The present invention relates to methods of treating cancer or infectious disease in which histamine is administered in conjunction with additional agents. The additional agent may be an agent which stimulates the cytotoxic activity of natural killer cells in a synergistic fashion with histamine. Alternatively, the additional agent may be a chemotherapeutic, antiviral, or antibiotic agent. Methods combining histamine, agents which act synergistically with histamine to increase NK cell cytotoxicity, and chemotherapeutic agents are also contemplated.
The invention is based on the surprising observation that despite previous reports of histamine's short half life in the body, it is possible to attain stable beneficial levels of circulating blood histamine and to maintain these beneficial levels for hours or days after the last administration of histamine. This observation facilitates treatments in which histamine administration to obtain beneficial levels of circulating blood histamine is combined with treatment with other agents. A brief review of the observations leading to the present invention is provided below to place the present invention in context.
A. Cell Types Involved in the Generation of an Immune Response
Recent anticancer strategies have focussed on utilizing the host immune system as a means of cancer treatment or therapy. The immune system has evolved complex mechanisms for recognizing and destroying foreign cells or organisms present in the body of the host. Harnessing the body's immune mechanisms is an attractive approach to achieving effective treatment of malignancies.
A wide array of effector cells, each having its own characteristics and role, implement the immune response. One type of effector cell, the B cell, generates antibodies targeted against foreign antigens encountered by the host. In combination with the complement system, antibodies direct the destruction of cells or organisms bearing the targeted antigen.
Another type of effector cell, the T cell, is divided into subcategories which play different roles in the immune response. Helper T cells secrete cytokines which stimulate the proliferation of other cells necessary for mounting an effective immune response, while suppressor T cells down regulate the immune response. A third category of T cell, the cytotoxic T cell, is capable of directly lysing a targeted cell presenting a foreign antigen on its surface.
An additional type of effector cell is the natural killer cell (NK cell), a type of lymphocyte having the capacity to spontaneously recognize and destroy a variety of malignant cell types. This characteristic of NK cells makes them an attractive candidate for exploitation in cancer treatments and therapies based on using the host's immune system as a weapon against malignant tumors.
B. Cytokines Involved Mediating the Immune Response
The interplay between the various effector cells listed above is influenced by the activities of a wide variety of chemical factors which serve to enhance or reduce the immune response as needed. Such chemical modulators may be produced by the effector cells themselves and may influence the activity of immune cells of the same or different type as the factor producing cell.
One category of chemical mediators of the immune response is cytokines, molecules which stimulate a proliferative response in the cellular components of the immune system.
Interleukin-2 (IL-2) is a cytokine synthesized by T cells which was first identified in conjunction with its role in the expansion of T cells in response to an antigen (Smith, K. A. Science 240:1169 (1988). Several studies have demonstrated that IL-2 has antitumor effects that make it an attractive agent for treating malignancies (see e.g. Lotze, M. T. et al, in "Interleukin 2", ed. K. A. Smith, Academic Press, Inc., San Diego, Calif., p237 (1988); Rosenberg, S., Ann. Surgery 208:121 (1988)). In fact, IL-2 has been utilized to treat subjects suffering from malignant melanoma, renal cell carcinoma, and acute myelogenous leukemia. (Rosenberg, S. A. et al., N. Eng. J. Med. 316:889-897 (1978); Bukowski, R. M. et al., J. Clin. Oncol 7:477-485 (1989); Foa, R. et al., Br. J. Haematol. 77:491-496 (1990)).
It appears likely that NK cells are responsible for the anti-tumor effects of IL-2. For example, IL-2 rapidly and effectively augments the cytotoxicity of isolated human NK cells in vitro (Dempsey, R. A., et al., J. Immunol. 129:2504 (1982); Phillips, J. H., et al. J. Exp. Med. 170:291 (1989)). Thus, the cytotoxic activity of NK cells treated with IL-2 is greater than the constitutive levels of cytotoxicity observed in untreated cells. Furthermore, depletion of NK-cells from animals eliminates IL-2's antitumor effects. (Mule, J. J. et al, J. Immunol. Invest. 139:285 (1987); Lotze, M. T. et al., supra). Additional evidence for the role of NK cells results from the observation that NK cells are the only resting human peripheral blood lymphocytes expressing the IL-2 receptor on their cell surface. (Caliguri, M. A. et al., J. Clin. Invst. 91:123-132 (1993).
Another cytokine with promise as an anti-cancer agent is interferon-.alpha.. Interferon .alpha. (IFN-.alpha.) has been employed to treat leukemia, myeloma, and renal cell carcinomas. Isolated NK cells exhibit enhanced cytotoxicity in the presence of IFN-.alpha.. Thus, like IL-2, IFN-.alpha. also acts to augment NK cell mediated cytotoxicity. (Trinchieri, G. Adv. Immunol. 47:187-376 (1989)).
C. In Vivo Results of Histamine and Histamine Agonist Treatments
Histamine is a biogenic amine, i.e. an amino acid that possesses biological activity mediated by pharmacological receptors after decarboxylation. The role of histamine in immediate type hypersensitivity is well established. (Plaut, M. and Lichtenstein, L. M. 1982 Histamine and immune responses. In Pharmacology of Histamine Receptors., Ganellin, C. R. and M. E. Parsons eds. John Wright & Sons, Bristol pp. 392-435.)
Examinations of whether histamine or histamine antagonists can be applied to the treatment of cancer have yielded contradictory results. Some reports suggest that administration of histamine alone suppressed tumor growth in hosts having a malignancy. (Burtin, Cancer Lett 12:195 (1981)). On the other hand, histamine has been reported to accelerate tumor growth in rodents (Nordlund, J. J. et al., J. Invest. Dermatol 81:28 (1983)).
Similarly, contradictory results were obtained when the effects of histamine receptor antagonists were evaluated. Some studies report that histamine receptor antagonists suppress tumor development in rodents and humans (Osband, M. E. et al., Lancet 1 (8221) :636 (1981). Other studies report that such treatment enhances tumor growth and may even induce tumors (Barna, B. P. et al., Oncology 40:43 (1983)).
D. Synergistic Effects of Histamine and IL-2
Despite the conflicting results when histamine is administered alone, recent reports clearly reveal that histamine acts synergistically with cytokines to augment the cytotoxicity of NK cells. Thus, therapies employing the combination of histamine and cytokines represent an attractive approach to anti-cancer strategies based on using the host immune system to attack the malignancy. Similarly, antiviral treatments using any of the well known antiviral agents is also contemplated.
Studies using histamine analogues suggest that histamine's synergistic effects are exerted through the H.sub.2 -receptors expressed on the cell surface of monocytes. For example, the H.sub.2 -receptor agonist dimaprit was capable of augmenting NK cell mediated cytotoxicity, while close structural analogues lacking biological activity failed to produce an effect. Additionally, H.sub.2 -receptor antagonists blocked the effects of histamine and dimaprit, implicating the H.sub.2 -receptor in the transduction of the histamine response. (Hellstrand, K. et al., J. Immunol. 137:656 (1986)).
Histamine's synergistic effect when combined with cytokines is not the result of a direct positive effect of histamine on NK cell cytotoxicity. Rather, the synergistic effects result from the suppression of a down regulation of NK cell cytotoxicity mediated by other cell types present along with the NK cells. The discussion below provides some of the evidence suggesting that histamine's synergistic effects result from the suppression of negative signals exerted by other cell types.
U.S. Pat. No. 5,348,739, which is incorporated herein by reference, discloses the synergistic effects of histamine and interleukin-2. As discussed above, IL-2 normally induces a cytotoxic response in NK cells. In vitro studies with NK cells alone confirm that cytotoxicity is stimulated when IL-2 is administered. However, in the presence of monocytes, the IL-2 induced enhancement of cytotoxicity of NK cells is suppressed.
In the absence of monocytes, histamine had no effect or weakly suppressed NK mediated cytotoxicity. (U.S. Pat. No. 5,348,739; Hellstrand, K. et al., J. Immunol. 137:656 (1986); Hellstrand, K. and Hermodsson, S., Int. Arch. Allergy Appl. Immunol. 92:379-389 (1990)). However, NK cells exposed to histamine and IL-2 in the presence of monocytes exhibit elevated levels of cytotoxicity relative to that obtained when NK cells are exposed only to IL-2 in the presence of monocytes. Id. Thus, the synergistic enhancement of NK cell cytotoxicity by combined histamine and interleukin-2 treatment results not from the direct action of histamine on NK cells but rather from suppression of an inhibitory signal generated by monocytes.
Without being limited to a particular mechanism, it is believed that the inhibitory effects of monocytes on NK mediated cytotoxicity result from the generation of H.sub.2 O.sub.2 by monocytes. It has been reported that the production of H.sub.2 O.sub.2 by monocytes suppresses NK cell cytotoxicity. (Van Kessel, K. P. M. et al., Immunology, 58:291-296 (1986); El-Hag, A. and Clark, R. A. J. Immuol. 133:3291-3297 (1984); Seaman, W. E. et al., J. Clin. Invest. 69:876-888 (1982)). Further evidence of the role of H.sub.2 O.sub.2 in suppressing NK cell cytotoxicity comes from in vitro studies showing that the addition of catalase, an enzyme which acts to remove H.sub.2 O.sub.2, to preparations of monocytes and NK cells exposed to IL-2 removes the inhibitory effects of the monocytes. (Seaman, supra.) Thus, histamine may exert its synergistic effects by reducing the level of H.sub.2 O.sub.2 produced by monocytes. Hellstrand, K., Asea, A., Hermodsson, S. Histaminergic regulation of antibody-dependent cellular cytotoxicity of granulocytes, monocytes and natural killer cells, J. Leukoc. Biol. 55:392-397 (1994).
Monocytes are not the only cell type which negatively regulates NK cell cytotoxicity. Experiments have demonstrated that granulocytes suppress both the constitutive and IL-2 induced cytotoxic activity of NK cells in vitro. Like the monocyte mediated suppression discussed above, granulocyte mediated suppression is synergistically overcome by treatment with IL-2 and histamine. (U.S. Pat. No. 5,348,739; Hellstrand, K., Asea, A., Hermodsson, S. Histaminergic regulation of antibody-dependent cellular cytotoxicity of granulocytes, monocytes and natural killer cells, J. Leukoc. Biol. 55:392-397 (1994).
It appears that the H.sub.2 -receptor is involved in transducing histamine's synergistic effects on overcoming granulocyte mediated suppression. For example, the effect of histamine on granulocyte mediated suppression of antibody dependent cytotoxicity of NK cells was blocked by the H.sub.2 -receptor antagonist ranitidine and mimicked by the H.sub.2 receptor agonist dimaprit. In contrast to the complete or nearly complete abrogation of monocyte mediated NK cell suppression by histamine and IL-2, such treatment only partially removed granulocyte mediated NK cell suppression. (U.S. Pat. No. 5,348,739; Hellstrand, K. et al., Histaminergic regulation of antibody dependent cellular cytotoxicity of granulocytes, monocytes and natural killer cells., J. Leukoc. Biol 55:392-397 (1994).
As suggested by the experiments above, therapies employing histamine and cytokines are effective anti-cancer strategies. U.S. Pat. No. 5,348,739 discloses that mice given histamine and IL-2 prior to inoculation with melanoma cell lines were protected against the development of lung metastatic foci. This effect was a consequence of synergistic interaction between histamine and IL-2, as demonstrated by the significant reduction in metastatic foci observed in mice given histamine and IL-2 as compared to mice given histamine or IL-2 alone.
In addition to the synergistic effects observed in the assay of lung metastatic foci, synergistic effects of histamine plus IL-2 treatment were also observed in assays in which NK cell cytotoxicity was measured by determining the ability of mice to kill malignant cell lines derived from both humans and mice which were injected into them. Id.
The above results demonstrate that strategies employing a combination of histamine and IL-2 are an effective means of treating malignancies.
E. Synergistic Effects of Histamine and Interferon-.alpha.
Histamine also acts synergistically with interferon-.alpha. to overcome the suppression of NK cell cytotoxicity by monocytes (Hellstrand et al., Regulation of the NK cell response to interferon-alpha by biogenic amines, J. Interferon Res. 12:199-206 (1992)). Like IL-2, interferon-.alpha. augments NK cell constitutive NK cell cytotoxicity. Id. Monocytes suppress the interferon-.alpha. mediated enhancement of NK cell killing of malignant target cells in vitro. Monocyte mediated suppression of NK cell cytotoxicity was overcome by treatment with histamine and interferon-.alpha.. The effects of histamine were blocked by H.sub.2 -receptor antagonists and mimicked by H.sub.2 -receptor agonists. Compounds bearing structural similarity to the H.sub.2 -receptor agonist dimaprit but lacking the activity of the agonist were unable to act synergistically with interferon-.alpha.. (Hellstrand et al. J., Interferon Res. 12:199-206 (1992)).
F. Human Treatments Combining Histamine, Interleukin-2 and Interferon-.alpha.
The in vitro and animal results discussed above suggested that histamine+IL-2+interferon-.alpha. was a promising method for treating human malignancies. In fact, combined histamine, IL-2, and interferon-.alpha. treatments have proven effective in the treatment of a variety of human malignancies, providing a 75% response rate significantly greater than that observed with IL-2 alone. (Hellstrand et al., Histamine in Immunotherapy of Advanced Melanoma: A Pilot Study, Cancer Immunology and Immunotherapy 39: 416-419 (1994). In the above study, subjects received a constant infusion of IL-2 (Proleukin.RTM., Eurocetus), 18.times.10.sup.6 U/m.sup.2 on days 1-5 and 8-12, repeated every 4-6 weeks, as well as interferon-.alpha. (6.times.10.sup.6 U daily, s.c.). In addition to the IL-2, eight of the subjects received histamine dihydrochloride (1 mg s.c.) twice daily. Id.
Only one subject in the group receiving IL-2 and interferon-.alpha. exhibited a partial or mixed response, a response rate of 14% (1 of 7). In contrast, the group receiving both IL-2, interferon-.alpha. and histamine showed an corresponding response rate of 75% (6 of 8). Only two of these subjects failed to respond. Id.
Thus, histamine+IL-2+interferon-.alpha. is an effective anti-cancer therapy.
G. Human Treatments with Histamine+IL-2+Chemotherapeutic Agents
Recently, the efficacy of treatments employing histamine, IL-2, and chemotherapeutic agents was examined in humans suffering from acute myelogenous leukemia (AML) (Brune and Hellstrand, Remission Maintenance Therapy with Histamine and Interleukin-2 in Acute Myelogenous Leukemia, Br. J. Haematology, March 1996).
In one set of experiments, killing of AML blasts by NK cells was examined in vitro. IL-2 induced NK mediated cytotoxicity, but this effect was suppressed by monocytes. Histamine did not affect the IL-2 induced cytotoxic response in the absence of monocytes but blocked the suppressive effects of the monocytes. However, in the presence of the H.sub.2 -receptor antagonist ranitidine, histamine was ineffective in overcoming the monocyte suppression. Id.
Additionally, AML patients in remission were treated with histamine+IL-2+the chemotherapeutic agents cytarabine and thioguanine and the duration of remission was measured and compared to the length of remissions prior to initiating the treatment. Five of the patients receiving histamine+IL-2+cytarabine+ thioguanine remained in complete remission ranging in duration from 9-27 months at the time of publication. Two patients relapsed after remissions lasting 8 and 33 months. In the five patients who had undergone a remission followed by a relapse prior to initiation of the histamine+IL-2+cytarabine+ thioguanine regimen, the duration of remissions following initiation of the regimen exceeded the duration of the prior remission. Id. Such "inversion of remission time" is rare in the natural course of AML and reportedly only occurs in a small fraction (&lt;10%) of AML patients treated with IL-2 as the single agent. Shepherd et al, Phase II Study of Subcutaneous rHU IL-2 in Patients with Acute Myelogenous Leukemia in Partial or Complete Second Remission and Partial Relapse, Br. J. Haematol. S87, 205 (1994).
Thus, histamine+IL-2+chemotherapeutic agents is an effective anti-cancer therapy.