Kigamicin D

Kigamicin D did not show any immunosuppressive activity in mixed lymphocyte culture reaction and mitogen induced lymphocyte blastogenesis in vitro and graft versus host reaction in vivo. Natural killer cell activity in spleen cells was not affected by oral administration of kigamicin D. Instead, delayed-type hypersensitivity response to sheep red blood cells was stimulated at a broad dosage level. It is concluded that kigamicin D increases cellular immunity to specific antigen.

The majority of cancers are caused by mutations of a few signal transducers such as the GTPase RAS, the kinase Src and the tumor suppressor p53. Thus, a group of specific chemical compounds called 'signal therapeutics', that block or reverse selectively these abnormally activated signaling pathways would be very useful for the treatment of these signally disordered cancers. More than 90% of human pancreatic cancers are associated with oncogenic mutations of RAS, in particular K-RAS at codon 12. We have previously shown that, PAK1, the Rac/CDC42-dependent Ser/Thr kinase, is essential for RAS/estrogen-induced transformation and neurofibromatosis (NF). Furthermore, we and others have demonstrated that the growth of mouse RAS-induced sarcomas allografts in mice is almost completely suppressed by either FK228 or a combination of two complimentary Tyr-kinase inhibitors, PP1 and AG 879, all of which block the RAS-induced activation of PAK1. Since, so far no effective therapeutic is available for the treatment of pancreatic cancer patients, we have examined the therapeutic potential of either FK228, the combination of these two Tyr-kinase inhibitors or GL-2003, a water-soluble derivative of AG 879, on human pancreatic cancer (Capan-1) xenograft in mice. Among these PAK1-blocking approaches, the PP1/GL-2003 combination is the most effective in the therapy of this cancer xenograft model. Its therapeutic potential is equivalent to those of gemcitabine and kigamicin D which suppress by 70-80% the growth of a similar human pancreatic cancer xenograft model. Also, this PP1/GL-2003 combination therapy has been proven to be very effective to suppress the estrogen-independent growth of an NF1-deficient multidrug/FK228-resistant human breast cancer (MDA-MB-231) xenograft in mice.

Kigamicin D is a novel anticancer agent that was identified using a new screening strategy that targets the tolerance of cancer cells to nutrient starvation [1, 2]. Oral administration of kigamicin D was previously described to show a strong antitumor effect in human tumor xenograft models of pancreatic tumors [2]. In this paper we describe that kigamicin D shows the same selective cytotoxicity against normal human cells such as lung fibroblast and prostate stromal cells under nutrient starved condition as against cancer cells. Kigamicin D inhibited tumor cell-induced angiogenesis in a dorsal air sac assay. On the basis of these results we tested other human tumor xenograft models and transplantable syngeneic tumor models in order to determine the spectrum of activity of kigamicin D against various cancers. Kigamicin D showed a weak antitumor effect against LX-1 and DMS-273 lung cancers, but had no effect on DLD-1 colon cancers. When tested against syngeneic tumors, kigamicin D showed a weak antitumor effect against colon26, but showed augmentation of tumor growth on IMC carcinoma at a broad dosage level. Kigamicin D does not show good antitumor activity against human xenograft tumors except pancreatic tumors and murine syngeneic tumors. We found that kigamicin D has excellent antitumor effect specific to pancreatic cancers. Surprisingly, high dosage of kigamicin D increased tumor growth of IMC carcinoma by than 200%. The phenomenon suggests that kigamicin D may cause some immunological response to the tumor.