Suramin in Adrenal Cancer: Modulation of Steroid Hormone Production, Cytotoxicity in Vitro, and Clinical Antitumor Effect*
R. V. LA ROCCA, C. A. STEIN, R. DANESI+, C. A. JAMIS-DOW, G. H. WEISS, AND C. E. MYERS
Medicine (R.V.L., C.A.S., R.D., C.A.J .- D., C.E.M.) and Surgery (G.H.W.) Branches, Clinical Oncology Program, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
ABSTRACT. Suramin, a drug known to have antiparasitic effects, has been previously shown to have adrenocorticolytic activity in primates. We now confirm preferential accumulation of this compound in the normal adrenal gland, evaluate its in vitro effect against two human adrenocortical carcinoma cell lines (SW-13 and NCI-H295), and report the clinical activity of suramin in 17 patients with metastatic adrenocortical carci- noma. Inhibition of colony formation occurred in both adrenal cell lines in vitro at concentrations that are clinically achievable in humans. In addition, suramin concentrations as low as 100 ug/mL were able to inhibit glucocorticoid, mineralocorticoid, and androgen production by the NCI-H295 cell line. Of 16 patients with adrenocortical carcinoma now evaluable for tumor response, 2 achieved a partial response, 2 had a minor response,
and 5 remained with stable disease for periods ranging from 3- 10 months; the remainder progressed. One of 7 patients with excessive steroid hormone production achieved a partial nor- malization of her steroid levels for the duration of suramin therapy in the setting of radiographic disease stabilization. An additional patient treated off-study for lack of radiographically measurable disease, achieved complete normalization of plasma aldosterone levels. We conclude that suramin preferentially ac- cumulates in adrenal cells, induces cytotoxicity and significant down-regulation of steroid hormone production in vitro, and has some therapeutic efficacy as a single agent in patients with metastatic adrenocortical carcinoma. (J Clin Endocrinol Metab 71: 497-504, 1990)
S URAMIN, a polysulfonated naphthylurea, repre- sents one of a series of compounds synthesized by Bayer AG as an antitrypanosomal agent in the early 1990s (1). Since then, many other important properties of this compound have been described, including its ability to bind and displace growth factors from their receptors in vitro (2), its immune system-modulating properties (3), and its inhibitory effect on a variety of cellular enzyme systems (1). Included among these are the DNA polymerases (4), ornithine decarboxylase (5), and the lysosomal enzymes iduronate sulfatase and ß- glucuronidase (6). We have, in addition, previously shown that suramin is capable of selectively inducing adrenocortical necrosis when administered to cynomol- gus monkeys (7). These observations have prompted our group to further evaluate the effect of this compound in
Address all correspondence and requests for reprints to: Renato V. La Rocca, M.D., Medicine Branch, National Cancer Institute, National Institutes of Health, Building 10, Room 12N-226, Bethesda, Maryland 20892.
* This is a U.S. government work. There are no restrictions on its use.
t Visiting fellow from the Instituto di Farmacologia, Facolta’ di Medicina e Chirungia, Universita di Pisa, Pisa, Italy.
a variety of pathophysiological systems and, in particu- lar, as a possible antitumor agent (8).
In this paper the preferential accumulation of suramin in the adrenal gland in vivo after bolus injection is described. In addition, we document the modulation of steroid hormone production and cytotoxicity induced by suramin in vitro and report the clinical activity of this agent when administered to patients with metastatic adrenocortical carcinoma.
Materials and Methods
Chemicals and supplements for cell culture
Suramin (NSC-34936), distributed by FBA Pharmaceuticals, Mobay Chemical Corp. (New York, NY), was obtained through the Pharmaceutical Resources Branch, Developmental Thera- peutics Program, Division of Cancer Treatment, NCI (Be- thesda, MD). [3H]Suramin (309 GBq/mmol; 17.3 MBq/mL in 50% ethanol) was purchased from Moravek Biochemicals, Inc. (Brea, CA). Tetrabutylammonium dihydrogen phosphate was purchased from Aldrich Chemical Co., Inc. (Milwaukee, WI). RPMI-1640, fetal bovine serum, penicillin, streptomycin, and L-glutamine were purchased from Biofluids, Inc. (Rock- ville, MD). L-15 culture medium, 1 mM EDTA, and 0.25% trypsin in Ca2+/Mg2+-free Hanks’ Balanced Salt Solution were
obtained from Gibco (Grand Island, NY). Gram crystal violet was obtained from Difco (Detroit, MI), and trichloroacetic acid was purchased from Baker Chemical Co. (Phillipsburg, NJ). Cell culture grade agar was acquired from Sigma Chemical Co. (St. Louis, MO).
Administration of suramin to BALB/c mice
This study was conducted in accordance with the NIH Guide for the Care and Use of Laboratory Animals. Seven-week-old BALB/c mice were used. For the first experiment, three female BALB/c mice received a dose of [3H]suramin (0.696 MBq/ mouse in 0.1 mL saline) as a single bolus injection via the tail vein. In the second experiment, four male BALB/c mice were given 6.96 MBq [3H]suramin/mouse in 0.1 mL saline, again via single tail vein injection. Seven days after drug administration the mice from both experiments were killed, and the adrenal glands were removed, weighed, and frozen at -70 C until analyzed for drug levels. In the latter experiment, given the difficulty in reproducible dissection of the adrenals from the surrounding perinephric fat, the adrenals (n = 8) were pooled, weighed, and analyzed as a single sample. The left renal vein of each mouse was transected, and blood was collected with a heparinized syringe to measure plasma drug levels.
Measurement of suramin levels
Drug levels in the adrenals and plasma from the BALB/c mice were measured by the method of Klecker and Collins (9) with modifications. The organ samples were placed in 12 × 75- mm polystyrene tubes (Falcon 2058, Beckton Dickinson Co., Lincoln Park, NJ) containing 0.1 mL of a 1 mg/mL solution of suramin as an internal standard. Sterile water (0.9 mL) was then added to each, and the samples were homogenized using a Polytron homogenizer (Brinkmann Instruments, West- bury, NY). The samples were then extracted three times with 2 mL of a solution of 50 mM tetrabutylammonium dihydrogen phosphate in 90% methanol and centrifuged for 5 min at 500 x g, and the supernatant was decanted and pooled. Chromatog- raphy was performed using a System 90XL (Gilson Medical Electronics, Middleton, WI), equipped with a RCM-100 holder containing an 8 × 100-mm Radial-Pak cartridge column packed with 4 um spherical Nova-Pak C18 stationary phase (Waters Associates, Milford, MA) and Guard-Pak precolumn module with a Nova-Pak C18 insert. Detection was performed at 316 nm and 0.32 AUFS with a Knauer no. 731.87 variable wave- length detector (Knauer GmbH, Berlin, West Germany) and a FLO-ONE\Beta radioactive flow detector (Radiomatic Instru- ments and Chemical Co., Inc., Tampa, FL). The peak area ratios of [3H]suramin to the cold suramin internal standard were plotted as a function of [3H]suramin amount. The best- fit straight line was determined by unweighted linear regres- sion; the amount of [3H]suramin in unknown samples was calculated using the results of the regression analysis. This result was then divided by the weight or the volume of the sample used, so the final results are expressed as nanograms per g tissue or nanograms per mL plasma.
Plasma suramin levels were also routinely measured in all patients enrolled in the clinical study and were determined by the method of Klecker and Collins (9).
Cell lines
The steroid hormone-secreting adrenocortical carcinoma cell line NCI-H295 was isolated and established from a patient with invasive adrenocortical carcinoma in 1980. The morphology and steroid-secreting properties of this cell line in defined culture medium have been described previously (10). The poorly differentiated nonsteroid-secreting SW-13 adrenal cell line (11) was purchased from the American Type Culture Collection (Rockville, MD). The NCI-H295 cell line was propagated in RPMI-1640 with 10% fetal calf serum, whereas SW-13 was grown in L-15 with 10% fetal calf serum. In each case, the culture medium was additionally supplemented with antibiotics [penicillin (100 U/mL) and streptomycin (100 µg/mL)] and L- glutamine (2 mM). The cells used throughout the study were harvested from exponential phase maintenance cultures grown in 175-cm2 flasks (Nunc 156502, Copenhagen, Denmark) in- cubated at 37 C in 5% CO2 with 100% relative humidity.
Colony formation assay
NCI-H295 and SW-13 cells were plated in 24-well tissue culture dishes (Costar 3524, Cambridge, MA) in 1 mL medium at 7.0 × 103 cells/cm2. After a 24-h incubation, suramin (75, 100, 150, 200, 300, and 400 ug/mL) was added. The culture plates were then incubated for 48, 96, and 144 h. SW-13 cells were harvested by incubation with 0.2 mL 1 mM EDTA and 0.25% trypsin in Ca2+/Mg2+-free Hanks’ Balanced Salt Solu- tion, and 500-1500 cells were plated in replicate 6-well tissue culture dishes (Costar 3506) in 4 mL drug-free medium and incubated for an additional 12 days. The resulting colonies were fixed with 1 mL methanol-glacial acetic acid (3:1, vol/vol) and stained with crystal violet. NCI-H295 cells (4 x 103) were plated in 0.25% agar. The colonies were stained with a 1 mg/mL solution of p-iodonitrotetrazolium violet. Cytotoxicity was measured by counting colonies with more than 50 cells and is expressed as percent survival compared to control cells (12).
Steroid analysis
NCI-H295 cells were exposed for 144 h to the following concentrations of suramin: 0, 100, 200, and 400 µg/mL. Cell number was then calculated, and the conditioned medium was assayed for the following steroid hormones and precursors: pregnenolone, progesterone, corticosterone, aldosterone, 17- hydroxypregnenolone, 17-hydroxyprogesterone, 11-deoxycorti- sol, cortisol, dehydroepiandrosterone, androstenedione, and de- hydroepiandrosterone sulfate. In addition, the concentrations of these steroids in RPMI-1640 with 10% fetal bovine serum with and without suramin 200 µg/mL were measured and were comparable. In each instance, these steroids were measured by RIA after column chromatography, as previously described (13- 17). The same methodology was used in assaying the circulating steroid levels in the patients on the study.
Patient selection
Adults with histological proof of metastatic or unresectable adrenal cortical carcinoma were eligible for this pilot clinical study. All were evaluated for protocol eligibility and subse-
quently received parenteral suramin at the NCI (Be- thesda, MD). The protocol was reviewed and accepted by the Institutional Review Board of the NIH. All patients were informed of the potential risks and benefits and signed an informed consent. They were also required to have documented evidence of disease progression upon entering the study and not to have received any form of chemo- or radiotherapy for the 4 weeks before the initiation of suramin therapy.
Baseline radiographic as well as steroid hormone assays were performed before the initiation of suramin treatment and were repeated on the average of every 4-6 weeks during therapy. Serial clinical examinations, chest x-rays, and chest and ab- dominal computed tomographic and magnetic resonance im- aging scans were used to evaluate response.
Treatment
The dose and schedule used to treat these patients changed over time as we gained knowledge of the toxicity and pharma- cokinetics of suramin. Two different modalities of suramin administration were employed: weekly iv bolus injection and continuous iv infusion. The dose of the former varied from 850-1400 mg/m2, whereas the continuous infusion was initiated at a rate of 350 mg/m2. day and then either interrupted upon attainment of a plasma suramin level approaching or greater than 300 ug/mL or reduced to a maintenance level of 50 mg/ m2. day. In light of this drug’s prolonged plasma half-life (45- 55 days) (18), achievement and maintenance of a plasma sur- amin level above 150 ug/mL were the common end points of the two different dosing schedules employed.
Response criteria
A complete response is defined as the disappearance of all evidence of malignant disease, and a partial response is a 50% or more decrease in the summed products of the largest perpen- dicular diameters of all evaluable lesions for at least two meas- urement periods separated by at least 4 weeks. A minor re- sponse is defined as a more than 25%, but less than 50%, decrease in the summed products of the largest perpendicular diameters of all evaluable lesions for at least 4 weeks. A stable disease is a less than 25% increase or a less than 25% decrease in measurable disease for at least a 3-month period. Progression of disease is defined as a more than 25% increase in measurable disease.
Results
Adrenal gland accumulation of suramin after bolus injec- tion in mice
In the first experiment, 7 days after the single iv bolus injection, suramin levels in the adrenal glands and plasma were 277.3 ± 23.61 ng/g and 68.4 ± 4.57 ng/ml, respectively (Fig. 1A). Assuming a tissue density of 1.0, the concentration of suramin in the adrenals after 7 days was 4.1 ± 0.33 times higher than that detected in plasma. In the second experiment, the concentration of suramin in the adrenals (pooled) was 1545.9 ng/g, with a plasma
Suramin (ng/g wet weight, ng/ml plasma)
A
300
200
100
0
Adrenal
Plasma
Samples
2000
Suramin (ng/g wet tissue, ng/ml plasma)
B
1000
0
Adrenal
Plasma
Samples
concentration of 290.9 ± 17.95 ng/ml, resulting in an adrenal/plasma ratio of 5.4 (Fig. 1B). With the exception of the kidneys, accumulation in the adrenal glands was from 3-20 times higher than that in a variety of other organs evaluated, including lung, muscle, liver, brain, spleen, and large bowel (data not shown).
Effect of suramin on adrenal cancer cells in vitro
The colony formation assay was used as a measure of effective cytotoxicity. Both cell lines were sensitive to suramin in a dose- and time-dependent manner. After 144 h of drug exposure, the suramin concentration re- sulting in 50% inhibition of colony formation of SW-13 with respect to the untreated control was approximately
100
Percent surviving (compared to control)
NCI-H295
SW 13
10
0
100
200
300
400
Suramin (ug/mL)
150 ug/mL, while that for NCI-H295 was between 300- 350 µg/mL (Fig. 2).
Effect of suramin on steroid hormone production in vitro by NCI-H295
As is shown in Table 1, the malignant NCI-H295 cell line produces detectable levels of androgens, mineralo- corticoids as well as glucocorticosteroids. In the presence of varying concentrations of suramin, including a con- centration that only marginally affects cell number and viability (100 µg/mL), a dose-dependent reduction in these steroid levels, calculated as nanomoles per L/106 cells and expressed as a percentage of control, was noted (Fig. 3, A, B, and C).
Clinical trial
A total of 17 patients with metastatic adrenocortical cancer have now been formally entered in this study (Table 2). There are 9 women and 8 men, with a median age of 34 yr (range, 25-65 yr). In addition, 11 of these 17 patients had progressed through therapy with o,p’DDD
(mitotane), 6 had received 1 or more cytotoxic chemo- therapy regimens before entering the study, and 5 had received prior radiotherapy. The cumulative dose of sur- amin administered to the 17 patients in the study varied from 7.7-27.6 g, with a median of 14.2 g. Seven of these 17 patients had elevated plasma levels of 1 or more steroid hormone precursors. Five of these 7 had failed prior therapy with mitotane.
Sixteen of the 17 patients formally enrolled onto this pilot study are evaluable for response, as measured by actual tumor shrinkage. There were no radiographic com- plete remissions. Two achieved a partial response of 2- and 6-month duration, respectively. In patient 7, this was characterized by marked shrinkage in the size of a pelvic mass, whereas in patient 9 suramin therapy re- sulted in complete disappearance of multiple pulmonary nodules and shrinkage in the size of a biopsy-proven tumor mass within the inferior vena cava. Both subse- quently relapsed after discontinuing suramin therapy and were not retreated. An additional 2 patients (no. 2 and 8) achieved minor responses of 3- and 1.5-month duration. Five patients remained with radiographically stable disease for periods ranging from 3-10 months. The remaining 7 patients either demonstrated radiographic evidence of disease progression or, in the cases of patients 5 and 6, succumbed within 4-5 weeks of initiating sura- min therapy, presumably as a result of tumor progres- sion, without having achieved a plasma suramin level above 150 µg/mL. In both of these instances, extensive bulky disease was present, and both patients had dem- onstrated a marked decline in their performance status at the onset of suramin treatment.
Only one of the seven patients in the study with abnormal secretion of steroid hormone and hormone precursors had a documented significant decline in these levels. In fact, in patient 1, after 1 month of suramin therapy, this approached a 50% decline of pretreatment values of the following steroid precursors: 17-hydroxy- pregnenolone, 17-hydroxyprogesterone, androstenedi- one, dehydroepiandrostenone, and dehydroepiandroste- rone sulfate. The two patients who achieved radiographic partial remissions did not have abnormal pretreatment levels of steroid precursors or hormones. In the four patients with abnormal steroid secretion who progressed
| Pregnenolone | 400 | 17-Hydroxypregnenolone | 310 | Dehydroepiandrosterone | 106.2 |
| Progesterone | 82 | 17-Hydroxyprogesterone | 22.8 | Androstenedione | 9.5 |
| Corticosterone | 6.6 | 11-Deoxycortisol | 110 | Dehydroepiandrosterone sulfate | 0.6 |
| Aldosterone | 11.5 | Cortisol | 74 |
Values are nanomoles per L/106 cells; the SEM was less than 15%. The values represent the concentration in the conditioned medium after 6 days. The concentrations of these steroids in the culture medium (RPMI-1640 plus 10% FBS) were also measured and were less than 4% of the absolute values of each steroid concentration shown (i.e. not controlled for cell number), with the exception of corticosterone (<9.4%) and cortisol (<18.2%).
A
100
Pregnenolone
Progesterone
Hormone levels in culture medium
Corticosterone
80
Aldosterone
(% of control)
60
40
20
0
0
100
200
300
400
Suramin (µg/mL)
B
100
17-OH-Pregnenolone
17-OH-Progesterone
Hormone levels in culture medium (% of control)
11-Deoxycortisol
80
Cortisol
60
40
20
0
0
100
200
300
400
Suramin (ug/mL)
C
100
Hormone levels in culture medium (% of control)
80
Dehydroepiandrosterone
Androstenedione
Dehydroepiandrosterone sulfate
60
40
20
0
0
100
200
300
400
Suramin (ug/mL)
radiographically, further increase in at least one of the steroid precursors was noted in each.
An additional patient with elevated plasma aldoste- rone levels, hypokalemia, and hypertension, but not ra- diographically evaluable disease, was also treated with suramin, but off-study. She became normotensive and normokalemic, with her supine plasma aldosterone level falling from a pretreatment value of 1859 to 316 pmol/L (normal range, 150-272 pmol/L, on a normal salt diet). In the course of therapy, she did develop suramin-related neurotoxicity, but subsequently recovered complete neu- rological function.
The median duration of survival of all patients from the time of initial study enrollment was 7 months (range, 1-18+ months).
Each of the 17 patients was evaluated for toxicity. The results of this analysis are shown in Table 3. Replace- ment doses of hydrocortisone were administered to each patient in the study in view of suramin’s ability to damage the adrenal cortex. The most serious toxicities related to suramin administration were the development of coagulopathy and polyneuropathy. The former predis- posed to four episodes of spontaneous hemorrhage in three patients early in the study who were receiving suramin by bolus injection (19). None of these episodes resulted in significant hemodynamic compromise, and subsequent modifications in the dosing schedule have virtually eliminated the incidence of this complication. Two patients developed a severe polyradiculoneuropathy characterized by the development of a flaccid extremity paralysis, elevation in cerebrospinal fluid protein levels, and, in one case, respiratory muscle compromise prompt- ing endotracheal intubation and mechanical respiration. Both subsequently recovered motor function and were discharged from the hospital. Additional suramin-related toxicities of significance included reversible renal insuf- ficiency, particularly in those patients whose baseline function has been partly compromised by prior surgery or nephrotoxic chemotherapy, and the development of thrombocytopenia, albeit transient, which appeared in some of the patients who had received prior therapy with cytotoxic chemotherapeutic agents. Vortex keratopathy, presenting as a foreign body sensation in one or both eyes, developed in five patients (20). In each instance these symptoms abated with conservative management,
FIG. 3. Effect of 144-h exposure to varying concentrations of suramin on steroid hormone production by NCI-H295 cells in vitro. Values were calculated as nanomoles per L/106 cells and thus are controlled for cell number at the time the steroid assays were performed. The results are expressed as a percentage of steroid hormone production by an equal number of plated cells not exposed to suramin (Table 1). A, Mineralo- corticoids. B, Glucocorticoids. C, Adrenal androgens. Points are the mean of two experiments. In each instance the SEM was less than 15%.
| Patient no. | Age (yr) | Sex | Prior therapy | Sites of disease | Method of admin. | Cumulative dose (g) | Maximum suramin level (µg/ml) | Response (months) |
|---|---|---|---|---|---|---|---|---|
| 1 | 42 | M | Surgery | Lung/IVC | Bolus/CI/ bolus | 23.6 | 386 | PR (6) |
| 2 | 31 | F | Surgery/RT | Liver/abdomen | Bolus | 14.2 | 242 | PR (2) |
| 3 | 27 | F | Surgery/mitotane/ RT | Lung/liver | Bolus | 26.8 | 283 | MR (3) |
| 4 | 44 | M | Surgery/mitotane/ RT, cisplatin, adriamycin + cytoxan | Lung/abdomen | Bolus | 11.6 | 170 | MR (1.5) |
| 5 | 40 | F | Surgery/mitotane | Abdomen | CI | 22.3 | 449 | SD (10) |
| 6 | 26 | M | Surgery/RT | Lung/abdomen | Bolus/CI | 27.6 | 302 | SD (8) |
| 7 | 34 | F | Surgery/cisplatin + VP-16 | Lung/liver/ab- domen | Bolus | 12.6 | 201 | SD (3) |
| 8 | 31 | M | Surgery/mitotane | Abdomen (ex- tensive) | CI | 13.8 | 369 | SD (3) |
| 9 | 51 | F | Mitotane | Lung | CI | 11.7 | 405 | SD (3) |
| 10 | 44 | M | Surgery/mitotane/ MTX + 5FU | Liver/abdomen | Bolus | 15.3 | 209 | POD |
| 11 | 27 | F | Surgery/mitotane | Lung/abdomen | Bolus | 19.1 | 193 | POD |
| 12 | 25 | M | Surgery | Lung/abdomen (extensive) | Bolus | 9 | 25 | POD |
| 13 | 63 | M | Surgery/mitotane | Abdomen (ex- tensive) | Bolus | 8.8 | 139 | POD |
| 14 | 33 | M | Surgery | Liver | Bolus/CI | 22.4 | 367 | POD |
| 15 | 26 | F | Surgery/mitotane, cisplatin, adria- mycin + cytoxan | Lung/abdomen | CI | 18.4 | 272 | POD |
| 16 | 65 | F | Mitotane/cisplatin + VP-16 | Lung | CI | 11.6 | 299 | POD |
| 17 | 44 | F | Surgery/RT/mito- tane, adriamycin | Abdomen | CI | 7.7 | 243 | NE |
CR, Complete response; PR, partial response; MR, minor response; SD, stable disease; POD, progression; NE, not evaluable; CI, continuous infusion; IVC, inferior vena cava; RT, radiotherapy, MTX, methotrexate; 5FU, 5-fluorouracil.
including the use of artificial tears, patching, and brief cessation of suramin therapy. Finally, the development of three episodes of fever and one episode of death presumably related to sepsis (patient 8, whose tumor was not steroid secreting) suggests that the administration of suramin may result in a significant degree of immuno- suppression.
Discussion
Suramin has previously been shown to inactivate dif- ferent enzyme systems critical to normal cell function and proliferation as well as to displace a variety of growth factors from their receptors, including platelet-derived growth factor and basic fibroblast growth factor, both of which have been postulated to have significant roles in adrenal cell biology (1, 2, 21, 22). In this report we have shown that the adrenal gland preferentially accumulates suramin with respect to plasma and many other tissues, and this may in part account for its selective adrenocor-
ticolytic effect. In addition, this compound is capable of exerting a significant cytotoxic effect on adrenal cancer cells in vitro, as determined by colony formation assay, at concentrations clinically achievable in humans. This effect was particularly pronounced against the SW-13 cell line, which has been previously shown to be sensitive to basic fibroblast growth factor (21).
The effect of suramin on steroid hormone production, presumably through binding and inhibition of adrenal steroidogenic enzymes, is pronounced even at relatively low concentrations. Suramin has been previously shown in vitro to decrease steroidogenic enzyme activities in a dose-dependent fashion in adrenal mitochondrial and microsomal preparations (23). These researchers dem- onstrated a 50% inhibition of enzyme activity in the range of 2-50 umol/L (~3-75 µg/mL) for four of the five enzymes tested. In our experiments, 6-day exposure of viable steroid-secreting NCI-H295 cells to 100 µg/mL suramin, which against this cell line has a relatively minor cytotoxic effect (see Fig. 2), resulted in a marked
| Toxic reaction | No. of patients |
|---|---|
| Malaise | 9 |
| Transient erythematous rash | 9 |
| Vortex keratopathy | 5 |
| Proteinuria (1-3 g/24 h) | 4 |
| Coagulopathy (prothrombin time > 13.7 s) | 14 |
| Hepatitis (reversible ALT/AST elevation) | 4 |
| Renal insufficiency (serum creatinine > 2 mg/dL - reversible) | 4 |
| Leukopenia (leukocytes 1-2 × 109/L) | 3 |
| Reversible thrombocytopenia | 2 |
| (platelets 30-100 × 109/L) | |
| Neurologic | |
| paresthesia (reversible) | 4 |
| polyradiculoneuropathy (variable recovery) | 2 |
| Death (presumed sepsis) | 1 |
reduction of various steroid hormones compared to the production by untreated cells. These observations are consistent with sublethal intracellular accumulation of suramin and inhibition of steroidogenic enzyme activi- ties.
Adrenocortical carcinoma remains a relatively rare endocrine neoplasm and is often diagnosed at such an advanced stage that therapeutic intervention proves of little benefit (24, 25). Surgical resection remains the mainstay of therapy for localized disease and has also been advocated by some in the setting of circumscribed liver and/or lung metastases (25, 26). O,p’DDD (mito- tane), a compound related to the insecticide dichlorodi- phenyltrichloroethane, induces some degree of objective tumor regression as a single agent in 34% of patients who are surgically unresectable (27). However, the side- effects of this agent when administered at dosages nec- essary to achieve therapeutic levels (14 µg/mL) are often severe and effectively limit treatment duration in many patients (28, 29). The use of conventional cytotoxic agents, alone or in combination, has, in general, yielded modest results (30, 31).
In this pilot study of suramin in the treatment of adrenocortical carcinoma, no complete remissions were achieved, but 4 of 16 evaluable patients did manifest some degree of tumor shrinkage. Administration of a cumulative dose of at least 10 g and reaching a steady state plasma suramin level of at least 150 ug/mL appear to be necessary prerequisites to both inhibition of malig- nant steroid hormone production and objective tumor regression.
Suramin is 99.7% bound to plasma proteins and has a long plasma half-life of 44-54 days (18). Drug elimination is primarily renal, and plasma metabolites of suramin have not been detected. The dose of suramin traditionally used for the treatment of parasitic diseases is a single 200-mg test dose, followed by 1 g, administered iv over 20 min, per week for up to 6 weeks (1). A similar dosing
regimen was used in the clinical trials of suramin in patients with aquired immunodeficiency syndrome (32). In our pilot study evaluating the antitumor activity of suramin, weekly bolus doses of 850-1400 mg/m2 or con- tinuous infusions starting at rates of 350 mg/m2. day were used. This represents an approximately 2- to 4-fold increase in the dose administered per week compared to the traditional regimen and resulted in the appearance of the two previously unknown and potentially serious suramin-related toxicities: coagulopathy and polyradi- culoneuropathy. The incidence of the latter, in fact, appears to correlate with the peak steady state plasma suramin level achieved (33). Serial measurements of plasma suramin levels during therapy have now helped to significantly reduce the incidence of these drug-related side-effects.
In conclusion, although the dosing regimens used in this study varied, suramin does have some activity in patients with surgically unresectable adrenocortical car- cinoma. Either serial bolus injection or continuous in- fusion of suramin are acceptable modes of administra- tion, provided serial monitoring of plasma suramin levels is performed, with dosing adjustments to maintain a steady state plasma suramin level below 300 mg/mL. The combination of suramin with other chemotherapeu- tic agents, including mitotane, for the treatment of this refractory neoplasm may be of value. The ability of suramin to decrease pathological steroid hormone pro- duction also suggests a role in the treatment of nonma- lignant conditions of adrenal cortical hyperfunction (ad- enoma or aldosteroma) and in the hormonal treatment of other malignancies, where the presence of adrenal steroids can result in a significant tumor proliferative effect (i.e. breast and prostate cancer).
Acknowledgments
The authors thank Rose Thomas, RN; Jane Cassidy, RN; and Sydne Loy for their assistance in data acquisition. In addition, the authors wish to thank Dr. Murray F. Brennan for many helpful discussions during the conduct of this trial and for referral of many of the patients in the study.
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