Evidence for Feedback Regulation Following Cholesterol Lowering Therapy in a Prostate Cancer Xenograft Model

BACKGROUND

Epidemiologic data suggest cholesterol-lowering drugs may prevent the progression of prostate cancer, but not the incidence of the disease. However, the association of combination therapy in cholesterol reduction on prostate or any cancer is unclear. In this study, we compared the effects of the cholesterol lowering drugs simvastatin and ezetimibe alone or in combination on the growth of LAPC-4 prostate cancer in vivo xenografts.

METHODS

Proliferation assays were conducted by MTS solution and assessed by Student's t-test. 90 male nude mice were placed on a high-cholesterol Western-diet for 7 days then injected subcutaneously with 1 × 10⁵ LAPC-4 cells. Two weeks post-injection, mice were randomized to control, 11 mg/kg/day simvastatin, 30 mg/kg ezetimibe, or the combination and sacrificed 42 days post-randomization. We used a generalized linear model with the predictor variables of treatment, time, and treatment by time (i.e., interaction term) with tumor volume as the outcome variable. Total serum and tumor cholesterol were measured. Tumoral RNA was extracted and cDNA synthesized from 1 ug of total RNA for quantitative real-time PCR.

RESULTS

Simvastatin directly reduced in vitro prostate cell proliferation in a dose-dependent, cell line-specific manner, but ezetimibe had no effect. In vivo, low continuous dosing of ezetimibe, delivered by food, or simvastatin, delivered via an osmotic pump had no effect on tumor growth compared to control mice. In contrast, dual treatment of simvastatin and ezetimibe accelerated tumor growth. Ezetimibe significantly lowered serum cholesterol by 15%, while simvastatin had no effect. Ezetimibe treatment resulted in higher tumor cholesterol. A sixfold induction of low density lipoprotein receptor mRNA was observed in ezetimibe and the combination with simvastatin versus control tumors.

CONCLUSIONS

Systemic cholesterol lowering by ezetimibe did not slow tumor growth, nor did the cholesterol independent effects of simvastatin and the combined treatment increased tumor growth. Despite lower serum cholesterol, tumors from ezetimibe treated mice had higher levels of cholesterol. This study suggests that induction of low density lipoprotein receptor is a possible mechanism of resistance that prostate tumors use to counteract the therapeutic effects of lowering serum cholesterol. Prostate 77:446-457, 2017. © 2016 Wiley Periodicals, Inc.

The effect of carbohydrate restriction on prostate cancer tumor growth in a castrate mouse xenograft model

BACKGROUND

No- and low-carbohydrate diets delay tumor growth compared to western diet (WD) in prostate cancer (PCa) xenograft studies. The effect of these diets in concert with androgen deprivation is unknown.

METHODS

A total of 160 male SCID mice were injected with 1× 10(5) LAPC-4 human PCa cells. Of these, 150 mice were castrated and randomized to an ad libitum WD or fed via a paired-feeding protocol with a no-carbohydrate ketogenic diet (NCKD), 10% carbohydrate diet, or 20% carbohydrate diet. The remaining 10 mice were not castrated and were fed an ad libitum WD. The mice were sacrificed once volumes reached 1,000 mm3 and survival tested using the log-rank test. Serum from the median surviving 8 mice/group was assayed for insulin, IGF-1, and IGFBP-3.

RESULTS

Body weights were roughly equal among groups. The 10 non-castrated mice experienced accelerated tumor growth. Among castrated mice, WD had the most rapid tumor growth; 20% carbohydrate diet the slowest (P = 0.046). Survival was not significantly different among the various carbohydrate restricted groups (P = 0.51). When pooled, there was a non-significant trend (P = 0.11) in improved survival among the carbohydrate restricted diets versus WD. No significant difference in serum insulin, IGF-1, and IGFBP-3 levels was noted among all groups at pre-randomization or at sacrifice.

CONCLUSIONS

A 20% carbohydrate diet slowed tumor growth versus a WD. Though the benefit of carbohydrate restriction was somewhat less than in prior studies in non-castrate mice, these data still suggest diets achievable in humans may play a role in PCa management.

Abstract 4611: Effect of pomegranate and diet on prostate cancer tumor growth and survival

Background: Pomegranate extract (POM) has been shown to slow prostate cancer (PC) growth in xenograft models. However, mice in these studies ate standard mouse chow, which is very low-fat (∼12% kcals) and not representative of the typical diet for men with PC. Whether POM slows PC growth when taken with a Western diet is unknown. As our group showed diet to separately affect PC xenograft growth, with a no-carbohydrate ketogenic diet (NCKD) being protective vs. a Western diet, we tested the effects of POM on PC growth and survival in mice fed a Western or NCK diet.

Methods: 120 male athymic nude mice (age 6-8 weeks) were fed an ad libitum Western diet and injected subcutaneously with 1×10⁁6 LAPC-4 cells. Two weeks later, mice were randomized to remain on Western diet alone or switched to Western diet + POM, NCKD alone, or NCKD + POM treatments (n=30 per arm). Western diet mice were fed ad libitum and NCKD mice via a modified pair-feeding protocol. POM arms received gavage with 0.8 mg POMx extract (PomWonderful) Monday-Friday and control mice received PBS (0.2 mL all arms). Mice were sacrificed when tumors exceeded 1,000 mm⁁3. Tumor volumes were compared between arms using Kruskal-Wallis. Survival between arms was tested using Cox proportional hazards.

Results: The study is currently on-going and results are preliminary for day 53 post-injection. To date, significant differences in tumor volume have been noted across the study arms (p=0.007) with NCKD + POM mice having significantly smaller tumors than mice fed base Western diet (p=0.03). In mice fed NCKD, the addition of POM resulted in a trend toward smaller tumors (p=0.07). In contrast, in mice on Western diet, the addition of POM resulted in a trend toward larger tumors (p=0.13). Diet type alone did not affect tumor volume (p=1.00). Preliminary survival data suggest that treatment group impacted survival (p=0.055). Specifically, survival for the NCKD + POM arm was better than either Western + POM or NCKD alone arms (all p<0.046).

Conclusion: In a xenograft mouse model, the combination of POM and dietary carbohydrate restriction slows PC tumor growth relative to a control Western diet and improves survival vs. either POM or NCKD treatments alone. Interestingly, our data show that POM delays tumor growth in mice fed NCKD but may actually accelerate tumor growth in mice fed a Western diet. Prior pomegranate studies reporting delayed tumor growth utilized very low-fat diets, which we have also shown to slow tumor growth vs. a Western diet, while our findings suggest that dietary background may profoundly influence the effect of pomegranate extract on PC tumor growth and survival. This is especially important given that men with PC are more likely to consume a Western diet.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4611. doi:10.1158/1538-7445.AM2011-4611

Abstract 4602: Cholesterol and ezetimibe: Effects on tumor growth and survival outcomes: An interim analysis

Introduction and Objectives: Prostate cancer (PC) is affected by cholesterol metabolism and cholesterol-mediating medications. Ezetimibe, a gut cholesterol-uptake inhibitor, inhibits angiogenesis in human PC xenografts when given as preventive therapy. We investigated the effect of ezetimibe on PC growth when given as treatment therapy.

Methods: We randomized 125 SCID mice into three initial diets: a high-fat, low-cholesterol diet (HFLC) (40% fat, 43% carbohydrates, 17% protein, 0.21% cholesterol), a high-fat, high-cholesterol diet (HFHC) (40% fat, 43% carbohydrates, 17% protein, 1.25% cholesterol), and a high-fat, high-cholesterol diet supplemented with ezetimibe (30mg/kg) (HFHC+Z). Mice were fed ad libitum. After two weeks, we injected 106 LNCaP cells into the flanks, with 5-10 mice/group serving as non-injected controls. At two weeks post-injection, half the injected and control mice in the HFHC diet group had ezetimibe added to their diet (HFHC+delayed Z). Tumor volumes and body weights were measured twice weekly. Mice were sacrificed once tumors reached 1000mm3. Body weights and tumor volumes were compared across groups using Kruskal-Wallis test. Interim survival outcomes for this on-going study up to 86 days post-injection were evaluated with Cox proportional hazards.

Results: At 1 day prior to injection, there were no significant differences in body weights across groups. At post-injection day (PD) 2, HFHC+Z mice with tumors were significantly lighter vs. all other mice (p=0.009). By PD 21, HFHC+delayed Z mice with tumors also became significantly lighter vs. the HFLC and HFHC mice with tumors (p<0.001). At PD 86, all mice with tumors were significantly lighter than their control counterparts without tumors (all p<0.013). Tumor volumes were not significantly different across groups (p=0.280). Likewise, survival was not significantly different across groups at PD 86 (p=0.125).

Conclusion: Preliminary evidence from this on-going study demonstrates that ezetimibe is associated with weight loss, but only in mice with PC xenografts. The administration of ezetimibe as preventive vs. treatment therapy does not appear to affect tumor growth or survival. Future studies to explore the interplay between cholesterol metabolism and PC include comparing serum levels of cholesterol, insulin, IGF-1, and IGFBP-3, and tumor markers of proliferation and angiogenesis including akt, pakt, mTOR, VEGF, HIF, CD31 (microvessel density) and ki67 (proliferation). Moreover, we are continuing to follow the mice for any differences in tumor growth or survival.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4602. doi:10.1158/1538-7445.AM2011-4602

Effect of intermittent fasting on prostate cancer tumor growth in a mouse model

Caloric restriction (CR) has been shown to have anti-cancer properties. However, CR may be difficult to apply in humans secondary to compliance and potentially deleterious effects. An alternative is intermittent CR, or in the extreme case intermittent fasting (IF). In a previous small pilot study, we found 2 days per week of IF with ad libitum feeding on the other days resulted in trends toward prolonged survival of mice bearing prostate cancer xenografts. We sought to confirm these findings in a larger study. A total of 100 (7- to 8-week-old) male severe combined immunodeficiency mice were injected subcutaneously with 1 × 10(5) LAPC-4 prostate cancer cells. Mice were randomized to either ad libitum Western Diet (44% carbohydrates, 40% fat and 16% protein) or ad libitum Western Diet with twice-weekly 24 h fasts (IF). Tumor volumes and mouse bodyweights were measured twice weekly. Mice were killed when tumor volumes reached 1000 mm(3). Serum and tumor were collected for analysis of the insulin/insulin-like growth factor 1 (IGF-1) hormonal axis. Overall, there was no difference in mouse survival (P=0.37) or tumor volumes (P ≥ 0.10) between groups. Mouse body weights were similar between arms (P=0.84). IF mice had significantly higher serum IGF-1 levels and IGF-1/IGFBP-3 ratios at killing (P<0.001). However, no difference was observed in serum insulin, IGFBP-3 or tumor phospho-Akt levels (P ≥ 0.39). IF did not improve mouse survival nor did it delay prostate tumor growth. This may be secondary to metabolic adaptations to the 24 h fasting periods. Future studies are required to optimize CR for application in humans.

Low-carbohydrate diets and prostate cancer: how low is "low enough"?

Previous studies indicate that carbohydrate intake influences prostate cancer biology, as mice fed a no-carbohydrate ketogenic diet (NCKD) had significantly smaller xenograft tumors and longer survival than mice fed a Western diet. As it is nearly impossible for humans to consume and maintain NCKD, we determined whether diets containing 10% or 20% carbohydrate kcal showed similar tumor growth as NCKD. A total of 150 male severe combined immunodeficient mice were fed a Western diet ad libitum, injected with the human prostate cancer cell line LAPC-4, and then randomized 2 weeks later to one of three arms: NCKD, 10% carbohydrate, or 20% carbohydrate diets. Ten mice not injected were fed an ad libitum low-fat diet (12% fat kcal) serving as the reference in a modified-paired feeding protocol. Mice were sacrificed when tumors reached 1,000 mm(3). Despite consuming extra calories, all mice receiving low-carbohydrate diets were significantly lighter than those receiving a low-fat diet (P < 0.04). Among the low-carbohydrate arms, NCKD-fed mice were significantly lighter than the 10% or 20% carbohydrate groups (P < 0.05). Tumors were significantly larger in the 10% carbohydrate group on days 52 and 59 (P < 0.05), but at no other point during the study. Diet did not affect survival (P = 0.34). There were no differences in serum insulin-like growth factor-I or insulin-like growth factor binding protein-3 at sacrifice among the low-carbohydrate arms (P = 0.07 and P = 0.55, respectively). Insulin was significantly lower in the 20% carbohydrate arm (P = 0.03). LAPC-4 xenograft mice fed a low-carbohydrate diet (10-20% carbohydrate kcal) had similar survival as mice consuming NCKD (0% carbohydrate kcal).

Effect of intermittent fasting with or without caloric restriction on prostate cancer growth and survival in SCID mice

INTRODUCTION

Caloric restriction (CR) delays cancer growth in animals, though translation to humans is difficult. We hypothesized intermittent fasting (i.e., intermittent extreme CR), may be better tolerated and prolong survival of prostate cancer (CaP) bearing mice.

METHODS

We conducted a pilot study by injecting 105 male individually-housed SCID mice with LAPC-4 cells. When tumors reached 200 mm(3), 15 mice/group were randomized to one of seven diets and sacrificed when tumors reached 1,500 mm(3): Group 1: ad libitum 7 days/week; Group 2: fasted 1 day/week and ad libitum 6 days/week; Group 3: fasted 1 day/week and fed 6 days/week via paired feeding to maintain isocaloric conditions to Group 1; Group 4: 14% CR 7 days/week; Group 5: fasted 2 days/week and ad libitum 5 days/week; Group 6: fasted 2 day/week and fed 5 days/week via paired feeding to maintain isocaloric conditions to Group 1; Group 7: 28% CR 7 days/week. Sera from mice at sacrifice were analyzed for IGF-axis hormones.

RESULTS

There were no significant differences in survival among any groups. However, relative to Group 1, there were non-significant trends for improved survival for Groups 3 (HR 0.65, P = 0.26), 5 (0.60, P = 0.18), 6 (HR 0.59, P = 0.16), and 7 (P = 0.59, P = 0.17). Relative to Group 1, body weights and IGF-1 levels were significantly lower in Groups 6 and 7.

CONCLUSIONS

This exploratory study found non-significant trends toward improved survival with some intermittent fasting regimens, in the absence of weight loss. Larger appropriately powered studies to detect modest, but clinically important differences are necessary to confirm these findings.

Abstract 2816: Low-carbohydrate diets and prostate cancer growth: How low is “low enough”

Introduction: Previous dietary studies indicate carbohydrate intake may influence prostate cancer biology, as LAPC-4 and LNCaP xenograft mice fed a no-carbohydrate ketogenic diet (NCKD; 84% fat-0% carbohydrate-16% protein kcal) had significantly smaller tumors and longer survival times compared to mice fed a Western diet (40% fat-44% carbohydrate-16% protein kcal). The NCKD mice were also found to have higher levels of circulating IGFBP-3 and the lowest levels of insulin, IGF-1, and IGF-1:IGFBP-3 ratio despite consuming more calories than the Western group. As it is nearly impossible for a human to consume and maintain a no-carbohydrate diet similar to that in the previous xenograft studies, we sought to determine whether diets containing 10% or 20% kcal from carbohydrates could slow tumor growth in a similar manner to the NCKD in a xenograft model.

METHODS: A total of 150 male SCID mice were injected with LAPC-4 cells and placed on a Western diet (35% fat-49% carbohydrate-16% protein kcal) ad libitum. Two weeks post-injection, all mice were randomized to one of three arms: NCKD, 10% carbohydrate, or 20% carbohydrate. Ten mice not injected with tumor were fed an ad libitum low-fat diet (12% fat-72% carbohydrate-16% protein kcal) and served as the reference group in a modified-paired feeding protocol for the other three groups. Calorie intake and body weights were measured thrice weekly and tumor volumes twice per week. Mice were sacrificed when tumors reached 1,000mm3.

RESULTS: Despite consuming 5-10% extra calories on average, all mice receiving low-carbohydrate diets were significantly lighter than the mice consuming the low-fat diet (p&lt;0.04). Overall, the mice fed a NCKD were significantly lighter than the other two arms at multiple time points (p&lt;0.05). There were no significant differences in tumor volumes among groups at any time except at Day 52 and 59, where 10% carbohydrate mice had larger tumors (p&lt;0.05). However, after adjusting for the fact that tumor volumes were compared at multiple time points (i.e. multiple comparisons), these were no longer significant. Dietary treatment did not impact overall survival (p=0.34). NCKD mice had significantly higher glucose levels at sacrifice compared to the mice fed 10% and 20% carbohydrates (p=0.001), but similar levels of urinary ketones (p=0.37).

CONCLUSIONS: LAPC-4 xenograft mice fed a low-carbohydrate diet (10-20% carbohydrate kcal) had similar survival to mice consuming a NCKD (0% carbohydrate kcal). Thus, the survival benefit of a NCKD may be achievable with less restrictive low-carbohydrate diets.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2816.

Combination versus single agent therapy in effecting complete therapeutic response in human bladder cancer: analysis of cisplatin and/or 5-fluorouracil in an in vivo survival model

An in vivo study of cisplatin (CDDP) and 5-fluorouracil (5FU) cytotoxicity was performed using a multidose matrix with a human bladder transitional cell carcinoma xenograft tumor line (DU4284) tested by subrenal capsule assay in 154 nude mice (NM-SRCA). Statistical analysis of initial growth inhibition at 20 days and host survival demonstrates therapeutic, cooperative interaction. Toxic doses of either CDDP or 5FU alone as well as low-dose combinations provided modest or no survival benefit. The single dose of CDDP (7 mg/kg) and of 5FU (100 mg/kg) was best (by analysis of efficacy and toxicity) of those tested and caused > 97% initial regression. While 94% of controls incurred tumor deaths by 225 days, 75% treated at this dose were tumor free and likely cured. Our conclusions were: (a) NM-SRCA human xenograft testing is excellent for rapid in vivo screening of promising treatment strategies to evaluate for efficacy at acceptable toxicity, but confirmation of true therapeutic impact should be sought by correlating initial growth inhibition with host survival; (b) enhanced survival seen only when CDDP/5FU are used together (versus either single agent) supports the value of pursuing histiotype-specific screening of potentially synergistic drug combinations; and (c) of clinical relevance, human transitional cell carcinoma is now identified as a histiotype in which a therapeutic, cooperative interaction between CDDP/5FU has been demonstrated in vivo.

The therapeutic impact of dipyridamole: chemopotentiation of the cytotoxic combination 5-fluorouracil/cisplatin in an animal model of human bladder cancer

Using an in vivo assay of tumor cytotoxicity (the subrenal capsule assay in nude mice), two therapeutic strategies for the treatment of advanced human transitional cell carcinoma have been evaluated: 1) the use of 5-fluorouracil in combination with cisplatin and 2) the ability of the chemosensitizer dipyridamole to augment the cytotoxicity of CDDP and 5FU. A moderate cytotoxic response of human TCC line DU-4284 to single agent CDDP was seen; it was dose dependent at minimally toxic doses [maximal cytotoxicity--27% tumor survival (%TS) relative to control]. Efficacy was further significantly enhanced by the addition of DP [11%TS (p = .008)]. 5FU at minimally toxic doses (100 and 150 mg./kg.) also demonstrated moderate dose-dependent cytotoxic activity (35 and 31%TS, respectively) which was further enhanced by DP [21%TS (p = .03) and 18%TS (p = .05)]. A constant dose ratio of CDDP/5FU when diluted showed dose-dependent cytotoxicity; at the highest dose dilution studied, substantial cytotoxic efficacy (17%TS) was attained. The cytotoxicity of 5FU/CDDP was order independent (p = .95). The addition of DP to this combination (5FU/CDDP) further enhanced efficacy; host toxicity was not substantially enhanced. A multiple regression analysis confirmed a statistically significant effect of DP with both CDDP and 5FU (p = .001 and 0.0001, respectively); tests for trend showed no significant interaction (p = 0.33 for all models). It is concluded that, in this preclinical in vivo model of human bladder cancer, 1) CDDP and 5FU show substantial enhanced efficacy when combined, and 2) DP serves as an in vivo chemosensitizer of both CDDP and 5FU; DP further augments the efficacy of this binary combination. These data would indicate the potential of this ternary (5FU/CDDP/DP) drug therapeutic regimen for clinical trial to treat advanced bladder cancer.

Establishment and characterization of a new human prostatic carcinoma cell line (DuPro-1)

A new human prostate adenocarcinoma cell line (DuPro-1) has been established from the athymic nude mouse supported xenograft DU5683. This was accomplished by embedding dispersed xenograft cells in 0.1 by 5.0 cm. spaghetti-like strands of Basement Membrane MATRIGEL [BMM (Collaborative Research, Inc.)], a unique technique facilitating the transition to tissue culture. Now passed over 30 times, the cells display anchorage and serum concentration independent growth with a doubling time of 22 to 24 hours. Cells exhibit pronounced morphological differences when grown on BMM coated culture dishes, assuming a pseudoglandular configuration, in contrast to typical homogeneous monolayer growth on plastic culture dishes. Light and electron microscopy show cohesive sheets of anaplastic epithelial cells, consistent with prostate carcinoma. Karyotypic analysis revealed all human chromosomes, near tetraploidy, 10 to 12 markers, and 3 to 4 X chromosomes, without a Y chromosome. Cells injected s.c. or embedded in BMM and implanted in the subrenal capsule space are equally tumorigenic in male and female athymic mice, suggesting that DuPro-1 cells are hormonally insensitive. Embedding cells in BMM may be useful in developing other tissue culture cell lines from neoplasms difficult to initiate in vitro. DuPro-1 should provide a valuable means to study the biology, immunology, and chemosensitivity of human prostate cancer.

Dipyridamole-cisplatin potentiation: enhanced in vivo cytotoxicity in xenograft models of human testicular and bladder cancers

The antitumor efficacy and host toxicity of dipyridamole (DP), methotrexate (MTX) and cisplatin (CDDP) alone and combined were evaluated in a nude mouse supported human bladder cancer model. Single agent post treatment tumor volume growth ratio [TGR] values of DP, MTX and CDDP were 97%, 65% and 49% of control. While the MTX/DP combination produced only mild cytotoxic enhancement, CDDP/DP and CDDP/MTX/DP reduced TGR to 20% and 17%, respectively. A second multi-dose evaluation of CDDP/DP using human testicular carcinoma in this model also showed a CDDP dose-dependent response with achievable complete tumor regression. Host toxicity was not substantially increased by DP. DP would appear to be effective in vivo as a chemosensitizer of CDDP; it may enhance the therapeutic efficacy of CDDP in a variety of tumors.

Enhanced in vivo cytotoxicity of recombinant human tumor necrosis factor with etoposide in human renal cell carcinoma. Evaluation in a pre-clinical model

The combination of tumor necrosis factor (TNF) and etoposide (ETP) was evaluated for potential cytotoxic efficacy against a human renal cell carcinoma xenograft using an in vivo assay employing an athymic mouse host with tumor implanted a the subrenal capsule site. Both antitumor efficacy (relative survival or RTS) and toxicity (weight loss) of TNF and ETP alone and in combination were evaluated. While TNF and ETP alone were mildly inhibitory (RTS 90% and 71%, respectively), the combination caused marked tumor inhibition (45% of controls). Host toxicity encountered with the combination did not exceed the toxicity associated with ETP alone, suggesting that the therapeutic index may have been augmented. It is concluded that enhanced antitumor activity without substantial augmentation of toxicity is observed with this combination, providing a rationale for further evaluation of tumor necrosis factor-based regimens for the treatment of advanced renal carcinoma.

Rationale for immunotoxin therapy of metastatic prostate carcinoma formatted as a multi-stage delivery system

A family of triple hybridomas secreting hybrid monoclonal antibodies has been developed in our laboratory. The hybrid monoclonal antibodies exhibit bimolecular specificity towards both antigenic determinants on the prostate carcinoma cell surface as well as toxin or toxic moieties (ricin A chain and pokeweed antiviral protein). These hybrid antibodies, when bound univalently to their cognate toxin, constitute the primary reagents responsible for selective in vitro prostate carcinoma cell kill; oncolytic impact is achieved by binding of the hybrid antibody-toxin complex (primary hybrid immunotoxin) to a prostate carcinoma cell surface-expressed antigen by the remaining univalent binding site of the hybrid antibody, allowing access of the toxin to the cytosol by internalization of the hybrid antibody-toxin complex. Internalization by endocytosis of a hybrid antibody-toxic subunit has been strikingly enhanced by the use of secondary monoclonal antibody reagents alone or in conjunction with other biomodifier reagents. For example, use of a second monoclonal antibody specific for ricin A chain to which ricin B chain (binding subunit) is chemically coupled results in selective and synergistic cell kill of targeted cancer cells. In vitro studies involving temporally staggered exposure of the cells to the individual components (primary hybrid antibody, toxin, and secondary antitoxin monoclonal antibody biomodifier) have been performed in a manner allowing maintenance of cytotoxic efficacy. It is concluded that sequential administration of these immunotherapeutic components, individually nontoxic, is a feasible strategy to develop an effective immunotherapeutic treatment of human prostate carcinoma.

Schedule-dependent enhanced lethality with combined administration of actinomycin D and tumor necrosis factor in mice

While additive in vitro antitumor cytotoxicity has been observed with tumor necrosis factor (TNF) in combination with cytotoxic agents, particularly actinomycin D (AMD), the critical issue of potentially enhanced host toxicity has not been assessed with such combinations. Dose- and schedule-dependent toxicity of AMD and recombinant human TNF (rHTNF) were studied in mice using sublethal single agent doses. Dose-dependent toxicity was tested using 500, 400, 250, and 50 micrograms/kg of AMD (i.p.) and 50, 25, and 5 micrograms/kg of rHTNF (i.v.). AMD was injected 2 h before TNF. The lethality from maximal doses of these agents alone was consistent with the LD10. However, in combination, an 83% (40/48) lethality was observed at the 500 micrograms/kg dose of AMD, and varying the TNF dose tenfold had no pronounced impact on mortality. A TNF dose response was observed with 400 micrograms/kg of AMD. No deaths occurred with the lower AMD doses (regardless of TNF dose). A similar pattern of lethality at the same doses of AMD and TNF was seen in immunocompetent heterozygotes from the same inbred strain. Toxicity was critically dose schedule (order and interval) dependent. Substantial lethality was seen only if AMD preceded TNF and was maximal at a dose interval of 15 min; this pattern was seen at two dose ranges. If AMD was given after TNF, essentially no lethality was seen. If Phase I clinical trials of AMD/TNF are to be contemplated, the design of such protocols must address (a) the likelihood that severe toxicity might occur at doses far lower than with rHTNF alone, (b) the importance of dose schedule on toxicity, and (c) the critical necessity for precise dose administration compliance if consistent results are to be achieved.

Recombinant human tumor necrosis factor alone and with chemotherapeutic agents. Effect on nude mouse-supported human bladder cancer heterografts

Although studies done in tissue culture (in vitro) have shown synergism between recombinant human tumor necrosis factor (rhTNF) and chemotherapeutic agents, whether such synergism exists in a complex in vivo environment with acceptable toxic side effects has not been determined, to our knowledge. The effect of rhTNF alone and in combination with cisplatin, etoposide, doxorubicin, or dactinomycin on the growth of heterotransplants of human bladder transitional cell carcinoma was studied using a modified subrenal capsule assay in athymic nude mice. Only etoposide potentiated rhTNF cytotoxicity; no increase in host toxicity was noted. Variably enhanced toxic side effects were seen with other combinations. It is concluded that rhTNF combined with etoposide may have potential clinically exploitable therapeutic "synergism" in the treatment of advanced bladder cancer.