Cancer cells despite defective DNA damage response (DDR) have unique ability to repair their DNA and continue
their DNA replication. The higher rate of DNA replication and heightened DNA repair activity (albeit error-prone)
though ensure uncontrolled proliferation but also produce genetic mutations at high frequencies in cancer cells.
This alteration of cellular DNA and dependency of cancer cells to incessant replication initially became the
justification for targeting DNA as a cancer therapy. Though successful to some extent, the major limitations of
DNA targeting drugs that are used in clinics today include life threatening toxicity, acquired resistance and
occurrence of secondary cancers. These problems mostly stem from the ability of DNA targeting drugs to
indiscriminately bind to cellular DNA or other non-DNA macromolecules resulting in DNA damage. We reason
new DNA interacting drugs that (1) display high sequence/region specificity (2) do not directly damage the DNA
and (3) target DNA-related processes that tumor cells use but not the normal cells could have favorable
therapeutic outcomes. In this proposal, we provide compelling evidence that Carbazole Blue (CB) may be one
such drug that we recently developed. We synthesized CB from carbazole, which is an active ingredient of coal
tar that is used for the treatment of Psoriasis. Using an unbiased genome-wide approach, we discovered that CB
interacts with A/T rich DNA regions. Importantly, using cell lines, patient-derived ex-vivo explants (PDEx),
patient-derived organoids (PDO) and xenografts (PDX) as well as orthotopic xenograft models, we found that in
contrast to chemotherapy drugs, CB is a potent and safe anti-cancer compound as systemic delivery of CB
inhibits growth and progression of TNBC and ER+ breast cancers (BCs) without inducing any toxicity. We
discovered that CB inhibits the activity of A/T rich binding protein HMGA1 and consequently expression of several
genes including CDK4, MCMs, GINS and CDC6 and that are highly expressed in these BCs and play critical
roles in replication and DNA repair. Importantly, HMGA1 and its target proteins are reported to regulate PARP
inhibitor (PARPi) and CDK4/6 inhibitor (CDK4/6i) responses in TNBC and metastatic ER+BCs, respectively.
Three Specific Aims are proposed: In Aim1, we will test the hypothesis that CB preferentially targets specific
domains in the DNA that are critical for cancer cell proliferation/progression to selectively induce cancer cell
death. In Aim 2, we will elucidate the mechanisms by which CB utilizes target genes such as HMGA1 to sensitize
PARPi and CDK4/6i responses leading to growth/metastasis inhibition of TNBC and ER+BCs, respectively. In
Aim 3, we will test the hypothesis that CB serves as a novel, safe and potent anti-tumor agent and therapeutic
adjuvant for treating BCs using PDX, PDO and PDEx models. We will also establish PK/PD parameters required
for future clinical development of CB. Successful completion of this study will set the stage for a new paradigm
of treating BCs using CB as a therapeutic.