Targeting executioner procaspase-3 with the procaspase-activating compound B-PAC-1 induces apoptosis in multiple myeloma cells

Abstract

Multiple myeloma (MM) is a plasma cell neoplasm that has a low apoptotic index. We investigated a new class of small molecules that target the terminal apoptosis pathway, called procaspase activating compounds (PACs), in myeloma cells. PAC agents (PAC-1 and B-PAC-1) convert executioner procaspases (procaspase-3, -6 and -7) to active caspase-3, -6, and -7, which cleave target substrates to induce cellular apoptosis cascade. We hypothesized that targeting this terminal step will overcome survival and drug-resistance signals in myeloma cells and induce programmed cell death. Myeloma cells expressed executioner caspases. In concert, our studies demonstrated that B-PAC-1 is cytotoxic to chemotherapy resistant or sensitive myeloma cell lines (n=7) and primary patient cells (n=11). Exogenous zinc abrogated B-PAC-1-induced cell demise. B-PAC-1-treatment-induced apoptosis was similar in the presence or absence of growth-promoting cytokines such as interleukin-6 and hepatocyte growth factor. Presence or absence of anti-apoptotic proteins such as BCL-2, BCL-XL, or MCL-1 did not impact B-PAC-1-mediated programmed cell death. Collectively, our data demonstrate the proapoptotic effect of B-PAC-1 in MM and suggests that activating terminal executioner procaspase-3, -6 and -7 bypasses survival and drug-resistance signals in myeloma cells. This novel strategy has the potential to be an effective anti-myeloma therapy.

Derivatives of Procaspase-Activating Compound 1 (PAC-1) and their Anticancer Activities

“…[15] PAC-1 and its derivatives induce apoptosis and are cytotoxic in cell culture to a diverse array of cancer cells, including cell lines derived from white blood cell cancers (lymphoma, [15, 42–51] leukemia, [15, 24, 44, 48–50, 52–55] and multiple myeloma [24, 55]), diverse carcinomas (breast, [15, 44, 48, 49, 52–54, 56–59] renal, [15] adrenal, [15, 60–62] colon, [15, 48, 55, 57–59, 63] lung, [15, 48, 49, 52–59, 63–67] cervical, [44, 55] gastric, [48, 49, 55, 57, 58, 63] ovarian, [55] liver, [48, 49, 55] prostate, [48, 49] and gallbladder [48, 49]), and other solid tumor types (melanoma, [15, 44, 48, 49] osteosarcoma, [55] neuroblastoma, [15, 55, 57, 58] and glioblastoma [48, 49, 68]). Patient-derived samples from colon cancer [15], chronic lymphocytic leukemia [23], and multiple myeloma [24] are also sensitive to PAC-1 and derivatives, and a therapeutic effect has been demonstrated in multiple murine tumor models [15, 48, 49, 56, 65, 66, 69] and in pet dogs with cancer. [44] In addition, PAC-1 displays potent synergy with the antitumor agent paclitaxel, [65, 66, 69] as well as 1541B ,[…”

“…[42, 43] All compounds were able to restore the enzymatic activity of procaspase-3 under these conditions (as assessed by the cleavage of the colorimetric caspase-3 substrate Ac-DEVD-pNA [96]), and five of the six hit compounds were more potent than PAC-1 . [46] Compound 36 { 18,7 }, also known as B-PAC-1 , was evaluated in patient-derived leukemia samples, [23] as well as multiple myeloma cell lines and primary isolates, [24] as discussed in Section 6.…”

“…Because many PAC-1 derivatives induce cell death in white blood cell cancer lines [15, 24, 43, 44, 46, 48, 49, 52–55] and primary isolates from leukemia [23] and multiple myeloma patients [24] in culture, the cytotoxicity of the compounds in a series of lymphoma and leukemia cell lines, including Jurkat (human leukemia), GL-1 (dog lymphoma), OSW (dog lymphoma), and EL4 (mouse lymphoma) cells, in order to complement the previously determined IC 50 values in U-937 (human lymphoma) cells. As shown in Table 13, comparable potency was observed across each given cell line.…”

“…[44, 47] WF-210 and WF-208 emerged from the oxadiazole library, and the compounds were evaluated in cell culture and murine xenograft tumor models. [48, 49] Finally, B-PAC-1 was synthesized as part of the 837-membered combinatorial library, [46] and the compound showed activity against primary isolates from leukemia patients, [23] as well as in cell lines and primary isolates from multiple myeloma patients [24] in culture. The remainder of this article describes the detailed evaluation of these four PAC-1 derivatives.…”

“…A complementary approach involves the small molecule-mediated activation of proapoptotic proteins, including procaspase-3. [15–18] Based on the downstream location of procaspase-3 in the apoptotic cascade relative to frequently mutated proteins, [2] the low frequency of procaspase-3 mutations in cancer, [19] and the robust expression of the procaspase-3 enzyme in a number of cancer types, including lymphoma, [20, 21] leukemia, [22, 23] multiple myeloma, [24] melanoma, [25, 26] glioblastoma, [27, 28] pancreatic cancer, [29] liver cancer, [30] lung cancer, [31–33] breast cancer, [34–37] esophageal cancer, [38] and colon cancer, [15, 39–41] the small molecule-mediated activation of procaspase-3 is actively being explored as an anticancer strategy. [15–18]…”