling time and an increase in tumor cell kill.Conclusions: Blocking integrin cleavage in vivo may be efficacious for increasing the IR responsiveness of slow growing, pro-metastatic human prostate cancer.

FXYD3 is overexpressed in pancreatic ductal adenocarcinoma and influences pancreatic cancer cell growth

The expression and localization of FXYD domain containing ion transport regulator 3 (FXYD3), a transmembrane protein that acts as a chloride channel or chloride channel regulator, was analyzed in pancreatic tissues derived from donors and patients suffering from chronic pancreatitis (CP) or pancreatic ductal adenocarcinoma (PDAC) as well as in pancreatic cancer cells using QRT-PCR, laser-capture microdissection and microarray analysis, in situ hybridization and immunohistochemistry. FXYD3 antisense expressing T3M4 pancreatic cancer cells were generated and compared to control cells using anchorage-dependent and independent growth assays, and xenotransplantation into nude mice. FXYD3 mRNA levels were 3.4-fold increased in PDAC tissues compared to donor specimens (p = 0.006), and 3.9-fold increased in microdissected cancer cells compared to normal pancreatic ductal cells (p = 0.02). FXYD3 was localized in the tubular complexes and PanIN lesions of both CP and PDAC, as well as in pancreatic cancer cells. Downregulation of FXYD3 by stable antisense transfection increased significantly the doubling time of T3M4 pancreatic cancer cells from 44 +/- 2 hr to 55 +/- 12 hr (p = 0.02). Nude mice transplanted with antisense transfected cells displayed a significant increase in tumor doubling time from 3.3 days +/- 1.0 to 4.3 days +/- 0.43 (p = 0.058). Anchorage-independent growth and sensitivity to 5-fluorouracil, gemcitabine and cisplatin as well as to MgCl(2) were not dependent on the level of FXYD3 expression. In conclusion, overexpression of FXYD3 in pancreatic cancer may contribute to the proliferative activity of this malignancy.

Preclinical evaluation of a prostate-targeted gene-directed enzyme prodrug therapy delivered by ovine atadenovirus.

Gene-directed enzyme prodrug therapy (GDEPT) based on the Escherichia coli enzyme, purine nucleoside phosphorylase (PNP), provides a novel strategy for treating slowly growing tumors like prostate cancer (CaP). PNP converts systemically administered prodrug, fludarabine phosphate, to a toxic metabolite, 2-fluoroadenine, that kills PNP-expressing and nearby cells by inhibiting DNA, RNA and protein synthesis. Reporter gene expression directed by a hybrid prostate-directed promoter and enhancer, PSMEPb, was assayed after plasmid transfection or viral transduction of prostate and non-CaP cell lines. Androgen-sensitive (AS) LNCaP-LN3 and androgen-independent (AI) PC3 human CaP xenografts in nude mice were injected intratumorally with an ovine atadenovirus vector, OAdV623, that carries the PNP gene under PSMEPb, formulated with cationic lipid for enhanced infectivity. Fludarabine phosphate was then given intraperitoneally for 5 days at 75 mg/m2/day. PNP expression was evaluated by enzymic conversion of its substrate using reverse phase HPLC. OAdV623 showed excellent in vitro transcriptional specificity for CaP cells. In vivo, expression of PNP persisted for > 6 days after OAdV623 injection and a single treatment provided 100% increase in tumor doubling time and > 50% inhibition of tumor growth for both LNCaP-LN3 and PC3 lines, with increased tumor necrosis and apoptosis and decreased tumor cell proliferation. OAdV623 significantly suppressed the growth of AS and AI human CaP xenografts in mice.

Antagonists of bombesin/gastrin‐releasing peptide inhibit growth of SW‐1990 human pancreatic adenocarcinoma and production of cyclic AMP

We investigated the effects of bombesin/GRP antagonists RC-3095 and RC-3940-II on the growth of SW-1990 human pancreatic adenocarcinoma cells xenografted into nude mice or cultured in vitro. Nude mice implanted with SW-1990 tumors received s.c. injections of RC-3095 and RC-3940-II or the vehicle (control) for 28 days. Chronic administration of RC-3940-II inhibited the growth of SW-1990 tumors, as shown by a reduction in tumor volume during the treatment and a significant increase in tumor doubling time. RC-3940-II decreased final tumor volume by 57.7% and tumor growth rate by 65%. Final tumor weights in mice treated with RC-3940-II were 75% lower than in controls. Treatment with RC-3095 induced smaller, and not significant, decreases in tumor volume and weight. In cell cultures, both RC-3095 and RC-3940-II effectively inhibited the proliferation of SW-1990 cells, inducing a dose- and time-dependent decrease in the number of cells. RC-3940-II again suppressed in vitro growth of SW-1990 cells more effectively than RC-3095. After 72 hr of culture, RC-3940-II and RC-3095 at 1 microM concentrations decreased cell numbers by 45.7% and 27.7%, respectively. The estimated EC50 value for RC-3940-II was 1 nM. When SW-1990 cells were cultured in the presence of 1 nM and 10 nM RC-3095 for 72 hr, cAMP levels in the incubation medium were decreased to 77.3% and 26.9% of the control value. Our results indicate that bombesin/GRP antagonist RC-3940-II can inhibit the proliferation of SW-1990 human pancreatic adenocarcinoma cells in vivo and in vitro. Our findings also suggest that this effect may involve the intracellular cAMP pathway.

Inhibition of growth of OV-1063 human epithelial ovarian cancer xenografts in nude mice by treatment with luteinizing hormone-releasing hormone antagonist SB-75.

Female athymic nude mice bearing xenografts of OV-1063 human epithelial ovarian cancer cell line were treated with potent luteinizing hormone (LH)-releasing hormone (LH-RH) antagonist SB-75 (Cetrorelix; [Ac-D-Nal(2)1, D-Phe(4 CI)2, D-Pal(3)3, D-Cit6, D-Ala10]LH-RH in which Ac-D-Nal(2) = N-acetyl-3-(2-naphthyl)-D-alanine, D-Phe(4CI) = 4-chloro-D-phenylalanine, D-Pal(3) = 3-(3-pyridyl)-D-alanine, and D-Cit = D-Citrulline) or with the agonist [D-Trp6]LH-RH. In the first experiment, SB-75 and [D-Trp6]LH-RH were administered in the form of microcapsules releasing 60 and 25 micrograms/day, respectively. In the second study, the analogs were given by daily s.c. injections in doses of 100 micrograms/day. In both experiments, tumor growth, as measured by reduction in tumor volume, percentage change in tumor volume, tumor burden, and increase in tumor doubling time, was significantly inhibited by treatment with SB-75 but not with [D-Trp6]LH-RH. Uterine and ovarian weights were reduced and serum LH levels decreased by administration of either analog. Chronic treatment with SB-75 greatly reduced the concentration of receptors for epidermal growth factor and insulin-like growth factor I in tumor cell membranes, a phenomenon that might be related to tumor growth inhibition. It is possible that the antitumoral effects of SB-75 on OV-1063 ovarian cancers are exerted not only through the suppression of the pituitary-gonadal axis, but also directly. In view of its strong inhibitory effect on the growth of OV-1063 ovarian cancers in vivo, the potent LH-RH antagonist SB-75 might be considered for possible hormonal therapy of advanced epithelial ovarian carcinoma.

Comparison of 131I- and 90Y-labeled monoclonal antibody 17-1A for treatment of human colon cancer xenografts

The choice of radionuclide remains an important question in clinical radioimmunotherapy. Therefore, a study was initiated, using an in vivo model system, to assess the relative merits of 131I- and 90Y-labeled 17-1A monoclonal antibody as therapeutic agents in the treatment of colon cancer. 131Iodine- and 90Y-labeled 17-1A were assessed in animal therapy trials using athymic nude mice bearing LS174T human colon cancer xenografts. 131Iodine-labeled 17-1A decreased tumor growth in a dose-dependent fashion without lethality. In contrast, the doses of 90Y-labeled 17-1A which were required to produce a significant increase in tumor doubling time also caused marked toxicity. Although similar tumor growth inhibition was produced by 250 μCi 90Y- and 150 μCi 131I-labeled 17-1A, Medical Internal Radiation Dose calculations based on biodistribution data estimated that the dose delivered by 90Y was greater than that delivered by 131I. To investigate this discrepancy, 3-dimensional dose distributions within LS174T tumors were assessed using autoradiography and 3-dimensional calculational techniques. It was found that a greater fraction of the dose was deposited in the tumor after treatment with 131I- compared to 90Y-labeled 17-1A. When the Medical Internal Radiation Dose calculations were adjusted using the 3-dimensional dose distributions, 250 μCi of 90Y- and 150 μCi of 131I-labeled 17-1A were found to deliver similar tumor doses. These studies suggest that 131I-labeled 17-1A is superior to 90Y-labeled 17-1A, since 131I-labeled antibody produced less hematological and animal toxicity and was more effective at inhibiting LS174T tumor growth than 90Y-labeled antibody across the range of radionuclide doses tested. Furthermore, they suggest that it will be necessary to perform 3-dimensional dose calculations in addition to Medical Internal Radiation Dose calculations in order to interpret tumor dosimetry.

Mechanism of Antitumor Activity of Tumor Necrosis Factor With Hyperthermia in a Tumor Necrosis Factor -Resistant Tumor

Cells from a radiation-induced fibrosarcoma (RIF-1) are exceedingly resistant to tumor necrosis factor alpha (TNF-alpha) in vitro. We tested whether the addition of mild hyperthermia (42.5 degrees C, 30 minutes) could enhance TNF-alpha activity against RIF-1 tumors growing in syngeneic hosts (C3H mice). TNF-alpha was administered intratumorally. Tumor cell killing essentially was not measurable following TNF-alpha, hyperthermia, or a combination of the two. Single-modality treatments also had no effect on tumor growth delay or on the x-ray dose (given 24 hours after the primary treatment) required to sterilize 50% of the tumors. The combination of TNF-alpha and hyperthermia, however, resulted in a marked increase in tumor doubling time and a highly significant reduction in the x-ray dose required to sterilize the tumors. Syngeneic lymph nodal lymphocytes and blood leukocytes did not appear to mediate the action of TNF-alpha on RIF-1 cells in vitro. Necrosis and hemorrhage were the most prominent histopathological alterations in the treated tumors. Electron microscopic studies 6 hours after therapy showed increased damage to capillary endothelial cells and accumulation of neutrophils in the capillaries of tumors treated with TNF-alpha with or without heat, suggesting that neutrophils may mediate the endothelial cell injury. These observations indicate a greater than additive tumoricidal effect of TNF-alpha with hyperthermia. Furthermore, they support the concept that the interaction between the two agents damages the vasculature, compromising the microcirculation and ultimately causing ischemic tumor necrosis.