Analysis of synergy between cyclophosphamide therapy and immunity against a mouse tumour

Efecto bimodal de la ciclofosfamida en la terapia antineoplásica

La Ciclofosfamida (Cy) es el agente alquilante más utilizado en el tratamento quimioterápico de diversas neoplasias humanas; habitualmente se la administra em combinación con otros citostáticos para lograr una mayor eficacia terapêutica. La mayoría de los protoeolos clínicos la emplean en dosis altas y suministrada en repetidas ocaciones a lo largo del tratamento antineoplásico, con Ias ya conocidas acciones colaterales, entre ellas la inmunodepresión. Sin embargo, en diferentes modelos experimentales en animales portadores de un tumor, la administración de uma dosis única y relativamente baja en un determinado momento de la respuesta inmune antitumoral, produce inmunopotenciación, a través de una inhibieión selectiva sobre los linfocitos T supresores. Posteriormente se demostró un efecto interesante y novedoso de éstas dosis bajas de Cy: su acción preferencial sobre células tumorales com fenotipo metastásico (probablemente debido a una inmunomodulación selectiva sobre dichas subpoblaciones celulares), ya que se observo una inhibieión total en la formación de Ias metástasis sin afectar el desarrollo dei tumor primário. Estos resultados senalan el efecto bimodal de la Cy sobre el sistema inmune dei huésped cuando se la utiliza en el tratamiento antineoplásico em diferentes dosis y esquemas de administración. La utilización de sustancias naturales denominadas “modificadores de la respuesta biológica”, ha derivado en lo que se conoce como cuarta modalidad terapêutica contra el cáncer. Se propone que la Cy sea considerada también dentro de ese contexto.

Immunomodulatory effect of cyclophosphamide on host humoral immunity in Dunning's R-3327 adenocarcinoma of the prostate

The object of the present investigations was delineation of the exclusive effects of cyclophosphamide (Cytoxan) on host humoral response to tumor, as evaluated by the level of circulating antigen/antibody complexes (AACs), which may reflect the chemo-responsiveness of hosts and provide a rationale for new therapeutic strategies. Our data, recorded in Copenhagen X Fischer rats bearing Dunning's R-3327 Mat Ly-Lu adenocarcinoma of the prostate, show no modulatory effect of cyclophosphamide at 10 mg/kg, a nonspecific immunosuppressive effect at 30 mg/kg, and a definite immunostimulatory effect on host humoral immunity at 100 mg/kg. Sequential determination of AAC levels at different stages of tumor growth, i.e. from the primary to the metastatic stage, performed with the original purpose of demonstrating that any disturbance in the immunoregulatory mechanism of the host was due to cyclophosphamide rather than to changes in tumor load, revealed that levels of AACs parallel disease progression in the initial stages of primary tumor growth but rapidly decrease to near-normal levels in the presence of heavy tumor burden.

Presence of an enlarged pool of MOPC-315-specific cytotoxic T lymphocyte precursors in the thymuses of mice that eradicated a large MOPC-315 tumor as a consequence of low-dose melphalan therapy

We have previously shown that, as a consequence of low-dose melphalan (L-phenylalanine mustard) treatment, thymocytes from mice bearing a large, day-10 MOPC-315 tumor, but not thymocytes from normal mice, acquire the ability to generate an enhanced level of antitumor cytotoxicity upon in vitro stimulation with MOPC-315 tumor cells plus low concentrations (9.0-90 IU/ml) of exogenous interleukin-2 (IL-2). Here we show that the time interval between tumor inoculation and low-dose melphalan therapy as well as the magnitude of tumor burden at the time of the chemotherapy are important for the ability of the drug to render thymocytes more responsive to in vitro stimulation with MOPC-315 tumor cells plus low concentrations of recombinant IL-2 (rIL-2). Specifically, the chemotherapy was found to be effective in enhancing the thymic antitumor reactivity only if the mice bore a large, late-stage tumor. Comparison of thymocytes from untreated mice bearing a large, late-stage tumor to thymocytes from normal mice revealed that tumor-bearer thymocytes contained approximately a three-fold higher frequency of cytotoxic T lymphocyte precursors (CTLp) for MOPC-315-associated antigens. Following curative low-dose melphalan therapy of mice bearing a large, late-stage MOPC-315 tumor, the frequency of CTLp for MOPC-315-associated antigens increased further, reaching a level approximately tenfold higher than that found among thymocytes of normal mice. At the same time, the frequency of CTLp for an antigenically unrelated allogeneic tumor (EL4) as well as the overall percentage of mature cells was not increased. The cells responsible for the exertion of the enhanced antitumor cytotoxicity following in vitro stimulation of thymocytes from mice treated with low-dose melphalan when they have a large, late-stage MOPC-315 tumor are of the CD8+/CD4- phenotype. Thus, the enhanced level of antitumor cytotoxicity generated by thymocytes from mice that are treated with low-dose melphalan when they have a large, late-stage MOPC-315 tumor is due, at least in part, to the presence of an enlarged pool of CTLp specific for MOPC-315-associated antigens, which mature into CD8+/CD4- effector cells upon stimulation with MOPC-315 tumor cells plus low concentrations of rIL-2.

Specificity of the generation and expression of enhanced anti-plasmacytoma immunity by spleen cells from melphalan-treated MOPC-315 tumor bearers

We have shown previously that low-dose melphalan (L-PAM) therapy of mice bearing a large MOPC-315 plasmacytoma enables their hitherto immunosuppressed spleen cells to exert potent anti-MOPC-315 cytotoxicity following in vitro immunization with MOPC-315 tumor cells. Here we show that, following in vitro immunization with MOPC-315 tumor cells, spleen cells from such L-PAM-treated MOPC-315 tumor bearers exhibited enhanced T-cell-mediated cytotoxicity not only against the MOPC-315 tumor, but also against another plasmacytoma (MOPC-104E) possessing surface immunoglobulin (SIg) of a different idiotype than the MOPC-315 cells, as well as against a variant of the MOPC-315 tumor which does not produce nor possess SIg (SIg- MOPC-315). The enhanced cytotoxicity was directed against target antigens which are not expressed on the surface of the syngeneic WEHI 22.1 thymoma or the natural killer-sensitive YAC-1 cells. Plasmacytoma shared antigens, other than immunoglobulins, were able to stimulate spleen cells from L-PAM-cured MOPC-315 tumor bearers to generate in vitro a secondary type anti-plasmacytoma cytotoxic response. L-PAM-cured MOPC-315 tumor bearers exhibited in vivo immunity against SIg- MOPC-315 tumor cells, which was sufficiently triggered by the SIg- cells to bring about the rejection of a challenge of at least 100-fold the minimal lethal tumor dose of the SIg- MOPC-315 cells. Thus, SIg- MOPC-315 tumor cells present among SIg+ tumor cells in the parental MOPC-315 tumor inoculum can be eradicated in the L-PAM-treated MOPC-315 tumor bearers by the immune response to SIg+ tumor cells as well as by the immune response to SIg- tumor cells themselves.

The difference between 5-fluorouracil and melphalan in their ability to promote antitumor immune response against MOPC-315 plasmacytoma

The anticancer chemotherapeutic drugs melphalan (L-phenylalanine mustard; L-PAM), 5-fluorouracil (5-FU), methotrexate (MTX), and daunorubicin (DAU) were tested for their toxic activity against MOPC-315 tumor cells in vitro. L-PAM, 5-FU, and DAU had a marked toxic effect whereas MTX did not affect the rate of thymidine incorporation in the tumor cells. L-PAM (7.5 mg/kg) induced permanent regression of large s.c. MOPC-315 plasmacytoma tumors, 5-FU (200-250 mg/kg) induced transient regression of MOPC-315 tumors with reappearance starting on the 6th day after the 5-FU injection and DAU (5 mg/kg) was not effective. L-PAM treatment restored the cytotoxic potential of spleen cells of tumor-bearing mice against target MOPC-315 tumor cells whereas spleen cells from tumor-bearing mice treated with 5-FU were unable to mount a cytotoxic response. L-PAM and 5-FU were also assayed for their effect in vitro on induction of suppressor T cells by ConA. L-PAM treatment in vitro markedly reduced the induction of suppressor T cells by ConA whereas 5-FU had no effect. It is suggested that anticancer chemotherapeutic drugs can be classified in "immunopromoting" (L-PAM as prototype) and "nonimmunopromoting" (5-FU as prototype) on the basis of their effect in vivo on established tumors and their effect on induction of suppressor T cells by ConA.

Effect of immunization or cyclophosphamide treatment on growth of EL-4 leukemia cells in syngenic C57BL/6 mice

Prolonged survival of C57BL/6 (B6) mice bearing syngenic EL-4 leukemia cells resulted from immunization with irradiated EL-4 cells on the day of inoculation of live leukemia cells. No prolongation of survival was observed if the irradiated cells were injected 6 or 13 days after live cell inoculation. Protection also was observed in EL-4-bearing mice that were treated with cyclophosphamide (CY) rather than by immunization, however, the protective effects were observed only when CY treatment was instituted 6 days after inoculation of live leukemia cells. No protection was seen when CY was administered on the day of, or 13 days after inoculation of live leukemia cells. In fact, administration of CY on the day live EL-4 cells were inoculated appeared to enhance the lethal effects of the tumor. In mice that underwent combined treatment, i.e., immunization and CY, prolonged survival was seen only in the group that received combined treatment 6 days after inoculation of live leukemia cells. No protection was seen in mice receiving combined treatment on the day of or 13 days after inoculation of live leukemia cells. The role that suppressor T cells might play in the observed results is discussed.

Chemoimmunotherapeutic effect of cyclophosphamide on the highly metastatic MAT 13762 tumor

We have observed that cyclophosphamide (CY) treatment of 13762 mammary adenocarcinoma tumor-bearing rats was found to cause tumor regression. Tumor-bearing animals cured with three low doses of CY were partially immune against IV and SC challenge with a high dose of 13762 cells. This immune protection mechanism in CY-cured animals appears to be a T (Ig-) cell-mediated response. Irradiated rats reconstituted with CY-cured animal spleen cells were also partially protected against IV and SC challenge with 13762 cells, whereas irradiated rats reconstituted with CY-control animal spleen cells were not. In vitro primary and secondary cell-mediated cytotoxic activity of CY-cured spleen cells against target 13762 cells was low. The possible relevance of this tumor-model study is in the understanding of CY-induced tumor immune response and its role in preventing metastases or perhaps recurrent tumor growth.

The effect of low-dose cyclophosphamide and immunologic exposure upon growth of established Dunning R-3327-G subline rat prostate adenocarcinomas

Utilizing the Dunning rat prostate adenocarcinoma, a low dose of cyclophosphamide (CY), 30 mg/kg, administered either alone or following diethylstilbestrol (DES) therapy, was as effective as higher levels of CY (100 mg/kg) in ability to initiate tumor regression. A lower dose (10 mg/kg) of CY was initially ineffective. Animals which had been injected with tumor an additional 10 days prior to initiation of CY treatment were apparently more responsive to this mode of chemotherapy. The effect of this additional 10 days of immunologic exposure supports the belief that the activity of CY is augmented by the presence of immunologic competence. All animals which responded favorably toward therapy utilizing CY, alone or in combination with DES, were similarly able to reject subsequent tumor challenges. It is thought that low-dose CY may reduce the immunosuppressive effects observed with higher levels and presumably preserve the helper T cell population necessary to mount secondary immune responses.

In vitro selective effect of melphalan on human T-cell populations

In vitro treatment with 2 micrograms/2 X 10(6) cells melphalan (L-PAM: L-phenylalanine mustard) significantly decreased the total number of T lymphocytes from peripheral blood (PBL) of healthy human donors and of the OKT4 population (precursor suppressor/helper/inducer) T cells as defined by monoclonal antibodies OKT3 and OKT4, respectively. No changes in the OKT+8 lymphocyte population (cytotoxic/mature suppressor cells) were observed following the same treatment. Preincubation of PBL with L-PAM at concentrations that do not affect the rate of DNA synthesis in PHA-stimulated lymphocytes inhibited the generation of T suppressor lymphocytes by ConA, as shown by their effect on PHA stimulation. Treatment of allogeneic PBL with L-PAM had no effect on mature suppressor T cells already induced by ConA, as shown by incubation of PBL with L-PAM after incubation with ConA.

Effect of melphalan administration on the activity of natural killer and natural cytotoxic spleen cells of normal and tumor-bearing mice

The effect of melphalan (L-PAM; L-phenylalanine mustard) administration on natural killer (NK) and natural cytotoxic (NC) activities of spleen cells from normal noninoculated BALB/c mice and mice bearing large MOPC-315 plasmacytoma tumors was investigated. Injection of L-PAM (7.5 or 15.0 mg/kg) had no effect on NK and NC activities of spleen cells from normal mice whereas stimulation by PHA was markedly suppressed. NK activity was markedly suppressed in spleens of tumor-bearing mice whereas NC activity was not affected. Therapy with L-PAM of tumor-bearing mice led to transient recovery of NK activity which was possibly related to the effect of L-PAM on macrophage suppressive activity on NK cells. It is concluded that NK and NC cell activities and the response to PHA stimulation are selectively affected by L-PAM administration.

Effects on metastases of drug therapy during developing and established tumor immunity

The effectiveness of treatment with cyclophosphamide, methotrexate and 5-fluorouracil was studied during the s.c. and pulmonary growth of syngeneic C3H/He mammary carcinomas. Treatments with cyclophosphamide, methotrexate and 5-fluorouracil during the primary induction of immunity against a mouse mammary carcinoma inhibited the growth of the tumor, but also inhibited the development of an effective immune resistance against subsequent implants of the same tumor. However, drug treatments of mice with established tumor immunity gave added benefit without detectable depression of immune resistance.

Increase in the effectiveness of melphalan therapy with progression of MOPC-315 plasmacytoma tumor growth

Following inoculation with 1 X 10(6) MOPC-315 tumor cells, a single injection of a very low dose of melphalan (L-PAM, L-phenylalanine mustard), 0.75 mg/kg, cured most of the mice bearing a day 11 large primary tumor (20 mm) and metastases, but failed to cure mice bearing a day 4 nonpalpable tumor. Treatment of mice bearing a nonpalpable tumor with the very low dose of drug compromised the ability of the mice to respond effectively to the same low dose of drug when the tumor became large (day 12). However, a nonpalpable tumor could be eradicated by treatment of tumor bearers with a low dose of L-PAM, if it was present concomitantly with a large tumor on the contralateral side. A high dose of L-PAM, 15 mg/kg, cured mice bearing either a nonpalpable or a large tumor. The eradication of the tumor induced by the high dose of L-PAM appeared to be due solely to the tumoricidal effect of the drug. On the other hand, the eradication of the tumor by the low dose of L-PAM also required the participation of antitumor immunity of the host, since subsequent injection of antithymocyte serum abrogated the curative effect of the drug in most mice. Mice cured by a high dose of L-PAM were not resistant to subsequent lethal tumor challenge. In contrast, mice cured by the low dose of L-PAM were able to reject a tumor challenge of 300 times the minimal lethal tumor dose. The results obtained with L-PAM therapy are similar to the results that we had previously reported with cyclophosphamide therapy. Thus, the timing of therapy with a low dose of drug for mice bearing a MOPC-315 tumor is critical for successful therapy. Moreover, the selection of a low dose rather than a high dose of drug to eradicate a large tumor offers the advantage that it results in long-lasting potent antitumor immunity as a consequence of the participation of host antitumor immunity in the eradication of the tumor.

Interference of anti-tumor and immunosuppressive effects of cyclophosphamide in tumor-bearing rats. Analysis of factors determining resistance or susceptibility to a subsequent tumor challenge

Adult rats were given 10(5) or 10(6) Yoshida ascites sarcoma (YAS) cells IP and were treated with cyclophosphamide (CY) given IP in single doses of 20 mg/kg or 100 mg/kg, 2 or 5 days after YAS inoculation. Both the curative effect of CY and subsequent resistance to tumor challenge in rats that survived depended on the dose of injected tumor cells and on the dose and time of administration of CY. These three factors determined whether the host's immune response to tumor antigens would develop and contribute to the overall anti-tumor effects of the chemotherapy. The curative effects of CY were significantly less pronounced in T-cell-deficient than in normal rats. Anti-tumor and immunosuppressive activities of CY exerted opposite influences on the ultimate result of the chemotherapy. Adverse immunosuppressive effects prevailed when the drug was administered early (2 days) after YAS inoculation. In this case the chemotherapy was less efficient and the surviving rats were susceptible to a subsequent tumor challenge. Further analysis showed that the injection of CY 2 days after inoculation of YAS antigens induced strong and specific immunologic tolerance to the tumor. In contrast, when a sufficient amount of tumor antigens (higher dose of tumor cells injected and CY injection delayed) elicited an anti-YAS immune response that was not suppressed by early injection of CY (CY administered 5 days after the tumor) effective eradication of tumor cells and anti-YAS resistance in cured animals were observed.