Sirolimus-mediated prolongation of rat cardiac allograft survival is enhanced by beta1 integrin very late antigen-4 blockade

The beta1 integrin very late antigen-4 (VLA-4) plays a key role in lymphocyte rolling and adhesion to endothelium, and in lymphocyte migration through fibronectin. Thus, VLA-4 blockade may modulate allograft rejection. Here, we examined the effect of WAY-279, a small molecule VLA-4 antagonist, combined with sirolimus in a model of vascularized heart allograft (BN --> LEW) in the rat. Recipients were treated with low doses of WAY-279 (10-50 mg/kg, bid) and/or sirolimus (0.04 mg/kg) for 14 days, starting on the day of transplantation. The median-effect principle and the combination index (CI) were used to assess the combined effect of WAY-279 and sirolimus (CI < 1: synergism; CI = 1: summation; CI > 1 antagonism). Low doses of WAY-279 or sirolimus alone slightly prolonged allograft survival as compared to control group (MST = 7 days). When recipients were treated with WAY-279 and sirolimus, the cardiac allograft survival was synergistically prolonged for up to 45 days (P < .001; CI = 0.174-0.970). We showed that a concomitant treatment of WAY-279 with sirolimus produced a synergistic effect in prolonging cardiac allograft survival in the rat.

Sirolimus: its discovery, biological properties, and mechanism of action

Sirolimus is the USAN-assigned generic name for the natural product rapamycin. Sirolimus is produced by a strain of Streptomyces hygroscopicus, isolated from a soil sample collected from Rapa Nui commonly known as Easter Island. Although sirolimus was isolated as an antifungal agent with potent anticandida activity, subsequent studies revealed impressive antitumor and immunosuppressive activities. Sirolimus demonstrates activity against several murine tumors, such as B16 43 melanocarcinoma, Colon 26 tumor, EM ependymoblastoma, and mammary and colon 38 solid tumors. Sirolimus is a potent inhibitor of antigen-induced proliferation of T cells, B cells, and antibody production. Demonstration of the potent immunosuppressive activity of sirolimus in animal models of organ transplantation led to clinical trials and subsequent approval by regulatory authorities for prophylaxis of renal graft rejection. Interest in sirolimus as an immunosuppressive therapy in organ transplantation derives from its unique mechanism of action, its unique side-effect profile, and its ability to synergize with other immunosuppressive agents. The molecular mechanism underlying the antifungal, antiproliferative, and immunosuppressive activities of sirolimus is the same. Sirolimus forms an immunosuppressive complex with intracellular protein, FKBP12. This complex blocks the activation of the cell-cycle-specific kinase, TOR. The downstream events that follow the inactivation of TOR result in the blockage of cell-cycle progression at the juncture of G1 and S phase.

Compromised kidney graft rejection response in Vervet monkeys after withdrawal of immunosuppressants tacrolimus and sirolimus

BACKGROUND

In nonprimates, organ allografts are often not rejected after withdrawal of immunosuppression. In this study, we examined whether such a phenomenon also occurs in primates.

METHODS

Vervet monkeys were transplanted with renal allografts and treated for 60 days with tacrolimus, or tacrolimus plus sirolimus. The drugs were totally withdrawn on day 61. The survival of the monkeys was monitored, and their response to donor- or third party-derived alloantigens was examined in vivo and in vitro.

RESULTS

The majority (80-100%) of the grafts survived for at least additional 30 days with no signs of acute rejection. The compromised rejection is donor-specific, because recipient monkeys failed to reject a donor-derived skin graft, but a third-party skin graft was rejected. In vitro mixed lymphocyte reaction and interleukin-2 production in the mixed lymphocyte reaction between the recipients and their donors or between the recipients and a third party had no discernable patterns, and thus did not reflect the in vivo status of the immune system. Although the recipients could not reject the graft acutely after drug withdrawal, the kidney grafts and the donor-derived skin grafts had pathological findings of chronic rejection.

CONCLUSIONS

The rejection response of the monkeys to an established graft after withdrawal of immunosuppression is compromised. The compromised rejection is specific and is not due to a permanent alteration of the immune system by the initial drug treatment. The allografts are not inert but have low levels of interaction with the recipient immune system.

Manipulation of the C(22)-C(27) region of rapamycin: stability issues and biological implications

A novel series of rapamycin derivatives with modifications in the C(22)-C(27) region has been prepared. These compounds are evaluated for their ability to prevent ring fragmentation while still retaining immunosuppressive capabilities.

Rapamune (RAPA, rapamycin, sirolimus): mechanism of action immunosuppressive effect results from blockade of signal transduction and inhibition of cell cycle progression

OBJECTIVE

Rapamune is a novel immunosuppressive agent in Phase III clinical trial in renal transplantation. Its unique mechanism of action has created great interest in its use as a biochemical probe of signal transduction pathways that has provided insight into its molecular mechanism of action. This article reviews the current state of our understanding of the mechanism of action of rapamune.

Tacrolimus (FK506) and sirolimus (rapamycin) in combination are not antagonistic but produce extended graft survival in cardiac transplantation in the rat

Combined use of tacrolimus (FK506) with sirolimus (rapamycin [RAPA]) was examined in a model of vascularized heart allograft in the rat. For prevention of acute rejection, three different combinations of low doses of FK506 and RAPA from day 1 up to day 14 after transplantation produced significantly longer cardiac allograft survival than each agent alone (P<0.05). Identical results were observed in a model of reversal of ongoing acute rejection, where two combinations of low doses of FK506 and RAPA from day 4 up to day 18 after surgery also demonstrated significantly longer graft survival than each immunosuppressant alone (P<0.05). All the low-dose-treated groups in these two models presented significantly longer heart graft survival than naive controls (P<0.05), confirming that both agents are potent immunosuppressants in the models chosen. These results also indicate that, in contrast with in vitro studies, the combined use of FK506 and RAPA in vivo did not produce antagonism, but rather had synergistic effect in prolonging the allograft survival as compared with each agent alone. It appears likely that the abundance of FKBP-12 available for binding in vivo prevents inhibitive competition of the two agents for their receptor.

Therapeutic blood levels of sirolimus (rapamycin) in the allografted rat

A study was conducted to determine the relationship among oral dose, trough whole blood levels, graft survival, and side effects in sirolimus-treated allografted rats. The heterotopic heart allograft model using Brown Norway donors and Lewis rat recipients was used. Rats were dosed daily with sirolimus or vehicle until graft failure or up to a maximum of 28 days. Upon graft failure, rats were bled for measurement of trough blood levels of drug and tissues sent for histopathologic analysis. Sirolimus blood concentration correlated positively with dose and graft survival. Significant graft survival occurred at whole blood trough levels of 0.5 ng/ml achieved at the 0.3 mg/kg/day dose. Analysis of the concentration-effect data using a sigmoidal Emax model calculated a whole blood EC50 of 2.0 ng/ml for graft survival. With mean trough concentrations of 7 ng/ml and higher, grafts survived after cessation of drug treatment. At the 0.8 mg/kg/day dose, there was a significant decrease in body weight gain in the rats. Histopathologic examination of sirolimus-treated animals detected thymic and lymphoid atrophy, both considered pharmacologic extensions of sirolimus's immunosuppressive activity and focal myocardial degeneration, an exacerbation of a spontaneous occurring lesion. These results demonstrate that sirolimus prolongs graft survival in rat in a concentration dependent manner with therapeutic whole blood levels of about 10 ng/ml.

Rapamune (Sirolimus, rapamycin): an overview and mechanism of action

Rapamycin (Sirolimus, Rapamune), a potent immunosuppressive agent, has been demonstrated to have remarkable activity in inhibiting allograft rejection in animal models of transplantation. It is currently in phase II clinical trials. Rapamycin belongs to the class of macrocyclic immunosuppressive drugs that are bioactive only when bound to immunophilins. Cyclosporin A and FK506, two other members of this class, selectively block the transcriptional activation of several cytokine genes, thereby inhibiting cytokine production. Although rapamycin and its structural analog FK506 bind to the same immunophilin (FKBP), rapamycin acts at a later stage in T-cell cycle progression by blocking cytokine-mediated signal transduction pathways. This inhibition is the consequence of modulation of activity of a target protein by the rapamycin: FKBP complex [sirolimus effector protein (SEP)]. Although the identification of SEP has recently been reported, its function in cell-cycle progression is not known. The biochemical events that rapamycin has been shown to inhibit are (a) activation of p70S6 kinase, (b) activation of cdk2/cyclin E complex, (c) phosphorylation of retinoblastoma protein, and (d) suppression of cdc2 and cyclin A transcription.

Rapamycin (sirolimus, rapamune)

Rapamycin is a novel immunosuppressive agent that is undergoing clinical trials for use in allograft rejection therapy. This paper reviews its in-vitro biological properties, the current state of knowledge concerning its mechanism of action, and its therapeutic applications.

Prolongation of renal allograft survival in a large animal model by oral rapamycin monotherapy

We assessed the efficacy of 5 dose levels of oral rapamycin for prolonging renal allograft survival in pigs. Untreated and triple therapy groups (cyclosporine, azathioprine, and prednisone) served as controls. Immunosuppression was administered for 28 days posttransplant and then stopped. Rapamycin whole-blood concentrations were followed weekly. Chemistry, hematology, and lipid values were monitored post-transplant. For rapamycin-treated pigs, median survival time (MST) correlated with both dose and trough levels (ng/ml). All kidneys had some degree of rejection seen on necropsy. After rejection, pneumonia was the most common cause of death. No specific end-organ toxicity was noted on histopathologic examination. Triglyceride and cholesterol levels increased in all treated pigs (both rapamycin and triple therapy) vs. untreated controls--however, all values were within normal limits. Mean ALT levels increased in weeks 2 to 4 in the higher-dose rapamycin groups but returned to baseline in pigs surviving after the drug was stopped. ALT levels did not increase above twice normal in any group. Creatinine levels correlated with the degree of rejection seen on biopsy. We noted no other toxicities. We conclude that rapamycin, given as oral monotherapy, is an effective and safe immunosuppressant in our large animal renal allograft model. Outcome correlated with dose and whole-blood levels.

Renal effects of rapamycin in the spontaneously hypertensive rat

The effects of rapamycin (RAPA), administered at therapeutic doses, were investigated in the spontaneously hypertensive rat (SHR). Additionally, the reversibility of RAPA's renal effects was investigated at a supratherapeutic dose. At doses that were active in preventing heart and kidney allograft rejection in the rat (0.01-0.08 mg/kg i.v.), RAPA had no effect on kidney function or rat body weight gain. At higher doses (0.8 mg/kg), RAPA produced significant changes in kidney function parameters and caused a loss in body weight. Histopathologic changes, including necrotizing vasculopathy and tubular atrophy, were noted at therapeutic doses. The effects of RAPA on kidney function were completely reversible after a 2-week washout period, though the histopathologic changes were still evident. These studies demonstrate that RAPA does not impair kidney function at therapeutic doses when administered for 2 weeks but does appear to accelerate the naturally occurring renal lesions of the SHR.

Rapamycin prolongs survival and arrests pathophysiologic changes in murine systemic lupus erythematosus

OBJECTIVE

To evaluate the effects of oral rapamycin (RAPA), a macrolide immunosuppressant that has been shown to interfere with T cell activation events, on the course of spontaneous disease progression in the MRL/MpJ/lpr/lpr (MRL/l) mouse model of lupus.

METHODS

RAPA treatment (6, 12, or 25 mg/kg 3 times per week) was evaluated by monitoring survival rates, autoantibody levels, and urinary albumin levels. Additionally, concanavalin A responsiveness, interleukin-2 (IL-2) production, lymphoid organ size, and histopathology were evaluated ex vivo.

RESULTS

RAPA prevented the typical rise in anti-double-stranded DNA antibody and urinary albumin levels and prolonged survival. Spleen and lymph node sizes were significantly decreased, inflammatory changes in the lung, liver, kidney, spleen, lymph node, and thymus were significantly reduced, and T cell mitogen-stimulated splenocyte proliferation and IL-2 production were restored.

CONCLUSION

Data from 3 independent experiments demonstrated that RAPA significantly reduced or prevented many pathologic features of lupus normally seen in the MRL/l mouse, and suggest that RAPA may be useful as a therapeutic agent in SLE in humans.

Rapamycin, a potent inhibitor of T-cell function, prevents graft rejection in murine recipients of allogeneic T-cell-depleted donor marrow

We investigated the ability of the macrolide antifungal agent rapamycin (RAPA) to inhibit the rejection of T-cell-depleted (TCD) donor bone marrow (BM) transplanted into major histocompatibility complex (MHC)-disparate irradiated recipients. RAPA (1.5 mg/kg) was administered for 14 days beginning on the day of transplant. In the present study, we have tested RAPA administration in two types of fully allogeneic BM transplantation (BMT) systems in which host T cells mediate the rejection of TCD BM grafts (DBA/1 transplanted into C57BL/6 and BALB/c transplanted into C57BL/6). In both instances, RAPA administration prevented the rejection of the donor graft, accelerated post-BMT hematopoietic recovery, and did not compromise recipient survival. Sequential post-BMT fluorescence-activated cell sorter analysis of the spleen showed that RAPA administration inhibited host CD4+ and CD8+ T-cell expansion that leads to graft rejection. To further investigate the effect of RAPA on T-cell subpopulations, we used two congenic donor mouse stains with isolated MHC class I (bm1) or class II (bm12) mutations. In these studies, we showed that RAPA administration can inhibit MHC class I-restricted CD8+ or class II-restricted CD4+ T-cell-mediated graft rejection without compromising recipient survival. The RAPA-facilitated alloengraftment is multilineage and durable. We have also shown that RAPA speeds hematopoietic recovery post-BMT. We conclude that RAPA represents a new therapeutic modality for promoting alloengraftment and accelerating hematopoietic recovery.

Murine recipients of fully mismatched donor marrow are protected from lethal graft-versus-host disease by the in vivo administration of rapamycin but develop an autoimmune-like syndrome

We investigated the ability of the macrolide antifungal agent rapamycin (RAPA) to inhibit murine graft-vs-host disease induced across the MHC barrier. An optimum dose (1.5 mg/kg) given for 14 days beginning on the day of transplant (and then three times weekly until 1 mo) effectively and significantly (p &lt; 0.001) protected 80% of irradiated B10.BR recipients of C57Bl/6 bone marrow/spleen grafts for over 90 days, whereas 80% of control mice died by day 37. Using a congenic model in which a mixture of Ly5.1+ bone marrow (T cell-depleted) and Ly5.2+ spleen cells allowed us to distinguish mature and immature cells, we found that RAPA inhibits the splenic expansion of mature donor-derived T cells in B10.BR recipients after bone marrow transplantation. In addition, phenotyping studies revealed that RAPA causes a massive reduction of immature CD4+CD8+ T cells in the thymus, indicating that RAPA probably interferes with maturation of immature CD3-CD4-CD8- T cells to CD4+CD8+ T cells. There was also a predilection toward development or intrathymic retention of the more mature CD3+CD4-CD8+ or CD3+CD4+CD8- cells in the thymus of long term survivors. These same observations were made in different experiments with mice given syngeneic bone marrow transplantation and RAPA. However, RAPA administration was associated with the occurrence of an autoimmune-like syndrome, consisting of ulcerative dermatitis, hepatic bile duct proliferation, and nondestructive lymphoid peribronchiolar infiltration of the lung. RAPA interfered with the deletion of potentially self-reactive T cells that occurs in thymic development. The failure of clonal deletion was observed in allogeneic and syngeneic transplants given RAPA, although only the allografted mice experienced an autoimmune-like syndrome. Some, but not all, of the nondeleted V beta populations were functionally active. These new findings bear certain dissimilarities to the syndrome and lesions observed with cyclosporin A treatment, particularly in the observation of bile duct proliferation and ulcerative skin lesions. Nonetheless, because of the potent effect of RAPA in preventing lethal graft-vs-host induced across the MHC, further investigation of the immune consequences of this highly effective compound is warranted.

Murine recipients of fully mismatched donor marrow are protected from lethal graft-versus-host disease by the in vivo administration of rapamycin but develop an autoimmune-like syndrome

We investigated the ability of the macrolide antifungal agent rapamycin (RAPA) to inhibit murine graft-vs-host disease induced across the MHC barrier. An optimum dose (1.5 mg/kg) given for 14 days beginning on the day of transplant (and then three times weekly until 1 mo) effectively and significantly (p < 0.001) protected 80% of irradiated B10.BR recipients of C57Bl/6 bone marrow/spleen grafts for over 90 days, whereas 80% of control mice died by day 37. Using a congenic model in which a mixture of Ly5.1+ bone marrow (T cell-depleted) and Ly5.2+ spleen cells allowed us to distinguish mature and immature cells, we found that RAPA inhibits the splenic expansion of mature donor-derived T cells in B10.BR recipients after bone marrow transplantation. In addition, phenotyping studies revealed that RAPA causes a massive reduction of immature CD4+CD8+ T cells in the thymus, indicating that RAPA probably interferes with maturation of immature CD3-CD4-CD8- T cells to CD4+CD8+ T cells. There was also a predilection toward development or intrathymic retention of the more mature CD3+CD4-CD8+ or CD3+CD4+CD8- cells in the thymus of long term survivors. These same observations were made in different experiments with mice given syngeneic bone marrow transplantation and RAPA. However, RAPA administration was associated with the occurrence of an autoimmune-like syndrome, consisting of ulcerative dermatitis, hepatic bile duct proliferation, and nondestructive lymphoid peribronchiolar infiltration of the lung. RAPA interfered with the deletion of potentially self-reactive T cells that occurs in thymic development. The failure of clonal deletion was observed in allogeneic and syngeneic transplants given RAPA, although only the allografted mice experienced an autoimmune-like syndrome. Some, but not all, of the nondeleted V beta populations were functionally active. These new findings bear certain dissimilarities to the syndrome and lesions observed with cyclosporin A treatment, particularly in the observation of bile duct proliferation and ulcerative skin lesions. Nonetheless, because of the potent effect of RAPA in preventing lethal graft-vs-host induced across the MHC, further investigation of the immune consequences of this highly effective compound is warranted.

Rapamycin, a potential disease-modifying antiarthritic drug

Rapamycin (RAPA), a potent immunosuppressive agent that prevents organ graft rejection in animal models of transplantation, possesses a mechanism of action different than that of cyclosporin A and FK-506. In this study, the pharmacological activity of RAPA in a variety of immune and inflammatory models was assessed in order to define better its potential utility as an antiarthritic agent. RAPA inhibited T cell-mediated inflammation in mouse methylated bovine serum albumin-induced delayed-type hypersensitivity (ED40 = 4.7 mg/kg p.o.) and produced oral ED50 of 2.0 mg/kg against developing adjuvant arthritis in rats (3-day dosing schedule) and 9.5 mg/kg in established adjuvant arthritis in rats (daily dosing schedule). In both models of adjuvant arthritis, effects of RAPA were maintained even after cessation of drug dosing. In contrast, after discontinuation of cyclosporin A (5- and 10-mg/kg doses), disease activity returned. RAPA was also effective in another T cell-mediated model, experimental allergic encephalomyelitis (ED50 approximately 5 mg/kg p.o.). At higher doses, RAPA significantly inhibited carrageenan paw edema in rats, a model of acute inflammation (ED40, 56 mg/kg p.o.), without increasing serum corticosterone levels. In this model, doses approximately 10 to 20 times greater than active doses in T cell-mediated models were required. RAPA at 1 to 50 microM did not inhibit in vitro human synovial phospholipase A2 or 5-lipoxygenase and cyclo-oxygenase activity in the human blood leukocyte assay. The total profile of RAPA suggests that it may be effective in the treatment of rheumatoid arthritis, multiple sclerosis and other autoimmune diseases.

A nonimmunosuppressive triene-modified rapamycin analog is a potent inhibitor of peptidyl prolyl cis-trans isomerase

A triene-modified analog of the potent immunosuppressive agent rapamycin was found to be a potent inhibitor of the peptidyl prolyl cis-trans isomerase activity of human FKBP (Ki = 12.5 nM). This analog was not immunosuppressive in a thymocyte proliferation assay itself, but was able to antagonize the effect of rapamycin. This new analog should be useful as a mechanistic probe for macrocyclic immunosuppressants.

Functional and histopathologic effects of rapamycin on mouse kidney

The effect of rapamycin (RAPA) on kidney function and histopathology was assessed in two strains of mice. Male C3H/HeJ mice were treated with RAPA for 4 days at doses of 25, 50, 75, and 100 mg/kg, ip and male C3H/HeJ or female Balb/cJ mice were both treated for 7 days at doses of 75, 150 and 200 mg/kg. Cyclosporine (CsA) was also administered to female Balb/cJ mice at doses of 50, 100, 150 and 200 mg/kg, ip. RAPA-treated mice had elevated BUN levels but the effect was not dose-dependent and was not present in the high dose, 7-day study conducted in the C3H/HeJ mice. Body weights were significantly depressed in both of the 7 day studies but not in the 4 day study. Histopathologic examination of the kidneys revealed the presence of intracytoplasmic vacuolization in the proximal tubules in both of the 7 day studies at the higher dose only. There were no drug-related deaths. In the CsA-treated mice, multiple deaths were recorded in both the 150 mg/kg and 200 mg/kg dose groups, probably related to neurotoxicity, and BUN levels were elevated in the 100 mg/kg dose group. In conclusion, RAPA's effects on kidney function were minimal at doses 50 times higher than its therapeutic dose established in the mouse. RAPA exhibited a better therapeutic index than CsA in the mouse.

A modification of the in vivo mixed lymphocyte reaction and rapamycin's effect in this model

Rapamycin, a novel macrocyclic immunosuppressive agent, suppresses murine T cell activation in vitro by mechanisms distinct from cyclosporin A (CsA). This study was designed to examine rapamycin and CsA in the host vs graft popliteal lymph node (PLN) model, an in vivo system of T cell-dependent lymphocyte activation. The PLN procedure was modified by using irradiated CTLL-2 cells of C57BL/6 origin, instead of primary mouse splenocytes, as the allogeneic stimulus in C3H/HeN recipient mice. PLN cell proliferation was determined by [3H]-thymidine uptake. We found that the host lymphocyte proliferative response to CTLL-2 cells (H-2b) is greater than the response to mouse Balb/c splenocytes (H-2d). Rapamycin (ip or po) produced a dose-related inhibition of the in vivo mixed lymphocyte reaction. By contrast, the effects of CsA and FK-506 were not dose related within the same dose range (0.006-12 mg/kg). These data indicate that rapamycin is an effective immunosuppressive agent and confirm its ability to affect the allogeneic T cell response in vivo. Furthermore, the pharmacological data suggest that this PLN model utilizing irradiated CTLL-2 cells as an allogeneic stimulus provides a reproducible system to examine mixed lymphocyte reactions in vivo.

Rapamycin prevents the onset of insulin-dependent diabetes mellitus (IDDM) in NOD mice

The effect of the immunosuppressive agent rapamycin (RAPA) was assessed in the non-obese diabetic (NOD) mouse which is an autoimmune model of IDDM. RAPA was prepared in a vehicle of 8% cremophor EL/2% ethanol and investigated in two studies. NOD/MrK female mice (six per group, study no. 1; 10 per group, study no. 2) were dosed three times per week p.o. by gavage from 56 to 170 days of age (study no. 1) or from 64 to 176 days of age (study no. 2). Mice treated with RAPA at 0.6 mg/kg, 6 mg/kg, or 12 mg/kg maintained normal plasma glucose through 170 or 176 days of age with 10%, 0%, and 0% incidence of diabetes respectively. In contrast, naive, vehicle-treated, or RAPA 0.06 mg/kg-treated mice exhibited elevated plasma glucose and disease incidence typical for female NOD mice. Mice which became diabetic had elevated levels of beta-hydroxybutyrate, triglycerides and cholesterol. These plasma lipid concentrations were positively correlated with the duration of hyperglycaemia (r = 0.85, 0.87 and 0.84 respectively). Outside of its ability to prevent diabetes, RAPA itself did not affect the lipid profile of the mice. Intervention therapy with RAPA was ineffective at reversing the course of disease after IDDM onset under these experimental conditions. Finally, we report here that prophylactic treatment with RAPA was able to protect against IDDM development in some RAPA-treated mice 41 weeks after cessation of treatment. These data show that orally administered RAPA is effective in preventing onset of disease in the NOD mouse, a relevant model of autoimmune type I diabetes in man.

Preclinical evaluation of a new potent immunosuppressive agent, rapamycin

Since individual immunosuppressive agents display pleiotropic arrays of nonimmunologic toxic complications when used at therapeutic concentrations, synergistic drug combinations proffer an attractive strategy. RAPA is a good candidate for this enterprise, because of its unique action to inhibit lymphokine signal transduction. Initial in vivo and in vitro studies using the rigorous pharmacologic tool, the median effect analysis, document a synergistic relation between RAPA and CsA in rodent and canine models. These preclinical findings compel careful Phase I trials, in order to assess the safety and synergistic efficacy of RAPA in combination drug regimens with other immunosuppressive agents.

FK506 and rapamycin: novel pharmacological probes of the immune response

The immune system is an intricate network of circuitry which is incompletely understood. Novel tools are needed to unravel the relevance of even the smallest components of this network. While the clinical potential of FK506 and rapamycin as selective immunosuppressants is the major reason for their current importance, preclinical studies described here by Joseph Chang and colleagues have already suggested several provocative ideas which may revise our biochemical concepts of T-cell activation. With the combination of molecular and cellular studies, the insights gained with FK506/rapamycin may lead to a better understanding of the biochemical circuits that are involved in the immune response. Ultimately, studies may lead to the identification of an endogenous immunosuppressive ligand that mimics FK506 or rapamycin.

Protective and restorative role of AS101 in combination with chemotherapy

The immunomodulator AS101 has been found previously by us to stimulate the secretion of high levels of interleukin 1 and colony stimulating factor (CSF) in vitro, as well as the production of CSF in vivo in mice models. These cytokines are known to induce proliferation and differentiation of hematopoietic progenitor cells from the spleen and bone marrow (BM) and to protect mice from DNA-damaging agents. The present studies were designed to evaluate the effects of prolonged treatment with AS101 on myelopoiesis, BM cellularity, and CSF secretion in mice treated with a sublethal dose of cyclophosphamide (CYP) and on the survival of mice undergoing treatment with lethal doses of this compound. In this model, the hematopoietic progenitors were suppressed during the overbound phase of myelopoiesis resulting from the cytotoxic effects of CYP. This allowed the detection of a significant proliferative effect of AS101 in vivo on BM colony-forming units granulocyte-macrophage progenitor cells, BM cellularity, and the secretion of CSF. Moreover, AS101 protected these animals from the lethal effects of high doses of CYP. These protective effects were demonstrable only when AS101 was administered to mice prior to CYP treatment. The only exception was CSF secretion by spleen cells that had been reconstituted when AS101 was administered both prior to and following CYP treatment. AS101 was found to have a synergistic effect with CYP in the treatment of tumor-bearing mice, suggesting that the combination of these two modalities provides a more effective treatment of their tumors. These results strongly suggest an immunoregulatory role for AS101 in counteracting the chemotherapy-induced hematopoietic suppression as well as usefulness as adjunct treatment of cancer when used in combination with CYP.

Cytokine secretion effected by synergism of the immunomodulator AS101 and the protein kinase C inducer bryostatin

AS101, a synthetic organotellurium compound, was found to have immunomodulating properties by initiation of cytokine production in vitro and in vivo. Phase I/II clinical trials currently in progress on AIDS and cancer patients treated with AS101 show significant increases in various immunological parameters, with minimal toxicity. Recently, AS101 and the protein kinase C (PKC) inducer, phorbol myristate acetate (PMA), were shown to synergize in the secretion of interleukin-2 (IL-2) and colony-stimulating factor (CSF) in vitro, by human and mouse lymphoid cells. The bryostatins, a group of natural macrocyclic lactones isolated from marine invertebrates (Bugula neritina) have been reported to be potent PKC activators with no tumour promoting activity. In this study, we investigated the synergistic effect of AS101 and a partially purified preparation of bryostatin on the production of several cytokines. Our data confirm the presence of synergism, which greatly enhances cell proliferation, IL-2, tumour necrosis factor (TNF) and interferon-gamma (IFN-gamma) secretion by human mononuclear cells (MNC) and the production of IL-2 and TNF by mouse cells. The absence of tumour-promoting activity of the bryostatins makes them particularly good candidates, in combination with AS101, for immunomodulation in vivo in clinically immunosuppressed conditions.

Disposition and biotransformation of 14C-etodolac in man

Four human subjects were given a capsule containing 200 mg of 14C-etodolac. At the peak (two hours after dosing), most of the radioactivity in serum was due to etodolac; subsequently, metabolites gradually appeared. The elimination half-life of etodolac from serum averaged six hours. Etodolac was greater than 99% bound to human serum proteins. An average of 73% of the dose was excreted in the urine and 14% in faeces within seven days, with 61% appearing in the urine during the first 24 h. Microbial transformation of etodolac was employed to biosynthesize sufficient amounts of two urinary metabolites to facilitate structure elucidation. Five metabolites, representing 65% of the radioactivity in urine collected 0-24 h after dosing (61% of the dose was excreted in urine within 24 h), were isolated and characterized by t.l.c., g.c., h.p.l.c., n.m.r (1H and 13C) and m.s. Most of the identified urinary components were conjugates of etodolac and three hydroxylated metabolites (6-hydroxyetodolac, 7-hydroxyetodolac and 8-(1-hydroxyethyl)etodolac). Two metabolites were identified as glucuronyl ester conjugates of etodolac and 7-hydroxyetodolac; the former represented about 20% of the urinary radioactivity. False positive tests for bilirubin in urine of patients treated with etodolac were found to be due to the two phenolic metabolites.

Activity of rapamycin (AY-22,989) against transplanted tumors

Rapamycin exhibits activity against several ascites and solid transplantable tumors; it is slightly active to inactive against leukemias. On a weight basis, rapamycin was less active than 5-fluorouracil, cyclophosphamide and adriamycin, but rapamycin's maximal activity against Colon 38 tumor was similar to that of 5-fluorouracil and cyclophosphamide. Its activity was such that it significantly inhibited tumor growth at any stage of development. In the active dose range, rapamycin appeared less toxic than the other drugs. In the Colon 38 tumor model, rapamycin at a given dose exhibited the same activity when administered ip, iv, im and sc; upon oral administration, its activity was reduced but not abolished. Rapamycin was compatible with 5-fluorouracil and cyclophosphamide. The sequential treatment 5-fluorouracil-rapamycin-cyclophosphamide was superior to the sequence 5-fluorouracil-adriamycin-cyclophosphamide in protecting Colon 38 tumor-bearing mice. 29-Demethoxyrapamycin exerted only marginal activity against P388 lymphocytic leukemia; it was inactive against B16 melanocarcinoma and Colon 38 solid tumor.

Demethoxyrapamycin (AY-24,668), a new antifungal antibiotic

Demethoxyrapamycin is a new antifungal antibiotic which is co-produced with rapamycin by Streptomyces hygroscopicus. It was isolated as a minor component during recovery of rapamycin. Its antifungal and antitumor activity is compared with that of rapamycin.

Ravidomycin (AY-25,545), a new antitumor antibiotic

A streptomycete was isolated from a Guatemala soil sample and found to inhibit Grampositive bacteria including mycobacteria. The antibiotic-producing microorganism was characterized, identified as a new species and named Streptomyces ravidus. The antibiotic principle was extracted with organic solvent from the mycelium, isolated in crystalline form and named ravidomycin. Ravidomycin is mainly active against Gram-positive bacteria including mycobacteria. It shows only weak activity against Gram-negative organisms and no activity against fungi. Ravidomycin exhibits potent antitumor activity against P388 lymphocytic leukemia, Colon 38 tumor and CD8F1 mammary tumor. Acute toxicity in mice is low.

Rapamycin (AY-22,989), a new antifungal antibiotic. III. In vitro and in vivo evaluation

The activity of rapamycin, a new anti-Candida antibiotic, was not affected by pH values between 6 and 8; at pH 4, however, activity was abolished. The MIC of rapamycin did not vary drastically with the size of inoculum: a ten-fold dilution of the inoculum reduced the MIC only two-fold. Serum binding was extensive. Serum levels obtained in mice were higher on subcutaneous injection than with oral administration. Dogs absorbed rapamycin after oral administration. Rapamycin cured systemic candidosis in mice: PD50 s.c. was 9.5 mg/kg: PD50 p.o. was 11 mg/kg. In the same experimental infections amphotericin B and nystatin exhibited PD50 values of less than 0.25 mg and greater than 4,000 units/kg respectively. Rapamycin and amphotericin B, administered at 1, 4 and 24 hours after infection, gave approximately the same percent survival after 30 days of observation. When the above treatment was extended by an additional daily treatment for 6 days, rapamycin by the subcutaneous route yielded a higher percentage of survival than either rapamycin or amphotericin B, administered orally, after a 30-day observation period. Vaginal candidosis in female rats was treated efficiently (91% cure) by rapamycin administered orally. No increase of resistance of C. albicans was observed during treatment.

Antimycin A fermentation. I. Production and selection of strains

Increase in antimycin A production was achieved through a parallel strain and medium improvement program: a 125-fold augmentation (75 to 9,500 mug/ml) was obtained. The selective system included antimycin A productivity, conidiation, sensitivity to ultraviolet radiation, growth rate and yield, and absence of pigment and actinomycin D production. Among the original strains tested one natural isolate possessed high productivity and several of the above characteristics, and was selected for mutagenesis. Spontaneous and induced variability was then exploited in isolating high-producing strains. The first mutagen used was ultraviolet radiation; it was replaced by ethylenimine when it became no longer efficient in increasing variability. As new, high producers were isolated, the medium was modified to best suit their requirements for still higher productivity. The critical environmental factors were absence of phosphate and organic salts, concentration of the nitrogen source and ratio organic/inorganic nitrogen, ratio ammonium sulfate/calcium carbonate, and addition of slowly utilizable carbon sources, such as lactose and oil; optimum temperature and initial pH were 25 degrees C and 7.0. Aeration/agitation requirements of improved strains were high. Fermentation was characterized by abrupt pH changes which impaired rapid accumulation of the antibiotic. Antimycin A was produced during both the trophophase and idiophase.