Flavone acetic acid (LM 975, NSC 347512). A novel antitumor agent.

Flavone acetic acid (FAA) is a synthetic flavonoid compound which has recently begun clinical trials as an antitumor agent based on its striking activity in solid tumor model systems. The pharmacologic behavior of FAA in animals appears to be predictive of both its cytotoxic efficacy and its toxicity to normal tissues (principally the central nervous system and gastrointestinal tract). The design and conduct of phase I studies in man are based upon these principles, with the goal of maximizing their safety and efficacy.

Potential roles for preclinical pharmacology in phase I clinical trials.

Concepts elucidated from preclinical pharmacology studies have made a substantial impact on the clinical use of anticancer drugs. However, the majority of animal pharmacology results have not been available until after drugs have entered clinical trials. Since clinical pharmacokinetic measurements are already part of many phase I trials, human data could be directly compared with mouse data if mouse pharmacology studies were completed before clinical trials were initiated. Once the starting dose in a phase I clinical trial has been evaluated, subsequent doses are escalated until the maximum tolerated dose is reached. The rate of escalation is empirically defined by a modified Fibonacci series. This universal escalation scheme is applied to all drugs, with no modifications based upon pharmacology or other factors. If the starting dose is far removed from the maximum tolerated dose, a large number of dose escalations are required. Consequently, most patients receive subtherapeutic doses, and the amount of resources allocated to each drug increases. We are exploring potential strategies for controlling the rate of dose escalation based upon pharmacokinetic determinations in mouse and man. Retrospective analyses indicate that 20%-50% savings in the total number of dose escalations are possible.

Plasma kinetics and effects of 5,6-dihydro-5-azacytidine in mice and L1210 tumor.

The plasma kinetics of 5,6-dihydro-5-azacytidine (DHAC) was determined in mice using an HPLC method following an intravenous dose of 2000 mg/kg (LD10). Pharmacokinetic parameters calculated from these single dose data were sufficient to predict steady state plasma concentrations produced by s.c. infusion of DHAC. Lethal toxicity (LD66) occurred at an infusion rate of 37 mg/kg/h (111mg/m2/h), corresponding to a plasma steady-state DHAC concentration 38 +/- 14 micrograms/ml when the infusion time was 96 h; no lethality occurred at infusion times of 72 h or less. In vitro clonogenic assays and in vivo therapeutic experiments with L1210 tumor indicated that increasing the exposure time at concentrations near 25 micrograms/ml from 24 to 72 h increased the cell kill only slightly. The maximum log cell kill of L1210 estimated from either in vitro or in vivo data was 1.5 logs.

Modification of chemotherapeutic effects on L1210 cells using hematoporphyrin and light.

Tissue culture experiments were done to evaluate the possibility of modifying the response curves of phenylalanine mustard (LPAM) and actinomycin D on L1210 cells, using moderately toxic levels of photodynamic injury provided by light and hematoporphyrin (HP). Cells were grown and treated in Roswell Park Memorial Institute Medium 1630 containing 20% horse serum. Cells were incubated with HP at concentrations of 1 to 50 microM for up to 48 hr. Illumination was provided by fluorescent light (4 milliwatts/sq cm), filtered through plastic to remove all wavelengths outside of the range of 400 to 800 nm. Ambient light was carefully controlled. When cells were incubated with 25 microM HP in the dark for 24 hr and then exposed to light for 1 hr, there were reductions in cloning efficiencies of 30 to 80% compared to the dark-HP-treated controls. When LPAM (1 to 30 microM) or actinomycin D (0.04 to 2.0 ng/ml) was incubated with cells for 1 hr following HP treatment, with or without light exposure, the LPAM response curves were modified to indicate a synergistic response of photodynamic toxicity and chemotherapeutic toxicity (one additional log). HP in the dark prior to and during LPAM exposure did not modify the LPAM response curve. The actinomycin D response curve was modified by prior HP and light treatment to indicate an additive effect of one additional log; a synergistic effect may be present in the range of 100 to 10% cloning efficiencies. It is concluded that the L1210-HP-light system offers possibilities for investigating the modification of chemotherapy effects.

Effect of dose, schedule, and route of administration on the in vivo toxicity and antitumor activity of two activated sulfhydryl derivatives of cyclophosphamide.

Two cyclophosphamide (CP) derivatives, 4-S-(hexane-6-ol)-sulfidocyclophosphamide (C-1) and 4-S-(propionic acid)-sulfidocyclophosphamide (C-2), that hydrolyze spontaneously under physiological conditions to 4-hydroxycyclophosphamide, are compared to CP for antitumor activity in male C57BL/6 x DBA/2 F1 mice with ascites L1210 leukemia or solid Lewis lung carcinoma. When C-1 or C-2 is administered i.p. as a single injection at 10% lethal dose (approximately LD10) to mice bearing L1210 (1 x 10(5) cells i.p.), early treatment produces a 5- to 6-log tumor cell kill and results in substantial numbers of long-term survivors (greater than or equal to 30 days). Such antitumor activity is comparable to that of CP treatment. However, i.p. administration of either sulfido derivative produces liver atrophy and fibrosis of hepatic capsular structures. Hepatotoxicity is eliminated if single-dose C-2 (less than or equal to LD10) is administered i.v.; however, when administered by this route, C-2 results in only a 1-log cell kill of i.v. implanted leukemic cells as compared to the 4-log tumor cell kill obtained with CP given i.v. In addition to hepatotoxicity, C-2 causes an acute and dose-limiting toxicity in mice, manifested by severe muscular spasms and cessation of breathing. In the treatment of advanced L1210, C-2 shows no therapeutic advantage over CP. When mice bearing s.c. Lewis lung carcinoma receive early i.p. treatment with CP, C-1, or C-2, each drug results in long-term tumor-free survivors. However, CP (< LD10) consistently cures all mice, whereas C-1 or C-2 (approximately LD10) produces only 10 to 30% tumor-free survivors. These data suggest that, in the L1210 and Lewis lung tumor systems studied, the two activated CP derivatives offer no therapeutic advantage over CP. In addition, two forms of toxicity occur with these derivatives that do not occur with CP.