melphalan and ambamustine

PTT-119 is an antineoplastic agent in which an alkylating moiety, m-sarcolysine, is linked to two amino acid analogs. Previous studies showed a higher "in vitro" cytotoxicity of PTT-119 when compared to free m-sarcolysine; the mechanisms of this enhanced activity are not completely understood. In this study we incubated peripheral blood cells from 8 chronic lymphocytic leukemia patients with both m-sarcolysine and equimolar concentrations of PTT-119, measuring the intracellular concentration of the alkylating moiety. We observed a significantly higher intracellular concentration of m-sarcolysine in cells incubated with the peptide-bound drug than with the free drug (58.3 +/- 39.6 versus 4.4 +/- 1.9 ng/10(6) cells; P = 0.013). This observation could explain the higher cytotoxic activity of PTT-119 and the lack of cross-resistance with melphalan.

Topics: Amino Acids; Biological Transport; Drug Combinations; Humans; Intracellular Membranes; Melphalan; Nitrogen Mustard Compounds; Osmolar Concentration

PTT.119 [p-F-phe-m-bis(2-chloroethyl)amino-L-phe-met ethoxy HCl], a synthetic tripeptide mustard, was evaluated for therapeutic efficacy against a spectrum of childhood rhabdomyosarcomas (RMS) maintained as xenografts in immune-deprived mice. These xenografts were established from previously untreated tumors, and sublines were selected in mice for resistance to L-phenylalanine mustard (L-PAM). PTT.119 caused regression of four of six RMS lines established from untreated tumors, and demonstrated activity similar to that of L-PAM in this model. Against tumors Rh18/L-PAM and Rh28/L-PAM, selected in situ for L-PAM resistance, PTT.119 had no significant activity. Rh28/L-PAM was cross-resistant also to oxazophosphorine mustards (ifosfamide, cyclophosphamide), and both tumors were cross-resistant to adriamycin and vincristine. PTT.119 caused hematologic toxicity similar to that of L-PAM, characterized by a marked decrease in white blood cells and thrombocytopenia.

Topics: Animals; Antineoplastic Agents; Cell Line; Drug Resistance; Drug Screening Assays, Antitumor; Female; Humans; Immunosuppression Therapy; Leukocyte Count; Melphalan; Mice; Mice, Inbred CBA; Neoplasm Transplantation; Nitrogen Mustard Compounds; Platelet Count; Rhabdomyosarcoma

Delivery of the bifunctional alkylating agent, PTT.119 [p-F-L-Phe-m-bis-(2-chloroethyl)amino-L-Phe-Met-ethoxy-HCl], into tumor cells is significantly greater compared to L-phenylalanine mustard (L-PAM) as demonstrated by the 2-fold reduction in PTT.119 dosage required to reduce the viable L1210 cell fraction by 50% (TCD50). This increased uptake and consequent cytolytic efficacy observed in Dulbecco's phosphate buffer was more apparent in culture medium; under this physiologic condition the TCD50 concentration of PTT.119 was 5 times lower than L-PAM. PTT.119 entry into leukemia cells was examined using competition transport assays assessing the ability of the tripeptide to compete with various amino acids and nonmetabolizable substrates for carrier receptors of the L, A and ASC transport systems. A 1-min exposure to a 1- to 50-fold excess of PTT.119 prior to addition of radiolabeled substrates significantly reduced within 60 s both sodium-dependent and sodium-independent uptake of leucine, methionine, threonine and alpha-[1-14C]-aminoisobutyric acid (AIB), but not MeAIB. In complimentary studies, L1210 cells were protected from PTT.119 cytolysis by an 8,000-fold excess of AIB, whereas beta-2-aminobicyclo[2.2.1]heptane-2-carboxylic acid (BCH) only abrogated tripeptide cytotoxicity by 95-97% even at BCH:PTT.119 ratios of 200,000. Leucine and methionine protection were significantly less effective; the TCD50 of leucine and methionine were 3.23 and 2.4 microM, respectively, compared to 11.41 microM for AIB and 7.96 microM for BCH. In addition, MeAIB and phenylalanine were totally unable to protect L1210 cells from PTT.119-induced cytolysis. The data indicate that L121 cells actively transport PTT.119 primarily by the BCH-sensitive, AIB-sensitive, MeAIB-insensitive L carrier system. A second, BCH-insensitive, AIB-sensitive and MeAIB-insensitive carrier which is also involved in tripeptide uptake is probably the ASC system.

Topics: Alkylating Agents; Amino Acids; Animals; Biological Transport, Active; Leukemia L1210; Melphalan; Nitrogen Mustard Compounds; Sodium; Tumor Cells, Cultured

PTT.119 [p-F-Phe-m-bis-(2-chloroethyl)amino-L-Phe-Met ethoxy HCl], a new synthetic tripeptide, was highly effective against the L-phenylalanine mustard (L-PAM) resistant (L1210/L-PAM and P388/L-PAM) tumor lines, as well as the sensitive L1210 leukemia. Cytolytic activity of PTT.119 against all three leukemias was significantly greater than equimolar doses of L-PAM. These in vitro results paralleled the significant increases in mean survival times of hosts and, in some cases, abrogations of tumor formation observed in the in vivo bioassays of PTT.119-treated L1210 and L1210/L-PAM cells. Dose-response studies failed to demonstrate cross-resistance to the tripeptide by L-PAM resistant cells. Doses of PTT.119 required to reduce the viable fraction by 50% (tissue culture dose 50, TCD50) or 100% (TCD100) were 1.3- to 3-fold lower for the L-PAM resistant cells than for the L1210 leukemia. In comparison, L-PAM was unable to completely eliminate cell survival; 0.2 to 3% of the cells in all three leukemias remained viable even at doses of 75 and 163 microM. In similar studies, L1210 leukemia cells made resistant to methotrexate (L1210 MTX) and cisplatin (L1210DDP) were also completely susceptible to PTT.119; TCD50 values of the two resistant lines were 1.94 microM for L1210 MTX and 0.525 microM for L1210DDP compared to 2.38 microM for the susceptible parent L1210S leukemia. Continuous low-dose PTT.119 treatment of MJY-alpha mammary tumor cells for 8 months and exposure of L1210 leukemia to escalating levels of tripeptide for over 100 passages failed to select or induce drug-resistant phenotypes in either cell line. PTT.119 appears to be a poor mutagen and is unlikely to readily increase the probability of drug-resistant mutants in the tumor cell populations.

Topics: Animals; Antineoplastic Agents; Cell Line; Cell Survival; Cisplatin; Dose-Response Relationship, Drug; Drug Resistance; Leukemia L1210; Melphalan; Mice; Mice, Inbred Strains; Neoplasms, Experimental; Nitrogen Mustard Compounds