Combination chemotherapy of advanced sarcomas in adults with "CYOMAD" (S7)

Mutational 'hot-spots' in mammalian, bacterial and protozoal dihydrofolate reductases associated with antifolate resistance: sequence and structural comparison

Human dihydrofolate reductase (DHFR) is a primary target for antifolate drugs in cancer treatment, while DHFRs from Plasmodium falciparum, Plasmodium vivax and various bacterial species are primary targets in the treatment of malaria and bacterial infections. Mutations in each of these DHFRs can result in resistance towards clinically relevant antifolates. We review the structural and functional impact of active-site mutations with respect to enzyme activity and antifolate resistance of DHFRs from mammals, protozoa and bacteria. The high structural homology between DHFRs results in a number of cross-species, active-site 'hot-spots' for broad-based antifolate resistance. In addition, we identify mutations that confer species-specific resistance, or antifolate-specific resistance. This comparative review of antifolate binding in diverse species provides new insights into the relationship between antifolate design and the development of mutational resistance. It also presents avenues for designing antifolate-resistant mammalian DHFRs as chemoprotective agents.

Increasing methotrexate resistance by combination of active-site mutations in human dihydrofolate reductase

Methotrexate-resistant forms of human dihydrofolate reductase have the potential to protect healthy cells from the toxicity of methotrexate (MTX), to improve prognosis during cancer therapy. It has been shown that synergistic MTX-resistance can be obtained by combining two active-site mutations that independently confer weak MTX-resistance. In order to obtain more highly MTX-resistant human dihydrofolate reductase (hDHFR) variants for this application, we used a semi-rational approach to obtain combinatorial active-site mutants of hDHFR that are highly resistant towards MTX. We created a combinatorial mutant library encoding various amino acids at residues Phe31, Phe34 and Gln35. In vivo library selection was achieved in a bacterial system on medium containing high concentrations of MTX. We characterized ten novel MTX-resistant mutants with different amino acid combinations at residues 31, 34 and 35. Kinetic and inhibition parameters of the purified mutants revealed that higher MTX-resistance roughly correlated with a greater number of mutations, the most highly-resistant mutants containing three active site mutations (Ki(MTX)=59-180 nM; wild-type Ki(MTX)<0.03 nM). An inverse correlation was observed between resistance and catalytic efficiency, which decreased mostly as a result of increased KM toward the substrate dihydrofolate. We verified that the MTX-resistant hDHFRs can protect eukaryotic cells from MTX toxicity by transfecting the most resistant mutants into DHFR-knock-out CHO cells. The transfected variants conferred survival at concentrations of MTX between 100-fold and >4000-fold higher than the wild-type enzyme, the most resistant triple mutant offering protection beyond the maximal concentration of MTX that could be included in the medium. These highly resistant variants of hDHFR offer potential for myeloprotection during administration of MTX in cancer treatment.

The treatment of soft tissue sarcomas with focus on chemotherapy: a review

Radical surgery remains the most effective treatment of soft tissue sarcomas. The postoperative addition of radiotherapy appears to reduce local recurrence in extremity lesions. To date, there are still only two drugs with major activity as a single agent in the treatment of soft tissue sarcomas: doxorubicin (DX) and ifosfamide (IFX). Doxorubicin should be administered preferably as 3-weekly bolus injections at doses higher than 60 mg/m2 because of its dose-response relationship. In combination chemotherapy ADIC and CYVADIC are probably the best choice. Although there are no definite data on increased activity with the addition of cyclophosphamide (CTX) and vincristine (VCR) to ADIC, we prefer CYVADIC because of the higher reported complete response rate. A limited number of patients with soft tissue sarcomas achieving a complete response with chemotherapy, will probably be cured, and for this reason it is important to aim at achieving a complete response. Preoperative intraarterial chemotherapy in locally advanced soft tissue sarcomas may further improve survival results, but before definite conclusions can be drawn, this technique should be investigated in randomized studies. Postoperative adjuvant chemotherapy should still be considered investigational, as no advantage has been observed in head, neck and trunk lesions, while data on extremity lesions are still conflicting.

Chemotherapy of patients with advanced soft tissue sarcoma with use of DVA (vindesine sulfate), adriamycin and cyclophosphamide (DAC)

Thirty-four patients with advanced soft tissue sarcoma were treated with a three-drug combination including vindesine sulfate (DVA), Adriamycin, and cyclophosphamide (DAC) (S9). Thirty-one patients are evaluable of whom 23 were previously untreated. Among the latter group there were six complete responses (26%) and five partial responses (22%), for a major response rate of 48%. No major responses were seen in the eight previously treated patients. The median duration of responses was 8 months. Leukopenia and peripheral neuropathy were the major complications of treatment. Gastrointestinal toxicity was mild. Adriamycin cardiotoxicity was seen in two patients. Although the overall response rate to DAC is comparable to that of other combinations, it may offer the advantages of an increased complete response rate and less gastrointestinal toxicity.