Donna Glover

WR-2721 and high-dose cisplatin: an active combination in the treatment of metastatic melanoma.

Cisplatin, alone or in combination with other chemotherapeutic agents, is relatively inactive against metastatic melanoma. Prior trials have demonstrated partial response (PR) rates of less than 10% with cisplatin alone. WR-2721 is an organic thiophosphate compound, which in the animal model, selectively protects normal tissues against the toxicity of cisplatin chemotherapy. During the course of a phase I trial of WR-2721 and cisplatin, objective PRs were noted in patients with far advanced metastatic melanoma. These observations led us to perform a phase II trial of WR-2721 and cisplatin. Thirty-six patients received 128 courses of WR-2721 before cisplatin (60 to 150 mg/m2). All patients had progressive disease before treatment. Objective PRs were observed in 19 of 36 evaluable patients (53%). Three additional patients had minor responses (MRs). PRs occurred in 53% of patients with prior chemotherapy (ten of 19). Sites of responding metastases were subcutaneous disease (15 of 19 patients), lymph nodes (16 of 21 patients), lung (four of ten patients), and liver (eight of 17 patients). The median duration of response was 4 months, with a mean of 4.5 months (range, 1 to 8 months). Transient nephrotoxicity was observed in less than 5% of courses. In all cases, renal function returned to normal within 1 to 2 weeks. Hematologic toxicity was mild and infrequent. Nine patients developed peripheral neuropathy following a median cisplatin dose of 670 mg/m2. Twenty patients experienced mild clinical hearing loss. These data suggest that WR-2721 may potentiate the antitumor activity of cisplatin in metastatic melanoma.

WR-2721 protects against the hematologic toxicity of cyclophosphamide: a controlled phase II trial.

WR-2721 S-2-(3-aminopropylamino) ethyl phosphorothioic acid, is an organic thiophosphate compound that in the animal model selectively protects against the hematologic toxicity of cyclophosphamide by factors of 1.5 to 2.0. Preliminary data from our controlled phase I trial of WR-2721 and cyclophosphamide suggested that WR-2721 protected against cyclophosphamide-induced granulocytopenia. Since variable drug doses and infusion rates were used in these early studies, we initiated a controlled phase II trial using constant drug doses to establish more precisely WR-2721s level of protection. Initially, 21 patients received 1,500 mg/m2 of cyclophosphamide alone and were retreated 4 weeks later after hematologic recovery was complete with 740 mg/m2 of WR-2721 before the same dose of cyclophosphamide. With WR-2721 pretreatment, 19 of 21 (90%) patients had improved WBC and granulocyte counts. The mean WBC increased from 1,760/mL with cyclophosphamide alone to 2,500/mL with WR-2721 pretreatment (P less than .0005). The mean granulocyte count increased from 541/mL on cyclophosphamide to 1,247/mL with WR-2721 and cyclophosphamide (P less than .0005). Following cyclophosphamide administration alone, neutropenic fevers developed in three patients. No patient experienced a febrile episode following WR-2721 and cyclophosphamide administration. Platelet nadirs below 100,000/mL were only noted in two patients treated with cyclophosphamide alone. Objective partial responses were observed in four of 19 (21%) patients with measurable or evaluable disease. These data suggest that WR-2721 provides significant protection against cyclophosphamide-induced hematologic toxicity.

Hypocalcemia and inhibition of parathyroid hormone secretion after administration of WR-2721 (a radioprotective and chemoprotective agent)

We investigated the causes of the hypocalcemia associated with WR-2721, an investigational drug that protects normal tissues against the toxic effects of radiation and chemotherapy. Sixteen patients with advanced cancers had serial measurements of serum calcium and other studies of blood chemistry before and after taking the compound. In all 16 patients (18 courses) the mean serum calcium level fell from 2.33 to 1.90 mmol per liter (9.33 to 7.62 mg per deciliter, P less than 0.001) after WR-2721, and in all 8 patients from whom data were obtained, serum calcium levels remained depressed at 24 hours. In 12 patients, ionized calcium levels dropped from 0.98 to 0.80 mmol per liter (P less than 0.01). Serum magnesium values fell from 0.96 to 0.74 mmol per liter (1.91 to 1.48 mg per deciliter, P less than 0.001). There were no changes in arterial pH or serum phosphate concentrations. In nine patients urinary calcium excretion rose from 3.96 to 10.68 mumol per minute (P less than 0.01) after WR-2721. Despite hypocalcemia, parathyroid hormone levels fell in all subjects. WR-2721 also inhibited the release of parathyroid hormone from bovine parathyroid cells incubated in vitro in low (0.5 mM) concentrations of calcium. We conclude that WR-2721 inhibits the secretion of parathyroid hormone and enhances calciuria, thereby leading to hypocalcemia.

Human pharmacokinetics of WR-2721☆

The pharmacokinetic properties of WR-2721 were investigated in 13 cancer patients given a 150 mg/M2 intravenous bolus dose of the drug. An average plasma clearance value of 2.17 L/min was obtained. Very little of the drug or the two metabolites, WR-1065 and WR-33278, were excreted in urine obtained after the blood collection schedule. Plasma concentrations of WR-2721 decreased by 94% within 6 minutes of drug administration. The mean value of 6.44 L obtained for the steady-state volume of distribution indicates that the extravascular space occupied by the drug is small. These observations suggest that in human cancer patients, WR-2721 is rapidly taken up by tissues and converted to metabolites.

Phase I trials of WR-2721 and cis-platinum

WR-2721 is a sulfhydryl compound which in the animal model improves renal tolerance to cis-platinum (DDP) by factors of 1.3 to 1.7. Phase I trials were initiated to establish the toxicity and dose modification factors when WR-2721 was given prior to escalating doses of DDP. Nineteen patients received 27 courses of WR-2721 (450-910 mg/m2) 20 minutes prior to DDP (50-120 mg/m2). Patients were prehydrated, but no mannitol or other diuretics were administered. Mild, transient nephrotoxicity was observed in only 2 of 15 courses of DDP 80-100 mg/m2 when WR-2721 was given prior to DDP. Although 5 of 9 patients treated with WR-2721 prior to 120 mg/m2 of DDP developed transient nephrotoxicity, their serum creatinines returned to normal baseline values within 1 to 2 weeks. Subsequently, the protocol was modified to include mannitol diuresis. Thirty-four courses of WR-2721 (740 mg/m2) prior to DDP 120-150 mg/m2 with mannitol diuresis were administered. Biweekly serum creatinine and monthly creatinine clearances have remained normal in all patients treated with 120 mg/m2 of platinum and WR-2721. Four of 10 patients treated with 150 mg/m2 of cis-platinum experienced transient nephrotoxicity 5-7 days after treatment. Mild ototoxicity was noted in 4 patients following 150 mg/m2 of DDP. WR-2721 does not appear to protect against the antitumor efficacy of DDP, as 57% of all patients achieved objective partial responses, lasting 1+ to 7+ months. Partial responses occurred in 3/4 (75%) of patients with melanoma and 7/10 (70%) patients with cancer of the head and neck. Compared to retrospective series, our data suggest that WR-2721 may provide some protection against platinum-induced nephrotoxicity, but the dose modification factors remain to be established.

Clinical trials of WR-2721 and cis-platinum☆

WR-2721 is an aminothiol compound; in the animal model it protects against the nephrotoxicity, neurotoxicity, and hematologic toxicity of cis-platinum. We initiated Phase I trials of WR-2721 and cis-platinum to determine toxicity when WR-2721 was given prior to escalating doses of cis-platinum. With mannitol diuresis and WR-2721, transient nephrotoxicity occurred in 9 of 30 (27%) patients treated with cis-platinum 150 mg/m2 and 7% of patients given with cis-platinum 120 mg/m2. Bone marrow suppression was mild and infrequent. Mild to moderate peripheral neuropathies occurred in 26% of patients courses following a mean cumulative cis-platinum dose of 725 mg/m2. Objective partial responses were observed in 53 of 118 (45%) patients with measurable disease. Antitumor responses were observed in 25 of 53 patients with metastatic melanoma, 12 of 22 patients with locally recurrent or metastatic head and neck cancer, and 7 of 13 patients with metastatic breast cancer refractory to conventional chemotherapy. Controlled studies of WR-2721 and cis-platinum will be performed in the Eastern Cooperative Oncology Group in these disease sites to better define the activity of this regimen and its toxicity.

Clinical trials of WR-2721 with radiation therapy

The radioprotector with clinical potential, S-2-(3 aminopropylamino)-ethylphosphorothioic acid (WR-2721) is undergoing two Phase I trials. The objectives of these trials are 1) to determine the maximum tolerated dose (MTD) of WR-2721 in a single dose and 2) to determine the highest dose of WR-2721 that can be tolerated daily in the greatest number of fractions per week. A total of 65 patients have been treated. The single maximum tolerated dose has not yet been reached, though 740 mg/m2 is well tolerated. A single dose of 910 mg/m2 has been successfully administered to one patient. The multiple dose MTD is at an early stage with patients currently receiving 170 mg/m2 four times a week. Among the toxicities noted in both trials are hypotension, hypertension, emesis and somnolence. In addition, in the multiple dose trial there have been three patients who have had allergic reactions including one which was life-threatening. Phase II studies are planned and will begin when the maximum tolerated dose is established from each Phase I trial.

Phase I Controlled trials of WR-2721 and cyclophosphamide

WR-2721 is an organic thiophosphate compound which in the animal model selectively protects against the hematologic toxicity of cyclophosphamide by factors of 1.5 to 2.0. Controlled Phase I trials of WR-2721 and cyclophosphamide were initiated to determine if WR-2721 protected against cyclophosphamides hematologic toxicity. Fifteen patients received WR-2721 (450-1100 mg/m2) prior to cyclophosphamide (1200-1800 mg/m2) and were subsequently retreated 4 weeks later with the same cyclophosphamide dose alone. With WR-2721 pretreatment, 11/15 (73%) patients had improved WBC counts. The mean WBC increased from 1800/mm3 on cyclophosphamide alone to 2700/mm3 with WR-2721 + cyclophosphamide (p = 0.008). In 11 patients who had nadir differential counts performed, 7 (64%) demonstrated improved nadir granulocyte counts with WR-2721. The mean granulocyte count increased from 765/mm3 on cyclophosphamide to 1274/mm3 with WR-2721 + cyclophosphamide (p = 0.05). In the second trial, 25 patients received the reverse sequence: an initial dose of cyclophosphamide (1200-1800 mg/m2) alone, followed 4 weeks later by WR-2721 (450-1100 mg/m2) prior to the same dose of cyclophosphamide. With WR-2721 pretreatment, 12/25 (48%) patients had improved nadir WBC counts. The mean WBC increased from 1550/mm3 on cyclophosphamide alone to 1850/mm3 with WR-2721 + cyclophosphamide (p = 0.02), while the nadir granulocyte count increased from 449/mm3 to 844/mm3 (p = 0.001). No patient developed microscopic or gross hematuria or inappropriate antidiuretic hormone secretion. One patient developed mild thrombocytopenia. These data suggest that WR-2721 provides significant protection against cyclophosphamide-induced granulocytopenia, but the dose modification factors and degree of clinical benefit remain to be established. The current recommended WR-2721 dose for Phase II trials is 740 mg/m2 administered over 15 minutes.

Treatment of hypercalcemia in parathyroid cancer with WR-2721, S-2-(3-aminopropylamino) ethyl-phosphorothioic acid

The chemoprotective and hypocalcemic agent WR-2721, S-2-(3-aminopropylamino) ethyl-phosphorothioic acid, inhibits parathyroid hormone secretion in vivo and in vitro. We report the first clinical use of WR-2721 in refractory hypercalcemia secondary to parathyroid cancer. After several days of saline diuresis the patient received WR-2721, 740 mg/m2 over 15 minutes, resulting in a fall in serum calcium from 11.76 to 9.06 mg/dL within 24 hours. Serum parathyroid hormone levels decreased from 675 to 140 microLeq/mL 2 hours after the infusion was complete. When hypercalcemia recurred the patient was retreated with differing doses and infusion rates to determine the optimal method of drug administration to provide a satisfactory hypocalcemic response without adverse effects. In this patient, WR-2721 in intravenous boluses of 150 mg/m2 was effective without adverse effects. Using high-pressure liquid chromatography with electrochemical detection, plasma pharmacokinetic studies showed that WR-2721s distribution half-life is 0.55 minutes.

Phase I clinical trials of WR-2721 with alkylating agent chemotherapy

Abstract WR-2721 is an organic thiophosphate which in the animal model provides selective protection of normal tissues against the toxicity of radiation and alkylating agent chemotherapy. Phase I trials of WR-2721 in man have been initiated to establish the dose modification factors for this agent when used in combination with escalating doses of alkylating agents beyond the level currently tolerated, and to determine whether protection of normal tissues and tumors occurs. Three Phase I trials are in progress. Initially, we used a fixed 450 mg/M2 dose of WR-2721 prior to escalating doses of either cyclophosphamide (CYC) or cis-platinum (PL) as single agents. More recently, the current maximum tolerated dose of WR-2721(740 mg/M2) was administered prior to PL and to nitrogen mustard (HN2). Ten patients received 19 courses of CYC after 450 mg/M2 of WR-2721. At the 1800 mg/M2 LV. dose level of CYC, moderate leukopenia was noted with a median WBC nadir of 1800/mm3 on day 10. Twenty-two courses of PL were administered to 13, patients after 450–740 mg/M2 of WR-2721. Hydration was used, but no mannitol diuresis was employed. Transient nephrotoxicity was noted in five courses at PL doses between 80–120 mg/M2. Mild to moderate leukopenia has been noted with HN2 at 10–16 mg/M2 following WR-2721 (450–750 mg/M2). Objective anti-tumor responses have been observed. These preliminary results suggest that WR-2721 may provide normal tissue protection when administered prior to cyclophosphamide or nitrogen mustard, although the level of protection is not yet of clinical benefit. However, using a 450–740 mg/M2 dose of WR-2721 did not provide protection against platinum-induced nephrotoxicity. WR-2721 does not appear to protect against the anti-tumor activity of alkylating agents (objective tumor responses were noted), nor does there appear to be increased acute toxicity when it is combined with alkylating agent chemotherapy.