Phase II trials of trimetrexate in advanced adult soft tissue sarcoma. Studies of the Canadian Sarcoma Group and the National Cancer Institute of Canada Clinical Trials Group

Phase II evaluation of oral trimetrexate in mixed mesodermal tumors of the uterus: a gynecologic oncology group study

OBJECTIVES

This is a Phase II group-wide study of the Gynecologic Oncology Group to determine the toxicity and objective response rate of trimetrexate (TMTX) in patients with advanced, persistent, or recurrent mixed mesodermal tumors of the uterus who have failed higher priority treatment protocols.

METHODS

TMTX was administered orally at a dose of 5 mg/m(2) BID for 5 days and repeated in 14 days. The maximum total dose was 50 mg/m(2)/week given every other week. The minimum treatment period was one course. Patients who had a complete response, partial response, or stable disease were continued on treatment for at least three courses.

RESULTS

Twenty-eight patients were entered into the study. Three patients were ineligible based on review of pathologic materials. Twenty-five patients were evaluable for toxicity, and 21 were evaluable for response, as 4 patients did not complete one course of therapy. Eleven patients had heterologous mixed mesodermal tumor (MMT) and 10 had homologous MMT. Of the 25 evaluable for toxicity, one patient had grade 4 platelet toxicity. No patient had grade 4 neutropenia, while 4 patients had grade 3 decrease in absolute neutrophil count. One patient had grade 3 gastrointestinal toxicity, while 2 had grade 4 toxicity. There were no complete responses noted and only one partial response, for an overall response rate of 4.8%. The duration of the partial response was 15.2 months.

CONCLUSION

Oral TMTX has insignificant activity in the treatment of advanced, persistent, and recurrent uterine MMT at the dose and schedule administered.

Trimetrexate in the treatment of recurrent or advanced leiomyosarcoma of the uterus: a phase II study of the Gynecologic Oncology Group

OBJECTIVE

This study was conducted to determine the objective response of trimetrexate in patients with advanced or recurrent leiomyosarcoma of the uterus.

METHODS

Eligibility was restricted to patients with measurable disease who had received no more than one prior chemotherapy regimen, who had adequate bone marrow, renal, and hepatic function, and who had recovered from previous therapy. Trimetrexate was begun at 5 mg/m2/day orally for 5 days every other week, with dose modifications specified by study design.

RESULTS

Of 28 patients entered into the study, 27 were evaluable for toxicity and 23 for response. Prior therapy included radiation (7 patients) and/or chemotherapy (10 patients). Measurable disease was extrapelvic in 20 cases and confined to the pelvis in 3. The overall response rate was 4.3%; there were no complete responses and 1 partial response. Toxicities were mild to moderate with no treatment-related deaths. Hematological toxicity was most common, consisting of leukopenia (grade 1 to 2, 8 patients; grade 3 or 4, 2 patients), thrombocytopenia (grade 1 to 2, 10 patients; grade 3 or 4, 1 patient), and anemia (grade 1 to 2, 6 patients; grade 3 or 4, 4 patients. Severe (grade 3 or 4) nonhematologic toxicity was uncommon: nausea/vomiting/gastrointestinal (3 patients) and neurological (1 patient). Progression-free and overall survival, in months, was 2.2 (range: 0.9-13.4) and 7.2+ (range: 1.0-13.4+), respectively.

CONCLUSION

Although toxicity is acceptable, trimetrexate at this dose and schedule is ineffective therapy for patients with recurrent leiomyosarcoma. Further development of this specific regimen for this indication is unwarranted.

New agents in the treatment of soft-tissue sarcomas

The list of agents with significant activity in soft-tissue sarcomas is very short and arguably, only includes doxorubicin and ifosfamide. Several other agents such as dacarbazine, cisplatin and etoposide, to name but a few, have marginal activity and are sometimes used in combination regimes. The need for the identification of new agents with activity against this disease is therefore paramount. Soft-tissue sarcomas are very rare and diverse and as a result, new drug trials are few and far fetched. The conventionally conducted Phase II trials, which include all histologies of soft-tissue sarcomas, run the risk of an inadequate assessment of the new drug in individual subsets, which may have variable biological behaviours. On the other hand, histology-specific Phase II trials are fraught with the problems of length due to the infrequent nature of the disease and the considerable running costs. The end result is that in this era of cost-containment, soft-tissue sarcomas are not high on the priority list of many funding agencies, thus explaining the lack of any significant progress over the past two decades. Efforts at optimising the dose intensity and schedule of administration of doxorubicin and ifosfamide, have resulted in superior activity when combined and improvement in the survival of patients with high-risk localised disease. However, efforts at identifying new agents with adequate activity have not had much success. Patients, physicians and pharmaceutical industries must be encouraged to participate in multidisciplinary clinical trials in order to improve cure rates for patients with advanced disease.

New chemotherapeutic strategies for soft tissue sarcomas

Advanced soft-tissue sarcomas are still incurable in the vast majority of patients. The currently available standard methods of treatment such as surgery, radiation therapy, and chemotherapy have a very modest impact on the natural history of advanced soft tissue sarcomas. Nevertheless, until new strategies become widely available and applicable to this disease, we are obligated to optimize the current resources and make the best use of these modalities. We discuss the approaches of standard chemotherapy used in a dose-intensive fashion (especially in high-risk patients at an earlier stage), attempts to find new drugs with activity in this disease, and tests of the concepts of anti-angiogenic and differentiation therapy. To improve cure rates, patients and physicians must be encouraged to participate in multidisciplinary clinical trials.

Multiple folate enzyme inhibition: mechanism of a novel pyrrolopyrimidine-based antifolate LY231514 (MTA)

Extensive biochemical and pharmacological evidence indicates that LY231514 is a novel antifolate antimetabolite. LY231514 is transported into cells mainly through the reduced folate carrier system and extensively metabolized to polyglutamated forms. The polyglutamates of LY231514 inhibit at least three key folate enzymes: TS, DHFR, and GARFT, and to a lesser extent AICARFT and C1-tetrahydrofolate synthase. The combined effects of the inhibition exerted by LY231514 at each target give rise to an unusual end-product reversal pattern at the cellular level that is distinct from those of other inhibitors such as methotrexate and the quinazoline antifolates. The metabolic effects exerted by LY231514 on the folate and nucleotide pools are also quite distinct from those of MTX and LY309887. The efficient polyglutamation, longer cellular retention and the multiple folate enzyme inhibition mechanism may all have contributed directly to the exciting antitumor responses now observed in Phase I and II studies. The multitargeted inhibition mechanism of LY231514 is particularly intriguing. This new level of mechanistic insight, which has evolved from the study of LY231514, challenges the traditional concept and paradigm of antifolate drug discovery and development which focused on developing very potent and selective inhibitors of single folate enzyme targets, such as DHFR, TS or one of the enzymes along the de novo purine biosynthetic pathway. Given the complex nature of folate metabolism and the critical role of folates in maintaining the physiological functions of living systems, it is completely reasonable to suspect that agents which can interfere at multiple sites in the folate pathway may trigger and cause more biochemical imbalance in the cellular DNA and RNA synthesis of malignant cells than agents that act on a single point (Fig. 5). In conclusion, LY231514 (MTA) is a new generation antifolate antimetabolite demonstrating inhibitory activity against multiple folate enzymes including TS, DHFR and GARFT. In current phase II studies, MTA is broadly active as a single agent and is showing very encouraging antitumor activity in multiple solid tumors including colorectal, breast and non-small cell lung cancers (38-43). The every three week dosing schedule has proven to be convenient and easy to administer and the clinical toxicities of LY231514 seem to be well tolerated. More advanced and extensive clinical trials of LY231514 are currently in progress.

Antifolates: current developments

In summary, the problem of MTX resistance has been approached in a mechanistic fashion, based on the wealth of information generated over the years. To date, these strategies have produced several new classes of anticancer drugs, with a variety of anticipated and unanticipated mechanisms of action. Several of these have shown promising preclinical activity, and these are moving into more stringent testing in the clinic.

Methotrexate resistance in an in vivo mouse tumor due to a non-active-site dihydrofolate reductase mutation

A series of methotrexate (MTX)-resistant L1210 leukemia murine ascites tumors were developed in vivo and analyzed for drug resistance. Three of 20 tumors studied expressed an altered dihydrofolate reductase (DHFR) and each was identical, having a C to T base transition at nucleotide 46 in the DHFR gene as demonstrated by PCR and direct sequencing. This transition results in a Gly to Trp substitution at amino acid 15 of the enzyme. Purified altered enzyme displays significantly lower binding affinity for the antifolates MTX, trimetrexate, edatrexate, and trimethoprim with respective Ki values 165-, 76-, 30-, and 28-fold higher than values obtained for enzyme isolated from parental tumor (wild-type enzyme). Substrate (dihydrofolate) and cofactor (NADPH) binding is also diminished for the mutant enzyme, although to a lesser extent (17.3- and 3.6-fold higher Km, respectively). Gly-15 is highly conserved for all vertebrate species of DHFR but has no known interaction(s), either directly or indirectly, with bound cofactor, substrate, or inhibitor. Protein molecular modeling reveals that the affected residue is 9-12 A away from the enzyme active site and located in a region analogous to the mobile Met-20 loop domain characterized for Escherichia coli DHFR.