Lonidamine as a Modulator of Alkylating Agent Activity in Vitro and in Vivo

We are searching for relatively nontoxic compounds that can positively modulate the efficacy of antitumor alkylating agents. Lonidamine inhibits cellular energy metabolism and could potentially increase damage by alkylating agents if cellular defenses are energy requiring. Exposure of cells to lonidamine (500 µM)for 2 h under hypoxic conditions followed by I-li exposures to lonidamine plus alkylating agents under normally oxygenated conditions in vitro significantly increased the cell kill achieved by m-diamminedichloroplatinum(ll) (CDDP) approximately re fold and by o-tetraplatin approximately 10-fold at 90% inhibitory con centration in MCF-7/CDDP (CDDP-resistant) cells. Carboplatin cytotoxicity, however, was little changed. In the MCF-7 parent cell line, treatment with lonidamine increased CDDP cytotoxicity by approxi mately 10-fold, D-tetraplatin by approximately 10-fold, and car hoplatin by approximately 8-fold at the 90% inhibitory concentration. For i - phenylalanine mustard (melphalan), Ar,A, jV -triethylenethiophosphoramide (thiotepa), and N,N'-bis(2-chloroethyl)-N-nitrosourea, little re sistance was evident in the MCF-7/CDDP lines compared with the parent line. Treatment with lonidamine increased the cytotoxicity of each drug by 1.5- to 3-fold in both cell lines. When exposure to lonidamine was extended to 24 h before and 12 h after drug exposure in MCF-7 normally oxygenated cultures, CDDP (250 µM)cytotoxicity was increased by approximately 100-fold, but melphalan cytotoxicity was increased only 2- to 3-fold over the concentration range tested. In the FSallC murine fibrosarcoma tumor system, five i.p. injections of 50 mg/kg of lonidamine over 36 h increased the tumor cell kill by CDDP and carboplatin approximately 2- to 3-fold over the dose range tested when the platinum complexes were given i.p. immediately after the third lonidamine injec tion. When cyclophosphamide and thiotepa were given in the same schedule, 10-fold increases in tumor cell killing were evident on tumor excision assay over the dosage ranges. The increase in bone marrow toxicity caused by lonidamine in addition to the alkylating agents was less than for tumor cells. Finally, in the EMT6 murine mammary carcinoma, use of lonidamine at 500 mg/kg twice daily along with CDDP, carboplatin, thiotepa, and cyclophosphamide significantly increased tu mor growth delays by approximately 1.6- to 3.0-fold. The results suggest that lonidamine can positively modulate antitumor alkylating agent cy totoxicity and may be a clinically useful adjunctive therapy with these drugs.